Patent ID: 6850370

Claim:
An image-forming optical system having positive refracting power as a whole for forming an object image, said image-forming optical system comprising: a first prism member formed from a medium having a refractive index (n) larger than 1 (n>1): and a second prism member formed from a medium having a refractive index (n) larger than 1 (n>1); said first prism member comprising: a first entrance surface through which a light beam from an object enters said first prism member; a first reflecting surface and a second reflecting surface, which reflect said light beam within said first prism member; and a first prism exit surface through which said light beam exits said first prism member; said second prism member comprising: a second prism entrance surface through which the light beam from said first prism member enters said second prism member; a third reflecting surface and a fourth reflecting surface; and a first exit surface through which said light beam exits said second prism member; wherein said first prism exit surface and said second prism entrance surface are positioned to face each other across an air spacing, wherein said first prism member forms first intersecting optical paths in which an optical path connecting said second reflecting surface and said first prism exit surface intersects an optical path connecting said first entrance surface and said first reflecting surface, wherein said second prism member forms second intersecting optical paths in which an optical path connecting said second prism entrance surface and said third reflecting surface intersects an optical path connecting said fourth reflecting surface and said first exit surface, wherein at least one of said first reflecting surface and said second reflecting surface has a curved surface configuration that gives a power to the light beam, said curved surface configuration being a rotationally asymmetric surface configuration that corrects aberrations due to decentration, wherein at least one of said third reflecting surface and said fourth reflecting surface has a curved surface configuration that gives a power to the light beam, said curved surface configuration being a rotationally asymmetric surface configuration that corrects aberrations due to decentration, wherein said first prism member and said second prism member are arranged to form an intermediate image plane in an optical path between said second reflecting surface and said third reflecting surface, and wherein said first entrance surface has a curved surface configuration that gives a power to the light beam, said curved surface configuration being a rotationally asymmetric surface configuration that corrects aberrations due to decentration.