Re: [ATM] newt and 75% ray

[Gary Seronik <gseronik@netway.com>]

Dan Delzell wrote:

> I've used newt to plot it, and it says that I have vignetting of the 75% ray
> at the focuser with 1.25" eye pieces. It looks significant in the focuser
> view.  
> 
>  
> 
> Is this something I should worry about? And how can I change my design to
> fix this problem?

No, it's not a problem -- except with the Newt software.  Although it is
faithfully reporting what is going on, the "75% ray" problem is nothing
but confusion.  Put it this way:  If you had a huge 100% illuminated
field because of a really big secondary, you'd still get vignetting of
the 75% ray.  Conversely, if you had a really tiny secondary that gave a
microscopic 100% field, you would *not* have vignetting of the 75% ray.
  So which is better?

There are better pieces of software for analyzing the illumination
profile of the focal plane -- Mel Bartels has one and there's an
excellent one available for free download at www.SkyandTelescope.com
too.  I urge you to check out one of those so that you understand what
is really going on.

Regards,
Gary Seronik


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