Flats problem advice needed

[bigal1]

Hi all so i've been out today to take some flat frames to see if i could improve my first dso images but for some reason the master flat does not look correct it looks too flat . I had the camera set to same iso and same exposure length as the lights aslo same focus and i had a white tshirt stretched over the objective and pointed the scope at a blank part of the sky , i was expecting to see some vignetting maybe and also a few dust spots but the master flat came out very very flat lol any advice would be most appreciated thanks .

[Photosbykev]

You have to reduce the exposure so that the flats aren't burnt out. If you set the camera to Av and use the same aperture as the subs you will be pretty close. Your shutter speed will be down well below 1 second. Check the histogram to ensure the highlights aren't clipped i.e too far to the right

[FraserClarke]

Yes, it's completely saturated. No need to have the same exposure time for the flats, use a much shorter exposure because the sky is so much brighter.

[bigal1]

Thanks for that Kev for some reason i thought the flats had to be taken at exactly the same settings as the lights , will try again tomorrow

[Photosbykev]

Thanks for that Kev for some reason i thought the flats had to be taken at exactly the same settings as the lights , will try again tomorrow

Ideally they should be taken before you touch the system after shooting the subs so that any dust bunnies etc are in the same position.