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Hackers Love Zuikos - an optical truth

Discussion in 'Adapted Lenses' started by docfox, Jun 24, 2011.

  1. docfox

    docfox Mu-43 Regular

    35
    Mar 26, 2011
    Hatfield, PA

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  2. addieleman

    addieleman Mu-43 All-Pro

    Aug 5, 2010
    The Netherlands
    Ad
    It's a nice story, but I have to disagree on one statement. It is not a good idea to focus wide-open and then stop-down and take the picture. Almost all of my lenses (Nikon, Minolta, Zeiss) exhibit focus shift and that means that you have to focus with the aperture you're going to take the picture with. Fortunately, the electronic viewfinders of our µ4/3 cameras offer splendid support for this way of working.

    In the past I have misjudged a number of lenses initially because I did what I now discourage you to do. Just try it: take one of your beloved legacy lenses, set it wide-open and focus on something. Take note of the distance set on the focussing scale. Redo this stopped down to f/5.6 and again take note of the distance set. See? :eek:
     
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  3. Ulfric M Douglas

    Ulfric M Douglas Mu-43 Hall of Famer

    Mar 6, 2010
    Northumberland
    Hacking? : Perhaps I'm missing something in the terminology...

    .pdf? Wot no webpage?
     
  4. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    Before adapters became mainstream, making adapters would be considered "hacking". :)
     
  5. docfox

    docfox Mu-43 Regular

    35
    Mar 26, 2011
    Hatfield, PA
    Your response is one of two recently received from Europe (related to two different articles), speaking of a “focus-shift” phenomenon encountered when a camera lens is focused at its widest aperture and is then stopped down to a smaller “taking aperture” for the exposure. This is the first time I have encountered discussion of such an optical characteristic and I felt obliged to investigate it a bit. I ran a simple test with two of my OM Zuiko lenses. My test results are available here for your review:

    https://drive.google.com/file/d/0B8bLj0xncj6UUlczY3BKS2o5MFk/view?usp=sharing

    They do not support your thesis. Neither my 50mm f/1.8 nor my 28mm f/2.8 OM-Zuiko lenses exhibited any detectable focus-shift when focused wide open, then stopped down to either the nominal “optimum resolution” (closed two stops from wide open) or “maximum depth-of-field” (fully closed aperture) settings. Frankly, this was not a surprise. Nearly three centuries of camera development suggest your claimed focusing problem is a non-issue.

    Photographers working under a cloth hood with view or field cameras (from the 1820’s to date) always view, compose and focus their (inverted and reversed) image on a ground-glass screen at maximum aperture first, then stop the lens down. In many cases, once you stop the lens down, you can no longer see much of anything, let alone with sufficient clarity to focus critically.

    Graflex introduced large sheet-film format single-lens-reflex (SLR) cameras around 1901. These gave the user the same focusing problems until about 1936 when Chicago baby photographer, Torkel Korling, was awarded U.S. Patent #2,029,238 for a spring-loaded preset lens diaphragm and licensed it to the Graflex Corporation. The recent photo shown here is me holding my 1946-built 3 ¼ x 4 ¼ Graflex Super-D fitted with a 152mm f/4.5 Ektar lens in Mr. Korling’s “automatic” stop-down mount. One selected the desired f/stop by positioning a movable pin to the desired hole. Then you cocked the lens which opened it to f/4.5, followed by a multi-step process to ready the rest of the camera. When you released the shutter, the lens closed to your previously pinned stop-choice. I used this jewel throughout my college years and I loved it! I never felt deceived by the focusing.

    1936 also saw the introduction of the Exakta 35mm “miniature” SLR camera. This was initially a “waist-level” camera. As with my Graflex, you looked down onto a ground glass to see an erect but left-to-right reversed image. The “pentaprism”, providing an erect and un-reversed eye-level image, did not appear until the 1948 Contax S was released. That same year Asahi introduced their Pentax with the first automatic diaphragm stop-down on a 35mm SLR. It took until 1959 when Nikon introduced the Photomic-F with all of these mechanisms integrated with electronic exposure measurement. Since then all SLR’s, film and digital sensor-based, have provided automatic diaphragm operation wherein focusing and composition is accomplished with the lens wide open, then the lens aperture closes down to a smaller f/stop at the instant of exposure.

    I have searched for a technical discussion or explanation of the “focus-shift” phenomenon. I found none on the printed pages within my library, but did find some discussions of the matter on the internet. The explanation proffered was that spherical aberration could cause a shift of focus with stop-down. The only example images I could find involved an extreme close-up using an f/1.2 lens. At the high image magnification presented, many other things could also explain the blurred secondary image at a smaller aperture including motion during the requisite longer exposure.

