How To: Disassemble a Canon EF 50mm f1.8 Lens

how_to_disassemble_the_canon_ef_50_18_ii_lens
If you have to clean the lens glass from inside, if you hear strange noises inside, if the focusing ring is stuck, if you have to “repair” it, if you’re plain curious, then there’s no problem, you can take this lens apart and put it back together after you’re finished. It’s pretty frustrating to start doing it if you don’t know where to start and what to do next. That’s what this page is for.

Disassembly

First of all, this is a cheap lens which means its design is very basic with only a few parts. If you’re reasonably handy and careful with your camera, everything will be all right, not many things can go wrong. For a detailed view of the lens take a look at this EF 50 1.8 II parts list.

To see a more detailed image, click on any of the images.

To start with let’s take a look at what we will end with after we have taken the lens apart.

As we can see, not so many parts and actually we can take it apart in under 15 minutes.

The only tool needed for the disassembly is a small screwdriver. Also, use a small box for the tiny parts.

So here’s the lens, before we start the surgery, and hopefully after we sew the patient back together ūüôā

  1. First, we take the rear cover off and unscrew the two tiny screws that hold the contact assembly.
  2. Turn the focusing ring so the lens sticks out of the body. Now push the contact assembly into the body. Gently pry open the rear cover with the screwdriver.
  3. Removing the rear lens assembly. You can do this now or later (see step 3.). Now is more awkward, later is messier.
    Turn the focusing ring so the rear lens assembly just sticks out of the body. Grip the barrel of the lens assembly firmly with the fingers and take care not to touch the glass. Firmly but carefully turn the assembly counterclockwise just a bit and then take it out. If it doesn’t budge try harder but still carefully, it will come out. When the rear assembly is out I suggest you put it someplace safe, take care not to scratch the convex side of the glass. Same goes for all the delicate parts.
  4. Put the contact assembly in the body and close the rear with the lens cover.
  5. Pry off the switch panel which is glued to the body. Start at the extreme bottom end near the switch. When you’ll put the lens together you’ll replace the glue with two-sided sellotape or you can use the remainder on the panel, you decide.
  6. Unscrew the metal limiter that you can see where the switch lever comes in the body.
  7. Turn the focusing ring so the lens recedes in the body as far as it goes. The ring will now turn a bit more because there’s no stopper. Take the barrel assembly out of the body.You can only put the barrel assembly back in the same extreme focusing ring position, remember this when you put the lens together.
    The above image still has the rear lens assembly attached, if you decided to skip step 3.
    In the inside of the body, there are 3 ways for the barrel assembly which are covered in white grease. If anybody knows what type of grease this is, please let me know. Some of this grease is also in the barrel assembly so take care not to be too messy.Detailed view of the main barrel assembly.
  8. If you skipped step 3, go back to it. Now you have better access to the rear lens assembly but have to grip the front greasy part more carefully, not to break anything.
  9. In the two opposing recesses of the barrel assembly, there are two spacers, covered in glue. Scratch the glue off, and take the spacers out.The purpose of these spacers is primarily to void the warranty if you messed with them ūüôā
    The other purpose is to prevent the front lens assembly coming out of the barrel.
  10. Removing the front lens assembly. Between the front lens assembly and the barrel, there’s a narrow gap. Use it to pry these two pieces apart.
  11. Voila, the lens is apart, now you can take the focusing ring off the front lens assembly.

Here’s a detailed image of the main barrel with the iris aperture partly closed. There is a small lever with which you can open and close the aperture. You can feel the discrete positions of stops that are built in the aperture.

The main barrel still consists of many parts, but access to these is quite obvious.

Here are all the parts you should have lying on the table.


Time to put the lens together

Basically go in the reverse order.

Putting the front lens assembly with the focusing ring back on the barrel is tricky. You have to use a lot of force and be careful not to break anything. Before you put them all together check the correct position of the front lens assembly and focusing ring in relation to the barrel. It looks as if there are two ways to put it together, but there’s only one.

I didn’t put the spacers back. The barrel assembly is pretty rigid as it is, but if you feel safer go ahead and put the spacers back in the recesses.

Before you put the barrel assembly back in the body, the focusing ring must be in the most recessed position.

If everything went according to plans the lens is as new, and there are no spare parts lying on the table ūüôā Good luck, enjoy shooting some great images¬†with your repaired camera.

Fungus and Camera Lenses

fungus lens
Fungal infections on camera lenses which, if left unchecked, can damage the surface of the lens.  A very wide range of fungi are responsible, these include the families Phycomycetes, Ascomycetes and Fungi Imperfecti, to name a few.

There are a number of myths often repeated about fungal infection in lenses, such as the belief that they are very contagious, and that once infected the lens is ruined beyond any hope of repair. The fact is that these myths are very largely untrue. While it is certainly true that in certain circumstances a lens can be so badly affected by a fungus that it is no longer economic to attempt the repair, in most cases the lens can be ‘cured’ and returned to service without any fear of transmitting the infection.

Some fungi secrete acids and other substances which will attack the coatings on the lens surface. In extreme cases, this etching can penetrate quite deeply into the coating. Some of these secretions are waste by-products of their biology, but often it is part of their way of collecting nutrients. Rectifying damage of this type involves removing the damaged coatings and re-coating the lens. This is rarely economic.

Fortunately, these very corrosive fungi are not the most common fungi to attack lenses, though the fact that many fungi are difficult to clean off the lens surface leads many to believe the opposite is true. Fungus growing into the lens cement is more problematic, as the elements have to be separated in order to clean them, and then re-cemented. Usually a job for a professional.

Because of the great variety of fungi, it is not possible to speak of any particular case and hold it up as a typical example. There are, however, a number of things which can be said about all fungi, which permit a general approach which should be effective in most cases.

About Fungi in General

First, it will help if we know something about fungi. This will give us an understanding of how to deal with fungal infections, the damage they can cause, and most importantly, how to prevent fungal infections in the first place.

Fungi do not photosynthesize, and cannot manufacture their own sugars, or amino acids from minerals in the way green plants do. Like animals, they are completely dependent on other organisms for sources of sustenance. Fungi, therefore, require a source of organic material to grow and thrive. The fungi do not themselves derive much, if any nourishment from the glass or its coatings, but live mainly off organic contamination found on lens surfaces, such as oil films, or dust, and in the materials used in the construction of lens assembly.

As with most organisms, they prefer a varied diet and tend not to thrive on a highly refined diet. In older lenses, the fungus penetrates into the ‘Canada balsam’¬†used to cement¬†lens elements together. Which as a naturally derived material, includes a range of impurities. Modern synthetic types of cement are less prone to this, as they don’t contain the variety¬†of nutrients.

The fungi themselves consist of fine filaments of fungal cells called hyphae, which form webs of white fibers in the infected materials. These fibers penetrate into the substance of the infected item, where they secrete enzymes and other chemicals to digest the material on which they feed. These secretions and the byproducts represent the corrosive agents which cause the damage in some infections.

Mushrooms and toadstools, with which we are all familiar are in fact only a tiny part of the particular fungi that produce them, and represent only the ‘fruiting bodies’ by means of which they propagate themselves. The fungus that produces the visible mushroom can be quite literally massive in extent. Often a single fungus can extend over several acres underground!

Fungi propagate by means of spores. These are commonly dispersed by means of the fungus’s fruiting bodies, which in many cases are quite small. These spores are microscopic and produced quite literally in their billions. These are in the air around us all the time, and will germinate anywhere they find the right conditions. Because of their small size and large numbers, they will find their way into almost any ventilated space.

Fungi also require a certain amount of moisture in order to grow. Some fungi once established, such as the dreaded ‘dry rot’ in buildings, can synthesize the water they require from the oxygen in the air, and hydrogen found in the attached organic material. No species, however, has spores which have this ability, and so fungal spores cannot germinate without moisture. In wood, this moisture level is about 15% by weight, which is rather on the damp side, and there is no reason to suspect that the fungus in lenses is any different.

The fact that the spores are so invasive has led many to assume that this is an indication of their infectious potential, and many lens repairers will have nothing to do with infected lenses lest the spores they carry infect other lenses in their workshop. This is probably a futile exercise unless they operate in ‘clean room’ conditions, as otherwise the workshop likely contains millions of fungal spores already. The reason that they are not already thick with fungus has more to do with moisture, or the lack of it, than the presence or otherwise, of fungal spores.

In effect, all lenses are probably already infected, and spreading of the infection from one lens to another is not the major cause of infestations. It’s poor storage conditions that have to be avoided, so the spores cannot germinate.

Avoiding Infection

As always prevention is better than cure.

What we now know about fungi, tells us that if we want to avoid fungal damage, we should keep our lenses clean and dry. So don’t keep your lenses in your kit bag, or in the garage, and always dry bags and cases thoroughly if they have become damp. (From rain for example.) Clean the outside of your lenses regularly to remove dust deposits, and don’t allow greasy deposits to remain on the lens surfaces should this occur.

Some photographers¬†will tell you that they never clean their lenses unless absolutely necessary for fear of scratching the coatings. My own view is it’s probably best not to get them dirty in the first place, and to check regularly to make sure that they are clean.

We should also keep them well away from possible sources of nutrients. This probably means that you shouldn’t be keeping your sandwiches in the kit bag either. In fact, the moisture from your sandwich would probably be enough to worry about in any case. Keep all kit bags and cases scrupulously clean.

It also tells us that attempting to keep fungal spores out of our lenses is probably a futile exercise. Given that there are plenty of places spores can get into most lenses, there is a very good chance that the lens body already contains sufficient spores just waiting for the right conditions.

Tests have demonstrated that almost any lens will begin to grow fungus within weeks (5 days in one instance!) of exposure to damp, dark, warm conditions. So, avoid such conditions whenever possible.

The good news is that drying a lens out thoroughly, and keeping it dry will effectively stop the fungal growth in the majority of cases, and will prevent any spores from germinating.

Killing Fungal Infections of Lenses

Killing fungal infections can be difficult, especially if you want to make sure that you have killed off all the hyphae, and that any spores are also killed. This means that any treatment should be applied to the lens as a whole, otherwise live spores may remain ready to re-infect the lens as soon as the opportunity arises.

Finding a suitable chemical agent that can be applied to all the lens components, preferably without entailing the disassembly of all the assemblies is something of a challenge. Ideally, the fungicide should have low toxicity, easy to use, penetrate all parts of the assembly, and should not damage the materials used in the lens construction. Ideally then, a fumigant of some sort is indicated.

Thymol, found in plants, is a naturally occurring antifungal. In its pure form, it consists of a white crystalline substance and is used in medical preparations as a preservative. It has also been experimented with in connection with preserving optical instruments with some success. It is available in fumigant form for use by beekeepers who use it to kill parasitic mites which infest their hives and can be most easily obtained in pure from Indian herbal medicine suppliers. I have not personally experimented with fumigation of affected lenses, but it is something I intend to try.

It occurs in herb thyme, oregano, and in high concentrations in the Indian spice Carom (Also known as Ajowan), so maybe a sachet of these in the lens case might help guard against fungal infestation. At very least it will give it a pleasant odor!

The acetic acid in the form of strong spirit vinegar, has been used as an antiseptic for treating wounds, (Remember Jack & Jill?) and also has good antifungal properties. So soaking in vinegar may prove effective.

Hydrogen peroxide has also been recommended (By Leitz, and others.) as a means of killing fungus, especially when combined with ammonia to act as a cleaning agent. I don’t see this as a practical way of cleaning the whole lens assembly, but should be used to clean the lens elements themselves.

Exposure to strong sunlight or hard UV has also been recommended, and some advocate the use of x-rays to penetrate deeply into the lens and kill fungal spores. (Maybe if I broke a leg…..)

