Zoom lens and optical apparatus incorporating the same

Abstract

A zoom lens disclosed herein, having excellent optical performance within a full zoom range, is appropriate for use as a photographing lens for a lens-shutter camera, a video camera, and a digital still camera. The zoom lens includes at least four lens units from the object side, i.e., a first lens unit of negative refractive power, a second lens unit of positive refractive power, a third lens unit of positive refractive power, and a fourth lens unit of negative refractive power. A zooming operation is performed by axially moving the lens units so that the spacing between the first lens unit and the second lens unit becomes wider at the telephoto end than at the wide-angle end, that the spacing between the second lens unit and the third lens unit becomes wider at the telephoto end than at the wide-angle end, that the spacing between the third lens unit and the fourth lens unit becomes narrower at the telephoto end than at the wide-angle end. With the focal lengths of respective lens unit set to satisfy a predetermined condition, a compact and high image-quality zoom lens thus results.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to a zoom lens and an optical apparatus incorporating the zoom lens, and, more particularly, to a zoom lens and an optical apparatus appropriate for use in lens-shutter cameras, video cameras, and digital still cameras.[0003] 2. Description of the Related Art[0004] As lens-shutter cameras, video cameras, and digital still cameras become compact in size, the need for a compact zoom lens having a high zoom ratio and a short overall length (from a lens surface of a first lens to the image plane) is mounting.[0005] With advances in peripheral circuits such as the electronic circuit for zoom lens driving, cameras, in particular, lens-shutter cameras are substantially miniaturized. Accordingly, a high zoom ratio and compact design are required of the zoom lens as a photographing lens.[0006] Three-unit zoom lenses, each composed of three lens units of positive, positive, and negative refractive power and having a high zoo...

AI Technical Summary

Problems solved by technology

Particularly with a high zoom ratio, cameras cannot provide excellent optical performance over an entire zoom range.

With a high zoom ratio, chromatic aberration becomes problematic during the zooming operation.

The back focus becomes too short, resulting in a large negative spherical aberration.

Correcting such a large negative spherical aberration is difficult.

When the composite refractive power drops below the lower limit on the other hand, the overall length of the lens system increases.

It becomes difficult to correct a variety of aberrations in a balanced manner over a full zoom range.

In excess of the upper limit, the positive refractive power of the third lens unit becomes so weak that it cannot compensate for the spherical aberration.

Correcting such a large negative spherical aberration with other lens units is difficult.

The zooming effect by the fourth lens unit during a zooming operation becomes weak.

At the same time, a curvature of image and astigmatism would disadvantageously occur.

As a result, high order spherical aberrations take place, which are difficult to correct.

In excess of the upper limit, a change in the spacing between the first lens unit and the second lens unit becomes too large.

When the change drops below the lower limit, a change in the spacing between the first lens unit and the second lens unit becomes too small relative to a change in the spacing between the second lens unit and the third lens unit, and it becomes difficult to correct variations in the chromatic aberrations generated during zooming.

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