    In short, thousands of camera designers on three continents have labored fearlessly over hundreds of years to provide photographers with the advantages of focusing and composing at a lens’ widest opening, followed by exposure at a smaller aperture. Camera manuals over the interval and more technical tomes tend not to discourage this quest. I submit it is inappropriate to frighten lens hackers away from this option based solely upon internet reports of a deleterious second-order effect of spherical aberration. If you really disagree with me, please present your supporting photographic proof.


    Respectfully,

    George
     

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  6. docfox

    docfox Mu-43 Regular

    35
    Mar 26, 2011
    Hatfield, PA
    Dear Ulfric,

    I feel you were really trying to tell me something regarding web pages and pdf files, but whatever it is has eluded me.

    Ned was quite correct regarding the term "hacking". It has been applied to lens-to-camera matings far longer than it has to software! In the old days, one had to personally manufacture hardware (or buy it cu$tom made) to mate a fine lens with a superb body. We often accomplished this by taking a hacksaw to a pair of extension tubes (one mating with the body, the other with the lens), then finding a way to join the two "hacked" parts with the proper seperating distance.
     
  7. mauve

    mauve Mu-43 Top Veteran

    892
    Mar 9, 2010
    Paris, France
    This is completely abusive. A hacker in computer speak qualifies someone of great skill able to write very clean software to achieve some great results in a completely new and brilliant way. The epitome of hackers were the researchers of the MIT lab in the 60s', and they certainly weren't anything less than genius.

    Cheers,
     
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  8. addieleman

    addieleman Mu-43 All-Pro

    Aug 5, 2010
    The Netherlands
    Ad
    What has Europe got to do with it?
    Where did you get the notion that I based myself on information from internet reports? The statement I made was based entirely on observations of my own.
    Fair enough, here goes.

    First of all, a comparison of the setting of the distance scale for f/2.8 and f/5.6 resp., obtained by carefully focussing on the same subject on the same distance. The Panasonic GH2 was set on a tripod and the EVF set to maximum magnification. The lens was a Minolta MD W.Rokkor 28mm 1:2.8, shown <a href="http://www.smugmug.com/gallery/15659560_a5qGJ" target="_blank">here</a>. The difference shown here is representative of many trials and appeared to be repeatable. A quick check with a Nikkor 50mm 1.8 AI also showed a difference in the focus point found between f/1.8 and f/5.6.<br />
    i-VPR3Kvn-XL. "Focus scale difference"/>


    And these are the results. The 3 pictures have been shot at f/5.6, but focussed at f/2.8 - f/4 - f/5.6. These are 100 % crops from the original raw file, processed in Adobe Camera Raw.

    i-GPnjkVj-X2. "Test pictures" />

    The middle picture is the sharpest to my eye, although differences are very subtle and the pictures at f/2.8 and f/5.6 are almost identical. I will not venture into any explanation because the experiment involves human judgment (my focussing abilities in particular) as an important part. I also cannot refute nor confirm your experience with OM lenses because I don't have any.

    So my conclusion for this setup is that it's best to focus at f/4 with this lens, which is neither the max. aperture neither the actual one. I expect other lenses will behave differently but I did not check this.
     
  9. docfox

    docfox Mu-43 Regular

    35
    Mar 26, 2011
    Hatfield, PA
    I updated the Hackers Love Zuikos paper with more material including example photographs from six lenses today. (The URL address remains the same.)

    With best regards,

    George
     
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  10. docfox

    docfox Mu-43 Regular

    35
    Mar 26, 2011
    Hatfield, PA
    I have updated the URLs for Hackers Love Zuikos and my simple test disclosing no focus shift with diaphragm closing. (The old Comcast addresses are no longer valid.)
     
  11. pellicle

    pellicle Mu-43 All-Pro

    Feb 10, 2010
    Southport, OzTrailEYa
    pellicle
    Hi

    strange, are they fixed focal length manual focus lenses from the 70's? I've personally never experienced this with any of my lenses and with LF lenses that's 100% the way to go and there is no focus shift.

    Can you post some evidence (like a photo exhibiting this).

    PS: I struck out the above, as I see after reading further that you posted some ... to me they demonstrate diffraction losses, I don't see the plane shifting. Can you perhaps explain how this phenomon occurs (like is it your own theory or have you read of this elsewhere too).

    thanks for providing some photographs and engaging in discussion (rare here)
     
  12. pellicle

    pellicle Mu-43 All-Pro

    Feb 10, 2010
    Southport, OzTrailEYa
    pellicle
  13. usayit

    usayit Mu-43 Hall of Famer

    This doesn't make sense to me either. Almost all film era DSLR lenses were designed to be focused wide opened and stopped down/metered just before taking the photo. In fact, it was considered a valuable feature when camera manufacturers figured out designs that would automatically stop down the lens at the time of shutter. It was later improved to allow metering wide open with a preset aperture.

