M13 Great Star Cluster Hercules, LRGB

[Padraic M]

Last night was my first night out with a new rig, using a C8 SCT and an OAG. Also my first attempt at a globular cluster although I've admired them through binocs many times. Where better to start, especially at this time of year, than M13 in Hercules?

10x 150s each of B,G,R. 1hr 15min total, Bortle 2.
Luminance created from all channels.

Celestron C8 with 0.63x FF/FR on a HEQ5 Pro - 1350mm FL. Celestron SCT focus motor with NINA autofocus for each filter.
Imaging: ASI160MM Pro @ 20c. Baader RGB filters.
Guiding: OVL OAG, ASI290MM Mini.
Software: NINA, PHD2, SharpCap PA. AstroPixelProcessor, Gimp.
30x darks, flats, dark flats.

CC greatly appreciated. There's definitely something kinky in my green flats, as they're not calibrating out that great big donut. Also, stars are a bit clunky, and the shapes in the corners are a bit beany. Is this what can be expected from a C8 with FF? Or do I need to collimate?

[Padraic M]

Update: I captured a new set of flats for all filters, and reprocessed as RGB only, which I think is a big improvement.

 

[AstroAndy]

Hi Padraic

The second one is a winner, if i hadn't seen the first one, I might not even have been aware of the dust bunny on the lower left. It's more defined (better resolved). Maybe I would have done a soft noise reduction on the dark areas in the image, but all in all a cracker the way it is, color is there, and not overdone, and the little blue stars are resolved nicely.

I was hoping to do some work on this myself with the big boi (C11, 0.7 reducer, EQ8), let's see how this goes, what with work, and having to travel to a dark site with the big rig and no astro-darkness. I guess this is the time of the short sub.

Andy

[Padraic M]

Thanks @AstroAndy. I did a touch of unsharp mask on the final result in Gimp that made a big difference. I considered noise removal (I use Noise Ninja) but it tends to soften the stars so I decided to leave it as is. I might experiment with masking the cluster and denoising around it.

Good luck with the C11. It's such a fuss moving these big beasts!

[newbie alert]

Very nice Padraic M.. this is my next target with my sct, so more or less the same rig.. the first pic is great, the second one pretty awesome.. and yes is agree that you need to collimate,  I've been using a tri mask.. really good for collimation.. keep thinking of getting a Duncan mask to try out

Btw, APT says I'm at 1306mm with the .63 reducer and my focal length reduced once I was properly collimated

Edited May 31, 2021 by newbie alert
Added info

[newbie alert]

[Padraic M]

@newbie alert thanks for that. Bob's knobs are on the way  🙂  this will be a new skill for me!

Focal length is reported from ASTAP and from astrometry as 1363, not quite what I would expect with 2032mm @ 0.63 reduction. I think my working distance may be a bit long. There are some suitable spacers in the same package as Bob's knobs.

Good luck with your own attempts. Very impressed with your mount - the CEM60 has a very loyal following!

 

[newbie alert]

I didn't go Bob's knobs myself, instead I got some hexbolts with the same thread pitch,  they're slightly longer than the original ones and you can get some really fine adjustment with a Allen key

The cem60 has been superb, not missed a beat so far