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  1. #21
    df cardwell's Avatar
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    Working with your method, I don't see how ANY comparable Biogon-type lens could outperform your Fuji.

    To make a more discerning test, you would need a target with much higher image contrast. Your Koren chart probably has a contrast of 16:1, which reduces most films to a fraction of their Resolution rating. You would also get potentially higher scores if your film were developed to a higher CI.

    But if the purpose of the test is to examine how, under field conditions, your 90 Fujinon would perform, it is a good test.
    But NO properly made lens will exhibit significantly higher scores than your Fuji, even if it somehow were capable of higher tests from an optical bench. The SYSTEM buffers a miraculously perfect lens. But it also buffers your lens ! How much better is IT than a Nikkor ? No way to tell. This is why old, decrepit and worn out photographers like myself don't test any more: if it makes a GOOD picture in the field, we know it will test as well as we can test the lens outside a laboratory. Taking normal pictures presses a lens more severely than will a lab test.

    On the Thalman-Perez Tests: for decades and decades, that type of test has not seen any serious use. First, the actual test has little bearing on normal image making, secondly it is open to misinterpretation, and most importantly, while it might describe the lenses in the test, it would need a LARGE sample to infer any performance from lenses outside those tested. It is interesting, but you should not pay any attention to it. Your photographs are excellent, and you have no reason to be concerned about the quality of either your vision, or your lens.

    If you DO want to get the maximum performance from your outfit, you might use a film like FP4, with PyroCat. It will bring every bit of imaging potential from your system. I hope to see more of your pictures, they are lovely. A high acutance developer, and PyroCat has the best imaging qualities of anything available today, will make more of a difference than changing lenses.

    (forgive my SHOUTING. I have arthritis in one hand and it has been a little harder lately to make B and I and U.)

    Oh, and here is a link to a Zeiss explanation of practical photographic resolution: http://www.dantestella.com/zeiss/resolution.html
    d

  2. #22
    pellicle's Avatar
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    Hi df


    Quote Originally Posted by df cardwell View Post
    Working with your method, I don't see how ANY comparable Biogon-type lens could outperform your Fuji.
    ok ... that's nice to know. Now, all I need to do is sort out that sticky seiko shutter. It really doesn't like the cold.


    But if the purpose of the test is to examine how, under field conditions, your 90 Fujinon would perform, it is a good test.
    it was ... I hadn't given it much thought before, but I guess that like hifi reviews tests are often intended to make a lens 'look' better than it is.


    On the Thalman-Perez Tests: for decades and decades, that type of test has not seen any serious use .... It is interesting, but you should not pay any attention to it. Your photographs are excellent, and you have no reason to be concerned about the quality of either your vision, or your lens.
    well I'm not good at taking compliments, but thanks :-)

    If you DO want to get the maximum performance from your outfit, you might use a film like FP4, with PyroCat.

    well perhaps, but I'm not after performance per-se I'd like to get it, but other criteria (like look) are more important to me (and I use colour a lot)

    (forgive my SHOUTING. I have arthritis in one hand and it has been a little harder lately to make B and I and U.)
    no stress ... I have to occasionally call my dad and tell him to take the caps lock off.


    Oh, and here is a link to a Zeiss explanation of practical photographic resolution: http://www.dantestella.com/zeiss/resolution.html
    d
    handy ... thanks!

    Its a struggle working with LF but the results are often worth it. I have a permanent quest to make the best image I can when I see something which deserves pulling out my 4x5 for ...

    Thanks for your inputs and information it all helps :-)
    Theory: you understand why it should work but it doesn't
    Practice: it works but you have no idea how
    Here theory and practice meet, things don't work and I don't know why
    Homepages: here Blog: here

  3. #23
    Ed Sukach's Avatar
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    Quote Originally Posted by df cardwell View Post
    Diffraction limit: f/22. ALL good lenses perform the same at f/22 (as soon as you image on film).

    From a practical point of view, a PERFECT lens will image no finer detail than .0125 mm at f/22.... 80 lp/mm
    (f/32 = 55 ------ f/16 = 110).
    Having worked with lens design parameters, I have questions regarding the above information...

    How was this diffraction effect calculated/ Has there been consideration given to focal lengths?

    An example of the calculation/s would be very helpful.
    Carpe erratum!!

    Ed Sukach, FFP.

  4. #24
    df cardwell's Avatar
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    Ballparking rayleigh criterion... 1760/f

    Here' the Zeiss take on the subject:

    http://www.dantestella.com/zeiss/resolution.html

  5. #25
    pellicle's Avatar
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    Hi

    Quote Originally Posted by Ed Sukach View Post
    Having worked with lens design parameters, I have questions regarding the above information...

    How was this diffraction effect calculated/ Has there been consideration given to focal lengths?

