Use Offset when Taking Flats?

[Brian V]

Q: Should the Offset be set to anything other than 0 when taking flats? My darks and lights are normally at an offset of 20, otherwise the histogram is crammed to the left.

Equipment:
Sharpcap 4.0
QHY294C Pro / Optolong L pro
8" SCT

[Menno555]

Hi Brian

Typically I always have the offset (and gain) of my flats the same value as my lights. The only thing i change with flats is the exposure time.

Menno

[admin]

Hi,

the strictly correct answer is that the offset when taking the flat must match the offset when taking the dark flat/bias frame that is used with the flat. It doesn't strictly matter whether it is the same as that when taking darks/lights (but those two must be the same).

To be honest though, I'd leave it the same for all of them... less chance of making a mistake that way.

cheers,

Robin

[Garysiegel]

I was originally told to follow the steps below when taking Flat and Dark frames. Am I creating them incorrectly?

Flat Frames Setup
Set Gain low “0”
Check "Capture and select bias frames"
Check "Create Monochrome Flat Frame"

Dark Frames Setup
Same exposure length as light frames
Same Gain as light frames
Same temperature as your light frames

[admin]

Hi,

yes, that's fine as the flat/bias will be taken at the same offset (whatever that is), and at gain 0 the offset is pretty unimportant.

Dark frames also fine as stated, but also make sure that the dark frame histogram is separated from the left hand side. Increase offset for both dark and light frames (to the same higher value) if it is not.

cheers,

Robin