Quote:
Originally Posted by The_bluester
Reiterating what people have said above, shoot flats for all filters as they will tend to produce slightly different vignetting even if you can keep them perfectly clean to avoid dust bunnies. I have found that the flats are better shot at gain 0. Shooting flats on gain 100 with my 2600's tended to produce some posterisation effects that showed in the lights. Per what others have said and the same as your MC, a master bias is good to calibrate flats, can be re-used for months and allows varying flat sub lengths to be used. I have not shot a dark-flat in a couple of years.
You may find that darks will improve the images as well. I have found, particularly with the newt that if I am stretching the data for really faint stuff, flats are absolutely required but if you use them without a master dark matching your light frames the corners tend to show brightening. The longer the subs the more pronounced the effect (I assume it is what little dark current there is on these sensors rearing it's head and being divided into visibility by the master flat)
If you are setting up and knocking down every session you might need to do flats per session but I leave the camera mounted and the flats are stable for a long time (While using the same pointing angle, I show a little asymmetrical vignetting from the secondary so if I rotate the camera I shoot new flats) so long as I clean the scope side lens of the Paracorr before shooting the flats and keep it clean. Anything further away from the sensor than that is so far out of focus that it is not noticeable.
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Thanks Paul,
I’ve always matched my flats Gain 100 with lights Gain 100. I’ll try your suggestion and try Gain 0 for Flats.
My TS GPU coma corrector is excellent and provides round pin point Star to edge of field but due to its 4 element design , the focal plane is shifted about 20mm and therefore moves light cone, which results in Vignetting in the corners. I do have TV Paracorr but only use it for visual work in my 12” Dob. The Paracorr is a heavy beast but a quality piece of optics.
Cheers
Martin