Cylindrical lens is used to correct astigmatism in the eye, and, in rangefinders, to produce astigmatism, stretching a point of light into a line.They are available in either plano concave or plano convex configurations. Plano-Concave Cylindrical lenses have a negative focal length and are used for image reduction or to spread light. Plano-Convex Cylindrical lenses have a positive focal length, which makes them ideal for collecting and focusing light for many imaging applications.