[Raytrace] A real world application

[Michael Peck]

At 18:10 12/28/2001 -0500, Peter Chen wrote:
>outside the scope.   Two examples:
>    a.  I understand that some ATMs are making 40" and 72" 
> scopes.   Definitely not main stream either.

Lord Rosse - who was basically just a well-heeled amateur astronomer - made 
a 72" telescope that he finished in 1845. It took him a lot less time than 
the group that's currently trying to make one too. Some things never 
change, and I expect 160 years from now amateurs with incurable cases of 
aperture fever will still be trying to make meter+ newtonian telescopes.

>(or frighten away) a large part of the audience.   However, you yourself 
>and Peter Smith and others on this list are experts on the subject -- and 
>doing it for fun!   I rest my case.   -:) smile.

Peter may be an expert, but I'm sure not! What I've got is a modicum of 
curiosity, a modest library of books (*), and a piece of free software 
that's reasonably competent & has a shallow enough learning curve that I 
can do stuff without making a career out of it. Curiosity is the main 
prerequisite for this, and tolerably easy to use software is a big help 
too. There are other powerful software products out there (Synopsis and 
Roadrunner come to mind) that force you to learn a scripting language and 
the authors' idiosyncratic notions of how to do optical design that I just 
don't have the patience to try learning.

>2.   Spherical mirrors are a rarity at the moment.  However, most of the 
>designs for very large telescopes of the future use spherical primary 
>mirrors for reasons of affordability.   I think it quite

Well, SCT's - which I think after import refractors are the most commonly 
owned telescope design - have spherical primaries, so spherical mirrors 
aren't at all rare. In an all reflective design I think you need at least 4 
powered mirrors to allow a spherical primary and still get good off-axis 
performance. I don't foresee ATMs wanting to step up to 4 mirror designs 
any time soon, and there's really no need to in amateur size telescopes 
since it's easier and cheaper to add refractive elements if needed.

(*) Here's an FAQ item. Books! What do list members own and recommend?

My list is a short one. I think Rutten & van Venrooij and both volumes of 
Wilson's "Reflecting Telescope Optics" are indispensable to the amateur 
telescope designer (I swiped that phrase from someone on the ATM 
list).  Some people might be put off by a book that has a 260 page chapter 
with over 500 numbered equations in it, but there's plenty of material 
besides the math in both volumes. It's also extremely well edited, which is 
a rarity these days even for technical books. That's about it. Schroeder's 
"Astronomical Optics" is worthwhile too (I prefer the 2000 2nd edition), 
but it's not as comprehensive as Wilson and is written more as a textbook.

I have yet to find a book on optical theory or general optical engineering 
that I consider a must own. Professional optical designers swear by Warren 
Smith's "Modern Optical Engineering" and I may get around to investing in 
it sometime (any thoughts?). I was a little disappointed by the 
Willmann-Bell book "Practical computer-aided lens design" by G.H. Smith, 
but it does have some useful material on interpreting the output of 
computer programs.

I've got a few other books in my personal optics library but Wilson is the 
one I turn to most often.

Mike Peck

_________________

Michael Peck
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