PixInsight -- separate flats for different filters?

Pleiades Astrophoto PixInsight Processing Calibration Stacking Solar System
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Andy Wray avatar
Andy Wray avatar
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 smile  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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Greg Meyer MD avatar
Greg Meyer MD avatar
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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andrea tasselli avatar
andrea tasselli avatar
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.
AstroDivers avatar
AstroDivers avatar
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!smile
Adel Kildeev avatar
Adel Kildeev avatar
Totally agreed, different flats for each filter every time, it is time consuming but necessary evil.
Minh Lết avatar
Minh Lết avatar
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.
Andy Wray avatar
Andy Wray avatar
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.
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