Taking advantage of contra light in scenes with
semi-transparent objects is quite favorable in many situations. Just take
a look at the wings of the bird or the flower below. The shiny effect here
provides a pretty interesting contrast to the "solid" body. Further objects
that fit very well for this kind of composition are e.g. hairs (portraits!),
ice or shells.
This light situation REQUIRES! a lens
hood - otherwise your pictures will suffer from extreme flare problems
and a significant loss of contrast!
The bird on the following picture receives
some midday sunlight so the feathers glow quite beautifully.
Photo by Detlev Franz
The next picture is probably a more typical
example due to the more common side-light situation.