Method for adjusting optical axis of imaging optical system and lens system

A method for adjusting an optical axis of an imaging optical system that comprises:

• a first lens element;
• a right-angle prism for bending light entered from the first lens at right angles;
• and a lens group that moves in a direction of an optical axis of the subject light emerged from the right-angle prism, wherein the imaging optical system is incorporated in a lens barrel, and the lens barrel comprises:
• a first holding member positioning and fixing the first lens and the right-angle prism;
• and a second holding member incorporating the lens group,
• the method comprising:
• when assembling the first holding member and the second holding member,
• positioning the first holding member relative to the second holding member;
• making inspection light incident into the first lens to pass through the first lens, the right-angle prism and the lens group in this order;
• and
• changing a relative position of the first holding member to the second holding member so that an image obtained from the inspection light takes a reference position, so as to coincide an optical axis of the subject light emerged from the right-angle prism fixed to the first holding member with an optical axis of the lens group incorporated in the second holding member.