Re: [ATM] Nasmyth secondary mirror cell ?

[Don Anderson <donanderson@direcway.com>]

> 
> 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


Best I've heard of thanks.
Don
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