JPH0749449A - Reverse galilean finder - Google Patents

Abstract

PURPOSE:To provide a reverse Galilean finder in which the distance from the final lens surface of an ocular to an eye point is extended, and a satisfactory finder image can be observed without vignetting even in water by properly constituting the lens structures of an objective lens and the ocular. CONSTITUTION:In a reverse Galilean finer having an objective lens L1 having negative refractive force and an ocular having positive refractive force in the order from an object side, the objective lens has, in the order from the object side, a negative meniscus-like eleventh lens L1a with a convex surface to the object side; and a negative twelfth lens L1b with both concave lens surfaces in which the curvature on the object side is high, compared with an image surface side, and the ocular has at least one positive lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reverse Galileo finder, and more particularly to a lens shutter camera of a photographic camera for 35 mm film, a video camera, etc.
The present invention relates to a reverse Galileo finder (albada-type reverse Galileo finder) for a so-called high eye point finder, which has a long distance from the final lens surface of the eyepiece to the eye point.

[0002]

2. Description of the Related Art Conventionally, a reverse Galileo finder (albada type reverse Galileo finder) has been widely used as a finder for a lens shutter camera or the like.

This reverse Galileo finder has a feature that a good finder image can be observed with a relatively simple lens structure.

Further, in recent years, a reverse Galileo finder for so-called high eye points, which has a long distance from the final lens surface of the eyepiece to the eyepoint, so that even a person wearing glasses can observe the viewfinder image without vignetting, Japanese Patent Publication No. 63-9202 and Japanese Patent Publication No. 2-5044
Various proposals have been made in Japanese Patent No. 6 and the like.

(Here, a point where a light ray outside the maximum angle of view light ray (light flux) intersects the optical axis is called an eye point).

In Japanese Patent Publication No. 63-9202, the objective lens is composed of first and second negative lenses in order from the object side, and the eyepiece is composed of first and second positive lenses. It is as large as 0.55 and the distance from the final lens surface of the eyepiece to the eye point is as long as about 30 mm, but the exit pupil diameter φ is 20.
It discloses an inverted Galileo finder which has a good optical performance in mm.

In Japanese Patent Publication No. 2-50446, it is composed of an objective lens having two negative lenses and an eyepiece lens having two positive lenses, and the viewfinder magnification is 0.
5 discloses an inverted Galileo finder with a short overall lens length.

[0008]

However, the reverse Galileo finder proposed in Japanese Patent Publication No. Sho 63-9202 has the advantages described above, but it becomes a considerably large finder as a whole device. There is a problem that it is difficult to reduce the size of the entire device.

The reverse Galileo finder proposed in Japanese Examined Patent Publication No. 2-50446 has the advantage that the total length of the finder lens is short, but for example, it makes good observation of the finder image even in water without vignetting. There is a problem that it is difficult to apply it to the viewfinder.

For this reason, for example, in the case of a finder, which is premised on observing a good finder image that is easy to see even underwater or with glasses, the distance from the final lens surface of the eyepiece to the eye point is set. If it is not set long, the peripheral rays of light will be vignetted in the finder field of view indicating the shooting range, and as a result, the finder image will be vignetted in the peripheral part of the finder field, and only the center part can be satisfactorily observed. Come on.

According to the present invention, by appropriately setting the lens configurations of the objective lens and the eyepiece lens, while ensuring a long distance from the final lens surface of the eyepiece lens to the eye point,
For example, it is an object of the present invention to provide an inverted Galileo finder that allows good observation of a finder image without vignetting of the light flux around the screen even in water or with glasses.

[0012]

The inverse Galileo finder of the present invention is (1-1) an inverse Galileo finder having an objective lens having a negative refractive power and an eyepiece lens having a positive refractive power in order from the object side. The objective lens has a negative meniscus eleventh lens having a convex surface directed toward the object side in order from the object side, and a negative twelfth lens having concave surface on both object sides, which has a stronger curvature on the object side than on the image side. However, the eyepiece lens is characterized by having at least one positive lens.

In particular, when the focal length of the objective lens is F1 and the radius of curvature of the object-side lens surface of the twelfth lens is R3, 1.0 <R3 / F1 <3.6 (1) It is characterized by satisfying the conditions.

