Warp <war### [at] tagpovrayorg> wrote:
> Stephen <mcavoys_AT_aolDOT.com> wrote:
> > Don?t use Merge, use Difference to subtract the spheres for the cornea. Then
> > Union a sphere slightly smaller than the inner surface of the cornea for the
> > Vitreous Humour. (To avoid coincidental surfaces)
>
>   Are you sure it makes a difference to use an outer layer consisting of
> the difference of two spheres, with a third inner sphere inside it,
> compared to just putting one sphere inside the other?
>
> --
>                                                           - Warp

There seems to be a slight difference in the refraction at the edges of the
inner sphere.  Which one is correct, I don't know for certain, but if you
try with two spheres of the same ior, the one without the difference looks
correct, i.e., looks like a solid sphere of continuous ior, while the
differenced one has refraction that is inconsistent.  When using fresnel
reflection, the differenced one will also give incorrect reflections on the
inner sphere, i.e., too intense.  Based on these observations, I think that
it is more correct to 'embed' the second sphere inside the first without
differencing.  Perhaps someone who knows the inner working of how POV
handles refraction has some better information on this.

-tgq

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