JPH07281087A - Variable power finder - Google Patents

Abstract

PURPOSE:To switch angles of view to/from each other as a whole by switching objective lenses to/from each other while setting image forming positions of the objective lenses constant, by rotating the objective lenses respectively corresponding to a wide angle and telephoto by 90 deg. by holding them so that the optical axes cross at right angles to each other in a lens barrel of the objective lenses. CONSTITUTION:A wide angle objective lens is composed of a concave lens L1 and a convex lens L2 in order from the object side, and a telephoto objective lens is composed of a convex lens L3. In a lens barrel of the objective lenses, the optical axis C1 of the wide angle objective lens and the optical axis C3 of the telephoto objective lens cross each other between the concave lens L1 and the convex lens L2, and a viewing window is arranged on the optical axis C3 of the telephoto objective lens, and an optical path is secured. The lens barrel of the objective lenses is formed in a structure capable of rotating by 90 deg., and the respective objective lenses corresponding to respective angles of view of a wide angle and telephoto are integrally held so that the optical axes cross almost at right angles to each other in the lens barrel of the objective lenses, and are rotated by about 90 deg., and image forming positions are set constant, and the angles of view are made to be switched to/from each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable magnification finder used for a video camera or a still camera which can switch the angle of view of the lens between a wide angle side and a telephoto side and uses a lens having a variable magnification ratio of about 2 to 3 times. It is about.

[0002]

2. Description of the Related Art There are various types of finder for a lens system capable of changing the magnification by a factor of 2 to 3 as compared with the conventional one.

The daylighting bright frame finder is
With a constant viewfinder magnification, a slit is formed in the frame part showing the field of view with metal or film, and the size of the frame is mechanically converted according to the conversion of the angle of view of the lens.

The real image type zoom finder forms an inverted image on a field stop by a zoom objective lens forming a real image,
An erecting image is formed by an erecting prism system or an erecting lens system, and observed with an eyepiece.

The Albada type zoom finder forms an optical image frame of a certain size with a concave mirror and a reticle, and an objective lens generally constitutes a zoom system consisting of convex, concave, and convex lens groups. Change the viewfinder magnification continuously.

There is also a system in which two reticles are provided and the two reticles are mechanically switched in association with zoom magnification by a modification of the albada type zoom finder.

[0007]

By the way, each of the above-mentioned conventional viewfinders corresponding to the variable power lens system has the following drawbacks.

The daylighting bright frame finder is
Since the size of the optical image frame changes without changing the magnification,
On the telephoto side, only the central part of the entire field of view of the finder is watched, and for example, when the angle of view is tripled, the area of the optical image frame becomes 1/9, which is very difficult to see. In addition, on the screen to watch,
Although the subject becomes larger at the telephoto end, it is difficult to see in the viewfinder.

In the real image type zoom finder, since it is necessary to move the lens group in the optical axis direction, the structure of the lens barrel is complicated and the cost is increased. Further, if there is a lens or prism surface near the position where the real image is formed, dust and scratches on the optical surface appear to overlap the field of view, making it difficult to eliminate these defects.

Compared with the real image type zoom finder, the albada type zoom finder cannot make the refracting power of the variator lens group strong because of its structure, so that the variable magnification cannot be increased or the size becomes extremely large.

In addition, the above-mentioned modification of the albada type zoom finder alleviates the defects of both the daylighting type bright frame finder and the albada type zoom finder, and introduces both of them.

Therefore, according to the present invention, in a finder capable of converting the angle of view in correspondence with a two-to-three times as many bifocal switching lens system, the corresponding lens barrel has a structure capable of rotating by 90 ° to provide a wide angle and a telephoto. The objective lens corresponding to each is held by the objective lens barrel so that the optical axes are orthogonal to each other,
The object of the present invention is to provide a variable magnification finder of a real image type in which the image forming position of the objective lens is constant by rotating about 90 ° and the objective lens is switched so that the angle of view can be changed as a whole.

