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Roland;
I think I know where you are
going with this, but I can't give you very accurate numbers. My 180mm f2.8 gives
sharper stars than the Schmidt, as I have painstakingly focused it for
Hydrogen-alpha light only, and it is less affected by bad seeing and guiding
errors. (I manually guide!) With the 180mm images on tech pan I took a 1200 dpi
scan (optical, not enhanced) of a print enlarged about 10x. This gives approx
12,000 dpi at the film plane, or 2 microns/pixel. My sharpest stars on tech-pan
have most light in a 5x5 square (10 microns), with most of the light spread
of the star contained in a 12x12 grid. This is really tough to measure
though, due to halation. The Schmidt is about 25-40% bigger on rare shots where
the seeing was good. I don't think 6.8 micron pixels is overkill for a tech pan
replacement with short FL, fast focal ratio optics - especially if they are
precision focused for one colour. 24 micron pixels will give square stars. Or am
I talking out of my touque? (toque in the US?)
John Mirtle
Calgary, Ab. Canada
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