For a variety of reasons during my recent visit to Wiruna I took my 10" F4.5 "Outreach" dob kit instead of the 16" with all the accessories. I was extremely lucky and had two clear nights. These two "all nighters" allowed me to have a good look at the GSO coma corrector. I didn't have my Paracor with me so was not able to directly compare the two units.
The scope is built around an old Meade 10" F4.5 primary that appears to have quite a good polish and figure although the coating is getting a little thin and should be redone. The secondary is a 2.6" Protostar - unheated. The finders and eyepieces are all heated. This lack of secondary heat caused me grief with a sudden ending to the first nights observing @ 0430 by suddenly dewing after a night of very heavy dew. The filter slide (also unheated) had given in to condensation at around midnight. The second night was essentially dew free
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The eyepiece set for this scope comproses a 30mm Vixen NLVW and 16mm, 7mm and 4mm UWAN eyepieces. F4.5 is a challenge for any eyepiece and the UWAN's certainly handle it better than the NLVW. Comparing the image on various types of objects with and without the GSO CC in place it was clear the GSO CC made a pretty good attempt at minimising the visible coma. I did not make any attempt to fine tune the images by moving the eyepiece with respect to the CC. Instead I just inserted the EP's to the shoulder and used them as is. This is how I set them up during outreach sessions.
Prior to leaving home I had moved the primary mirror cell 15mm closer to the secondary to allow for the GSO CC infocus requirements.
The 7mm and 4mm UWANs became essentially sharp almost to the edge with the GSO CC in place although the seeing never allowed the 4mm to show its true capability. The 16mm cleaned up nicely but the remaining field curvature meant the outer 1/4 of the field was not as sharp as it could be. OK for general use though. The NLVW was also cleaned up by the GSO CC however some residual coma and astigmatism was still visible in the outer 1/4 of the field.
Frome previous experience with this scope kit and the Paracor I would say the only difference I have noted is the 30mm NLVW shows a slighty better image with the Paracor as opposed to the GSO CC. The 3 WO eyepieces appear to perform the same with either CC.
While I didn't accurately measure it the GSO CC appeared to give an apparent increase in focal length of about 10% based on estimated FoV reduction.
Would I buy the GSO CC again? Sure would as it works just fine for me for the intended task.
Cheers,