Patent ID: 8570668

Claim:
An imaging optical system, comprising: an imaging lens group having at least one lens; and an image side prism that bends light which has passed through the imaging lens group toward an image pickup device arranged at a predetermined position, wherein the image side prism includes a reflection surface which reflects, toward the image pickup device, incident light proceeding from the imaging lens group, and an exit surface from which light reflected from the reflection surface emerges, the image side prism has a cut surface formed by cutting off a vertex portion between the reflection surface and the exit surface such that a whole normal light incident area within which normal light is incident on the reflection surface remains, the cut surface is a non-diffusing surface, and when N p denotes a refractive index of the image side prism, N o denotes a refractive index of a medium outside the image side prism and α denotes an angle formed between the exit surface and the cut surface, the imaging optical system satisfies a condition: α>π/2−SIN −1 ( N o /N p ) (1).