[ATM] Effects of a too small secondary

["Steve Chambers" <Steve@pmdo.com>]

Hello,

Its been several years since I last posted here while building a series
of Newtonians.  Now I have some ideas for another scope.

My plan is to use a 19"dia 100" FL mirror in a Dob type scope.  However
as the eyepiece can get a little inaccessible I had the idea of using a
large secondary (6" minor axis) 69" from the primary.  Then it gets a
bit strange.  I plan to mount the tube from a 4" f5 refractor complete
with focuser on the secondary in place of the normal Dob type focuser.
Finally its finished off with a diagonal and a may be a bino viewer.

I think this would give a dob that’s fun to use without steps.

The problem I am having is finding a 6" secondary that not too expensive
and ideally that I can get in a couple of months so the scope could be
ready for Autumn star parties.

So the question is.  What would happen if I used a 4" flat that I
already have?  The design is far from optimised anyway and would most
likely be used with mid range 30mm 1.25 inch eyepieces in an inexpensive
binoviwer.  

Would the scope loose a lot of light making it perform as a much smaller
mirror?

Regards

Steve

-- 
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.394 / Virus Database: 268.9.2/370 - Release Date:
20/06/2006
 

_______________________________________________
ATM mailing list http://www.atmlist.net/