Image-forming optical system

An image-forming optical system having a positive refracting power as a whole for forming an object image, said image-forming optical system comprising:

• a prism member formed from a medium having a refractive index (n) larger than 1 (n>1), said prism member having:
• a first entrance surface through which a light beam from an object enters said prism member;
• a first reflecting surface, a second reflecting surface, a third reflecting surface and a fourth reflecting surface, which reflect the light beam in said prism member;
• and
• a first exit surface through which the light beam exits from said prism member;
• wherein an optical path connecting said second reflecting surface and said third reflecting surface intersects an optical path connecting said first entrance surface and said first reflecting surface, and the optical path connecting said second reflecting surface and said third reflecting surface intersects an optical path connecting said fourth reflecting surface and said first exit surface,
• wherein at least either one of said first reflecting surface and said second reflecting surface has a curved surface configuration that gives a power to a light beam, said curved surface configuration being a rotationally asymmetric surface configuration that corrects aberrations due to decentration, and at least either one of said third reflecting surface and said fourth reflecting surface has a curved surface configuration that gives a power to a light beam, said curved surface configuration being a rotationally asymmetric surface configuration that corrects aberrations due to decentration, and
• wherein an intermediate image plane is formed between said first reflecting surface and said fourth reflecting surface.