A zoom optical system according to an embodiment of the present invention includes a first lens group, a second lens group, a third lens group, and a fourth lens group which are sequentially disposed in a direction from an object side to an image side, wherein the second lens group and the third lens group are movable, a total track length (TTL) is less than 20 mm, and an effective focal length (EFL) in a telephoto is greater than 25 mm.

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.

A zoom optical system according to an embodiment of the present invention includes a first lens group, a second lens group, a third lens group, and a fourth lens group which are sequentially arranged in a direction from a subject side to an image side, wherein the second lens group and the third lens group are movable, and an effective focal length (EFL) in a telephoto mode is defined by an expression below.

[00001]$11.5<\frac{{\mathrm{EFL}}_{\mathrm{tele}}}{H_{\mathrm{imageD}}}<12.5$

Here, EFL.sub.tele is the EFL of the zoom optical system in the telephoto mode, and tele H.sub.imageD is a half value of a diagonal length of a pixel area of an image sensor.

A lens assembly includes a first lens group, a second lens group, a third lens group, a fourth lens group, and a reflective element. The first lens group is with refractive power. The second lens group is with positive refractive power. The third lens group is with positive refractive power. The fourth lens group is with refractive power. The reflective element includes a reflective surface. A light from an object sequentially passes through the first lens group, the second lens group, the third lens group, and the fourth lens group to an image side along an axis. The reflective element is disposed between an object side and the image side along the axis. Intervals of the lens groups are changeable when the lens assembly zooms from a wide-angle end to a telephoto end.

A zoom optical system according to an embodiment of the present invention comprises a first lens group, a second lens group, a third lens group, and a fourth lens group which are successively arranged from an object side to an image side, wherein the first lens group to the fourth lens group each comprise two lenses, wherein the second lens group and the third lens group are movable, and wherein the telephoto effective focal length (EFL) is defined by the mathematical expression below:

[00001]$9.0<\frac{{\mathrm{EFL}}_{\mathrm{tele}}}{H_{\mathrm{imageD}}}<9.5$ where, EFL.sub.tele refers to the effective focal length of the zoom optical system in the telephoto, and H.sub.imageD refers to a value of half a diagonal length of an image sensor pixel area.

A zoom optical system according to an embodiment of the present invention comprises a first lens group, a second lens group, a third lens group, and a fourth lens group which are sequentially arranged in a direction from a subject side to an image side, wherein each of the first lens group to the fourth lens group includes at least two lenses, the second lens group and the third lens group are movable, and an effective focal length (EFL) in a wide angle mode is defined by an expression below.

[00001]$5.5<\frac{{\mathrm{EFL}}_{\mathrm{wide}}}{H_{\mathrm{image}D}}<6.5.$

Here, EFL.sub.wide is the EFL of the zoom optical system in the wide angle mode, and H.sub.imageD is a half value of a diagonal length of a pixel area of an image sensor.

An optical apparatus that is capable of improving impact resistance thereof. A holding member holding the optical element is movably attached to a first member so that the optical element is movable between an entering position where the optical element enters into an optical path and a retracted position where the optical element is retracted from the optical path. The first member is movably attached to a second member. A driving member engages with the holding member and drives the holding member. A regulation member regulates a moving amount of the first member with respect to the second member. The regulation member is arranged so that a distance from an engagement position of the holding member and the driving member at the entering position to the regulation member is longer than a distance from the engagement position at the retracted position to the regulation member.

A lens unit L100 is removably mounted on an image pickup apparatus generating control information used for a vibration control that vibrates a correction lens L105 and moves a vibration center of the correction lens L105, includes an image pickup optical system including a magnification varying lens L102 and the correction lens L105, a storage unit storing first information indicating a relation between positions of the magnification varying lens L102 and the correction lens L105, and a lens controller performing a predetermined control in which the correction lens L105 moves in accordance with the movement of the magnification varying lens L102, and the lens controller sends information relating to the magnification varying operation to the image pickup apparatus, and overlaps the vibration control of the correction lens L105 based on the control information in accordance with the information relating to the magnification varying operation with the predetermined control.

A zoom lens includes a first lens group and a second lens group. A relative movement between the first lens group and the second lens group is allowed, whereby the zoom lens zooms between a wide-angle end and a telephoto end. While the zoom lens is switched from the wide-angle end toward an intermediate state, the first lens group is moved toward the image side. While the zoom lens is switched from the intermediate state toward the telephoto end, the first lens group is moved toward the object side.

An image lens assembly includes four lens groups: a first lens group, a second lens group, a third lens group and a fourth lens group along an optical path. The four lens groups include nine lens elements: a first lens element with positive refractive power, a second lens element with negative refractive power, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element, a seventh lens element, an eighth lens element and a ninth lens element along the optical path. At least one lens element of the image lens assembly has at least one inflection point. At least five lens elements of the image lens assembly are made of plastic material. When focusing or zooming, the first lens group and the fourth lens group stay stationary, while the second lens group and the third lens group move along an optical axis.