Originally Posted by
sanking
View Camera Technique by Stroebel treats this topic.
See page 99 ( if you have the 5th edition). Stroebel provides a diffraction-limited formula for resolution. It is R=1800/f-N, where R is the resolution in lines/millimeter, 1800 is a Constant, and f-N is the f-number. The formula is approximate because diffraction is different for Red, Green and Blue light, and the Constant of 1800 is an average figure.
Diffraction-limited resolution is an absolute, and is the highest possible resolution that can be had at a given aperture. The formula works for all lenses regardless of focal length. The diffraction-limited resolution at a given f-stop is the same for a lens of 200mm as for one of 800mm. It has nothing to do with depth of field, depth of focus or circle of confusion. Ole is correct in that it is dependent on f/stop. It is also dependent on how the Constant for wavelength is calculated.
Sandy King
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