Re: [ATM] Vignetting at focuser/Crayford protrusion

[Gary Seronik <gseronik@netway.com>]

Hi Jay:

At 09:15 AM 6/2/2004 -0600, Jay Kirkland wrote:
>
>But tho I'm committed (the focuser will probably be mostly finished by the
>time you read this), I'm still wondering: am I interpreting my drawing and
>NEWT correctly? Does vignetting of the 75% ray in fact mean that all the
>light gathered by large  primaries with typical Obsession-style (close to
>the secondary) focuser placement is not reaching the eyepiece? 

Sigh.  Another victim of the 75% ray.  Newt is a terrific program, but it's
not the best for figuring out the size of your secondary mirror -- Alan
Adler's program "Sec" (available at SkyandTelescope.com for free) or Mel's
program are vastly better.  Don't worry about the 75% ray -- if you were
vignetting the 100% ray you'd have a problem, but not with the 75% ray.

Gary

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