An attachment optical system includes a first converter optical system attachable to an object side of an imaging optical system, and a second converter optical system attachable to an image side of the imaging optical system. The first converter optical system includes a dome-shaped cover and at least one positive lens. A predetermined condition is satisfied.

An attachment optical system includes a first converter optical system attachable to an object side of an imaging optical system, and a second converter optical system attachable to an image side of the imaging optical system. The first converter optical system includes a dome-shaped cover and at least one positive lens. A predetermined condition is satisfied.

An optical apparatus includes a display that displays an image, and an optical system that includes a filter (a reflective polarizing plate) and a lens (a half mirror surface) arranged on a downstream side and an upstream side, respectively, on an optical axis L of a display and magnifies the image by at least the lens (half mirror surface). The optical apparatus drives the lens along the optical axis L with respect to the filter by a mobile device, or changes the surface shape or the lens power of the lens having a variable surface shape or variable lens power. Thus, the optical path is folded back twice between the filter and the lens of the optical system, and the image is magnified by the lens (the half mirror surface), so that the position of the magnified virtual image can be adjusted according to the diopter of the user.

An optical apparatus includes a display that displays an image, and an optical system that includes a filter (a reflective polarizing plate) and a lens (a half mirror surface) arranged on a downstream side and an upstream side, respectively, on an optical axis L of a display and magnifies the image by at least the lens (half mirror surface). The optical apparatus drives the lens along the optical axis L with respect to the filter by a mobile device, or changes the surface shape or the lens power of the lens having a variable surface shape or variable lens power. Thus, the optical path is folded back twice between the filter and the lens of the optical system, and the image is magnified by the lens (the half mirror surface), so that the position of the magnified virtual image can be adjusted according to the diopter of the user.

An extender lens changes a focal length of an entire lens system after replacement to a longer focal length side than a focal length of a master lens by replacing a part of the master lens with the extender lens. The extender lens consists of, in order from an object side to an image side, a first lens group, and a negative second lens group. The first lens group is a lens group that has a positive refractive power as a whole and has a shortest focal length among lens groups consisting of one lens component or a plurality of consecutively arranged lens components. The extender lens satisfies a predetermined conditional expression.

An optical system includes, in order from an object side toward an image side, a first lens unit having positive refractive power, and a second lens unit having negative refractive power. A distance between consecutive ones of the lens units changes when focusing is performed. The first lens unit is stationary during focusing. The second lens unit is moved toward the image side when focus is changed from an object at infinity to an object at a short distance. Lateral magnification β2 of the second lens unit when focusing on the object at infinity, focal length f1 of the first lens unit, and focal length f2 of the second lens unit are set appropriately to satisfy predetermined mathematical conditions.

An optical system includes, in order from an object side toward an image side, a first lens unit having positive refractive power, and a second lens unit having negative refractive power. A distance between consecutive ones of the lens units changes when focusing is performed. The first lens unit is stationary during focusing. The second lens unit is moved toward the image side when focus is changed from an object at infinity to an object at a short distance. Lateral magnification β2 of the second lens unit when focusing on the object at infinity, focal length f1 of the first lens unit, and focal length f2 of the second lens unit are set appropriately to satisfy predetermined mathematical conditions.

A rear conversion lens, which may include a plurality of lenses may be disposed at a side of master lenses facing an image side for varying a focal length, and may include: a first lens having a positive refractive power; a second lens having a biconcave shape; a third lens having a positive refractive power; a fourth lens having a positive refractive power; and a fifth lens having a negative refractive power. The first to fifth lenses may be sequentially arranged in a direction from an object side to the image side.

A zoom lens is provided which has at least one front optical group with fixed optical power, adapted to receive rays from an observed object, at least one rear optical group with fixed optical power, adapted to convey the rays towards an image plane of a sensor, a lens opening positioned between the front optical group and the rear optical group, a front adaptive lens positioned between the at least one front optical group and the lens opening, and a rear adaptive lens positioned behind the lens opening. The front and rear adaptive lenses are controllable to vary the respective optical power to adjust focal length, magnification, and working distance of the zoom lens.

A rear attachment lens according to the aspect of the embodiments is configured to vary a focal length of a system by being attached to an image side of a master lens. The rear attachment lens includes a positive lens arranged closest to the image side in which a lens surface on the image side of the positive lens has a shape convex toward the image side. A focal length of the rear attachment lens, a magnification of the rear attachment lens when attached to the master lens, and a distance from the lens surface on the image side of the positive lens to a rear principal point position of the rear attachment lens when attached to the master lens are appropriately set.