1. Field of the Invention
The present invention relates to a zoom lens suitable for a television camera, a motion-picture camera, a video camera, a photography camera, and a digital camera, and more particularly, to a zoom lens having a high magnification, a small size and light weight, and little aberration deviation due to focus adjustment, and to an image pickup apparatus including the zoom lens.
2. Description of the Related Art
Conventionally, as for a zoom lens in which focus adjustment is performed by a lens unit disposed closer to an object side with respect to a magnification-varying lens unit, there are proposed various types of systems.
For instance, Japanese Patent Application Laid-Open No. 2004-309761 discloses a zoom lens in which a focus lens unit having positive refractive power as a whole includes, in order from an object side, a first lens unit having negative refractive power, a second lens unit having negative refractive power, and a third lens unit having positive refractive power. In addition, Japanese Patent Application Laid-Open No. 2004-309761 proposes a method in which the second lens moves to the object side in focus adjustment to an object at a short distance.
In addition, Japanese Patent Application Laid-Open No. 2004-85846 discloses a zoom lens in which a focus lens unit having positive refractive power as a whole includes, in order from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, and a third lens unit having positive refractive power. Further, Japanese Patent Application Laid-Open No. 2004-85846 proposes a method in which the third lens unit moves to the object side in focus adjustment to an object at a short distance.
The zoom lens used for a television camera, a motion-picture camera, or the like is desired to achieve a higher magnification as well as a small size and light weight in order to secure mobility and to improve flexibility of photography. In addition, the zoom lens is required to have high performance with little aberration deviation due to focus adjustment.
The focus adjustment method of Japanese Patent Application Laid-Open No. 2004-309761 is suitable for a wide-angle zoom lens, but is difficult to achieve a high magnification. In the disclosed embodiment, a zoom ratio is approximately three. In order to achieve a high magnification, a diameter or an entire length of the first lens unit is increased.
The focus adjustment method of Japanese Patent Application Laid-Open No. 2004-85846 is suitable for a telephoto zoom lens, but is difficult to achieve a high magnification. In the disclosed embodiment, a zoom ratio is approximately 2.5. In order to achieve a high magnification, a diameter or an entire length of the first lens unit is increased.