(1-2) In an inverse Galileo finder having an objective lens having a negative refractive power and an eyepiece lens having a positive refractive power in order from the object side, the objective lens is a negative eleventh lens and a negative lens in order from the object side. The twelfth lens is a positive second lens and a second positive lens in order from the object side.
The objective lens has a focal length of F1, and the eleventh lens and the twelfth lens have focal lengths of f1 and f1, respectively.
When f2 is set, 1.8 <f1 / F1 <2.7 (2) 1.6 <f2 / F1 <2.6 (3) The condition is satisfied. .

The focal length of the eyepiece lens is F2, and the focal lengths of the 21st and 22nd lenses are f3 and f, respectively.
When it is set to 4, 1.0 <f3 / F2 <2.0 ... (4) 2.1 <f4 / F2 <3.8 ... (5) The condition is satisfied. .

[0016]

1 to 5 are lens cross-sectional views of Numerical Examples 1 to 5 of the present invention described later, and FIGS. 6 to 10 are aberration diagrams of Numerical Examples 1 to 5 of the present invention.

In FIGS. 1 and 3 to 5, L1 is an objective lens having a negative refracting power, which is a negative meniscus eleventh lens L1a having a convex surface directed in order from the object side to the object side.
And a negative twelfth lens L1b whose concave surface has a stronger curvature on the object side than on the eyepoint side (image surface side), of which a lens surface on the eyepoint E side of the twelfth lens L1b A reflecting surface such as a half mirror surface is provided on the entire peripheral surface of the lens surface M4 around the peripheral portion of M4,
A light flux from a finder field frame S described later is reflected.

Reference numeral L2 denotes an eyepiece lens having a positive refractive power, which includes a positive 21st lens L2a having a convex surface directed toward the eyepoint E side from the object side, and a positive 22nd lens L2.
b, and a finder field frame S is provided on the object-side lens surface M5 of the 21st lens L2a.

In the numerical example 2 of FIG. 2, the objective lens L
1 is the same as Numerical Examples 1 and 3 to 5, but the eyepiece lens L2 is composed of one positive 21st lens L2a.

Generally, in order to reduce the size of the finder system and set a long distance from the final lens surface of the eyepiece to the eye point, each element (lens) may be set so that the finder magnification becomes small.

In the present embodiment, for example, the finder magnification is set low so that the distance from the final lens surface of the eyepiece to the eye point is long so that a good viewfinder image can be observed in water.

Therefore, in the finder lens structure of this embodiment, both the focal length F1 of the objective lens L1 and the focal length F2 of the eyepiece L2 are first set to be short to shorten the total lens length. Finder magnification is F1 / F
Therefore, by setting only the focal length F1 of the objective lens to be shorter, the distance from the final lens surface of the eyepiece to the eye point E is set to a desired length.

That is, in this embodiment, the objective lens L1
And the eyepiece L2 both have strong refracting power to shorten the total length of the finder system lens, and further the objective lens L1.
By increasing the refracting power of the eyepiece, the distance from the final lens surface of the eyepiece to the eye point E is increased, and the size of the entire apparatus is reduced.

At this time, if the refracting power of the entire lens system, especially the objective lens, becomes strong, the aberrations will be greatly generated, and it will be difficult to correct the aberrations. In particular, when the refracting power of the objective lens becomes strong, the problem that distortion aberration becomes large occurs.

Therefore, in this embodiment, in order to correct the distortion, the negative refractive power of the entire objective lens L1 is shared by the two negative single lenses L1a and L1b so as to be as uniform as possible. As a result, the total length of the lens is short and the viewfinder image is easy to see by obtaining the freedom of aberration correction.

That is, as described above, the objective lens L1 has a negative meniscus shape with the convex surface facing the object side in order from the object side.
The first lens L1a and the negative twelfth lens L1b, which has a concave surface on the object side where the curvature on the object side is stronger than that on the image surface side, are used to reduce distortion.

Among the two negative lenses constituting the objective lens in the above-mentioned conventional Albada type reverse Galileo finder, the lens surface on the eyepoint side of the negative 12th lens on the eyepoint side is the light flux from the viewfinder field frame. Is configured as a reflection surface or a half mirror surface. For this reason, the degree of freedom of aberration correction of the twelfth lens is limited, and therefore the refracting power of the twelfth lens is weak, so that the eleventh lens on the object side must be provided with a correspondingly strong refracting power. did not become. Therefore, it is difficult to correct aberrations with the conventional objective lens shape.

