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Help with an oddball lens

Discussion in 'Adapted Lenses' started by Runslikeapenguin, Oct 6, 2012.

  1. Runslikeapenguin

    Runslikeapenguin New to Mu-43

    Oct 6, 2012
    So i have this lens that i really really want to mount to something but I'm having some trouble.

    So i got this old 60's BBC TV camera that was broken and i couldn't get it to work, i couldn't sell it and i couldn't give it away, so i tossed it. But i kept the lens that was on it because i could feel the potential. It was a 20mm-100mm F1.8 zoom lens in C mount.

    Now here's the problem, the lens needs to be serviced/ cleaned and the zoom isn't working for some reason but the glass is clean and fungus free. But secondly i don't own a mirrorless camera to use this on, and thirdly I have come to read that there are two C mounts, C and CS and the latter will not work.

    So my conundrum is this, I want to buy an EP1 because the prices are good and i would like to give a 4/3 try but i don't really want to buy one if i can't use this lens. If anyone could offer me some advice on how to figure out if this thing is CS or C i would be in their debt.



  2. McBob

    McBob Mu-43 Regular

    Apr 22, 2012
    Buy a $10-20 C-MFT mount adapter from an eBay or Amazon vendor. If it doesn't work, re-sell it.

    I can tell by looking at it that's it's most definitely C-mount.
  3. Spuff

    Spuff Mu-43 Top Veteran

    Dec 5, 2010
    Berkshire, UK.
    I was thinking that looks a bit small for a TV camera lens then I saw this:

    so maybe not.
    Please post the results.
  4. Crdome

    Crdome Mu-43 Hall of Famer Subscribing Member

    Sep 11, 2011
    West Central Indiana
    I suspect it is a CCTV lens which would provide the coverage. Google the cameras name and model. That should provide some information regarding it's format. also the information around the lens including manufacture, and the 1:1.8 f =20-100. If is a CCTV there is a huge chance it won't cover the sensor.
  5. Runslikeapenguin

    Runslikeapenguin New to Mu-43

    Oct 6, 2012
    Yeah i projected the image circle through the front of the lens with a flashlight and then measured the distance it took to get sharp and it looks like its bigger than C mount so i guess i could shim the distance. but something else i noticed was that the image circle was only like 8mm. That seems really really small.
  6. Runslikeapenguin

    Runslikeapenguin New to Mu-43

    Oct 6, 2012

    Scratch that, i was measuring the wrong circle, the flashlight i was using was making bounds. The actual image circle is around 17mm maybe a tad bigger.
  7. KBeezie

    KBeezie Mu-43 All-Pro

    Sep 15, 2012
    Grand Rapids, Mi
    Karl Blessing
    Sounds like a c-mount, which most of them cover the vertical on MFT, but will vignette at the sides. The gears of course were designed for electronically controlled camcorders I think where you can zoom via button push.
  8. Crdome

    Crdome Mu-43 Hall of Famer Subscribing Member

    Sep 11, 2011
    West Central Indiana
    Did you measure the circle at 20mm or 100mm? Almost all c-mount lenses minimally must be 25mm or longer to provide full 4/3 sensor. My Cosmicar Television 1.5/20~90mm doesn't provide full until about 40-45mm.

    is a great reference chart.

  9. Runslikeapenguin

    Runslikeapenguin New to Mu-43

    Oct 6, 2012
    Thats a good question. the zoom function of the lens is stuck. The inner part is all the way down at the bottom so . . not sure which focal length its at. If it was full wide then that would mean it would progressively cover more image area the longer the focal length . . right?
    Or am i thinking of that backwards?
  10. Crdome

    Crdome Mu-43 Hall of Famer Subscribing Member

    Sep 11, 2011
    West Central Indiana
    Lenth matters, I don't think aperture does.

  11. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL
    There is no certainty that the coverage would increase as the lens is zoomed toward the tele end, though that is the general trend. Also, coverage generally increases as you stop the lens down, though with many designes the increase is small.
    • Like Like x 1
  12. RobWatson

    RobWatson Mu-43 Hall of Famer

    The back focus distance a the big clue to tell CS from C. Set focus to infinity and find where the rays converge - something like 17mm will be C and something like 12mm will be CS. Should be fairly easy to tell the difference.

    Hard enough to get C to work so CS will be likely impossible.

    If you are lucky the zoom is seized from years of accumulated gunk and hardened grease. Not too tricky to fix that.

    A great many of those types of lenses were used with 1" vidicon tubes so will illuminate a 16mm circle which is not great but likely good enough to get servicable images in MFT.
    • Like Like x 1
  13. speedandstyle

    speedandstyle Mu-43 Hall of Famer

    Yes CS is impossible with m4/3. The lens would have to be 5mm closer to the sensor. CS should work on the Pentax Q but not on any other camera.

    That BBC lens is a C-mount for sure and possibly a very nice one. Strange that there is no branding on it. The geared rings are either for a motorized zoom and focus or for a follow focus set-up{depends on how the camera was used}.
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