This is an example of a ray diagram for a double lens system in which the image from the first lens is "downstream" from the second lens. This is the case in which the image from the first lens serves as a "virtual object" for the second lens. For the first lens, the object distance and image distance are positive. If the 2nd lens were not present, the image from the first lens would have formed in a position downstream from the position of the second lens. For the second lens, the object distance (the distance from the 2nd lens to location of the image from the first lens) is negative. This negative object distance can be plugged into the thin lens equation to predict the location of the image from the 2nd lens, which is the image ultimately created by this two lens system.
#apphysics #optics
