Lens -- find the focal length 1. An object 3.0 cm tall is placed 20 cm in front of a converging lens. A real image is formed 10 cm from the lens. What is the focal length of the lens? 2. 1/f = 1/do + 1/di 3. 1/f = 1/do + 1/di 1/f = 1/20 + 1/10 f = 6.667 cm I'm not sure if this is right and if you can can you show me how the diagram would look like. Thank You!!