RE: ATM 2nd post - first scope : ) 4.25" off axis sphere

["donovan" <donovan@bravoz.com>]

Thanks for the response. It makes sense, but I need clarification on one
thing. When you say "tilted, and off axis" what's the difference between
those two?

Donovan

> -----Original Message-----
> From: Sidor . Kurt [mailto:KSidor@drc.com]
> Sent: Thursday, July 12, 2001 6:44 AM
> To: donovan
> Cc: 'atm@shore.net'
> Subject: ATM 2nd post - first scope : ) 4.25" off axis sphere
> 
> 
> Donovan,
> 
> If you use a 4.25" F #10 spherical mirror tilted, and off 
> axis, I do not
> think you will get very good performance.  If your 4.25" mirror was a
> cored-out off axis section of a larger parent mirror, the 
> full size mirror
> would have been say about a 10" diameter mirror of 10 times 
> 4.25" or about
> 43" focal length.  That would make the full size (on axis 
> mirror) a 10" F
> #4.3 mirror.  If this parent mirror were left spherical and 
> not parabolized
> it would have about 6 waves of surface deviation from the 
> ideal paraboloid.
> Your off axis portion would have about 5 waves of that error at least.
> Using your 4.25" F #10 mirror as an on-axis Newtonian your 
> mirror would only
> deviate from the ideal paraboloid by about a 1/5 of a wave (@510 nM).
> Despite the central obstruction this would produce a much 
> better performing
> instrument.
> 
> Good Luck!
> 
> Kurt Sidor
> Mechanical Engineer
> Dynamics Research Corp.
> Encoder Division
> 
>