A biconvex lens has a positive focal length and can focus parallel light rays onto a single point, thus its function is similar to that of a plano convex lens. Its two surfaces are spherical and have the same curvature radius, thus minimizing spherical aberration. When the distance between the object and the image and the lens is equal or approximately equal, not only is the spherical aberration minimized, but also coma, distortion, and chromatic aberration will be cancelled out due to symmetry.