Stacking multiple sessions in DSS

[Swillis]

Hi,

I have a couple of nights of data from a dslr which I plan to stack in DSS.  From what I understand I need to put my flats and bias frames in the main group and each nights light and darks into their own group?  That way the flats and bias get applied to each group but the correct darks are associated with the correct night lights?

Thanks in advance

[almcl]

Not quite. 

The Bias should go in the main group as they don't change, but the flats may very well be different, particularly if any dust has moved around, so you should take flats for each session and group them with the lights.

You don't say what camera you are using, is it cooled?  Are all the darks at the same temperature and gain or ISO?  If they are, then they shouldn't vary much between nights and many re-use a 'dark library' for several months at a time.  If the camera is an uncooled DSLR howeever, you may find that the darks do more harm than good and may not be at the same temperature as your lights, although experiences and individuals vary quite a bit on this.

[Swillis]

Hi,

I'm using a DSLR, Canon 350d with a 75-300mm lens. Quite a basic setup. 

I don't have flats from each session. I'm assuming a set of flats covering all sessions would be better than none?

The darks were taken straight after the lights. But I had read recently about differing views on of they should be used for DSLRs. I then read in another thread this evening that Canon DSLRs don't need them as they have internal dark calibration. Not sure if that's the case with the 350d or just more modern ones!

[happy-kat]

There are quite a few recent threads on darks and bias, I find with my canon flats are a must, darks and bias add more noise and I usually use dark flats but am just trying using a master bias instead for the dark flat file in DSS.

https://stargazerslounge.com/topic/388605-dark-frames-will-this-work

[The Lazy Astronomer]

1 hour ago, Swillis said:

I don't have flats from each session. I'm assuming a set of flats covering all sessions would be better than none?

This holds true so long as you kept the camera and lens connected between nights.

Flats map the illumination of the sensor as well as any shadows from dust particles so the lights can be corrected during calibration. If you've disconnected and remounted  the lens (or significantly changed the focus), it's likely that the 'map' of the flats won't match the lights and it can lead to more issues than it resolves.

That said, it can't hurt to try anyway - you might get lucky! 

[Swillis]

@happy-kat thanks, I had been reading that thread. Very interesting. 

@The Lazy Astronomer it was all left connected and the focal length was taped down throughout so hopefully it hasn't shifted.  I'll give it a go and see what I get 🤞

Thanks