From: "Tom Krajci" 
To: "'scottythefiddler'" ,
         
Reply-To: "Tom Krajci" 


From: scottythefiddler [mailto:scottythefiddler{at}cogeco.ca]

>Nine point secondary support is easy, Tom.

>Simply fasten (with RTV?) three 2" diameter flat washers to your
secondary
>cell, and fasten the mirror to the washers with three optimally placed
>blobs of RTV....

That sounds reasonable, and considering that my 16 inch mirror (1.5 inches
thick) does well with only six supports...a 9 point support should work
well with secondary mirrors larger than any amateur may ever make...unless
they win the lottery.

>...My guess, rather than using PLOP, which compensates for the changing
>thickness/load/strength of the primary mirror, it might be more
suitable to
>use the method described in the ATM series, where each point supports
equal
>weight.

Analysis by Richard Schwartz and David Lewis, and others, shows that the
'equal area' approach does not give optimum results.

>...This should give a close enough approximation to be suitable for
>the size of secondaries which concern us.

Yes, for the size of secondary mirrors most amateurs will ever use...9
point support, even if not optimized, should be adequate.

>BTW, with the 9 point support for my 10" mirror, (1-3/8" thick) I
suspended
>the triangles under the cell, rather than 'standing' them above the
cell,
>and it gives a stable 'wiffletree', and a lower profile to the cell....

Got any diagrams or pictures?

Tom Krajci
Tashkent, Uzbekistan


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