Testing new TS Optics GPU Coma Corrector

[Startrek]

It’s taken me nearly 4 years to realise the Baader MPCC coma corrector has its limitations. I was never totally happy with Star shape in the corners of my field and over the past month or so tried to fiddle around with 0.2mm to 0.5mm spacers to try and resolve it ( never did )
The guys at Sidereal put me on to the TS Optics GPU 4 element 1.0x coma corrector which is ideal for f4 but also works well at f5 and f6 systems which I use.
Did some star testing on Monday night my new 10” f5 Carbon fibre Newt and found nice tight round Stars to edge of frame with 60 sec unguided subs. Quite pleasing
Also did some testing last night with my little 6” f6 GSO Newt and imaged M104 Sombrero Galaxy for a while with the new TS GPU coma corrector. Again really happy with Star shape across the whole field to the edges
The Baader MPCC Mk3 has been a workhorse for a long time but will now be retired

92% waning moon over head
Bortle 7/8
6” f6 Bintel GSO newt
EQ6-R pro mount
ZWOASI2600MC cooled to -10C , Ascom Gain 100 LRN
No filters , just internal UV/ IR cut
TS Optics GPU 4 element 1.0x coma corrector
62 x 90 sec dithered guided subs
40 x Flats
40 x Bias
PHD2 Multistar guiding (conditions deteriorated into the night 0.65 to 0.85 arc sec error total)
EQMOD,Stellarium, APT
Stacked in DSS
Processed in Startools V1.7 OSC linear data set
Obviously loads of noise gradient mainly due to moon glare and LP , tried to mitigate it as much as possible
Limited data on a dim object doesn’t help either. For a OSC and relatively short focal length under those conditions you really need 3 or 4 hours on a target like this , however my main objective was to test the coma corrector

Original frame
Crop version

Comments welcome
Thanks

[gregbradley]

Lovely round stars to the corners. Its a really nice result when you see a download come off the camera and just one sub looks terrific.
Star shapes play a big part in a good astro image.

Greg.

[Startrek]

Thanks Greg
Your certainly right
Tight round stars is what we all try to achieve and makes any image satisfying
Martin

[Ryderscope]

It very satisfying when thing just work. Part of what drives us in this hobby I guess. Particularly if it lands ok after a lot of hard work. You will be very pleased I’m sure.

[Startrek]

Yes , we have so many obstacles and hurdles to overcome with our equipment and procedures so finding a great piece of kit that’s works well is gratifying
The Baader MPCC Mk3 did a reasonable job for a longtime but it’s not until you try something new that’s been strongly recommended, that you realise what you’ve been missing.
Cheers
Martin

[Paul Haese]

That looks good Martin. I have been using GPU's for years. The MPCC is good for visual but does as you point out have its limitations for imaging, particular in the core of the image I found.

[Startrek]

Thanks Paul
Yes the GPU is a quality piece of gear and sits really snug and square in the focuser
I always had an issue with the Baader MPCC, it had so much play , definitely wasn’t a snug square fit into the focuser and only had a 22mm neck whereas the GPU has a 105mm long shaft with a 25mm long brass sleeve at the top to reduce slop and play and enable your thumbscrews to really bite and clamp tight.
Do you use the latest version 4 element 1.0 x

Cheers
Martin

[Camelopardalis]

Nice result, Martin :thumbsup:

Have the added the ability for the corrector to thread into the focuser yet? My older version doesn’t and can be hit and miss from a tilt point of view :sadeyes:

[Paul Haese]

The two versions I have are both 4 element versions. One I have had for about 4 years or so. Both units I use via screw threads too. I don't clamp the units into the focuser.

[pkinchington]

Hi Martin,
Excellent work getting the stars round what was the backfocus for your corrector?
Cheers Kanga

[Startrek]

Thanks
My 6” f6 newt was 55mm
My new 10” f5 Carbon fibre newt was 55mm ( I’m still building this scope but unguided 60 sec subs were excellent across the whole frame )
Haven’t tested my 8” f5 newt as it’s in my Dome on the South Coast NSW and I’ve been in Sydney for a few months , but probably 55mm too.

Prior to narrowing down the issue of Star shape in the off axis regions to the coma corrector, I did check and test for the following possible causes -
Polar alignment ( including image shift / rotation )
Primarily mirror pinched optics
Camera tilt
Guiding especially Dec backlash
Collimation
And so on ....

Cheers
Martin