[0013]

The variable magnification finder of the present invention has the following structure.

According to the structure of claim 1, in the variable magnification finder of the real image type capable of switching between wide angle and telephoto, the objective lens barrel has a structure capable of rotating by approximately 90 °, and corresponds to the respective angle of view of wide angle and telephoto. The objective lens is integrally held by the objective lens barrel so that the optical axes thereof are substantially orthogonal to each other.
It is characterized in that the image forming position is fixed and the angle of view is switched by rotating by °.

According to a second aspect of the present invention, the wide-angle objective lens is composed of a concave lens L ₁ and a convex lens L _{2 in this} order from the object side, and the telephoto objective lens is composed of a convex lens L ₃ , and the objective lens barrel is the concave lens. The optical axis of the wide-angle objective lens and the optical axis of the telephoto objective lens intersect each other between L ₁ and the convex lens L _2, and a viewing window is provided on the optical axis of the telephoto objective lens to secure the optical path. And

According to a third aspect of the present invention, the material of the concave lens L ₁ , the convex lens L ₂ and the convex lens L ₃ is made of plastic, and at least one surface of each is made aspheric.

[0017]

The above structure will be described in detail.

According to the structure of claim 1, since the focal length of the finder objective lens can be changed without moving the lens group in the optical axis direction, only a simple rotating mechanism is required as the zooming mechanism of the lens barrel. Even without using a high-cost motor, you can switch the magnification manually instantly, and you can realize a low-cost variable magnification mechanism.

The second aspect of the present invention is a means for realizing the configuration of the first aspect with a minimum lens configuration, and it is possible to easily achieve a high zoom ratio, although the number of lenses is smaller than that of the zoom finder.

The structure of claim 3 is a means for realizing the structure of claim 2 more specifically at low cost and with high performance. The telephoto objective lens is a plastic single lens which is the cheapest structure. A lens is used to correct each aberration by making at least one aspherical surface, the wide-angle objective lens is retrofocused, and the back focus is aligned with the telephoto objective lens, thereby enabling the configuration of claim 1.
In order to reduce the Petzval sum to facilitate the correction of the field curvature, the retrofocus type has a minimum two-lens configuration, and each aberration is corrected in good balance by the plastic aspherical surface.

[0021]

EXAMPLES Examples of the present invention will be described below.

In FIG. 1, in the state in which the wide-angle side is set, the wide-angle objective lens is composed of the concave lens L ₁ and the convex lens L _{2 in} order from the object side, and the light flux is bent toward the erector lens by the convex lens L ₄ of the field lens. , The first image forming surface is formed behind it, and the convex lens L ₅ and the concave lens L ₆ constitute an erector lens to convert an inverted image into an erected image so that the luminous flux reaches the pupil by the convex lens L ₇ of the field lens. Then, a second image forming surface is formed behind it, and a virtual image is formed by the convex lens L _{8 serving} as an eyepiece lens, thereby forming a real image type variable power finder as a whole.

The telephoto objective lens is composed of a convex lens L ₃ , and the objective lens barrel (not shown) has a wide-angle objective lens optical axis C ₁ and a telephoto lens between the concave lens L ₁ and the convex lens L ₂ constituting the wide-angle objective lens. The optical axis C ₃ intersects with the objective lens, and a viewing window (not shown) is provided on the optical axis C _{3 of} the telephoto objective lens to secure the optical path. Further, the objective lens barrel is structured to be rotatable by about 90 °, and the objective lenses corresponding to the wide angle and the telephoto angle are integrated so that the optical axes of the objective lens barrel are substantially orthogonal to each other. By holding it at 90 ° and rotating it by about 90 °,
The angle of view is switched. Further, the concave lens L ₁ , the convex lens L _2, and the convex lens L ₃ are made of plastic, and at least one surface thereof is aspherical.

Numerical examples on the wide-angle side of this embodiment are shown in Table 1.

