GSO 8" RC vs. GSO 10" RC

[Moon]

Does anyone know, from a theoretical point of view, the gain in performance the extra 2 inches will bring?

I'm especially interested in the off axis performance across a typical CCD chip.

[dpastern]

Well, 50% extra light gathering ability with the 10". I don't think either will be a real issue with a typical CCD chip, but I'd still recommend a flattener due to field curvature being part of the RC design, at least as far as I understand it.

Dave

[Moon]

I'm going to answer my own question here.

GSO currently have RC scopes with sizes 6", 8", 10" and soon there will be a 12" version and then a 16"

I wanted to know if these larger scopes would support a larger CCD sensor without a field flattener?

After much google searching, I believe the answer is no, they won't.
No matter how big the RC aperture gets, the diffraction limited area stays about the same - (about 14 to 18 mm in diameter)

This is the document that had the answer I was looking for: link (http://www.heavensgloryobservatory.com/stats/RCfieldflattenersFINAL.pdf)
Check out the last page.

With a field flattener the image circle size jumps to over 40mm.

James

[telecasterguru]

The flattener/reducer has not been made available for the 10" yet as I am waiting for them to be released to see how they actually affect the scope.

Frank

[Moon]

Another document on that site also confirms my practical experience: Correct collimation of an RC scope must include an analysis of off axis performance. Link (http://www.heavensgloryobservatory.com/stats/RCalignFINAL.pdf) (Read the last sentence in bold)

Correct collimation of an RC scope is not trivial. I know this is not the news many people want to hear, but it's true.

For anyone interested, this is how I do it these days. Link (http://deepspaceplace.com/gso8rc.php)
If anyone has figured out a better way, by all means, please share!

James