FZ200 Diffraction Limit - Panasonic Tech Service

Started 8 months ago | Discussions thread
J C Brown
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Re: FZ200 Maximum Desirable F-Number to achieve adequate "Sharpness"
In reply to Stephen Barrett, 7 months ago

Stephen Barrett wrote:

Thanks Detail Man,
Your approach is much more sophisticated than mine, which is quite crude.
I don't really know anything about the low-pass filters in cameras, or about de-mosaicing algorithms or details about Bayer arrays. What I have called "sensor resolution" also has an implicit "fudge factor" of 2" so maybe my "sensor resolution" could be considered to include some of these factors that you mention.
Combining my "lens resolution" and "sensor resolution" in quadrature has some cited precedent, but I have seen an argument ( http://www.normankoren.com/Tutorials/MTF.html ) that they should be combined linearly. For now though, I have kept the quadrature combination because it seems to match the resolutions that I see in my tests for a variety of situations (telephoto, macro & telemacro). In particular, the linear combination of factors predicts that the camera should not be able to resolve things that it can resolve, whereas the quadrature combination seems to work well. Because of the quadrature combination, only the larger of the two is noticeable when one is much larger than the other. The smaller factor only becomes noticeable when it grows to a size that is comparable to the larger one. This seems to match what people report seeing. For example, people do not report any diffraction effects at short focal lengths but, as focal length is increased so that images on the sensor are spread out over more pixels, the limits of lens resolution become apparent rather suddenly. The same thing seems to happen with change of aperture.

Most of us are probably unwilling or unable to deal with MTF functions and Bessel Functions, demosaicing algorithms etc. Is it possible to derive a simpler formula that combines several factors in order to compute resolution? Perhaps it would have to be calibrated for each camera + lens combination. The formulas that I have proposed seem to work well for my camera, but I don't really know about other cameras. Are these formulas reasonable, even if they are crude? Can they be corrected or refined? Any insight that you have on this would be much appreciated.

Hi Stephen,

Though I can't recall if I posted a comment in a related thread, when it was drawn to my attention last year I read the following article with interest:

http://www.dpreview.com/articles/4110039430/detail-of-sx3040-vs-compact-slr

I too have adopted a relatively simple approach to assessing and measuring the resolution of a digital camera as described in my FZ50 report which is available for download as a 6 MB PDF file from here.

As discussed in Section 2 of that report, due to the effect of the edges of the lines of a black and white grid partially overlapping adjacent pixels, the resolution of a line pair, i.e. one black line and one white line, requires three pixels, i.e. 1.5 pixels per line width. Consequently the maximum resolution of a digital camera can be estimated with reasonable accuracy by dividing the number of pixels in the height of the sensor by 1.5.

Thus for the FZ200 which has a  4000 x 3000 pixel sensor the maximum resolution would be estimated to be 2000 lines per picture height, LPH. That value is within 5% and 10% respectively of the vertical resolution values for the JPEG and RAW images in the DPR FZ200 review.

As discussed in that report due to the effect of diffraction the resolution is reduced from the maximum value as the aperture is reduced. In addition for large apertures including the maximum value there is some loss of resolution due to several factors including shape imperfections and off axis effects. Both of these effects can be seen in the following image.

For compact travel cameras such as the TZ30 (ZS20) in which the maximum aperture of the lens has been restricted to limit its physical size the loss of resolution at maximum aperture may not be present. See for example the images included in my TZ30 report here

I hope you will find my alternative approach of some interest.

Jimmy

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J C Brown

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