How lenses have two focus points (f) to form images. What replaces v and c for lenses. Converging lenses, such as biconvex lenses, are thickest at the center. Diverging lenses, such as biconcave lenses, are thickest and the outer edge. The image produced by a converging (positive) lens can be located using just two of three theoretical rules: An incident ray which is parallel to the optic axis is refracted and passes through the second focus f of the lens. An incident ray which passes through the first focus f of the lens is refracted parallel to the optic axis. An incident ray which passes through the optic center of the lens is not bent at all. Case 1 object farther that 2f: parallel: refracted through focus, focal: refracted through parallel, central: passes (straight) through. Parallel rays from a distant object, like a star or the sun, are refracted and form an image on the focal plane.