Re: 12.5" RC or RCA?

Todd Klaus

Thanks Jim, I'll check it out!

--- In ap-gto@..., Jim Ehlers <equinerider@...> wrote:

Hi Todd,

I have a group called classicalcassegrain on Yahoo. We talk about
all the designs: RC,DK,CC.

You may want to ask there too?



tklaus <toddklaus@...> wrote:

There's no Ritchey-Chretien group that I could find, so I thought I
would post this question here since many AP owners also have RCs (I
have an AP900).

I'm trying to decide between the RCOS 12.5" (f/9) and her less
expensive sister, the new RCOS 12" Astrograph (f/6.6).

I like the fact that the RC has 16.8% more clear aperture (smaller
central obstruction) and that there's more back focus, but the RCA is
attractive because of the lower cost and the fact that it's a native
f/6.6 (which with my ST-10XME, would give me a image scale of
0.68"/pix). The main problem with the RCA is that with the 6.5" back
focus, there's not enough room for a PIR *and* and AO-7 (I don't have
an AO-7 at the moment, but it would be nice to keep the option open).

Of course, the RC has the Astro-Sitall zero-expansion mirrors vs. the
Pyrex in the RCA, but I wonder if that would make much practical
difference under my coastal San Jose, CA skies (FWHM averages around
3, with good nights dropping to around the low 2's).

Any thoughts, comments, speculations, etc. welcome!


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