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I tried PixInsight for the first time tonight for stacking and was quite impressed. I was using the WeightedBatchProcessing script and really liked the way that it automatically split all my subs by filter and created master stacked images by filter (all star-aligned) in one go  I was surprised, however, that it insisted on separate flat frames by filter. I managed to fudge that by copying my flats into separate sub-directories.My question is: Do any of you take separate flats for each filter? I can see the logic in it, but haven't seen much mention of it online. |
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yes, separate flats. Each filter has it's own particular dust marks, and irregularities that should be subtracted from the subs.
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Separate flats for all filters is a must, as other posters have remarked. Not so much for different dust pattern in each (which should be way out of focus) but for the difference irradiance each filter have. And vignetting.
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Absolutely! I do it every night on whatever filter I plan to use. Each filter will need likely also a different intensity of the light or exposure time! |
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Totally agreed, different flats for each filter every time, it is time consuming but necessary evil.
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I am surprised that you get by with taking one flat and applying to all the frame. Especially narrowband flat and broadband flat can have really big differences in vignetting, sensor response.
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Thank you all. It makes total sense to me to need separate flats for each filter. It's just that I've only just got into narrowband and have only had one night of imaging with a mono camera (see below)  I've also only used DSS so far and it has no warnings about the flat mismatch with filters. It's not really an issue going forwards as flats are really quick and I can modify my flat routine in APT. Thanks again all ... good advice as always. |
