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diggy
sage
Reged: 05/09/04
Posts: 303
Loc: Vancouver Island, Canada
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How big is a star..in pixels??
08/09/08 07:22 PM
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I've been stumbling on the black art of focusing a DSLR at prime focus without the recommended computer connected tools. One question is how big would a star be in pixels, if the image is "ideally" focused. I realize the question is probably over-simplified: I'm sure it depends on a bunch of factors. So, for an example:
I shot the double cluster (12 subs 25" ISO 400) with a Nikon D70s (3008x2000 pixels) through a 110mm refractor with a 0.8 focal reducer/field flattener. The "largest" star in any of the raw images measured 12 pixels across; the smallest about 4 pixels wide. After processing through DSS the largest was reduced to 9 pixels. So, is there any info I can gather from that about focus: should stars be smaller?
Thanks in advance for any guidance here.
Diggy
-------------------- WO 110mm Megrez doublet on an HEQ-5 mount
Nikon 10x50 binocs
"Beyond here be there"
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