Stacking the stacks

[Nyx]

This is a stack of 5 x 30 minute Live Stacks which gave a good result

https://www.astrobin.com/330099/

Dave

This looks good indeed. He did exactly what I want to try. He only stacked 5 love stacks which is a bit too few for sigma clipping, but still, not bad at all. I wonder if he used sigma clipping when creating the live stacks. In my opinion, one should live stack with the default stacking algorithm, if the intention is to use the live stacks in a traditional stacking program later on.

Thank you for the link Dave!

[celkins]

Stacking dark & flat corrected subs…

Example:

I have 1000 subs. I calibrate them using APP and save the calibrated subs. I take the first 20 subs (in chronological order) and stack them in APP using no outlier rejection. I repeat the same process 49 times more. I now load all 50 stacks as Lights and stack them again, this time using outlier rejection.

I am aware that stacking all 1000 subs in one go will produce a better image, but it will also take an astronomical amount of time to finish.

The time is relative, when you consider how long we wait between clear nights…

Taking that into account, how is creating 20-sub stacks in SharpCap using the same rules (dark/flat calibration and no outlier rejection) different than doing it in APP?

Given that neither Robin, nor Mabula publish their algorithms, then you’d have to ask them: suffice it to say that the perceived wisdom is to do all processing within a single package…

Now imagine shooting the same target over multiple nights using 15s subs. Stacking e.g. 20k subs is unrealistic, which is why the the idea of creating small 5-minute stacks in SharpCap crossed my mind in the first place.

I use an 11” F2 system, but I don’t use such short subs: I regularly collect hundreds of subs over several nights, and them do a processing run over the next few inevitably cloudy nights.

Clear skies,
Carl

[lowenthalm]

I do this exclusively. I use dark and flat field correction in sharpcap live stacking and get multi-minute images of between 5 and 7 minutes composed of several dozen images. I use Fitswork for stacking, but have also used DeepSkyStacker. You just feed your stacking tool "lights" and stack it. I used a color camera for my imaging. This is actually what confuses things the most in stacking programs from what I have seen.

Use the 32-bit (floating point) images that Sharpcap puts out, not the 16-bit. Your images will have a large dynamic range because bright stars won't saturate as often, so you will have more than 16 bits deep of data in your images, depending on how many images you stack. I have used both default and sigma clipping stacking successfully, but prefer to use sigma clipping. You can use sigma clipping again when stacking the live-stacks. No harm done, as bad pixels and satellite tracks will sometimes get past Sharpcap.

I have compared stacking individual subs saved from a live-stacking session in Sharpcap and stacking the live-stack 32 bit floating point images. The differences is pretty subtle to non-existant as far as I can tell.

Here is a recent image I did using this technique using 4 second exposures live stacked for 5 minutes :

https://astrob.in/lciy5l/0/

I do this pretty much exclusively to avoid the need for the complications of guiding and to beat the seeing without filling my hard disk up!