JP3075540B2 - Real image finder optical system - Google Patents

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 for a photographic camera or a video camera.

[0002]

2. Description of the Related Art In a real image type finder optical system, a Porro prism is often used, for example, as described in JP-A-1-131510 in order to make an observed image an erect image. Porro prisms are often used because they can be made smaller than other optical systems that invert up, down, left and right, such as image rotators and relay optics. 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 imaging position is relatively long, the entrance surface of the objective lens system to the exit surface of the eyepiece lens system. However, there is a problem that the finder configuration length up to this point becomes long.

Therefore, a configuration has been conventionally adopted in which an intermediate image forming position by the objective lens system is placed inside the Porro prism, and the objective lens system is made closer to the Porro prism system to shorten the finder configuration length.

[0004]

However, since it is necessary to provide a field frame for determining the field of view at the intermediate image forming position, when the intermediate image forming position is to be placed inside the Porro prism, the Porro prism must be provided. Split into multiple prisms,
Generally, an intermediate imaging position is determined in a space generated by the division, and a field frame is set there. Therefore, if the back focus length of the objective lens system is not set to a length that is appropriate for the way the prism is divided, the intermediate imaging 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, the optimal range of the back focus length of the objective lens system is narrow, and this is a constraint condition when designing the objective lens system, which causes a problem that the optical performance is deteriorated.

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. It is an object of the present invention to provide a real image type finder optical system which is compact while having the same.

[0006]

A real image type finder optical system according to the present invention comprises an objective lens system having a positive refractive power and a plurality of reflecting members for converting an intermediate image formed by the objective lens system into 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, the first reflecting member of the image erecting system has an incident surface having a negative refractive power. A prism having at least one reflecting surface and always satisfying the following condition: B _f / f _w <0.8, and further having a surface having a positive refractive power near an intermediate image forming position by the objective lens system. It is characterized by having been provided. Here, _Bf is the axial distance from the exit surface of the first reflecting member to the intermediate image forming position, and _fw 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 entrance surface of the first prism of the divided Porro prism has a negative refractive power, the light converging by the objective lens system is reflected by the entrance surface of the first prism. The divergent action works,
The intermediate imaging position is moved to the eyepiece system side. Therefore, even when 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 necessary for inserting the first prism of the Porro prism into the back focus portion cannot be obtained, By providing the incident surface with 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 back focus length is increased by increasing the negative refractive power of the entrance surface of the first prism more than necessary, the distance from the final surface of the objective lens system to the entrance surface of the first prism increases, and The configuration length of the finder from the entrance surface to the exit surface of the eyepiece system becomes long. Conversely, if the exit surface of the first prism is separated from the intermediate imaging 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 viewfinder 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 _Bf / _fw <0.8, an intermediate image is formed near the exit surface of the first prism, which is most effective. Can be downsized.

If a surface having a positive refracting power is set at the intermediate image forming position, a converging effect is exerted on the off-axis light beam diverging from the objective lens system to make it closer to parallel light. The surface having the refracting power serves as a field lens for miniaturizing the subsequent second prism and the eyepiece system. The surface having the positive refractive power may be set as the entrance surface of the second prism, which is also near the intermediate image forming surface as in the exit surface of the first prism. It plays the role of a field lens without impairing the effect of increasing the back focus length. still,
An optical system combining a field lens and a mirror may be used instead of the second prism.

The first prism of the present invention can be a prism having a reflecting surface that reflects twice or three times depending on the type of the objective lens system. However, in general, as the number of reflecting surfaces increases and the optical path length increases, the first prism moves from the incident surface to the exit surface. That is, the distance to the intermediate image is increased, and the spread of the light beam on the incident surface is increased, which may increase the aberration. In such a case, aberration can be effectively corrected by making the incident surface aspherical.

Further, as described above, the focal length of the eyepiece lens system can be shortened by approaching the intermediate imaging position (coincident with the front focal position of the eyepiece lens system) by the objective lens system with respect to the eyepiece lens system. Therefore, the finder 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 to the focal length f _R of the eyepiece lens system.

[0011]

Next, an embodiment of a real image type finder optical system according to the present invention will be described. Embodiment 1 FIG. 1 is a perspective view of Embodiment 1, and FIG. As shown in the figure, the objective lens system 1 includes a first group 2 of negative lenses, and a second group 3 composed of a positive lens and a negative lens and having a positive refractive power as a whole.
And a third group 4 of positive lenses. As is apparent from FIG. 2, the finder magnification changes from low to middle to high by moving the second group 3 and the third group 4 in the objective lens system 1 toward the object side while changing the relative distance. It is made to be made.

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

The intermediate image obtained by the objective lens system 1 is magnified and observed by an eyepiece system 9 composed of a positive single lens.
Although not shown, when this is used in a camera, a photographic lens system is provided in parallel with the finder optical system, and the magnification of the photographic lens system and the magnification of the finder optical system are interlocked. Become.

