This is an example of how to use both ray tracing and the thin lens equation to analyze a system of two lenses (aligned along the same axis). I first show how to do ray tracing on one lens at a time to locate the first image and then use that image as the "object" for the second lens. After finding a final result, I then verify the ray tracing answer by using the thin lens equation (twice). The essential point is to consider each lens one at a time, pretending that no other lenses exist in the universe.
