[Raytrace] Where To Start?

[Dan Chaffee]

>I'd also suggest - if the site owner and list administrators are willing -
maintaining a file upload/download area for list members (maybe the public
too). I think Peter Smith is right that the best way to learn this stuff is
to play around with existing designs. I learned what little I know by
entering published designs from any source I could find into OSLO, and
gradually learned new capabilities of the program by trying to extend and
optimize existing designs. I've never gotten beyond capabilities that can
be accessed with spreadsheet entries, menu selections, or taskbar clicks,
but you can do quite a lot without ever mastering the programming language
>that's part of OSLO.

Mike, All,

This really sums it up for my experience as well. I've manipulated radii and
glass types from the simple achromat example you sent me a year ago
and learned how to balance enough of the factors to design a decent
176mm f/18(!) BK7-F2 oiled doublet. I wanted to KISS and keep all
surfaces spherical since I don't have a reference flat big enough for a
double bypass knife edge test. Within the simple parameters of the ray
analysis, wavefront evaluation, spot diagrams, and PSF, I've allegedly
got a design that should be well color corrected, very low LA on axis
in 546nm, and coma no worse than a longish newtonian. Actually, I
also arrived at a Fraunhofer of the variant same f/#  that is clearly better
with off axis performance, but I wanted the advantages of the oiled R2&3
for better transmission and reduction of scatter. The advice on designing
lenses in R&V is good and spells out  the proccess of trial and error
for balancing achromatism with acceptable OSC very well.

Here are the specs for the oiled doublet:
R1=1490mm
R2=-1373
R3=-1373
R4=-14900
T1=17mm
T2=16mm
Glass 1 is BK7 with Nd=1.51678,Vd=64.15
Glass 2 is F2 with Nd=1.619; Vd-36.34

und der Fraunhofer:
R1=2004mm
R2=-1106
Air gap= 3.6
R3=-1116
R4=-4330
T1=18
T2=15
Same glasses

If anyone wants, I'll email the actual OSLOlt lens files.
I had Roger C. run my design through Zemax and he seemed to feel it
would be a good performer. I'd welcome anyone elses comments if they
are interested.
At any rate, the grinding is 98% complete, so I'll know shortly whether
or not this will perform to my liking. One possible problem is in the melt
data from the glass broker, which gave an odd rationality of dispersion.,
but was within the range of what is acceptable per the written guarantee,
so I couldn't return it. The sales rep I complained to made the mistake of
telling me he sold glass to Roland Christian. Naturally, I contacted Roland
about the specs and this broker in particular. He advised me to ignore the
supplied melt data, since glass brokers rarely have equiptment accurate
enough to read indicies and dispersions to justify values under .01. At best
their values can only ahow a general trend in higher or lower indicies
resulting
from the fine & precision annealing that they do. He  also said he'd long
since done
business with the broker in question....

Dan Chaffee