Pentacon Six & Biometar 80 focus problem

Discussion in 'Medium Format Cameras and Accessories' started by Tor-Einar Jarnbjo, Sep 11, 2017.

  1. shutterfinger

    shutterfinger Subscriber

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    If your camera and lens were in my possession I would have
    1. set the camera up on my Berlebach or zone 6 tripod and leveled the camera.
    2. set up one of the test targets I have on 20 x 30 inch foam core parallel to the film plane.
    ISO 12233 ISO_12233-reschart_full copy.jpg , USAF 1951 USAF1951w.jpg , multiple 2 inch square copies at various angles in a + and X pattern, or the ones available at http://www.normankoren.com/Tutorials/MTF5.html Lenstarg_50_7086p_20g_25is.png
    3. mounted a ground glass at the film plane and focused the old and new Biometers using an 8x loupe and comparing the results to the view screen using the loupe.

    I guarantee all readers that I would have found the focus error within the first hour and possibility had the view screen adjusted so that any lens attached to the body was in perfect focus at the film plane and view screen.
    If the body were warped from a drop a more serious focus problem would exist.

    Search engine Lens Test Target for full resolution versions and others, print them on a photo printer at its highest resolution.
    Glossy photo paper produces the sharpest image.
     
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    As you can read further back in the thread, I have already done such a test. With the old lens, the focus on the groundglass in the viewfinder and the groundglass substitute mounted in the film plane matches. With the new lens, I can see the same focus difference in this test, as I can see on the real exposures.

    It is also obvious, and it has also been discussed, that I can raise the groundglass to solve the focusing issue with the new lens. If you have a solution to how to do that without ruining the ability to focus with the old lenses, please speak up.
     
  3. shutterfinger

    shutterfinger Subscriber

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    If the camera technician you left the camera with does not fix it then send the camera and lens to me and I will.

    I have encountered solutions to problems with equipment that defied theory and operation logic.
    I believe your body was set up with an f4 lens attached that acted like an f3.8 or 3.9 and your older f2.8 lens is more like a f3 or f3.1 so it appears in focus but the newer lens is more like an f2.6 so its off focus.
    I deal more with large format gear and have encountered lens that would hold infinity focus wide open for .001 to .002 inch of focus movement. (.0254 to .0508 mm)

    An optical test bench is the best as it can act as an f1 lens.

    I prefer the Norman Koren lens test targets for critical focusing test. I have several copies printed on 8x10 paper on the foam core. Different line widths show at different distances and focal lengths.

    P.S.
    Fewer focusing problems exists when ground glass and focusing screens are set up using an infinity target at least 5000 feet/1524 meters away that has fine detail such as a high rise office building with lots of windows.
    Some travel may be necessary to find a suitable target. Use an online map and measure the distance via the scale on the map in a direct line from your location.
    The moon and bright stars are excellent infinity targets.
     
    Last edited: Nov 29, 2017
  4. barzune

    barzune Member

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    I've been following this thread since the beginning, and am fascinated with the problem.
    Have you tried the "adjusted" camera? Has the focusing issue been resolved, with all lenses?
    D.
     
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    No, not yet. I'll call tomorrow and ask if the camera is ready and I hope to have time to pick it up. I am usually working so late, that it is difficult to get to the repair shop after work before they close, but I will try to do it either tomorrow or on Saturday. Not sure though when I will have time to actually test it.
     
  6. moto-uno

    moto-uno Subscriber

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    Well, I for one have my fingers crossed for you ! Regards,Peter
     
  7. John Koehrer

    John Koehrer Subscriber

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    Me too, it's a real puzzle.
     
  8. shutterfinger

    shutterfinger Subscriber

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    Slip out on lunch.:smile:
     
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    I picked up the camera on Friday and did a new round of test shots with both the old and the new lenses today. The problem is fixed, I can now actually focus properly with all my lenses. The service shop did not charge more than 35€ for the repair.

