Am 10.02.2017 um 15:09 schrieb Nicki:
> I want to visualize opaque spheres inside a transparent spherocylinder (a
> cylinder with hemispherical caps at the ends).
> When I do so I get weird red spots on the spheres even though they should not be
> touching the transparent sphere. I have to make the spheres significantly
> smaller then the outer transparent spherocylinder so that this problem
> disappears.
> In the following I show you three scene-files and the corresponding images that
> show this problem.
> I would be happy to hear suggestions on how to get rid of this problem.

What you're seeing is a long-standing problem known as "[near]
coincident surfaces": If POV-Ray encounters one transparent or
semi-transparent surface, the ray traced from there onward will ignore
any surface within a particular distance.

The rationale for this behaviour is that the ray can't erroneously
re-encounter the transparent surface (or any surface truly coinciding
with it) again, which could happen due to rounding errors, and might
lead to a potentially infinite loop.

As a consequence, you need to make sure that you leave a bit of a gap
between any transparent or semi-transparent objects and adjacent objects.

Since the required minimum distance is a constant, scaling up the entire
scene allows you to get away with a smaller /relative/ distance.

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