1. Field of the Invention
The present invention relates to a zoom lens. More particularly, the invention relates to a photographic optical system used for an image pickup apparatus such as a video camera, a digital still camera, a broadcast camera, and a silver-halide film camera.
2. Description of the Related Art
A photographic optical system used for an image pickup apparatus is required to ensure a high zoom ratio, miniaturize the entire size, and particularly provide a zoom lens capable of reducing the camera thickness. A retractable zoom lens is known to miniaturize the camera size and ensure a high zoom ratio. During a non-photographing state, the retractable zoom lens retracts lens units into a camera body by reducing a distance between the lens units so that the reduced distance differs from the distance used for photographing. Additionally, an optical-path-bending zoom lens is known to reduce the camera thickness. The optical-path-bending zoom lens includes a reflective member in an optical path. The reflective member includes a reflecting prism that reflects an optical axis at 90 degrees in the photographic optical system.
Furthermore, a retractable optical-path-bending zoom lens is known as a combination of both systems. During the non-photographing state, the reflective member moves to leave a space to retract the lens unit located at the object side of the reflective member.
A retractable zoom lens may be provided with a reflective member that reflects the optical path of the photographic optical system. Such a retractable zoom lens can easily ensure a high zoom ratio and reduce the camera thickness if used for a camera. For achieving these effects, however, it is important to appropriately configure the zoom lens, the reflective member, and the arrangement in the optical path.
Zoom lenses discussed in U.S. Pat. No. 7,692,869 and Japanese Patent Application Laid-Open No. 2007-293052 include, in order from an object side to an image side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, and a rear lens group including a plurality of lens units. The second lens unit contains the reflective member for reflecting the optical path. The second lens unit is fixed during zooming. During non-photographing, the reflective member and lens units located the image side thereof are moved toward the image plane. A space is thereby ensured and is used to store a lens unit located on the object side of the reflective member.
However, the zoom lenses discussed in U.S. Pat. No. 7,692,869 and Japanese Patent Application Laid-Open No. 2007-293052 provide the second lens unit with a low refractive power. Thus, zooming increases the amount of movement of the first lens unit, making it difficult to ensure a high zoom ratio. For ensuring a high zoom ratio and miniaturizing the entire camera, the retractable optical-path-bending zoom lens requires an appropriate lens configuration, such as the number of lens units, allocation of refractive powers to the lens units, and movement conditions of the lens units during zooming. Moreover, the reflective member needs to have an appropriate length in the optical axis direction and needs to be appropriately positioned in the optical path. These configurations need to be appropriately taken into consideration to achieve the above-mentioned effects.