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Thread: Diffraction

  1. #1
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    Diffraction

    Ok, I see mentions of diffraction happening at apertures of f/16 and higher all over the place. However, having read "Understanding Exposure, Third Edition" by Bryan Peterson a couple of months ago, I don't know what to think.
    In the book he says there's nothing to it, and he uses f/22 all the time, and nobody has ever turned his pictures down because they were shot at f/22.
    So, what say you? I'm leaning towards following his advice, since he's been doing this for a few decades...

  2. #2
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    I'm not an expert, but if he's been doing this for decades, he probably used film which could be safe for f/22, compared to digital sensors.
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  3. #3
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    Diffraction isn't a myth, and you can test it yourself quite easily. Take a picture of something with a lot of fine details at F8 and then at F22 and compare the pictures. Job done.

  4. #4
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    the key here is to use the aperture that the shot demands. diffraction is, to put it really simply, a loss in sharpness and a general reduction of IQ. it relates to the bahaviour of light when compressed into smaller and smaller holes. look it up for more detailed info if you like. this is a matter of light physics so its irrelevant how long or not someone has been taking pictures...the laws of physics changes for no man...not even ken rockwell !

    think of it this way...most lens' reach their peak performance at f5.6 or f8 depending on the lens. take the 85/1.4 for example. i shoot that at 1.4 all the time, and i mean ALL the time. thats not where the lens' peak performance is but its the aperture i require for the shots i take so i choose to get the DOF rather than the peak lens performance. same as f22, if the shot demands it, then you need to shoot with it.

    where you hear most people talk about diffraction as an issue is when there is no NEED to shoot at f32 and f8 would have been sufficient. eg: recently in the POTD thread there was a pick of DC at night. the aperture selected was f32 i think. for that shot, the entire frame of what you wanted in focus was at infinity and there was nothing in the foreground to require such a DOF. in this case, you can have the IQ you desire by shooting at a larger aperture AND you get the dof you need for the shot.
    Last edited by Rooz; 11-26-2010 at 02:00 PM.
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  5. #5
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    Quote Originally Posted by Rooz View Post
    ...the laws of physics changes for no man...not even ken rockwell !
    You may be pushing it, Rooz! Ken is the Chuck Norris of photography! Legend has it that if Ken was ever going to get a shot "crooked", the world would move so that the shot was straight.

  6. #6
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    Quote Originally Posted by Rooz View Post
    where you hear most people talk about diffraction as an issue is when there is no NEED to shoot at f32 and f8 would have been sufficient. eg: recently in the POTD thread there was a pick of DC at night. the aperture selected was f32 i think. for that shot, the entire frame of what you wanted in focus was at infinity and there was nothing in the foreground to require such a DOF. in this case, you can have the IQ you desire by shooting at a larger aperture AND you get the dof you need for the shot.
    nailed it chris, thats the best explanation you are going to get.
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  7. #7
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    So you are telling me that the sunny 16 rule we all learnt in film days is rubbish.

    Guess i'll go throw the film camera away now.

  8. #8
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    Sunny who? What's film? Which camera? lol
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  9. #9
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    Quote Originally Posted by XaiLo View Post
    Sunny who?
    funny though, ive never ever forgotten it, despite the fact i havent used it in years.
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  10. #10
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    There is definately a place for using F/22, however when you do it you just need to be sure it's required because you are losing sharpness doing it.

    If you want things in focus that are appreciably further away from each other then F/22 is worth using. Eg a dramatic shot with a kid in the very close foreground and an interesting building in the far distance.

    There is a thing called hyperfocal distance where everything beyond that point is so close to in focus you'll never notice the difference. When everything is this far away then you may as well focus on the hyperfocal object and use F/8 or F/11.

    Here's the link to the thread where I asked and learnt the same question
    http://www.dcresource.com/forums/sho...ighlight=depth
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