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By the way, how do you deal with a large number of subs, say luminance with something like 40 subs? Would you stack them all in one go? And, do you ever combine differing sub exposures? I did in this case and just let CCDStack put in a weighting factor.[/QUOTE]
In the case of my Proline 16803 the files are 32mb each so I tend to process in batches of 10 subs. My computer would not handle 40 subs.
I then stack the resulting combines of 10 files each to make a final master.
As far as differing lengths, firstly, I tend not to do that, but I probably have a few times. I made no allowance at all and simply added them into the combine. I suppose a weighting makes sense. For me that would usually be 10 and 15 minute subs. Now that I think about it I did them separately, all the 15minute subs into a master, all the 10 minute subs into a master. For one thing they would have used different dark masters for dark subtraction. I find though with the FLI cameras and the SX Trius dark subtraction is not that fussy except for when I am using the CDK17 in which case it seems to make a huge difference to the success of the flats for some reason I don't fully understand.
Generally with a large number of subs it makes sense to flick through them and watch star sizes, guiding, perhaps gradients, clouds, satellites, wind affected and weed out the lousy ones. Then combine after callibration,registration, normalising and data rejection.
A few lousy subs can worsen. 30 subs combined may make a nicer image than 40 combined with 10 poor subs.
Greg.
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