"nick" wrote in message
ups.com...

It is possible to make a compact SCT corrected for spherical,
coma and astigmatism. For an f/8 system with f/2 primary, ~30%
minimum secondary and ~40% c.obstruction, it would require primary
conic of ~0.5 (oblate ellipsoid) and spherical or near-spherical
secondary. Corrector would be nearly twice stronger than in an
f/10, but the chromatism wouldn't change significantly, due to
lower secondary magnification.

But there is no basis whatsoever to call this design Ritchey-Chretien.
As Valery said, the RC has two hyperboloidal mirrors correcting for
spherical and coma. Any corrector that would significantly change this
configuration couldn't be called an RC. And two fast hyperbolical
mirrors with the rest of the package would definitely require higher
price, even for only decent optical quality. Still puzzled...

Vlad



What is the diference between the new meade scope compared to the vixen
VC200L?
It states an aspherical primary but I am not sure about the secondary. It
has a field flattener behind the mirror and no corrector plate.


Terry B
Moree
Australia