Came across a curious thing today.
Here's a picture of the GSO coma corrector sold at Andrew's:
http://www.andrewscom.com.au/images/...acorrector.jpg
Here's the product description:
COMA CORRECTOR (CO-001) just arrived! Proven ideal for 8", 10" and 12" Newtonians. Coma corrects SCTs well and improves their field of view, too! Customers report very impressive results. Notably improves visual performance of GSO RC telescopes, too. Not for refractors.
The idea that a Newtonian field corrector will improve an otherwise aplanatic optical system such as an RC seems a bit suspect to me. It has been a while, but my experiments using ray tracing software trying to find a two mirror cassegrain (DK or RC) that would benefit from an off the shelf coma corrector left me with the conclusion that it was a complete waste of time. I'd be curious to know the basis of the claim in the product info.
Also, it appears that the GSO coma corrector on Andrew's web site is not the same as the one everyone else is selling (pictured below) you can tell by the length of the lens housing.
http://www.opticstar.com/images/astr...or-594x235.jpg
Incidentally, the corrector is made from 4 lenses in two groups. The slight magnification (1.1x) suggests to me that this could be a derivative of the paracorr which has the same lens groupings. There is certainly enough optical degrees of freedom in that configuration to make a superb corrector, with any luck GSO might have come up with a winner.
fwiw) This is not a paracorr clone, the magnification is slightly different as is the back focal distance, which is slightly longer.