OM-1 Light meter electronics

film Sep 25, 2019

My film camera uses an older style battery that is difficult to find, the form factor is ok, but the voltages are different in modern batteries. This affects the meter readings on the camera light meter.
One option is to install a diode in series with the battery, using something like this diode

The fix is relatively straight forward, you remove the bottom of the camera housing

Remove the battery spring clip and desolder it from the wire, place the diode in series between the two and reassemble

The above images are from this link (thanks Tim Hughes)

I'll put together a better pages when I get around to actually doing this, in the meantime, In the past I was adjusting for the high metering by guess/gutfeel. More recently I have been setting the ISO slightly lower to compensate.

ie if the Box speed on the film is 400, I have been setting the ISO dial to 320 and metering 'normally'. The idea being that the meter is reading too high (saying there is more light than there really is) due to the higher voltage battery, so I set the ISO meter to a slower ISO (one that would need more light) to compensate. This seems to work pretty well, and I don't have to think about 'over exposing' as much. This is a good thing because, if anything, it is better to over expose with film (unlike digital)