JPH1020191A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens capable of shortening the depth and making the diameter of a front lens small in a zoom lens mainly used for a video camera. SOLUTION: This lens a mainstream of a zoom lens currently used for a public video camera. In a so-called a four group inner focus zoom lens, a right angle prism P is arranged behind a three group fixed lens L3 and the optical axis is bent by 90 deg.. Consequently, the depth of the zoom lens is shortened and the miniaturization of the zoom lens and the whole video camera are enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a small zoom lens used for a video camera or the like.

[0002]

2. Description of the Related Art For example, in a consumer video camera, a zoom lens composed of four lens groups of convex, concave, convex and convex in order from the object side is generally used, which is suitable for miniaturization and cost reduction. I have.

[0003]

However, in the zoom lens of the conventional consumer video camera described above, the ratio of the total length from the front lens at the telephoto end to the focal point with respect to the focal length at the telephoto end, the so-called telephoto ratio, is 1 or less. There are no examples. Increasing the refractive power of each lens unit is advantageous for miniaturization, but fluctuations in field curvature during zooming and fluctuations in field curvature due to subject distance on the telephoto side are unavoidable, and distortion at the wide-angle end is increased. Inevitably increase.

[0004] The depth dimension of the zoom lens includes not only the entire length of the optical system but also the terminals of the image sensor and the electric components mounted on the circuit board, and furthermore, a part of the driving device for driving the fourth lens group. May protrude backwards. The depth of the components behind these image planes occupies 10% or more of the entire optical length, which is a major obstacle in reducing the depth.

[0005] On the other hand, video recording media have been digitized, increased in density, and miniaturized. In order to miniaturize cameras, the demand for miniaturization of lenses tends to become stronger.

It can be said that the miniaturization of the video lens has been most attributable to the miniaturization of the screen size of the solid-state imaging device such as a CCD and the enhancement of the sensitivity. To reduce the screen size while maintaining the number, there is a feeling that the limit is approaching, and it has become difficult to reduce the size of the zoom lens on an extension of the conventional technology.

Accordingly, the present invention is to provide a zoom lens in which the depth of the optical system can be reduced as much as possible to further reduce the size.

[0008]

A first lens group fixed in order from the object side, a second lens group movable mainly for changing magnification, a third lens group fixed, and correction of image movement by zooming. In a zoom lens composed of a movable fourth lens group for focusing, a right-angle prism is arranged between the third lens group and the fourth lens group so that the optical axis becomes approximately 9%.
It is bent at 0 °.

As a result, the depth dimension of the zoom lens is reduced, and the size of the zoom lens is reduced. When this zoom lens is used in a video camera or the like, the overall size of the video camera or the like can be reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a zoom lens according to an embodiment of the present invention. The zoom lens is mainly used for a video camera, and in particular, to reduce the depth dimension and the front lens diameter. It is an object.

The structure of this zoom lens is as follows: from the object side, a fixed first lens unit L1, a movable second lens unit L2 for mainly changing magnification, a fixed third lens unit L3, and an image formed by zooming. In a zoom lens composed of a movable fourth lens unit L4 for correcting movement and focusing, a right-angle prism P is disposed between the third lens unit L3 and the fourth lens unit L4, and the optical axis C is set to about It is characterized by being bent 90 °.

As described above (as described in the section of the problem to be solved by the invention), the depth dimension of the zoom lens is such that the total optical length exceeds 1 at the telephoto ratio, and the parts protrude beyond the image plane. It can be said that it is extremely difficult to make the focal length shorter than the telephoto end including the projection. Therefore, in the embodiment of the present invention, the optical axis C is bent by about 90 ° by the right-angle prism P to achieve the object. As a basic configuration of the zoom lens, the above-described four-group inner focus zoom lens, which is easy to configure with a small number of lenses, was used. As the arrangement of the prisms, the four-group configuration is left as it is, and the whole zoom lens is set up by placing it on the entrance side, that is, in front of the first lens group, or placed between the exit side, that is, between the fourth lens group and the image sensor. By bending only the image sensor, the eccentricity of the zoom lens system can be prevented, and the effect of the mechanical accuracy of bringing the prism into the optical system can be minimized. The prism volume is too large and the depth can be shortened the most, but the area of the prism entrance surface (corresponding to the diameter of the front lens) becomes large, and the objective cannot be achieved. In the case where a part of the driving device protrudes backward because the effect of shortening the depth is less than the cost increase of the prism and the moving direction of the fourth lens group does not change. Yes, the result of the case depth can not be shortened.

According to the structure of the zoom lens, the stop S
Is disposed immediately before the third lens unit L3, and the first lens unit L
Since the configuration up to the first and second lens units L2 and the stop S is the same as the conventional configuration, it is an optimal arrangement for reducing the diameter of the front lens, and the light rays incident parallel to the optical axis C are transmitted through the second lens unit L2. By arranging the right-angle prism P immediately after it becomes a divergent light beam and becomes nearly afocal in the third lens unit L3, the volume of the right-angle prism P can be small, and it can be close to afocal and off-axis. Since the inclination of the traveling principal ray is small, total reflection can be applied to the reflecting surface of the right-angle prism P, and loss of transmittance can be minimized. For example, when the optical axis C is bent downward by the right-angle prism P, the fourth lens unit L4 moves up and down, and the driving device is moved to the fourth lens unit L.
If it is arranged beside 4, even if a part of the driving device protrudes toward the image side, it only extends downward, and the depth dimension is determined from the first lens unit L1 to the rear edge of the right-angle prism P.

