Can anyone help me choose a coma corrector for the Skywatcher 200PDS?

[Mega_Parsec]

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.

 

[rl]

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. 

[Stefan73]

13 hours ago, Mega_Parsec said:

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

It's possible it would as I've never used it with a 200PDS but it doesn't with my 130PDS.  It moves the focus position outwards by about 20mm so there less of the tube impinging on the light path.  I've been very happy with it.

[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 😊