The invention relates to an electronic image pickup system whose depth dimension is extremely reduced, taking advantage of an optical system type that can overcome conditions imposed on the movement of a zooming movable lens group while high specifications and performance are kept. The electronic image pickup system comprises an optical path-banding zoom optical system comprising, in order from its object side, a 1-1st lens group G1-1 comprising a negative lens group and a reflecting optical element P for bending an optical path, a 1-2nd lens group G1-2 comprising one positive lens and a second lens group G2 having positive refracting power. For zooming from the wide-angle end to the telephoto end, the second lens group G2 moves only toward the object side. The electronic image pickup system also comprises an electronic image pickup device I located on the image side of the zoom optical system.

A projection optical system includes: a plurality of lenses; a lens frame that holds at least one lens of the plurality of lenses; a first diaphragm provided on the light incident side of the lens frame; and a second diaphragm provided on the light exiting side of the lens frame.

There is provided an optical imaging system including a prism, a first fixed lens group, a first movable lens group, a second movable lens group, and a second fixed lens group. The prism is configured to refract light reflected from an object side toward an imaging plane and a reflecting member. The prism is disposed on the first fixed lens group and the first movable lens group is configured to change a position of the imaging plane so that an overall focal length is changed. The second movable lens group is configured to adjust a position of the imaging plane so that a focal length for an object is adjusted. The imaging plane is disposed on the second fixed lens group.

A rear converter lens consists of three lens groups of, in order from its object-side, a first lens-group having positive refractive power; a second lens-group having negative refractive power; and a third lens-group having positive refractive power. The first lens-group consists of a cemented lens of a negative lens having a concave surface facing an image-side of the rear converter lens and a positive lens cemented together in order from the object-side. The second lens-group consists of a cemented lens of a negative lens, a lens having a biconvex shape, and a negative lens cemented together in order from the object-side. The third lens-group includes a lens having a convex surface facing the object-side furthest toward the object-side. When the focal length of the third lens-group is f3 and the focal length of the rear converter lens is cf, conditional expression (1) (1.9<f3/cf<0.4) is satisfied.

An image capture apparatus and a zoom lens are provided. The zoom lens in accordance with an exemplary embodiment of the invention includes a mount, a guide unit, a plurality of lens groups and a driving device. The guide unit is disposed in the mount in a first direction. The lens groups are disposed in the mount and include at least one movable lens group which can be moved along the guide unit. The driving device is configured for driving the movable lens group. The driving device includes magnets and coils. The magnets are fixed to one of the movable lens group and the mount, while the coils are fixed to the other of the movable lens group and the mount. The magnets and/or the coils are arranged in the first direction.

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.

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: $9.0<\frac{{\mathrm{EFL}}_{\mathrm{tele}}}{H_{\mathrm{imageD}}}<9.5$ 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. $5.5<\frac{{\mathrm{EFL}}_{\mathrm{wide}}}{H_{\mathrm{image}D}}<6.5.$
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.

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. $11.5<\frac{{\mathrm{EFL}}_{\mathrm{tele}}}{H_{\mathrm{imageD}}}<12.5$
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.