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A Couple New Cameras for the Repair Bench: Olympus OM-1 and Yashica Atron (Minox type)

The prism of the OM-1 has residue from the decaying foam. Probably they all have this.
I'm going to take the top off and clean the prism.
 
With the top off, the black goop residue from the decaying foam rubber is evident.
 
Cleaning off the goop reveals that as it decayed it removed the silvering from a portion of the prism. That is OK because the prism works OK without the silvering. By cleaning it to make a smooth transition from the silvered to the bare glass (green arrow shows bare glass) the deformity in the viewfinder is almost completely eliminated.
That is the key to the repair.
 
All done cleaning. Green arrows show bare glass. This fixes the problem! The viewfinder image is near normal. No need to replace the prism.
 
All clean. Meter and shutter checks to follow.

I may need to take the top off again, but all the fasteners have been loosened, so easy to come off the second time.

BTW I have been experimenting with using some very sticky two sided mounting tape instead of spanners. Everything here came off that way, no marks.
 
I never use 50mm lens, so I have to find a lens for this camera. Need something unique. f1.2 or fisheye or something like that.
 
ic-racer said:
I never use 50mm lens, so I have to find a lens for this camera. Need something unique. f1.2 or fisheye or something like that.
Click to expand...

Well, you can get the 55mm f/1.2. It's not 50mm and it is a f/1.2 lens.
 
In spite of this being a common camera which is decades old there is very little on youtube about repairing these. One video called "Olympus OM-1 Disassembly" claims "this is a Vlog, 'I don't do tutorials'" and another, called "OM-1 Breakdown" claims "Don't do this (showing the mirror box off) as you will break the camera."
 
Out of curiosity, is this the relatively short production run OM-1 or the much more common OM-1 MD?
The latter is badged MD on the front lower right of the body, when looking at it from the front.
 
ic-racer said:
The prism of the OM-1 has residue from the decaying foam. Probably they all have this.
I'm going to take the top off and clean the prism.
Click to expand...

I had an early OM-1 (it was identified internally, in pencil, as an M-1) where the decaying foam de-silvered a larger part of the prism. The defect was noticeable, but the camera was still usable.

Ic-racer, have you checked the functioning of the meter? Another common OM-1 defect is for the wire from the battery to the meter to corrode and disintegrate at the battery end. I had that happen in more than one OM-1.
 
Before getting into the meter and shutter results I wanted to point out an error in the service manual. The first curtain and second curtain tensioning stars are labeled wrong.

If you also have the Camera Craftsman May-June 1974 issue on Olympus OM-1, it does show the correct labels for the tensioning springs.

 
The next thing to point out is the recommended curtain travel times. There are a few different numbers, depending on the measurement device (distance between the measuring points).

Olympus Tester 7F7L1 and/or 7F7L3 (32mm distance calculated) : 11.7 to 12.1
36mm distance : 13.5 milliseconds
Camera Craftsman Test Camera (1974) ("Edge to Edge") 14.5 milliseconds
 
MattKing said:
Out of curiosity, is this the relatively short production run OM-1 or the much more common OM-1 MD?
The latter is badged MD on the front lower right of the body, when looking at it from the front.
Click to expand...

It was my brothers camera, he got it I 1973. I think the MD version was in production but this non-MD was what was on the shelf at the store.
 
That is the model that I got - in 1974 in my case.
It was traded in on an OM-2s a few years later, but it served me very, very well.
 
The shutter speeds were not far off, but at 1/1000 (as is frequently the case with these older cameras) the exposure was not even across the frame.
I was able to improve it. Not perfect, but it will do.

The tester shows the first part of the frame the slit is too narrow (-0.29 EV) slightly under exposing and the second half of the frame under exposes 0.19EV. Not perfect but both are about the same.



 
Shutter speeds before and after tweaking:

Blue is before and Green is after. X-axis is shutter speed fraction and Y-axis is EV deviation of the shutter speed. 0.3 = one-third stop off, etc.

 
I did some light meter tests using various batteries and a regulated power supply:
 
My results show the Zinc battery has a linear response in my camera, so I'm going with that for now.

I could spend a lot of time altering the 3 resistors in the light meter circuit (per the manual) to get it to read correctly but for this camera, I'll just adjust the ASA dial accordingly for the exposure compensation.

 
I replaced the deteriorated foam along the back of the camera. First I scrapped out the old residue (tape to protect the shutter). Then I cut new strips of adhesive-backed foam rubber to place back in the groove.

 
The deteriorated foam in the mirror box was also carefully removed. Taking care none of the dust got behind the focus screen.
Then, new strips of foam were cut to size. This foam was thinner than the foam used for the camera back.

Foam rubber came from McMaster Carr.

 
MattKing said:
Out of curiosity, is this the relatively short production run OM-1 or the much more common OM-1 MD?
The latter is badged MD on the front lower right of the body, when looking at it from the front.
Click to expand...

I bought my om-1 in june 1974. If the md was at the market at that time, I would have known. It came later.
My camera is still working like new after 50 years. Thanks to http://www.om-doktor.de/wir-ueber-uns.html who serviced it several times over the years and repaired the lightmeter last year.
 
The story that circulated around the time that the OM-1 was replaced with the OM-1 MD was that the original OM-1 was designed to be suitable for return to the factory to have the modification done to permit use with a motor drive. It was assumed that very few customers would be interested in having that done. When the camera burst on to the market, a much higher percentage than expected were sent by customers for the modification, and people at the retail level got pushback from potential customers about the connected delay and expense. So the decision was made to incorporate the modification for all new bodies going forward, and those cameras had the MD designation added.
 
How exactly did you feather the edge of the silvering on the mirror? Solvent? Mild abrasive? I have a Pentax K2 with a bad prism and I'm not sure how easy it will be to source a new one.
 
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