"Lutz-Peter Hooge" <lpv### [at] gmxde> wrote in message
news:3e7e5f0c$1@news.povray.org...
> Lutz-Peter Hooge <lpv### [at] gmxde> wrote:
>
> > When using reflection{0,1 fresnel} there is a reflection,
> > but I wasn't sure if the result of using the range 0...1
> > would be the physical correct reflection, thats because I asked.
>
> Ok, I searched the source files for 'fresnel' and found the
> relevant part. If I understand it corrently
> 'reflection{0,1 fresnel}' should indeed give the correct result.
>
> However I discovered something that might be a bug:
> The fresnel function used there seems to be the one that describes
> how the energy splits up in the reflected/refracted part.
> I'm not entirely sure, but I think the function for the intensitys
> should be used instead...?
>
> Lutz-Peter

According to Fresnel formulas the minimum reflection (on a scale of 0 to 1)
occurs at an angle of incidence of 0 degrees and is a function of the index
of refraction.

The formula is: min = pow((ior - 1.0) / (ior + 1.0), 2.0)

Your ior of 1.5 (Glass) would be 0.040. Diamond (ior 2.417) would be 0.172.
A minimum reflection of 0.0 would be for an ior of 1.0 (Air).

The maximum reflection occurs at an angle of incidence of 90 degrees and is
always 1.0.

To make this all work properly you need to have the statement "conserve
energy" so that the remaining light after reflection is refracted.

This reflection/refraction occurs when the light enters and leaves the
transparent media. I have seen a single ray of light being reflected
internally over 50 times in gemstones. If your object is complicated (such
as a gemstone) I suggest that the max_trace_level be increased to 20 or 25.

Dick Conley
dic### [at] localaccesscom

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