Quote:
Originally Posted by gregbradley
What was the scope and setup?
It seems very even. Most of my flats show more uneveness no matter what scope. Some scopes seem more even than others and some show round bright circle with darker outside edges (FSQ with reducer for example).
I even had one that showed bright squares in the centre for some reason (filter related?).
How many images, how bright is the exposure (ADU) how did you stack them?
Greg.
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Greg: square filters that don't have blackened edges will give clearly visible artifacts in the flats. Most pronounced in the green, clear, [OIII] and sometimes blue filters. Typically not so bad with Red and Halpha
you ought to blacken the edges. See this:
http://www.edmundoptics.com/techSupp...ned-optics.pdf
ciao
rdc