Out of the sub-pixel realm: End image effects

Started Jan 14, 2013 | Discussions thread
OP Marianne Oelund Veteran Member • Posts: 6,711
Aperture cutoff

Leo360 wrote:

I should also point out how flat the curves are for the f/10.5 cases above 1.6*Nyquist. This demonstrates the cutoff behavior of the lens aperture; above the cutoff point, response goes to true zero and there is no information remaining.

Is it the cut-off due to lens diffraction or it is cut-off due to the finite sensel size (fill factor) which acts as a LPF in its own right with cutoff frequency slightly over Nyquist ??

It is an effect of the aperture itself.  There is a cutoff frequency associated with the aperture size, dependent on wavelength. The "toe" of the curve at cutoff would be more abrupt with a single wavelength of light.  Since the diffraction contour that I use is for a mix of wavelengths, the toe is more gradual - but it still goes to absolute zero above the cutoff for the shortest wavelength used to produce the diffraction contour.

The LPF effect of the sensel size doesn't have a complete cutoff; it just keeps attenuating more as the signal frequency rises.

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