A zoom lens has, in order from an object side, a focusing unit including a focusing lens group moving for focusing, a variable magnification unit including at least two variable magnification lens groups moving while changing a mutual interval for variable magnification, an aperture stop, and an image forming unit including an image forming lens group. The image forming unit consists of, in order from the object side, an M1 lens group, an M2N lens group, and an M3 lens group. The M2N lens group is replaceable with an M2E lens group that enlarges an image forming magnification. The M2E lens group satisfies predetermined conditional expressions (1) to (4).

A reduction optical system disposed on an image side of a main optical system, a composite focal length of the main optical system and the reduction optical system being shorter than a focal length of the main optical system, includes a first lens element disposed closest to an object side and having a positive refractive power, a second lens element disposed closest to an image side and having a positive refractive power, and a positive lens and a negative lens disposed between the first lens element and the second lens element.

In a converter device that is attached between a lens device, which is attachable to and detachable from an image capturing apparatus, and the image capturing apparatus, and that has a reimaging optical system configured to reimage a primary image formed by the lens device on an image plane as a secondary image, the imaging magnification of the reimaging optical system and imaging positions of a primary image and a secondary image are appropriately set.

In a converter device that is attached between a lens device, which is attachable to and detachable from an image capturing apparatus, and the image capturing apparatus, and that has a reimaging optical system configured to reimage a primary image formed by the lens device on an image plane as a secondary image, the imaging magnification of the reimaging optical system and imaging positions of a primary image and a secondary image are appropriately set.

A system for adjusting an optical path length includes a camera body having a camera body opening, an image sensor coupled to the camera body, and an optical device movably coupled to the camera body. The movable coupling of the optical device to the camera body includes a first coupling position of the optical device relative to the camera body and a second coupling position of the optical device relative to the camera body. In the first coupling position, the optical device is located at a position that intersects a path between the image sensor and the camera body opening. In the second coupling position of the optical device, the optical device is located at a position that does not intersect the path between the image sensor and the camera body opening.

An image pickup apparatus includes: a mount to which an interchangeable lens is mountable; an image sensor; an optical system having a refractive power and imaging an object point located on an image side of a most-object-side surface of the optical system onto the image sensor; and an optical filter arranged between the optical system and the image sensor, and a distance on an optical axis from a flange surface of the mount to the object point located on the image side of the most-object-side surface, a distance on the optical axis from the flange surface of the mount to the image pickup element, and a lateral magnification of the optical system when the interchangeable lens is mounted to the image pickup apparatus and the object point located on the image side of the most-object-side surface, is imaged onto the image pickup element, are appropriately set.

An image pickup apparatus includes: a mount to which an interchangeable lens is mountable; an image sensor; an optical system having a refractive power and imaging an object point located on an image side of a most-object-side surface of the optical system onto the image sensor; and an optical filter arranged between the optical system and the image sensor, and a distance on an optical axis from a flange surface of the mount to the object point located on the image side of the most-object-side surface, a distance on the optical axis from the flange surface of the mount to the image pickup element, and a lateral magnification of the optical system when the interchangeable lens is mounted to the image pickup apparatus and the object point located on the image side of the most-object-side surface, is imaged onto the image pickup element, are appropriately set.

An image pickup apparatus includes: a mount to which an interchangeable lens is mountable; an image sensor; an optical system having a refractive power and imaging an object point located on an image side of a most-object-side surface of the optical system onto the image sensor; and an optical filter arranged between the optical system and the image sensor, and a distance on an optical axis from a flange surface of the mount to the object point located on the image side of the most-object-side surface, a distance on the optical axis from the flange surface of the mount to the image pickup element, and a lateral magnification of the optical system when the interchangeable lens is mounted to the image pickup apparatus and the object point located on the image side of the most-object-side surface, is imaged onto the image pickup element, are appropriately set.

An image pickup apparatus includes: a mount to which an interchangeable lens is mountable; an image sensor; an optical system having a refractive power and imaging an object point located on an image side of a most-object-side surface of the optical system onto the image sensor; and an optical filter arranged between the optical system and the image sensor, and a distance on an optical axis from a flange surface of the mount to the object point located on the image side of the most-object-side surface, a distance on the optical axis from the flange surface of the mount to the image pickup element, and a lateral magnification of the optical system when the interchangeable lens is mounted to the image pickup apparatus and the object point located on the image side of the most-object-side surface, is imaged onto the image pickup element, are appropriately set.

Provided is a rear converter optical system which is detachably mounted on an image side of a main lens system to increase a focal length of the main lens system, in which an effective diameter im of an imaging area of the main lens system, an effective diameter cr of a lens surface closest to the image side of the rear converter optical system, a lateral magnification c of the rear converter optical system in the case where the rear converter optical system is mounted on the main lens system, a backfocus skc in the case where the rear converter optical system is mounted on the main lens system are appropriately set.