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  1. #1

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    Olympus OM-1n exposure meter conversion

    Yup, another discussion about mercury batteries, but different than I could find in the archives. I don't want to re-start the same old discussion on Wein cells and hearing aid batteries. The best solution to the mercury battery problem is to adjust the meter circuit to use silver oxide bateries. I say this after looking at the curves of voltage verses temperature and current of the series diode solution. The series diode is a "sloppy" solution. I am looking for someone who has adjusted the meter to use silver oxide cells who is willing to share the procedure. I have done camera repairs, CLA and electronics bench work, so I am not afraid to tackle the job, I just don't want to "re-invent the wheel". Thanks.

    Best regards,
    Chris

  2. #2

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    You'd figure with all teh advanced electronics we have today someone would have designed a voltage regulator small enough to fit in a meter or camera to correct this problems.


    http://www.linear.com/products/switc...FQXd4Aodu30OoA

    The regulator I like for many applications is this one LT 1302 or something like it...

    http://www.linear.com/product/LT1302
    Anyone can make a Digital print, but only a photographer can make a photograph.

  3. #3
    Jerevan's Avatar
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    Can I assume you mean the zener diode solution (like the CRIS battery converter)?

    Maybe John Hermanson has any ideas? (www.zuiko.com)
    “Do your work, then step back. The only path to serenity.” - Lao Tzu

  4. #4

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    I generally would simply forget about the meter and not using it. If I have to tackle this problem I would want first a schematic diagram of the meter circuit. From there one could study how the meter work before trying to figure out how to correct this problem.

  5. #5
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    Another reason I like the FX-3...built in voltage regulator 1.25V +/- 0.15V in the meter circuit.

    I'm sure there are a lot of busted FX-3s out there with intact voltage regulators. Perhaps it could be used in the OM1 circuit ("Vreg" on the diagram).

    Too much bother for me; I use zinc cells in all my equipment that requires mercury cells.



  6. #6
    BobD's Avatar
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    Something wrong with these?

    http://www.criscam.com/mercury_battery_adapters.php

    Just asking.

  7. #7

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    I've been using the over the counter alkiline replacement batteries in my old meters n have no problems with my negatives or readings. I think if you just standardise your meter to your film, you will find the meters are very accurate n reproduceable. If you keep comparing meters to other meters, even the best of em will not agree msot of the time. Meters are for exposures, not racing against eachother. And BYW the battery last so long it will take several years to experiance the voltage drop off point. Rplace your battery regularly and you won't have any problems.

    I like that voltage regulator circuit in the FX3 idea but still takes up too much room.
    Anyone can make a Digital print, but only a photographer can make a photograph.

  8. #8
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    Quote Originally Posted by paul ron View Post
    I've been using the over the counter alkiline replacement batteries in my old meters n have no problems with my negatives or readings. I think if you just standardise your meter to your film, you will find the meters are very accurate n reproduceable.
    Oh, horrors! Many years ago I conducted a test with my OM-1n (I am the original purchaser), with mercury oxide cell and with alkaline cell. There was definitely an error in the meter reading when I used alkaline 1.5v battery rather than the 1.35v mercury oxide cell. The amount of metering error is NOT constant and cannot be simply compensated with adjustment of ISO value. The amount of metering error depends not only upon the precise voltage being out out by the alkaline chemistry (which varies as the cell depletes), but also based upon the amount of light in the scene being metered!!!

  9. #9
    ic-racer's Avatar
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    Quote Originally Posted by paul ron View Post

    I like that voltage regulator circuit in the FX3 idea but still takes up too much room.
    ???? the voltage regulator is a tiny, only a few millimeters long. It is "Vreg" in the second diagram and is so small it does not show up in the picture of the camera with the top off. I don't have a parts camera on hand at the moment but now that I think about it I suspect that it is a Zener diode and a resistor! Again it specs out at 1.25V +/- 0.15V. Why don't you like Zener diodes?
    Last edited by ic-racer; 12-19-2011 at 08:18 PM. Click to view previous post history.

  10. #10

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    WOW I'll definately have to see that regulator, sounds interesting. That will level the playing field for sure.

    Metering is not accurate compared to what? Can you reproduce the same readings of the same 18% gray card over n over in the same situations using alky bats? It only has to give you a reproduceable reading that you standardize to your film vs develping vs printing to make it do exactly the same thing every time. Meters are only as stupid as the user.

    Whetstone bridges are a balancing act of current. They don't know light... just curent. It reads the photo cell as a variable resistor limiting curent on one side vs the other so the same amt of current will make the meter deflect the same amt every time. Linear? No, log.

    Depleation of batteries is a few years down the line. I had batteries in my analog PentaxSpot meter for 5 years that kept saying the same florecent overheads in my shop are exactly the same exposure as the day I put em in. Change the battery regularly and you will never see the end of the curve where it breaks down. How long do your batteries last? Do they depleat every time you take a reading?

    BTW if you have any old spotmeters (maybe any meters or cameras) that use mercury batteries you want to throw in the trash because they are not accurate enough with alkys, I'll take em all off your hands, I'll pay the postage. PM me?

    Anyway... to each his own, how do your pictures look in the end is all that counts, not how accurate a meter you have. Many old timers never use meters, I hardly ever, except maybe as a referance starting point. I see it as a crutch like having a GPS take the place of my map n compass n the brain between my ears.

    .
    Anyone can make a Digital print, but only a photographer can make a photograph.

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