Re: [ATM] Secondary Cage Sizing?

["Richard Schwartz" <richas@earthlink.net>]

75% illumination is very BAD if you are doing photometry by brightness
comparison.   Variable star observers do visual observations to 0.1
magnitude.   That is a 9% brightness difference.   So your toleration of
75% illumination is about 0.25 magnitude... and errors like that would make
you the laughting stock of the AAVSO.

. . . Richard


> [Original Message]
> From: Michael Lindner <mikell@optonline.net>
> To: MATTHEW SIMMONS <msimmonsmcse@msn.com>; <atm@atmlist.net>
> Date: 4/19/2004 8:42:35 AM
> Subject: Re: [ATM] Secondary Cage Sizing?
>
> On Saturday 17 April 2004 11:49 pm, MATTHEW SIMMONS wrote:
> > So I have a design conundrum here....My specs are as follows:
> >
> > 13.1" f4.5
> > 2.6" (?)
> > .25" focuser board
> > 1.55" Moonlite Crayford +.25" racked out
>
> Read the newt documentation. Vignetting the 75% ray is GOOD, not bad. It
means 
> the edge of your field is more than 75% illuminated. A couple of other 
> things. If this is a Coulter optical set, the diagonal is probably 3" not 
> 2.6" (at least the few I've measured were all 3"), and the moonlite
crayford 
> is a 2" focuser (I don't think they ever made a 1.25" crayford).
>
> IMHO anything from 13 to 15" diameter will wind up producing a fine
scope. The 
> vignetting will be negligible at the eyepiece.  Worry less, build and
observe 
> more!
>
> Clear skies.
> -- 
> Michael Lindner
> http://www.starastronomy.org *** http://home.att.net/~mikel
> http://www.atmsite.org *** http://www.atmlist.net
>
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