On the other hand, in this embodiment, the eyepiece lens L2
The finder field frame S is provided on the object-side lens surface M5 of the positive 21st lens L2a, and the luminous flux from the finder field frame S is twelfth lens L1b having the above-described shape.
By reflecting the light from the lens surface M4 on the eyepoint E side, the finder field frame S is observed together with the finder image at a good diopter.

That is, in this embodiment, in order to satisfactorily correct the aberration when projecting the viewfinder field frame S, the first
The curvature of the lens surface M4 of the two lenses L1b is made as small as possible, and the lens surface distance between the lens surface M4 and the lens surface M5 of the 21st lens L2a of the eyepiece lens L2 is made as long as possible.

Further, the curvature of the object-side lens surface M3 of the twelfth lens L1b is made as strong as possible on the object side as compared to the eyepoint E side, so that the twelfth lens L1b has a strong refracting power, whereby the eleventh lens. L1a and the first
The refracting power of the objective lens L1 is equally shared by the two lenses L1b, and the aberration is corrected well.

Further, when the eyepiece lens L2 is composed of two lenses, the lens surfaces of the two lenses of the positive 21st lens L2a and the positive 22nd lens L2b have curvatures from the object side to the eye point E side. It is configured to be strong. Further, when the eyepiece lens L2 is composed of one lens, it has the same lens shape. Thereby, the objective lens L1,
In particular, the coma aberration, the distortion aberration, and the like generated on the lens surface M3 of the twelfth lens L1b are removed to obtain good optical performance.

Next, the technical meaning of each of the above conditional expressions (1) to (5) will be described.

Conditional expression (1) relates to the curvature of the object-side lens surface M3 of the twelfth lens of the objective lens. When the value goes below the lower limit of conditional expression (1), the curvature of the lens surface M3 becomes strong, and coma aberration becomes large, which is not preferable.

When the upper limit of conditional expression (1) is exceeded, the curvature of the lens surface M3 becomes gentle, and the refracting power of the twelfth lens becomes loose. Is not good as it grows.

Conditional expressions (2) and (3) are the first objective lens
The present invention relates to the distribution of the refractive powers of the first lens and the twelfth lens.

When the lower limit value of the conditional expression (2) and the upper limit value of the conditional expression (3) are exceeded, the refractive power share of the eleventh lens increases and the distortion is increased similarly to the condition of the upper limit value of the conditional expression (1). It is not good because the aberration becomes large.

If the upper limit value of the conditional expression (2) and the lower limit value of the conditional expression (3) are exceeded, the distribution of the refractive power of the twelfth lens becomes strong similarly to the condition of the lower limit value of the conditional expression (1). This is not good because the generation of aberrations increases.

The conditional expressions (4) and (5) relate to the distribution of the refracting powers of the 21st lens and the 22nd lens when the eyepiece lens is composed of two lenses.

When the upper limit value of the conditional expression (4) and the lower limit value of the conditional expression (5) are exceeded, the refracting power of the twenty-first lens becomes strong, and the inverse Galileo finder in this embodiment has a high eye point design, so that the eyepiece is used. Lens aperture φ is 20m
Since it is as large as m or more, when projecting the viewfinder frame,
This is not good because the flare caused by the lower rays (off-axis rays) becomes large.

When the lower limit value of conditional expression (4) and the upper limit value of conditional expression (5) are exceeded, the refracting power of the 21st lens, which has a low incident height of axial rays, becomes strong, and the incident height of axial rays becomes high. 22nd high
Since the refracting power of the lens becomes weak, spherical aberration when projecting the field frame becomes over (overcorrection), which is not good.

The object of the present invention is achieved by satisfying the above conditional expressions (1) to (5), but the following conditional expressions (6) and (7) are further satisfied. By doing so, the optical performance can be further enhanced.

That is, when the air gap between the lens surface M4 on the eyepoint side of the twelfth lens of the objective lens and the lens surface M5 on the object side of the twenty-first lens of the eyepiece lens is D4, 0.32 <D4 / F2 <0.43 ············································ can be satisfied.

