Guiding while stacking and the problems encountered

[yomamma]

I have a sequence set up so that I can get time on two objects every night and I run from about 10:30 or 11 PM til about 5 AM then shut it down. I autofocus every hour and pause live stacking and guiding while this is going on. Lately I have been imaging the Fireworks Galaxy until about 1:45 AM then moving to Andromeda until 5 AM. I have not had any problems with the first half of my run but I ran into a problem with the Andromeda imaging that I have experienced in the past with other sequence runs.

The problem occurs when after I slew to Andromeda, plate solve, and focus. The first image on the stack was not a good image as it had a bit of gradient throughout which was probably from my neighbors laser beam corner house light that comes on when the deer go by at night. Other wise I was only 2 or 3 days from the new moon and it was dark my bortle here is around 4-5 and the images that preceded Andromeda were good although from a much higher altitude which will affect things.

From what I can tell it looks like the sequencer uses the first image for alignment for all subsequent images and if it is not a good image then the entire stack will not save which is what I have had happen a couple of times(I shoot from my driveway in the neighborhood so lights come on and off a lot). Has anyone had any experience with this and did you find a solution? As a part of my hourly focus routine I could stop and restart stacking which should not be a big deal and would start give a new image for the master of the stack.

[admin]

Hi,

you are quite correct that the stacking treats the first image as the reference for the rest of the process, so if that image is bad then it may reject following good images. This is of course fine for the usual use of stacking in live imaging sessions, since you would just press 'reset' if the first image was bad. When you link in automation via the sequencer then a bit more caution is perhaps required.

One thing you could do is to put in a dummy step to either delay or take a single frame capture after the slew to allow time for whatever problem is happening to pass. If the problem is due to a light that may or may not be on then this will probably not help though. Other things to try are to use the FWHM filter in live stacking which might help if the bad frame has poor FWHM readings. Alternatively as you say, take a number of shorter stacks or perhaps save the raw frames from stacking to allow a reprocess later if the problem occurs.

cheers,

Robin

[yomamma]

Thanks for the response.

I started off with my sequence doing live stacking as I was there to watch it. I have just rewritten the sequence without stacking using still mode and I have been able to write a tighter script will test on the first clear night