RE: ATM An $18.00 Null Test

["Bertapelle, Ken" <Bertapelle.Ken@tci.com>]

Dave, et. al.,

Another basic question, from the highly uninformed.  Can you summarize
the process one goes through in designing a null test?  What I mean is,
what tools are used, what is the sequence of steps, and what intermediary
results are developed?

For example, following up on my question of a couple days ago, I would
be most interested in a Ross null test used with a slitless Focault 
tester.  The critical parameters to such a test (I think) are: 1) the ROC
of the primary; 2) the size and shape of the plano-convex lens; 3) the 
placement of the lens; and 4) the placement of the knife edge.

#1 is known by simple measurement, and #4 varies around the primary ROC.
#2 and #3 seem to be the crux of the test design.

I gather that ray tracing is a set of techniques that can be used to 
answer nos. 2 & 3, although, at the moment I know very little about it.
(I'm currently downloading the free Oslo LT program, so maybe this
situation will soon improve.)  

Anyway, thanks in advance, and apologies too if this question is too 
similar to Mel's, "What's a telescope?", example.

- KenB

> -----Original Message-----
> From: Aplanatic@aol.com [mailto:Aplanatic@aol.com]
> Sent: Wednesday, July 28, 1999 10:21 AM
> To: atm@shore.net
> Subject: Re: ATM An $18.00 Null Test
> 
> 
> 
> Hello again.
> 
> <snip>
> Indeed, ray tracing IS magic in optical design and test as it 
> allows us to 
> easily devise tests that would be impractical to analyze on paper.
> 
> <snip>
> I have extensively analyzed several examples of this test on 
> my ray tracer, 
> including the 10" f/6 example given in my original post.  
> 
> <snip>
> Unfortunately, the only way to see the accuracy of this test 
> relative to the 
> Ross or Dall Null tests (at the RoC) in light of lens or placement 
> inaccuracies is to ray trace it for yourself.
> 
> Dave Rowe
> Torrance, CA
> Medium Format Astrophotography:
> http://members.aol.com/aplanatic/photos/astro.html
> 
> 
> 
>