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  1. #31

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    Your right, Richard: i have no clue what you do or do not know.
    And i am not assuming anything.

    But i do know that anyone (no matter who, or what i might know or not know about him or her) who doesn't know the relation between aperture and diffraction, and the effect it has on image quality, still has a bit to learn.

    I have no idea no: who is HIM?

  2. #32
    keithwms's Avatar
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    Alright, look here, this has gone on long enough hasn't it

    Q.G. is correct that diffraction always limits resolution (actually there is one notable exception but it is technical and I will not bore you with it; suffice it to say that it's a well-known mechanism that I and many others get paid to research).

    But... this is a big but... stopping down does not necessarily reduce resolution. It does at frame center, but not at the edges until you stop down really far. This is clearly seen in the flashlet I linked earlier and it also makes sense.

    People need to look back at that applet/flashlet that I mentioned a few pages ago, then all will be crystal clear.

    Seems to me that most of the tension in this thread comes from equating diffraction with stopping down, without completing the story in a clear way.

    It's as simple as this: stopping down can actually improve off-center performance substantially. Just look at the freaking applet diddle the aperture setting between 5.6 and 11 and all will be clear! What is happening in that applet is quite typical. It applies to LF as well, look at these lovely charts....

    http://www.hevanet.com/cperez/testing.html

    Note that almost all LF lenses give quite poor corner performance wide open, relative to center performance (which, by the way, hardly matters for many typical LF enlargement factors). But look at the charts: if you average across the frame, almost every single lens achieves best overall performance at f/16 or f/22 or so. How important that is to you? Well you have the liberty of deciding that yourself. Like I said before, aperture selection is usually best guided by artistic vision, not by charts.

    ~~~

    And...

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    Brevity is the soul of wit, y'all!
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  3. #33

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    Useful forum feature!

    Ed, Ian and Richard,

    Other than when others quote his posts, I've been blissfully Q.G.-free for more than six weeks. In the words of Fred Picker, "Try It!"

    http://www.apug.org/forums/820321-post18.html
    Last edited by Sal Santamaura; 08-13-2009 at 04:09 PM. Click to view previous post history.

  4. #34
    Ian Grant's Avatar
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    Another option Sal would be to use the quote system to list the image links & apertures used by John Sexton in every anwer to his posts.

    Q.G. you should go look at Sexton's work, you don't have to like it but his technique can't be faulted and he uses f22. f32. f45 etc and just blows away everything you're trying to say, and so does the work of a huge percentage of other LF users.

    Ian

  5. #35

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    How hard is it to accept that nature works in a particular way, despite what people, in their innocence, like or don't like?

    Apparently very hard.

  6. #36
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    Call me practical, but the theoretical cost of diffraction doesn't interest me very much. I would much rather hear about the "sweet spot" for various lens designs based on actual use and experience. I believe Ian when he says that Tessars are best when stopped down—I have found the same—and I believe he is also correct in stating that most large format lenses are optimized for f22. But many large format lenses are surprisingly good at wider apertures—it depends on the lens. I wouldn't normally shoot an Angulon wide open, but a Super Angulon would be a different story. And of course uncorrected aberrations at wide apertures can be useful for some purposes—I love a portrait of my mother shot wide-open with a Tessar-clone.
    Charles Hohenstein

  7. #37
    Ed Sukach's Avatar
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    I am not going to respond directly to "Q.G." The more he writes, the more convinced I am that it is ...HIM!!! - Posting yet again, under yet again, a different name... form St. Louis. Perhaps the moderators could check this out - I really do NOT want to form an opinion of anyone based on suspicion. I admire his tenacity, but he seems to be tenaciously abusive.

    Possibly I can do something to straighten out this snarled mess. There is a basic truth here ... taken out of context, and extrapolated, there is the transferrence of a LOT of misinformation.

    From an unamed source:

    "But despite not knowing, it is always there (diffraction limitation) getting worse as you stop down. So the "f/22 and be there" thing comes at a cost. At f/22 it is the limiting factor, and it's there, without a chance for a let off. There is nothing design can do about it."


    Truth:

    in a *PERFECT* optical system (in this case, a camera lens), the final resolution WILL be limited by "diffraction". N.B. "PERFECT"!!

