JP3033139B2 - Variable magnification finder optical system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable magnification finder optical system, and more particularly, to a real image type variable magnification finder optical system used for a lens shutter camera or the like.

2. Description of the Related Art A real image type variable magnification finder optical system including a positive objective lens system, a positive condenser lens and a positive eyepiece lens system in order from the object side is disclosed in, for example, JP-A-61-156018.
Nos. 61-156019, 61-160713, 62-7017, JP-A-1-65519, 1-65520, 1-1116616 and the like. These variable magnification finder optical systems use a two-group zoom objective lens system.

Above all, JP-A-61-156018, JP-A-62-7017, JP-A-1-65519, JP-A-1-65520 and JP-A-1-116616 use a two-group zoom objective lens system consisting of negative and positive lenses. ing.

On the other hand, JP-A-61-156019 uses a two-group zoom objective lens system composed of positive and negative lenses.
For the number, a two-group zoom objective lens system composed of positive and positive lenses is used.

In addition, there is an apparatus using a three-group zoom objective lens system having negative refractive power and positive refractive power.
No. 1510).

SUMMARY OF THE INVENTION In a finder optical system in which a two-group zoom objective lens system composed of negative and positive lenses is used, high magnification cannot be achieved unless the amount of movement of each group is increased. There is a problem that aberration deterioration is large.

Further, in the above-described two-group zoom objective lens system composed of negative and positive lenses, distortion that becomes negatively large on the low magnification side occurs in the negative first lens group. In general, the lens does not affect light rays passing near the center, but gives a large amount of aberration to light rays passing around the center. In the negative / positive two-unit zoom, at low magnification, the distance between the negative first lens (LI) and the positive second lens (L II) is wide as shown in FIG.
The luminous flux having a large angle of view passes around the first lens unit (LI). As a result, there is a problem in that the difference between the distortion in the low magnification state and the distortion in the high magnification state (hereinafter, referred to as “distortion difference”) increases to an unacceptable level.

In the finder optical system using the positive / negative two-group zoom objective lens system, there is a problem that it is difficult to take up space for providing a reversing optical system necessary for a real image type finder.

In the finder optical system using the positive / positive two-group zoom objective lens system, there is a problem that it is difficult to correct aberration.

Further, in the conventionally known virtual image finder, the diameter of the front lens needs to be the largest in the optical system, so that there is a problem that the finder becomes large.

The present invention solves such a problem and has high optical performance,
It is an object of the present invention to provide a variable magnification finder optical system capable of achieving high magnification with a small moving amount of each group.

Means for Solving the Problems In order to achieve the above object, according to the present invention, in a real image type variable magnification finder optical system comprising a positive objective lens system, a positive condenser lens and a positive eyepiece lens system in order from the object side, The objective lens system comprises, in order from the object side, a negative first group, a negative second group, and a positive third group, and the second and third groups move on the optical axis during zooming. I have.

For example, at the time of zooming, the third lens unit moves on the optical axis as a variator to perform zooming, and at least the second lens unit moves on the optical axis as a compensator to correct diopter correction (from a higher magnification to a lower magnification). When zooming to the side, move to the pupil side)
Can be configured. Here, the first group may be composed of a fixed lens during zooming.

Further, all the groups constituting the objective lens system may be configured to move at the time of zooming. In particular, it is preferable that the third group has at least one aspheric surface.

As shown in FIG. 11, the first group (I) having a negative refractive power
And the second unit (II) serves to position the principal point (H) of the lens system behind the third unit, that is, to extend the lens back (the distance between the third unit (III) and the image plane). There is. The third positive lens unit (III) functions to converge and form an image.

In the case of a real image type finder, an inversion optical system is indispensable, but by extending the lens back, a space for accommodating a prism, a mirror, and the like can be secured.

As described above, the cause of the large distortion difference that has been a problem in the conventional negative and positive two-unit zoom is the first unit (LI). In the present invention, the refractive power is 2 by dividing the negative first unit (LI) of the negative / positive two-unit zoom into two.
In this case, the influence of the generated distortion can be reduced. This is because the influence of the light rays passing through the first lens unit (I) when the light beam passes through the first lens unit (I) in the negative and positive three lens units as in the present invention is the first negative lens unit in the negative and positive two lens units. This is because the influence of the light ray when passing through the second lens unit (II) is small because the light ray passing through the second lens group (II) passes near the center of the lens.
Since aberration correction can be easily performed in this manner,
Accordingly, higher magnification can be achieved.

