1. Field of the Invention
The present invention relates to a zoom lens. More specifically, the present invention relates to a zoom lens used for an image projection apparatus, such as a liquid crystal projector.
2. Description of the Related Art
It is desired that a conventional zoom lens used for an image projection apparatus, such as a liquid crystal projector, have a long back focal distance and a wide angle of view so that a large size image can be projected at a short distance. Various zoom lenses (variable-power projection lenses for an image projection apparatus) have been proposed, which can project a large size image at a short distance.
Japanese Patent Application Laid-Open No. 2003-015037, Japanese Patent Application Laid-Open No. 2003-015038, and Japanese Patent Application Laid-Open No. 2005-077548 each discuss a zoom lens including first through sixth lens units having negative, positive, positive, negative, positive, and positive refractive powers, respectively, in order from an enlargement side (i.e., from the front side (projection plane side)) to a reduction side (i.e., the rear side (liquid crystal display element side). Furthermore, Japanese Patent Application Laid-Open No. 2004-252084 discusses a zoom lens including first through fifth lens units having negative, positive, positive, negative, and positive refractive powers, respectively, in order from the enlargement side.
In the zoom lens discussed in each of Japanese Patent Application Laid-Open Nos. 2003-015037, 2003-015038, 2005-077548, and 2004-252084, a lens unit closest to the enlargement side and a lens unit closest to the reduction side are stationary during zooming. Additionally, the zoom lens is telecentric on the reduction side. However, the above-described conventional zoom lens cannot respond to a growing desire for achieving a wider angle of view.