Plano-convex cylindrical lenses focus incident light onto a line with a positive focal length, consisting of a plane and a convex cylinder, and are often used to focus parallel or diverging beams onto a line or to change the aspect ratio of an image. Traditional The spherical lens has a symmetrical effect on the incident light in two directions, while the cylindrical lens has only one effect on the incident light in one direction. A typical application is the use of a pair of cylindrical lenses to achieve anamorphic beam shaping. A pair of positive cylindrical lenses can be used to collimate and circularize the output of a laser diode; another possible application is to use a single cylindrical lens to focus a diverging beam onto a detector array. To minimize spherical aberration, when converging a collimated beam into a line, the collimated light should be incident on the curved surface of the lens, and when collimating a linear light source, the line light source should be incident on the plane of the lens.