However, as we have already noted, it may not be necessary to kill the fungal spores, as they cannot germinate without moisture. I suspect that recurring infestations have more to do with fungal hyphae remaining in the lens, and failure to keep the lens in suitably dry conditions.

Practical Methods for Cleaning Fungus From Lenses

Cleaning fungus from the lens is a delicate operation, and not always successful. If a fungus has etched¬†into the coating, the only cure is re-polishing and re-coating the lens elements. This is a highly specialized job and is unlikely to be an economic proposition for any but the most valuable lenses. In any case, as pointed out, many repairers won’t touch lenses with fungal damage for fear of infesting their workshops. (This is probably a little paranoid, but one can hardly blame them.)

Neither is it possible to make an accurate assessment of the extent of the damage until the lens is dismantled. Most fungi cause little or no damage to the lens surface, but as mentioned earlier, others are very aggressive, and they are nigh impossible to tell apart by visual examination.

The lens must first be disassembled to assess the extent of the infestation. Fungus growing in between cemented elements often means that the lens is not economically repairable. Lenses cemented with Canada balsam can be separated by the careful application of heat to soften the cement, but cementing them back together properly is a specialist job. Surface fungi can often be cleaned off and the lens returned to service. The lens may contain fungal spores, however, and it will be almost impossible to remove hyphae which have penetrated into the waxes and glue often found in lenses, which will start to grow if given the chance.

One problem is that even if the fungus is dead, and is itself completely removed, they can leave a deposit behind which is very firmly attached to the lens. This is often mistaken for etching damage.

Hydrogen peroxide, or bleach, can be used to kill the fungus. According to Leitz, a fungus treatment of 94% distilled water, 4% clear ammonia, and 2% hydrogen peroxide should be used. The lens element should be soaked in the mixture for an hour or more before cleaning.

The hydrogen peroxide is included in order to destroy any fungal spores, and hyphen but unless the whole of the lens including the housings etc. is treated, it is difficult to see that much benefit will be gained. It does, however, make an effective cleaner.

Many photographers report that household spirit vinegar can be effective for lens cleaning. Given that it has marked anti-fungal properties, and easily obtainable I would recommend giving it a try.

Other reports state that ordinary cold cream is also effective. I have no idea how that works, and I haven’t tried it myself!

As a last resort,¬†a very light swabbing with a soft metal,¬†polish¬†can remove fungus from glass surfaces, quite effectively.¬†Don’t use a polish designed for a hard metal, such as¬†might be used for chrome, these¬†often contain very hard abrasive materials which could remove the coating. (The same may be true of some glass polishes!) I have found the silver polish to be extremely effective, cutting the fungus quite effectively with no apparent damage to the coating. (This would be noticeable as a color shift in most coatings.)

If done carefully the most fungus can be removed without also damaging the lens coatings, and properly cleaned and thoroughly dried, there is no reason that a lens so treated should not last for many more years. Even if there is a slight risk of damaging the lens surfaces, the alternative is usually consigning the lens to the scrap bin.

Lenses can be protected from fungal infections by keeping them in dry clean conditions. The paranoia associated with fungal infection of lenses is largely unfounded, and most cases can be treated with a great degree of success. Spreading of fungal infection between lenses is not a major problem, and is very unlikely to be a cause of the fungal infestation. There is usually no need to dispose of an affected lens.

Meter Modifications For Spotmatic Series Cameras

The metering circuit of the Spotmatic range is a little sensitive to the battery voltage. This is because when correct exposure is indicated, a current of 3uA flows through the ammeter. That’s because Pentax decided that a good way of indicating that the meter was turned off, would be to have the needle dipped low when there was no current flowing through it.

I guess they thought it was a good idea at the time, but the current flowing through the meter with the meter centered is always a fraction of the total current in the metering circuit, for a given light level. The total current will be higher if the battery voltage is higher, and so will the meter current. This means that the needle indicates a higher exposure if the battery voltage is also higher. In this case, you will end up underexposing the negative.

In fact, the error is not actually huge, and it actually depends on the light conditions. If you conduct a fair test in different lighting conditions, you will find that under most outdoor daytime lighting situations the error is less than 1/10 stop, but this rises to 1/4 to 1/3 of a stop under dim indoor conditions. This in itself is no cause for concern, but it is worth remembering that the factory calibration of the meter and shutter speeds were considered OK if within half a ‘stop’ each. So the 1/3 stop could be 1/3 stop on top of that!

Despite many offering this as a camera repair, my own view is that the error is generally acceptable, (provided the shutter is properly adjusted), and not really worth worrying about, but there may be situations where this would not be the case.

(In case you were wondering, the later K’ series does not suffer this problem. That’s because it uses a meter with two coils, one drives the needle up, the other down. As long as the currents are equal, the needle is centered irrespective of the size of the currents involved. All that happens if the battery voltage changes are that both currents change by the same amount, and the needle stays centered.)

This means of course that whatever power source is used, it needs to provide a stable voltage that does not change much with time, temperature, or the amount of current required by the circuit. While this can be provided these days using special circuitry to provide a stable fixed voltage, back then most electronics was still being designed using vacuum tubes, and stable voltage references were in any case specially manufactured batteries.

These requirements could only really be provided in a compact and convenient form by a mercury battery.

Unfortunately, mercury is quite toxic, and this has led to the banning of these cells in most of the world. While this is no bad thing, it leaves the owners of many older cameras with a problem.

In fact two problems.

First, most mercury batteries came in different shapes from almost all modern batteries, and the battery used by the Spotmatics (Mallory RM640), is no exception.

Secondly, there are no modern cells which provide precisely the 1.35 volts provided by the mercury cell.

The first problem can be solved by using a smaller cell and providing a means of centering and stabilizing the cell. My favorite method for doing this is described in the link below.

The second is more difficult. In the following pages, I will describe three different ways of solving this problem. The methods described cover a range of accuracies and difficulty, so you should be able to find one which suits you.

After making these modifications, the metering circuits may need re-calibrating. To do this it is useful if you have a handheld meter for another reference.

How to fit a smaller cell.

This describes my preferred method of fitting a smaller cell. All the modifications described use a cell of the same size. The cell dimensions are 3.6mm high, and 7.9mm diameter. Depending who made the cell, and what standard they use you will find these marked 392 or PR41, but it’s best to use the dimensions as a guide, there are lots of standards.

Zinc-air and other cells.

Once you know how to fit the smaller cell the first thing you may want to try is using a zinc-air cell. This is often touted as the ideal solution as the zinc-air cell has a nominal cell voltage quite close to the ideal, but there are a number of reasons why this may not actually be the case. Let’s take a look.
Note: The ‘Wein cell’ is a zinc-air solution, using selected zinc-air cells to provide a closer match to the original mercury battery. They are essentially a standard zinc-air cell with a plastic ring already fitted in a similar fashion to my method described in ‘How to fit a smaller cell’. They are however much more expensive, but you might want to buy one in order to save the trouble of making your own adapter.

Germanium diode modification

This is the quickest, cheapest and easiest modification, which is probably the reason that it is the preferred method employed by professional camera repairers. Essentially the diode is used to reduce the battery voltage to a more acceptable level by inserting it into the battery supply. It is not, however, the most accurate modification. The reasons for this are explained in the technical description of the modification.

Germanium diode technical description

How to modify the metering circuit using a germanium diode

Meter sensitivity modification

This modifies the metering circuit to reduce the sensitivity of the meter used in the Spotmatic metering circuit using two small resistors.
This modification requires that the top casings of the camera be removed to access the circuitry, which requires the use of some special tools. However, these tools are not difficult to make for yourself.

The modification instructions are based on the values given for the meter properties given in the Pentax service manual, but as these cameras were made over a period exceeding ten years, your particular example may be slightly different. The technical description tells you how to calculate the precise values required by your meter if you wish to get this exactly right. However, the difference is not likely to amount to much in practice.

Meter modification technical description.

How to modify the meter circuit sensitivity to use silver oxide cells.

If you have read all the above pages, you should no know how to modify your Pentax Spotmatic to meter correctly. These modifications should work with all the Spotmatic range of cameras (SP500, SP1000, etc.), and I hope that reading the descriptions has given you some insight into how to go about modifying the circuitry of other cameras designed to use mercury cells.

How To: Disassemble and Clean the F1.4 50mm Super Takumar

F1.4 50mm Super Takumar
When this lens was first manufactured in 1964, it was one of the sharpest 50mm lenses available. Even now it beats most commercial lenses, and I suspect more than one or two ‘pro lenses. In fact, this can be said about all of the Pentax Takumar lenses.

If you get the chance to buy any of the series you are unlikely to be disappointed. Even if less than perfect, they are still very good. You can sometimes find them in ‘car boot’ sales, at a range of prices and conditions, and various Internet auctions. I have even found them in the ‘surplus stock’ bin in camera shops! (It’s usually not worthwhile for the shop owner to spend time cleaning the dust of such an old lens. Besides, he might find something nasty under the dust anyway. So he won’t get very much for an example in anything but ‘mint’ condition. But I’m not complaining!)

The lens went through a number of variations and improvements until eventually discontinued in 1975. The original version had 7 elements arranged in 8 groups. This changed to 6 elements in 7 groups in 1966. In 1972 the lens gained a multi-coating and a lug for use with Spotmatic ES and F models. The later super multi-coated types are to be preferred over the earlier single coated types, simply for the sake of the better coating, but be aware that the lug may cause problems with some M42 mount cameras.

Other variations include different numbers of diaphragm blades, ranging from six to eight. This article shows the disassembly of a late 8 blade type.

Problems peculiar to this lens type.

Many examples show yellowing of the inner elements. This is due to the use of radioactive Thorium in the glass formulation. I believe that the cause of the discoloration may be attributable directly to the effects of the radiation itself as the Thorium decays. However, there is no need to worry, the level of radiation is very low, and is mostly stopped by the glass anyway. I am told that some lenses used for aerial surveillance in WW2, are hot enough to fog film after a few days!

This can (Reportedly) be rectified by exposure to UV for a period of two or three weeks. This method works quite well if the source of UV is Californian sunshine, but living in Britain I have not been available to verify the sunlight cure. It is claimed that artificial UV lighting will clear the glass in a little more time. My own experiments suggest that only ‘hard’ UV will suffice. (The sort that is produced by tanning lamps, or (more extreme) arc-welding equipment.) This type of UV can also be harmful and can cause severe burns and cataracts, so caution is advised.

However, for many users, this may not be a problem, as it is usually only a very light ‘straw’ shade, and at worst adds a slight warmth to Color Images.

As with other lenses problems encountered may include fungal growth and stuck diaphragms. Provided the fungal growth is slight the lens performance will not be discernibly affected, but cleaning the fungus out is still advisable. Stuck diaphragms are usually due to grease on the blades, which will need cleaning. Both of these operations will require dis-assembly of the lens.

The Subject

The lens I am dismantling here came with an SP500 bought on the internet. It has a dented filter ring, a sticky aperture, discolored, elements, fungus, and it appears someone has already attempted some repair and scratched the front trim quite badly. All these factors usually add up to a junker, but it makes an ideal subject for this purpose!

This lens often baffles attempts to dismantle it, but with the right tools, and know-how it is not normally too difficult to do. In the case of this lens, the dent in the filter ring is going to be the most difficult obstacle.

Disassemble

As always in camera repair, the first place to start is with a careful examination of the subject.

OK, the filter ring and the front trim of this lens is damaged. The front trim damage probably results from a previous attempt to open the lens.

Notice that there are no obvious means of unscrewing the front element.

