Imaging optical system and imaging apparatus

An imaging apparatus, comprising:

• an imaging optical system;
• and
• an image pickup device,
• wherein the imaging optical system includes:
• an imaging lens group having at least one lens;
• an image side prism having an entrance surface on which light passed through the imaging lens group is incident, a reflection surface from which the light passed through the entrance surface reflects, and an exit surface from which the light reflected from the reflection surface exits toward the image pickup device located at a predetermined position;
• and
• a first shielding member formed to shield at least a part of a region on the entrance surface of the image side prism, wherein the region on the entrance surface is located from an edge line of an apex between the entrance surface and the exit surface to a position corresponding to a height h from the edge line,
• wherein when L represents a length of the exit surface defined in a cross sectional plane orthogonal to both of the entrance surface and the exit surface, α represents an angle formed in the cross sectional plane between the reflection surface and the exit surface, n represents a refractive index of a surrounding area of the image side prism, and n′ represents a refractive index of the image side prism, the height h satisfies a following condition (1):
• h=L×cos {α+sin−1(n/n′)} (1).
• wherein the image pickup device is arranged such that a sensor surface of the image pickup device is positioned on an image plane of the imaging optical system.