Mamiya Universal Extension Tube Recalibration

Discussion in 'Medium Format' started by morgan_bellinger, Jul 22, 2012.

  1. I love shooting Polaroids with my Mamiya Universal, and that's what I primarily use it for.
    However, I have always been frustrated at the minimum focusing distance for this camera. If it only went a foot or two closer, it would be enormously more useful to me.
    It occurred to me that a sensible solution might be to add the smallest extension tube. However, it seems like this only works with a ground glass back - quite incompatible with the handheld photos that I'm hoping to take with this configuration.
    I recently purchased a spare Mamiya Universal camera body, and I'm wondering if I could just recalibrate the rangefinder with the extension tube installed, leave the tube permanently on the spare body, and just switch to that camera body whenever I wanted to take closer pictures. This led to a few questions - I'm hoping that some of you who are more experienced with the Mamiya Press line may have answers or suggestions:
    a) Is such an adjustment even possible within the adjustment limits of the rangefinder mechanism?
    b) Would the same adjustment work for all of my lenses?
    c) What's the difference between the extension tubes (between lens and body) and the extension boxes (between back and body) and is there one that would be preferable for this procedure? Do I have to use both?

    Thanks so much in advance!
  2. With an extension tube, I think the rangefinder coupling wouldn't even reach the body (you'd have to construct some mechanical linkage to pass it on). The rangefinder coupling would still be active with the spacers between the body and the back, but just screwing a close-up lens onto the front of the lens would maybe be more convenient.
    As for whether the rangefinder adjustment is sufficiently flexible to allow this, I don't know. Another possibility would be to physically alter the mechanism on the lens or the body (preferrably reversibly). This might seem attractive for the 150mm lens, which focuses only to 2m, whereas the rangefinder mechanism works for lenses that focus as close as 1m. Unfortunately, the thing on the lens that transfers the distance information moves into the lens (away from the body) as the lens focuses closer - if it was the other way around, one might be able to just add something on the end of it (or to the thing it contacts in the body). This way, it seems one would need to file away part of one of these parts. And even if that way one got the rangefinder to read correctly when the lens + closeup lens was focused as close as possible, I don't know whether it would read correctly at other focus distances (which wouldn't extend to infinity, of course), though adjusting for that might well be within the flexibility of the rangefinder adjustment mechanism.
    Or one could tape a new distance scale onto the lens, and then guess...
  3. So when I posted this, I hadn't realized that the extension tubes don't have any sort of focus coupling to the rangefinder mechanism in the body of the camera. Thus, the only way to focus when extension tubes are installed is via ground glass or the tape measure-vs-distance scale method. I should have realized this before asking, sorry!
    However, I'm wondering if it's possible to achieve a shorter focusing distance with the spacers that fit between the back and the camera body.

    Were those spacers only designed to be used in conjunction with the extension rings? Or will they work on their own? Seems like it shouldn't matter where the extra space between lens and film plane comes in relative to the body (focusing mechanism) but I want to make sure I'm not overlooking something. Thanks in advance!

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