Re: [ATM] Autocollimation Oil Test

["Jeff Baldwin" <bald@centurytel.net>]

If you attach the back of your mirror with silicon RTV or two-sided tape in 
an arrangement that is just like a 9-point flotation cell (or other number 
of contacts), then the telescope won't care if it is looking up or looking 
down.  The safety clips are a secondary system.  If the 2-sided tape fails, 
or the RTV fails, the mirror won't come crashing down into your face or oil 
or bust in a zillion pieces because the clips will catch it.  If you can 
hold an 8" wide cassegrain secondary mirror with RTV, then  you can hold a 
primary upside down with it as well.  RTV would be a pain in the butt to 
take on and off and on ... while testing, polishing, testing, ..., so 
2-sided tape could work.  The good stuff.

You can then do the autocollimation test right at the eyepiece location on 
the scope.  If you want to test your primary mirror alone, you can mount a 
digital camera, or a video camera, live-feed to a TV/VCR above the oil 
facing toward the zenith, place a ronchi grating with an LED on its back 
side in front of the lens of the camera, and do the primary alone (prime 
focus rather than newtonian focus, paraboloids only).  You may want to block 
the central area of the primary, the reflection of the led near the center 
will be 600 times brighter than the test information.
JBald

JBald

Jeff and Glenda Baldwin
Beaver WA
http://home.centurytel.net/bald



> Friends;
> I've tried to follow this thread from the start. Please pardon my
> confusion, I gather you set your telescope, ( or mirror test stand)
> with the mirror under test nearest your roof, supported by its retaining
> clips, pointed down vertically towards a pool of oil. (The telescope is
> inverted) You then test from the position where your eyepiece would
> normally be placed? I don't understand how is the mirror supported.
> Thanks to all for any clarification.
> Jeff Rowe


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