Beginner workflow - M51 and M27

[Padraic M]

New equipment acquired over the last week has finally allowed me to image with phd2 autoguiding and a cooled mono camera (asi1600mm Pro). Not yet an ideal setup, but long past the part where I get to blame my kit for poor outcomes!

Samples included below are LRGB for M51 and M27. For both, I shot 5x180sec subs in each of lrgb, and attempted to stack in DSS.

M51 was a disaster. I think poor focus has ruined the data, as DSS refuses to stack ANY of the channels. So, the jpg below is just 3 minutes each of lrgb, with darks, flats and biases applied. fyi, L is binned 1x1 and RGB each binned 2x2; I'm all over the place when it comes to stacking workflow and processing, given that L resolution is twice RGB, so how to align in DSS, and how to overlay layers in Gimp?

M27 fared better; focus still not great, but not as bad as above. DSS is happy to stack everything except the Green channel; it can't find more than 4 stars in the fits image. I've just manually aligned one  green sub - possibly needs to be scaled slightly too. Interestingly, the DSS-aligned layers didn't line up perfectly in Gimp. Why do DSS autosave.tifs have different resolutions?

Flats aren't working for either image, there's lots of vignetting which I've cropped. I think the material I'm using to cover the scope is too opaque. Will need more experimentation.

Setup for now is Celestron C8 with FR (FL 1300mm) on HEQ5 Pro; ASI1600MM Pro imaging; AA Starwave 50mm guidescope with ASI290MM Mini. phd2 was showing ~1.6" total error which is a lot for 1x1 imaging with that setup. 

Areas for immediate improvement:
- Focus (auto focuser on order)
- More binning or Longer subs required, to get more usable stars esp. in green channel?
- Bin L the same as RGB until I understand the alignment process more
- Sort out flats capture process

All other suggestions welcome, as long as it's not "quit while you're ahead, you're not cut out for this"!

Edited July 20, 2020 by Padraic M

[wimvb]

Nice start. It seems to me that you’re trying to do too much at once. For one, don’t bin rgb data when you use a cmos camera. Binning cmos data doesn’t give you the same advantage as with ccd, and it adds complexity. Focusing will be a lot easier if you use a Bahtinov mask. In dss use one and the same sub to align all others. That sub doesn’t have to be part of the stack.

good luck and have fun

[Padraic M]

Thanks @wimvb for the support. I see what you mean about binning - I'll leave that out on my next session. Will definitely make processing easier. Bahtinov mask also on order.

[Padraic M]

So, another great night imaging last night - CO said cloudy, but it was a night of superb Bortle 2 skies. Unfortunately I had to close up shop at 1:30 as it was a work night.

Trying to build on earlier attempts above - took onboard some great advice. Changes made:

- Great attention to focus, although still manual. The night was still and seeing was good which helped.
- All channels un-binned (1x1 on ASI1600MM)
- 4x300 subs on each channel giving 1hr 20 of data. Took one 300-sec dark, and reused flats and bias from earlier.

First attempts to stack (DSS) and process (Gimp) were disappointing. Images needed manual aligning, and the green channel was way too strong. Lessons learned which produced the image below include:

- For some reason applying both bias and dark frames blew out the green channel. Not the others. Applying either dark or bias on its own was fine. Flats worked fine in all cases.
- Stacking with 'Standard Mode' alignment means that the dimensions of the reference frame are used for all outputs (LRG and B autosave.tifs). I had used 'Intersect Mode' previously, which meant that each output file had slightly different dimensions. Hence the manual alignment.
- All loaded into Gimp perfectly, with the same dimensions, and fully aligned. I masked off the DSO itself, and applied auto-levels to the background. Colours are slightly funky but I think much better than I could do manually at the mo.

Overall, I think this is a much better attempt than the ones above. I think the optical setup is mis-matched (C8 & 1600mm / Starwave 50mm & 290mm), so the next night out I will bin the frames 2x2 or even 3x3 to give a better pixel ratio for guiding. My phd2 guiding was at ~1.7"/px, and the main imaging pixel scale is ~0.5"/px so hence big fat stars.

Comments?