Just to clarify: Stack the stacked files and calibrate that?

Discussions of Electronically Assisted Astronomy using the Live Stacking feature.
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couchcaptain
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Joined: Tue Mar 30, 2021 2:20 am

Just to clarify: Stack the stacked files and calibrate that?

#1

Post by couchcaptain »

Hello everyone!
I got a question that I've been wondering regarding live stacking.

On the bottom, we have the option of "save/clear at every ____ minutes (pick whatever limit of minutes).

So assume of instead of letting it run without checking this and keep stacking even like up to an hour, I pick "save and clear at ever 5 minutes".

So assume I saved them as .fits - so I'm producing some number of 5 minute stacked files.

Would this be an ideal to later stack those 5 minute exposures together with a stacking software or even with Sharpcap's folder option stacking?
Let's say I have 10 of those, so stack the 10x 5 minutes?

Or let's say I did live stacking , but I didn't use any calibration files, like a master dark or flat.

Let's assume I made a 60 second master dark file (same gain/offset as my live stacking lights) ,
Also assume I live-stacked 5 minutes, made out of 60 second subframes.
Should I be using the 60 second master dark for that, or should I create a 5 minute -long master dark?

I mean this is probably like a captain-obvious question for many, but I just wanted to be sure.
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Re: Just to clarify: Stack the stacked files and calibrate that?

#2

Post by admin »

Hi,

the answer is that you should not use calibration files if you are planning to stack those live stacked images - the results will be horrible.

The reason is that as part of live stacking, each new frame is aligned with the previous ones on the stack - this may involve moving the frame or rotating it slightly to get alignment. So, when you save the stack after 5 minutes, the data that makes up the pixel at X=20, Y=30 didn't all come from that particular pixel on the camera - it came from a range of pixels, depending on how much the image drifted/rotated.

If you try to apply darks of flats after live stacking then the results won't be right because the darks/flats require pixel-for-pixel alignment with the light image to work properly.

The result of all this is that if you are planning to stack the live stack results you need to use the dark/flat correction options in SharpCap.

The other option is to save the RAW frames during the stack and then stack all of those afterwards, in which case you would use darks/flats when stacking.

cheers,

Robin
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