F-theta Lenses are plane field objectives, which are commonly used in combination with XY galvanometer scanner. Contrary to a normal lens which focuses a input collimated beam on a spherical image plane, a F-theta lens focuses on a flat image surface. At the same time, it maintains almost constant spot size over the entire field when the input beam scans with input angle ??The position of the spot on the image plane is directly proportional to the scan angle, i.e. F-theta condition: y '=f '*?Daheng F-theta lens series (GCO-31) fulfils the F-theta condition better than 0.1%.