Plano-convex lenses, convex on one side and flat on the other, have a positive focal length and are commonly used for related applications such as reducing the beam, reducing the focal length, or enlarging an image. In order to reduce spherical aberration, when a plano-convex lens is used for collimating beam focusing, the beam should be incident on the surface of the lens. When used for point source collimation, the beam is incident on a plane.Most suitable where one conjugate is more than five times, the other. e.g. in sensor application or for use with near collimated light. Also where both conjugates are on the same side of the lens, e.g. as an add-on lens to increase the numerical aperture.