Patent ID: 8724229

Claim:
A decentered optical system provided that projects an image on an image display device onto the viewer's eyeball as a virtual image comprising: a decentered prism which is located in opposition to the image display device, in which there are at least three optical surfaces mutually decentered with at least two thereof being in rotationally asymmetric shape, and which is filled inside with a medium having a refractive index of greater than 1, and a decentered lens which is interposed between the viewer's eyeball and the decentered prism, and is made up of mutually decentered two surfaces and filled inside with a medium having a refractive index of greater than 1, and in which on the image display device side with respect to an on-axis chief ray incident from a center of the image display device on a center of an exit pupil, there is a lens portion having positive power, and on an opposite side thereof, there is a lens portion having negative power, wherein a Y-direction power profile of the decentered lens becomes small in descending order of a Y-direction angle of view, provided that a Z-axis is defined by an axis provided by a straight line that connects the on-axis chief ray exiting out of the decentered optical system with a center of the exit pupil, a Y-axis is defined by an axis that is orthogonal to the Z-axis and lies in each of decentered surface portions of the surfaces forming the decentered optical system, and an X-axis is defined by an axis that is orthogonal to the Z-axis and the Y-axis alike.