JPH05164964A - Real image type finder optical system - Google Patents

Abstract

PURPOSE:To make the finder constitution length of the real image type finder optical system short, to give excellent optical performance, and to make the optical system compact. CONSTITUTION:The real image type finder optical system is constituted by arranging an objective system 1 which has positive refracting power, an image erection system 5 consisting of plural reflecting members for erecting an intermediate image formed by the objective system 1, and an ocular system 9 which has positive refracting power in order; and the 1st reflecting member of the image erection system 5 is a prism 6 which has an incidence surface with negative refracting power and >=1 reflecting surface and satisfies a condition of Bf/fw<0.8 and a surface having positive refracting power is provided nearby the position of the intermediate image formation by the objective system 1. Here, Bf is the on-axis distance from the projection surface of the 1st reflecting member to the intermediate image formation position and fw is the focal distance of the objective system 1 including the 1st reflecting member.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a real image type finder optical system used in a photographic camera, a video camera or the like.

[0002]

2. Description of the Related Art In a real image type finder optical system, a Porro prism is often used in order to make an observation image an erect image as described in, for example, JP-A-1-131510. The Porro prism is often used because it can be made smaller than other optical systems such as an image rotator and a relay optical system that invert vertically and horizontally, but it is generally used in the vicinity of the entrance surface of the integrated Porro prism by an objective lens system. In many cases, an image is formed. Therefore, when the back focus of the objective lens system, that is, the distance from the final surface of the objective lens system to the intermediate image formation position is relatively long, the entrance surface of the objective lens system to the exit surface of the eyepiece system. There was a problem that the finder configuration length up to became long.

Therefore, conventionally, a structure has been adopted in which the finder structure length is shortened by placing the intermediate image forming position of the objective lens system inside the Porro prism and bringing the objective lens system close to the Porro prism system.

[0004]

However, since it is necessary to install a visual field frame for determining the visual field range at the intermediate image forming position, when the intermediate image forming position is placed inside the Porro prism, the Porro prism is Divide into multiple prisms,
It is general to set an intermediate image forming position in the space generated by the division and install a visual field frame there. Therefore, unless the back focus length of the objective lens system is set to an appropriate length according to how the prism is divided, the intermediate image formation position will enter the prism and the field frame cannot be installed, or the viewfinder optical system will not be installed. The system becomes large. Therefore, there is a problem that the optimum range of the back focus length of the objective lens system is narrow, which becomes a constraint condition when designing the objective lens system, which is one of the factors that deteriorate the optical performance.

In view of the above problems, the present invention is a real image type finder optical system that obtains an erect image by a Porro prism system composed of a plurality of reflecting members, but has a short finder configuration length and good optical performance. The present invention is intended to provide a real image type viewfinder optical system which is compact in size.

[0006]

A real image type finder optical system according to the present invention comprises an objective lens system having a positive refracting power and a plurality of reflecting members for making an intermediate image by the objective lens system an erect image. In a real image type finder optical system in which an image erecting system and an eyepiece lens system having a positive refractive power are sequentially arranged, a first reflecting member of the image erecting system has an entrance surface having a negative refractive power. A prism having at least one reflecting surface and satisfying the following condition B _f / _fw <0.8, and further providing a surface having a positive refractive power in the vicinity of the intermediate image forming position by the objective lens system. It is characterized by that. However, B _f is the axial distance from the exit surface of the first reflecting member to the intermediate image forming position, and f _w is the focal length of the objective lens system including the first reflecting member.

[0007]

In the finder optical system according to the present invention, since the incident surface of the first prism of the divided Porro prism has a negative refracting power, the incident light of the first prism is incident on the light beam which is being converged by the objective lens system. Divergent action works,
The intermediate image forming position is moved to the eyepiece system side. Therefore, even if the back focus length from the final surface of the objective lens system to the intermediate image forming position is short and the optical path length required to insert the first prism of the Porro prism in the back focus portion cannot be obtained, the first prism By giving the entrance surface a negative refractive power, the back focus length can be made longer than the required optical path length, and as a result, the first prism can be inserted into the back focus portion. However, if the negative refracting power of the entrance surface of the first prism is increased more than necessary and the back focus length is increased, the distance from the final surface of the objective lens system to the entrance surface of the first prism widens, and The finder configuration length from the entrance surface to the exit surface of the eyepiece system becomes long. On the contrary, if the exit surface of the first prism is separated from the intermediate image forming position in order to shorten the finder configuration length, the volume of the Porro prism system increases, and the height or width of the Porro prism system increases, and The optical system cannot be miniaturized. Therefore, when the refractive power of the entrance surface of the first prism is set so as to satisfy the conditional expression B _f / _fw <0.8, an intermediate image is formed near the exit surface of the first prism, and it is most effective. Can be miniaturized.

