Binoculars and an ocular lens have an excellent optical performance. Binoculars include: a first lens-barrel and a second lens-barrel having an objective lens and an ocular lens; and an Abbe-Koenig prism which is an erecting optical element included in the first lens-barrel and the second lens-barrel, and is characterized in that the product of an effective diameter (mm) of the objective lens and the real field of view () is 450 mm or larger.

Provided is a zoom lens including: a lens unit Ln1 having a negative refractive power; a lens unit Ln2 having a negative refractive power; a lens unit Lp1 having a positive refractive power; and a rear lens group including one or more lens units, the lens unit Ln1, the lens unit Ln2, the lens unit Lp1, and the rear lens group being successively arranged in order from an object side to an image side, in which the lens unit Ln1 and the lens unit Lp1 are moved along the same locus during zooming, and in which the lens unit Ln2 is moved toward the object side during focusing from infinity to proximity.

An imaging optical system includes: a first lens group having negative power; a second lens group having positive power; a third lens group having negative power; and a fourth lens group having power, which are arranged in this order such that the first lens group is located closest to an object and the fourth lens group is located closest to an optical image. The first lens group includes: a first negative lens; a second negative lens; and a third negative lens which is a meniscus lens having negative power and a convex surface facing the optical image, which are arranged in this order such that the first negative lens is located closest to the object and the third negative lens is located closest to the optical image. During focusing from an infinity focus point toward a close focus point, the third lens group moves along an optical axis.

A zoom optical system consists of a first lens group having negative refractive power, a second lens group having positive refractive power, and a rear lens group which are disposed in order from an object. The rear lens group comprises a last lens group and an F lens group in order from a side closest to an image. Lens groups forming the first lens group, the second lens group, and the rear lens group are configured in such a manner that, upon zooming, the respective lens groups move and a distance between the lens groups adjacent to each other changes. At least a part of the F lens group is configured to move upon focusing. Further, the following conditional expression is satisfied.
0.220<f1/fE<0.280
where f1: a focal length of the first lens group, and fE: a focal length of the last lens group.

A zoom optical system consists of a first lens group having negative refractive power, a second lens group having positive refractive power, and a rear lens group which are disposed in order from an object. The rear lens group comprises a last lens group and an F lens group in order from a side closest to an image. Lens groups forming the first lens group, the second lens group, and the rear lens group are configured in such a manner that, upon zooming, the respective lens groups move and a distance between the lens groups adjacent to each other changes. At least a part of the F lens group is configured to move upon focusing. Further, the following conditional expression is satisfied.

0.220<f1/fE<0.280 where f1: a focal length of the first lens group, and fE: a focal length of the last lens group