Mercury vs alkaline batteries on OM-1

compur · Feb 25, 2013

A friend was having trouble with underexposure on her Olympus OM-1 and brought her camera to me. The OM-1 was made to use the old 1.35 volt PX13/PX625 mercury cells which are now gone and most of the current replacement batteries are 1.5 volt alkaline cells. The battery in her camera was a 1.5 volt type which I tested and it was reading at its correct voltage. I used a modern Sekonic meter to test the camera's meter with this battery and then we tried it with new 1.35 volt Wein cell zinc/air battery and the difference between the two really surprised me.

The difference between the alkaline and the Wein cell was 4 stops! The alkaline cell was producing under exposure by that amount. I tested it several times and it always came out as a 4-stop difference. I don't know if that's due to a peculiarity of the OM-1 meter but I now have a renewed respect for using Wein cells (or other voltage regulation means) in cameras that originally took mercury cells.

Just thought I'd pass that along.

BrianV · Feb 25, 2013

Wow, FOUR F-Stops!

I've tested Canonets, Canon FT-B, and Minolta Hi-Matic 9 using alkaline batteries against a Nikon F2AS- found it was about 2/3rds of a Stop. I adjusted the Canonet's Pot and it seemed good. On the FT-B, just cranked the ISO setting down lower by a stop.

usayit · Feb 25, 2013

Yes... that is surprising...

I've been working under the assumption of no more than 1 stop difference.

Dikkie · Oct 6, 2018

I've got an Agfa Selectronic S for a few weeks now, shot my first rolls.
The batteries inside seemed to work as the meter was active, but the light bulb for long exposures and test button weren't flickering.
So the first roll was underexposed.
Put in some new batteries, (Varta 625 U 1,5volt alcaline), the light bulbs are flickering and test button works too, so the batteries and light meter are in good condition now.

However, again underexposured roll...
Probably the same reason, it needed to be an 1,35 volt mercury cell.
Would I try to put ISO 100 to 50, or better to 25, in order to get a correct exposure?
It's for night shots in well lit city streets. (long exposures with tripod)

cooltouch · Oct 8, 2018

There's another problem with alkalines -- discharge profile. The original 1.35v mercury battery had an almost completely flat discharge profile, whereas the alkaline's discharge profile looks like a sharp spike in comparison. Fortunately the zinc-air batteries have an almost identical discharge profile to that of the old mercury's.

I don't use Wein cells. They're way too expensive, and they only last a few months, which is a characteristic of zinc-air batteries. Instead I use the 675 hearing aid batteries. Size wise it's smaller with about the same diameter as the 1.5v batteries -- like the A76 and others -- that Nikon and others use. This smaller diameter is usually not a problem. You can use an o-ring or a bit of wire in the battery compartment to take up the slack. Or you can buy metal rings that fit onto the battery to bring it up to the same diameter (I think this is what Wein does). I've found that, with my old Canons -- FTb and F-1 models, in particular, the spring pressure from the battery cap is sufficient to keep the battery centered. 675 batteries are dirt cheap. You can buy a pack of 6 or so at the drug store for about the same price as a single Wein cell. Or you can do like I do and buy a card of 48 of 'em at Costco for less than $10. $8.95, I think. That's 19 cents per battery! Bought this way they're so cheap that, if I haven't had a camera out in a while -- say a month or two -- rather than take a chance with its charge, I just drop in a new battery.

I've checked my F-1's meter against a Gossen Luna Pro F, which I know is accurate to within a quarter stop, and it usually agrees exactly with it. So no worries.