Further, if a surface having a positive refractive power is set at the intermediate image forming position, the off-axis light beam diverging from the objective lens system can be made to have a converging action so as to be close to parallel light. The surface having a refracting power serves as a field lens for downsizing the second prism and the eyepiece lens system thereafter. This surface having a positive refracting power may be set as the entrance surface of the second prism, and since this surface is also near the intermediate image forming surface like the exit surface of the first prism, as described above, It functions as a field lens without impairing the effect of increasing the back focus length. still,
An optical system in which a field lens and a mirror are combined may be used instead of the second prism.

The first prism of the present invention may be a prism having a reflecting surface that reflects twice or three times depending on the type of the objective lens system. Generally, however, as the number of reflecting surfaces increases and the optical path length becomes longer, the entrance surface becomes the exit surface. That is, the distance to the intermediate image becomes long and the spread of the light beam on the incident surface becomes large, so that the aberration may become large. In such a case, the aberration can be effectively corrected by making the incident surface an aspherical surface.

Further, as described above, the focal length of the eyepiece lens system can be shortened by bringing the intermediate image forming position of the objective lens system (which coincides with the front focus position of the eyepiece lens system) closer to the eyepiece lens system. Therefore, the viewfinder magnification β can be increased. The finder magnification β is a value determined by the ratio β = f _T / f _R of the focal length f _T of the objective lens system and the focal length f _R of the eyepiece lens system.

[0011]

EXAMPLES Next, examples of the real image type finder optical system of the present invention will be shown. Example 1 FIG. 1 is a perspective view of Example 1, and FIG. 2 is a development view of Example 1 at the low magnification end, the middle, and the high magnification end. As shown in the figure, the objective lens system 1 comprises a first group 2 of negative lenses and a second group 3 having a positive refracting power as a whole, comprising a positive lens and a negative lens.
And the third lens group 4 of the positive lens. As is clear from FIG. 2, the second group 3 and the third group 4 in the objective lens system 1 move toward the object side while changing the relative distance, and the finder magnification changes from low magnification to intermediate magnification to high magnification. It is supposed to be done.

The image erecting system 5 comprises two first prisms 6 and a second prism 7, and these two prisms 6 and 7 have an image erecting function equivalent to that of a Porro prism. As is apparent from FIG. 1, the first prism 6 is a right-angled prism having a concave entrance surface, a negative refracting power, and a flat exit surface, and has one reflecting surface. The second prism 7 has a convex incident surface facing the exit surface of the first prism 6 and a positive refracting power, a flat exit surface, and three reflection surfaces. A field frame 8 is provided between the first prism 6 and the second prism 7, and this position is the intermediate image formation position of the objective lens system 1. Therefore, the incident surface of the second prism 7 functions as a field lens. Further, the image formed by the objective lens system 1 is made erect by a total of four reflections by one reflecting surface of the first prism 6 and three reflecting surfaces of the second prism 7.

An intermediate image formed by the objective lens system 1 is magnified and observed by an eyepiece lens system 9 composed of a positive single lens.
Although not shown, when this is used for a camera, a photographic lens system is provided in parallel with this finder optical system, and the variability of the photographic lens system and that of the finder optical system are linked. Become.

The data of this embodiment are as follows, and FIG. 3, FIG. 4 and FIG. 5 show the aberration curves at the low magnification end, the middle and the high magnification end of this embodiment, respectively. Magnification 0.45 to 1.14, Viewing angle (2ω) = 5
2.4 ° to 19.8 ° r ₁ = −13.1360 d ₁ = 1.0000 n ₁ = 1.58362 ν ₁
= 30.37 r ₂ = 13.7360 (aspherical surface) d ₂ (variable) r ₃ = 5.6100 (aspherical surface) d ₃ = 4.1750 n ₂ = 1.49230 ν _{2
= 57.71 r 4 = -43.8590 d 4} = 1.0220 r 5 = 9.8180 d 5 = 1.2930 n 3 = 1.58362 ν 3
= 30.37 r ₆ = 4.9250 d ₆ (variable) r ₇ = 6.9330 (aspherical surface) d ₇ = 1.7970 n ₄ = 1.49230 ν _{4
= 57.71 r 8 = -75.4320 d 8} ( _{variable) r 9 = -10.8400 d 9 =} 11.4120 n 5 = 1.49230 ν 5
_{= 57.71 r 10 = -79.7800 d 10} = 1.9200 r 11 = 10.4590 d 11 = 29.7810 n 6 = 1.49230 ν 6
= 57.71 r ₁₂ = ∞ d ₁₂ = 0.7000 r ₁₃ = 12.6840 (aspherical surface) d ₁₃ = 2.0780 n ₇ = 1.49230 ν ₇
= 57.71 r ₁₄ = -54.8790 d ₁₄ = 15.0000 r ₁₅ (eye point)

