Alain <ele### [at] netscapenet> wrote:
> Alain nous apporta ses lumieres en ce 2007/10/16 11:57:
> > inhahe nous apporta ses lumieres en ce 2007/10/16 05:18:
> >> I'm not an advanced user of POVRay, but I thought only advanced users
> >> would
> >> be knowledgeable enough to answer my question.
> >>
> >> i want to do refraction where colors are separated, like in the prism
> >> effect.  afaik the feature that does this is photon mapping.  but from a
> >> little bit of reading I get the impression that photon mapping would only
> >> project colors onto surfaces, not onto the camera.  so, e.g. if i
> >> created a
> >> diamond i wouldn't see it shine with various colors.
> >>
> >> but i had an idea.  let's say I create a white surface, with a
> >> lens-shaped
> >> refracting object in front of it, and put a black box around it except
> >> for
> >> the lens, like a camera.  then i point this contraption toward the
> >> diamond
> >> or whatever, and put the povray camera inside the contraption pointing
> >> toward the white surface.  then of course when the image is rendered I
> >> flip
> >> it horizontally and vertically.
> > Overkill.
> >>
> >> will this work?
> > Maybe.
> >> is it necessary?
> > NO!
> >>
> >>
> > Whenever you add dispersion you get coloured difraction. If the camera
> > see, directly or not, the dispersing object, you'll see the colours. You
> > don't need photons for that. Photons will make the caustics that hit
> > some surface coloured also.
> > To see the colours, you need an interior block like:
> >
> > interior{ior 2.5 dispersion 1.2}
> >
> > Here,the default dispersion_samples of 7 is unualy enough.
> > Diamond's ior is about 2.5 and it have a relatively strong dispersion,
> > over done here.
> > If the diamond is "free floating", that's all you need.
> > If the diamond is resting on something, and you want to see the effect
> > on that surface, THEN you need photons:
> >
> > object{Diamond interior{ior 2.5 dispersion 1.1 dispersion_samples
> > 15}photons{target refraction on difraction on collect off}}
> >
> > A larger number of dispersion samples is needed to get smooth coloured
> > caustics unless very close to the diamond.
> > You don't need to add a photons block to the light_source, nor to the
> > surface.
> >
> I forgot, you should add:
> finish{specular 0.8 roughness 0.0001} or the light won't cause any highlight.
> Very small roughness value due to the diamond's very hard and smooth surface.
>
> --
> Alain
> -------------------------------------------------
> Why do psychics have to ask you for your name?

oh, thanks for the info, but i'm not actually doing a diamond
i'm going to make a glass christmas tree. with branches, subbranches, and
needles.  many many needles.  not next to a surface.

what would be the best settings for that? (i want it as realistic as
possible, preferably the same ray could refract through many objects, if
that's possible)

it's ok if it takes a week to render.

and what ARE photons useful for?

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