Mega_Parsec

16 hours ago, rl said:

I've always got on well with the Skywatcher version of the TS GPU using an Orion Optics 8" f/4.5 Newtonian scope

https://www.harrisontelescopes.co.uk/acatalog/skywatcher-f4-aplanatic-super-coma-corrector-20231.html?gclid=Cj0KCQiAgqGrBhDtARIsAM5s0_mv-Uo3fQMBxxh8U9XWrb7BvWgo9VvMZGAworUmuHZ4WeMzutnGUQIaAimzEALw_wcB

There seem to be several versions of this CC by different manufacturers, all using the same Hungarian design. Frequent imitation might be a good recommendation in itself.  It fills an APS-C size sensor without much residual distortion in the corners, and I've always been pleased with the results. For me it worked better than the Baader MPCC mk2. You will also need the M48 to M42 adapter which is another 20 quid. Not sure how you would mate it to eyepieces; I use an old Paracorr for visual. If you are intending it for visual as well, your eyepieces need to have the other distortions reduced to a low enough level to see the coma in the first place; you need ones with good edge correction for both CA and astigmatism, and a flattish field. With your average Plossl or Erfle the view does get improved, but not by much considering the financial investment. I made this mistake.....

Some of the cheaper CCs do seem to work by re-introducing the spherical aberration taken out by the parabola. If you know you are going to be using a Newtonian long-term (i.e you don't mind the diffraction spikes) then it's probably worth investing in something above the bottom rung on the ladder. These generally have 3 or 4 elements. 

Thank you. 

I'm definitely sticking with my reflector... I've gone for the Skywatcher aplanatic. If I'm ever tempted by an f/4 imaging scope then it'll be good for that too 😊

Hi all, 

I'm struggling to decide on a coma corrector for my Skywatcher 200PDS.

I am still fairly early in my astrophotography journey (using an EOS 550D) and have the expected comet shaped stars outside the centre of images. 

Occasionally I also do visual observing so if possible I'd like to be able to use the CC for visual too. 

I've been looking at some options but when I google I seem to find significant negatives associated with each. 

For example, the Skywatcher 0.9x CC, I've read that it requires the focuser tube to be wound in so far as to take bite marks out of stars, and also that it doesn't do a fantastic job of eliminating coma across the whole image. 

Sky-Watcher 0.9x Coma Corrector | First Light Optics

Secondly I looked at the TS GPU 1.0x CC, which I understand would give a better corrected image (and I'd prefer to stay at 1000mm focal length) but I understand that this also impinges on the light path due to its length: 

TS 1.0x GPU Superflat 4-element 2" Coma Corrector | First Light Optics

Finally I have looked at the TS 0.95x CC, which I see has an advantage over the TS 1.0x in that it's shorter and doesn't impede into the light path, but I've read that it introduces some spherical(?) distortion meaning that you can either focus on stars in the centre of the image or the outside but not both.

TS .95x Maxfield Coma Corrector | First Light Optics

I'm wondering if anyone can share their own experiences with any CC with the Skywatcher (or another) f/5 reflector? 

I'm not necessarily expecting absolute perfection, but I need to avoid spending say £200 on a corrector and being disappointed enough that I later have to go out and buy an even more expensive one later. 

Many thanks.

4 minutes ago, ONIKKINEN said:

Looks great for a third shot, certainly much better than whatever i conjured up as my third shot.

In my personal opinion denoising has gone too far if the image looks denoised and often its better to leave the grain as is and just try to very slightly even it out. Before denoising i would recommend just a selective desaturation on the background to reduce colournoise. This usually goes a long way to make the image look less noisy and denoising might not even be necessary. Then maybe just a bit of denoising if needed, again selectively, just on the background by using some kind of layer masking with just the background selected. To even out the denoised background and untouched signal you could run denoising on the galaxies as well but with a much lower setting.

I find that Topaz goes too far in the low light mode even with denoising set to just 1 or 2, which is why i run it like that and then fade that with the original layer with a low percentage to get a smaller effect. Typically i find that more than 50% faded will look denoised in the end because the tool is so aggressive on astrophotos (designed for daytime use, where it works great).

Thanks for the detailed feedback, I will give this a try. I need to get to grips with layer masking but I can see how useful this will be 👍🏻

20 minutes ago, tomato said:

That’s a great M81/82 for a first go, much better than I achieved with more high end kit. I dare say your image was quite noisy if the moon was up and there was high cloud. Your application of a de-noise algorithm has smoothed the background but I think it’s blurred some of your galaxy detail.

The coma corrector will help in giving you sharper stars and detail in the galaxy, I think it is a sensible next step.👍

Thanks for the feedback tomato, I think you're right 👍🏻

Hi all, 

I'm fairly new to imaging (this is only my 3rd DSO capture, after M51 and M13) and I consider my kit to be at the budget end of the scale. 

That said I'm learning a lot from others posts and experiences which has helped me up the learning curve a lot. 

This was 31x90s with a Skywatcher 200PDS on an NEQ6 mount, Canon 550d, Altair 60mm guidescope/GPCAM2 mono guide cam, 50% moon and somewhat murky sky conditions (there was a large halo visible around the moon for a lot of the time). 

I took only 5 dark frames (it was very late on a school night) and no other calibration frames. 

Processed with DSS, Affinity Photo, Astro Flat pro, and a fairly gentle application of Topaz Denoise AI.

It took a few goes at processing to find a balanced image, I still have a lot to learn with respect to techniques such as star masking, use of layers etc. 

My next purchase will be a coma corrector, if anyone has experience with either the Skywatcher or the Baader corrector with this scope then I'd be very grateful to hear your experiences. 

Thanks for looking, 

Rick