1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens, and more particularly, to a zoom lens suitable for use in an image pickup apparatus, such as a video camera, an electronic still camera, or an image pickup apparatus such as a camera using a silver-halide film.
2. Description of the Related Art
In recent years, image pickup apparatuses with increased functionality and decreased size have become very appealing. Incidentally, there is an increased demand for a zoom lens having compact size, wide angle of view, high zoom ratio and high resolving power, as an imaging optical system for use in such image pickup apparatuses.
A zoom lens is known in which a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a rear group including at least one lens unit are arranged in order from an object side to an image side. For purposes of the following description, the side of a lens where an object to be imaged is placed is called the object side or front side of the lens; and the side of the lens where the image is formed is called the image side or back side of the lens. Thus, for example, a zoom lens including, in order from the object side to the image side, four lens units having positive, negative, positive, and positive refractive powers is known.
U.S. Pat. No. 7,206,137 discloses a zoom lens having a zoom ratio of 15 or more and an imaging angle of view of 62 degrees at a wide angle end.
U.S. Pat. No. 7,286,304 discloses a zoom lens that includes, in order from the object side to the image side, five lens units having positive, negative, positive, positive, and positive refractive powers.
U.S. Pat. No. 7,177,092 discloses a zoom lens that includes, in order from the object side to the image side, five lens units having positive, negative, positive, positive, and positive refractive powers.
To reduce the size of the entire zoom lens while maintaining a predetermined zoom ratio, the refractive powers (optical powers=reciprocals of focal lengths) of lens units that constitute the zoom lens are increased, and the number of lenses is reduced. In such a zoom lens, however, the lens thickness increases to ensure an edge thickness with the increases in refractive powers of the lens surfaces. In particular, the front-lens effective diameter increases, and it is difficult to sufficiently reduce the size of the entire zoom lens. At the same time, it is difficult to aberrations, such as chromatic aberration, at the telephoto end.
To obtain a high optical performance in the above-described four-unit and five-unit zoom lenses while achieving a high zoom ratio and a compact lens system, it is important to properly set the refractive powers, lens configurations, and moving conditions for zooming of the lens units. In particular, it is important to properly set the refractive powers of the second and third lens units and the moving conditions of the first, second, and third lens units for zooming.