The Olympus OM cameras are famous for their relatively large and bright viewfinders. Yet, the nice view through the viewfinder is often spoiled by a damaged penta-prism. The damage I am referring to is the deterioration of part of the prism's reflective coating caused by a disintegrating foam light seal. Even if your camera doesn't suffer from such a malaise it is a good idea to check and replace the foam seal, if it hasn't been done, yet.
To do this, one first needs to remove the camera top. Luckily, it is not difficult - at least in theory. Difficulty can arise, if some of the items to remove have been screwed in very tight. Let's hope that that's not the case.
Removing the top cover of the Olympus OM-1 / OM-1N
Open (or remove) the camera back, place a suitable item between the prongs of the film rewind shaft to prevent it from rotating and unscrew the rewind knob counter clockwise. Note, that on the Olympus the rewind shaft is made of a fairly soft metal, so if the knob is hard to unscrew the prongs can bend out of shape. You will know if this has happened when later, as you pull up the rewind shaft to open the door latch, the rewind shaft gets stuck in the raised position. One way to prevent this could be to make use of an old film spool instead of sticking a screwdriver in between the prongs.
You will find two screws under the rewind knob. Take them out.
Next, assuming that the accessory shoe is already off the camera, unscrew the little chrome ring on top of the prism housing. For this a spanner wrench tool comes handy, such as the one on the picture below.
The last thing to do is to remove the film wind lever. Now, you might think that this is a simple matter; just stick your spanner wrench into the two holes on the cap (they seem to invite you to do so) and unscrew. But this should be the last resort. First try to employ a piece of suitable rubber and use friction to turn the cap.
The truth is that the black disk you see there is only for cosmetics. It is a thin piece of metal. The actual cap-screw is the chrome part. That also has two holes in it which might or might not properly align with the holes on the black cover disk. Here is a picture to help understand what I mean.
As you can see, the cover disk (shown turned upside down) was glued onto the cap-screw. It is all too easy to scratch the surface of the cover disk with a slipping tool or to enlarge the holes on it, if the cap-screw is very tight. If the rubber method doesn't work the next best thing would be to pry off the black cover disk first. But, if such a large amount of glue was used as on the picture, then that might be impossible, too.
As you dismantle the film wind assembly you'll get to an aluminium ring - the last piece - which also needs to be unscrewed. After that, the top can be removed. There is no need to touch the film-speed setting dial other than to make sure it is set to one of the common values (e.g. 100) indicated by yellow print.
Depending on the model, there will be two or three items, which are easily lost if you don't pay attention:
- a spring at the far left corner (near the rewind shaft),
- a washer on top of the A shaped flash shoe mounting bracket (inside),
- a small insert on the underside of the film wind lever.
You can find all three on the next picture. This is an earlier OM-1 model.
The red arrow on the next picture points to the culprit. After removing the accessory shoe mounting bracket (two screws), carefully clean off the crumbling foam from all affected parts. Pay attention to the wires.
Optionally, you can remove the penta-prism to clean the viewfinder's optical elements. It is easy to do. However, don't do what I have done and leave the focusing screen in place. Debris will land on it which is then hard to clean off without causing damage. Take the focusing screen out before starting the disassembly.
I have written at some lenght about viewfinder cleaning in another blog you might want to read.
Re-assembly
There is really only one thing to look out for when repositioning the camera top. You'll see some lines (or grooves) on top of the galvanometer. They mark those film-speed settings which, on the ASA dial, are printed in yellow. On the picture the red arrow points to the line that corresponds to the current setting (in this case 200) on the ASA dial.
When you replace the top, but before putting back all the screws, knobs, etc., put a battery in the camera and make sure the light meter switch and the ASA dial work properly.
Some differences between the various models
The above disassembly instructions apply to pretty much all OM-1 and even OM-2 models. The differences are so insignificant that simple common sense will suffice to overcome any discrepancies. Nevertheless, on the above picture and the next picture I'd like to point to some of the variations you might encounter.
The green arrow points to a simple light-meter switch found on some earlier models. The blue arrow shows that on some cameras the plastic piece which houses the viewfinder eye-piece is rather large and incorporates the galvanometer. This makes cleaning the viewfinder eye-piece somewhat more difficult. Since we don't want to disturb the galvanometer, the removal of the penta-prism will be necessary to do the cleaning job well.
On the picture below there is a welcome solution to the foam light seal problem; an enlarged plastic cover over the penta-prism AND the gap between the penta-prism and the viewfinder eye piece. One wonders why at Olympus they did not do it like this in the first place?
An attempt to fix a damaged penta-prism
Lastly, I would like to describe an unsuccessful attempt to repair a damaged penta-prism. Although it has been a failure, I want to tell about it so that others don't waste their time doing the same. Or, perhaps someone can see where I went wrong and improve on the method.
I carefully scraped off the affected areas on the prism down to the clear glass. I then painted it with the product you see on the picture. This came in a spray-can, but rather than spraying (which looked too difficult), I took some paint out of the can and used a brush instead. I used many coats as the paint was very thin. After the silver paint dried, I painted it over with black paint.
The result was hardly any better than what I had started out with. Looking into the viewfinder I could still see two distinct shaded areas. The 'mirror effect' wasn't perfect at all.
The hard-to-open back door problem
On some cameras, where you are supposed to open the back door by pulling up the rewind knob, you may find that no matter how hard you pull, the door just won't click open. One cause of this may be that the door latch got stuck.
On old cameras the leather cover often starts to peel back at the edges, and if someone applied glue to stick the leather back near the place where the door meets the body, that glue could have found its way into the door lock area and interfere with the movement of the latch. The next picture makes clear what I mean.
Here, the glue seeped inside through a gap and settled on the latch restricting its movement. What I have done with this OM-1 is to lay a piece of thin wire into the gap, thus blocking off the glue from entering. One has to be careful, though, not to push the wire in too deeply, because it, too, can prevent the latch from sliding freely.
When you remove the screws and open up the door lock, watch out for the two little spacers you see on the first picture. Lose them, and you'll have a hard time finding a suitable replacement.
Further reading:
- a similar problem with some Canon cameras
- some other camera and lens restoration work I have done
- common problems with older lenses
- cameras in my collection
On a different topic see Roland FP-30 'secrets'; playing GS instruments on the Roland FP-30 digital piano.
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