Zoom lens and camera device

Abstract

The invention provides a zoom lens with a high rate and a heavy caliber, and a large rear cut-off distance can be obtained with a small number of lenses. Wherein the object side is consequently provided with a positive first lens group which is fixed relative to the optical axis direction during the zooming, a negative second lens group which is moving during the zooming to change the rate, a positive third lens group which is fixed relative to the optical axis direction, and a positive fourth lens group which is moving during the zooming, modifying with the change of the image surface position and do focusing. In addition, the third lens group is composed of a positive first lens and a negative second lens with the concave surface facing the object side; the fourth lens group possesses a negative lens and more than two positive lenses; and in addition, the Abbe number with the d line as the reference is set as vd31, and the following conditional expression is satisfied: vd31 is more than 16 and less than 35.

Description

technical field [0001] The present invention relates to a zoom lens with high magnification and large aperture ratio and an imaging device equipped with the zoom lens. Background technique [0002] At present, in the zoom lenses adopted in TV broadcasting cameras and high-quality civilian cameras, a three-plate imaging method using a dichroic prism is known (for example, each color of red, green, and blue uses a dedicated imaging element respectively. A zoom lens that performs color image capture). As the type of lens used in these zoom lenses, there are many proposals to have a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power in order from the object side. A zoom lens composed of 4 groups of the four lens groups, the fourth lens group having a positive refractive power, or a zoom lens composed of 5 groups with an additional lens group. [0003] A zoom lens suitable fo...

AI Technical Summary

Problems solved by technology

For example, if the refractive power of the fourth lens group is weak, the amount of movement of the fourth lens group at the time of zooming and focusing becomes large, resulting in an increase in the size of the zoom lens.

On the other hand, in order to miniaturize the zoom lens, it is necessary to increase the power of the third lens group, which is a lens group having the same positive refractive power as the fourth lens group, but it is difficult to increase the back focus in this way.

On the contrary, if the optical power of the fourth lens group is increased too much, the effective diameter of the fourth lens group becomes large, and the problem that focusing cannot be performed smoothly and effectively will arise.

In this way, in a zoom lens with a high magnification and a large aperture ratio, it is difficult to obtain a large back focus after the third lens group and a small number of lenses.

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