Re: [ATM] Focal Length Accuracy

["Anthony Anconetani" <Anthony.Anconetani@genband.com>]

Good morning Jim,

Hehehe.. You know, someday hope to actually understand what you've said
let alone try to figure to that accuracy.

Thanks for your insight.

-Anthony

> -----Original Message-----
> From: Jim Burrows [mailto:burrjaw@earthlink.net] 
> Sent: Wednesday, May 23, 2007 6:59 PM
> To: Anthony Anconetani
> Subject: RE: [ATM] Focal Length Accuracy
> 
> At 2007-05-23 09:13 -0500, you wrote:
> 
> >You have asked why I want the focal length to be as close to 
> 36 inches 
> >as possible.
> >
> >No particular reason really. Just practice. 8-)
> 
> Anthony,
> 
> It's incredibly difficult to figure to a "double goal" - R (radius of
> curvature) and b (conic constant, -1 for a parabola).  I 
> won't say how long I've been fiddling with an RC cass 
> secondary to match a finished primary.  The goal is R = 
> 674.634 mm and b = -4.764.  At the moment I'm typing this, 
> the wavefront RMS is 581 nm, and the smallest so far is ~ 250 
> nm; the goal for that is < 40 nm <sob>.  Another forcing 
> function in this case is a finished OTA as well as the 
> primary, which forces me to a back focus of close to 300 mm, 
> so actually that's a triple goal - avoid if possible.
> 
> Anyway, I'd suggest that figuring a good parabola of a 
> reasonable focal length is practice enough.
> 
> Regards,
> 
> Jim Burrows 
> 
> 
> 
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