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  1. #31

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    Not how I'd do it but it might work if you can get rings with the appropriate threads and if everything is very tight so that the rings are loaded only in tension.

  2. #32
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    "Photography, like surfing, is an infinite process, a constantly evolving exploration of life."
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  3. #33

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    Quote Originally Posted by Dan Fromm View Post
    Not how I'd do it but it might work if you can get rings with the appropriate threads and if everything is very tight so that the rings are loaded only in tension.
    Dan, the only way to mount Rodagon-G 210 M72 lens on Copal #3 seems to be screwing it to the shutter's front thread, which is recessed about 6 mm. I do have a high-quality M58-M72 0.75 step-up adapter with threads longer than those usually found on Chinese adapters. But it's outer diameter is larger than the front opening of #3 shutter and I'd need an approx. 10 mm M58 extension ring of comparable quality and thread length. The only such ring I know of is a really expensive Schneider extension tube for Unifoc system, and I don't know if the threads are long enough to have everything tight. Or did you perhaps have a totally different idea for mounting a M72 lens in front of a Copal #3?

  4. #34

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    If I wanted to do it right I'd pay a machine shop -- my machinist of choice is skgrimes, there are others -- to make a threaded stepped bushing. A male end to go into the shutter's front tube as the rear of a lens' front cell would, a female end to accept the lens' mounting threads.

    If I wanted to do it wrong I'd look for T-mount extension tubes and try to bodge something up that would fit the shutter and accept a T-mount tube and that would fit the rear of the lens and screw into a T-mount tube. I don't know if the adapters needed exist. I've done similar with LTM tubes and custom adapters.

  5. #35

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    Dan, not wanting to ruin either the lens or the shutter, I'll take your suggestion seriously and have an adapter such as this custom-machined:

    Click image for larger version. 

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  6. #36

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    That's the idea.

    FYI, I have one fairly heavy lens in barrel that's held on a lens board by a stepped bushing. A retaining ring holds the bushing to the board, the front of the bushing has male threads that go into the barrel's internal rear threads; these look like filter threads but are in fact baffles to control stray light. I had Steve Grimes make the bushing that way because a cup-shaped bushing that accepted the lens' mounting threads would have been very expensive 'cos the mounting threads are around three inches forward from the end. Taking that approach with your Rodagon-G will make for a simpler bushing.

    This brings up another point I've had to remind SKGrimes about from time to time. The bushing should be threaded internally, the threads like filter threads. You'll get much less flare that way than with a smooth interior.

    Three thoughts about y'r sketch. The shutter end should go as deep into the shutter as possible, I'm not sure the bushing should butt up against the shutter's face plate, and there's no reason to make the bushing's walls as thin as possible. Stronger is better, you want something that is up to being stepped on. Not that I've ever dropped any of mine and stepped on them, but I sooner or later will. I've been spoiled; the shutters I use for front mounting are #1s, don't have conical face plates like the #3.

    To contradict myself, now that I'm fully aware that the #3's face plate gets in the way putting the shutter in front of the lens might make life easier for the machinist. You'll still want a stepped bushing, but the step will be at 90 degrees.

    Oh, and by the way, if you use an experienced photographer's machinist such as skgrimes explain the problem and explain how you'd solve it, then ask the machinist to propose what it sees as the best solution. The Dau brothers sometimes come up with solutions that are much better than mine.
    Last edited by Dan Fromm; 10-25-2012 at 11:19 AM. Click to view previous post history.

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