ATM Alternatives to Newtonians

[Rod Brackenridge <rjb@netconnect.com.au>]

lifedata@vol.com wrote:

> Does anybody make Gregorians any more?
>

Jim,

I don't hear of many people making them.  A Gregorian secondary with a
5x amplification is normally the same diameter as  a cassegrain
secondary with 3x amplification.  The final instrument is physically
longer and the final effective focal ratio is usually very long compared

with a cassegrain.

The secondary is a concave ellipse and therefore relatively easy to make

and test but that seems to be the only advantage.

Regards,

Rod Brackenridge
Daylesford
AUSTRALIA