JPH07174971A - Zoom lens - Google Patents

Abstract

PURPOSE:To provide a zoom lens appropriately preventing distortion aberration and having high accuracy, to facilitate the production and to reduce the production cost. CONSTITUTION:A plastic lens 20 for restraining the distortion aberration, whose 1st surface is an aspherical shape and whose 2nd surface is a spherical shape so as to be formed in nearly equal thickness, is arranged at the front position of the 1st lens 21 of a 1st lens group A arranged on the object side among plural lens groups A, B and C arranged on the optical axis, and, a spherical lens is used as the 1st lens 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and particularly to eliminating distortion aberration in a super wide-angle zoom lens,
The present invention relates to a zoom lens configuration that facilitates lens manufacturing.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional example of a zoom lens used in a video camera. This zoom lens includes a first lens group A, a second lens group B, and a third lens group C from the object side.
No. 3, No. 3, No. 3, and each have negative, positive, and positive combined focal lengths. The first lens group A is the first lens 1
0, the second lens 11, and the third lens 12 are included. The first lens 10 has a negative focal length, the second lens 11 has a positive focal length, and the third lens 12 has a negative focal length. D is an auto iris, E is an image plane, and the first lens group A and the second lens group B move in the optical axis direction during zooming, and the third lens group C moves in the optical axis direction during focusing. To focus on the image plane E.

[0003]

By the way, the angle of view is 60
In the case of an ultra-wide-angle zoom lens having an angle of more than 70 ° or 70 °, it is necessary to use a lens having a large effective diameter as the first lens 10 of the first lens group A. However, if the effective diameter of the lens is increased, distortion will occur. Since it becomes a problem, it is necessary to remove this distortion. Therefore, in the conventional ultra wide-angle zoom lens, the first surface of the first lens is designed to be an aspherical shape to suppress distortion. The first lens 10 is manufactured by a glass mold formed by pressing molten optical glass. Since a concave lens is used as the first lens 10, a large and aspherical concave lens as described above is manufactured. Is difficult in terms of manufacturing technology,
There are problems that productivity is inferior, yield is poor, and manufacturing cost is high.

The present invention has been made to solve these problems, and it is possible to effectively suppress the distortion aberration of a wide-angle zoom lens, facilitate the manufacture of the lens, and use it suitably for a video camera or the like. An object of the present invention is to provide a zoom lens capable of

[0005]

The present invention has the following constitution in order to achieve the above object. That is, of the plurality of lens groups arranged on the optical axis, the first surface is an aspherical surface, and the second surface is in front of the first lens of the first lens group arranged on the object side.
It is characterized in that a plastic lens, which has a spherical surface and is formed to have a substantially uniform thickness, is arranged to suppress distortion, and a spherical lens is used as the first lens.

[0006]

By disposing a plastic lens having an aspherical first surface and a spherical second surface in front of the first lens, distortion of the optical system is suppressed. By using the plastic lens, the first lens of the first lens group
The lens can be a spherical lens, and the glass lens can be easily manufactured. Since a plastic lens can be easily formed into an aspherical shape, it is possible to reduce the manufacturing cost of the zoom lens as a whole. Further, by making the plastic lens have a substantially uniform thickness, the plastic lens acts as a lens having substantially no degree, and it is possible to prevent the influence of temperature change on the plastic lens and prevent deformation of the plastic lens during molding.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is an explanatory diagram showing the configuration of a zoom lens according to the present invention. In the figure, the first lens group A,
The configurations of the second lens group B and the third lens group C are substantially the same as those of the conventional example shown in FIG. 2, and have negative, positive, and positive combined focal lengths, respectively. The first lens group A has a plastic lens 20 arranged at the frontmost part of the lens group, and a first lens 21, a second lens 22, and a third lens 23 arranged behind it. The first lens 21 has a negative focal length, the second lens 22 has a positive focal length, and the third lens 23 has a negative focal length.

