Today I tried to process my Narrowband data of the Elephant Trunk nebula from the last 2 nights and found 2 issues.
The first one is that dithering in RA only completely ruined my 3 hours worth of data because of diagonal banding across the whole image and I have no idea how to get rid of it (I might have to mix a lot more data with dithering in DEC as well to cover up the mistake but that will take some time).
The second issue is that I think even after stacking 3 hours worth of good frames (after using SubframeSelctor) I noticed that there is still a lot of noise in the stacked image. When I check other peoples images on astrobin using the same camera and with mostly the same gain and offset settings, their Ha narrowband images looks much more sharp and with "more dynamic range?" (dark nebulas are dark and not littered with grey pixels).
The best way to explain what I'm talking about is to post some examples:
TS Photoline 560/80 x0.8
ASI 1600MM Pro unity gain -15C
300'' subs with 12nm Ha Astronomik 2'' filter
This is the stacked 3,5h of data. Notice the diagonal banding shaped like "/"
This is the 1,2h stacked with dithering in RA and DEC. Notice there is 0 banding issue
This is the 2.3h stacked with RA only dithering. You can see that there is lots of diagonal banding
EDIT: I just realized that the banding direction is on the RA axis because I didn't dithered in DEC the banding just stacked as signal. Makes sense now.
side by side comparison
So the banding was easy to fix by enabling dithering in DEC even with high backlash but it worked well on the last session.
The main concern is the low SNR in the stacked image. I tried stacking without flats nor darks and the final image is pretty much identical.
I considered that maybe the 12nm Ha is not narrow enough and the full moon sneaks into my light frames and reducing SNR?
Or maybe I'm just stacking it wrong. I'm following these steps found here:
I'm pretty much a newbie as far as mono cameras goes and their settings so maybe you can give me advice to improve.
Edited by BoskoSLO, 17 July 2019 - 11:09 AM.