Conditional expression (6) relates to the air gap between the twelfth lens and the twenty-first lens. If the lower limit of conditional expression (6) is exceeded, the air distance between the twelfth lens and the twenty-first lens becomes short, and spherical aberration when projecting the field frame becomes excessive (overcorrection), which is not preferable. On the other hand, if the upper limit of conditional expression (6) is exceeded, the air gap becomes long and spherical aberration when projecting the field frame becomes under (undercorrection), which is not preferable.

When the radiuses of curvature of the lens surfaces M3 and M4 on the object side and the eyepoint side of the twelfth lens are R3 and R4, respectively, -0.7 <R3 / R4 <-0.1 ... (7 ) It is better to satisfy the following conditions.

Conditional expression (7) relates to the ratio of the radius of curvature between the object-side lens surface M3 and the eyepoint-side lens surface M4 of the twelfth lens.

When the value goes below the lower limit of the conditional expression (7), the curvature of the lens surface M3 becomes tight and coma aberration occurs, which is not preferable. If the upper limit of conditional expression (7) is exceeded, the lens surface M
This is not good because the curvature of 4 becomes so tight that the aberration when projecting the field frame becomes worse.

As described above, in this embodiment, by appropriately setting the lens configurations of the objective lens and the eyepiece lens as described above, the exit pupil system φ (20 mm to 27 mm) is large and the low magnification finder magnification β (X- 0.39 ~ X-0.4
In 5), an inverse Galileo finder is obtained in which the distance (38 mm to 62.5 mm) from the final lens surface of the eyepiece to the eye point can be lengthened and the lens aperture of the objective lens can be reduced.

Although the eyepiece lens is composed of two positive lenses in this embodiment, the present invention is the same as that of the first embodiment even if it is composed of one positive lens as in Numerical Embodiment 2 which will be described later. It is possible to obtain various effects.

Next, Numerical Examples 1 to 5 of the present invention will be shown. In each numerical example, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are i-th order from the object side, respectively.
The refractive index and Abbe number of the glass of the th lens.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples. Numerical Example 1 β = 0.44 2 ω = 58 ° R 1 = 37.05 D 1 = 1.50 N 1 = 1.58306 ν 1 = 30.2 R 2 = 13.01 D 2 = 5.43 R 3 = -21.15 D 3 = 1.30 N 2 = 1.58306 ν 2 = 30.2 R 4 = 105.00 D 4 = 13.30 R 5 = ∞ D 5 = 2.90 N 3 = 1.49171 ν 3 = 57.4 R 6 = -28.28 D 6 = 0.29 R 7 = -221.82 D 7 = 2.10 N 4 = 1.58306 ν 4 = 30.2 R 8 = -41.21 D 8 = 38.00 R 9 = ∞ (eye point) Eye point = 38 Numerical Example 2 β = 0.39 2 ω = 58 ° R 1 = 198.49 D 1 = 1.70 N 1 = 1.58306 ν 1 = 30.2 R 2 = 16.90 D 2 = 11.02 R 3 = -67.73 D 3 = 1.58 N 2 = 1.58306 ν 2 = 30.2 R 4 = 109.82 D 4 = 18.27 R 5 = ∞ D 5 = 3.95 N 3 = 1.58306 ν 3 = 30.2 R 6 = -29.64 D 6 = 60.00 R 7 = ∞ (eye point) Eye point = 60 Numerical example 3 β = 0.43 2 ω = 58 ° R 1 = 57.94 D 1 = 2.00 N 1 = 1.58306 ν 1 = 30.2 R 2 = 18.19 D 2 = 7.95 R 3 = -30.37 D 3 = 1.73 N 2 = 1.58306 ν 2 = 30.2 R 4 = 169.57 D 4 = 19.18 R 5 = ∞ D 5 = 4.20 N 3 = 1.49171 ν 3 = 57.4 R 6 =- 34.55 D 6 = 0.30 R 7 = -242.71 D 7 = 2.10 N 4 = 1.58306 ν 4 = 30.2 R 8 = -70.00 D 8 = 60.00 R 9 = ∞ (eye point) Point = 60 Numerical Example 4 β = 0.39 2 ω = 58 ° R 1 = 142.65 D 1 = 2.00 N 1 = 1.58306 ν 1 = 30.2 R 2 = 17.25 D 2 = 6.57 R 3 = -22.81 D 3 = 1.73 N 2 = 1.58306 ν 2 = 30.2 R 4 = 160.00 D 4 = 15.56 R 5 = ∞ D 5 = 4.10 N 3 = 1.49171 ν 3 = 57.4 R 6 = -32.38 D 6 = 0.30 R 7 = 7017.87 D 7 = 2.70 N 4 = 1.58306 ν 4 = 30.2 R 8 = -58.07 D 8 = 62.50 R 9 = ∞ (eye point) Eye point = 60 Numerical example 5 β = 0.41 2 ω = 58 ° R 1 = 67.93 D 1 = 1.50 N 1 = 1.58306 ν 1 = 30.2 R 2 = 14.13 D 2 = 5.67 R 3 = -20.35 D 3 = 1.30 N 2 = 1.58306 ν 2 = 30.2 R 4 = 136.71 D 4 = 13.65 R 5 = ∞ D 5 = 3.50 N 3 = 1.49171 ν 3 = 57.4 R 6 = -26.16 D 6 = 0.29 R 7 = -372.86 D 7 = 2.10 N 4 = 1.58306 ν 4 = 30.2 R 8 = -50.00 D 8 = 40.00 R 9 = ∞ (eye point) Eye point = 40