Guide for Dismantling a Nikon F-301 Camera

Nikon F-301
Dismantling a Nikon F-301 camera can be a bit tricky. This camera marked a new phase in the design of the Nikon SLR. For one thing, it includes its own auto-winder, which is capable of clocking up a respectable 2.5fps. Another departure from the ‘classic’ Nikon in the use of plastic for some of the body parts.

The use of plastic caused many to claim that this camera represented the beginning of the end for the Nikon as the ‘camera of choice’ for many professionals. In service, however, these cameras have proved reliable and robust as it’s all metal predecessors. This may be due to the fact that most of the body is still metal, but that it is designed with the same attention to the requirements of the professional for a tough workhorse. This may sound like an odd thing to say about a camera with a fixed focusing screen, and without such features as a mirror lock or depth-of-field preview, but this should not detract from this 1985 offering from one of the world’s most famous marques.

This particular example was bought from a car-boot sale for next to nothing, with no lens. The mirror had jumped it’s mountings, (a common camera repair for these models.) probably as a result of dropping the camera onto a hard surface (possibly concrete) from five or six feet.

Most cameras would stop working in this scenario, many would not be repairable afterward. This camera just requires the mirror re-mounting on its pivot!

The body shows some signs of the impact, which seems to have been directly on one corner, and there are a number of marks indicating heavy use. A perfect candidate for an exploratory operation. If I completely mess it up, I have lost little, and learned a lot!

Tools Required

There are no special tools required to disassemble this camera. That may have something to do with the Nikon design philosophy on serviceability. There are some obvious features that illustrate this to be encountered during the work here.

Starting Disassembly

As always, before starting to disassemble the camera, make sure that you have a notebook and pencil handy. The camera you have may have some differences to the one here, particularly with respect to wire coloring.

Begin by removing the film door. In common with many cameras, this unclips by means of a spring-loaded hinge pin.

 

The next item to go is the film rewind crank. Remove this the usual way.

 

The film speed dial is held in by means of a ‘C’ clip as shown here. It looks a little odd but comes out easily using a couple of small flat-bladed screwdrivers.

 

Once removed you can see the film speed selector contacts. These can’t be removed yet, but you should be able to see if there’s a problem with the contacts here.

 

Now we have to get to one of the cover screws hidden beneath the soft rubber covering.
This is one place where we can see evidence of the thought given to servicing the camera. There is a convenient tag on the side of the body which makes peeling the covering off easy, without risking scratching the paint!

 

Just grab hold of the tag,

 

and start peeling.

 

Continue peeling unit lit’s off.

 

The screw revealed just needs to be loosened a bit.

If you intend to completely disassemble the camera you will need to peel the other side off too.

 

Now simply remove all the other screws holding the cover on as shown. Take note of which screw goes where they look very similar but are not identical.

 

Once the screws are removed the top cover can be eased off.

The viewfinder bezel should be held in place while lifting the cover and removed once the cover is lifted.

It’s a good idea to disconnect the wires to the hot-shoe now. Accidentally pulling a couple of wires off leaves you with a rather scary guessing game, especially when you consider some flashguns have trigger voltages of hundreds of volts. Guessing wrong could connect that to the voltage sensitive logic circuits in the camera!

At the very least you could waste a lot of time in the trial-and-error wiring. (Two wires and two solder tags give two ways of connecting them, three wires have six combinations. You can work the rest yourself!)

 

These four wires connect to the LED and the sounder.

 

You may find it easier to remove some of the wires at the flex board.

 

With that out of the way, you can now remove the bottom cover, and battery compartment. Just remove the five screws.

Four here.

 

One here.

 

Unsolder the battery wires.

 

Take a moment to examine the arrangement of levers visible underneath (above?) the battery cover. When reassembling the cover you will need to place these in the same relationship as they are now. (Assuming that the fault is not due to a problem here. That is not likely to be the case unless someone has been messing about in here!)

 

Now we want to remove the wires connecting the shutter to the electronics. As you can see there are quite a few wires to choose from.

The wires indicated below all connect to the shutter. The two wires connecting to the hot-shoe are the sync wires and should already be disconnected.

Four of the six remaining wires connect to the shutter solenoids, the remaining two connect to contacts on the closing curtain mechanism.

 

 

Now disconnect the DX contact wires. Make sure you take a careful note of their locations, as getting this wrong won’t stop the camera working, but DX-coded films won’t be exposed correctly. There are a lot more ways of getting it wrong than right.

 

Once the body is separated you can see the DX contact connections.

 

Now disconnect the wires for the battery and the winder motor. Immediately beneath these is a flex-strip connecting to the control PCB. Unsolder this quickly and carefully. Too much heat will cause the copper tracks to become unstuck from the strip. If you have a data back, this won’t work if this strip is damaged.

 

Now you need to release the film selector dial.

 

Remove the three screws here.

 

Now remove the body screws. Note the screw arrowed is different from the rest.

The screws on the other side.
Note the trimmers accessible here. Another well thought out feature. I don’t know exactly what they all do, but at least I can access them with the camera in one piece!

 

There are screws on the sides of this camera as well.

Once the screws are removed, ease the front of the camera up, and forwards a little. Lift the control PCB up at the rear, and push the sprocket drive shaft gear downwards to free the control PCB. Provided you have unsoldered all the wires, once the shaft is free the front of the body should lift away easily.

The Shutter

The Copal shutter is a lesson in pure simplicity. There is the absolute minimum of parts required to perform the task.

I’ve removed it from the body here to show you in better detail, but unless it’s been physically damaged it is very unlikely to need attention.

 

This is normally under a dust cover, but I’ve removed that so you can see the simplicity of the design. There are just two solenoids which hold each shutter in the charged position, against their springs. Turn off the current, and they release them. There are no mechanical latches to wear-out or jar out of alignment.

 

In addition, there are two sets of gold-plated contacts like this. One set closes when the opening shutter is just open. (Flash sync.) The other set closes when the closing curtain has closed. So the camera knows it can return the mirror.
There is not the usual mechanical linkage from the mirror to shutter, and back to the mirror as there is in other designs, which is often the source of a lot of failures. The electronics control the sequence, something that electronics is very good at!

Mirror Lifting and Shutter Charging

 

The crank arm here simply lifts a lobe on the opening shutter mechanism, which in turn pushes the closing shutter both into the charged position. A lever driven by a cam on the winder mechanism presses on point 2, and point 1 actually presses onto the shutter lobe.
During picture taking another arm presses on 3, driving charging the mirror spring, and tripping the mirror release at the end of its travel.

 

This lever coupled to a braking mechanism and also trips a switch which causes the activation of the solenoids. Another solenoid holds the braking mechanism and switch engaged during the mirror lifting period. As soon as the mirror is in its upper position, the shutter is electronically fired.

Putting it all back together

 

When putting it all back, check that the cam and lever shown here are in the position shown. Note the lever arrowed can cause problems. Make sure that it moves freely when the screws holding the PCB are fully driven home, while at the same time it is not flopping about all over the place.

 

The lever shown here at the bottom of the camera should be in this position.

 

Also, release the gear here in the position shown. You will have to release the locking dog (Arrowed)to do this.

 

To keep the flex strip out of harm’s way when putting the front and back together, hook the motor wires around it as shown.
The rest of the reassembly should be fairly plain sailing. Though it’s worth remembering that if you decide to test anything before assembly is complete, and the film door is closed the camera will not fire the shutter and will attempt to load film on every press of the release button.

 

Conclusion

That just about does it for this one. You have seen how to dismantle one of these Nikon cameras and noted one or two features of the Nikon design philosophy contributing to the popularity of these cameras among professional photographers, and serious amateurs. Admittedly, the approach does not result in the most compact and lightweight design, but they do result in a tough reliable design which is relatively simple to maintain in that state, which is after all that is called for.

Just in case you were wondering. After putting the mirror back onto its pin, it all works perfectly.

How to Service Pentax Vertical Run Shutters

How to Service Pentax Vertical Run Shutters

How to Service Pentax Vertical Run Shutters

How to Service Pentax Vertical Run Shutters like the one used in the ‘M’ series of Pentax automatic cameras. The shutter, mirror cage, and body parts are essentially the same for the whole range from the ME, through to the world’s first commercial autofocus SLR, the ME-F.

Here I show one method of checking the shutter speeds and timing, and how to rectify any problems in the shutter itself.

First, let me list the problems normally attributable to the shutter.

  • Erratic exposure.
  • Uneven exposure top-to-bottom.
  • Partially obscured images with flash.
  • Dark bands at top or bottom of the image. (Sides for horizontal run shutters.)
  • Shutter only operating on ‘X’ or ‘B’ speed settings.
  • Unreliable flash triggering.
  • Jammed shutter (Rarely).

Note that the shutter itself is only rarely the cause of the shutter jamming, or the camera locking up. (Unjamming ME-Supers is the most common camera repair I am generally asked to do!) This is usually caused by a problem with the mirror mechanism. If there is no obvious damage to the shutter curtains, or a foreign object, or substance (Commonly marmalade!) has got into the camera, then the cause is most likely elsewhere.

If your camera is locked, please look at the ME-Super disassembly page on this site. The problem is common in older examples and usually has a simple cause, and solution.

Also, note that shutter speeds as such are not the responsibility of the shutter itself. Incorrect speeds are due to a problem with the electronics. (Look for cracks and breaks in circuit boards and loose wires.)

Let’s start with checking the shutter operation in situ.

Shutter Checking Equipment.

It is, fortunately, possible to check the shutter and diagnose most shutter problems without and disassembly.

It does, of course, require the use of equipment not normally to be found in the average toolkit, but if you happen to have an oscilloscope or have access to one you can check the shutter operation without much extra equipment.

This method is fairly straightforward and can be applied to any 35mm SLR with a focal plane shutter.

I keep promising myself that someday soon I am going to build myself a compact, self-contained, and inexpensive shutter tester, and when I do I will publish the drawings. Until I do, however, this method works well enough for most camera repair situations.

This page does not show you how to calibrate the shutter, you should look at my ME Super calibration page for that. It does show you how to check the shutter and diagnose and fix any problems with the shutter. This is most important, as there is little point in attempting to re-calibrate the shutter if it is not working correctly.

Focal Plane Diode Sensor

Assuming you have access to an oscilloscope, (A dual-trace type, is ideal, but those are quite common these days.) you will need to construct a focal plane sensor.

This can be done with a piece of prototyping board, two photodiodes, and some black velvet or felt. (Or similar black material.)

The one I made looks like this.

From the back

From the front

The back view shows a couple of resistors, of about 100k. These are simply arranged in parallel with the photodiodes and serve to reduce interfering noise. (It also reduces the size of the signal by about 50%, but the ‘hum’ signal is much reduced. Proper screening would probably be a better idea!)

The black ‘felt’ used here is a type sold specifically for use in cameras as an anti-reflection covering. It is essential to use some sort of light absorber in order to get a reliable signal. It is quite surprising how reflective the back of the shutter curtains are. (Especially considering their function!)

In fact, the black¬†felt should cover all of the photodiodes except for a small hole right above the black rectangle of the diode. This helps give sharp edges to the ‘scope trace, making it much easier to read. I haven’t shown it like that here, as you would not be able to see the diodes if I did!

Also, note the orientation of the diodes. The actual active area of the diode is a square. The edges of the square should be parallel to the edges of the board, that helps too. Also, note the spacing of the diodes on your own version. Make sure you measure from the same edges of each diode. That is bottom edge to bottom edge for example. You will need this number when checking the curtain speeds.

I have connected the anodes of the photodiodes together to give a common earth for convenience.

In use this is simply strapped to the film plane, using rubber bands,

and check that the photocells can be seen.

