For many ATMs, having a good ray trace program on hand is pretty valuable. Uses range from checking coma on standard telescopes, to optimizing the design of an aspheric astrocamera or other advanced design. I've been keeping a list of available programs; here, wearing my critic’s hat, is a review of them:

RAYTRACE: This software, which is available with the book Telescope Optics, is quite primitive and has an inconvenient user interface. Its companion TDESIGN and LENSDES programs can be useful, however, for homing in on an initial design. It is sold for $25.00 with the above book by Willman-Bell; their website is:

http://www.willbell.com

IRT: This program, Interactive Ray Tracer, first showed up about five years ago. You edit an ASCII file of high level commands, and open it in IRT. It is a slick Windows package with great graphics, but my most recent machine (Win95 OSR2) now encounters many error messages. There doesn't seem to be any web presence of the author, nor continuing operation or support. Functional, freely downloadable versions still exist on some ATM sites. Not recommended, but a URL is:

http://atmpage.com/optic.cgi

BEAM 2, 3 and 4: The most basic version, BEAM 2, can handle many amateur needs, and is priced at an affordable $89.00. My own experience is with a version that is several years old, but the user interface seemed pretty clunky, and the documentation was light. They may have improved both in recent years. Their web site is at:

http://www.stellarsoftware.com/

OSLO LT: This is the freeware Windows version of OSLO - it is limited to 12 surfaces, but is otherwise amazing. It is very powerful, with every conceivable feature and analysis option, including effective optimizers. The documentation is quite good, and the only potential drawback is a bit of a learning curve before you become fluent. A must for power users. The key to the learning curve is that the detailed info resides in the multi-level helps; also examine the examples. You can download it from:

http://www.sinopt.com/index.htm

KDP: This is another powerful, freeware Windows raytrace package. It has extensive documentation, but the 500 page manual hints at the degree of investment needed in coming up to speed. I haven't yet. OSLO seemed easier, and equally powerful. If you're still interested, it can be downloaded from:

http://www.kdpoptics.com/

ZEMAX: This is yet another powerful, Windows raytrace package. While you can download a demo version, it cannot save files, and the only options are to spring for the full version (>$1,000), or to figure out the ASCII file format, and edit using a text editor. It can come in handy to view the designs of people who did spring for it. The demo version can be downloaded from:

http://www.optima.co.uk/ZEMAX/DOWNLOAD.HTM

TRACE: This freeware program wins the contest for 90% of the ATMs out there - for that matter, it was written by one. It runs in a DOS prompt, and shows you all you need in one screen. Three graphs show spot diagrams at three field angles, in three colors, and everything about the design and the plots can be modified and retraced with a few keystrokes. It handles curved focal planes and Schmidt plates, and has two multi-parameter optimizers and an F2 focus-find. You enter a design off-line using any text editor, and then load that file into TRACE. Most important of all, the manual is only two pages long, and consists of 13 commands with parameters. You can learn it and be fully up to speed in half an hour. While it doesn't handle tilts and de-centers, it does handle the majority of designs that ATMs would attempt. You can download it from:

http://members.aol.com/drowesmi/trace.html

CODE V: This is by all accounts the king of the heap, but you really don't want to know how much it costs. For that matter, you can't even buy it - they will only lease the program, for hefty monthly or annual fees. It's produced by Optical Research Associates, and if you want to window shop, their web site is at:

http://www.opticalres.com/cv/cvprodds.html

In conclusion, I'd recommend TRACE as being the best for most ATMs, especially if you are in a hurry, or have a casual interest in raytracing. If you prefer more sophisticated analysis, a slick Windows package, or are working with more advanced designs, by all means try OSLO LT. Both are free, which is a pretty awesome deal. I'd be happy to field questions about either.

Kevin McCarthy