    Early zoom lenses did exhibit focus shift at the turn of the zoom ring. So zooming in, focusing, then zooming and vice versa did not guarantee accurate focus.

    However, most lenses do perform their best 2-3 stops down from max aperture. This can be noticeable but it is not focus shift.
     
  14. pellicle

    pellicle Mu-43 All-Pro

    Feb 10, 2010
    Southport, OzTrailEYa
    pellicle
    lastly, this point explains why I've never seen evidence of it:

    as I've seldom had a lens faster than 1.8 till really recently (and that's been 35mm lenses with m43) and I still tend to focus at taking aperture (often f2.8) unless I'm actually using it at f1.4 and shooting it at f1.4

    I don't tend to focus at f8 though, so to some extent the truth lies in the middle (and towards the focus open and stop down) end of the spectrum.

    been interesting thanks for this topic :)
     
  15. usayit

    usayit Mu-43 Hall of Famer

    This is the most important part of that article. Focus shift is not something you would worry about in most cases. If you focus wide and take picture wide you are compensating for the focus shift. If you focus wide open and stop down (as in most manual camera operations), in most cases the focus shift is nominal to the DOF.

    It does matter for focusing mechanisms that position lens based on absolute positioning; phase and rangefinder for example. I do know that Leica redesigned their 35mm Summilux to include a floating lens element to compensate. Focus shift always existed in that design but was more apparent on digital when pixel peeping and cropping was more common.

    For our micro 4/3rds with adapted lenses, I'm pretty sure that what you will see noticeable is not focus shift but simply most lenses do not perform at their optimal wide open. It may be difficult to focus at those wide apertures.

    Learn a little more each day.
     
  16. PacNWMike

    PacNWMike Mu-43 Hall of Famer

    Dec 5, 2014
    Salish Sea
    guess?
    Wait a minute! Isn't that exactly the way auto-aperture works on film cameras? And as you stop down dof increases and focus error decreases. :sorry: I ain't buying it.
     
  17. T N Args

    T N Args Agent Photocateur

    Dec 3, 2013
    Adelaide, Australia
    call me Arg
    Back to the OT -- does anyone know of online test reports of older MF-era lenses on modern cameras with adapters, using the same measures as for modern lenses?

    I still wonder if these older lenses really are technically up to the modern standards for peak sharpness and wide open sharpness, both centre and edge. People rave about them, sometimes, but I'd like to see them pass a test of something other than image aesthetics.
     
  18. woof

    woof Mu-43 Top Veteran

    511
    Oct 18, 2011
    The present.
    Pentax used to refer to this as "bright-filed focusing" in their manuals. It went for presets, Autos and Super Takumars with some variation in the procedure. In all my years of shooting Pentax and Nikon film cameras I never experienced anything remotely like focus shift. I am not saying it never happened, but I never saw it. That seems adequately explained above.

    Anyway, use of the term is interesting, as are the mechanics and especially the evolution of the level of automation used to accomplish this from fully manual to fully automated. The following links show how Pentax accomplished this. I have seen Olympus lenses that had the same cocking mechanism as the Auto-Takumars.

    Bright field focusing on a preset lens is descibed in the 1957 Asahi "AP" manual on page 9 here: http://www.camerac.nl/scans/asahi/pentaxapman.pdf
    Bright field focusing on an Auto-Takumar as described in Heiland H2 manual on apage 13: http://www.cameramanuals.org/pentax_pdf/pentax_heiland-1.pdf
    Bright field focusing for Super-Takumars and Spotmatic type cameras described well at page 11 here: http://www.butkus.org/chinon/pentax/pentax_sp500/pentax_sp_500.pdf

    In each case the idea is to open the aperture to max for focusing, closed down for exposure, the only differenc being the level of automation used to accomplish this. The term was used obviously used as early as 1957, though I am certain it has been a term of art for a very long time.
     
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  19. Ross the fiddler

    Ross the fiddler Mu-43 Hall of Famer

    The other thing that I think can effect focus (or appearance of focus) with SLR lenses is the filter stack (thickness) in front of the sensor. I can't remember who did that article on that (I did save a copy, but can't find it).
     
  20. RnR

    RnR Mu-43 All-Pro

    Sep 25, 2011
    Brisbane, Australia
    Hasse
    Don't see the point when the image aesthetics is all that matters and its the main reason why folk use old glass.

    Here - http://www.lensrentals.com/blog/2014/06/sensor-stack-thickness-when-does-it-matter - wide and fast are affected, but also depends on exit pupil - rangefinder lenses sometimes have troubles with thick sensor stacks, which is why the KolariVision mod for the Sony A7 series is popular.