Hi everyone and Hi Doug ! My CCD is STXL 1102 I have a problem with these frames and i dont' know what cause it. Each frame is 600 second long in Bin1 at -30 I noticed that in the lower left corner there is a very obvious artifact and I don't know what it is due to. It is certainly not a nebular signal (or yes) ! It is present in all three frames R G B but in the relative flat field is not present !!! Can it be a frosting effect or what ???