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Thread: Helicoid for dummies

  1. #1
    aero
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    Helicoid for dummies

    Hi Folks,

    Apologies for the newb question, but the concept of a "helicoid" just came on the scene for me, and I'm confused. Mainly, is there a reason why such a thing doesn't exist for M mount to M mount cameras? Looks like it would be fun to pop something like that on my Ricoh GXR A12 M mount. I can understand how this might not be useful for a rangefinder - perhaps that's why it's not been made?

    Edit note for other dummies, I found a good description of the concept here: http://savazzi.freehostia.com/photog...g_helicoid.htm

    Thanks,
    AD

  2. #2
    Super Duper
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    Re: Helicoid for dummies

    Quote Originally Posted by aero View Post
    Hi Folks,

    Apologies for the newb question, but the concept of a "helicoid" just came on the scene for me, and I'm confused. Mainly, is there a reason why such a thing doesn't exist for M mount to M mount cameras? Looks like it would be fun to pop something like that on my Ricoh GXR A12 M mount. I can understand how this might not be useful for a rangefinder - perhaps that's why it's not been made?

    Edit note for other dummies, I found a good description of the concept here: http://savazzi.freehostia.com/photog...g_helicoid.htm
    It's basically a focusing mount for lenses that don't have them, or for extra (variable) extension for macro work.

    They exist but, as you surmise, they're mostly not useful for a rangefinder camera. You need a TTL viewing system to see what's happening with the focus.

    You wouldn't be able to fit an M-bayonet lens on the front of a focusing helicoid fitted to an M-bayonet camera and hope to get infinity focus.

  3. #3
    aero
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    Re: Helicoid for dummies

    Thank you Godfrey! My GXR has TTL like the NEX systems if I'm not mistaken, so that should be ok. Is there anything different about the NEX cameras that allows them to use an adapter like the one from Hawk and also be able to achieve infinity focus?

    There's a thread here that talks about the ability to successfully achieve infinity, though some have expressed otherwise. My friend has his NEX fitted with this system and it's quite nice with all of his Leica glass!

    Thanks again for your knowledge and time!
    -Dan


    Quote Originally Posted by Godfrey View Post
    It's basically a focusing mount for lenses that don't have them, or for extra (variable) extension for macro work.

    They exist but, as you surmise, they're mostly not useful for a rangefinder camera. You need a TTL viewing system to see what's happening with the focus.

    You wouldn't be able to fit an M-bayonet lens on the front of a focusing helicoid fitted to an M-bayonet camera and hope to get infinity focus.
    Last edited by aero; 14th November 2011 at 21:03.

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    Re: Helicoid for dummies

    Quote Originally Posted by aero View Post
    Thank you Godfrey! My GXR has TTL like the NEX systems if I'm not mistaken, so that should be ok. Is there anything different about the NEX cameras that allows them to use an adapter like the one from Hawk and also be able to achieve infinity focus?
    ...
    The NEX cameras have a mount register of 18mm, Leica M-bayonet mount register is 28mm. To achieve infinity focus and operate as designed, a lens must be positioned on a mounting flange at the design spec register distance.

    So ...

    The GXR A12 Camera Mount is M-bayonet register, which is the register the lenses were designed for, so there is no room to fit an additional component between lens and mount and still achieve infinity focus.

    The NEX cameras' register is 10mm shorter than M-bayonet, adapters have to space the lens flange to the proper register for the lens to work correctly. So NEX cameras have 10mm worth of space to put an auxiliary focusing mount between an M-bayonet lens and the native E mount.

  5. #5
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    Re: Helicoid for dummies

    As Godfrey says.
    It works with the NEX because it's part of the mount . . . . the only way it could work with the GXR is if Ricoh had made it part of the mount.
    There's no reason not to have a m4/3 helicoid M adapter, I don't know if there is one or not.

    Just this guy you know

  6. #6
    aero
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    Re: Helicoid for dummies

    Got it, thanks for explaining this clearly.
    -AD

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