A lens or mirror can bend rays of light to make an image. There are two different kinds of lenses: converging and diverging. There are two different kinds of images: real and virtual. Optical devices that you look through use virtual images; those that project images use real images. Parallel rays are converged at the focal point, beyond the lens. Rays continue after passing through the focal point. Focal point is in front of the lens. Rays appear to diverge from the focal point. For two lenses in close proximity, ptotal = p1 + p2. A converging lens has a focal length of 10 cm is placed next to a second lens with a focal length 20 cm. Rays leave a point on the object in every direction. All the rays leaving one point in the object plane that reach the lens are refracted by it and converge to one point in the image plane.