M8 in LRGB

[barx1963 (Malcolm)]

This is my first attempt at an LRGB image. M8 (the Lagoon nebula) in Sagittarius. Done with the following gear:
Stellarvue SVR102T with 0.8 reducer flattener at f5.6
Atik One 6.0 camera with Astronomik LRGB filter set
Orion AZ/EQ G mount
Guided with Orion ST80 and Orion SSAG pro guide camera
Guided with PHD2 and image aquisition by Atik Artemis

Subs consisted of 9 x 120s each of LRGB
Darks applied, no flats or bias frames, stacked in DSS and final image put together in PS CC2015.

I obtained most of my processing idea for doing the LRGB process here https://www.youtube.com/watch?v=b9ePip4rdsI and then applied much of what I learnt at the last Snake valley camp from John Glossops excellent processing workshop he conducted there.

I have done two images first one I haven't been as aggresive with some stretching with the final combined image, the second one i went a bit nuts.

Main issue that I see with the image is that the brighter stars do have a bit of a blue halo. My focusing is purely manual and I certainly noticed that the subs that came out of the blue filter definitely had more bloated stars, so that may be the reason. This is particularly obvious with the bright stars in NGC6530. Being an open cluster one would expect them to be a bit blue anyway.

Anyway, I am pretty happy with the result so far with this new setup!!

Malcolm

[Atmos (Colin)]

Is that scope a doublet or a triplet? Also, are you refocusing between each filter?

It is a nice start It looks like you have picked up some somewhat faint stuff there which is good.

[barx1963 (Malcolm)]

It's a triplet. I confess (newbie imager that I am) that I didn't refocus, I am still working out all the "workflow" issues that I have to do to get the best image I can.
I do have a fully motorised focuser system o its way which should make the process of refocusing a little easier.

Malcolm

[Atmos (Colin)]

That there is your problem ⎌Even in the vast majority of triplets you need to check the focus between filters. In both of my imaging refractors LRG have been virtually spot on but B has always been a little off. Ha, OIII and SII have all been a bit different as well. Sometimes less than local seeking (on a poor night) but noticeable on a good one.

[barx1963 (Malcolm)]

I figured as much as soon as I saw the blue halos. Live and learn I guess!!

Malcolm

[Atmos (Colin)]

Indeed You're best refocusing each filter anyway so that you can also combat focus shift due to temperature change. My previous refractor seemed far more temperature sensitive than my new one. Different design.

[barx1963 (Malcolm)]

Thanks Colin
One issue that cropped up in processing was that I understood with LRGB the colour frames can be done with binning to increase sensitivity. So I did the Lum frames at 1x1 and the colour at 2x2.
When I came to combine in PS obviously the two were not matching. I assume I am better off resizing the RGB frame (in this case just one as I had made a single RGB image before adding in the Lum) to make it bigger?

Am I correct?

Malcolm

[Atmos (Colin)]

Yep, you want to change the resolution of the RGB to that of the luminance. I have personally never tried doing 2x2 binning in RGB, do need to test it one day