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  1. #1

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    Adjusting focus on Mamiya M645 Super

    I have a Mamiya M645 Super that can use focus adjustment. When focused through prism finder and focused EXACTLY using 2x magnifier, the image isn't actually focused. I did a controlled test today using MIRROR UP and tripod, AND using high-enough shutter speed, it is confirmed that the focus is off enough to be a problem.

    Looking at the lens mount, I know there is a small screw to adjust the resting position of the mirror. But question is.... how the heck do I do this? I can't adjust this with lens on, and I can't possibly detach and attach the lens without disturbing focus. I am guessing, the task is to focus the image on the film plane (by using ground glass instead of film?) and have it focus simultaneously on the view finder, but HOW?

    I have already verified, my focus screen is NOT on backwards. (it is physically impossible on this model)
    Develop, stop, fix.... wait.... where's my film?

  2. #2

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    By the way, professional CLA is out of question as cost is prohibitive. I am going to use this M645Super as a learning tool and try to do it myself. If I damage it... oh well...
    Develop, stop, fix.... wait.... where's my film?

  3. #3

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    I haven't done it myself, but my approach would be to tape some ground glass or a spare focus screen in place of the mirror insert, then put the camera on a tripod and focus on something, then use the MUP lever to pop the mirror up so you can check focus through the back. If adjustment is needed, then pull the lens, adjust the screw a little one way, then repeat the exercise and see if it's better or worse.

    Then repeat until you're happy with it.

  4. #4
    MattKing's Avatar
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    Are you sure the problem isn't with the focussing screen itself?

    I have never changed the screens on my Mamiya 645s, but I know that they can be swapped with other screens. Someone may have messed up an earlier screen replacement.

    With other cameras, there are sometimes shims used to ensure that the screen is in the right position.

    I would first check the focus at the film plane, to see that infinity focus is correct. If it is, then the problem is with either the screen or the mirror - but most likely the screen.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  5. #5

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    You don't say whether you've owned and used the camera for some time and the fault has just appeared or you've just bought it, but your second post suggests the latter. If you've always used autofocus (I know it's unlikely after 421 posts but this is for other readers too) you may not know that it's important to use the split-image rangefinder correctly - viewing off-axis will give inaccurate results.
    I wouldn't adjust the mirror stop until other possibilities had been eliminated - two faults cancelling each other out isn't ideal.
    First & easiest check is infinity focus at the screen with the split image. A church steeple (or similar, at "infinity" and not through a window), a loupe or a 50mm. lens from a 35mm. camera and a makeshift but flat focus screen on the film rails indicates the degree of error. If one screen is in focus when the lens is at its infinity stop then the other may be where the fault lies.
    Next I would check lens' apparent flatness of field at both screens with the mirror/newspaper test.
    With unfamiliar equipment I spent a lot of time on close visual examination - check the insert, the back and its door, the body, the screen, the lens mount, the lens and the fit of everything looking for clues. Something not quite straight, screws missing or damaged by careless work, rough edges, anything that rattles or feels loose, anything that may have been previously "adjusted" etc. etc.
    I've had cameras for repair with your symptom which have had their mirrors flipped over by unscrupulous sellers. The back of a scuffed mirror looks brand new but throws focus out by the thickness of the glass. The previous owner of my LF reflex viewer had put a brand new and very expensive mirror in - wrong way round. Two minutes to fix.
    Check everything, then adjust the mirror stop if you have to. If you've confirmed the lens' infinity stop is actually at infinity it's easy. Otherwise sticky tape with a sharp pencil line for infinity. Camera on tripod, church steeple, adjust mirror in small increments until split-image aligns.

  6. #6
    Curt's Avatar
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    The interchangeable screens are seated on tiny screws that are factory installed at +/- tolerance. You might consider adjusting the height of the screen to the body, either up or down. The screen must agree with the film plane, when the lens is focused on the screen it must also be in focus on the film.
    Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand

  7. #7

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    Thanks everybody for replies.

    I had this camera for a while and I recently confirmed the problem when I did some test shots under controlled environment. That is, close forcus using 150mm f/3.5 to minimize the depth of focus. I also repeated the test with 50mm f/2.8. I've used manual focus cameras so I am familier with how split screen works and micro prism works. I also used 2x magnifier to ensure exact focus.

    I suspected mirror adjustment be off because if I remove the lens and look into the cavity, I can see bottom of the mirror isn't parallel with bottom of the opening. That is, it's higher on right where the stop is located and lower on the left where it just floats in air. In other words, it is supported on one side only and it's sagging. Looking closely at the stop itself and back of the mirror, I can see some wear.

    Here are some Qs...

    Can I trust infinity focus of the lens? Obviously, this is a mechanical stop within the lens. Over decades, wouldn't they drift due to wear or be affected by expansion/contraction due to temperature?

    I understand there are two focus planes - film and focus-screen. My job is to bring them into agreement. Since I cannot change the distance from lens to film (is this a correct assumption?), all I can adjust is mirror. (is this a correct assumption?) I don't see any ways to adjust the height of focus screen other than using shims. (there isn't any right now)

    What are suitable materials for a temporary focus screen at the film plane? I don't have any spare focus screens.

    Thanks again.
    Develop, stop, fix.... wait.... where's my film?

  8. #8

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    You cannot adjust focus at close distances it has to be infinity.
    I use groundglass at he film plane to check the lens first. If focus is good, but the lens isn't at it's infinity stop, the lens needs to be adjusted. If the lens is at the stop consider the focusing screen. The mirror stop is absolutely the last thing to fiddle with.
    I have seen one camera where the focus was off because the mirror was sitting at an angle, one side of the mirror had come free of it's retaining spring. Look at the mirror, if one side has a small piece of metal on the front surface, the other side should have one too. These are from a spring that holds the mirror into it's frame.
    Heavily sedated for your protection.

  9. #9

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    Hi, mirror's lower edge at an angle doesn't indicate a maladjustment of the stop but a problem with the hinge mechanism at the top of the mirror or a twisted mirror carrier frame. With the mirror up and the shutter open you may be able to see the cause of the problem in good light with a magnifier. Hold the shutter open with a locked cable release to avoid damaging it.
    Looking at the underside of the mirror through the lens mount and the gate it should be possible to tell if it's horizontal and central, or is skewed in any way.
    If the mirror carrier or hinge mechanism needs straightening remove the mirror first for safety.
    Sorry to repeat myself but don't do anything until you're certain you know the exact cause of the problem.

  10. #10

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    Sorry, got busy, had to go.
    To your specific Q's:
    Inf. stop on the lens is sometimes "beyond" to allow for expansion as you noted.
    Just makes setting the screen easier if it's spot on at the stop. It's not necessary to adjust it though - and you can't do it anyway until you have a screen at the film plane...
    Lens mount rings on cameras are often shimmed to meet specification when new. Common practice in fact.
    Clear, rigid plastic sheet about 2mm. thick can easily be cut to size (about 65 x 42 here I think. Measure your pressure plate on the insert), lightly and randomly sanded one side with 600-grit or finer wet & dry. Used on film rails with sanded side towards lens. If you have a loupe you hold it in place with that. Easy-peasy.

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