Also, in the present invention, the refractive power of the group having the negative refractive power is changed by dividing the negative first group of the conventionally known negative / positive two-group zoom into two parts and changing the distance between them. It is configured to be able to. As a result, the focal length can be changed even if the movement of the group having a positive refractive power is small. Therefore, if the movement amount of each group is made substantially equal to that of the conventional two-group zoom, a higher magnification objective lens system can be realized. Further, aberration correction accompanying an increase in magnification can be easily performed.

As shown in FIG. 9, in the case of the virtual image type finder including the negative whole group (L _F ) and the positive rear group (L _R ), the light beam is shifted away from the pupil (E) and closer to the object side, so that the optical axis (A _X ). That is, the front lens (L _F ) needs to have the largest diameter in the optical system. On the other hand, in the case of a real image type viewfinder as in the present invention, a real image is formed at least once inside the optical system. As can be seen from the configuration of the real image type finder optical system including the objective lens system (L ₀ ), condenser lens (L _C ), and eyepiece lens system (L _E ) shown in FIG. Since the path of the light beam can be changed by disposing the condenser lens (L _C ), the diameter of the front lens (the diameter of the objective lens system (L ₀ )) can be reduced. Further, in this case, since the light does not pass through a portion having a strong refractive power around the lens, aberration correction is easy.

In the negative / negative / positive three-unit zoom such as the objective lens system used in the present invention, the difference between the negative second unit and the positive third unit greatly affects the error sensitivity to diopter change. This effect is maximized especially on the high magnification side.

The magnification of the entire viewfinder optical system on the high magnification side
_T , the refractive power of the objective lens system on the high magnification side is φ _T , and the combined refractive power of the first and second units on the high magnification side is φ
_12T , the refractive power of the third group on the high magnification side is φ ₃ , and the distance between the principal points of the third group and the group obtained by combining the first and second groups is
e _123T, LB a distance from the third group rear principal point to the image plane _T, the refractive power of the ocular lens system and _{φ e, Γ T = φ e} / φ T φ T = φ 12T + φ 3 -e 123T · φ _12T · φ _{3 (wherein, φ 12T <0, φ 3} > is _{0) LB T = (1-} e 123T · φ 12T) / φ T is satisfied.

Therefore, the influence of the air spacing on the image plane position variation is as follows: Is represented by Further, between the change in the image plane position (ΔLB _T ) and the diopter change (ΔD _T (diopter)), ΔLB _T = (1/1000) · (1 / φ _e ² ) · ΔD _T Equation holds, and therefore Becomes

From the above formula and Gamma _T is because a value determined as a viewfinder specification, it is possible to control the error sensitivity to the diopter of the air gap be determined phi _12T.

Since the zoom configuration of the objective lens system in the present invention is negative, positive, and positive, φ _12T <0. Therefore, if the above equation is transformed, Can be obtained. Here, it depends on manufacturing constraints Sets the upper limit of | φ _12T |.

Therefore, the present invention is preferably configured to satisfy the following conditional expression.

| Φ _12T | <{10 × 1 / (1000Γ _T ² )} ^1/2 φ However, φ _12T <0.

This conditional expression is for suppressing a change in diopter due to a manufacturing error in the interval between the second and third units to a certain range.

If the upper limit of the conditional expression is exceeded, adjustment is required to suppress a change in diopter, which may cause an increase in cost or a decrease in yield. It also has an effect on optical performance.

Examples Examples of the variable magnification finder optical system according to the present invention will be described below.

However, in each embodiment, r _i (i = 1, 2, 3,...) Is the radius of curvature of the i-th surface counted from the object side, t _i (i = 1, 2,
3, ...) indicates the i-th axial top surface distance counted from the object side, and N _i (i = 1,2,3, ...), ν _i (i = 1,2,3, ..). .) Is the refractive index for the d-line of the i-th lens counted from the object side,
Indicates Abbe number. Γ indicates the finder magnification.

| Φ _12T | and ｛10 in the conditional expression in each embodiment
^{_{× 1 / (1000Γ T 2)}} } are also shown ^1/2.