Aspheric surface coefficient Second surface E = -0.1448 × 10 ^-3 , F = -0.8142
0 × 10 ⁻⁵ , G = 0.5918 × 10 ⁻⁶ Third surface E = −0.77814 × 10 ⁻³ , F = −0.556
77 × 10 ⁻⁵ , G = −0.53661 × 10 ⁻⁶ Seventh surface E = −0.29784 × 10 ⁻³ , F = 0.2074
0 × 10 ⁻⁵ , G = −0.21629 × 10 ⁻⁶ 13th surface E = −0.71782 × 10 ⁻⁴ , F = −0.146
30 × 10 ^-5 , G = 0.31012 × 10 ^-7

Low fold Medium high fold d ₂ 12.296 5.823 1.851 d ₆ 1.782 4.643 2.961 d ₈ 1.957 5.569 11.223 B _f / f _w = 0. 20

Embodiment 2 FIG. 6 is a perspective view of Embodiment 2, and FIG. 7 is a development view of Embodiment 2 at the low magnification end, the middle and the high magnification end. As shown in the figure, the basic configuration is the same as that of the first embodiment. The objective lens system 1 is composed of the first group 2 to the third group 4, but differs from the example 1 in that the second group 3 is a positive single lens. The image erecting system 5 is divided into a first prism 6 and a second prism 7, each of which has two reflecting surfaces.

The data of this embodiment are as follows, and FIGS. 8, 9 and 10 show the aberration curves at the low magnification end, middle and high magnification end of this embodiment, respectively. Magnification 0.42 to 0.76, Viewing angle (2ω) = 5
2.8 ° -28.2 ° r ₁ = -10.1420 d ₁ = 1.0000 n ₁ = 1.58362 ν ₁
= 30.37 r ₂ = 6.7010 (aspherical surface) d ₂ (variable) r ₃ = 6.1200 (aspherical surface) d ₃ = 1.4730 n ₂ = 1.49230 ν _{2
= 57.71 r 4 = -83.9140 d 4} ( variable) r ₅ = 16.1990 _{(aspherical) d 5 = 4.1210 n 3 =} 1.49230 ν 3
_{= 57.71 r 6 = -7.1150 d 6} ( _{variable) r 7 = -18.5620 d 7 =} 18.4000 n 4 = 1.49230 ν 4
= 57.71 r ₈ = ∞ d ₈ = 1.0000 r ₉ = 10.4460 d ₉ = 29.2570 n ₅ = 1.49230 ν _{5
= 57.71 r 10 = ∞ d 10} = 1.5000 r 11 = 10.6420 ( _{aspherical) d 11 = 4.7960 n 6 =} 1.49230 ν 6
_{= 57.71 r 12 = 301.7560 d 12} = 15.0000 r 13 ( eye point)

Aspherical surface coefficient Second surface E = -0.11968 × 10^-2 , F = -0.119
31 x 10^-Four, G = −0.73834 × 10^-Five Third surface E = −0.11077 × 10^-2 , F = 0.5575
2 x 10^-Four, G = −0.156333 × 10^-Four Fifth surface E = −0.11892 × 10^-2 , F = -0.302
48 x 10^-Four, G = 0.52155 × 10^-Five  11th surface E = −0.12684 × 10^-3 , F = -0.100
63 x 10^-Five, G = 0.57479 × 10^-8

Low double Medium high double d ₂ 3.989 1.916 0.933 d ₄ 3.417 2.717 1.000 d ₆ 1.000 3.773 6.473 B _f / f _w = 0

Third Embodiment FIG. 11 is a perspective view of the third embodiment, and FIG. 12 is a developed view of the third embodiment at the low magnification end, the middle and the high magnification end. In this embodiment, the objective lens system 1 is composed of the first group 2 of negative lens groups and the second group 3 of two positive lenses, and the finder magnification is lowered by moving each group. It can be changed from middle to high.

The image erecting system 5 comprises a first prism 6, a field lens 10 and a mirror 11. And
The first prism 6 has three reflecting surfaces, the field lens 10 is located directly above the exit surface thereof, and the mirror 11 is located above the field lens 10, and has the same effect as a Porro prism as a whole. The field frame 8 is located between the exit surface of the first prism 6 and the field lens 10.

