Decentration optical system, and image display apparatus and imaging apparatus incorporating the same

A decentration optical system, comprising at least five optical surfaces, wherein:

• the optical surfaces are each decentered with respect to an axial chief ray in a Y-Z plane in an XYZ coordinate space, and at least one surface is decentered in an X-Z plane orthogonal to the Y-Z plane;
• at least two of the multiple optical surfaces are rotationally asymmetric surfaces;
• at least one of the at least two rotationally asymmetric surfaces is a rotationally asymmetric surface having an X odd-numbered degree term;
• light exiting out from an image display plane for displaying an image enters the decentration optical system and then exits out from the decentration optical system to form an exit pupil for projection onto a viewer's eyeball;
• and
• the decentration optical system is made up of, in order along a path taken by light from entering the decentration optical system up to exiting out from the decentration optical system, a first surface that is a combined entrance and transmitting surface, a second surface that is an internal reflection surface in opposition to the first surface, a third surface that is a combined internal reflection and exit surface in opposition to the second surface, a fourth surface that is an internal reflection surface in opposition to the third surface and adjacent to the second surface, and a fifth surface that is an internal reflection surface adjacent to the fourth surface and in opposition to the third surface.