Lens problems and the optical power lab

In a problem convert distances to metres and set signs correctly: for a converging lens F > 0, for a real image f > 0, for a virtual image f < 0; for a diverging lens F < 0. The basic relations are 1/F = 1/d + 1/f, Γ = f/d, D = 1/F. Combining them gives f = dF/(d – F) and Γ = F/(d – F). In a camera problem the image forms close to the focal plane: Γ = h/H (h – image, H – object height), so d = F(1 + Γ)/Γ; for a distant object d ≈ F·H/h. For a virtual image put f negative and read the lens type from the sign of F. If the image is enlarged, |Γ| > 1. Check that the answer makes sense: for d > 2F the image must be reduced.