1. The problem statement, all variables and given/known data Formulate an expression that gives the focal length of a corrective lens, to be used in conjunction with a fixed lens. You may assume that both lenses are on the same plane, i.e. that they are very close together. The corrective lens should allow an object at a specified distance from the lenses to produce an image at a specified distance from the lenses. You may assume that the corrective lens is “weaker” than the other lens, i.e. |f0| < |fc|. 2. Relevant equations Assuming they are both thin lenses: Thin lens equation: 1/do+1/di = 1/f (1/object distance + 1/image distance = 1/focal length) 3. The attempt at a solution So I have to derive this equation myself and I'm really lost on where to start. I tried to draw out a good picture of the situation but am still confused. Do I want to start with the thin lens equation as my starting out point?