Testing exposure meter voltage

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Photon Harvester

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Can someone tell me how to check the voltage on my camera's exposure meter? I have a VOM but only know how to check batteries with it. Don't be afraid of insulting me by making your explanation too basic. Thanks for your help.
 
Might help if you were a bit more explicit - the voltage of what? The meter doesn't have a "voltage" of its own. What sort of meter is it, or what camera? Why do you need to measure it, because it's not working or idle curiosity or what?
 
Photon Harvester said:
Can someone tell me how to check the voltage on my camera's exposure meter? I have a VOM but only know how to check batteries with it. Don't be afraid of insulting me by making your explanation too basic. Thanks for your help.
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I would depend on what kind of metering media the camera uses. On the camera's that uses a selenium cell or the like I would say you will have to find the cathode and anode from the selenium cell on the camera measure from there. Now,on digital cameras, that's something else :).

Nevertheless, pretty gruesome task. Why do you need to find the voltage?
 
wolves3012 said:
Might help if you were a bit more explicit - the voltage of what? The meter doesn't have a "voltage" of its own. What sort of meter is it, or what camera? Why do you need to measure it, because it's not working or idle curiosity or what?
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Just as Wolves said. Meter doesn't have a voltage of its own. Probably the cell or whatever is getting the light could be generating the voltage (like selenium meters or the like, like on old cameras and handheld meters). Don't know for sure but I don't think that's the case of Digital cameras.


Regards.
 
You're right, I should have provided more information. This is for a Rollei 35. I have a functional mercury battery for it, but the light meter has always been "off" compared to hand-held meters or the meters in other cameras - it tells me to overexpose by a stop or more. I've learned to work around this fairly well. But I got to wondering whether a previous owner might have had the camera converted so that it will accept a 1.55v battery instead of the 1.35v mercuty battery. I thought, perhaps incorrectly, that I should be able to measure this. Alternately, I suppose I could simply try a 1.55v battery. I haven't been able to puzzle out whether the voltage difference would explain the exposure readings I've seen.
 
Just a thought, but due to the fact that Rollei 35 had an odd voltage (5.6v), I think its unlikely that it was tampered to convert it. Any thought, anyone?
 
Without details of how the metering circuitry works, it's impossible to know if the error could be down to battery voltage. Too much or too little voltage at the supply could have over or under-reading consequences or, if the meter is well designed, no effect at all (within limits). Unless you're prepared to dismantle the camera, there won't be any accessible way to measure anything, let alone whether it's been altered. You cannot simply measure a voltage somewhere and draw conclusions, sorry. As an example of a well-designed meter, the Pentax Spotmatic used a mercury battery but used a bridge circuit that did not need an exact voltage to remain accurate. Other manufacturers certainly used circuits that were voltage-sensitive and relied on the stable voltage a mercury cell produces to give consistency.
 
Thanks very much for your responses. It looks like what I imagined might be a simple task is actually way too complex for my limited skills. It's good to know that early rather than after I've wasted a lot of time and maybe bungled something. I'll have to find another way to address the problem.

This is my first post to RFF. I'm impressed by the promptness and helpfulness of your input. Thanks again folks.
Rick
 
I wonder if it is so much a voltage issue as possible deterioration of the metering cell. As the Rollei 35 is getting to be "vintage," I think it may use a CDS (Cadmium Sulfide) element, which I understand can wear out eventually.

One place that can apparently fix any meter is, or was, Quality Light Metrics, on Hollywood Boulevard in L.A. When I tried to google them just now, there are plenty of references to them, but they don't seem to have a website currently--so I don't know if he is still in business. However, I think the thing to do is to send the Rollei in to be checked by a technician. maybe someone here will have info on Quality Light Metrics, or another place that can service the Rollei.

Good luck with it! I have thought of buying one of those from time to time (never got around to it).
 
Probably the best course of action is to find a tech who can investigate. Most meters are adjustable, internally, for calibration so it may be possible to correct it. Whether the cost is worth it to you is, of course, a different matter. Actually, it's selenium cells that age and wear out, CdS cells and silicon-blue diodes don't have an issue, although of course anything can fail in the end. CdS cells are used in street-lighting "dark" sensors, where they sit in sunlight for days at a time and for year after year and they take that abuse.
 
Rob-F said:
One place that can apparently fix any meter is, or was, Quality Light Metrics, on Hollywood Boulevard in L.A. When I tried to google them just now, there are plenty of references to them, but they don't seem to have a website currently--so I don't know if he is still in business.
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The last address I found (in the large format photography forum, from about six years ago) is:

QUALITY LIGHT METRIC CO.
7095 Hollywood Blvd. #550,
Hollywood, CA 90028
Phone: 323-467-2265
georgepmilton@worldnet.att.net
 
wolves3012 said:
Actually, it's selenium cells that age and wear out, CdS cells and silicon-blue diodes don't have an issue, although of course anything can fail in the end. CdS cells are used in street-lighting "dark" sensors, where they sit in sunlight for days at a time and for year after year and they take that abuse.
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True, CDS cells don't necessarily deteriorate with age. That doesn't mean that they can't deteriorate for any reason. Here is a reference. Pages 14 and 15 explain how and when a CDS cell can deteriorate and/or change is resistance characteristics.

http://educypedia.karadimov.info/library/CdS-Photocells.pdf

There is really nothing too much to measure with a VOM, except for the battery voltage. Assuming the OP knows that his battery is OK, that leaves the CDS cell and the connections to look into. Corrosion in battery terminals, or a dirty wiper contact in the adjustment potentiometer should also be checked for (I ought to have mentioned these-this is really the place to start).

A dirty wiper contact can be cleaned by spraying with electronic tuner cleaner, then following up with cailube MCL (Moving Contact Lubricant), a spray made for this purpose by Caig laboratories. Some potentiometers are fully enclosed, making this difficult or impossible; while others are open enough to facilitate access.

What it all boils down to, though, is that the work should be done by a qualified technician. There are so many Rollei 35's around that there have to be people who are well familiar with this job.

I hope this is helpful.
 
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