Wide-angle optical system, image pickup apparatus, and image pickup system

A wide-angle optical system comprising:

• at least a pair of front side lens units, each of the pair of front side lens units has a negative refractive power;
• an optical member comprising:
• at least a pair of planar inclined surfaces disposed such that a line intersecting the at least pair of planar inclined surfaces is formed on an object side;
• and
• a bottom surface;
• and
• at least a pair of rear side lens units, each of the at least pair of rear side lens units includes at least one positive lens positioned on an axis of rotational symmetry, and the axis of rotational symmetry for each of the at least pair of rear side lens units are parallel to each other;
• wherein the wide-angle optical system has at least two optical paths,
• intersection of two light rays and reflection of the two light rays occur at the optical member,
• the intersection and the reflection occur after the two light rays are transmitted through the pair of planar inclined surfaces and before the two light rays are transmitted through the bottom surface, and
• following conditional expression (1) is satisfied:
• 2 mm<HB<10 mm (1)
• where,
• HB denotes a length in a transverse direction of the bottom surface, where
• the transverse direction is a direction orthogonal to the axis of rotational symmetry of each of the at least pair of rear side lens units.