The data of this embodiment are as follows.
3, FIG. 14 and FIG. 15 show aberration curves at the low magnification end, the middle and the high magnification end of this embodiment, respectively. Magnification 0.45 to 1.15, Viewing angle (2ω) = 5
2.0 ° to 20.0 ° r ₁ = −14.9140 d ₁ = 1.0000 n ₁ = 1.58362 ν ₁
= 30.37 r ₂ = 16.6510 (aspherical surface) d ₂ (variable) r ₃ = −9.0540 d ₃ = 2.8110 n ₂ = 1.49230 ν _{2
= 57.71 r 4 = -7.6940 d 4} = 0.1000 r 5 = 10.8890 d 5 = 2.3350 n 3 = 1.49230 ν 3
= 57.71 r ₆ = -20.7890 (aspherical) d _{6 (variable) r 7 = -49.1540 d 7 =} 30.0000 n 4 = 1.49230 ν 4
_{= 57.71 r 8 = ∞ d 8} = 1.0000 r 9 = 14.3780 d 9 = 2.0000 n 5 = 1.49230 ν 5
= 57.71 r ₁₀ = ∞ d ₁₀ = 18.0904 r ₁₁ = 64.6310 d ₁₁ = 2.1470 n ₆ = 1.49230 ν ₆
= 57.71 r ₁₂ = -12.8090 (aspherical) d ₁₂ = 15.0000 r ₁₃ (eye point)

Aspheric surface coefficient Second surface E = -0.33284 × 10 ^-3 , F = 0.127
3 × 10 ⁻⁴ , G = −0.16750 × 10 ⁻⁵ Sixth surface E = 0.25866 × 10 ⁻³ , F = −0.1963
9 × 10 ⁻⁵ , G = 0.63589 × 10 ⁻⁷ 12th surface E = 0.11251 × 10 ⁻³ , F = 0.31703
× 10 ^-6 , G = 0.62827 × 10 ^-8

Low Low Medium High High d ₂ 13.228 5.976 1.720 d ₄ 1.000 5.101 11.252 B _f / f _w = 0

However, in each of the above embodiments, r ₁ , r ₂ ,
... is the radius of curvature of each lens surface, d ₁ , d ₂ , ... is the wall thickness and lens spacing of each lens, n ₁ , n ₂ , ... is the refractive index of each lens, ν ₁ , ν ₂ , ... is each lens Is the Abbe number.

The aspherical surface shape in each of the above embodiments is expressed by the following equation using the aspherical surface coefficient. However, the coordinate in the optical axis direction is X, and the coordinate in the direction perpendicular to the optical axis is Y.

[0028]

[Equation 1]

Here, r is a paraxial radius of curvature. Further, although the optical element of the objective lens in each of the above embodiments is made of plastic, glass may be used as the material if it is costly.

[0030]

As described above, the real image type finder optical system according to the present invention is a real image type finder optical system in which an erected image is obtained by a Porro prism system composed of a plurality of reflecting members. In addition to having good optical performance, it has the practically important advantages of being compact and having a high finder magnification.

[Brief description of drawings]

FIG. 1 is a perspective view of a real image type finder optical system according to a first embodiment of the present invention.

FIG. 2 is a development view of Example 1 at a low magnification end, an intermediate magnification, and a high magnification end.

FIG. 3 is an aberration curve diagram for Example 1 at the low magnification end.

FIG. 4 is an aberration curve diagram in the middle of Example 1.

FIG. 5 is an aberration curve diagram for Example 1 at the high magnification end.

FIG. 6 is a perspective view of a second embodiment.

FIG. 7 is a development view of Example 2 at a low magnification end, an intermediate magnification, and a high magnification end.

FIG. 8 is an aberration curve diagram for Example 2 at the low magnification end.

FIG. 9 is an aberration curve diagram in the middle of Example 2.

FIG. 10 is an aberration curve diagram for Example 2 at the high magnification end.

FIG. 11 is a perspective view of a third embodiment.

FIG. 12 is a development view of Example 3 at a low magnification end, a middle magnification, and a high magnification end.

FIG. 13 is an aberration curve diagram for Example 3 at the low magnification end.

FIG. 14 is an aberration curve diagram in the middle of Example 3.

FIG. 15 is an aberration curve diagram for Example 3 at the high magnification end.

[Explanation of symbols]

 1 Objective Lens System 2 1st Group 3 2nd Group 4 3rd Group 5 Image Erecting System 6 1st Prism 7 2nd Prism 8 Field Frame 9 Eyepiece System 10 Field Lens 11 Mirror

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[Procedure amendment]

[Submission date] January 25, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

[0028]

Claims (1)

[Claims] 1. An objective lens system having a positive refractive power, an image erecting system comprising a plurality of reflecting members for making an intermediate image by the objective lens system an erect image, and an eyepiece lens having a positive refractive power. In a real image type finder optical system in which a system is sequentially arranged, the first reflection member of the image erecting system has an incident surface having a negative refractive power and one or more reflection surfaces, and the following condition B A real image type viewfinder optical system characterized by being a prism satisfying _f / _fw <0.8, and further having a surface having a positive refractive power in the vicinity of an intermediate image forming position by the objective lens system. However, B _f
Is the axial distance from the exit surface of the first reflecting member to the intermediate image formation position, and _fw is the focal length of the objective lens system including the first reflecting member.