I'm assuming the angle of incidence to be the number of degrees from a perpendicular line on the side of a prism the ray starts passing through... I'm trying to figure out the angle the ray would be off of a perpendicular line that intersected the side of the prism that the ray exited.
Is there a formula to calculate this?
Background: I'm trying to use anamorphic prisms to stretch an image by a specific ratio... I can do it by trial and error and pretty much get what I am looking for but I wanted to see what the math was behind what was happening... I'm using 2 prisms with a 20 degree angle and made of BK7.