The camera should be fixed in place and illuminated from the front. You could mount it on a tripod, but I have just stuck it to the tabletop with blu-tak. The light source here is a small laser filched from a broken laser pointer with the lens removed, but it works just as well with a halogen desk lamp. (I’m only using the laser because it was just lying about, and it runs for days on a single battery.)

Connecting the oscilloscope probes now helps find the best position for the light source.

I really should cover the back of the sensor to exclude stray light, but it works OK as it is. Just glue a small plastic box over the back once you know everything is right.

These tests do not calibrate the meter, this has to be done separately, and is dealt with on another page. Once calibrated, however, the manual speeds, and calibration can be checked at higher speeds with these tests.

The tests here mainly check that the shutter is properly set-up mechanically. Unless this is done the meter calibration may be of little use!

If you think your meter is in need of calibration check the calibration page first.

Testing

Curtain speed

The first thing to check is the curtain speeds. With a focal plane shutter, the two curtains are driven by separate springs. The tension of these springs will determine the speed that they travel across the focal plane.

It is important that the curtains maintain a certain minimum speed. If they are too slow, then the curtains may not be open fully when the flashgun is fired. If this is a problem with your camera, then this must be checked first.

It also is important that the two curtains travel at as near exactly the same speed as can be achieved. If they do not, then the exposure will change progressively across the frame. This will be specially marked at higher speeds. If your camera exhibits such symptoms, then the problem lies here.

To check the manual x-sync speed select 125X and set the scope first to trigger from the first photodiode exposed. You should get a trace something like this.

If like me you don’t have a digital storage ‘scope you will probably have to turn the trace brightness all the way up, to get a decent impression of the trace. In this still from a video of the scope, the time base is set at 1ms/division, and we can just about see that the opening curtain is crossing the distance between the two photodiodes in about 4.5ms. The distance between the photodiodes is 18mm, and the manual for the ME-Super states that it should take 6ms or less to cover 21mm, and scaling this up this comes to 5.25ms, so that’s ok.

(If you do not know what the curtain speed should be on another camera, just check what the x-sync speed is. The shutter needs to be fully open when the flash triggers, and so the curtains should cross the whole of the film plane in less than that time. Allow ten to twenty percent less for safety, and use that as the curtain speed. It is important not to set the curtain speed to high, as that risks stressing the springs which could become weakened or even break. With silk shutters, it also controls the shutter tension, too high and the shutter ribbons will tear.)

This should be done several times to ensure that the speed is constant. If it is erratic suspect contamination of the curtain blades with grease or other substance, or that the shutter mechanism needs lubrication. It is also possible that a foreign object has got stuck between the shutter blades. (I have found washers actually inside the shutter curtain guides before!)

With cloth shutters, this would indicate that oil lubricating the rollers need replacing, or that there is some problem with the curtain rollers themselves.

The same operation should then be repeated for the closing curtain. This time the ‘scope’ should be set to trigger on the falling edge, and the trace will appear inverted.

Shutter speeds

If the camera is calibrated correctly, then the manually selected speeds and the automatic speeds should be within half a stop of each other. The manually selected speeds are only expected to match more closely if the light level is such that the automatic control determines that the precise exposure should be that speed exactly. That is because the automatic speeds change continuously, rather than being selected at the nearest fixed speed.

Check the manual speeds at all settings. If you get speeds greatly in excess of or less than the indicated speed, that there is a problem with the shutter timing circuits. A common cause of this is the crack in the white ceramic PCB, on top of the pentaprism, but you may have to do some deeper investigation to determine the cause.

Shutter speeds greater than a second can be checked using a stop-watch, higher speeds need the oscilloscope.

For this test, you only look at one photodiode at a time. At the higher speeds, you should compare the speeds for each diode.

We start with the ME-Super by checking the x-sync speed, which is a purely mechanical default. I get this trace.

When measuring the times on these traces always measure to the beginning of the change. The time starts when the trace first begins to rise and ends just when it starts to dip at the other end. This trace is just short of 9ms, say 8.8ms. That corresponds to 1/114s, which is a little slower than the advertised 1/125, which is 8ms exactly. This is just within 10% and is not a cause for concern given that the curtain speeds are within limits.

The speed should be checked at each speed up to 1/1000s. Check each speed several times to ensure it is consistent. If not, it is likely that the shutter mechanism needs cleaning and lubricating. (Shown later on this page.)

Speed matching

The two blinds should cross the entire focal plane within, (at the worst) 0.1ms of each other. Fine adjustment can be achieved by comparing the shutter speeds at the top and bottom of the run for high shutter speeds.

To do this, select ‘AUTO’ with the batteries removed. This should give you a shutter speed greater than 1/2000s.

At this speed, it is important that the two diodes in the sensor board, and the windows letting the light through, are pretty closely matched. The windows less than 0.5mm across, otherwise you won’t get a clear picture of what’s going on.

Remember that the shutter curtains take about 6 milliseconds to cross the focal plane, so that means at 1/1000s the shutters will be separated by 21/6 millimeters apart, or about 2.4mm, at 1/2000 this is 1.2mm. We are trying to get a good look at something of about 1/3000s-1/4000s. If you are having trouble with this, try using the sensor board the other way up, so that the two diodes change places. This will tell you if the differences you are seeing are really due to the shutter or differences between the diodes.

We don’t really care what the separation between the photodiodes is here just that they have a good separation between them.

First, check measure the shutter speed at the top of the shutter travel. This should be fairly regular, it should be pretty much the same for each firing. (Within 10% certainly, but 5% is achievable.) If this is erratic, then the manual shutter speed escapement needs cleaning and lubricating, before you can check the speed matching.

Using an average of several readings of the upper diode shutter speeds as a reference, measure the speed at the bottom of the travel. Again average several readings, and compare the averages.

If the lower diode shows slower speeds, then the closing shutter is running slow. Increase the tension on the upper spring, by one click and re-check the speeds. Stop when the speeds are within 0.03ms of each other. (This may just be a single click on the spring adjuster.)

If the lower diode is faster, then the opening shutter is running slow. Adjust this the same way as the closing shutter.

That is more-or-less all the tests you need to do, the next section shows you the important parts of the shutter, and how to correct any problems that may have been shown up.

Servicing The Shutter

Much of what follows can be performed with the shutter still in the camera, but most of the shutter problems are due to lubrication and dirt, and require the mirror cage to be removed. The ME-Super is not a difficult camera to work on, as it most of the ‘M’ series, and so there is little reason not to disassemble the camera to the point where the shutter can be removed.

The development of shutter faults should be seen as a signal that the camera needs an overhaul in any case, and you should accordingly equip yourself with the required materials and tools to perform a complete service. The page to refer to is ‘Disassembly of the Pentax ME Super Camera’

Overview of the shutter

The shutter is a vertical run metal curtain shutter. It is triggered mechanically, the opening curtain operating completely mechanically. Two mechanical ‘speeds’ are provided 1/125s and ‘bulb’, all other speeds are determined by a retarding solenoid, which holds the closing curtain open for an electronically determined period.

The selection of the operating mode is determined by the position of a lever protruding from the top of the mechanism housing. Viewed from the front of the camera, the leftmost position (Default) selects ‘B’, the rightmost position releases the closing curtain simultaneously with the opening curtain, putting the shutter under solenoid control. An intermediate position provides the x-sync mechanical default speed of approximately 1/125s.

The x-sync contacts are built into the shutter.

Examination and maintenance of the shutter

Starting with the mode selector and default speed rocker.

  1. Selector’s arm.
  2. Selector latch. Actually an extension of the selector’s arm.
  3. Opening curtain latch. This prevents the closing curtain from releasing before the opening curtain is released.
  4. Mechanical speed rocker. This transfers the motion of the mechanical release cam to the closing curtain release providing the 1/125s mechanical speed.

No oil or grease is used here.

This is the retarding solenoid. When energized it prevents the shutter closing. The solenoid current is switched on just before the mirror reaches its picture taking position by the camera electronics.

This is the solenoid armature. This is pulled into the solenoid when the solenoid is activated.

The mechanical speed cam. Just to the right of the pointer, you can see the cam follower on the end of the mechanical speed rocker. The shutter is in the cocked position ready to fire.

  1. Is the shutter cocking lever. Moving this in the downward direction in the picture cocks the shutter.
  2. Is the opening curtain release. This is operated by the mirror actuator as the mirror reaches the taking position. It latches the release cam.

This is the mirror ‘scissor’, not part of the shutter itself, but the spigot just above it engages the cocking lever (Just visible.) during film advance.

The shutter in situ, showing the engagement of the cocking lever with the spigot on the cocking arm.

Indicated is the mirror return striker. It’s coupled to the closing shutter and strikes the mirror return release as the shutter comes to rest.

Circled is the opening curtain latch. The curtain is locked and engaged with the latch. The arrowed part is the opening curtain anti-bounce latch. This prevents the opening curtain bouncing back into the focal plane aperture in conjunction with the opening curtain brake.

In the open position, the opening curtain is latched.

Lubrication

  1. The old lubricant on this cog and the idler pinions it engages with is the cause of erratic shutter speeds, especially noticeable at high speeds.
  2. The pin and rubber roller form a brake for the opening curtain which is important in eliminating curtain bounce.

These parts should be thoroughly cleaned with isopropyl alcohol.

It may even be necessary to use a dental probe to gently scrape old dry lubricant from the gears.

After cleaning the gear and associated components should be lubricated with a small quantity of light silicone oil. The type sold in spray cans in motor parts shops can be used. (Spray a quantity into the cap of the can first, and dip probe into the silicone to transfer the lubricant.) Don’t use mineral oil, not even specialist camera or watch oil. This can soak into the nylon parts making them swell, and can make them brittle. Mineral oil will also attack the rubber of the brake.

Note that this gear can be lubricated from the bottom of the camera by just removing the bottom plate.

Also clean and lubricate the cocking arm as indicated below.

Hold the cocking arm in the position shown. Use only the tiniest drop of oil and a light smearing of grease. Failure to lubricate here will cause the cocking lever to stick in this position, jamming the camera.

The screw indicated in the picture below is important and should not be disturbed unless it proves impossible to achieve the maximum shutter speed. It forms part of a contact opened by the opening curtain mechanism and is set to provide a timing reference to the electronics.

The other half of this contact is the gold-plated wire indicated. Dirt or oil on this wire where it makes contact with the set screw could be a cause of erratic speeds or intermittent operation.

The connection to the contact. The brown and the blue wires connect to the solenoid. They can be interchanged, the solenoid does not need to be connected a particular way about.

This ratchet sets the tension of the closing curtain spring. Turn this a few clicks clockwise to increase the speed of the closing curtain. Note that the ratchet only appears to allow increasing the tension. Springs are not likely to become stronger with age.

The lower one adjusts the opening curtain.

This is the x-sync connection. Unsoldering the solenoid and the contactor wire allows the removal of the PCB with the contact intact.

The flash contact here shows some pitting and black deposits caused by arcing. This is due to being used with older flash units which have trigger voltages ranging from fifty to five hundred volts or so. There are a lot of these flash units still in circulation, and this illustrates the sort of long-term damage that can be caused.

In fact, this contact has not seen an awful lot of use and works perfectly well. You can imagine what the result of heavy flashgun use would be like. Devices are available to prevent this from happening but are rather expensive. I have instructions on how to build one for yourself elsewhere on this site and can supply a kit, including a PCB to build it at very much less. (I am looking into the possibility of supplying completed units for those who would prefer it.)

Testing a shutter out of the camera

You may, of course, need to check a shutter without the shutter being in the camera.

You need to make sure that the shutter is held securely in place over the sensor without interfering with the shutter action. Either use the shutter mounting holes or as here only support the shutter at its corners.