In this embodiment, in order to minimize the depth dimension of the optical system of the lens, the third lens unit L3 is a plano-convex single lens having a convex surface facing the object side, and the plane and the entrance surface of the right angle prism P Characterized by being joined to a flat surface.
With this configuration, it is not necessary to separately hold the third lens unit L3 and the right-angle prism P, which is effective for reducing the depth dimension. Thus, the size of the zoom lens can be further reduced, and the size of the entire video camera using the zoom lens can be reduced. Further, if the third lens unit L3 and the right-angle prism P are assembled so that the optical axes C thereof coincide with each other in the joining step, an eccentricity error is less likely to occur than in the case where the respective lenses are separately held.

The configuration of the fourth lens unit L4 includes, in order from the object side, a cemented lens of a concave lens and a convex lens and a convex lens
It is characterized in that it is constituted by sheets. Since the fourth lens unit L4 is disposed behind the right-angle prism P, the distance from the stop S to the fourth lens unit L4 is longer than that of the conventional four-unit inner focus zoom lens, and the principal ray passing through the fourth lens unit L4 Becomes higher. Conventionally, in many cases, the fourth lens group is composed of a cemented lens composed of a concave lens and a convex lens. However, if the height of the chief ray is increased in this configuration, the fourth lens group mainly has a cemented surface that functions to correct astigmatism. A large aberration occurs, and it is difficult to correct the two-element configuration. The positive refracting power of the fourth lens unit L4 is divided into two lens units, and the lens on the object side having a wide light flux is used as a cemented lens of a concave lens and a convex lens to correct astigmatism and moderate the curvature of the cemented surface. To prevent an increase in frame collection and dispersal.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

The zoom lens shown in FIG. 1 has a fixed first lens unit L1 in order from the object side, a movable second lens unit L2 for mainly changing the magnification, a fixed third lens unit L3, and a zoom lens. A movable fourth lens unit L4 for performing correction of image movement and focusing;
A right-angle prism P is disposed between the lens unit L3 and the fourth lens unit L4, and the middle of the optical axis C is bent by about 90 °. The first lens unit L1 includes, in order from the object side, a cemented lens of a concave lens and a convex lens and a convex meniscus lens, and the image side surface of the cemented lens is aspheric. The second lens unit L2 includes, in order from the object side, a concave lens and a cemented lens of a concave lens and a convex lens. The third lens unit L3 is a single plano-convex single lens with the convex surface facing the object side, the convex surface being an aspheric surface, and the plane joining the entrance surface of the right-angle prism P. The fourth lens unit L4 includes, in order from the object side, a cemented lens of a concave lens and a convex lens and a convex lens, and the convex single lens has a double-sided aspheric surface. In FIG. 1, Q
Is a flat glass corresponding to a filter, and K is an image plane.

Next, Tables 1 to 3 show numerical examples of the above embodiment.

[0020]

[Table 1]

In the above, r _i : the radius of curvature of the i-th surface of the lens d _i : the distance between the i-th surfaces of the lens _ni : the refractive index of the i-th medium of the lens at the e-line n _e v _i : the lens of the lens The Abbe number ν _e of the i-th medium at the e-line is shown.

[0022]

[Table 2]

[0023]

[Table 3]

Definition of aspherical surface: Assuming that the depth of the aspherical surface is χ _i , and the height from the optical axis is H, it is expressed by the following equation 1.

[0025]

[Number 1] ^{_{χ i = H 2 / r i}} {1+ (1-H 2 / r i 2) 1/2}
+ ΣA _i · H ⁱ FIGS. 2, 3 and 4 show that f = 4.30 and f = 18.1.
3, and aberration curve diagrams at respective focal lengths of f = 43.00 ((a) shows spherical aberration, (b) shows astigmatism, and (c) shows distortion).

Although the zoom lens of a video camera has been described in the above embodiment, it is needless to say that the embodiment can be applied to a zoom lens of another camera such as a still camera.

[0027]

As described above, according to the present invention, the fixed first lens group, the movable second lens group that mainly changes the magnification, the fixed third lens group, In a zoom lens composed of a movable fourth lens group for performing correction of image movement by zooming and focusing, a right-angle prism is arranged between the third lens group and the fourth lens group to set the optical axis at about 90 °. By bending, the depth dimension of the zoom lens can be reduced at low cost, and the size of the entire zoom lens can be further reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a zoom lens according to the present invention.

FIGS. 2A, 2B, and 2C are aberration curve diagrams showing spherical aberration, astigmatism, and distortion at a wide-angle end focal length (f = 4.3).

FIGS. 3A, 3B and 3C are aberration curve diagrams showing spherical aberration, astigmatism, and distortion at an intermediate focal length (f = 18.13).

FIGS. 4A, 4B, and 4C are aberration curve diagrams showing spherical aberration, astigmatism, and distortion at a telephoto end focal length (f = 43.00).

[Explanation of symbols]

L1 first lens group, L2 second lens group, L3 third
Lens group, L4: fourth lens group, P: right angle prism, C
…optical axis.

Claims (3)

[Claims] A first lens group fixed in order from an object side;
A movable second lens group that mainly changes magnification, and a fixed third lens group
In a zoom lens composed of a lens group and a movable fourth lens group for performing image movement correction and focusing by zooming, a right-angle prism is arranged between the third lens group and the fourth lens group to form an optical axis. A zoom lens characterized by being bent about 90 °. 2. The zoom lens according to claim 1, wherein the third lens group is a single plano-convex lens, and a plane thereof and an incident surface of the right-angle prism are joined to be integrally formed. 3. The zoom lens according to claim 1, wherein the fourth lens group includes, in order from the object side, a cemented lens of a concave lens and a convex lens and a convex lens.