Re: 12.5" RC or RCA?


Aug 19, 2007

 


----------------------------

#18997 Aug 19, 2007

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!



Thanks,

Todd



----------------------------

#18998 Aug 19, 2007

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?



Regards,



Jim



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!



Thanks,

Todd













[Non-text portions of this message have been removed]



----------------------------

#19006 Aug 20, 2007

Thanks Jim, I'll check it out!



--- In ap-gto@yahoogroups.com, 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?

>

> Regards,

>

> Jim

>

> 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!

>

> Thanks,

> Todd

>

>

>

>

>

>

> [Non-text portions of this message have been removed]

>


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