The selection arm will have to be held in the ‘manual’ speed positions, central for 1/125s, and to the right for the maximum speed. I usually Blu-tac a matchbox or a rubber eraser to the bench to keep it in place, but usually, I do this with the shutter mounted in the camera body which is easier.

The default operating mode is ‘bulb’, so operating the opening and closing curtains separately is possible. In this case, the desk lamp serves as the light source.

Conclusion

That’s all you probably need to know about this shutter. There are plenty of the cameras using it still around, and with a little work, most can be restored to full, faultless operation. Perhaps even better than when they left the factory!

How to Clean the Canon EOS Shutter

canon eos shutter repair

How to Repair a Canon EOS Shutter

If you examine the shutter of almost any EOS more than 10 years old or so, you will find a black sticky deposit on the shutter curtain. Below we get some pointers on Cleaning a Canon EOS Shutter.

In some cases, the goo has not yet built-up to the point where it interferes with shutter operation, but it will before too long.

The deposit can be cleaned off with care, which will temporarily restore shutter function, but the problem will return shortly, and the shutter will need to be cleaned again. Obviously repeatedly cleaning a delicate component like the shutter curtains is fraught with risk, and sooner or later, this will result in permanent damage to the shutter. Replacing the shutter in any SLR is an expensive operation involving quite a bit of labor, and most cameras with damaged shutters are discarded as write-offs. Obviously, this is an undesirable situation. Don’t despair, however, the problem has a solution, which anyone can apply with a little patience and care. This page illustrates fixing this problem on an EOS 750 camera. If you have a different EOS, the procedure will not be too different. Check my other pages for the particular camera you have, I may have already documented your particular model. The particular specimen illustrated came to me with a stuck shutter problem, and some apparent debris in the viewfinder which reset on mode switching and power-up, and the cause of this fault is also illustrated.

What Causes the Problem?

And, what necessitates the Cleaning a Canon EOS Shutter? This is not a particularly difficult camera repair, but before we can fix this, it is important to understand the cause of the problem. This is a picture of a partially disassembled shutter. If you look below the deposits on the shutter blades, near the bottom edge of the shutter assembly, you should see a rectangular block, with an oval protrusion. It’s a rubber buffer, and it is the source of the problem. Basically, it has started to decay, and the black goo is pretty well all that’s left of it. To fix the problem permanently this has to be removed.

You might think that removing this buffer would have a serious adverse effect on the operation of the shutter, but in practice, it makes no difference.

Its function appears to be to reduce the stress on the shutter hinges as the blades come to a rapid stop, but the effectiveness of this is doubtful. If you are worried, you could, of course, glue a piece of rubber cut from an old rubber mat or something to replace it. (In fact, an old inner tube would be ideal. The type of rubber used is very good at absorbing shock.) Make sure that if you do, that you don’t choose a replacement which is going to perish quickly, such as an elastic band! In fact breakdown of doubtful rubber components is a common cause of camera failure, see my other pages for examples. To get at this you have to partially disassemble the camera. I have taken care to ensure that the amount of disassembly is the least that is required. There is quite a lot of stuff inside the EOS cameras. Most other OES’s using the same shutter are less complicated, and you may be able to adapt this to other models. Disassembly of other EOS models (Including the EOS 600 / EOS 630) are illustrated elsewhere on this site and will be added to as I obtain samples requiring maintenance.

Disassembling the EOS 750 to Access the Shutter

Before you start, you will need some tools. Thankfully Canon has elected to build these cameras using fairly standard fasteners, and all the tools should be easy to find. You will need some jeweler’s cross-headed screwdrivers. These should include sizes ‘0’ and ’00’. A fine tipped soldering iron is also required, of 15 to 25 watts rating should be fine, a temperature regulated iron is perfect.. (Don’t use a portable gas soldering iron. The hot exhaust is very good at melting plastic.) A good pair of tweezers is also desirable. One tool which you may find useful is a fine spring-hook (Or preferably a set of spring-hooks.) This is simply a dental probe with the end turned over to form a hook, and is very usefully for fitting and removing springs in awkward places. Sets of dental probes can be had for very little money from most electronics tool stockist’s. IMPORTANT: Take your own notes as you disassemble the camera. Wire colors especially may differ between different cameras of the same make and model. Do not force anything that is stiff, or does not appear to be completely free. Usually, this means you have missed something. Do not unscrew anything without first examining closely how the parts relate to each other. (It takes ages of trial and error to figure out how they should have been!) ESPECIALLY do not tamper with any screws that are fixed with colored varnish, or pitch. These are almost always to do with calibrating the camera in some way. If you do not have the know-how and proper equipment it will not be possible to reset these correctly.

Door Latch

The disassembly begins with removing the door latch. Just two screws here. The latch cover has lugs which engage with the front, top, and bottom covers. Removing those is much easier with this removed. Here you can clearly see the lugs on the front and top covers. The parts you can see here are best removed and saved in a safe place, but accessing the spring requires removal of the front cover. At the moment the back cover is keeping the parts secure, so don’t open the back until we remove these parts.

Front Cover

Removing the front cover is fairly straightforward, but don’t forget the screw lurking underneath the flash hood. Notice the small rectangular transparency with the “P” on it. This normally fits on top of the indicator lamps in the viewfinder. The fact that it is loose leads me to suspect that the camera has been dropped. (In fact, it’s a bit lucky that it is still in there, the screen is interchangeable on these, and it would have been little trouble to remove the screen and drop this out. I also have to admit I’ve lost one of these before!) The front cover removed with its screws. Make sure that you take note of which screw goes where. They are not all the same.

Bottom Cover Removal

Ok, the cover is off. The next task is removing the bottom cover. Again this is a simple matter of removing screws. Also again the screws are different. There are five screws. Once the bottom cover is off, we see further evidence that the camera has been dropped. You can see the door latch spring at the top of the picture.

Latch Components

Now we should remove the door latch components, this is where a spring-hook comes in handy. You can see how it makes the job of manipulating springs much easier, even on this relatively accessible spring. Once spring and latch slide are removed, this interlock arm should also be removed. Now it’s safe to have a good look at the camera.

Camera Tour

The large metal plate on the bottom of the camera does not need to be removed. It contains the gear train driving the film advance. In other EOS cameras, the film advance is driven by a separate motor built into the film take-up spool. On the left, as we see it, there is some tape covering some flex-board circuitry. This tape has to be removed, and the screws passing through the flex-board have been taken out to release it. This is made more difficult by the fact that it has also been glued in place. I have no idea why this was deemed necessary, but the glue effectively clogs the screw heads. You will have to carefully dig out the glue from inside the screw heads before you will be able to remove them. Use a dental probe to do this, and get as much out as you can before attempting to remove the screws, they can be very tight. There are quite a lot of wires that need to be unsoldered before the mirror cage and shutter assembly can be removed. The following pictures record the locations of the various wires so that they can be replaced correctly. Take care that you check the colors of your own camera can be recognized from the pictures. The colors displayed often appear different from the actual wires and may cause confusion. The preceding images show the wires on the battery side of the lens mount. All of these wires need to be disconnected.

Flash Circuit

This PCB and the wires can be left in place, it is the voltage inverter for the built-in flash. BEWARE HIGH VOLTAGES ON THIS BOARD. There are components on this board which can store a high voltage charge for quite some time, even without the battery. While it is probably not enough to kill a healthy person, receiving a shock is quite an unpleasant experience.

Removing the Top Cover

Before removing the top cover, I find it convenient to remove one or two parts and do some unsoldering. There is no real physical reason for this except that I like to avoid balancing the camera on the exposed circuitry under the top cover while working on the top and sides. First, locate the battery switch on the bottom. It’s right next to the flash circuit board so check the section above before proceeding. Remove the retaining screw, and save the glass-fiber insulator. Once this is done, the flex-board on the bottom plate should be detached from the plate. (Provided of course that you have successfully removed the screws embedded in the glue!) At the other end, the two blue wires should be unsoldered, and the solder tag next to it should also be unsoldered. The six tabs here should be unsoldered too. We should now remove the top cover. To do this we must first remove the retaining screws. Two of these are behind the eyecup. Another two are partly concealed. One in the battery compartment. Another here. Before lifting the cover set the selector dial to ‘Lock’. Lift the lid carefully, and… If this looks a bit scary, don’t worry. Just note the position of the selector. (The big round transparent thing on the right.) You will need to make sure of the position when replacing the top. The green board in the middle of the shot will need some of its wires unsoldering but not yet. Make sure you make a note of the wire locations on this. WARNING: THIS BOARD CONNECTS TO THE FLASH TUBE, IT MAY BITE!

Preparing to Separate the Film Transport

In order to access the shutter, we need to separate the film transport system, from the rest of the camera containing the shutter, mirror cage, prism, lens standard, and the bulk of the electronics. First, we need some room to work in. These tapes on the inside of the cover should be removed. This tangle of wires should not need disturbing, but in case you pull one out, I’ve included a couple of shots. The coil you can see here releases the flash head, so don’t be surprised if it pops open should you tinker with it. Now back to the little green board, you need to unsolder some wires here. You can, of course, unsolder the lot if you want, but you should at least unsolder upper white and blue wires, grey and pale blue, the brown, and the one which is in this picture on the right of the board. (The sleeving is transparent.) Take care that none of the tracks short out on this board. There are quite large voltages in play here and there is the risk that should they end up in the wrong place they could cause considerable harm to any digital circuits. Now unscrew the little board. More wires need to be unsoldered before we proceed. What we are trying to achieve is to remove the bare minimum to disconnect the circuitry attached to the PCB from the film transport components. There are five wires in this group, note the black wire, and take special note of the location of the brown wire. Next, remove the release button PCB. And then remove the screws holding the frame counter mechanism. There’s a small spring bearing against a nylon spigot that drives the counter under the assembly. Take note of how it is fitted. Unsolder the wires from the battery terminals, and remove the screws from the power PCB. You can then disengage the PCB from the battery terminals with the aid of a soldering iron. Lifting the PCB reveals three tags connecting to the selector which need to be unsoldered. The five next to them connect to the shutter. There is no need to unsolder these unless the shutter needs complete removal. (In this case, it transpired that it did. The impact had dislodged one of the shutter coils so that it no longer releases the curtain.) The photocell assembly should now be freed. There are another three tags needing to be unsoldered here, near the front of the prism. This should be all that’s required on this side. Now move to the other side, and unhook this tab from the housing. It should now be possible to unwrap the flexi-board from the top of the camera and over the prism. It’s not completely released from the camera body, but we don’t’ want to do that anyway.

Rewind Gear

Under the flexi-board, the rewind gear housing is revealed. Remove this and the gear underneath. Take note of the location of the spring. We should now be ready to remove the mirror cage and shutter assembly.

Removing Cage and Shutter

Remove the screw at the bottom. Then the two screws at the front. The two lower screws shown below should be the last. The whole mirror, prism, shutter, and a whole bunch of circuitry should now be free. To remove it all, tilt it forward in the body slightly, lift a fraction, and draw it forwards. (If I have missed something, you will spot it now!) The shutter should now be accessible.

Disassemble and Clean the Shutter

To clean the curtains the small silver screw at the bottom left should be removed, and the back plate slid to the left to release it. The offending rubber buffer is now removable. As I mentioned earlier, the shutter works OK without it, but cutting a piece of inner tube to replace it may be advisable. This spacer can be removed to allow the removal of the curtain for cleaning. The other curtain is beneath a second plate spaced by a washer on the locking screw spigot. Clean carefully by gently wiping the blades with a cotton bud dipped in isopropyl alcohol while supporting the blades on a flat surface. Don’t forget to wipe in between the blades. After cleaning, the shutter can be reassembled, and the camera should go back together in the reverse order of disassembly.

