Adjusting TLR focusing lens

Discussion in 'Medium Format' started by james grehan, Sep 14, 2003.

  1. So I've taken appart my new (old) russian TLR, a Lubitel 166B. It had
    severe fungy spots in the inner part of the "taking" lense, but
    fortunatly it is now almost clean. Problem is, of course, the
    markings I put on the two lenses to be able to put them back again
    are no good because I actually unscrewed both lenses all the way to
    be able to take them completly appart. So my question is:

    Is there a specific way to match these two lenses focusing? I've
    managed to get the correct settings for the "Focusing/Viewing" lense
    no problem, but of course the "Taking" lense is a different issue. Do
    I have to stick a sheet of tracing paper where the negative goes, and
    try to focus the image there? Are there any other tricks I don't know?

    Of course I've checked but I can't find any assembling stock marks to
    get it correct.

    Please help!

    Cheers,

    James
     
  2. I have no knowledge of Lubitel cameras, but the essential thing
    with any twin-lens is that the the images on the film and the
    viewing screen be in focus at the same time. I've been able to
    adjust discrepancies in Mamiya C330 lenses by placing a
    ground glass in the back of the camera and adding shims to one
    lens until the images on the glass and in the viewing screen
    matched focus. If your Lubitel lenses are independently
    adjustable, you can do the same sort of thing. A piece of drafting
    medium can stand in for a ground glass at the film plane. I used
    a high-contrast, flat test pattern –– a newspape –– brightly
    lighted. I sharpened the focus on one lens and shimmed the
    other one till it matched. You might want to work outdoors and
    set the focuses at infinity to ensure infinity focus is sharp.
     
  3. With Rolleiflex/cords; the taking lens is adjusted first; to be at infinity focus; when the lens scale is at infinity. Then the viewing lens is adjusted; to match the taking lens's focus. Most have viewing lenses are rotated in their threaded mounts. Some have set screws that lock in place; others have a jam/locking nut. Many also have paint/gylptol/glue ; to also lock the focus position. Most TLR's have a matched set of lenses; with the focal length of both about equal. This is so the infinity and close focus will track.
     
  4. I just did about the same with a yashica-D that had serious alignment problems, unparallel lens plane / film plane. See my previous thread.
    Be very very careful to first set the infinity for the taking lens to correspond to the infinity marking of the scale, in the way described above. I personally first did it with a closeby, well lit object, put the object at 1m and aligned the sharpness with the 1m scale looking on a tracing paper in the negative's place with a strong loupe - WRONG. The problem is, you don't exactly know how to measure that 1m distance! I adjusted the viewing lens to the taking lens, put the covers back, and then it turned out, that i couldn't reach infinity focus anymore. But i was able to focus down to 80 cm instead of 1m ;o)
    So i had to do it again, beginning with infinity setting.
    The problem is, as i noticed, that when you align at a short distance, your distance measuring error is large relative to the distance itself (it DOES matter where you measure that 1m from, the lens surface, the leaf shutter, etc) while in the infinity case, it does not matter. In the same time, with close objects it's much easier to focus it well - the shallower DOF will throw out of focus anything that's a few centimeters closer or further, while in the infinity case things at 30m or 300m are hardly discernable in sharpness. So, after setting the infinity scale, i checked with the close focusing too. Still have to use a test roll through the camera.
    By the way, i do not advise you to stick anything "where the negative goes". It's enough if you make it just fit, and push it in; glue might give you lots of trouble later on.
    Good luck.
     
  5. wax paper instead of film can be used for checking focus - no glue required ;)
     
  6. "wax paper"...yeah...that's the name I was looking for:eek:)
     
  7. Thank you all!

    You have given me very valuable tips and information. I am going to try it as soon as I get home tonight and I'll let you know. Also, I've seen this interesting way to find infinity focus. Check this link:

    http://www.willegal.net/photo/srt/srt-focus.htm
     
  8. Ok, firstly, the last reply was 19 years ago but what the hell, I found this invaluable as I've just gone back to my old Lubitel and I'm going to fix the focusing problem. Thank you, thank you, thank you.

    Dean
     
    John Seaman likes this.
  9. It's a while since I had a Lubitel, but from memory, the taking lens is held by three screws accessible from inside the body. These screws are in over sized holes so that by loosening (NOT removing) the screws, the taking lens comes loose enough to disengage it from the geared focusing. You can then adjust the focus without disturbing the viewing lens, and re-tighten the screws when complete. Hope this helps.
     

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