Piotr 'utak3r' Borys <pio### [at] gmailcom> wrote:
> BUT - whenever I try to use photons, those shadows become pure black 

  That's actually physically correct (assuming light doesn't arrive
from anywhere else (eg. reflected from other surfaces) to the shadow).

  A solid refracting object of a certain shape, such as a glass sphere
(or a really dense spherical diamond like your object seems to be)
concentrates the light passing through it. Since the light is concentrated
at a smaller spot, no light arrives at the other places of the shadow of
the object. It's logical and physically accurate.

  It's difficult to demonstrate this in real life because you would need
a glass sphere and an environment where light does not illuminate the
shadow of the sphere (iow you would beed a room with completely black
non-reflecting walls).

  The most common household glass object is a drinking glass. This is
a completely different shape because its an almost cylinderical hollow
glass object with a very thin surface, which causes it to have an almost
inexistent concentration-of-light effect. Most light passes through
such glass without concentrating on a small area, and thus the "shadow"
of the glass is quite evenly illuminated by the light passing through
the glass.

  So there are two elements in play here: The shape of the object (some
objects concentrate light or otherwise deviate it significantly so that
the shadow of the object has areas where light does not arrive) and
the light coming from other sources illuminating the shadow (usually
reflected from other surfaces, something which povray's radiosity feature
simulates).

  Just because the image you are seeing doesn't look correct to you
doesn't mean it's not physically correct (given the parameters you
have set for the scene). Some things in real life indeed do not work
exactly as one would expect, even though they might feel as common
and everyday things. (One reason for this phenomenon is that people
usually don't pay close attention to some details in real life, but
when they are rendering a scene they suddenly do, and those unexpected
details suddenly jump out.)

-- 
                                                          - Warp

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