In the examples, the surface marked with * is attached to the radius of curvature, which indicates that the surface is constituted by an aspheric surface, and is defined by the following expression representing the surface shape of the aspheric surface.

Where X: deviation from the reference plane in the optical axis direction r: paraxial radius of curvature h: height in the direction perpendicular to the optical axis A _i : i-th aspherical coefficient ε: quadratic surface parameter .

<Example 1> Γ = −1.094 (high magnification side) to −0.739 (intermediate magnification) to −0.
499 (low magnification side) Aspheric coefficient r ₁ : ε = 0.10000 × 10 A ₄ = 0.67946 × 10 ^-4 r ₅ : ε = -0.65943 × 10 r ₁₂ : ε = 0.10000 × 10 A ₄ = 0.52489 × 10 ^-4 A ₆ = 0.25961 × 10 ⁻⁵ A ₈ = −0.50187 × 10 ⁻⁷ | φ _12T | = 0.0586466 {10 × 1 / (1000 _T ² )} ^1/2 = 0.0914421 <Example 2> Γ = −0.991 (high magnification side) to −0.787 (Intermediate magnification) --0.
627 (low magnification side) Aspheric coefficient r ₅ : ε = −0.69730 × 10 r ₁₀ : ε = 0.0 A ₄ = 0.39271 × 10 ⁻⁴ A ₆ = −0.11626 × 10 ⁻⁶ A ₈ = 0.45297 × 10 ⁻⁸ | φ _12T | = 0.0547722 ｛ ^{_{10 × 1 / (1000Γ T 2}} )} 1/2 = 0.1009589 < example 3> Γ = -1.191 (high magnification side) - - 0.688 (intermediate magnification) ~-0.
397 (low magnification side) Aspheric coefficient r ₁ : ε = 0.10000 × 10 A ₄ = 0.74521 × 10 ^-4 A ₆ = -0.17382 × 10 ^-5 A ₈ = 0.61139 × 10 ^-7 A ₁₀ = -0.78923 × 10 ^-9 r ₅ : ε = _{^{-0.13960 × 10 2 r 10: ε}} = -0.27727 × 10 | φ 12T | = 0.0527046 {10 × 1 / (1000Γ T 2)} 1/2 = 0.0839437 < example 4> Γ = -1.109 (high magnification side) ~ -0.667 (intermediate magnification) --0.
401 (low magnification side) Aspheric coefficient r ₃ : ε = −0.12974 × 10 ² r ₅ : ε = −0.56825 × 10 r ₁₀ : ε = −0.20905 × 10 A ₄ = 0.14544 × 10 ^-4 A ₆ = −0.25910 × 10 ^-7 A ₈ = 0.69616 × 10 ^-9 | φ _12T | = 0.0463468 {10 × 1 / (1000 _T ² )} ^1/2 = 0.0901568 FIGS. 1 to 4 are lens configuration diagrams corresponding to the first to fourth embodiments. In each drawing, the lens arrangement on the high magnification side (a), the intermediate magnification side (b), and the low magnification side (c) are shown. Note that (A) in each drawing represents a pupil plane.

In the first embodiment, a biconcave negative first lens (first group (I)), a second lens including a negative meniscus lens concave on the object side (second group (II)), and a biconvex lens are arranged in this order from the object side. Positive third
Consisting of a positive objective lens system consisting of a lens (third group (III)), a positive condenser lens consisting of a flat plate and a positive plano-convex lens convex on the object side, and an eyepiece lens system consisting of a biconvex positive lens Have been. The object-side surface of the first lens, the object-side surface of the third lens, and the object-side surface of the eyepiece are aspherical.

In the second embodiment, the first lens (first group (I)) composed of a negative meniscus lens concave to the object side in order from the object side, the negative bi-concave second lens (second group (II)), and the biconvex lens A positive objective lens system composed of a positive third lens (third group (III))
Positive plano-convex lens convex on the object side (condenser lens)
And a biconvex positive eyepiece system.
The object-side surface of the third lens and the pupil-side surface of the eyepiece are aspherical.

In the third embodiment, a bi-concave negative first lens (first group (I)), a second lens (a second group (II)) including a negative meniscus lens concave on the object side, and a biconvex lens are arranged in this order from the object side. Positive third
A positive objective lens system composed of a lens (third group (III)), a positive condenser lens composed of a positive plano-convex lens convex on the object side, and an eyepiece lens system composed of a biconvex positive lens. I have. The object-side surface of the first lens, the object-side surface of the third lens, and the object-side surface of the eyepiece are aspherical.

