1. The problem statement, all variables and given/known data What is the focal length of a dewar window distorted by a pressure difference? As a result of the pressure difference, the radius of the first surface of the window is R1 = 100 meters. The window is 3 mm thick, with an index n = 4 at l = 4 um. 2. Relevant equations I think I can just use the thin lens equation? 1/f=(n-1)/R 3. The attempt at a solution My concern with using the thin lens equation is I'm not sure if a distorted window creates a lens? I know the focal length of a window is naturally infinite. If its bent does it then act as a lens? If not what formula do I use to prove it still acts as a window? Thanks for any help!