Re-assembly Notes

Re-assembly should be largely the reverse of disassembly, the only points to note are to check the alignment of the selector dial when replacing the top, and double check the placement of all wires when soldering them back. This should be straightforward. (Provided you have not skimped in taking your own notes.)

How To: Pentax MX Disassembly

For the Pentax¬†enthusiast, it’s important to know about the Pentax MX disassembly. This camera was originally released in 1976 as an up-market lightweight manual camera for the commercial market. The camera was at the time the smallest and lightest SLR on sale. (Until the ME, released a little later that year!)

The design incorporates a mechanically timed cloth horizontal-run shutter, with the three color LED TTL exposure meter using five LEDs, with shutter speed, and aperture displayed in the viewfinder, depth-of-field preview.

What follows is the basic disassembly of the camera into its major sub-assemblies. The camera illustrated had been used in South Africa for about ten years. (Or so I was told.) The heat and dust had taken its toll, and it simply did not work. These usually respond well to camera repair, but this seemed much worse than generally encountered, and I had to disassemble further than I would normally have to in order to clean all the parts thoroughly.

I picked it up for the price of the lens, but after stripping, cleaning, and reassembly, bench testing showed perfect shutter timing, and the meter calibration was bang on. Not at all bad!

I’m not going to show all the fine details of that. It’s all a bit too much to take in at one go, and I suspect that you won’t have to go that far in any case to sort any problems with your own camera.

Disassembly.

Before starting, make sure that you have provided yourself with a notebook and a pencil. There are a number of variants of the internal wiring, and these may not correspond with the camera shown here.

Also, make sure that you have a tray for small parts, and be prepared to spend several hours on the job.

If during the procedure after releasing a part it is stiff, or difficult to remove, stop and check that all the screws, wires etc’ have been removed. Remember the golden camera repair rule: Never try forcing apart, you risk permanent damage if you do.

If you start to get tired, stop and come back to the job. You will make mistakes that you will regret later, and you are much more likely to lose your temper with stubborn fixings if you allow yourself to get too tired. (I am speaking from experience here!)

Also, it is likely that your camera has not been disassembled for servicing since it first left the factory. If this is indeed the case, all the internal light seals will probably require replacement. As this Pentax MX disassembly will expose all of the seals these should be replaced at this time. Deterioration of the seals will not only increase the risk of film fogging, but they actually fall apart and crumble.

The resulting particles consist of a sticky black goo which gets into the viewfinder and shutter, it is difficult to clean off and corrosive. If you have paint flaking off the film door margins, the cause is the door seals dissolving the paint! If it gets onto the focusing screen, the only way to get it off is to use an ultrasonic cleaning bath. Don’t be tempted to try solvents. (Some household bleaches can be useful for breaking up the goo deposit, but unless you are sure…. ) That will completely ruin the screen! Small ultrasonic cleaners can be bought for less than ¬£100 these days, or you could take it to your local jewelers who will probably have one and perhaps could clean it for you.

Suitable seal kits can be had from a number of internet camera repair vendors, and are not expensive. Shop around for the most comprehensive, a wide range of types and thickness of material may be encountered in a single camera.

Procedure.

Before starting any disassembly it’s as well to get an idea of what might need doing, and if there is anything, in particular, to watch out for.

The mirror cushion shown here has deteriorated, which is indicates that the internal seals are in poor condition, and so I know that I’m going to have to strip out the main assemblies to access those.

A fair bit of brassing here. This just shows that the camera has been used a lot. Examination of the lower part of the case showed very little brassing. That suggests that it was kept in its leather case a lot of the time. In my experience, the two factors of lot’s of use, and in the case most of the time suggest a one time cherished possession. Which is a good sign!

It’s also worthwhile examining screw heads under a magnifying glass. These collect a good sample of much of the muck that the camera may have been exposed to. (I just stripped a K1000 that had been dunked in a good strong cup of very sweet coffee. Once dried that really jammed it up good!) This one was well bunged up with caked dust. To make sure that your screwdriver gets a good purchase you want to clean any muck out before attempting removal. It also can show if the camera has had any clumsy maintenance!

In this case, I removed the bottom cover before I started, as I already new the camera needed a good internal clean, and a quick squirt of lighter fluid freed the shutter to the point of allowing shutter release albeit with crazy shutter speeds, and squealing noises!

We’ll start by removing the film-advance lever. This is easier on this camera than others in the Pentax range, as there are holes in the cap. Beware though, this is a left-handed screw. So make sure you don’t break it by turning it the wrong way!

You can also see some of the fine dust still adhering to the outside of the camera.

The advance lever is retained only by the cap in this model. (The shiny round object in the foreground is a blob of solder, not a part of the camera!)

Then remove the collar shown.

Next, remove the selector. This can be done with the improvised tool described elsewhere. The Pentax service manual recommends setting the speed to 1/1000 and selecting 100 ISO for reference.

Take care that you don’t lose the film selector locking stud. Take careful note also of how it fits into the selector assembly.

The position of the selector coupling and potentiometer should be noted.

And remove the trim collar.

The selector parts removed.

To remove the rewind knob, lock the rewind shaft with a screwdriver.

Once the rewinder is removed you can remove the retaining bush.

(You might want to unclip the film-door at this point. If the winder drops into the body opening the back will be quite difficult.)

Now remove the two screws on the top of the cover,

and the two either side of the viewfinder.
The top cover should lift off easily now.

With the top removed, take a good look around. You will need to be sure you have a good idea where everything goes, especially the wires. (You can’t test-fit these to see if you have it right!)

Note the large foam seal here. This is only just holding together, and will soon become crumbly, and disintegrate. If you can imagine how much particulate muck this will generate, you just about got the reason why we need to check these out!)

This seal will be replaced with new material once we have cleaned it all up!

The leatherette trim should now be removed. To do this first remove the self-timer lever. First, the screw cap should be removed.

Then the Leatherette can be carefully peeled off. Start the edges with a dental probe.

Note the metal plate beneath the right-hand side.

This covers the shutter release adjustments. It’s a good idea to leave this well alone for the time being.

The bottom cover is retained by three screws.

Don’t lose this plastic bit. All that keeps it in place is the bottom cover.

Take a minute or two to explore.

Note especially the location of all the springs.

If you’re thinking that this all looks a bit complicated, you’re right.

The reason is that unlike the older Spotmatic and K’ cameras, a good part of the shutter mechanism is under the bottom cover.

The low-speed cams, and escapement are all accessible from under this cover, as well as the mirror priming gear.

If you are having problems at low shutter speeds, often a good washing out of this lot with lighter fluid or similar solvent, and lubricating with a couple of drops of shutter or watch oil will fix it.

(Always use as little oil as you can. Apart from it being a bit on the expensive side(!), too much oil causes problems elsewhere. It isn’t total immersion lubrication system!)

With the top, bottom covers, and the leatherette out of the way the front standard can be removed

Try not to disturb these washers, or at least get them mixed up. These are used to set the lens registration distance essential for accurate focusing, and they are not all the same.

Check that there are no washers stuck underneath the standard.

The easiest way to avoid losing these washers (and indeed the screws themselves) is like this!

Now you want to remove the electronics.

Start by removing the speed-resistor.
Unsolder both the brown wires, and remove the two screws holding it to the speed selector assembly.

The resistor removed.

Unsolder any other wires connecting them to the board from the camera. Be sure to record the location of each wire. The pictures shown here may not correspond exactly to your own camera!

With the wires, disconnected proceed by loosening the clamp screw, and remove the screw securing the LED PCB.

The hot-shoe contacts should be removed to free the photocell board.

Once this is done you should be able to remove the meter board.

If you haven’t already done so, remove the focusing screen before proceeding. Keep it somewhere safe.

It will be easier also it the prism and associated parts are removed at this stage.

This is most easily achieved by loosening one of the set-screws at one side of the prism. Leave the other in place as a reference.

Alternatively removing the two screws holding the viewfinder lens will allow removal of the viewfinder frame complete.
Do not disturb the small set screws fixed with lacquer, or glue unless you want to spend the rest of the day setting the screen focusing up again!

In order to remove the mirror cage, you will have to disconnect some more wires and remove the transfer gear that operates the shutter speed indicator dial.(You will have a jolly time setting this up again, so it’s worth considering whether you really need to remove the cage at all!)

The cage itself is secured by two screws accessed from underneath.

Before lifting the mirror cage out, check that all the wires are disconnected, also check that the mechanical linkages are free. This usually means that the shutter should be charged before removing the cage.

with the cage removed it’s easy to see how the mirror mechanism works.

Servicing the cage is simply a matter of cleaning away all the old oil and grease, and replacing any corroded light seal foam etc.

I find that the easiest way for me is to remove all the foam, wash the moving parts liberally with lighter fluid (total immersion in a jam jar works well!)and after mopping up the excess I drop the whole lot into an ultrasonic bath with water and a good detergent will get all the remaining dirt off. (It also cleans the mirror at the same time!) Washing the whole assembly in clean water is then required to remove all the cleaning fluid.
The mechanism should be dried immediately (You can use a hairdryer!), and lubrication applied.
Light oil should be used for each of the pivots, but a thin smearing of grease should be applied to the release catches where they bear against spring-loaded levers. (Note: Thin, means very thin. Too much may prevent the catch from setting properly.)

You should now have access to the shutter itself, the shutter mechanism and the shutter rollers.

Carefully washing the moving parts with lighter fluid while operating the shutter mechanism will wash out the old oil from the mechanism. Don’t forget the shutter rollers.

Try not to get lighter fluid on the shutter blinds. The rubberisation won’t like it much, and the longer it is before you need to replace the shutter cloth the better. It is not an easy task!

Once the mechanism has been cleaned, you should replace any foam seals, before lubrication, as you will find that however careful you are, you will get some oily stains just where you would like to put a seal, and they won’t stick!

Now re-lubricate the mechanism. You should obtain specialist shutter oil, or watch oil for this purpose. These are especially light oils, and other heavier oils may just gum everything up. Also, they are designed to last a long time without needing replacement, which is not the case with a general purpose or cycle oil.

Slow moving parts such as winder gears etc. should be lightly greased. I find that dissolving a little grease in a solvent will allow an even application of the minimum amount of grease, and help distribution throughout the gear train.

Re-assembly is largely the reverse of disassembly, but if you have removed the transfer gear you will have to temporarily fit the selector knob, to show which speed you have selected.
With the prism in place, you will have to adjust the position of the transfer gear so to obtain the correct indication of the selected speed between the index marks at all speeds.
If you have not done this before, this could take some time, so be prepared for a long frustrating session! (It gets easier with time.)
Take care that you don’t allow the activating cord to become dislodged from its pulleys, as this also can be a pain to get back on track!

How To: Pentax Vertical Run Shutter Maintentance

This shutter is used in the ‘M’ series of Pentax automatic cameras. So, it’s smart to know about Pentax vertical run shutter maintenance. The shutter, mirror cage, and body parts are essentially the same for the whole range from the ME, through to the worlds first commercial autofocus SLR, the ME-F.

Here I show one method of checking the shutter speeds and timing, and how to rectify any problems in the shutter itself.

First, let me list the problems normally attributable to the shutter.

Erratic exposure.
Uneven exposure top-to-bottom.
Partially obscured images with flash.
Dark bands at top or bottom of the image. (Sides for horizontal run shutters.)
Shutter only operating on ‘X’ or ‘B’ speed settings.
Unreliable flash triggering.
Jammed shutter (Rarely).
Note that the shutter itself is only rarely the cause of the shutter jamming, or the camera locking up. (Unjamming ME-Supers is the most common camera repair I am generally asked to do!) This is usually caused by a problem with the mirror mechanism. If there is no obvious damage to the shutter curtains, or a foreign object, or substance (Commonly marmalade!) has got into the camera, then the cause is most likely elsewhere.

