Opal nous apporta ses lumieres en ce 2008/04/06 21:05:
> Hi there,
> 
> I'm trying to render the most realistic diamond there can be. To do so I need
> realistic IOR value and dispersion value. At first I found them in consts.inc
> shipped with POV-Ray, namely IOR value = 2.47 (or sth) and dispersion value =
> 1.035. Then I got across some scientific page about diamonds. As of 2003, the
> most accurate value for diamond's IOR is 2.4175, and dispersion value of 0.044.
> 
> So my question is: how does 1.035 from POV-Ray relate to 0.044 from the web?
> The 0.044 value is said to be "disspersion strength":
> 
>   Index of
>   Colour    Refraction  Source Line    Wavelength
> 
>   Red       2.407       Solar  B-line   687   nm
>   Yellow    2.417       Sodium D-line   589.3 nm
>   Violet    2.452       Solar  G-line   431   nm
> 
> The difference between the indexes of refraction (2.452 - 2.407) is the
> dispersion (0.044). (There is a small rounding error.)
The dispersion is not a difference but a quotiant.
> 
> http://www.folds.net/diamond_design/index.html#ed_note_04
> 
> I'd appreciate any help.
> 
> Best regards,
> Opal
> 
> 
The only value you need to compute is the dispersion.
The dispersion value is the quotiant of the violet ior divided by the red ior: 
2.452/2.407 = 1.0186955
But, the value you have are not from the extreme ends of the visible spectrum. 
The resulting dispersion is thus slightly smaller than the real dispersion value.

To render the most realistic diamond possible, you'll need to take into acount 
the birefringeance of the diamond, whitch is not possible at present. You'd need 
a syntaxe like:
ior{ior1, ior2, neutral_axis}
where
ior1 is tha base ior, sphericaly constant.
ior2 is the secondary ior perpendicular to the neutral_axis, not constant.
neutral_axis is the axis where the 2 iors have the same value.

-- 
Alain
-------------------------------------------------
I find the affluence of incahol to be totally, whatever he said

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