ASTAP Stacking Experience share
I have had very positive experience with ASTAP in terms of features and support from Han the developer, so given that ASTAP now features as a platesolve option in SGP, I thought I would share my use case for ASTAP as an image stacking tool, which is another of its key functions.
Context:
My astro setup is a galaxy imager with FOV approx 25 X 20 Arcmins, consisting of a Celestron C11 with a 0.8X reducer attached to an SBIG STT8300M with self guiding filter wheel. Approx FL = 2200 mm. Scale 0.5 Arcsec/ pix
Situation:
I had groups of 5 and 10 minute subs in LRGB of NGC3628 and 10 darks for each time. I did an initial visual inspection of the Blue subs using SGP and one of the ten was obviously bad, so discarded. Without going into too much detail, stats for the subs were ‘typical’ in my experience. I started to explore ASTAP initially because the stacker I normally used would not stack more than 3 out of 10 of the Blue group. It was better with the Red and Green but still not good. The help forum for that product was a bit dismissive of my data (without inspection), so I tried ASTAP, configured to use the G18 star database (mag down to 18).
Initial attempts to stack the Blue subs showed the same difficulty but after some discussions with Han in the support forum, we found the following ASTAP settings worked well and stacked 8 out of the nine blue subs.
In the Alignment tab select the following:
astrometric alignment
Star Database used G18 (G17 did not work as stars down to mag 18 were required)
Calibrate Prior to solving
Ignore stars less than 2.5
In the Stack Method Tab, I typed in Sigma factor 1.5 (not currently in the drop down, but you can type) and this got rid of satellite tracks in a few subs.
I left all other settings as their defaults.
Although I have not tried this yet, it is possible to load all your LRGB lights into the Images Tab and all your darks corresponding with those lights into the Darks Tab. Then in the bottom of the dialog, in the ‘Classify by’ select ‘Image filter’ and ‘dark exposure time’ and ASTAP will associate the correct darks with the lights.
Conclusion
I found using ASTAP as a stacking tool was straightforward and fast (14 seconds to stack 9 subs and darks on my machine) and support is very good. I was pleased with the stack results and an image formed from the RGB stacks was good.
ASTAP can be found here: