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:


Thanks very much for your kind remarks. I must say that I am somewhat confused by your statement that you thought that the letter E looked fairly legible most of the time and your question about a sentence sample at one pixel per line width. I assume that the image for which you state that most of the Es are legible is the one for which the Es have a line thickness of 1.5 pixels.


When I said that the E looked legible most of the time with 1 pixel per line width, I was referring to your greyscale simulation, not the actual camera test. There are 11 Es at different heights with respect to the pixels and 10 of them are recognizable as Es. Only the middle one lost its arms and looks like a letter I.

The question that I asked was stupid, as a result of posting in a hurry before I had to go somewhere. What I had in mind was some telephoto tests that I did with my Canon SX30, resolving about 30 microradians (~9% MTF line-pair resolution using the USAF test chart). At the same time, I did some tests with printing "The quick brown fox jumped over the lazy dog." using various fonts. With simple fonts, the printing became legible at a height corresponding to 55 microradians. This is probably a poor test because I knew the words ahead of time and, even if I that were not the case, one could probably guess a lot of the words from a few legible letters and the shape of the word. So your tests with a single letter make more sense.

In spite of my the obtuseness of my question, I think that you answered it when you said that 1.4 pixels per line width might be enough for intelligibility, but not 1.3.
Thank you.


Thanks for clarifying your comments about the 1 pixel per line width images. Having looked again at these images I realised immediately that the legibility of the Es in the simulation is very much higher than in the recorded image and that the difference is due to the large difference in the shades of grey in the adjacent pixels, with those in the recorded image much darker.

As explained in my previous post the shades of grey used in my simulations are in direct linear proportion to the percentage overlap and were calculated using an R,G,B scale of 0,0,0 for black and 255,255,255 for white.

In contrast the shade/colour of each pixel in the image recorded by my FZ50 has been derived from the amount of red, green or blue light received by that pixel and several adjacent pixels and combined by a demozaicing algorithm the properties of which as Detail Man suggests are known only to Panasonic.

Though I am not familiar with the USAF test chart I seem to recall that it consists of several sets of five parallel lines with the line thickness of each set progressively reduced to allow the resolution to be assessed in line pairs per mm.

As I have been used to working with milli and micro radians since the early 1970s I found it interesting to discover that you also are familiar with measuring resolution in micro radians and relating the height of a font to a subtended angle in micro radians. It is almost six years since I joined the Panasonic forum and this is the first time that I have come across someone else who thinks in these terms.


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J C Brown

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