In article <399467BF.48D6C480@yahoo.com>, Adam <bel### [at] yahoocom> 
wrote:

>   It seems obvious. Of course Povray should allow you to do all those
> things. The only thing that should be real is the light and its
> behavior. But consider this. When I was starting, I wanted to simulate
> the effect of an oil slick on water. So, I made two thin surfaces with
> different indexes of refraction, hoping to get the effect. Boy, was I
> surprised that the irridescence property can achieve the interference
> effect on a single surface. In reality, that's impossible.

Effects of light wavelength are not calculated...some of these these are 
very difficult to write and slow to compute. The iridescence feature 
fakes thickness of the surface for it's calculations.


>    So here are several technical problems I'm facing now. First, I want
> to make a realistic looking CD. Now, it wouldn't be wise to make a disk
> with millions of dents in it, would it. So what do I use to fool the
> viewer? A rainbow, a halo, what?

One method is to use a very fine spiral, onion, or wood normal, 
iridescence, and high anti-aliasing settings. Rainbow isn't useful for 
this, and if your version of POV uses "halo", you need to upgrade.(it 
has been replaced by "media", which, BTW, won't help with this)
There is another method of using averaged textures being discussed in 
povray.binaries.images right now...


> Or how about this: as you may know, if
> you shine a strong, monochromatic, coherent light.right at a penny, you
> should get a bright spot in the center of its shadow as a result of
> light diffraction. I can certainly achieve the effect, but how much of
> it would be attributed to properties of light? Or, how about Young's
> double-slit experiments and light fringes, diffraction gratings, or
> polarized light. And what about "materials" with unusual optical
> properties. Gypsum, for example, is trasparent but it creates a double
> image of anything viewed through it. How much can you assign and let
> Povray take care of it, and how much do you have to take upon yourself
> to model?

Again, these optical effects(diffraction, double refraction, 
polarization...) are either too application-specific or too difficult to 
code/computationally expensive to compute. POV-Ray isn't a complete 
optics simulation, no program is(though some come close).

BTW, I don't think gypsum is double refracting, I think you mean calcite.

POV can calculate direct light, diffuse light(radiosity), refraction of 
light going to the camera, and with photon mapping(in MegaPOV), the 
refraction of light from light sources to surfaces in the scene. There 
is another MegaPOV patch which simulates dispersion(wavelength dependant 
refraction). You shouldn't rely on it simulating more.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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