Confused about Master Dark & Master Flat creation

[ribuck]

Hi All,

I've been following a few tutorials and i'm a bit confused about Master Darks & Master flat creation.  So i've created my Master bias, and then created a SuperBias and then calibrated all my dark files with the super bias.

Next i created a master dark for each sub length (300secs , 600secs etc) ...........So far so good i think.

So next i need to calibrate my flats with Master Dark & Master bias, but this is where i am confused.  So if i have a master dark for each sub length,   which one should i use to calibrate my flats ?

Many Thanks,
Rich

[pfile]

generally speaking you should use the master dark that most closely matches the exposure time, be the target frame a light or a flat.

because my flats are usually short (2-5sec) i just use the master bias (or superbias) to calibrate my flats.

rob

[ribuck]

Hi Rob,

Many thanks for the reply. So it looks like I'm going to have to create darks to match the flat exposure lengths as there is a big difference in the exposure length for a Lum flat vs a Ha or SII flat.

Wow that's a pain just to calibrate the flats or am I misunderstanding.

Rich.

[pfile]

well, in the absence of an exact dark match, people usually take long darks and then let the software scale them down. so your 600s darks might work unless your SII flats are longer than that?

rob

[ribuck]

Thanks rob,

I've got some 30 sec darks so I'll just use them and let it scale them accordingly. Is there any specific setting to enable the scaling or will it be done by default.

Rich.

[pfile]

if during flat/light calibration you tick "optimize" in ImageCalibration under the Master Dark section, the dark will be scaled. of course you should also load your master bias / superbias.

since you've already calibrated your master dark, don't tick "calibrate".

rob

[ribuck]

Many thanks rob, it all makes a bit more sense now.