Positive cylinders have one flat surface and one convex surface, and are made of BK7. Negative cylinders have one flat surface and one concave surface and have a negative focal length. Rod Lenses are polished on the circumference and ground on both ends. Optical performance is similar to a cylinder lens. Collimated light passing through the diameter of the rod will be focused into a line. These components are used in a variety of laser and imaging applications.