Inaccurate light meter om1

Curlypengling · Jul 8, 2017

Hi I just bought a great kit consisting of the OM 1 and the zuiko 35, 50,and 100mm lenses. They are all good but when I pop in a 625 wein cell the meter doesnt respond untill the lens is wide open and the speed is slower then a 4th. Any ideas on how to get it back to decent accuracy?

Bill Burk · Jul 8, 2017

You might have rotted mirror foam on the needle. If so, you could take it apart and clean it yourself. I've done that and it wasn't too hard. Or get it professionally cleaned. John Hermanson at zuiko.com put a sticker in one of my OM. Or you could use an external meter. The external meter would be my choice (but you could easily see I think of them as playthings)

Curlypengling · Jul 8, 2017

Bill Burk said:
You might have rotted mirror foam on the needle. If so, you could take it apart and clean it yourself. I've done that and it wasn't too hard. Or get it professionally cleaned. John Hermanson at zuiko.com put a sticker in one of my OM. Or you could use an external meter. The external meter would be my choice (but you could easily see I think of them as playthings)

Yeah I have a gossen meter, but yeah I noticed also that the prism is loose? I can see like glue marks in the prism. But yeah I wanted to not have to take my eye off of the subject to adjust the exposure or to take a reading

albada · Jul 8, 2017

If the needle swings freely when you quickly rotate the camera in the vertical axis, then the needle's movement is not being hindered. But the CdS cells in one of my OM-1s lost several stops of sensitivity, while others are close to accurate. I'll second the advice of using a handheld meter, or perhaps a shoe-mount meter.

Mark Overton

Curlypengling · Jul 8, 2017

albada said:
If the needle swings freely when you quickly rotate the camera in the vertical axis, then the needle's movement is not being hindered. But the CdS cells in one of my OM-1s lost several stops of sensitivity, while others are close to accurate. I'll second the advice of using a handheld meter, or perhaps a shoe-mount meter.

Mark Overton

How costly would it be to repair the cds cell?

chriscrawfordphoto · Jul 8, 2017

Curlypengling said:
Yeah I have a gossen meter, but yeah I noticed also that the prism is loose? I can see like glue marks in the prism. But yeah I wanted to not have to take my eye off of the subject to adjust the exposure or to take a reading

Those aren't glue marks, they're damage to the glass in the prism caused by rotting foam. The OM-1 and OM-2 originally had the prism held in place by a metal bracket on top of the prism, with a piece of foam between the bracket and the prism. They later stopped using the foam because the stuff had a tendency to rot and turn to a goo that was corrosive to the glass prism, permanently damaging the prism. The bad foam can be removed, and John Hermanson always does this whenever he works on an OM-1 or OM-2, but if the glass has already been damaged, the only way to fix it is a new prism.

Curlypengling · Jul 8, 2017

Curlypengling said:
How costly would it be to repair the cds cell?

I opened the bottom plate and found the the solder point was broken from the battery terminal and the even when the LM is off the needle responds to mechanical movement. So hopefully it's not the whole wire that's shot, but just the contact point

Curlypengling · Jul 8, 2017

chriscrawfordphoto said:
Those aren't glue marks, they're damage to the glass in the prism caused by rotting foam. The OM-1 and OM-2 originally had the prism held in place by a metal bracket on top of the prism, with a piece of foam between the bracket and the prism. They later stopped using the foam because the stuff had a tendency to rot and turn to a goo that was corrosive to the glass prism, permanently damaging the prism. The bad foam can be removed, and John Hermanson always does this whenever he works on an OM-1 or OM-2, but if the glass has already been damaged, the only way to fix it is a new prism.

Thanks for that info I'm gonna see if I buy proper tools to tinker with it

colin wells · Jul 8, 2017

I think you can use a later prism from a OM10 as a replacement

nsurit · Jul 8, 2017

You might ask John at zuiko.com before you tear into it. His price is a little higher when he has to repair what you "fixed."

albada · Jul 8, 2017

colin wells said:
I think you can use a later prism from a OM10 as a replacement

This is true, and I've done this p-swap several times. The OM10 had no foam above their prisms.

Curleypengling: Good point about a rotted connection at the bottom causing the meter to be far off. So let's not blame the CdS cell quite yet.

nsurit: Agreed! Somebody with no experience should never open a non-junker camera! Practice first on junkers until you know how to properly handle tools, and until you know how cameras are constructed. Thomas Tomosy published two books on repairing classic cameras called "Camera maintenance and repair"; I recommend them if you can find them.

Mark Overton

colin wells · Jul 8, 2017

The books 1 and 2 are still in print and available they contain invaluable information and how to's

thuggins · Jul 9, 2017

chriscrawfordphoto said:
if the glass has already been damaged, the only way to fix it is a new prism.

This is simply not true. The fix has been discussed ad nauseum on this forum. What you see as a damaged area when you look thru the viewfinder is the discontinuity between the damaged and undamaged silvering.

Remove the prism and the nasty foam, then peal off the damaged silvering. Then with Simichrome or toothpaste, feather the edge of the silvering to make a smooth transition between the silvering and unsilvered area. When you replace the prism, the unsilvered area is still reflective and there is no sign of damage.

I have done this fix several times and it works great; much easier than trying to find an undamaged prism.

Inaccurate light meter om1

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