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Thread: Does changing aperture move the focus point

  1. #21
    Alan Klein's Avatar
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    Re: Does changing aperture move the focus point

    Quote Originally Posted by Drew Bedo View Post
    Maybe testing the lens described in the OP would help. However, shooting LF film today can be costly and takes time. A slightly inclined ruler or yard stick/meter stick under strong flood lights would allow a visual check of focus shift as it is stopped down.
    Have you ever done this, Drew? Was there focus shift?

  2. #22

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    Re: Does changing aperture move the focus point

    I have never had the problem with any of my Dagors, in fact I have never had to stop down when using any lens other than a few from the 18th century. I do recheck focus after stopping down and if there is any focus shift, it is too small to detect on the ground glass.

  3. #23

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    Re: Does changing aperture move the focus point

    Quote Originally Posted by tenniss_balls View Post
    The lens is a Goerz 12" dagor it's barrel mounted and I have the sinar copal shutter. . .
    I will not tolerate focus shift. If I suspect that a lens has focus shift, it's going to get SOLD! And, longer Dagors are known to demonstrate this aberration. Life is complicated enough as it is; I will not add focus shift to that mix.

    There are too many other options in a 12" lens; go for one of those. For example, I recently purchased a Fuji, 300mm f5.6 with inside lettering for 8x10. This lens has excellent coverage, and I'm not worried about focus shift with this lens. It's single-coated; but, I decided to stick with single-coated lenses for 8x10. (It's less expensive.) One nice thing about this lens, it takes 77mm filters, versus something larger.

    I'm also seeing some decent DBM options on EBay.

  4. #24

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    Re: Does changing aperture move the focus point

    How I have checked my vintage lenses for a focus shift:

    1. Set up my palm sized LED flashlight on one side of my basement. It has 4 rows of 6 LEDs in a rectangular pattern.
    2. On the other side of the basement I set up my Sinar at an equal height to the LED flashlight.
    3. Set my back standard to the "0" setting and focus with the front standard with the lens wide open.
    4. Stop down the lens and move the back standard back and forth noting the "range of focus".

    If the "0" setting is in the center of the "range of focus", then there is no focus shift. If the "0" is not in the center of the "range of focus", then I have a focus shift.

    addendum: when I wrote "center of the range of focus", I should have said the approximate center.
    Last edited by Greg; 31-May-2021 at 15:40. Reason: addendum: added

  5. #25
    Drew Bedo's Avatar
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    Re: Does changing aperture move the focus point

    Quote Originally Posted by Alan Klein View Post
    Have you ever done this, Drew? Was there focus shift?

    No, I have never done exactly that. I have not felt the need to.

    I do not recall setting up a shot where some focus shift was that critical to the composition.

    In all openess though; I am visually impaired with no vision in my formaerly dominant eye and something like 20/150 vision in my "good" eye. When doing table-top compositions I often set high contrast focus aids in several places when focusing wide open. I get some shots I am really proud of and many that I just don't show anyone.

    However, my professional experience, before losing my sight, involved medical imaging with isotopes. We did a LOT of calibration and QA work before setting up the equipment for a routine patient study.

    The OP identified an effect that seems to be a variable for his way of doing LF photography . . .OK, my suggestion is based on what I know of LF technique and years of isolating variables in an imaging process. Its a cheap and not overly complicated or elaborate bit of experimentation. Shouldn't be much to do it and it could give some answers.

    As an aside: My working set of lenses are of mid to late 1980s vintage by Nikon, Fuji and Rodenstock. I just can't make my photo budget take the jump to the latest AP
    O formulations. Looking for s bargain on a Petzval that will cover 8x10 though.
    Drew Bedo
    www.quietlightphoto.com
    http://www.artsyhome.com/author/drew-bedo




    There are only three types of mounting flanges; too big, too small and wrong thread!

  6. #26
    Lachlan 717
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    Re: Does changing aperture move the focus point

    Shine a laser pointer onto a wall in the dark. Bung a Bahtinov mask on the lens, stop down and use the defraction spikes to focus. Done.
    Lachlan.

    You miss 100% of the shots you never take. -- Wayne Gretzky

  7. #27
    Alan Klein's Avatar
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    Re: Does changing aperture move the focus point

    Quote Originally Posted by Drew Bedo View Post
    No, I have never done exactly that. I have not felt the need to.

    I do not recall setting up a shot where some focus shift was that critical to the composition.

    In all openess though; I am visually impaired with no vision in my formaerly dominant eye and something like 20/150 vision in my "good" eye. When doing table-top compositions I often set high contrast focus aids in several places when focusing wide open. I get some shots I am really proud of and many that I just don't show anyone.

    However, my professional experience, before losing my sight, involved medical imaging with isotopes. We did a LOT of calibration and QA work before setting up the equipment for a routine patient study.

    The OP identified an effect that seems to be a variable for his way of doing LF photography . . .OK, my suggestion is based on what I know of LF technique and years of isolating variables in an imaging process. Its a cheap and not overly complicated or elaborate bit of experimentation. Shouldn't be much to do it and it could give some answers.

    As an aside: My working set of lenses are of mid to late 1980s vintage by Nikon, Fuji and Rodenstock. I just can't make my photo budget take the jump to the latest AP
    O formulations. Looking for s bargain on a Petzval that will cover 8x10 though.
    I'm glad you're still shooting. That's great.

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