FZ200 Diffraction Limit - Panasonic Tech Service

Started 11 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, 10 months ago

Stephen Barrett wrote:

J C Brown wrote:

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.

Just to clarify, when you say "2000 lines per picture height", I assume that this means the same thing as 1000 line-pairs per picture height (1000 white and 1000 black).

Thank you for your comments, Dr. Brown.

I have downloaded your paper and will read it with interest.

Stephen

Hi Stephen,

Thanks very much for your kind remarks. Your understanding that 2000 lines per picture height corresponds to 1000 line pairs per picture height (1000 white and 1000 black) is correct. Consequently for the 24 mm height of a 3000 pixel high full frame sensor a vertical resolution of 2000 lines per picture height (LPH) would correspond to a resolution of 41.67 line pairs per mm.

As discussed in my FZ50 report, based on a "Yes" "No" "Yes" response a 3000 pixel high sensor would be expected to be able to resolve 1500 pairs of alternate black and white lines.

The human eye with its ability to interact with the brain forms a control system which enables the eye to "home in" on the black and white lines bringing them into register with the "rods and cones" of the retina which acts as a sensor.

Unlike the human eye a digital camera doesn't have a control system to bring the black and white lines into register with the pixels on the sensor. Consequently the position of the edges of the lines in relation to the edges of the pixels will be entirely random with a very low probability that the edges of the black and white lines will be in exact register with the pixels.

If they do occur a zero overlap will result in alternate black and white pixels while a 50% overlap will result in the response of all of the pixels being a uniform 50% grey.  All of the possible other overlap proportions will result in adjacent pixels alternating between light and dark grey of shades which depend on the percentage overlap.

There is very clear evidence of that behaviour in the images of the tapered black and white lines of the resolution test chart used in the resolution measurements presented in the DPR camera reviews. IMHO that effect makes it rather difficult to assess the resolution of a camera from an image of that test chart.

It was that effect combined with the realisation that the arrangement of the red, green and blue pixels in the Bayer matrix was likely to affect the resolution of different colours that led me to design the colour resolution test chart described in my FZ50 report.

My experience with using that chart which uses a single letter of each colour in each row led me to conclude that I should be able to make more accurate and reliable measurements with a chart which used groups of eleven letters of each colour with each of the eleven letter raised above the preceding one by a step of 0.1 of the thickness of the lines in the smallest letters.

Although they are too large to comply with the requirements of the DPR gallery copies of that chart and a black and white version of it are available for download here.

Jimmy

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J C Brown

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