Marvin,
Surprisingly, they don't seem to be found a lot in nature, so far
as I can tell. Lenses are abundant in nature, convex lenses that is.
Convex lenses are in all eyes, helping creatures to focus images and
see. Another interesting place convex lenses are found is on the body
of a sea creature called a brittlestar. This creature has a network of
convex lenses on its surface to help it focus light and detect the
shadows of approaching predators. However, when I looked to find where
concave lenses were found, I really didn't find much, except your lens
in your eye changes from convex to slightly concave to focus some
images better. Concave lenses are very much man-made, found in cameras,
eyeglasses, and binoculars, but are not found in many places in nature.
But, lenses are being discovered in lots of new places everyday, so
they might be found somewhere soon.
Thanks for your question!
-Kim-
(published on 10/22/2007)