You know a patch is big hit, when other people give the correct answer
long before the patch author gets around to reading the question  :-)


Just want to clarify some details.   The IOR in the dispersion patch is
an exponential function of color number.  By color number, i mean i'm
counting subrays that are traced, from 1 to disp_nelems.   In other
words, each subray uses an IOR a certain ratio higher than the previous
subray.  This is not based on physics, but ease of implementation and
good looks.  IMHO, a linear function did not look good enough.   Real
physical materials have a variety of dipserson curves, which would be
fun to model, but I use povray for art not physics.

Each subray is traced, and contributes some amount of a pure hue to the
sum.  The formula for converting the nth ray into a color is purely
ad-hoc, chosen to look good, again no real physical laws were refered
to, and to match some mathematical criterea, mainly that it had to sum
all-equal subrays into pure white.  For looks, I want a nice yellow, and
violet at the low-wavelength end.

At no point in the process do i calculate or use wavelengths.  

With the  source code out there, it's just a matter of time before
someone tweaks it to behave more in accordance with real optics.    I'm
too lazy, and have a totally different ray tracer for good physics
rendering.

-- 
Daren Scot Wilson
dar### [at] pipelinecom 
www.newcolor.com
----
"A ship in a harbor is safe, but that is not what ships are built for"
                                            -- William Shedd

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