    The easiest way to start is to draw attention to a necessary assumption: "Diffraction limitation" **IS** "always there", but it does not have an - ANY effect until it is applied to the performance of a "PERFECT" optical sytem. IF!!, n.b. "IF", you had a system capable of resoving 500 lines/ mm. you would see the ultimate resolution decreased. As far as I know, no one here HAS a "perfect" optical system - and I have never seen one in *MANY MOONS* worth of "looking". At the risk of intorducing a similie, I could install a governor on my Honda Accord to limit my top speed to 500 M.P.H. ... If that engine was in fact, "perfect" it might make it. It is not ... so there will be *NO** effect from the governor. I will NOT see my engine producing less power at 2, 5.6, 22, 11 MPH, or any less speed than 500.

    My Honda Accord is DESIGNED to comply with certain design parameters - and it does that very well, thank you.

    Do I feel the need to muck about with a theorectical limitation that has *NO* effect on what I am doing at the present...?, or even suggest some sort of magic to ... solve?? a problem that does NOT exist?
    Not even! I do KNOW the "structure" (pretty much) of diffraction and its effects ... and I'm NOT going to worry about it.

    My advice - final: Worry about something worth worrying about - "limiting dffraction" HAS been considered - and taken care of by most of the lens manufacturers. Feel fre to use any aperture you have.


    Hmmm ... I wonder if it COULD be "HIM!!".
    Carpe erratum!!

    Ed Sukach, FFP.

  8. #38

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    Quote Originally Posted by Ed Sukach View Post
    I am not going to respond directly to "Q.G." The more he writes, the more convinced I am that it is ...HIM!!! - Posting yet again, under yet again, a different name... form St. Louis. Perhaps the moderators could check this out - I really do NOT want to form an opinion of anyone based on suspicion. I admire his tenacity, but he seems to be tenaciously abusive.
    You think you found a new refuge from your embarrasement?



    The only misinformation here is
    a) that you are very learned in this matter, as you have shown (and again show) not to be,

    b) your implied - by offering your assumed learnedness as proof - believe that you, at any time, have been right at all,

    c) the content of your attempts (continued now again) to wriggle out of this "snarled mess".

    d) that you have not been abusive: your entire stance has been one of disdain. Ironically, you vehemently resent that, now that you realise that the egg is on your face.

    e) that there is a basic truth here (there indeed is. One you repeatedly said you never heard or read anything about) taken out of context: your attempts to save face are the only instances of where this matter is taken out of context.

    For instance; when or where was a "perfect" optical system mentioned in which diffraction is the only thing that limits resolution, except in your post above?
    And how does that have anything to do with the fact that you denied - on your authority - the "basic" "truth" that diffraction and aperture size go hand in hand?
    Nowhere.
    And it doesn't.

    So lots of misinformation spread by mr Ed Sukach.


    And you follow it up with even more:

    You obviously still do not grasp the concept.
    No optical system needs to be perfect, since when you reduce the aperture far enough every single one (!) will be diffraction limited.
    N.b. "EVERY SINGLE ONE"!!

    Still optics 1.0.1

    Luckily, you do apparently do know that "diffraction limitation is always there".

    Just too bad that you dragged that PERFECT thingy into it.
    And again started rambling about your very own perceived reality (based upon your many moons again).
    There is no refuge either in alluding to a non-PERFECT world in which all you say is true. The problem is very real (that you say that you never come across anything like it again says something about you. Not about optics or lenses).
    People do "muck about" with lenses that are best wide open. Those are by no means PERFECT lenses, but still only get worse when they are stopped down. And you should (! you probably still don't though) know by now what it is that makes them worse.

    And your advice?
    Very good: if we are to rely on lens manufacturer's, read what Zeiss had to say again.


    And finally: the slimmest hope there might be that you had started to understand the matter is dashed by your "limiting dffraction" HAS been considered - and taken care of by most of the lens manufacturers."

    You clearly do not understand that it cannot be taken care of anymore than gravity.
    You clearly do not understand it at all.

  9. #39
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    This thread has taken a decidedly ugly turn. Everyone's point has been made. A round of beers on me...

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