    An example of the calculation/s would be very helpful.
    perhaps the following will help

    RN Clark's page has a good table just below where this link goes to. Take care that you get to that point on the page its really long. After page has loaded just refresh to make sure it takes you to the anchor (hes an astrophysicist and into photographing with telescopes)

    Roger (we have communicated a few times) has a few "limitations" with writing simply and for the layman. He basicaly says (buried on that page)

    where:
    • w = wavelength
    • f = focal length,
    • D = aperture diameter, and
    • f_ratio is the f/ratio of the optical system
    ,

    Diffraction spot diameter = 2 * 1.22 w * f / D

    Since the Fnumber and it is defined as:
    The ratio of the focal length divided by the diameter of the hole. It will be a constant for all focal lengths.


    so f_ratio is f / D so we can reduce this to

    Diffraction spot diameter = 2.44 * w * f_ratio,

    Roger then cites:
    Dawes limit = 1/(Fw) in line pairs per mm, where
    Rayleigh limit = 1/(1.22*Fw) in line pairs per mm, where
    50% MTF ~ 0.39 * Dawes limit.
    80% MTF ~ 0.16 * Dawes limit.

    and then provides a table where
    f16 = 100lp/mm
    f22 = 75lp/mm and
    f32 = 51lp/mm

    so its falling off fast at f32 but (in my opinion) still acceptable (all other factors considered) at f22 (which is why I pick it often enough when I can't quite fudge all parts in focus with some tilts and swings)


    also this is a good page which is a little introductoyr and has a calculator as well.

    HTH
    Theory: you understand why it should work but it doesn't
    Practice: it works but you have no idea how
    Here theory and practice meet, things don't work and I don't know why
    Homepages: here Blog: here

  6. #26
    Ed Sukach's Avatar
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    Quote Originally Posted by df cardwell View Post
    Ballparking rayleigh criterion... 1760/f

    Here' the Zeiss take on the subject:
    http://www.dantestella.com/zeiss/resolution.html
    I've read the article addressed here (from Camera Lens Magazine No. 2, Fall 1997) and I will disagree with the application of some the results.

    Mainly, there is the necessity of remembering that the subject lens in question was, in fact, a perfect lens, and at the same time, acknowledging that such a lens does not exist. Offshore, I've learned that this article was intended as a sort of rough primer describing the effects of diffraction for those not familiar with optics and lens design.
    That "roughness" leads to my disagreement. The only way to determine just how "rough" it is would be to compare the results cited here with the traditionally accepted formulae, which if bruised memory serves me, was discoverd by Carl Zeiss, himsef in the late - or not so late 1800's.

    I've been searching for copies of my work with that formula, but so far I haven't been able to find them.

    If anyone has any information about these formulae, pleas post it here - it would save a great deal of time. Until then, my search will continue.

    Now, the article itself i not completely wrong, but it is in danger of misappication.
    As an example in opening the aperture of a PERFECT lens one stop, the resolution in L/mm will invarably be increased. In a lens designed for use by us mere mortals, resolution at the larger apertures is already limited by other factors; the design itself, manucacturing errors and compromises, so diffraction has no effect. It is a grave errror to consider "perfect lens data' and extrapolate it indiscriminately to "ordinary" lenses.

    More when I recover the formula.

    may application
    Last edited by Ed Sukach; 02-14-2009 at 03:33 AM. Click to view previous post history. Reason: Typos, typos, typos....
    Carpe erratum!!

    Ed Sukach, FFP.

  7. #27
    df cardwell's Avatar
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    "It is a grave errror to consider "perfect lens data' and extrapolate it indiscriminately to "ordinary" lenses."

    Both the Abbe formula and the Rayleigh criterion were used as a reference to establish a limit, or ceiling, to what could be expected from testing a photographic lens. While I haven't looked too hard, I've yet to come across a photographic lens that can perform better than Abbe or Rayleigh predicted.

    If a perfect lens could perform no better than X, the limit of an imperfect lens would therefore be less than X.

    This was done to back up the notion that using film and a camera lens is so packed with buffering elements that the 'controlled tests' were both unverifiable and incapable of proving whether or not a good field lens was better than another.

    It is what a teacher called the Theophilus Principle:

    Theophilus Thistle, the successful thistle sifter,
    While sifting a sieve full of unsifted thistles,
    Thrust three thousand thistles through the thick of his thumb.

    Now, if Theophilus thistle, the successful thistle sifter,
    While sifting a sieve full of unsifted thistles,
    Thrust three thousand thistles through the thick of his thumb,
    See that thou, while sifting a sieve full of unsifted thistles
    Thrust not three thousand thistles through the thick of thy thumb.


    The point being that a perfect film and perfect lens would break down in the OP's field test. If a perfect lens and a perfect film could not yield magical results, what hope was there for a merely excellent lens and film to not fall apart ?

    Which is what I think I hear you saying.

    As for Zeiss, if the object of the exercise is to demonstrate why stopping down too far is undesirable, Zeiss seems a pretty good advisor. I'm sure there is somebody in Oberkochen who could make your head melt if you wanted to argue optics. I have no interest in it, I’m just a photographer, and a damned poor one at that. But this about trying to establish expectations for testing a LF camera and lens in the field.

    And Carl Zeiss was a machinist.

    The other two guys were Otto Schott and Ernst Abbe.

    Schott made glass. Abbey was the numbers guy.

    d

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