A zoom optical system comprises, in order from an object: a first lens group (G1) having positive refractive power; a second lens group (G2) having negative refractive power; and a subsequent group (GR) including at least one lens group. Upon zooming, distances between the first lens group (G1) and the second lens group (G2) and between the second lens group (G2) and the subsequent group (GR) change. The subsequent group (GR) comprises a focusing group (Gfc) having negative refractive power for focusing. The first lens group (G1) comprises a 1-1st lens that has positive refractive power and is disposed closest to the object. A following conditional expression is satisfied:
0.20<f1/fR<0.85 where, f1 denotes a focal length of the first lens group, and fR denotes a focal length of a lens component, in the subsequent group, closest to an image surface.

A zoom lens includes, in order from an object side: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group; a fourth lens group having positive refractive power; a fifth lens group having negative refractive power; and a sixth lens group having positive refractive power, wherein, during zooming, an interval between adjacent two lens groups varies among the first lens group, the second lens group, the third lens group, the fourth lens group, the fifth lens group, and the sixth lens group, the sixth lens group includes at least one negative lens, and the following Conditional Expression (1) is satisfied:

0<ft/fl0.42(1) where ft represents a focal length of an entire system at a tele end, and fl represents a focal length of the first lens group.

A zoom lens includes, in order from an object side: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group; a fourth lens group having positive refractive power; a fifth lens group having negative refractive power; and a sixth lens group having positive refractive power, wherein, during zooming, an interval between adjacent two lens groups varies among the first lens group, the second lens group, the third lens group, the fourth lens group, the fifth lens group, and the sixth lens group, the sixth lens group includes at least one negative lens, and the following Conditional Expression (1) is satisfied:

0<ft/fl0.42(1) where ft represents a focal length of an entire system at a tele end, and fl represents a focal length of the first lens group.

A zoom optical system comprises, in order from an object: a first lens group (G1) having positive refractive power; a second lens group (G2) having negative refractive power; and a subsequent group (GR) having at least one lens group. Upon zooming, distances between the first lens group (G1) and the second lens group (G2) and between the second lens group (G2) and the subsequent group (GR) change. The subsequent group (GR) comprises a focusing group (Gfc) having negative refractive power for focusing. The first lens group (G1) comprises a 1-1st lens having positive refractive power and is disposed closest to the object. A following conditional expression is satisfied:
0.85<n1P/n1N<1.00 where, n1P denotes a refractive index of a lens with largest positive refractive power in the first lens group, and n1N denotes a refractive index of a lens with largest negative refractive power in the first lens group.

The imaging lens consists of, in order from the object side, a first positive lens group, a stop, a second positive lens group, and a third negative lens group. During focusing, the first lens group and the second lens group move integrally. The first lens group consists of three or less lenses. The first lens group includes a cemented lens in which a negative lens and a positive lens are cemented in order from the object side. The third lens group consists of, in order from the object side, a negative aspheric lens, a negative lens, and a positive lens. The lens closest to the image side in the second lens group is a biconvex lens, and the imaging lens satisfies a predetermined conditional expression regarding the radius of curvature of the surface of the biconvex lens.

A zoom lens includes a first lens group having negative refractive power; a second lens group having positive refractive power; a third lens group having negative refractive power and a fourth lens group having positive refractive power. Upon varying magnification, distances between the first lens group and the second lens group, between the second lens group and the third lens group and between the third lens group and the fourth lens group vary. The second lens group includes a front lens group, an aperture stop, and a rear lens group. Each of the front lens group and the rear lens group includes at least one positive lens. At least a part of the lenses in the second lens group is moved as a group to have a component in a direction perpendicular to an optical axis.

A zoom optical system (ZL) comprises, in order from an object: a first lens group (G1) having positive refractive power; an intermediate group (GM) including at least one lens group and having negative refractive power as a whole; an intermediate side lens group (GRP1) having positive refractive power; a subsequent side lens group (GRP2) having positive refractive power; and a subsequent group (GR) including at least one lens group. The subsequent side lens group (GRP2) moves upon focusing. A following conditional expression is satisfied:
2.5<f1/fRP1<5.0 where, f1 denotes a focal length of the first lens group (G1), and fRP1 denotes a focal length of the intermediate side lens group (GRP1).

A projection optical system (1) that projects from a first image plane on a reducing side to a second image plane on an enlargement side, including a first refractive optical system (11) that includes eight lenses (L1) to (L8) and forms a first intermediate image (31) on the enlargement side using light that is incident from the reducing side, a second refractive optical system (12) that includes six lenses (L9) to (L14) and forms the first intermediate image (31) on the reducing side into a second intermediate image (32) on the enlargement side, and a first reflective optical system (20) that includes a first reflective surface (21a) with positive refractive power that is positioned closer to the enlargement side than the second intermediate image (32).

A projection optical system (1) that projects from a first image plane on a reducing side to a second image plane on an enlargement side, including a first refractive optical system (11) that includes eight lenses (L1) to (L8) and forms a first intermediate image (31) on the enlargement side using light that is incident from the reducing side, a second refractive optical system (12) that includes six lenses (L9) to (L14) and forms the first intermediate image (31) on the reducing side into a second intermediate image (32) on the enlargement side, and a first reflective optical system (20) that includes a first reflective surface (21a) with positive refractive power that is positioned closer to the enlargement side than the second intermediate image (32).

A solid-state image sensor is provided with a pixel array including a measuring pixel and an imaging pixel, a compression circuit that applies compression processing to a signal obtained by the measuring pixel, and an output circuit that outputs the signal obtained by the measuring pixel and a signal obtained by the imaging pixel. The solid-state image sensor is configured to operate in a first mode in which a signal that is obtained by the measuring pixel and then applied the compression processing is output, and in a second mode in which a signal that is obtained by the imaging pixel and then not applied the compression processing is output.