Image-forming optical system and viewing optical system

An image-forming optical system for forming an image of an object, said image-forming optical system comprising:

• a first prism and a second prism, each of said first prism and second prism being formed from a medium having a refractive index (n) larger than 1.3 (n>1.3);
• said first prism being placed closer to the object than said second prism;
• said second prism having four optical surfaces that transmit or reflect a light beam, said four optical surfaces including:
• a first surface through which a light beam from an object side of said second prism enters said second prism;
• a second surface that reflects the light beam entering through said first surface in said second prism;
• a third surface that reflects the light beam reflected from said second surface in said second prism;
• and
• a fourth surface through which the light beam reflected from said third surface exits from said second prism;
• wherein said first surface and said second surface are positioned to face each other across said medium, and said third surface and said fourth surface are positioned to face each other across said medium so that an optical path connecting said first surface and said second surface intersects an optical path connecting said third surface and said fourth surface;
• wherein at least one of said second surface and said third surface has a curved surface configuration that gives a power to a light beam, said curved surface configuration having a rotationally asymmetric surface configuration that corrects aberrations due to decentration;
• said first prism having at least:
• a decentered reflecting surface having a curved surface configuration and internally reflecting a light beam in said medium, said reflecting surface having a rotationally asymmetric surface configuration that gives a power to a light beam and corrects aberrations due to decentration;
• an entrance surface through which a light beam enters said first prism;
• and
• an exit surface through which the light beam exits from said first prism;
• wherein an intermediate image surface is formed between the entrance surface of said first prism and said fourth surface of said second prism, which is an exit surface of said second prism.