Olympus OM-1 meter is off

[iamthejeff]

I've had two OM-1's in the past couple of years and they both suffered from incorrect meters. Before everyone jumps on me about the battery, yes I know they take the now unavailable 1.35V mercury batteries and modern alkalines are not suitable.

With my current OM-1, I have tried both the 675 zinc air battery with an o-ring, and the fancy MR9 adapter with corrective circuitry. Even still, it seems to want to overexpose by 1-2 stops depending on subject.

The MR9 adapter works wonderfully with my Spotmatic F and my Olympus 35 SP, so I know the adapter is not faulty.

Are OM-1's prone to failed meters or did I just happen to find two duds in a row?

 

[John Bragg]

Best replacement, silver oxide cell. Just need to adjust meter either internally or on asa/iso dial.. I have found.the sweet spot with these is ISO 320 for a real result of.@200..that then agrees with my Leica M6 and my Nikons. They last a long long time.

http://www.smallbattery.company.org.uk/sbc_s625px.htm

 

[MattKing]

Make sure that your cameras haven't already been adapted for silver oxide cells.

An OM-1 is fairly old. It may never have been serviced. It may perform well after a CLA.

 

[Ricardo Miranda]

You're doing right with the battery and that's mostly not a problem related to them unless someone fitted a diode.
Try it with an SR44 and an O'ring to see if they are correct.
It might be the meters are just out of place. If they have never been serviced, that is to expect.
Whenever you move the shutter ring or the aperture in a lens, all they do to the meter is to pivot it side to side.
The meter might be out of place.
You'll need to test for high light and low light accuracy. Is it the same 2 stops?

 

[albada]

I have noticed that CdS cells often (but not always) weaken with age. For example, my Lafayette CdS meter that I bought in High School in 1973 has lost about 1 stop of sensitivity when used with a 1.35 volt mercury cell. But my clip-on CdS meter for a Minolta SR-1 (or SR-7?) is accurate. I suggest that you put an alkaline (1.5v) battery in your OM-1, and check its light-readings against a known-accurate meter in both bright and dim light. You can compensate for inaccuracy by changing the ASA setting on the OM-1.

Don't forget that CdS has a short-term memory: When going from bright to dim light, give the cell at least 15 seconds to acclimate to the new light-level.

Mark Overton

 

[thuggins]

Matt's suggestion to check if it has already been modified is sound. If the camera has been CLA's this is done as a matter of course. It is actually a real pain in the butt as both the zinc-air and MR-9 adapters are great replacements for the old mercury cell and with a mix of modified and not, you have to put a note on it or be sure to check each camera before using it. I've had to be emphatic that the PEN-FT's be left original when they were serviced.

If the top plate has ever been removed it is possible that the ASA dial was not aligned properly or it could increased resistance in the circuit over time. Personally, I've had very good luck with OM meters.

 

[iamthejeff]

I tried with a 1.5V alkaline and it's still inaccurate, so something is still off.

 

[John Bragg]

I tried with a 1.5V alkaline and it's still inaccurate, so something is still off.

It would originally have been set for 1.35 volts so 1.5 needs compensation.

 

[wiltw]

On the OM-1, the degree of error with alkalines is dependent upon two factors:

1. actual battery voltage
2. how bright/dim is the ambient lighting you are trying to meter

...and for that reason there is not a single compensating offset which you can simply dial in and be correct for all cases.

OP, how are you determining the amount of error seen with your OM-1's...are you taking a reading of a uniformly illuminated blank surface with a known-good meter, and comparing that reading to your OM's?

 

[nsurit]

Zuiko.com does good work should you decide to have a CLA. Sounds a little like you may be beyond needing a CLA. If you are interested in a body that has been converted to modern batteries, send me a pm.

 

[Xmas]

All my OM1n are within a 1/3 stop of a OM4 with the same lens bright to dark with a new or leaking hearing air cell. They leak on our climate before they expire 4-5 months life.

There is no point in trying an alkaline their service voltage falls under load like stone.

The meter needs a constant 1.3v if you want accurate exposure readings.

Most OMs have never needed a service they are well reliable you need to use sunny side /16 or have the meters repaired/adjusted.

Cheaper buying another with a return if unsatisfactory.

The damaged prisms only need cleaning to be like new.