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Thread: Adapter problem with Zeiss ZM lenses?

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    Super Duper
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    Adapter problem with Zeiss ZM lenses?

    Here is a riddle for you. I am unable to achieve infinity focus with my Zeiss ZM lenses using the CQ M to G1 adapter on the G1. No infinity focus problem with the same lenses on the M8. Also, my CV lenses do not have infinity focus problems using the same CQ adapter on the G1. I'm waiting to receive John's new GM adapter so I can check the same lenses again for infinity focus on the G1 with a different adapter. Any ideas on why this is happening?
    Here are some 100% center crops:

    Zeiss 50mm f/2 Planar set at f/2 and infinity stop on both the M8 and G1 with CQ adapter:


    CV 75mm f/2.5 Color Heliar set at f/2.5 and infinity stop on both the M8 and G1 with CQ adapter:
    Last edited by scho; 16th February 2009 at 06:57. Reason: change text

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    Re: Adapter problem with Zeiss ZM lenses?

    i took some time to make sure the GM adapter would achieve infinity focus on the G!, however, my test lens was a new 75 cron, which is more revealing of defects in focus compared to a shorter focal length. I machined the adapters with a tiny bit of leeway so they could focus past infinity slightly.
    why your Zeiss would not achieve focus and the C/V would is puzzling. i am guessing the Zeiss has a hard stop for infinity focus set more accurately than the C/V, which may be inadvertently traveling past true infinity for that lens.

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    Re: Adapter problem with Zeiss ZM lenses?

    Quote Originally Posted by jlm View Post
    i took some time to make sure the GM adapter would achieve infinity focus on the G!, however, my test lens was a new 75 cron, which is more revealing of defects in focus compared to a shorter focal length. I machined the adapters with a tiny bit of leeway so they could focus past infinity slightly.
    why your Zeiss would not achieve focus and the C/V would is puzzling. i am guessing the Zeiss has a hard stop for infinity focus set more accurately than the C/V, which may be inadvertently traveling past true infinity for that lens.
    Thanks John. That certainly sounds like a reasonable explanation for this problem. I'll look forward to receiving your new GM adapter when they are ready.

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    Re: Adapter problem with Zeiss ZM lenses?

    Finally got around to shooting this test again with the same two lenses mounted to the G1 with the new Milich GM adapter. This time the Zeiss 50 Planar was sharp at the infinity stop (see image below) and the 75 CV Heliar came into sharp focus before the infinity stop. Thickness of the two adapters, as measured with my cheapo calipers, was approximately 8.44mm for the Milich GM adapter and 8.56mm for the CQ adapter. Seems as though John's original hypothesis was correct about the difference in infinity stop adjustment of the two lenses.


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    Re: Adapter problem with Zeiss ZM lenses?

    Another thing to consider is that there isn't necessarily any one "correct" value for the flange distance at infinity. Lenses designed for cameras made during the film era had to make allowances for the fact that film cameras don't locate the film at a specific exact depth; the film "floats" in a channel that's sized wide enough to allow it to be advanced without scratching.

    Different manufacturers would make different assumptions about how wide the channel should be, how much the film would curl in it (which would vary the distance), and even whether the user would advance the film just before shooting or just after shooting (which would alter the amount of curl depending on how much time the film sat in the gate.)

    I ran into this firsthand using the various ultra-speed Canon rangefinder lenses on non-Canon cameras; a close reading of the Canon 7s repair manual suggested to me that Canon had adopted a different assumption about film flatness than (e.g.) Leica, leading to a situation in which a lens that focused perfectly on a Canon body would be slightly "front focused" (too far from the film plane) on a non-Canon body.

    So it seems to be a situation in which there are multiple "right" answers that all have to be addressed by the designer of an adapter.

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