Zoom lens and camera device

Abstract

The invention provides a zoom lens, wherein the zoom lens realizes miniaturization of diameter of a front lens and shortens total length of the lens system in light axis direction apart from maintaining high optical performance. The zoom lens comprises four lens assemblies from a first lens assembly (G1) to a forth lens assembly (G4). The first lens assembly (G1) and the third lens assembly (G3) are fixed, and the second lens assembly (G2) is moved when zooms in or out, and the forth lens assembly (G4) is moved to correct image plane position of the zoom and focus. The first lens assembly (G1)comprises a negative lens and two positive lens. The second lens assembly (G2) comprises four lens with one negative lens having a aspheric surface. The following conditional expression (1), (2) aresatisfied: 6.0<f1 / fw<8.0 (1), 0.10<H2f / fw<0.20 (2). Further more, f1 means focal distance of the first lens assembly, fw means focal distance of the entire system on a wide-angle end, H2f means distance from object side of a lens that nearest to the object side of the second lens assembly to an light axis of a principal point on an object side of the second lens assembly.

Description

technical field [0001] The present invention relates to a zoom lens and an imaging device, and more specifically, to a zoom lens suitably used for a video camera, an electronic still camera, a surveillance camera, and the like, and an imaging device including the zoom lens. Background technique [0002] In the past, as zoom lenses used in consumer video cameras and the like, zoom lenses of the 4-group or 5-group type have been proposed many times. For example, Patent Documents 1, 2, and 3 disclose a zoom lens having a high zoom ratio of about 10 times and an F-number of about 1.8, including three lenses that constitute a second lens group that moves when zooming. Patent Document 4 discloses a 5-group type zoom lens including a total of 15 lenses that constitutes the second lens group with four lenses. Patent Document 5 discloses a zoom lens using a composite aspheric lens in which an aspheric resin is formed on a glass spherical surface. [0003] Patent Document 1: Japanes...

AI Technical Summary

Problems solved by technology

[0010] The zoom lens described in Patent Document 4 has a 15-lens structure in the entire system, which is not sufficient from the viewpoint of miniaturization of the total length of the lens system in the optical axis direction.

The zoom lens described in Patent Document 5 uses a composite aspheric lens in the second lens group, and the second lens group cannot have such a large negative refractive power. Therefore, the movement amount of the second lens group is large, and there is light Concerns about enlargement of the lens system in the axial direction

[0011] In addition, the zoom lens described in Patent Document 5 cannot bring the object-side principal point of the second lens group too close to the object side, so the diameter of the front lens tends to be large.

In order to reduce the diameter of the front lens, it is necessary to study the structure of the second lens group. In this regard, the zoom lenses described in Patent Documents 1 to 3 have room for improvement.

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