1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus. In particular, the present invention relates to a technical field of a rear focus zoom lens having a high zoom ratio and of an image pickup apparatus including the zoom lens.
2. Description of the Related Art
In recent years, a compact image pickup apparatus, such as a digital video camera or a digital still camera, has become popular. Such an image pickup apparatus is desired to be reduced in size. Owing to this, it is demanded to reduce the whole length of a photographic lens, more particularly, a zoom lens. In addition, it is demanded to increase a lens performance of the photographic lens to meet increase in the number of pixels of an image pickup device.
As an example of such a zoom lens capable of being reduced in size and increased in lens performance may be a rear focus zoom lens in which lens groups other than a first lens arranged at the most object side are moved for focusing. The whole lens system of the rear focus zoom lens is easily reduced in size, and the rear focus zoom lens can provide an image forming performance suitable for the image pickup device with a large number of pixels.
An exemplary rear focus zoom lens includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power, in that order from the object side. In the rear focus zoom lens, for example, the second lens group and the fourth lens group are moved in an optical-axis direction for zooming, and the fourth lens group is moved for focusing (for example, see Japanese Patent No. 3015192).
As the above-described rear focus zoom lens, a zoom lens has been suggested which has a bending optical system to reduce the front-rear length of the zoom lens by bending an optical path between the first lens group and an image plane.
An exemplary four-lens-group zoom lens with the bending optical system includes, for example, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, in that order from the object side (for example, see Japanese Unexamined Patent Application Publication No. 2000-131610).
The zoom lens disclosed in Japanese Unexamined Patent Application Publication No. 2000-131610 performs zooming by moving the second lens group and the fourth lens group in an optical-axis direction. The first lens group includes a first lens which is a single lens having a negative refractive power, an optical member (prism) for bending the optical path, and a second lens which is a single lens having a positive refractive power, in that order from the object side.
An exemplary five-lens-group zoom lens with the bending optical system includes, for example, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power, in that order from the object side (for example, see Japanese Unexamined Patent Application Publication No. 2004-354871).
The zoom lens disclosed in Japanese Unexamined Patent Application Publication No. 2004-354871 performs zooming by moving the second lens group and the fourth lens group in an optical-axis direction. The first lens group includes a first lens which is a single lens having a negative refractive power, an optical member (prism) for bending the optical path, and a second lens which is a single lens having a positive refractive power, in that order from the object side.
USPTO Backgrounds
USPTO Backgrounds