1. The problem statement, all variables and given/known data A 50 mm focal length thin lens in air is used to image a 250 mm x 250 mm object onto a 10 mm x 10 mm detector. What is the overall object-to-image distance (throw)? Besides the exact solution, can you think of a reasonable approximation? 2. Relevant equations Throw, T = l' - l For a thin lens: (1/l') = (1/F) + (1/l) For a thin lens in air: f = -F 3. The attempt at a solution Since f = 50 mm was given, F = -50 mm. I'm thinking that if I could find either l' or l, I could then use the second equation to find the remaining unknown, and then plug into the equation for T. I'm not sure how to use the given dimensions for the object and detector. I know of no equations that incorporate the area, and I can't determine what else they could be used to describe.