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Focus shift on Trioplan 50mm f2.9

Discussion in 'Adapted Lenses' started by gnarlydog australia, Oct 13, 2015.

  1. gnarlydog australia

    gnarlydog australia Mu-43 Top Veteran

    967
    Feb 23, 2015
    Brisbane, Australia
    Damiano Visocnik
    I have acquired two Meyer Optik Trioplan 50mm f2.9. One is a "V" version (coated?) one is not.
    So I wanted to do a quick ghetto test last night and see which one is sharper.
    I placed some fine printed info (paper material) on a flat surface an shot with the lenses at 90° angle.
    At wide open f2.9 it was kind of hard to focus really accurately (subject 10 feet away) and I resorted to magnified view (14X) on my back screen of a Olympus E-P5.
    Then I proceeded to stop down the lens to see how the sharpness improved.
    To my amazement the lens did not sharpen the image although it was more contrasty than wide open. At f5.6 the image was way worse than at f2.9.... WTF?
    Wait a minute, I said.
    So, start again at wide open, get it sharp and then close it down.
    This time I check the focus as I stop down and guess what: substantial focus shift!
    As I stopped down I readjusted my focus and things got indeed better than wide open.
    What was focused sharp at f8 was NOT at f2.9, and th eother way around.
    The same happened on the second Trioplan 50mm :-(
    So, my old school learning are not holding true on this lens.
    For years I have been achieving best sharpness with (auto) lenses by focusing at wide open and then the lens stopped down to the desired f-stop setting when the shutter was pressed.
    That is from film days with Nikon lenses, Minolta and Schneider (on Hasselblad).

    Do any of you notice serious focus shift on your vintage lenses?
     
  2. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    I've written posts about it in the past however all it means is the aperture is not in the correct physical location. If you stop down to f4 then there should be no focus shift after this as the aperture blades are acting as the aperture. At 2.9 something else within the body is acting as the effective aperture.
     
    • Informative Informative x 1
  3. gnarlydog australia

    gnarlydog australia Mu-43 Top Veteran

    967
    Feb 23, 2015
    Brisbane, Australia
    Damiano Visocnik
    OK, will test some more at f4 for correct focus and then see if it does shift past that
    and while I am at it I will also check focus shift with the SMC Takumar 50mm f1.4 as I am suspecting something fishy going on there too...

    Link to your post please?
     
  4. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    https://www.mu-43.com/threads/13496/page-2#post-778509

    Here's one post about it, the numbers are talking about traditional lens designs rather than telephoto/retrophocal and it gets even more complex with telecentric designs currently in use, however the example works for most older lenses.
     
  5. Turbofrog

    Turbofrog Mu-43 Hall of Famer

    Mar 21, 2014
    Interesting! That makes total sense, but I wouldn't have thought of it that way.
     
  6. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    Note that the Aperture is probably in the correct location for infinity however when you focus closer without a floating element design some aberrations become apparent and cause the focus shift, it's all pretty boring stuff really :p

    There's a theory that some lenses were designed with a large amount of spherical aberration because it renders out of focus areas in a more flattering way for portraits (think soft focus lenses), almost all Canon f1.2 lenses can be used as examples of this (and most exhibit huge amounts of focus shift at closer distances). I personally believe that lens design has just come a long way in the 30-40 years since they were designed, if they were to be made again today the design would account for it.