FZ200 Diffraction Limit - Panasonic Tech Service

Started Aug 27, 2013 | Discussions thread
Detail Man
Detail Man Forum Pro • Posts: 16,782
Re: FZ200 Diffraction Limit - Panasonic Tech Service

MoreGooderPhotos wrote:

So in summary, all of this theory was to say that the lens and sensor combination of the FZ200 is diffraction limited to around F3.5. At higher stop values, fine details (resolution) begins to taper off due to diffraction of light due to the aperture blades. Does that sum it up properly?

Not according to my calculations. For the FZ200, I get around F=5.6 as being the point (at 700 nM worst-case wavelength, and with a typical strength "AA" filter assembly)) where the MTF of the lens-system diffraction begins to actually limit the highest spatial frequencies of the composite spatial frequency (MTF) response:

Detail Man wrote:

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 response 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.


The MTF of the lens-system diffraction (itself) is always decreasing as the mathematical product of F-Number multiplied by Wavelength increases. These effects will also attenuate the composite system MTF magnitudes existing at higher spatial fequencies (though not "extincting" them, as is calculated for above).

At what point a failure partially reduce (some) optical aberrations (by varying amounts, depending on the aberration), as well as also pass upper ranges of spatial frequencies so that individual eyes may (individually, and subjectively) deem an "optimum" sharpness is not an easy number to "nail down" (as it essentially involves subjective human perceptual judgments).

On the other hand, a state of a lens-system being "diffraction limited" (which is not the same thing as a "diffraction limit" !) is defined as the F-Number (at a particular Focal Length) at which point the measured spatial resolution begins to decrease (instead of increase) with increasing F-Number.

Focal Length (and the amount of optical lens-aberrations) that we are talking about also matters.

If that's the case, how is it possible to get a long depth of field without loss of resolution with any bridge camera? Granted, a bridge camera isn't designed specifically for landscapes and architectural shots, it does seem to do a pretty good job of them by what I've seen. I suppose that it is fair to say that in such wide angle shot, fine detail resolution is far less important anyway.

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