PURPOSE: To obtain a compact lens with a wide visual field and a large diameter by fixing a focal surface on a slanting surface of a prism cemented to the parallel reverse surface of the upper part of an off-axis plano-convex cylindrical lens body.

CONSTITUTION: A figure shows the photodetection characteristics of this lens. Namely, when the prism 4 with the slanting surface C is cemented to the top surface of the lens body 3, an optical system is separated at a surface F if deviation in focal surface from a surface C occurs owing to a size error of parts, thereby correcting the deviation easily by the movement of the upper-side prism 4. In a figure, a line detector 5 is shown.