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  1. #1
    rjs003's Avatar
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    Biasing the ASA to compensate for 1.5v Battery

    I have been thinking about this for some time now and wonder if anybody else is doing as I have done. I have a few older rangefinders ie. Konica Auto S2 and Yashicia that orignally used mercury batteries which are no longer available. In the absence of these batteries I'm using 1.5v and 6v batteries and biasing the ASA setting to compensate for the larger voltage. I have read that using the higher voltage batteries will cause the auto function to over expose the film. Has anybody done any scientific research on this matter, or just plain experimented as I have done.

  2. #2
    PhotoJim's Avatar
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    Since your meter readings will vary as the battery ages, you're chasing a moving target. For colour print film you might be able to find a compromise setting that will work alright, but otherwise you'll never get accurate exposures.

    The only exception is that some cameras (eg most Pentax Spotmatics) use a circuit that only wants voltage, and it doesn't care what voltage it gets. In this case, no compensation is necessary.

  3. #3
    Donald Qualls's Avatar
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    The best alternative, for accurate exposure, for the old mercury batteries is either a zinc-air cell like a hearing aid battery (short life) or Wein cell ($$$); these have almost identical voltage and discharge curve (albeit over shorter lifespan) as the original mercury cells. Next best, and probably most efficient, is silver oxide. Though these cells have too much voltage (1.55 V instead of the 1.35 V the meter usually wants), they have very similar discharge curves, and make offsetting the film speed a usable technique. They cost a good bit more than alkaline, but they also last a lot longer; enough so that, unless you get your alkalines at the dollar store (I get LR44 10/$1), it'll just about pay the difference in cost. And once you find the correct offset for your meter (easily done by comparing against a good meter with the correct battery), it'll be right until the cell dies.
    Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.

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    Marco Gilardetti's Avatar
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    Okay. Now REALLY, HONESTLY, did you notice any kind of difference in your exposures? Really, ANYTHING that makes you think that you need a compensation?
    I know a chap who does excellent portraits. The chap is a camera.
    (Tristan Tzara, 1922)

  5. #5
    rjs003's Avatar
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    Yes.... especially when using color film. But then again I only use the manufactures ASA guide numbers as just that, a guide. I have found that using my own personal guide numbers produces the best results. By the way I shoot mostly Black and white.

    When shooting EFKE 100 using my view camera, I generally rate it at ASA 50 and get really well exposed negatives. This may be a function of my hand held meter or it may be just the way I shoot.

  6. #6
    juan's Avatar
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    I do that for my Nikon F - I use a silver oxide battery. I also have a Nikon FG which takes an alkaline battery. I found a full contrast scene - from Zone II to VIII, put the FG on a tripod with a 50mm lens, and pointed it at the scene. I adjusted the shutter and f/stop to get the meter centered. Then I replaced the FG on the tripod with the F, transferred the lens to the F, and set in the same shutter speed and f/stop. Then I adjusted the ASA setting until I got the meter centered.

    Is this scientific? I don't know, but I now reliably shoot color negative film using the F's internal meter.
    juan

  7. #7

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    If you're willing to spend the money (~$30) you can get an MR-9 adapter that will step down the voltage, so you can use a non-mercury battery. I got one for an OM-1 and it seems to work fine, eliminates the need to offset the ASA speed.

  8. #8
    Jim Jones's Avatar
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    Quote Originally Posted by rjs003
    I have been thinking about this for some time now and wonder if anybody else is doing as I have done. I have a few older rangefinders ie. Konica Auto S2 and Yashicia that orignally used mercury batteries which are no longer available. In the absence of these batteries I'm using 1.5v and 6v batteries and biasing the ASA setting to compensate for the larger voltage. I have read that using the higher voltage batteries will cause the auto function to over expose the film. Has anybody done any scientific research on this matter, or just plain experimented as I have done.
    My Yashica TLectro SLR (the version that uses two 1.35 Mallory PX-640 mercury cells) meters accurately over a range of battery voltages like at least some Pentax Spotmatics. However, there is a caveat on Michael Butkus' site Michael Butkus' site about using 1.5 volt batteries in that Yashica in place of the original 1.35 volts.

  9. #9

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    Another alternative, if you are handy with a soldering iron, is to insert a diode in the battery circuit to drop the voltage of a silver oxide battery down to 1.35. An 1N34A germanium diode is used. You can get then for about a quarter. There are instructions on the web.

  10. #10
    Flotsam's Avatar
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    I use Silver batteries in my Nikon F and adjusted the film speed to match a known accurate handheld.
    I had heard that voltage changes over the life of the batteries would cause readings to change over time so I checked it fairly frequently figuring that I'd just make further compensations as time went by. It only takes a moment as I'm going out the door and is by far the least expensive way to deal with the problem.

    Funny thing, after about two years, I haven't had to make any further film speed compensations since I did initially when I first put the batteries in. I guess the discharge curve in silver batteries can't be that big a problem.
    That is called grain. It is supposed to be there.
    =Neal W.=

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