On Mar 19, 2006, at 6:15 PM, K.Takeshita wrote:
I seem to remember, while reading about the red eye reduction, that
some
animals, particularly dogs and cats, have an extra "reflective"
layer behind
the retina which often reflects the different colour (bluish or
greenish).
Human eyes of course reflect the blood vessel at retina.
If you light dogs in the night, their eyes reflect the light more
brightly
and that is because of this reflective layer (so I understand).
Correct. Many animals have a reflective greenish layer behind the
retina. This is called the tapetum. It is a light amplifier,
because in reflecting the light back it sends it to the
photosensitive cells again. It doesn't quite double the sensitivity,
but increases it greatly. Animals that are strictly diurnal lack
this extra layer and produce "redeye" in flash photos. Night animals
produce strong reflections like this raccoon.
This sort of reflection, if you don't want it, indicates that the
flash is too close to the lens axis. Getting the flash away from the
lens will reduce or eliminate the effect.
Bob
