1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Wider viewing angles

  1. Dec 12, 2012 #1
    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?
     
  2. jcsd
  3. Dec 12, 2012 #2

    K^2

    User Avatar
    Science Advisor

    Refraction. Ray hitting water from outside at nearly 90° is going to continue at critical angle under water. That means that cone of ± critical angle gives you a 180° view of world above water.
     
  4. Dec 12, 2012 #3

    Ibix

    User Avatar
    Science Advisor

    It can be easier thinking of this one backwards - treat the fish as the source. Draw a point below a line. The line is the water surface and the point is the fish. Draw rays coming out from the fish to the surface, refract them, and see where they go. You can draw as many as you like, but the obviously interesting angles are all that you really need.

    Rays coming from above the surface to the fish look exactly the same. Remember that the diagram is symmetric about the vertical.
     
  5. Dec 12, 2012 #4
    Yes I get that but how is it 2c?
     
  6. Dec 12, 2012 #5

    K^2

    User Avatar
    Science Advisor

    attachment.php?attachmentid=53853&d=1355309082.png

    Here, [itex]\small \alpha[/itex] is the critical angle. So the full FOV is [itex]\small 2\alpha[/itex].
     

    Attached Files:

  7. Dec 12, 2012 #6
    Thanks a lot. I tried a bit more and got it by saying how the inside angles of the triangle are 90-alpha and then getting it.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Wider viewing angles
  1. LCD view angle (Replies: 4)

Loading...