An ultra wide angle imaging optical system includes, in order from an object side, a first lens group, an aperture stop, and a second lens group. The first lens group includes, in order from the position closest to the object side, a negative meniscus lens element convex to the object side, a negative lens element, and a negative lens element. The second lens group includes a plurality of positive lens elements. The first lens group and the second lens group each includes at least one anamorphic surface having different optical powers with respect to a first section extending in a first direction on a flat plane substantially orthogonal to an optical axis, and with respect to a second section extending in a second direction substantially orthogonal to the first direction. The first lens group includes the lens element satisfying the following conditional formula (1): ?in-line-formulae description="In-line Formulae" end="lead"?-0.6(Ph-Pv)*(fh+fv)-0.1 (1)?in-line-formulae description="In-line Formulae" end="tail"? where Ph: an optical power in the first direction where a viewing angle is large; Pv: an optical power in the second direction where the viewing angle is small; fh: a focal length in the first direction with respect to the entirety of the optical system; and fv: a focal length in the second direction with respect to the entirety of the optical system.
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