FZ200 Diffraction Limit - Panasonic Tech Service

Started Aug 27, 2013 | Discussions thread
J C Brown Senior Member • Posts: 1,617
Re: Does the Panasonic FZ50 violate the laws of Physics?

Stephen Barrett wrote:

Detail Man wrote:

Stephen Barrett wrote:

Something is wrong with my last post. The test result of 1.3 pixels per line-pair for the FZ50 doesn't make sense. Either the test is too good or I blundered in my calculation. Too bad i have to go out now. It's going to drive me nuts.

Two photosites cannot be enough - simply because of the spatial frequency spectrum of periodic line-pairs (a "square wave" containing higher order harmonics as well as a fundamental spatial frequency), the Shannon-Nyquist sampling theorem, and the random-phase of aligning projected periodic line-pairs onto an image-sensors array of photosite locations. It's that simple.

DM ...

Thanks Detail Man.
That is the reason that I said something was wrong with my previous post.
The question is:
How can you explain J C Brown's and Cameralab's test results?
By my calculations in my previous post, they seem to be resolving above the Nyquist freqency.
Cameralabs claims a resolution of 2100 line pairs per picture height for the Panasonic FZ50. The sensor height has 2737 pixels ==> 1.3 pixels per line-pair, so how do they get that resolution? If you click on the Cameralabs link that I posted, you can see the evidence. Also J C Brown's test is similar, claiming slightly less resolution, corresponding to 1.5 pixels per line-pair. So, what is going on? Did I drop a factor of 2 somewhere? Or, does the Panasonic FZ50 sensor violate the laws of physics to get twice the resolution of the sensor in my Canon SX30?

Hi Stephen,

You are correct in suspecting that you dropped a factor of 2 somewhere. As explained below the resolution figures you quote are for lines per picture height not line pairs per picture height.

In your previous post "http://www.dpreview.com/forums/post/52101765" you wrote:

"J C Brown's assessment of the FZ50 (Section 7 of his paper for Black & white resolution) is that it can resolve at least 1850 lpph (line-pairs per picture height).

The Cameralabs review says 2100 lpph at f/4.0.

The sensor has 3648 x 2738 pixels, so the number of pixels per line-pair is
2738 pixels / 2100 line-pairs = 1.3 pixels per line-pair. This seems to give somewhere around 10% MTF total camera resolution, including the sensor, lens and and all the "filters", demosaicing algorithms and crosstalk etc."

If you check section 7 of my FZ50 report you will see that all of my measurements are in LPH, lines per picture height as defined here: http://www.dpreview.com/glossary/digital-imaging/resolution. The maximum resolution measured in any of my FZ50 tests was 1954 LPH, 2736/1.4.

The  "1.5 pixels per line" rule of thumb in my FZ50 report was based on a relatively crude graphical simulation which as I recall I prepared in 2001 or 2002. Based on the results of my subsequent tests I would regard a figure of "1.4 pixels per line" as more accurate.

It seems that your confusion may have been caused by the use of the abbreviation "lpph" instead of "LPH" in the Cameralabs review definition of resolution.

If the 2100 lpph at f/4.0 figure which you quote from the Cameralabs review was correct a resolution of 2100 line pairs per picture height would correspond to a picture height of 4200 line which for a sensor height of 2736 pixel is clearly impossible.

If you haven't already seen it you may find the comparisons between my graphical simulations and the corresponding sections of my test images in the following post of interest.

See: http://www.dpreview.com/forums/post/52102009


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J C Brown

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