Keep Darks' Bias' a Flat frames

[Taff]

Hi' What i like to know with Darks' Bias' and Flat frames after your captures of the night sky.Can you save them to use again, or do you have to take fresh captures' Thanks.Mark

[tooth_dr]

No expert here Mark but:

1) Bias you can reuse

2) Flats can only be reused if you don’t touch the camera or scope and leave everything in the same position between sessions

3) Darks are temp dependent so depending on what camera you use ie if can you control the temp then you can save a library and reuse them. If a DSLR then you would need to take them that night, but even then darks aren’t always used.

[ollypenrice]

10 hours ago, tooth_dr said:

No expert here Mark but:

1) Bias you can reuse

2) Flats can only be reused if you don’t touch the camera or scope and leave everything in the same position between sessions

3) Darks are temp dependent so depending on what camera you use ie if can you control the temp then you can save a library and reuse them. If a DSLR then you would need to take them that night, but even then darks aren’t always used.

I agree but would add that the value of darks from non set-point cooled cameras is questionable, with many users preferring to use a master bias as a dark combined with dithered guiding at capture. In our observatories flats may last months before some new bit of dust appears.

Olly

[Ouroboros]

To a first order approximation is it really necessary to take flats every time? I do but have never noticed any obvious difference between them despite being taken at different camera orientations. As long as the centre of the chip lies on the focal axis of the telescope, I would have thought the vignetting was uniformly symmetric around that axis. 

PS I was forgetting about particles of dust which of course might change between runs - particularly if like me you have the camera on and off the telescope between sessions.