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Creating and processing data sub-sets


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Having cut my imaging 'teeth' with a DSLR, and been pleased with 5-10min subs, I now have an ASI1600MM-Cool. Still capturing 5min subs though. On a number of threads relating to these new CMOS cameras, their proud owners are capturing a great many very short subs. I'm reluctant to follow this trend at the moment, as many subs eats up storage space and takes an age to pre-process in one go.

So, just thinking out loud really...

Suppose I captured 1000 x 30sec subs. That would amount to over 30Gb of subs! Would it make sense to calibrate and stack them in sets of say 40 subs each, and then stack the resulting stacks? Is there a good reason to not do this?

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AFAIK, this large a number of subs is stacked by other than "standard" stacking software (e.g. DSS, PI). The astrophotographer who was one of the first to use and ASI camera for short exposures of DSOs is Emil Kraaikamp, the developer of AutoStakkert*. He uses this program to stack lots of short exposure subs. Note however that he used subexposures of only 1 second or so.

I'm not convinced that stacking 1000 30 sec exposures would give you much gain over, say 100 - 200. My guess is that you would see some decrease in noise, but probably nothing dramatic over stacking 100+ frames.

Stacking subframes in sets is possible, but the results may vary. Many stacking programs give subs a wieght, depending on characteristics such as noise or star "tightness" (fwhm). Also, you would use one sub as a reference for all sets. This will align all subs to this single reference.

*The idea itself is not new, shooting many short subs, and selecting only the best, is common practice in planetary AP. It's a way of taking seeing variations out of the mix. If you want to go this route, I suggest you have a look at AutoStakkert.

HTH

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Taking many hundreds of short subs only helps if you can subsequently analyse and then select just the best of them for stacking (it's called 'lucky' imaging - it being just lucky that a particularly good sub happened when the atmosphere was very still/transparent). Stacking ALL the hundreds of subs regardless of quality gets you nowhere (or rather, nowhere better than stacking the first 30 or so randomly selected).

ChrisH

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