The plastic lens 20 is arranged in front of these lens groups and is used for suppressing distortion. That is, in the conventional example shown in FIG. 2, a concave lens in which the first surface of the first lens 10 is an aspherical surface and the second surface is a spherical surface is used, but in this embodiment, the plastic lens 20 is used.
The first surface is made aspherical and the second surface is made spherical to reduce distortion. It should be noted that the plastic lens 20 has a substantially uniform wall thickness in order to reduce the influence of temperature change and prevent deformation during molding.
Form with almost no occurrence. Since the first surface of the plastic lens 20 is formed in an aspherical shape and the second surface is formed in a spherical shape, the plastic lens 20 is not formed to have a uniform thickness, but the curvatures thereof are set to be substantially equal to each other to be formed to have a substantially uniform thickness. Forming the plastic lens 20 to have a substantially uniform thickness means that the curvatures of the first surface and the second surface are substantially equal to each other.

As described above, by making the plastic lens 20 almost non-existent, the optical system forming the first lens group A, the second lens group B and the third lens group C is the same as the conventional optical system. It can be used as it is. By disposing the plastic lens 20 for removing the distortion aberration in the front position of the first lens group A as described above, the first lens 21 may be manufactured as a spherical lens, so that it is a considerably large glass lens. Can be easily manufactured by the method of manufacturing a spherical glass lens. Thus
With regard to the optical system using glass lenses, it is possible to improve the production efficiency because the difficulties in manufacturing technology can be eliminated.
The yield can be improved and the lens manufacturing cost can be reduced.

On the other hand, the plastic lens 20 can be manufactured more easily than a glass lens, and can be formed into an aspherical shape more easily than a glass lens, and since the productivity is high, even if one plastic lens 20 is added. Looking at the zoom lens as a whole, it is possible to improve productivity and reduce the overall cost. Further, since the plastic lens 20 to be used is formed to have a substantially uniform thickness, it is possible to suppress the defect of the plastic lens that is easily affected by the temperature change and to configure a zoom lens with high accuracy. is there.

The second lens group B, the third lens group C, the auto iris D, and the image plane E in the above embodiment are the same as those in the conventional example shown in FIG. The first lens group A and the second lens group B are controlled to move in the optical axis direction to perform a zooming function, and the third lens group C functions to focus on the image plane E. The lens configurations of the first lens group A, the second lens group B, and the third lens group C can be appropriately designed depending on the product, and the lens configuration of the first lens group A is not limited to the above embodiment. Absent. Further, there are differences in the configuration of the lens groups depending on the product, such as 4 groups, 5 groups, etc., and in these cases also, the zoom lens should be configured using a plastic lens as in the above embodiment. Is possible.

[0012]

As described above, according to the zoom lens of the present invention, by disposing the plastic lens for suppressing the distortion aberration in front of the first lens group, the zoom lens, particularly the wide-angle zoom lens, can be produced. It becomes possible to suitably suppress the distortion aberration. Also, by using a plastic lens, it becomes possible to manufacture a glass lens as a spherical lens, and it is possible to eliminate the difficulty in manufacturing an aspherical glass lens, especially an aspherical concave lens, and to manufacture the entire zoom lens. The cost can be reduced. Further, by forming the plastic lens to have a substantially uniform thickness, it is possible to suppress the influence of temperature change, which is a weak point of the plastic lens, to a small extent, and it is possible to provide a zoom lens with high accuracy, and so on.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of an example of a zoom lens.

FIG. 2 is an explanatory diagram showing a configuration of a conventional example of a zoom lens.

[Explanation of symbols]

 10 1st lens 11 2nd lens 12 3rd lens 20 Plastic lens 21 1st lens 22 2nd lens 23 3rd lens

Claims (1)

[Claims] 1. A first surface is an aspherical surface and a second surface is a spherical surface in front of a first lens of a first lens group of the plurality of lens groups arranged on the optical axis, which is arranged on the object side. The zoom lens is characterized in that a plastic lens for suppressing distortion aberration formed in a substantially uniform thickness is disposed as, and a spherical lens is used as the first lens.