Conventional image pickup (image capturing) apparatuses such as digital cameras and digital video cameras are now in wide use by consumer households. There has therefore in recent years developed a strong desire that image pickup apparatuses be made smaller without sacrificing optical performance. Because a zoom lens mounted on an image pickup apparatus is, in particular, a proportionally large element in the image pickup apparatus, miniaturization of the zoom lens very significantly influences miniaturization of the overall image pickup apparatus. For that reason, a number of techniques relating to the miniaturization of the zoom lens have been proposed.
As one example, Japanese Patent Laid-Open Publication No. 2003-202500 discloses a zoom lens whose light path is bent by an optical element such as a prism to reduce its overall length. This zoom lens includes first to fourth lens groups having refractive powers of positive, negative, positive, and positive, in order from an object side, wherein the first lens group includes a single lens having negative refractive power, the prism for bending the light path and a single lens having positive refractive power. This zoom lens performs zoom operation by movement of the second and fourth lens groups.
Japanese Patent Laid-Open Publication No. 2004-354869 also discloses a zoom lens including an optical element for bending the light path. This zoom lens includes first to fifth lens groups having refractive powers of positive, negative, positive, positive and negative, in order from the object side, wherein the first lens group includes the prism for bending the light path. This zoom lens performs zooming by moving the second and fourth lens groups and performs focusing by moving one of the fourth and fifth lens groups.
The techniques according to Japanese Patent Laid-Open Publication No. 2003-202500 and Japanese Patent Laid-Open Publication No. 2004-354869 can significantly reduce the overall length of the zoom lens. However, both the techniques of Japanese Patent Laid-Open Publication No. 2003-202500 and Japanese Patent Laid-Open Publication No. 2004-354869 perform zooming by moving the second and fourth lens groups. With such a configuration, it is necessary to move one or both of the second and fourth lens groups nonlinearly, which introduces a problem that movement control and a movement mechanism of the lens groups become complicated.
From their disclosures, it is clear that Japanese Patent Laid-Open Publication No. 2003-202500, and Japanese Patent Laid-Open Publication No. 2004-354869 all focus on improvement in performance capabilities in regards to zooming, but neglect consideration of improvement in performance capabilities in regards to focusing. More specifically, Japanese Patent Laid-Open Publication No. 2003-202500 nowhere refers to the focusing operation, while Japanese Patent Laid-Open Publication No. 2004-354869 simply states that the fourth or fifth lens group is moved during focusing, without anywhere describe the specific contents thereof. No reference shows any consideration given to improving the form of a lens group capable of improving focusing characteristics such as, for example, imaging performance and focusing speed.