I am not sure if having a match needle requires no adjustment is correct. As far as I know, my Rollei 35S which originally used either a 1.35V Mercury PX 13 or a PX625 now requires the usage of a 1.5V PX625 A alkaline battery unless an adapter is used. Everything that I have read and Krikor the Rollei repairman has indicated and has made the adjustment to the meter to compensate for the variation due to the voltage difference. The adapters do the same thing so that the meter not be adjusted, but allows for the usage of a different 1.5V alkaline battery.
To be precise, match needle meters in which the needle rests at the center (zero-in position) when the battery is removed makes correct exposure reading regardless of the small voltage difference due to battery replacement. Olympus OM-1 and Pentax Spotmatic are examples of this type of cameras.
Originally Posted by naturephoto1
I agree with you that a few months is not very useful, but these Wein zinc air cells I mentioned above claim to last 1 year. I think the manufacturer may have achieved this by reducing the oxygen port hole diameters on the cell's surface.
Originally Posted by Ryuji
Ultimately as you say it comes down to what we are willing to put up with. Most motor drive (i.e. non manual advance) cameras will need fresh batteries at least every few months if used regularly and most of us have put up with that !
And yet I do.
Originally Posted by Ryuji
After reading this site I got my Konica C35 to work with 675 hearing aid batteries. Should help other cameras too. http://rick_oleson.tripod.com/index-111.html
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I did forget lithium batteries in my list of available batteries. I guess they are just too new-fangled for me. :-)
My point about not using alkaline batteries is that the steep discharge curve of these batteries makes them more and more inaccurate with use. The discharge curve for silver oxide cells are quite flat in comparison making them a better choice.
Match needle meters use a bridge circuit and are less dependent on battery choice.
There are several sites on the web which discuss camera battery replacement and I would suggest those interested google to find them. At least one of them has a warning that using the wrong battery can damage the camera.
A simple solution when a silver oxide battery would be a good replacement is to lower the voltage by using a germanium 1N34A diode. This diode is cheap less than a dollar. Again their are web sites describing this modification.
Mercury batteries are 1.35V, Alkaline batteries are 1.5V (fresh). That's a difference of 11% or less than 1/10 stop if the meter error is linearly dependant on battery voltage (and for CdS cells there should be insignificant non-linearity).
Have you ever done an instrumental comparison between Alkline discharged to 1.35V and fresh ones. I'm betting that you'll barely see the meter needle move.
The response of the meter to voltage depends on the circuit. I have seen posts on the web saying the error can be 1/2 to 1 stop when substituting an alkaline or silver oxide battery for the mercury battery.
Originally Posted by OldBikerPete
A fact or two
All through this thread I've been reading personal experiences and assumptions, many about the OM-1. None of those OM-1 experiences match up with mine. I have one of my OM-1's with me at work today, so all the responses finally got me off my rear and into the electrical lab to see how the meter reading would actually vary with voltage.
I meter Tri-X at 250. With a silver oxide battery in the OM-1, matching the shutter and aperture readings to my Nikon F3 and Sekonic 508 need an ISO setting of 40.. a 2 2/3 stop difference! Set this way, I get negatives that are as well exposed as I produce on any other camera I have, limited only by my metering skill.
I set up on the bench, I varied the voltage to the OM-1, and metered the same area, adjusting ASA until the needle was centered in the +/- area (the OM-1 is not truly a match needle, in the way an SRT-201 is). A look at the OM-1 meter schematic (http://olympus.dementia.org/Hardware), shows that it is not a bridge circuit, so it there is no reason it shouldn't be sensitive to battery voltage.
Here are my readings for this camera:
1.30V 112* (100 was low, and 125 was high, by equal amounts)
The OM-1 measurements seem to show about a 1 to 1 1/3 stop shift between the mercury voltage of 1.35 and a silver oxide voltage of 1.5 to 1.55.
This OM-1 appears to have an extra f-stop and a bit shift even at the mercury battery voltage range of 1.30 to 1.35. The meter coupling system has strings and springs and pulleys, so I'm guessing that something in that mess is also off.
What is also quite clever is the OM designers apparently designed the meter response to be less sensitive to battery voltage around the mercury battery voltage range. The camera works fine as designed, but was never optimized to have a higher batter voltage range.
My conclusions? If I ever tear this OM-1 down, I'd try to fix my meter error of a stop, and probably add a germanium diode in series, as is suggested several places around the internet, to get my drop close to the original design voltage. Together, those steps should get me close the original calibration of the meter. Most likely, I'll just keep Silver Oxide batteries in it, remember that ISO 250 is 40 and happily make pictures with it.