If your camera is locked, please look at the ME-Super disassembly page on this site. The problem is common in older examples and usually has a simple cause, and solution.

Also, note that shutter speeds as such are not the responsibility of the shutter itself. Incorrect speeds are due to a problem with the electronics. (Look for cracks and breaks in circuit boards and loose wires.)

Let’s start with checking the shutter operation in situ.

Shutter Checking Equipment.

It is, fortunately, possible to check the shutter and diagnose most shutter problems without and disassembly.

It does, of course, require the use of equipment not normally to be found in the average toolkit, but if you happen to have an oscilloscope or have access to one you can check the shutter operation without much extra equipment.

This method is fairly straightforward and can be applied to any 35mm SLR with a focal plane shutter.

I keep promising myself that someday soon I am going to build myself a compact, self-contained, and inexpensive shutter tester, and when I do I will publish the drawings. Until I do, however, this method works well enough for most camera repair situations.

This page does not show you how to calibrate the shutter, you should look at my ME Super calibration page for that. It does show you how to check the shutter and diagnose and fix any problems with the shutter. This is most important, as there is little point in attempting to re-calibrate the shutter if it is not working correctly.

Focal Plane Diode Sensor

Assuming you have access to an oscilloscope, (A dual-trace type, is ideal, but those are quite common these days.) you will need to construct a focal plane sensor.

This can be done with a piece of prototyping board, two photodiodes, and some black velvet or felt. (Or similar black material.)

The one I made looks like this.

img1

From the back.

sensor2

From the front.

The back view shows a couple of resistors, of about 100k. These are simply arranged in parallel with the photodiodes and serve to reduce interfering noise. (It also reduces the size of the signal by about 50%, but the ‘hum’ signal is much reduced. Proper screening would probably be a better idea!)

The black ‘felt’ used here is a type sold specifically for use in cameras as an anti-reflection covering. It is essential to use some sort of light absorber in order to get a reliable signal. It is quite surprising how reflective the back of the shutter curtains are. (Especially considering their function!)

In fact, your felt should cover all of the photodiodes except for a small hole right above the black rectangle of the diode. This helps give sharp edges to the ‘scope trace, making it much easier to read. I haven’t shown it like that here, as you would not be able to see the diodes if I did!

Also, note the orientation of the diodes. The actual active area of the diode is a square. The edges of the square should be parallel to the edges of the board, that helps too. Also, note the spacing of the diodes on your own version. Make sure you measure from the same edges of each diode. That is bottom edge to bottom edge for example. You will need this number when checking the curtain speeds.

I have connected the anodes of the photodiodes together to give a common earth for convenience.

In use this is simply strapped to the film plane, using rubber bands,

and check that the photocells can be seen.

The camera should be fixed in place and illuminated from the front. You could mount it on a tripod, but I have just stuck it to the tabletop with blu-tak. The light source here is a small laser filched from a broken laser pointer with the lens removed, but it works just as well with a halogen desk lamp. (I’m only using the laser because it was just lying about, and it runs for days on a single battery.)

Connecting the oscilloscope probes now helps find the best position for the light source.

I really should cover the back of the sensor to exclude stray light, but it works OK as it is. Just glue a small plastic box over the back once you know everything is right.

These tests do not calibrate the meter, this has to be done separately, and is dealt with on another page. Once calibrated, however, the manual speeds, and calibration can be checked at higher speeds with these tests.

The tests here mainly check that the shutter is properly set-up mechanically. Unless this is done the meter calibration may be of little use!

If you think your meter is in need of calibration check the calibration page first.

The tests.

Curtain speed

The first thing to check is the curtain speeds. With a focal plane shutter, the two curtains are driven by separate springs. The tension of these springs will determine the speed that they travel across the focal plane.

It is important that the curtains maintain a certain minimum speed. If they are too slow, then the curtains may not be open fully when the flashgun is fired. If this is a problem with your camera, then this must be checked first.

It also is important that the two curtains travel at as near exactly the same speed as can be achieved. If they do not, then the exposure will change progressively across the frame. This will be specially marked at higher speeds. If your camera exhibits such symptoms, then the problem lies here.

To check the manual x-sync speed select 125X and set the scope first to trigger from the first photodiode exposed. You should get a trace something like this.

If like me you don’t have a digital storage ‘scope you will probably have to turn the trace brightness all the way up, to get a decent impression of the trace. In this still from a video of the scope, the time base is set at 1ms/division, and we can just about see that the opening curtain is crossing the distance between the two photodiodes in about 4.5ms. The distance between the photodiodes is 18mm, and the manual for the ME-Super states that it should take 6ms or less to cover 21mm, and scaling this up this comes to 5.25ms, so that’s ok.

(If you do not know what the curtain speed should be on another camera, just check what the x-sync speed is. The shutter needs to be fully open when the flash triggers, and so the curtains should cross the whole of the film plane in less than that time. Allow ten to twenty percent less for safety, and use that as the curtain speed. It is important not to set the curtain speed to high, as that risks stressing the springs which could become weakened or even break. With silk shutters, it also controls the shutter tension, too high and the shutter ribbons will tear.)

This should be done several times to ensure that the speed is constant. If it is erratic suspect contamination of the curtain blades with grease or other substance, or that the shutter mechanism needs lubrication. It is also possible that a foreign object has got stuck between the shutter blades. (I have found washers actually inside the shutter curtain guides before!)

With cloth shutters, this would indicate that oil lubricating the rollers need replacing, or that there is some problem with the curtain rollers themselves.

The same operation should then be repeated for the closing curtain. This time the ‘scope’ should be set to trigger on the falling edge, and the trace will appear inverted.

Shutter speeds.

If the camera is calibrated correctly, then the manually selected speeds and the automatic speeds should be within half a stop of each other. The manually selected speeds are only expected to match more closely if the light level is such that the automatic control determines that the precise exposure should be that speed exactly. That is because the automatic speeds change continuously, rather than being selected at the nearest fixed speed.

Check the manual speeds at all settings. If you get speeds greatly in excess of or less than the indicated speed, that there is a problem with the shutter timing circuits. A common cause of this is the crack in the white ceramic PCB, on top of the pentaprism, but you may have to do some deeper investigation to determine the cause.

Shutter speeds greater than a second can be checked using a stop-watch, higher speeds need the oscilloscope.

For this test, you only look at one photodiode at a time. At the higher speeds, you should compare the speeds for each diode.

We start with the ME-Super by checking the x-sync speed, which is a purely mechanical default. I get this trace.

When measuring the times on these traces always measure to the beginning of the change. The time starts when the trace first begins to rise and ends just when it starts to dip at the other end. This trace is just short of 9ms, say 8.8ms. That corresponds to 1/114s, which is a little slower than the advertised 1/125, which is 8ms exactly. This is just within 10% and is not a cause for concern given that the curtain speeds are within limits.

The speed should be checked at each speed up to 1/1000s. Check each speed several times to ensure it is consistent. If not, it is likely that the shutter mechanism needs cleaning and lubricating. (Shown later on this page.)

Speed matching

The two blinds should cross the entire focal plane within, (at the worst) 0.1ms of each other. Fine adjustment can be achieved by comparing the shutter speeds at the top and bottom of the run for high shutter speeds.

To do this, select ‘AUTO’ with the batteries removed. This should give you a shutter speed greater than 1/2000s.

At this speed, it is important that the two diodes in the sensor board, and the windows letting the light through, are pretty closely matched. The windows less than 0.5mm across, otherwise you won’t get a clear picture of what’s going on.

Remember that the shutter curtains take about 6 milliseconds to cross the focal plane, so that means at 1/1000s the shutters will be separated by 21/6 millimeters apart, or about 2.4mm, at 1/2000 this is 1.2mm. We are trying to get a good look at something of about 1/3000s-1/4000s. If you are having trouble with this, try using the sensor board the other way up, so that the two diodes change places. This will tell you if the differences you are seeing are really due to the shutter or differences between the diodes.

We don’t really care what the separation between the photodiodes is here just that they have a good separation between them.

First, check measure the shutter speed at the top of the shutter travel. This should be fairly regular, it should be pretty much the same for each firing. (Within 10% certainly, but 5% is achievable.) If this is erratic, then the manual shutter speed escapement needs cleaning and lubricating, before you can check the speed matching.

Using an average of several readings of the upper diode shutter speeds as a reference, measure the speed at the bottom of the travel. Again average several readings, and compare the averages.

If the lower diode shows slower speeds, then the closing shutter is running slow. Increase the tension on the upper spring, by one click and re-check the speeds. Stop when the speeds are within 0.03ms of each other. (This may just be a single click on the spring adjuster.)

If the lower diode is faster, then the opening shutter is running slow. Adjust this the same way as the closing shutter.

That is more-or-less all the tests you need to do, the next section shows you the important parts of the shutter, and how to correct any problems that may have been shown up.

Servicing The Shutter.

Much of what follows can be performed with the shutter still in the camera, but most of the shutter problems are due to lubrication and dirt, and require the mirror cage to be removed. The ME-Super is not a difficult camera to work on, as it most of the ‘M’ series, and so there is little reason not to disassemble the camera to the point where the shutter can be removed.

The development of shutter faults should be seen as a signal that the camera needs an overhaul in any case, and you should accordingly equip yourself with the required materials and tools to perform a complete service. The page to refer to is ‘Disassembly of the Pentax ME Super Camera’

Overview of the shutter.

The shutter is a vertical run metal curtain shutter. It is triggered mechanically, the opening curtain operating completely mechanically. Two mechanical ‘speeds’ are provided 1/125s and ‘bulb’, all other speeds are determined by a retarding solenoid, which holds the closing curtain open for an electronically determined period.

The selection of the operating mode is determined by the position of a lever protruding from the top of the mechanism housing. Viewed from the front of the camera, the leftmost position (Default) selects ‘B’, the rightmost position releases the closing curtain simultaneously with the opening curtain, putting the shutter under solenoid control. An intermediate position provides the x-sync mechanical default speed of approximately 1/125s.

The x-sync contacts are built into the shutter.

Examination and maintenance of the shutter.

Starting with the mode selector and default speed rocker.

Selector arm.
Selector latch. Actually an extension of the selector arm.
Opening curtain latch. This prevents the closing curtain from releasing before the opening curtain is released.
Mechanical speed rocker. This transfers the motion of the mechanical release cam to the closing curtain release providing the 1/125s mechanical speed.
No oil or grease is used here.

This is the retarding solenoid. When energized it prevents the shutter closing. The solenoid current is switched on just before the mirror reaches its picture-taking positing by the camera electronics.

This is the solenoid armature. This is pulled into the solenoid when the solenoid is activated.

The mechanical speed cam. Just to the right of the pointer, you can see the cam follower on the end of the mechanical speed rocker. The shutter is in the cocked position ready to fire.

Is the shutter cocking lever. Moving this in the downward direction in the picture cocks the shutter.
Is the opening curtain release. This is operated by the mirror actuator as the mirror reaches the taking position. It latches the release cam.

This is the mirror ‘scissor’, not part of the shutter itself, but the spigot just above it engages the cocking lever (Just visible.) during film advance.

The shutter in situ, showing the engagement of the cocking lever with the spigot on the cocking arm.

Indicated is the mirror return striker. It’s coupled to the closing shutter and strikes the mirror return release as the shutter comes to rest.

Circled is the opening curtain latch. The curtain is cocked and engaged with the latch. The arrowed part is the opening curtain anti-bounce latch. This prevents the opening curtain bouncing back into the focal plane aperture in conjunction with the opening curtain brake.

