Optical system, and imaging apparatus and imaging system including the same

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 does not image the object at the opening in a first cross-section parallel to the first direction and forms an intermediate image of the object at the opening in a second cross-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 cross-section and focuses the light beams on different locations in the second cross-section,
• a light beam that is emitted from the front group and that enters the opening is non-parallel light in the first cross-section, and
• a sign of power of the front group and a sign of power of the rear group differ from each other in the first cross-section.

An inspection method comprising:

• a first step of imaging an object by using an optical system to obtain image information about the object;
• and
• a second step of inspecting the object, based on the image information,
• wherein the optical system includes a front group, a light-shielding member, and a rear group that are arranged in this order in a direction from the object toward an image,
• the light-shielding member is provided with an opening elongated in a first direction,
• the front group does not image the object at the opening in a first cross-section parallel to the first direction, and forms an intermediate image of the object at the opening in a second cross-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 cross-section and focuses the light beams on different locations in the second cross-section,
• a light beam that is emitted from the front group and that enters the opening is non-parallel light in the first cross-section, and
• the front group and the rear group have positive power in the second cross-section.