Hi, I need to know whether Refraction changes current focal length of a camera..I have a camera focused at the bottom of a water tank(without water). After filling water to the tank i cannot see the bottom anymore focused..I need to calculate how much should I move the camera vertically to see the bottom again focused..(camera is not perpendicular to the water surface, 45°) I think this can be solved using Snell's law and ray tracing..but I don't know how to go on with it.. I'm not a physics person and my high schools physics are bit rusty now.. I'm really grateful, if somebody can tell me how to go on with this..or point out relevant literature in internet..or book.. Thanks in advance..