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A comment on Dirty lens article.

Re:Dirty lens article by _paulc on Saturday January 31, 2015 @05:59PM (#8978413)
Long time since I did any optics but this basically just convolution. The impact at the output plane of dust/imperfections on the lens is (approximately) a 2D fourier transform of the dust/imperfections. If you have a single dust particle (essentially an impulse) on the lens this will be convolved into a dc response at the focal plane.

[1] http://en.wikipedia.org/wiki/Fourier_optics#Fourier_transfor...

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Re:Dirty lens article by darkmighty on Saturday January 31, 2015 @07:40PM (#8978649)
It's approx. convolution and the impulse response varies with the distance to focal plane: at focal plane it's impulsive but near the lens it's quite flat (almost DC -- it's simply a "zoomed in" aperture, which is a big circle usually).
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