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I calculate the "critical" (minumum) Photosite Aperture dimension to be:

Pa = ( Pa / ( K * Pp ) ) * ( Fz ) * ( W * N )

where:

Pa is Photosite Aperture;

K is the Bayer-arrayed and de-mosaiced "fudge factor";

Pp is Photosite Pitch;

Fz is the fraction of the spatial sampling frequency (which is equal to the reciprocal of Photosite Pitch) at which the first zero magnitude response occurs in the composite Optical ("AA") Filter combined (convolved in the spatial domain, multiplied in the spatial frequency domain) with the Photosite Aperture);

W is the Wavelength;

N is the F-Ratio of the lens-system.

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Solving for the simple case of a 100% Fill Factor (Photosite Aperture equals Photosite Pitch), setting the value of K to conservative value equal to 2, and setting the value of Fz to 1/2 (the strongest possible "AA Filter" (resulting in a zero magnitude response at the Nyquist spatial frequency), the identity presented above simplifies to the following form:

Pa = ( W * N ) / 4

Re-arranging to solve for the maximum F-Ratio (N) as a function of Wavelength (W) and Photosite Aperture (Pa):

Nmax = ( 4 * Pa ) / W

http://www.dpreview.com/forums/post/51858399

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For the DMC-FZ200, Pa ~ 1.5 Microns. For a worst-case Wavelength (W) of 700 nM, it appears that (in the base case), diffraction "extinction" is not an issue until F=8.571 (which exists, in fact, above the maximum F-Number adjustment value of F=8.0 for the FZ200).

The above case being for an optical low-pass ("AA") filter yielding a zero response at the Nyquist (1/2 of the spatial) frequency itself, a more likely situation is one where the optical low-pass ("AA") filter yields a zero resonse at (around) 2/3 of the spatial sampling frequency. In that case, the result of the above calculations being applied result in a maximum value equal to F=5.714.

Probably little reason to "sweat it" about F-Numbers lower than F=6.3. It might seem that a "stuperzoom" lens-system that is constricted by design to maintain a constant F-Number of F=2.8 might (perhaps) suffer from opticall aberrations that are not (in any event) very effectively controlled - especially as the Focal Length increases to longer than "wide-angle".

Thus, the down-side of the FZ200's around 1.5 Micron sized Photosites would seem to be that the F-Number of the camera system probably should not be raised above around F=5.6 in attempts to mitigate the various optical aberrations which just may be present in such an interesting, yet likely somewhat ambitious, lens-system design.