In the fourth embodiment, a first lens (first group (I)) including a negative meniscus lens concave to the pupil side in order from the object side, a biconcave negative second lens (second group (II)), and both A positive objective lens system including a convex positive third lens (third group (III));
It comprises a positive condenser lens composed of a positive plano-convex lens convex on the object side, and an eyepiece lens system composed of a biconvex positive lens and a biconcave negative lens. The object side surface of the second lens, the object side surface of the third lens, and the object side surface of the object side eyepiece are aspherical.

The real image formed by the objective lens system including the negative first unit (I), the negative second unit (II), and the positive third unit (III) is passed through a condenser lens arranged near the image plane to form an eyepiece. Observe with a lens system. During zooming from the high magnification side to the low magnification side, the third group (III) moves toward the pupil side, and the second group (II) moves for diopter correction.

In the first, second and fourth embodiments, the first lens unit (I) is fixed during zooming, but in the third embodiment, the first lens unit (I) moves toward the object side during zooming from the high magnification side to the low magnification side. . Group 2 (I
By moving the first lens unit (I) in addition to the third lens unit (III) and the third lens unit (III), it is possible to control the passing position of a light beam with a high angle of view at each focal length, from the high magnification side to the low magnification side. Can be reduced. Therefore, a higher zoom ratio can be achieved.

The aspherical surface provided in the third lens unit (III) is formed so that the positive refractive power becomes weaker toward the periphery. As a result, distortion and astigmatism can be reduced.

5 to 8 are aberration diagrams corresponding to Examples 1 to 4, in which (a) is a high magnification side, (b) is an intermediate magnification, and
(C) shows the aberration with respect to the d-line on the low magnification side.
The dotted line (DM) and the solid line (DS) represent astigmatism on the meridional surface and the sagittal surface, respectively.

As described above, according to the variable magnification finder optical system of the present invention, in the real image type variable magnification finder optical system including the positive objective lens system, the positive condenser lens, and the positive eyepiece lens system in order from the object side. The objective lens system includes, in order from the object side, a negative first group, a negative second group, and a positive third group, and the second and third groups move on the optical axis during zooming. With this configuration, it is possible to realize a variable magnification finder optical system that has high optical performance and achieves high magnification with a small amount of movement of each group.

[Brief description of the drawings]

FIG. 1, FIG. 2, FIG. 3, and FIG. 4 are lens configuration diagrams corresponding to Examples 1 to 4 of the present invention, respectively. FIG. 5, FIG. 6, FIG. 7, and FIG. 8 are aberration diagrams corresponding to Examples 1 to 4 of the present invention, respectively. FIG. 9 is an optical path diagram of a virtual image type finder optical system for explaining the size of the front lens in the present invention, and FIG. 10 is a real image type finder for explaining the size of the front lens in the present invention. It is an optical path diagram of an optical system. FIG. 11 is a diagram showing the refractive index arrangement of the objective lens system according to the present invention. FIG. 12 is an optical path diagram of a conventional example.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Ichiro Kasai 2-3-3 Azuchicho, Chuo-ku, Osaka-shi, Osaka Osaka Kokusai Building Minolta Camera Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (5)

(57) [Claims] 1. A real image type variable magnification finder optical system comprising a positive objective lens system, a positive condenser lens and a positive eyepiece lens system in order from the object side, wherein the objective lens system is a negative first lens system in order from the object side. A zoom finder optical system, comprising: a lens group, a negative second lens group, and a positive third lens group, wherein the second lens group and the third lens group move on the optical axis during zooming. 2. The variable magnification finder optical system according to claim 1, wherein said first group comprises a fixed lens at the time of zooming. 3. The variable magnification finder optical system according to claim 1, wherein all the units constituting the objective lens system move during magnification change. 4. The variable magnification finder optical system according to claim 1, wherein said third lens unit has at least one aspherical surface. 5. The first variable magnification finder optical system according to claim, characterized by satisfying the following _{condition; | φ 12T | <{10} × 1 / (1000Γ T 2)} 1/2 Here , Φ _12T : combined refractive power of the first and second groups on the high magnification side Γ _T : magnification of the entire finder optical system on the high magnification side, where φ _12T <0.