A convex lens is a converging lens which works much like a concave mirror. This kind of lens is thicker in the middle and thinner towards the edges, like the lens in a magnifying glass. The image is changed by the position of the object in relation to the focal length and the radius of curvature. If the object is beyond 2F, the image is real, inverted and reduced, at 2F real, inverted and the same height, between F and 2F real, inverted, and magnified, at F there is no image, and in front of F, the image is virtual, erect, and magnified.

     A concave lens is a diverging lens which works similar to the convex mirror. This lens is thicker towards the edges and thin in the middle and are used in helping correction of nearsightedness. All images produced by concave lenses are virtual, erect, and reduced. There is an error in lenses, most notably in concave lenses called chromatic aberration, referring to the fact that the focal length of a lens can vary with the wavelength of light that is passed through it. This can be corrected by cementing two lenses together (one convex, one concave) into a single lens.