Re: [ATM] Nasmyth secondary mirror cell ?

[Andy Saulietis <iss@pvtnetworks.net>]

>  an 8 in. secondary, and a 2+/- in.
>tertiary.  The secondary will be as optically flat as I can manage and will
>be perpendicular to the optical axis, thereby avoiding astigmatism.  I have
>thought of two designs for the secondary mirror cell.  I am not satisfied
>with either and am open to suggestions.  The designs are:
>1. full thicknes mirror glued to the cell with clips for safety.
>2. the mirror face sitting on three pads which are supported from the sides
>with a sling to support the mirror on the side.

My 16" f15.6 Nasmyth Cassegrain alt-az mounted scope has a
6" dia x 1" thick secondary. I mounted this in an open-back
threaded cell, like a refractor objective. The cell and retaining
ring were lined with thin cork, the mirror has a *slight* amount of play
in the cell. The cell was attached to the spider on a 3-point
bayonet mount, allowing it to be removed/replaced without losing
collimation. Overall dia was 6.4", the cell was made of aluminum.
The open back design allows faster thermal equalization of the
secondary.

The cell did not induce any astigmatism or distortion..the
sec mirror was null tested in the OTA using the above cell
design with the OA horizontal. Having the sec mirror quickly removable
and replaceable was invaluable during figuring as the scope stayed
collimated.


Andy Saulietis
ISS Enterprises
10 Milky Way
Mayhill NM 88339


World's first astronomy land development:

http://www.pvtnetworks.net/~iss/starend1.htm

11 of 17 lots sold to astronomers as of 4/08/04

505-687-3067 voice/fax, call voice or e-mail to set up
e-mail: iss@pvtnetworks.net

Also available: Custom large telescopes/mounts,
25 & 50 mm manual filter wheels, HDPE worm gears & clutches,
HDPE friction drives, CCD sliders & turrets, custom
telescope parts machining.



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