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  1. #91
    Ed Sukach's Avatar
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    Quote Originally Posted by DrPablo View Post
    His response will be, as it has been time and again in this thread, that that doesn't prove that it's diffraction limiting the resolution. He'll argue that maybe you can strongly demonstrate a correlation between higher f/number and lower resolution, but that isn't inductive proof of diffraction being responsible. He'll then ask us why he should care about resolution.
    May I ask who you are talking about here?

    "It doesn't prove that it is diffraction limiting the resolution"? What "doesn't prove?" At some point, diffraction will; I've tried to make the point that that aperture will be beyond the range allowed by the manufacturer ... and given that restriction, we do not have to worry about diffraction.

    I never said that we should not care about diffraction itself, only that its effect at common f/stops is negligible - and not worth the worrying effort.

    And even if it is NOT me - I think that the batteries in your crystal ball - or whatever other device/ means you use to predict what others WILL "say" are in dire need of replacement.
    Carpe erratum!!

    Ed Sukach, FFP.

  2. #92
    Ed Sukach's Avatar
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    Quote Originally Posted by Ed Sukach View Post
    Despite? That IS exactly what it says ... With a 35mm format and f/22, the lens Is diffraction limited.
    Wooops!! My ERROR - It does indicate that a lens for the 35mm format is NOT "diffraction limited" at f/22 ... and it does not become so until f/32. That WAS a surprise!!!

    I know that one of the 50mm f/2 lenses for the new Zeiss Contax does stop down to f/22.

    I wonder if the diaphragms for all 50mm lenses are located, in fact, at 50mm from the film plane? ... Or if there is some degree of "telephoto-ness" involved...?
    Carpe erratum!!

    Ed Sukach, FFP.

  3. #93
    Michel Hardy-Vallée's Avatar
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    94 posts down the line, what the HECK are you guys still bickering about? We all know that stopping down a lens corrects certain aberrations, thus helping resolution, but also that past a "sweet spot" that is relative to each lens, more stopping down will in fact decrease resolution because of diffraction.

    What is there more to argue about?
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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  4. #94
    Snapshot's Avatar
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    Well, I know I received quite an education on diffraction and the issues associated with it.
    "The secret to life is to keep your mind full and your bowels empty. Unfortunately, the converse is true for most people."

  5. #95
    Ed Sukach's Avatar
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    Quote Originally Posted by mhv View Post
    ... We all know that stopping down a lens corrects certain aberrations, thus helping resolution, but also that past a "sweet spot" that is relative to each lens, more stopping down will in fact decrease resolution because of diffraction.
    No, we DON'T all know that beyond the "sweet spot" it is ALL diffraction ... because it ISN'T.

    Check out the sites listed ... to determine when diffraction is significant.
    Carpe erratum!!

    Ed Sukach, FFP.

  6. #96

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    Quote Originally Posted by Ed Sukach View Post
    No, we DON'T all know that beyond the "sweet spot" it is ALL diffraction ... because it ISN'T.

    Check out the sites listed ... to determine when diffraction is significant.
    Dear Ed,

    At the risk of appearing combative -- and I have to confess myself genuinely ignorant here, so I do not wish to tread upon your toes -- which aberrations commonly become worse on stopping down?

    Cheers,

    R.

  7. #97
    Ed Sukach's Avatar
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    I don't take you as "combative".

    There are a number of factors that affect the focal plane of a lens... glasses with different refractive indices are used with different curves, both spherical and aspherical to converge all light rays onto the same plane ... as perfectly as possible (within reason, in any event). The image seen at "full aperture" is a collection of many ray traces, some in good places - others not. We see, and the film is affected by, an average, or root-mean-square ... or something like that ... of all of them.

    Limiting the ray traces to those in the center of the lens CAN - and usually is, to a point - a "good thing". Depending on the design, favorable ray traces MAY be eliminated as well, lessening the overall quality. At some aperture, diffraction, which is separate from refraction, will be the dominant factor. Rarely is the aperture affording the "best" quality, a.k.a. "sweet spot", located close to the point of "diffraction dominance," Rarely, although possible. Most of the time, the design will converge the rays best at the aperture expected to be used the most ... near "wide open" for fast lenses; near the "middle" for ordinary camera and enlarging lenses.

    As a side comment ... Optical Design Engineers are, as a class, the most intelligent, best damn engineers of all. Every one I've ever met seemed to be a cut above the rest.... They have to be ... Optics is one of, if not THE most, difficult field of all.
    Carpe erratum!!

    Ed Sukach, FFP.

  8. #98

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    Surfaces, Steve, not elements.

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