Viewing optical system and image display apparatus using the same

A viewing optical system comprising:

• reflection type image display means placed in an image plane;
• an ocular optical system for leading an image displayed on said reflection type image display means to a position of an exit pupil where an observer's eyeball is to be placed;
• illuminating means placed at a position of an entrance pupil conjugate to said exit pupil with respect to said ocular optical system, said illuminating means being formed from a plurality of juxtaposed illuminating light sources of different colors;
• illuminating light guide optical means for guiding an illuminating light beam from said illuminating means, said illuminating light guide optical means being placed between said entrance pupil and said reflection type image display means so that the illuminating light beam can be applied to a display surface of said reflection type image display means from a front side thereof;
• and
• chromatic aberration producing means placed between said entrance pupil and said illuminating light guide optical means, said chromatic aberration producing means being arranged to superimpose images of said plurality of illuminating light sources on one another in said exit pupil;
• wherein said ocular optical system includes a decentered prism formed from a medium surrounded by three optical surfaces and having a refractive index larger than 1,
• said decentered prism having:
• an entrance surface through which a display light beam reflected from said reflection type image display means enters said decentered prism after passing through said illuminating light guide optical means;
• a first reflecting surface for reflecting the light beam entering through said entrance surface;
• a second reflecting surface for reflecting the light beam reflected from said first reflecting surface;
• and
• an exit surface through which the light beam reflected from said second reflecting surface exits said decentered prism;
• wherein said first reflecting surface and said exit surface are formed from a single surface serving as both a refracting surface and a reflecting surface.