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Thread: DLA is Nonsense! It should be deleted from the reviews.

  1. #31
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    Re: DLA is Nonsense! It should be deleted from the reviews.



    Quote Originally Posted by pin008
    DLA is calculated under Rayleigh criterion(1.22λf/D).

    A particular lambda is used for DLA, but yes, that's about right.


    Quote Originally Posted by pin008
    Rayleigh criterionsays an18MP sensor should have the same resolution as a 10MP sensor when the aperture is narrower than 10MP's DLA, which is not true.

    It does *not* say that. Did you read my above post? Do you disagree? If so, why?


    Quote Originally Posted by pin008
    That's why I doubt DLA.

    DLA is not a statement. It can't be true or false. Saying "I doubt DLA" is like saying "I doubt table."


    If you mean "I doubt DLA places hard limits on resolution", then you aren't alone. But no one is claiming that it does.



  2. #32
    Senior Member neuroanatomist's Avatar
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    Re: DLA is Nonsense! It should be deleted from the reviews.



    Quote Originally Posted by pin008
    That's why I doubt DLA.

    Be careful what you doubt. DLAcan be fractally beautiful. DLA gives us snowflakes. DLAmay even be the reason we have a planet to live on. DLA might sue you. Worse yet, DLA might bomb you to oblivion.


    But mostly, for me, it's a useful number that can help guide, but not dictate, mandate, or override creative influence on, the choice of aperture in photography. [:P]

  3. #33
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    Re: DLA is Nonsense! It should be deleted from the reviews.



    Quote Originally Posted by Jon Ruyle
    It just means that DLA does not mean what you think we think it means.




    I've been trying to follow this thread, and I think this line sums up the entire debate. This line is great!


    Stephen

  4. #34

    Re: DLA is Nonsense! It should be deleted from the reviews.



    I think the real question is "Can you compose a pleasing image?"


    Sorry....just trying tolighten ita bit. One must be able to "point - counterpoint" on a forum....othwerwise it's kinda stale.


    I like the graphs....but the pragmatist in me says that my 85 1.2 L is tough to get sharpness wide open unless you practice (due to razor thin depth of field)....regardless of who's right on the technical explanation.


    I guess though that's the point.....why? Maybe we should start a "light scattering physics" website as an offshoot of Brian's site. Meanwhile the rest of us schleps will go about composing, capturing, and pleasing.


    Cheers,


    Jeff

  5. #35
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    Re: DLA is Nonsense! It should be deleted from the reviews.



    You agree that DLA is based on Rayleigh criterion. My textbook tells Rayleigh criterion determineslimiting resolution of a telescope set by diffraction. it is a hard limit on resolution (1.22λf/D).


    If you don't think DLA places hard limits on resolution, please tell me why?

  6. #36
    Senior Member Bill W's Avatar
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    Re: DLA is Nonsense! It should be deleted from the reviews.



    Count me as one of the schleps Jeff....this thread is like a discussion on religion, politics, camera brands (hmm, that has a familiar ring to it), etc.


    Ithas continued to ad nauseum....just agree to disagree, appreciate Bryan's effortsandget back to shooting pix.


    Finire


    Bill

  7. #37
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    Re: DLA is Nonsense! It should be deleted from the reviews.



    Quote Originally Posted by neuroanatomist


    But mostly, for me, it's a useful number that can help guide, but not dictate, mandate, or override creative influence on, the choice of aperture in photography. [img]/emoticons/emotion-4.gif[/img]
    <div style="CLEAR: both"]</div>
    What I use for guideis the THE BEST APERTURE.

  8. #38
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    Re: DLA is Nonsense! It should be deleted from the reviews.



    DLA is the aperture where diffraction begins to visibly affect image sharpness at the pixel level.








    [img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.46.61/airy.jpg[/img]



  9. #39
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    Re: DLA is Nonsense! It should be deleted from the reviews.



    Hi all.


    I have to say, it's so difficult to figure out the "tone" everyone is using when there is no sound with the words


    My comment for this topic is that the other side of the Rayleigh equation needs to be stated in full:


    sin(theta) = 1.22(lambda)/D


    The DLA for each camera is calculated based on its angular resolution, which is different for each camera due to each camera having different sized pixels. The angular resolution can be defined as:


    sin(theta) = L/f where L is the spatial resolution and f is the focal length of the lens.


    So these are all lens parameters and have nothing to do with the sensor. But, if you use the definition that L = 1 pixel width (probably should be at least 2, but we'll leave that for another discussion), then the DLA becomes:


    D/f = 1.22(lambda)/(L) which is f-# = (L)/(1.22(lambda))


    So as L gets smaller (higher resolution for a given sensor size i.e. APS-C), the minimum f-# becomes smaller.


    Remember, this is for an ideal lens with no aberrations. If you add aberrations, then all bets are off as it becomes difficult to separate the two phenomena without getting specific MTFs (shudder, shudder).


    The DLA is useful for one thing and one thing only, at what aperture can you expect diffraction to become an important factor in image quality. It makes no statements on the quality of the lens (direct correlation to how well aberrations are controlled), or the actual focal length.


    Last thing, I looked at the DLA before I got my 7D and all that it told me was that if I could stay below the DLA, I should try. But, fireworks, misty water, large depth of field and sunlight say use whatever f-# you need to get the image and DLA be damned

  10. #40
    Senior Member neuroanatomist's Avatar
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    Re: DLA is Nonsense! It should be deleted from the reviews.



    Quote Originally Posted by pin008
    What I use for guideis the THE BEST APERTURE.

    IMO, there is no such thing as a 'BEST' aperture, or any other setting. Choice of aperture is influenced bythe available aperture range of your lens,the desired exposure, the desired depth of field, the effect of diffraction, etc. Photography, like much of life, involves compromise. Sometimes I'll choose to use a very small aperture even though I know that will result in loss of sharpness from diffraction, because I want a deeper depth of field. Sometimes I choose a high ISO even though I know that will result in elevated noise, because I want a shutter speed fast enough to freeze motion.

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