Ritchey Chretien's and image curvature.

[pmrid]

I be grateful to hear of other people's experiences with the GSO RCs - particularly the 8". It's amazing how little information there seems to be on the architecture and optical design of the GSO scopes. There is a bit, but not a lot on RCs generally, and the RCOS site is certainly interesting but if you are looking (as I am) for specific info on how the GSO versions perform with a DSLR (as opposed to a large format CCD camera), then you'll be disappointed (or have to lean new skills in Googling the right keywords).
I'm reading that the GSOs have no coma but significant image curvature. I'm afraid I don't know what that means. It's part of what I'm trying to find out - I think.

Peter

[jase]

Hi Peter,
I have no experiences to share with regards to the GSO RC's. Everyone is quick to give an opinion, I'll refrain from doing so as it provides little value.

Now to coma and field curvature confusion. I would recommend some research courtesy of telescopes-optics.net;
COMA (http://www.telescope-optics.net/coma.htm)
FIELD CURVATURE (http://www.telescope-optics.net/curvature.htm)

You can obtain more information on optics from their site;
http://www.telescope-optics.net/

Cheers

[gregbradley]

Hi Peter,

I wouldn't worry about the curavture in the GSO RC. Judging by Paul's images it simply is not an issue. Any RC has curvature. I had a 12.5 inch RCOS and it had curvature and you can buy a special field flattener for it for US$1500. Is it worth it? No. But there is some minor improvement mainly to the star sizes off axis.

Greg.

[Satchmo]

If someone can give me an approx. figure for backfocus ( primary to focal plane) and the seperation from primary to secondary, I can reverse engioneer the design and post some raytrace spot diagrams without a field flattener.

[pmrid]

Hi Mark. I just took delivery of a GSO RC 8" today. If you can sketch out a rough graphic of the measurements you need, I'll certainly send them down.
Jase and Greg: Thanks for your input.

Peter

[Tandum]

Pete,
I found a page on Proper Positioning of a Focal Reducer
on a Ritchey-Chrétien Cassegrain Telescope (http://www.rc-astro.com/resources/reducer.html)which may come in handy.
Get the calculator out :)

[Geoff45]

Nice site!