    The repair guy still insisted that I could never have focused properly with that camera and any lens. Both the mirror and the groundglass were displaced and have now been adjusted. If I understood it correctly, the groundglass was at the right height, but slid sideways, causing the center of the curved surface to be off-center in relation to the projected image.
     
  10. Theo Sulphate

    Theo Sulphate Subscriber

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    An interesting diagnosis. Congratulations on getting the problem fixed!
     
  11. shutterfinger

    shutterfinger Subscriber

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    Excellent! Happy shooting.:D
     
  12. Marco Gilardetti

    Marco Gilardetti Member

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    It will remain forever a mistery how it could happen that the groundglass sled sideways with one lens and not with the other, but now let's forget about it. I'm very glad that the issue is fixed and that your beloved camera is reliable again. Enjoy! :wink:
     
  13. itsdoable

    itsdoable Member

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    One of your lenses is decentered differently from the other....
     
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    'Sliding groundglass' is likely a secret terminology within the exorcist guild for a particular type of poltergeist.

    I honestly tried to get a reasonable explanation for the behaviour from the service technician, but the French messieur just shook his head and mumbled something about 'quel malheur' and 'grande catastrophe'.
     
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    Based on what? The service technician checked all my lenses last week and found no issues with them.
     
  17. shutterfinger

    shutterfinger Subscriber

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    I did a google search for pentacon six service manual and found this https://kupdf.com/embed/pentacon-six-service-manual_58f6396ddc0d60e36fda983b.html?sp=0 but it won't download, go figure.
    Screen capture for setting the mirror and image field lens:
    pentacon six.jpeg
    I believe the image field lens is what the technician refereed to as the sliding ground glass.

    Remember, do not strap the camera to a shock tower on your car then drive down a road full of pot holes, it will likely jar the optical system out of alignment. :D
     
  18. moto-uno

    moto-uno Subscriber

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    ^ Now for some photos ! Please, Regards,Peter
     
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    I'll spare you the boring focus test shots I did on Sunday evening.

    I had done some outdoor photography on Saturday and Sunday as well, but didn't have time to develop the films until tonight. I now feel a dire need to bang my head against the wall or at least throw the camera from somewhere high. Yes, the focus is ok, but the shutter seems to fuck up again(!), likely due to cold weather. The entire roll of focus test shots I did indoor on Sunday evening were all exposed properly, but almost all the outdoor photos I made over the two days are blank, without even the faintest sign of exposure on the film. On a few exposures, it looks as if the shutter slit gets stuck and only exposes a narrow, vertical stripe on the film:

    [​IMG]
     
  20. moto-uno

    moto-uno Subscriber

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    ^ Wow , it never rains unless it pours , what a streak of rotten luck ! Peter
     
  21. piu58

    piu58 Member

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    > shutter seems to f**k up again(!), likely due to cold weather.
    That is the reason I switched to a Kiev 60. Not a beauty, but much more reliable, especially in the cold.
    I got always too long times if temperature was below around 5 deg C.
     
  22. anfenglin

    anfenglin Subscriber

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    Hmm, I seem to be the only one with a fully functional P6.
    I did a test in the cold lately, it works perfectly, apart from the slow speeds of course, but I don't use them anyway.
     
  23. E. von Hoegh

    E. von Hoegh Member

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    That's frustrating, to put it mildly.
    It's -20c here this morning. While my recently overhauled cameras (synthetic oil, good to some abyssmally low temp.) will work ok, the fingers do not do so well.
    I've found that the larger fp shutters, like yours, with relatively slow travelling curtains work well in cold conditions if properly lubricated, Moebius makes an "arctic" grade symthetic that I used in mine, it also can be used at normal -but not hot- ambient temps. Nye also makes a good cold weather oil.
     
  24. moto-uno

    moto-uno Subscriber

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    ^ I'm hoping the new year coming brings some better fortune ( and pics :cry: ) Regards,Peter