| CPC G02B 9/14 (2013.01) [G02B 7/021 (2013.01); G02B 9/16 (2013.01); G03B 17/14 (2013.01); H04N 23/12 (2023.01); H04N 23/64 (2023.01)] | 20 Claims |

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1. An imaging optical system consisting of:
a first lens group having positive power;
a second lens group having negative power; and
a third lens group having positive power,
the first lens group, the second lens group, and the third lens group being arranged in this order such that the first lens group is located closer to an object than any other lens group of the imaging optical system is,
the first lens group and the third lens group being fixed with respect to an image plane, with the second lens group moving along an optical axis, while the imaging optical system is focusing to make a transition from an infinity in-focus state toward a close-object in-focus state,
the first lens group consisting of:
a sub-lens group G1A;
an aperture stop; and
a sub-lens group G1B,
the sub-lens group G1A, the aperture stop, and the sub-lens group G1B being arranged in this order such that the sub-lens group G1A is located closer to the object than the aperture stop or the sub-lens group G1B is,
the sub-lens group G1A including, as a plurality of lenses:
a lens L1A1 having negative power and disposed closest to the object in the plurality of lenses;
a lens L1A2 having negative power and disposed second closest to the object in the plurality of lenses; and
a lens L1A3 having negative power and disposed third closest to the object in the plurality of lenses.
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