A variable magnification optical system consists of, in order from an object side to an image side, a first lens group, a second lens group, and a subsequent lens group. The variable magnification optical system satisfies a predetermined conditional expression for a partial dispersion ratio related to F line, C line, and a wavelength of 1970.09 nm, a d-line back focus of the variable magnification optical system at a telephoto end, a back focus in any one wavelength from a wavelength of 1300 nm to a wavelength of 2325.42 nm at the telephoto end, and a d-line focal length of the variable magnification optical system at the telephoto end.

A lens barrel includes one or more movable lens groups, and a cam barrel associated with the one or more movable lens groups and configured to balance a center of gravity of the one or more movable lens groups.

An optical system includes, in order from an object side to an image side, a first lens unit fixed during focusing, a second lens unit having a positive refractive power, configured to move during focusing, a third lens unit having a negative refractive power, configured to move during focusing, and a fourth lens unit fixed during focusing. During focusing from infinity to a short distance end, the second lens unit and the third lens unit move to the object side while a distance between the second lens unit and the third lens unit changes. A predetermined condition is satisfied.

An interchangeable lens attachable to a camera body, the interchangeable lens including: a focusing optical system configured to vary a focal position of the interchangeable lens; and a transmitter configured to transmit a first value and a second value to the camera body, the first value indicating a relationship between an amount of movement of the focusing optical system and an amount of movement of an image plane at a position to which the focusing optical system has moved, the second value indicating a relationship between an amount of movement of the focusing optical system and an amount of movement of the image plane, the second value being equal to or smaller than the first value.

A lens apparatus that can secure a necessary lens moving distance while avoiding growing in size and that is able to firmly hold a lens. The lens apparatus comprises a first lens group holding member, a second lens group holding member, an exterior cylinder disposed on an outer peripheral side of the first lens group holding member, a first cam cylinder disposed to be rotatable around an optical axis and movable in an optical axis direction corresponding to a rotation angle, a guide cylinder having a diameter fitting portion rotatably holding the first cam cylinder around the optical axis, and a second cam cylinder. The exterior cylinder does not have a cam groove or a guide groove for guiding another member, and is driven to a position at which part of the exterior cylinder is exposed to an outside corresponding to a rotation angle of the second cam cylinder.

An interchangeable lens attachable to a camera body, the interchangeable lens including: a focusing optical system configured to vary a focal position of the interchangeable lens; and a transmitter configured to transmit a first value and a second value to the camera body, the first value indicating a relationship between an amount of movement of the focusing optical system and an amount of movement of an image plane at a position to which the focusing optical system has moved, the second value indicating a relationship between an amount of movement of the focusing optical system and an amount of movement of the image plane, the second value being equal to or smaller than the first value.

A lens barrel which prevents an increase in driving force for optical units in a direction of an optical axis to downsize a power transmission mechanism, save power and also prevents undesired movement of the optical units even when they are urged by urging forces large enough to prevent rattling. The optical units move in the direction of the optical axis, and they are urged by urging member in the direction of the optical axis. A camshaft provided on outer peripheries of the optical units extends in the direction of the optical axis and is cam-engaged with each of the optical units. The power transmission mechanism transmits driving force, which is for rotating the camshaft, to the camshaft. A torque generated in the camshaft by the urging member urging one of the optical units and another torque generated in the camshaft by the urging member urging another one of the optical units are opposite in direction.

Disclosed herein is an optical imaging lens group, including, in order from an object side to an image side along an optical axis: a first lens group having a refractive power, in which an image side surface of a lens closest to an imaging side is concave; a second and a third lens group having a refractive power; and a fourth lens group having a negative refractive power, in which an image side surface of a lens closest to the imaging side is concave and includes at least one inflection point, wherein the first lens group is a fixed group, and the second, third and fourth lens groups move on the optical axis to realize continuous zoom from a wide-angle end to a telephoto end; and an on-axis distance TTL and an effective focal length ft of the optical imaging lens group at the telephoto end satisfy: 0.8<TTL/ft<1.5.

A zoom lens forms an intermediate image at a position conjugate to a reduction side imaging plane and forms the intermediate image again on a magnification side imaging plane. The zoom lens includes a plurality of lens groups including at least two movable lens groups, which move by changing spacings between the groups adjacent to each other in a direction of an optical axis during zooming, at a position closer to the reduction side than the intermediate image. Among the plurality of lens groups, a final lens group closest to the reduction side has a positive refractive power, and remains stationary with respect to the reduction side imaging plane during zooming. The zoom lens satisfies predetermined conditional expressions (1) and (2) about the focal lengths of the movable lens groups.

A projection optical device includes a fourth lens group movable along an optical axis, a fifth lens group provided in a position maintained within the projection optical device, a fourth lens frame holding the fourth lens group and having cam pins, a guide tube having a rectilinear groove, the cam pins inserted into the rectilinear groove, and a cam tube rotated with respect to the guide tube to guide the cam pins with the rectilinear groove and the cam groove, and moving the fourth lens frame along the optical axis, wherein the cam pins are formed on an upstream side in an optical path of the fourth lens group in a direction along the optical axis, and the fifth lens group is provided on the upstream side in the optical path of the fourth lens group.