Device for splitting light from an objective lens

摘要

A phase type diffraction grating and a microprism for splitting the light beam from an objective lens into three light beams. The three light beams are split in one direction by the diffraction grating and are directed onto three rows of line sensors disposed on the same plane. In the two optical paths between the diffraction grating and the line sensors, there is disposed an optical path length difference imparting element for forming on the line sensors images at a predetermined focal plane of the objective lens and planes forward and rearward of the predetermined focal plane. Thus, the line sensors detect the images at the predetermined focal plane and at planes forward and rearward of the predetermined focal plane.