In the open position, the opening curtain is latched.

Lubrication

The old lubricant on this cog and the idler pinions it engages with is the cause of erratic shutter speeds, especially noticeable at high speeds.
The pin and rubber roller form a brake for the opening curtain which is important in eliminating curtain bounce.
These parts should be thoroughly cleaned with isopropyl alcohol.

It may even be necessary to use a dental probe to gently scrape old dry lubricant from the gears.

After cleaning the gear and associated components should be lubricated with a small quantity of light silicone oil. The type sold in spray-cans in motor parts shops can be used. (Spray a quantity into the cap of the can first, and dip probe into the silicone to transfer the lubricant.) Don’t use mineral oil, not even specialist camera or watch oil. This can soak into the nylon parts making them swell, and can make them brittle. Mineral oil will also attack the rubber of the brake.

Note that this gear can be lubricated from the bottom of the camera by just removing the bottom plate.

Also clean and lubricate the cocking arm as indicated below.

Hold the cocking arm in the position shown. Use only the tiniest drop of oil and a light smearing of grease. Failure to lubricate here will cause the cocking lever to stick in this position, jamming the camera.

The screw indicated in the picture below is important and should not be disturbed unless it proves impossible to achieve the maximum shutter speed. It forms part of a contact opened by the opening curtain mechanism and is set to provide a timing reference to the electronics.

The other half of this contact is the gold-plated wire indicated. Dirt or oil on this wire where it makes contact with the set screw could be a cause of erratic speeds or intermittent operation.

The connection to the contact. The brown and the blue wires connect to the solenoid. They can be interchanged, the solenoid does not need to be connected a particular way about.

This ratchet sets the tension of the closing curtain spring. Turn this a few clicks clockwise to increase the speed of the closing curtain. Note that the ratchet only appears to allow increasing the tension. Springs are not likely to become stronger with age.

The lower one adjusts the opening curtain.

This is the x-sync connection. Unsoldering the solenoid and the contactor wire allows the removal of the PCB with the contact intact.

The flash contact here shows some pitting and black deposits caused by arcing. This is due to being used with older flash units which have trigger voltages ranging from fifty to five hundred volts or so. There are a lot of these flash units still in circulation, and this illustrates the sort of long-term damage that can be caused.

In fact, this contact has not seen an awful lot of use and works perfectly well. You can imagine what the result of heavy flashgun use would be like. Devices are available to prevent this happening but are rather expensive. I have instructions on how to build one for yourself elsewhere on this site and can supply a kit, including a PCB to build it at very much less. (I am looking into the possibility of supplying completed units for those who would prefer it.)

Testing a shutter out of the camera

You may, of course, need to check a shutter without the shutter being in the camera.

You need to make sure that the shutter is held securely in place over the sensor without interfering with the shutter action. Either use the shutter mounting holes or as here only support the shutter at its corners.

The selection arm will have to be held in the ‘manual’ speed positions, central for 1/125s, and to the right for the maximum speed. I usually Blu-tac a matchbox or a rubber eraser to the bench to keep it in place, but usually, I do this with the shutter mounted in the camera body which is easier.

The default operating mode is ‘bulb’, so operating the opening and closing curtains separately is possible. In this case, the desk lamp serves as the light source.

Conclusion

That’s all you probably need to know about this shutter. There are plenty of the cameras using it still around, and with a little work, most can be restored to full, faultless operation. Perhaps even better than when they left the factory!

How To: EOS 600 Disassembly

Here I disassemble an EOS 600 camera. The Canon EOS 600 Disassembly process is not all that difficult in most cases. You will need to do this to clean the shutter sooner or later, due to a design flaw. (See Cleaning_The_Shutter_on The EOS 750 for details.) Another common reason for partial dis-assembly is to disconnect the LCD backlight which can develop an internal short which shortens battery life.

This dis-assembly goes much further than that which might be required for any particular operation. That’s because one of the cameras documented was dropped into the sea at some point, and was left for quite some after that allowing corrosion to finish the job. This camera will never work again, and I am breaking it into salvageable parts. So the disassembly is pretty thorough.The other camera was disassembled in order to access the shutter for cleaning.

Drowning Aside

If your camera gets properly dunked in the sea, the best thing to do is to wash it with clean fresh water as soon as possible. (Remove the film, focusing screen, and batteries first!) Rinse the whole thing thoroughly several times, until you are absolutely sure that all the salt has been washed out. Put it in a warm well-ventilated place to dry, preferably without its covers. When you are sure it is completely dry, you might find if you are lucky, that you have got away with it. It will probably need the prism, and viewfinder etc. cleaning later, but your camera is not completely ruined, and it will be possible to put it to rights. If you just leave it with salt water in the works, it will be completely beyond repair in a very few days. So you have nothing to lose.

Tools

Unlike many cameras, there are no particularly special tools required to take one of these apart. You might find a spring-hook handy to deal with the door latch spring though. Otherwise, a reasonably good quality set of crosspoint screwdrivers, a pair of tweezers, a small soldering iron, and solder sucker should be enough.

A pencil and some paper are also essential for recording details like the locations of wires etc. I often use a compact digital to help out with this,( Which is where most of these pictures come from.) but beware of color rendering differences. The colors of many of the wires shown will appear different in the pictures than they actually are. Don’t rely solely on pictures. (It won’t help if you are also color blind!)

For general information on tools, and dealing with things like stuck screws check my tools page.

Removing the Covers.

As always begin with a good examination of the outside. I can see at least two screws in this picture, but here are a couple more over to the extreme right, which is lost in the murk.

Ok, nothing peculiar about the battery cover/grip. (Wonder why I took the picture?)

Ok, there’s a screw at the back….

and some under the grip.

Quite a lot actually. Note that the screws are not identical. If you are worried about getting them mixed up, or losing them. Then stick a piece of Blu-Tac next to the hole and push the screw into it. As soon as the part it’s holding is removed, you can either put this aside with the screws still stuck or put the screws back into the hole they came out of.

(Here’s a tip about putting screws in. Always start by turning the screw the wrong way when putting it back, and feel for a click before screwing in. That way you ensure proper engagement of the threads, avoiding damage and loose screws.)

You should now be able to pull the bottom panel off. Read the note below before trying this!

Note: the screws in the front need to be removed if all you want to do is remove the bottom. This is because of a tag on the front cover which engages with the bottom cover. You need to ease the front cover forwards to release this.

If you are going to remove the front cover anyway, then leave the bottom on until the front is removed.

To remove the front cover you first need to remove the door latch. This is a bit more complicated than most.

First, remove the two screws.

The release button sits in a keyhole slot, closing the back releases it. Watch for the spring beneath.

Remove the latch button and slide.

Removal of the latch mechanism cannot be completed until the front cover is removed. Leave the film door closed to keep the parts in place until then. Notice also the large lug to the right of the coil spring. That engages with a protrusion on the latch cover and is why it needs to be removed first.

Remove all of the screws holding the front cover, and lift it off. Take care of the two buttons on the side of the lens, mount, these are liable to fall out.

After unhooking the coil spring on the latch, and removing the latch plate, this locking arm is uncovered. Check the relationship between this and the parts of the short end. (Circled)

To remove the top cover, first, remove the two screws shown.

There is a screw beside the strap-lug here,

and three screws here. You only need to remove the middle one.

IMPORTANT: Set the mode selector to the position shown before attempting to lift the cover. Failure to do this will lead to breakage of the mode selector. Replacements can be hard to find.

Now lift the top cover. It should come off easily. If you experience any resistance, stop and find out why.

See the selector switch circled here, remember this setting. Also, note (arrowed) the black deposit on the shutter. This camera would need disassembly to rectify the cause of this in any case. If you check the EOS disassembles on this site, you will see how common this is! Sooner or later, this will jam the shutter.

With the cover lifted to examine the mode selector switch, and note it’s position. Also, remove the buttons shown and the rubber molding beneath them.

You can begin to see the extent of the salt damage here.

Hot Shoe Connections

Before continuing, the location of the wires connecting the hot shoe and sounder should be noted, and the wires unsoldered. Don’t be tempted to leave them in place without noting their locations. I can promise that whenever you make that decision, one or more of the wires will come off, and you won’t know where it came from!

The camera without its clothes.

Unsoldering the Electronics

Now move to the bottom, and remove the tripod mount, and unsolder the black wire you can see in the middle of this board. You can see the mess that leaving the camera full of salt makes.

Now unsolder the gray and the black wires here.

Unsolder these also.

Unscrew the board and lift it out of the way. Lift this insulating sheet out, and put it somewhere you will remember.

Unsolder the wires indicated and remove the screws circled.

Remove the screws indicated.

Remove the panel and the rubber molding underneath. The flex-board can be lifted out and you should be able to unwrap the board from the bottom of the camera.

Unsolder these tabs.

Unclip the back, and remove these screws.

Unscrew the digital back connector, and pull it away from the back.

Unsolder these two tags.

Unscrew the co-axial wire here, and unscrew the selector edge-wheel.

This wire is the supply to the backlight, this is the wire you remove if you are having battery problems. Also, remove the screws from the metal bracket on the LCD, and remove the rubber buttons.

The film cassette switch should be unsoldered from the flex-board.

Separate the Front & Back

Remove the screws from the metal plate next to the motor.

Remove the two screws holding the switch and gear cover.

At the other side, lift the LCD out of the way, and then unsolder the three tags circled. Also, unsolder the thick red and black wires.

It should now be possible to remove the film transport from the shutter, mirror, and the electronics.

Unscrew the screws that fit here.

Remove these screws also.

The mirror and shutter assembly is now free to be separated from the film transport.

This gear is a loose part at this stage, it should be kept safe.

This part operates the film cassette switch. It is also loose.

Viewfinder Removal

If you need to remove the viewfinder and metering photodiodes, these screws and their counterparts need to be removed.

This is the metering diode array.

In this close-up, you can just see the division of the sensor into the zones. (Each one is a separate diode, but they are all made on the same piece of silicon. This ensures that they are very closely matched.)

image

Prism Mount

You will need to remove the light meter diodes and unwrap the flex-board from the top of the pentaprism to remove it. After that, it’s just four small screws. On reassembly, these brass shims should be replaced as shown in this blurry image. (Damn autofocus!)

The mirror and shutter gear is best left in one piece. If it needs disassembly to replace a damaged part, take care to make notes as you take it apart. The operation of the mechanism is not immediately clear, and difficult to see prior to disassembly.

Shutter Details

For those who have a shutter problem that requires removal of the shutter, the following may prove useful.

This side view of the shutter shows the major components of the shutter. You may find on examination, that the problem can be diagnosed without removal of the shutter.

The connection to the shutter is made by five the five pins highlighted. Dry joints here will cause shutter problems. Unsolder these first if you intend to remove the shutter.

The shutter is held in place by three screws. Look out for this light seal as you remove the shutter.

The shutter removed.

This type of shutter uses two solenoids. Applying current to each one operates the release for the curtain controlled. There is no manual speed default on these shutters. To test for curtain speed matching, either the shutters have to be timed separately, or a means of electronic release devised.

This lever charges the shutter.

Manually tripping the shutter is simply a matter of depressing the solenoid armature. Fine tuning is achieved by screw adjustment of the opening curtain.

Miscellany

If you are going to dismantle further, you may find the following pictures useful.

This object is the autofocus system sensor.

If you take it apart (Not recommended!), the sensor is revealed.

Ok, now all you have to do is put it back together!

Conclusion

That just about wraps it up for now. There are a couple of items not covered here, but you should be able to figure it out. I’ll be adding a few more details later as and when I get the chance.