Optical system, optical device, and method for manufacturing optical system

A method for manufacturing an optical system comprising a splitting plane that transmits a first part of incident light and reflects at least a second part of the incident light different from the first part, and that forms images of first light that is at least a part of light reflected by the splitting plane and second light that is at least a part of light transmitted through the splitting plane, the method including:

• arranging a first optical system to include, in order from an object side, a front lens group having negative refractive power, an optical path splitter having the splitting plane, and a first rear lens group on which the first light is incident;
• arranging a second optical system to include, in order from the object side, the front lens group, the optical path splitter, and a second rear lens group on which the second light is incident;
• and
• configuring the second optical system to have a total focal length different from a total focal length of the first optical system.