Re: ATM Alternatives to Newtonians

[Hugues_Laroche@ses-astra.com]

Andy wrote:
>IIRC  there was a 'folded' Gregorian shown in S+T that used a
>small diagonal mirror facing away from the Newt focuser, the focus was
>at at the first focus of the concave Greg tertiary which was mounted
>on the OTA opposite the focuser. The second focus was at the focuser
>with the converging beam passing around the secondary. I think it would
>be possible to have a Newt config as well by moving its sec and the focuser
>closer to the primary.

Search the archives for Johnsonian, Gene Cross (BTW, I tried to join him once,
did his email change, does somebody know?) talked about this design which is
about what you are describing. I made an attempt recently, but the extremely
fast
ellipsoidal secondary (f/1.5) revealed too hard to figure for me. Otherwise it
is a great design, where
one can hope coma-free field at for example f/5, with an obstruction in the 15%
approx.,
and this with reflections only, so no chromatic aberration else than from the
eyepiece,
and moderate outward field curvature. All this with a very compact OTA.

Hugues