I suspect others have noted this but at least with my Alnitak flat panel, if you set up a sequence of flats, the first 30 seconds or so of flats will have lower and sometimes inadequate levels compared to later frames using the same filter, intensity, and time. It appears that the panels have a “warm up” time to reach the correct brightness.
It might be nice to have a “X” seconds “pre-start” for flat panels using the brightness of the first set.
Not a big deal since I just turn the panel on before hand but figured I would mention it.
I have one of these panels and NEVER heard of this or noticed this in flats, but I never looked for this either. Is this a cold weather only issue? Guess I’ll have to establish a workaround just to be safe. Perhaps just do one flat for 30 seconds to get it warmed up before doing the regular flats. Thanks for sharing.
It might be worse in the cold but I know it also shows up when it is not very cold. One would not notice it unless you compare the individual frames within the first set (filter and intensity). It may ultimately have little effect on the quality of the final master flat due to averaging or rejection processing of the component flats.