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Night Sky Flats

bodon
edited January 9 in PixInsight
GDay all.
When you get time; just a couple of questions Ta.
Without boring you to tears..I decided to use my viewing telescope (SW250pds) to take a few photos for the 1st time.  Stuck my televue CC, filter wheel, OAG-L and 2600mono camera on and turned to the Helix; turned out nice with Ha and Oiii only....thanks to your video.  However, My prob here...subs had a shadow and the flats took care of that with the Helix.  So back to the sky and took subs of the Sculptor Galaxy.  I needed flats as I new a shadow would be on my subs..yup not looked at the shadow problem as yet but still took photos.  However, this time the flats did not work on the green filter.  Smudge and dust...but It showed in the green master flat and hence straight to the final image on combination.  Shadow was gone but not the smudge and dust halo remained.   I tried a couple of your substitution tricks but the green remained, even seen your vid on 50/50 substitution and it did not work for me as the area is a tad larger. To my disgust I went to PS to fix.  My flats are taken on my reflector pointing to the ceiling, white plastic bag over the scope, piece of diffused plastic and led light...works fine on my refractor.  I attached a pic. (The flat has been darkend for the pic only with stf)  But Im after info for night flats as it has ticlked my fantasy a tad.
In regards to night flats:  how many would I need, do I keep taking them in the same spot for a while and then move the scope a tad and take more, am I after a star only area (as I may get a nebulae etc) and just use one filter; say a lum.  With darks..any darks as long as they match time, temp etc as per a normal dark?  And this master flat..I use it only and for all the filter 'colours' in wbpp?
Regret long winded post.  Regards

Comments

  • BlockHeadBlockHead
    Hi,

    First the fact that the shadow was corrected...but the smudge and other stuff was not corrected  is indicating your optics are changing (the smudge and dust) So, something got onto your green filter... after you took your data (if I understand the order you did things). This is a common issue. 

    I am not certain night flats are the solution based on what you are describing... we know the problem is that you got stuff that is on your filter for your flats that was not on your filter when you took the data. You need the same stuff on your fliter(s) for both the data and the flats. (This is why the shadow and any vignetting was corrected).

    -the Blockhead
  • bodon
    Thank you for the quick response. 
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