Unfortunately I never created flat frames in the past. It seemed laborious to me. White T-Shirt and so on… I didn’t realize that I was already equipped to make flat frames. My netbook with a non-reflecting display (Asus X205T).
It’s really worth to take flat frames. It removes vignette and any particles on the lense, like dust. How to use them in the stacking process in PixInsight can be found here.
Now I understand where this gray/green/blue centered halo comes from in some of my past images. I often had to fight with that… A pity I never did flats 🙁
To capture flat frames I use a white full screen background. Since the display of my netbook is not powerful, it’s on full brightness.
My DSLR settings for flats are 1/100 exposure time and the same aperture and ISO values like the lights (in my case f5.6 and ISO1600). This gives me a centered histogram curve which should be optimal according to informations I found in the net. I take around 30-50 flat frames directly after the lights (then finally I take darks and bias).
Of course flat’s should be taken directly after the light’s, if possible. Dust particles on the lense should be at the same position as during light’s creation.
The integrated result is fantastic, compared to the no-flats integration.
This are the raw integrated images, only color balanced with LinearFit and stretched with HistogramTransformation in PixInsight:
For better resolution right click and open in new window/tab:
Maybe I’ll buy a flat field generator someday, but until then this seems to be a good solution 🙂