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A comment on FFTs and Optical Lenses. Parent comment

Re:FFTs and Optical Lenses by gsteinb88 on Wednesday May 28, 2014 @02:48AM (#7808718)
Also, ignores that Fourier optics only holds for the paraxial approximation (i.e. the small angle approximation). I'd put the rule of thumb somewhere around a numerical aperture of 0.3 [0] -- beyond that, polarization effects start to come into play, and beyond 0.5-0.6, it becomes an issue in, for example, microscopy.

[0] http://en.wikipedia.org/wiki/Numerical_aperture -- Similar to f-number from photography, and describes how big the aperture of the lens is in relation to its focal length. Specifically, it's the sine of the angle from the optical axis to the ray extending from the focal point to the edge of the lens, for a single lens system.

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Re:FFTs and Optical Lenses by frozenport on Wednesday May 28, 2014 @04:38AM (#7808966)
>>around a numerical aperture of 0.3

From experience you are being overly conservative. Foremost polarization effects depend on the rigidity of your surface and the bandwidth of your light source. The correction is minimal. Most importantly oil immersion 1.4 NA is common and nobody complains.

>>Also, ignores that Fourier optics

Although there is another good point. After making the born approximation you get this kind of dish shape in the Fourier transform, but on the other hand the dish is compensated on both sides of the lense

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Re:FFTs and Optical Lenses by gsteinb88 on Wednesday May 28, 2014 @08:45PM (#7813949)
Ah yeah, to be fair it's not a _huge_ correction, but in what I do (single-mode confocal microscopy) it definitely becomes an issue around NA=0.3 when trying to characterize spot sizes and collection efficiency functions. Namely, the overlap integrals can change significantly if your source is also polarized. Also, I'm probably more sensitive to these things than most since I'm at the single-photon level usually.
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