OPTICAL SYSTEM AND OPERATION METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide an optical system dispensing with the replacement of a diffraction lattice even if the number NA of the apertures of a work to be measured is changed, and an operation method therefor. SOLUTION: The optical system has the diffraction lattice 15 and a drive part 32 for the diffraction lattice. The optical system comprises a liquid crystal panel 31 having a large number of shading elements 33 arranged in a linear, strip-like or lattice-like state and capable of independently changing over the respective shading elements to a light transmission state and a light cutting-off state. In the drive part 32, a light transmission part 34 and a light cutting-off part 35 are formed on the diffraction lattice so as to leave a predetermined interval in a predetermined direction, and the interval is adjusted corresponding to the number NA of apertures of a lens 14.