Zoom lens

Abstract

The invention belongs to the technical field of optical devices, and specifically relates to a zoom lens. The zoom lens comprises a first lens group G1 with positive diopter, a second lens group G2 with negative diopter, a third lens group G3 with positive diopter and a fourth lens group G4 with positive diopter in sequence from the object side to the image surface side. When zooming is carried out from the wide-angle end to the telescoping end, the first lens group G1 is fixed, the second lens group G2 moves from the object side to the image surface side, the third lens group G3 firstly movesfrom the object side to the image surface side, turns back in the midway and then moves from the image surface side to the object side, and the fourth lens group G4 moves from the image surface sideto the object side. The first lens group G1 includes a negative-diopter front group G1a consisting of three negative lenses, a middle group G1b consisting of two positive lenses and a positive-diopterrear group G1c, wherein the middle group G1b moves from the object side to the image surface side to achieve focusing when an object moves from the infinity to the close distance. The zoom lens provided by the invention has the effects of compact size, high performance and low cost, and the zoom ratio is more than three times.

Description

technical field [0001] The invention belongs to the technical field of optical devices, and in particular relates to a zoom lens. Background technique [0002] At present, most of the known zoom cine lenses are fixed with the first group whose diopter is positive, and there are many structures that combine with several moving groups. The positive diopter is fixed, and the negative diopter group 2, the negative diopter lens group 3, the positive diopter group 4, and the fixed positive diopter group 5 are composed of multiple components. When moving from infinity to short distance, the focus group is the middle part of the first group, moving toward the image plane to achieve focus. [0003] There is also the disclosure of Japanese Patent Application No. 2015-18083: from the side of the object, the first group of positive diopters is fixed when zooming, and the second group of negative diopters, the third lens group of negative diopters, and the negative diopter are moved res...

AI Technical Summary

Problems solved by technology

[0004] Although the above structure achieves high performance, including a zoom function of more than 3 times, there are too many moving groups, the structure is too complicated, and the aspheric correction is used, resulting in bulky, difficult to manufacture, and high cost.

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