Zoom lens and imaging device

Abstract

PROBLEM TO BE SOLVED: To obtain a large back focus with a small number of lenses in a zoom lens of high variable power and great diameter ratio.SOLUTION: The zoom lens has: a positive first group of lenses G1 which are fixed in the direction of an optical axis when varying power; a negative second group of lenses G2 for varying ratio by being moved when varying power; a positive third group of lenses G3 which is fixed in the direction of the optical axis when varying power; and a positive fourth group of lenses G4 for correcting and focusing the variation in an image surface position occurring along with the varying of power by being moved when varying power are arranged in this order from the object side. In this case, the third group of lenses G3 comprises two lenses which are the positive third group first lens and a negative third group second lens with a concave surface facing the object side. In addition, the fourth group of lenses G4 includes a negative lens and two or more positive lenses. Furthermore, a conditional expression (1):16<νd31<35 is satisfied when the Abbe number with a line d of an optical member forming the third group first lenses as a reference is νd31.

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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