The data of the present embodiment is as follows. FIGS. 3, 4 and 5 show aberration curves of the present embodiment at the low magnification end, the middle and the high magnification end, 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 v _{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)

Aspherical 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 7th surface E = −0.29784 × 10 ⁻³ , F = 0.2074
0 × 10 ⁻⁵ , G = −0.21629 × 10 ⁻⁶ th surface 13 E = −0.71782 × 10 ⁻⁴ , F = −0.146
30 × 10 ⁻⁵ , G = 0.31012 × 10 ⁻⁷

Low magnification Medium middle High magnification d ₂ 12.296 5.823 1.851 d ₆ 1.782 4.663 2.961 d ₈ 1.957 5.569 11.223 B _f / f _w = 0. 20 (at low magnification)

Second Embodiment FIG. 6 is a perspective view of the second embodiment, and FIG. 7 is a developed view of the second embodiment 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 includes a first group 2 to a third group 4, but differs from the first embodiment 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 the present embodiment are as follows. FIGS. 8, 9 and 10 show aberration curves of the present embodiment at the low magnification end, the middle and the high magnification end, 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 = 6.11200 (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 surface) d ₁₁ = 4.7960 n ₆ = 1.49230 ν ₆
= 57.71 r ₁₂ = 301.7560 d ₁₂ = 15.0000 r ₁₃ (eye point)

Aspheric surface second surface E = −0.11968 × 10^-2 , F = −0.119
31 × 10^-Four, G = −0.73834 × 10^-Five Third surface E = −0.11077 × 10^-2 , F = 0.5575
2 × 10^-Four, G = −0.15633 × 10^-Four Fifth surface E = -0.11892 × 10^-2 , F = −0.302
48 × 10^-Four, G = 0.52155 × 10^-Five  Eleventh surface E = -0.12684 × 10^-3 , F = −0.100
63 × 10^-Five, G = 0.57479 × 10^-8

[0020] During low magnification in high magnification _{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 a low magnification end, an intermediate position, and a high magnification end. In the present embodiment, the objective lens system 1 is composed of a first group 2 of negative lens groups and a second group 3 of two positive lenses. It can be changed from middle to high magnification.

The image erecting system 5 includes a first prism 6, a field lens 10, and a mirror 11. And
The first prism 6 has three reflecting surfaces, and a field lens 10 is provided immediately above the exit surface, and a mirror 11 is provided thereon, and has the same operation as the 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 is as follows.
3, 14 and 15 show aberration curves of the present embodiment at the low magnification end, the middle, and the high magnification end, 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 v ₃
= 57.71 r ₆ = -20.7890 (aspherical surface) d ₆ (variable) r ₇ = -49.1540 d ₇ = 30.0000 n ₄ = 1.492230 ν ₄
= 57.71 r ₈ = ∞d ₈ = 1.0000 r ₉ = 14.3780 d ₉ = 2.0000 n ₅ = 1.429230 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 surface) d ₁₂ = 15.0000 r ₁₃ (eye point)

Aspheric surface second surface E = −0.33284 × 10 ⁻³ , F = 0.2127
6th surface E = 0.25866 × 10 ⁻³ , F = −0.1963, 3 × 10 ⁻⁴ , G = −0.16750 × 10 ⁻⁵
9 × 10 ^-5 , G = 0.63589 × 10 ^-7 twelfth surface E = 0.12551 × 10 ^-3 , F = 0.31703
× 10 ^-6 , G = 0.62827 × 10 ^-8

Low magnification Medium middle High magnification 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 ,
... curvature radius of each lens surface, d _1, d _2, ... is the thickness and lens distance of each lens, n _1, n _2, ... is the refractive index of each lens, ν _1, ν _2, ... each lens Is the Abbe number of

The aspheric shape in each of the above embodiments is represented by the following equation using the aspheric coefficient. Here, the coordinates in the optical axis direction are X, and the coordinates in the direction perpendicular to the optical axis are Y.

[0028]

Here, r is a paraxial radius of curvature. Although the optical element of the objective lens in each of the above embodiments is made of plastic, glass may be used if cost is appropriate.

[0030]

As described above, the real image type finder optical system according to the present invention is a real image type finder optical system for obtaining an erect image by a Porro prism system composed of a plurality of reflecting members, but has a short finder configuration length. It has practically important advantages that it has good optical performance, is compact, and has a high finder magnification.

[Brief description of the drawings]

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

FIG. 2 is a development view at a low magnification end, a middle, and a high magnification end of the first embodiment.

FIG. 3 is an aberration curve diagram of Example 1 at a low magnification end.

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

FIG. 5 is an aberration curve diagram at the high magnification end of the first embodiment.

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

FIG. 7 is a development view at a low magnification end, a middle magnification, and a high magnification end of the second embodiment.

FIG. 8 is an aberration curve diagram at the low magnification end of the second embodiment.

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

FIG. 10 is an aberration curve diagram at the high magnification end of the second embodiment.

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

FIG. 12 is a development view at a low magnification end, a middle, and a high magnification end of the third embodiment.

FIG. 13 is an aberration curve diagram at the low magnification end of the third embodiment.

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

FIG. 15 is an aberration curve diagram at the high magnification end of the third embodiment.

[Explanation of symbols]

 DESCRIPTION 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

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04 G03B 13 / 00-13/28

Claims (1)

(57) [Claims] An objective lens system having a positive refractive power, an image erecting system including a plurality of reflecting members for converting an intermediate image formed by the objective lens system into an erect image, and an eyepiece having a positive refractive power And a real image type viewfinder optical system in which a first reflecting member of the image erecting system has an incident surface having a negative refractive power and one or more reflecting surfaces, and is always <br / A real image finder, wherein the prism satisfies the following condition: B _f / f _w <0.8, and a surface having a positive refractive power is provided in the vicinity of an intermediate image forming position by the objective lens system. Optical system. However, B _f
Is the axial distance from the exit surface of the first reflecting member to the intermediate imaging position, and _fw is the focal length of the objective lens system including the first reflecting member.