[0025]

[Table 1]

Here, r _i is the radius of curvature of the i-th surface in order from the object side, and d _i is the surface distance between the i-th surface and the (i + 1) th surface.

Table 2 shows numerical examples of the aspherical surface coefficient on the wide angle side.

[0028]

[Table 2]

FIG. 2 shows the state set to the telephoto side.

Next, Tables 3 and 4 show numerical examples of the telephoto side and numerical examples of the aspherical surface coefficient of this embodiment.

[0031]

[Table 3]

[0032]

[Table 4]

Definition of aspherical surface: χ _i = H ² / r _i {1+ (1-H ² / r _i ² ) ^1/2 where χ _{i is} the depth of the aspherical surface and H is the height from the optical axis. } + ΣA _j H
^j Finder magnification: Wide-angle side 0.233 times, Tele-side side 0.698 times Diopter: Infinity point at wide-angle side and telephoto side -1D Apparent field of view of field diaphragm: Vertical 9.12 degrees, horizontal 12.1
6 degrees, diagonal 15.3 degrees Eye point: Rear of the r ₁₆ surface 28 Astigmatism and distortion of the virtual image on the wide-angle side and the telephoto side of the object point at infinity in this numerical example are shown in FIGS. 3 and 4. Show.

[0034]

As described above, according to the present invention, the zooming mechanism is simplified and the number of optical components and mechanical components can be greatly reduced as compared with the prior art, so that the manufacturing cost can be reduced. can do.

In the zoom finder, the light beam passes through the same lens on both the wide-angle side and the telephoto side, so there is a large degree of aberration variation during zooming, and the degree of freedom in aberration correction is low. As the interchangeable lens is replaced, the wide angle side and the telephoto side can be independently corrected for aberrations, and the degree of freedom in design is increased, so that good performance can be easily obtained.

In the case where the taking lens system is a variable magnification lens system that instantly converts wide angle and telephoto, the zoom finder shows an image in the middle of varying magnification that cannot be seen in the taking lens system. If it is configured so that the magnification can be changed instantly by linking with the lens, there is little discomfort.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a state in which a real image type variable magnification finder according to an embodiment of the present invention is set on a wide angle side.

FIG. 2 is a configuration diagram showing a state in which the real image type variable power viewfinder is set on a distant side.

3A to 3C are aberration curve diagrams showing spherical aberration, astigmatism, and distortion in a state where the real-image variable magnification finder is set to the wide-angle side.

4A to 4C are aberration curve diagrams respectively showing spherical aberration, astigmatism and distortion in a state where the real image type variable power viewfinder is set on the far side.

[Explanation of symbols]

L ₁ ... Concave lens L ₂ ... Convex lens L ₃ ... Convex lens C ₁ ... Wide-angle objective lens optical axis C ₃ ... Telephoto objective lens optical axis

Claims (3)

[Claims] 1. In a variable magnification finder of a real image type capable of switching between a wide angle and a telephoto, an objective lens barrel has a structure capable of rotating about 90 °, and an objective lens corresponding to each angle of view of the wide angle and the telephoto is described above. Variable magnification finder characterized in that the objective lens barrel integrally holds the optical axes so that they are substantially orthogonal to each other, and by rotating them by about 90 °, the imaging position is constant and the angle of view is switched. . 2. The variable power finder according to claim 1, wherein the wide-angle objective lens comprises a concave lens L ₁ and a convex lens L _{2 in this} order from the object side, and the telephoto objective lens comprises a convex lens L _3. The lens barrel has the concave lens L ₁
The optical axis of the wide-angle objective lens intersects the optical axis of the telephoto objective lens between the convex lens L ₂ and the convex lens L _2, and a viewing window is provided on the optical axis of the telephoto objective lens to secure the optical path. Magnification finder. 3. The variable power finder according to claim 2, wherein the concave lens L ₁ , the convex lens L ₂ and the convex lens L ₃ are made of a plastic material, and at least one surface of each is aspherical. Variable magnification finder.