combining images from different days

[bcstein12]

I have several groups of DSLR images taken over 3 days.  All are at the same ISO and exposure but different temps.  I hae taken darks and bias in group according to the temp.  How do I comdine these images in preprocessing since the darks and bias need to be associated with a specifc group? THanks for ya'lls help

[Geoff]

 I would preprocess each group separately then combine the stacked masters. As far as I am aware, you can use one frame for registration of all the images, even if it doen't belong to the particular group you are processing.

[niteman1946]

What I do (the manual method):

1. Group your lights in temperature ranges.  Say one group at 40F, one at 50F and the last group at 60F.
2. Select darks to match these three temp ranges and create your three Master Darks (i.e. 40F, 50F, 60F).   (I treat bias and flats as temp insensitive).
3. Calibrate your light groups each using the matching temp darks.

Now that the three groups are calibrated with their darks (and flats and bias), you can treat all the calibrated lights the same.
4. Select an image you like and use it for reference (al la Geoff).  Star align all cal lights at once.
5. Integrate all aligned cal lights together.

Hope this helps.
Mark

[bcstein12]

thanks for the help

[jkmorse]

Mark,

One thing to watch out for is the stupid imaging trick I tried about a month ago.  I typically shoot over two nights, but my situation is eased  by using a temp controlled CCD.  But my "brilliant" plan that night was to shoot all reds, then blues, then greens.  When the inevitable happened and my focus slipped a bit on the second night I had greens that had a higher FWHM than my reds and blues, leaving me with a horrible green halo around all my stars.  Could only fix it by unsaturating all the stars, which is hardly the ideal. 

My hope is you are a lot smarter than me and realized as soon as you started reading this note that, as my wife says, you can't fix stupid, and would never do this yourself.  But people (or at least me) get crazy ideas standing outside in the dark all night and those kinds of "clever" ideas are routinely punished by the gods of astroimaging.

Best,

Jim

[bcstein12]

Well this is what I ended up with?  I don't know if its good or bad.  I was surprised to see that my images were so "far off" but the center seemed good. Looking at each individual image they did not seem that rotated.  I had the dithering set to 6.  Did this move the frame that much?  I then used the dynamic crop.  How does the background noise look?

[niteman1946]

Well this is what I ended up with?  I don't know if its good or bad.  I was surprised to see that my images were so "far off"

Well, 99.99% likelihood that your camera shifted during one of your sessions.  But I recently had an issue where only one sub caused a very similar look.  And it was in a session that otherwise aligned properly.  Don't remember how I found it, but once removed, all was fine.  You might try inspecting each sub individually.
Anyway, looks like you got good results.

Mark

[bcstein12]

Work in progress made it to the "real stretch"  Any comments?   I think I need to work on the stars next.  Any suggestions?  Thanks for everyones help!