A rough and ready way to check Rangefinder Focus?

Discussion in 'Medium Format Cameras and Accessories' started by hoffy, Jun 8, 2010.

  1. hoffy

    hoffy Member

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    I have been contemplating my navel again tonight. This time I have been wondering whether the rangefinder focus on my Koni-Omega is at all accurate. Sure the negs shot at infinity @ F8 and greater look OK, but what about closeup focus at F3.5?

    So, I thought....hmm, no ground glass to use for checking. What could I do? How about tracing paper! So, off with the back, get close to a bright light source (in this case, one of those gawd awful low power fluro bulbs, but hey, it has a cool pattern which should be good for checking focus) , cut some paper and stretch over the film plane....and cut me off at the knees and call me stumpy, it worked!

    OK, OK, I know, I haven't checked critical focus (yes, a loupe and ground glass would be in order), but it still seemed to work. Would this be a fair rough and ready way to check focus? Am I missing something? This seemed way too easy!
     
  2. Rick A

    Rick A Subscriber

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    I've always used waxed paper for a makeshift GG to check my cameras. I.ve seen others use frosted cello tape to attain same.
     
  3. alexmacphee

    alexmacphee Member

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    I use baking parchment, cut into a 120-sized strip, and spooled, with sticky tape holding it firmly to the supply side spool. This lets me keep it nice and taut over the film gate.
     
  4. hoffy

    hoffy Member

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    Thanks guys,

    I know it was a "Wow" moment for me. Just never figured that it would be so straight forward!
     
  5. df cardwell

    df cardwell Subscriber

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    Take a picture at 2 meters or so. Wide open, from a tripod. If it is sharp, you are in focus.

    This isn't meant to be a joke: you can tell with far more accuracy if you shoot the darn thing than trying to cobble together an optical bench.

    If it isn't focus accurately at 2 meters AND at infinity, pack it up and send it away.

    It really is a bullet proof and simple system. If the mechanism is off, it is unlikely that it happened in years of use: somebody tried to 'fix it".

    There, I've condensed 40 years of Koni shooting for you.

    If you are determined to take it apart, you can google "Koni Omega rangefinder adjustment" and have a go.

    Good luck.
     
  6. Christopher Walrath

    Christopher Walrath Subscriber

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    Posted wirelessly..

    Or measure ten feet away and put a high contrast subject like a lamp in front of the camera. Wide open, zero in on it and see if your final focus is indeed ten feet. That's what I would do. Then verify with the above suggestion of a print.
     
  7. Matus Kalisky

    Matus Kalisky Member

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    I have used unexposed developed BW films as an "ground glass" to check my Bessa R3A together with 8x loupe with rectangular base so that the film was lying nicely flat.
     
  8. John Koehrer

    John Koehrer Subscriber

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    If the focus is on at infinity, it is what it is at close focus.
    There's only one focus adjustment on a fixed focal length lens. Many zooms have near & far adjustments though.
    As I remember infinity is considered 500X the focal length. so you can fudge a little bit at that point if your distance scale is off a bit. Some scales can be adjusted independently of focus but May also be your infinity stop. So the focus can be on but the indicated distance can be incorrect
     
  9. michaelbsc

    michaelbsc Member

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    And who might you suggest for Koni-Omega CLAs?

    This is timely for me. I just picked up an old Koni-Omega 100 last week. It looks used but not abused. However I do question the rangefinder accuracy. Haven't had a chance to develop the single roll of film I shot with it yet to check, but just focusing, then looking at the distance on the knob's scale seems like it's focusing too far away.

    For another question, the camera has the Omegon 90mm lens. Is this a rebadged Hexanon? Or something different?
     
  10. MattKing

    MattKing Subscriber

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  11. Ian Grant

    Ian Grant Subscriber

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    Just lay a metal tape measure out on a long table and from a couple of feet above with the zero rough as near as possible to the focal plane, focus and shoot at various distances on the ruler using the rangefinder to focus on say 2 metres, 5 metres etc, shooting at full aperture, then process and see what distance is actually sharp.

    I've just done that to calibrate a Wray range finder, but the vertical alignment also needs slight tweaking, it's not difficult just painstaking :D

    Ian
     
  12. Jeff Searust

    Jeff Searust Member

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    engineering or tracing vellum--- you can usually get the local blueprint place to give you a piece off the floor big enough for years of cutting small pieces off it for MF cameras.
     
  13. Ian Grant

    Ian Grant Subscriber

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    Only shooting film will give you the accuracy a Range finder deserves, a screen is only ball park.

    Ian