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:

J C Brown wrote:

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

Dear Dr. Brown,

I am reading your report and learning a lot from it.

I find your graph of resolution for different colours to be surprising because I would have expected red to give the poorest resolution rather than the best. In your paper, you say:

Though the difference is not great, it is clear that the resolution is highest for the red and black Es, with magenta and blue slightly lower, followed by green then by yellow and cyan which show the poorest resolution. Part of that variation may however be due to differences in the relative intensities of the individual colours on the printed chart, which would of course depend on the accuracy with which my Canon printer printed the colours.

If aspects such as intensity and the particular shade or hue can move "red" from worst to best, how can the graph be used? My interpretation of the graph is that the average resolution decreases from approx 1800 LP/picture height at f/3 to about 1350 at f/11 and that there are colour/ intensity / hue / tint variations of approximately +/- 200. Would that be a fair interpretation if you were taking a picture of, say, a red flower and could not assess what kind of red it was?

Thanks for your comments. Stephen

I'm pleased to hear that you are finding my report useful but as I have no idea why you would expect red to give the poorest resolution I'm puzzled by your statement "I find the graph of resolution for the different colours surprising".

In your quotation from my report, marked in italics in your post, the significance of the second sentence is simply that as I am working in a domestic environment I don't have access to the calibrated sensors which would be required to check the accuracy of the six colours used in the chart.

As my Canon printer uses cyan, magenta and yellow inks to print these colours plus red, green and blue I have to rely on the accuracy with which my printer can reproduce the colours which I used to create the chart using the numerical values in Photoshop Elements and my visual assessment of that accuracy.

As any inaccuracies in the colour of the printed letters are in my opinion likely to be fairly small I wouldn't expect them to have a significant effect on the validity of any test results derived from them.

While I regard your assessment of the average values of the chart as fair I don't understand the significance of your question about assessing the kind of red when taking a picture of a red flower.

My main purpose in developing the colour resolution test chart was to allow the variation of resolution with colour to be assessed and compared with that of other cameras. The chart is not intended for use in assessing the colour accuracy of a camera,

I hope that I've managed to provide a satisfactory answer to your questions.

Jimmy

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J C Brown

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