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Thread: Diffraction vs sharpening, and high res sensors

  1. #1
    Senior Member Lars's Avatar
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    Nov 2007
    Sunnyvale, California
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    Diffraction vs sharpening, and high res sensors

    I've wondered for a while now about the conventional wisdom re diffraction limit in lenses.

    Diffraction limit is ususally measured as the point where the MTF falls below a certain percentage.

    However, as I understand it, this does not mean a complete loss of information but rather a softening of the image, a loss of local contrast.

    In theory, it should then be possible to recover detail finer than the stated diffraction limit, by applying a local contrast enhancement such as highpass filtering. Compare to the 1-dimensional application in sound - a muffled recording can still contain rich treble details which a highpass filter can recover (as long as the higher frequencies have not been completely clipped).

    The application here is of course higher resolution image sensors, specifically if it makes sense to use sensors approaching 30+ megapixels limited by 35mm format, or if diffraction limitations eliminate the benefit of higher resolution.


  2. #2
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    Re: Diffraction vs sharpening, and high res sensors

    The problem (or a problem anyway) is that diffraction is not just an attenuation of the higher frequency components, it's a form of distortion. In effect, the energy in a particular "ray" of light gets spread across multiple pixels. That shows as a form of noise in the image, and is at best very difficult to process away.


  3. #3
    Sr. Administrator Jack's Avatar
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    Oct 2007
    Los Altos, CA
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    Re: Diffraction vs sharpening, and high res sensors

    Plus it destroys micro-contrast, which is virtually impossible to recover or re-create in post...

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

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