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  1. #1

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    Mamiya 7 - all speeds the same on autoexposure

    Here's one for the archives. Perhaps it'll save someone a bit of future heartache.

    I recently received a new-to-me, but used, lens for my Mamiya 7. I had a half-used roll of FP4+ in the camera so figured I'd use the last frames as a quick test, setting to autoexposure and varying the aperture from min to max. All the speeds sounded the same, and fast, which struck me as a little odd, but it was a bright day...

    I developed the film and, sure enough, the test frames were underexposed and I could see the increasing underexposure from closing the aperture. Hmmm. The seller said the lens worked, so I removed the lens and gently cleaned its electrical contacts with a pink pencil eraser. After that it worked properly. The contacts had appeared fine before cleaning, but there was obviously some crud on at least one of them that came off with the eraser treatment.

    As a precaution I cleaned the body contacts too, as well as the other lens I plan to take with me on vacation in a week's time. The eraser now lives in my travel kit.

  2. #2
    benjiboy's Avatar
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    Quote Originally Posted by Steve Goldstein View Post
    Here's one for the archives. Perhaps it'll save someone a bit of future heartache.

    I recently received a new-to-me, but used, lens for my Mamiya 7. I had a half-used roll of FP4+ in the camera so figured I'd use the last frames as a quick test, setting to autoexposure and varying the aperture from min to max. All the speeds sounded the same, and fast, which struck me as a little odd, but it was a bright day...

    I developed the film and, sure enough, the test frames were underexposed and I could see the increasing underexposure from closing the aperture. Hmmm. The seller said the lens worked, so I removed the lens and gently cleaned its electrical contacts with a pink pencil eraser. After that it worked properly. The contacts had appeared fine before cleaning, but there was obviously some crud on at least one of them that came off with the eraser treatment.

    As a precaution I cleaned the body contacts too, as well as the other lens I plan to take with me on vacation in a week's time. The eraser now lives in my travel kit.
    That ironicaly might be why he sold it.
    Ben

  3. #3

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    Ben, that thought occurred to me, though I had and still have no a priori reason to doubt the seller's honesty. The two most likely scenarios seem to be:

    1) the lens was not used for several years (the seller told me this) and a film built up on the contacts unbeknownst to the seller, or

    2) the seller knew, but didn't know about the eraser trick.

    I tend to believe the first case, because the seller is an active photographer but sold his M7 body some time ago, thus would have been unable to test the lens and shutter functions. But either way, I got a very nice lens, probably KEH EX+ or better, for less than half of KEH's bargain-grade price, and am very happy with that. And I already had a Pink Pearl (brand name) eraser, so I accrued no additional expense beyond a few wasted frames of film.

  4. #4

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    a pencil eraser is rather abrasive for lens contacts, though id use one on battery contacts if they were corroded already.

    Id treat them like optical surfaces qtip or qtip damp with water you don't need to remove any of the gold plate.

  5. #5

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    Plated gold contacts are surprisingly tough. They're usually plated onto a barrier metal, typically nickel, to improve adhesion to the underlying (usually) copper. Back in the old days it was not uncommon to take an eraser fairly aggressively to the gold-plated backplane fingers on printed circuit boards to fix intermittent contact issues - this was the fix of first resort in my first EE job out of university.

    That being said, I used the eraser very gently and with minimal pressure. A cotton cloth dampened with isopropanol would probably have been even better, come to think of it.

  6. #6
    benjiboy's Avatar
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    The best thing to use is electrical contact cleaner on a Q Tip.
    Ben

  7. #7
    benjiboy's Avatar
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    Quote Originally Posted by Steve Goldstein View Post
    Ben, that thought occurred to me, though I had and still have no a priori reason to doubt the seller's honesty. The two most likely scenarios seem to be:

    1) the lens was not used for several years (the seller told me this) and a film built up on the contacts unbeknownst to the seller, or

    2) the seller knew, but didn't know about the eraser trick.

    I tend to believe the first case, because the seller is an active photographer but sold his M7 body some time ago, thus would have been unable to test the lens and shutter functions. But either way, I got a very nice lens, probably KEH EX+ or better, for less than half of KEH's bargain-grade price, and am very happy with that. And I already had a Pink Pearl (brand name) eraser, so I accrued no additional expense beyond a few wasted frames of film.
    Perhaps you're right Steve, I've become very cynical in my old age, it comes from being let down by people so many times in the past .
    Ben

  8. #8

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    It's possible that tho lens did work fine for the seller, when you put it on your body the contacts mated up on different spots than they did on the seller's body - which spots were dirty. It doesn't take much to stop the voltages used in camera electronics.

    I use the eraser trick too, and have since the 70s. Nice that it was such a simple fix!



 

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