There's a para in my textbook which doesn't make much sense to me: An observer or a fish under water looks up to see a compressed view of the outside world. The 180 degree view from horizon to horizon is seen through an angle of 96 degrees (twice the critical angle). A lens, called fish eye lens used in special photographs, similarly compresses a wide wiew. What on earth does that mean? Where did 96 degrees and twice the critical angle come from? Can someone explain how they got that?