Live stacking and flats

[ciaranr]

Another newby. Same question. read as much as I can get my hands on but still no joy.
I have an asi533 pro with a 6" SCT and hyperstar. I wanted to use the live stacking feature. So far ... so good.
I noticed that my live images had a central glow. On reading I discovered that this is vignetting and can be fixed with flat frames. Onwards and upwards. I create flats according to what seem to be simple rules. Use a lightpanel (tracing panel), use a white t-shirt, Drop the gain to as low as possible. Play with the exposure time till the histogram is at ~50. Get the flats.
But ... when I apply the flat to the live stack instead of a slight glow in the center of the image I have a small dark area in the middle that is surrounded by a sea of white in increasing intensity to the edges of the image. I have experimented with taking flats with the histogram being at 10 up to 70 and still the same.
I do not use darks. Is it as simple as adding in a dark frame or is there something more sinister going on?

This is most frustrating.

[admin]

Hi,

yes, the first step is to make sure you are using darks as well as flats when capturing and also to either use bias frames or dark frames when capturing the flat frames.

You can kind of get away without dark frames when you are using flat frames to get rid of dust spots for solar/lunar/planetary, but for deep sky you will tend to get either overcorrection (which you are seeing) or undercorrection of you are not using dark frames.

You can find more useful info here : https://docs.sharpcap.co.uk/4.0/#Gettin ... Correction

cheers,

Robin

[ciaranr]

Thanks Robin.
I cant see the woods for the trees.
I'll make a darks library and have another crack tonight.
Sorry for the inconvenience.

Ciaran

[ciaranr]

well

you, sir, have nailed it.

Stack_383frames_766s.jpg (424.86 KiB) Viewed 2285 times

[admin]

Looking good - glad you got there in the end

cheers,

Robin

[Buckrogers]

oh wow, that looks gorgeous, well done.