[0051]

[Table 1]

[0052]

According to the present invention, by properly setting the objective lens and the eyepiece lens as described above, the distance from the final lens surface of the eyepiece lens to the eye point can be lengthened, and the entire viewfinder can be used. While making it small
For example, it is possible to achieve an inverted Galileo finder that can observe a finder image satisfactorily without vignetting even when underwater or wearing glasses.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 3 of the present invention.

FIG. 4 is a lens cross-sectional view of Numerical Example 4 of the present invention.

FIG. 5 is a lens cross-sectional view of Numerical Example 5 of the present invention.

FIG. 6 is a diagram showing various types of aberration in Numerical Example 1 of the present invention.

FIG. 7 is a diagram of various types of aberration in Numerical example 2 of the present invention.

FIG. 8 is a diagram showing various types of aberration in Numerical Example 3 of the present invention.

FIG. 9 is a diagram showing various types of aberration in Numerical Example 4 of the present invention.

FIG. 10 is a diagram of various types of aberration in Numerical example 5 of the present invention.

[Explanation of symbols]

 L1 Objective lens L1a 11th lens L1b 12th lens L2 Eyepiece L2a 21st lens L2b 22nd lens S Finder view frame E Eyepoint

Claims (4)

[Claims] 1. An inverse Galileo finder having an objective lens having a negative refractive power and an eyepiece lens having a positive refractive power in order from the object side, wherein the objective lens is a negative meniscus having a convex surface directed in order from the object side to the object side. -Shaped eleventh lens and a negative twelfth lens having concave concave lens surfaces on the object side having a stronger curvature on the object side than on the image surface side, and the eyepiece has at least one positive lens Reverse Galileo finder characterized by that. 2. When the focal length of the objective lens is F1 and the radius of curvature of the object-side lens surface of the twelfth lens is R3, 1.0 <R3 / F1 <3.6 is satisfied. The reverse Galileo finder according to claim 1, which is characterized in that. 3. An inverse Galileo finder having an objective lens having a negative refracting power and an eyepiece lens having a positive refracting power in order from the object side, wherein the objective lens is a negative eleventh lens and a negative twelfth lens in order from the object side. The objective lens has a positive 21st lens and a positive 22nd lens in order from the object side, the focal length of the objective lens is F1, and the focal points of the 11th lens and the 12th lens are An inverse Galileo finder, wherein the conditions satisfy 1.8 <f1 / F1 <2.7 1.6 <f2 / F1 <2.6 when the distances are f1 and f2, respectively. 4. The focal length of the eyepiece lens is F2, and the focal lengths of the 21st and 22nd lenses are f3 and f, respectively.
4. The inverse Galileo finder according to claim 3, wherein the condition of 1.0 <f3 / F2 <2.0 2.1 <f4 / F2 <3.8 is satisfied.