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  1. #1

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    Not sure whether to use an MR9 adaptor in my OM 1

    I bought an OM 1 recently (serial number is 986689 so presumably an early one) which has a fresh (I think) Varta V 625 PX battery in it. I haven't been able to find much info about this battery but it appears that this is a 1.5v battery which, according to what I've read here and elsewhere, will throw the meter out by about 3 stops. I use negative film so this won't be a problem.

    I had the camera CLA'd and the meter has been calibrated, presumably to work with the 1.5v battery. The fellow said that using 1.5v batteries isn't a problem because the camera has a voltage regulator (which I don't think is true according to what I've read).

    Should I just keep using V625U (1.5v) batteries and let the latitude of the neg film cope with the meter inaccuracy, or would it be best to buy the MR9 adaptor that John Hermanson sells? Would the meter need re-calibrating if I use the MR9?

  2. #2

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    new old stock

    I doubt the battery is fresh. Worldwide, production of mercury batteries ended years ago. Old batteries have a tricky way of silently leaking an acidic liquid which usually destroys (at least) the battery wire. I suggest dumping that battery and getting an MR9, then change that battery yearly.

  3. #3
    Steve Smith's Avatar
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    If you can, measure the voltage of the cell you have at the moment. If it is a 625 it should be 1.3 volts but if it as 625A (alkaline version) it will be 1.5 volts.

    If your camera is metering accurately at the moment then the voltage you measured is the correct one for your camera.

    If it is set up for 1.3 volts and you put a 1.5 volt cell in there you will probably find the meter tending to under-expose as it thinks there is more light than there really is.

    I have some old mercury cells which still measure 1.3 volts so it is possible that yours is still at the correct voltage.

    The other option is internally wiring a schottky diode in series with the cell to drop the voltage by 0.2 volts.

    Here is a description of how to do it (in this case to a Minolta SRT): http://www.rokkorfiles.com/conversion.htm

    EDIT: Here's an even more comprehensive description relating to the Olympus OM: http://olympus.dementia.org/Hardware...odeVer2_1C.pdf




    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  4. #4

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    Thanks for the .pdf , I have put it on my HD for future reference.

    Peter

  5. #5
    Prest_400's Avatar
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    The adapter can get lost, but it don't need to modify the circuitry. If (not probable) the Silver oxide battery gets discontinued. You won't need to mess more with the circuitry. But that should be an extreme case, as far I know Silver Oxide batteries don't have anything for get it discontinued.
    I believe it's OK to modify the circuitry.

  6. #6

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    OM-1 meter isn't all that accurate even with the right battery. I would simply use alkaline battery and check to see how much it is off then compensate.

  7. #7
    wiltw's Avatar
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    BS that OM-1 meter has a voltage regulator in it. It needed the constant 1.35v output from a mercury oxide battery (vs. the 1.5 v variable output from alkaline or silver oxide) With the 1.35v mercury oxide there was no need for a voltage regulator!
    BS that an OM-1 meter isn't all that accurate.

    The 3EV error changes with the ambient light level as well as with the voltage level of the battery, so it is not possible to simply offset the reading!

  8. #8

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    675 hearing aid zinc air batts...

    super cheap easiest route is hearing aid batteries...super cheap from a chemist.
    then fix a rubber grommet from a plumbers store...
    if you want the batts to last longer cover up a couple of the air vent holes on the batt..
    http://farm3.static.flickr.com/2108/...4945da56e6.jpg
    i have 10 different types of camera cine and stills and i use this system...
    good solid exposure..much better than alkaline with camera conversion..

  9. #9

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    "the OM-1 meter isn't accurate, even with the right battery" ? Wrong. If you're comparing it to a known calibrated light source, it is accurate. Using an alkaline battery by itself can throw it off 2-3 stops. In some cases (less than 1%) cds cells go bad and can cause meter to become non-linear. These problems are all fixable or adjustable. John , www.zuiko.com

  10. #10

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    Forgot to mention that the alkaline battery alone will make the OM-1/1N meter non-linear. John, www.zuiko.com

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