CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of International Patent Application No. PCT/JP2019/021657, filed May 31, 2019, which claims the benefit of Japanese Patent Application No. 2018-109863 filed Jun. 7, 2018, and No. 2019-044280 filed Mar. 11, 2019, all of which are hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an optical system for use in an imaging apparatus that splits a light beam from an object and that obtains image information and is suitable for inspection and evaluation in industrial fields such as manufacturing industry, agricultural industry, and medical industry.

Background Art

A known optical system splits a light beam from a test object (object) into light beams at different wavelengths and focuses the light beams on different locations. U.S. Pat. No. 7,199,877 discloses an optical system that focuses a light beam from an object at a slit that is elongated in one direction by using a cylindrical mirror and subsequently splits the light beam by using a diffraction grating.

In U.S. Pat. No. 7,199,877, however, the curvature of field at the slit due to the cylindrical mirror is not considered. In the case where the curvature of field is generated at the slit, there is a possibility that a part of a light beam is not focused on the slit and is shielded.

SUMMARY OF THE INVENTION

The present invention provides an optical system that can successfully correct the curvature of field at a slit, and an imaging apparatus and an imaging system that include the optical system.

One of aspects of the present invention provides an optical system comprising: a front group; a light-shielding member; and a rear group that are arranged in this order in a direction from a side of an object toward a side of an image, wherein the light-shielding member is provided with an opening elongated in a first direction, the front group has an aspherical surface, does not image the object at the opening in a first section parallel to the first direction, and forms an intermediate image of the object at the opening in a second section perpendicular to the first direction, the rear group has a diffractive surface that splits a light beam that passes through the opening into light beams at different wavelengths in the second section and focuses the light beams on different locations in the second section, and a curvature radius of the aspherical surface in the second section at an on-axis position in the first direction differs from that at an outermost off-axis position in the first direction.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

