FZ200 Diffraction Limit - Panasonic Tech Service

Started Aug 27, 2013 | Discussions thread
Detail Man
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Re: FZ200 Diffraction Limit - Panasonic Tech Service
In reply to LTZ470, Aug 27, 2013

LTZ470 wrote:

DM wrote:

"In addition, lens-system aberrations will also reduce the magnitude of the composite system MTF, and increasing the F-Number to the point where the composite system MTF response is maximized makes sense (regardless of any other factors, such as calculated Airy disk diameters). At F-Numbers above that point (for any given Focal Length), the system is "diffraction limited".

So the FZ200 is diffraction limited regardless of focal length?

The net composite effect at the photosite level (the "RAW" level) of lens-system diffraction, combined together with lens-aberrations, optical filter-stack characteristics, photosite aperture, shape, and "pitch" ...

... which then is also "filtered" by the (potentially non-limear) spatial frequency response of the de-mocaiscing algorithm that readies a RAW-level image for (in-camera, or external) further processings, many of which will (themselves) "filter" the image-data further.

Then (on some particular viewing medium at some particular physical size in some given ambient light environment at some distance), depending somewhat on mood (perhaps), and that final end-product is what viewers then gaze at - typically through all kinds of varying fideltiy monitor-screens as well as browser color-management. No one single unifrom "elephant to be seen" there.

We are assuming zero focus-error (or the MTF becomes more complicated still, and not in simple ways), zero net camera-motion (or the perfect cancellation of such), of course. In real life, these tangible and oft-present annoyances very likely completely "swamp-out" any significant "diffraction" concerns, anyway ...


Diffraction itself is (solely) a characteristic of the lens-system. It is measured in spatial frequency units (using MTF curves).

"Diffraction Limited" describes a range of lens-system F-Numbers where the (essentially linear) net-decrease of the numerical magnitude of the MTF curve (also described as the "contrast" amount) as spatial frequency increases dominates over the (also present) optical aberrations.

This is complex, in that "stopping-down" only reduces (some) aberrations (some by direct divisions of the effects of the aberrations, some by division proportional to the square of the F-Number). But those optical aberrations are still there - only somewhat lessened from "stopping" down.

At some particular F-Number (for a given lens-camera combination), the measured (spatial frequency) resolution will exist at a maximum numerical value. Or, perhaps not in this case (below).

and the f/4 sharpness just comes from lens characteristics?

See above explanation.

Nothing to do with diffraction because it is already in the lens from when you turn it on?

Diffraction effects occur on their own within the lens/aperture system only.

Once past f/4 I see a degradation quickly on the FZ200, but could be related to shutter speed as well...

Not in Aperture Priority mode. I am assuming that you would be in Aperture Priority shooting mode, and then control the Shutter Speeed to some comfortably higher level via (negative direction) adjustment of the manual Exposure Compensation control (so as to achieve a constant Live Histogram reading) ? All of the above optical/electronic effects are independent of the time of the exposure (of the image-sensor surface to incoming light).

All the scientific lingo is a bit much for my old brain…and I am reading work related programs for now...

I emailed Panasonic Japan to see how they respond…If panasonic doesn't know their own camera and lens then we are definitely in trouble! Leica's next...x

Well, there you go ...

So it could very well be at where we are seeing the sudden degradation at f4.5 and higher? And the f/3.5 to f/4.0 holds true as it is the sharpest?

What you see is what you get (but nobody else can ever know or understand what your own perceptual mind envisions). The FZ28 lens (x18) was best at it's minimum F=2.8 F-Number. Things only got (slowly, gradually) worse above minimum F-Number.

"Stopping-down" only reduces (some) optical lens-system aberration effects (at any F-Number).

It (may) be that rather than think in terms of a certain and well defined peak "sweet spot" (of F-Number) here, it (may, in actual behavior) be more like a gradual reduction of resolution (measured usig MTF curves) starting (at or near) the lowest F-Numbers. At which point, there is no (other base F-Number setting-value) "point" (in the value of F-Number) to call some (reasoned to be a well-defined peak "maximum").

Now when you use EZ Zoom how does that affect Diffraction? as it crops the sensor, but then it's only 8mp...same lens though...

Indeed. The resolution will be reduced by the fraction of the original image-dimension (used in calculations) that the sensor-cropping comprises. There is absolutely no free-lunch on that. There still (may) be some particular F-Number that you might want to be at - but not so if the FZ200's lens-system is similar to the FZ18's (18x) telephoto zoom lens-system. I do not know.

At longer lens-system Focal Lengths, it would seem to my (near zero understanding of optical lens-system design) likely (some) optical aberrations must allowed to exist in order for a lens-system to achieve a constant F-Number over such a wide range of multiples of Focal Length.

But I should let others much better speak to the various trade-offs of optical lens-system designs.

DM ...

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