"Thomas Lake" <tla### [at] homecom> wrote in message
news:3b6b4850$1@news.povray.org...
> I was playing around with dispersion a little last night, great feature! I
> especially like the sphere example posted on the MegaPov examples page,
the
> one where you can see some dispersion in the reflection of two box's with
> high ambient:
>
> http://users.skynet.be/smellenbergh/demopictures/disp2b.jpg

I believe the dispersed parts are refracted through the glass from
reflections showing up inside the sphere opposite the external reflections.
So no, dispersion doesn't affect reflections.

> I got to wondering in what situations do you need to specify the spectrum
of
> a light source? In the above example no spectrum has been specified yet
> dispersion can be clearly scene in the reflection of the two ambient
boxes.
> Is a spectrum only necessary if you want the caustics cast to contain
> colours? I tried specifying a spectrum for the light in the sphere scene
but
> all I managed to do was wash out the scene or get a very harsh yellow
tinted
> light, it didn't seem to change the caustics or the dispersion. Do you
need
> objects with sharp corners to get good results from caustics and photons,
> such as a diamond or prism? I also took a look at the macro in the prism
> example for creating the spectrum. Now I'm not very good at writing, let
> alone reading scripts, but from some of the experiments I did and from
what
> I can understand of the macro it seems to simply create a color_map which
> with the specified number of entries that blends through the colors of the
> rainbow, ROYGBIV. When I specified my own colour map using seven entries,
> ROYGBIV, I got pretty much the same results as the macro. Is this really
all
> the macro does? The code makes it seem more complicated than that. Thanks
> for listening to this babble:-)

Isn't it all some kind of babble anyway?

Sure, it's only a color_map doing any range of colors to blend that you want
it to be if making a custom one.  The fancier one provided attempts to
correct for colors you'd expect to see from sunlight, I think, but not
positive about that.
It's for photon caustics.  Regular POV caustics only use the filtered color
of the object pigment.  I don't think the light_source color_map has
anything to do with object interiors, aside from the photon mapping produced
with dispersion.

Maybe someone will correct me if I'm wrong about any of that.

Bob H.

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