06-20-2016, 07:38 AM
Just catching up on the thread. I think perhaps a better way to think about diffraction is there is a point where it starts to visibly "soften" the image, and there is a later point where it is the final limiting factor. Photographers tend to refer to the former, whereas I think Wim is referring to the latter.
There are times where it is still advantageous to work well into diffraction limited region. Anyone tried planet imaging? My scope would be, in photographic terms, 2000mm f/10. With barlows (think of them as functioning like teleconverters) I also tried 4000mm f/20, and 6000mm f/30. Of the three, the best results were obtained around f/20, as I was into the noise of my sensor at f/30, and the subject was too small at f/10. The sensor had just over 4 micron pixel pitch if you want to work out an effective MP to compare with photographic sensors, but I think that was in the rough ball park as 18MP APS-C from memory.
There are times where it is still advantageous to work well into diffraction limited region. Anyone tried planet imaging? My scope would be, in photographic terms, 2000mm f/10. With barlows (think of them as functioning like teleconverters) I also tried 4000mm f/20, and 6000mm f/30. Of the three, the best results were obtained around f/20, as I was into the noise of my sensor at f/30, and the subject was too small at f/10. The sensor had just over 4 micron pixel pitch if you want to work out an effective MP to compare with photographic sensors, but I think that was in the rough ball park as 18MP APS-C from memory.
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