Help with c-mount lens identification and infinity focus on my GH1

Discussion in 'Adapted Lenses' started by Myzorki, Jul 22, 2011.

  1. Myzorki

    Myzorki New to Mu-43

    4
    Jul 22, 2011
    Hello,
    today i've received nice TV Lens1,4/25mm Made in Japan. Please help with identification.

    Here are the pictures:
    farm7.static.flickr.com/6027/5964063977_672bb33f8e_m.jpg
    farm7.static.flickr.com/6029/5964621600_f143b5ca41_m.jpg
    farm7.static.flickr.com/6139/5964064267_1708688960_m.jpg

    Unfortunatelly i can focus only about 0,7m with aperture close to 16.
    I think that my c-mount adapter have problem with rear metal ring of the lens.

    I've read about unscrewing screw, please take a look at the picture:
    farm7.static.flickr.com/6003/5964621858_3668b85f10_m.jpg
    Is it enough or should i machine work with the back lens element :(

    Thank you!
    best regards
    Myzorki
     
  2. lenshoarder

    lenshoarder Mu-43 All-Pro

    Nov 7, 2010
    Is this your only c mount lens? The problem might be your adapter and not your lens. My first c mount adapter was bogus. I couldn't focus to infinity with my first c mount lens. I thought it was the lens. After about my 3rd c mount lens still couldn't focus at infinity I decided it was the adapter.
     
  3. Myzorki

    Myzorki New to Mu-43

    4
    Jul 22, 2011
    Hi,
    thank you, for your answer. This is my first c-mount lens and unfortunatelly i don't want to buy another lens. Well my adapter is look like this:
    https://farm7.static.flickr.com/6013/5964819942_c1fa4e3db9_m.jpg
    Maybe you are right. I'm little confused.. I don't have possibility to try another lens or adapter without buying :(
    Thank you!
    Best regards
    Myzorki
     
  4. the.growler

    the.growler Mu-43 Regular

    Looks to me that the base of the lens is simply too wide to fit into the recess of the adapter, which is keeping the rear lens element from being brought close enough to the sensor for normal focusing distances. When the lens is screwed into the mount as far as it can go, does any part of the C-mount thread stick out past the threaded hole in the adapter?

    In my limited experience, most M 4/3 adapters will accept bases that are 37mm or less in diameter. Anything wider and you need to file or lathe the base to fit - which is not always possible, given the design of the lens. What is the diameter of the base of your lens?
     
  5. Myzorki

    Myzorki New to Mu-43

    4
    Jul 22, 2011
    Hi,
    thank you for answer.
    Here are dimensions of my lens: lens dimensions | Flickr - Photo Sharing!

    of course measured not like the arrows - this is only picture.

    When i screw lens to adapter there is only about 1mm - 2mm inside the adapter hole.
    As you wrote maximum size 37mm, my is 43mm base.. So it is too wide... Is it possible to mount it anyway with some machining?
    Thank you!
    best regards
    Myzorki
     
  6. lenshoarder

    lenshoarder Mu-43 All-Pro

    Nov 7, 2010
    Can you take apart the base. Many of my c mount lenses don't fit either. But the base comes apart leaving the threads. It looks a little funny but works fine.
     
  7. RobWatson

    RobWatson Mu-43 Hall of Famer

    Not unless you mean to machine the MFT mount on the camera...
     
  8. the.growler

    the.growler Mu-43 Regular

    Here's the way to find out. Remove the screws holding the base to the lens body. The base should pull straight out. Now you can see the diameter of the bottom of lens body where is attaches to the base and see how thick the walls of the base are.

    My guess is that the bottom of the lens body is less than 37mm but not by much and that you wouldn't be able to file or machine the walls of the base down enough to make it fit and still hold the lens in place. :frown:
     
  9. RobWatson

    RobWatson Mu-43 Hall of Famer

    What growler said but try free lensing to verify that infinity focus works before commencing to hack. If it does you at least have a rough idea of how much space there is to fit into.
     
  10. Myzorki

    Myzorki New to Mu-43

    4
    Jul 22, 2011
    I'm not sure, but i think that back of the lens - silver with the thread is one piece of metal. So i can't remove it.

    I'm wondering if it is better to send it back to seller and buy no name china 25mm lens. I'm not good with metal work.

    Thank you all for help.
    best regards
    Myzorki
     
  11. the.growler

    the.growler Mu-43 Regular

    The no-name 25mm will fit without any modification, as will a Fujian 35mm C-mount (which is a very nice lens, especially at the price). Good luck!
     
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