JP3708340B2 - Compact real-image zoom finder - Google Patents

Description

【００７１】
以上説明したように、本発明による小型の実像式ズームファインダーは、特許請求の範囲に記載の特徴と併せ、以下（１），（２）に示す特徴も備えていることが好ましい。
【００７２】
（１）上記対物光学系の第４群は上記正立正像系の一部と一体化されていることを特徴とする請求項１に記載の実像式ズームファインダー。
【００７３】
（２）変倍の際、上記対物光学系の第１群は固定されることを特徴とする請求項１乃至３又は上記（１）の何れかに記載の実像式ズームファインダー。
【００７４】
【発明の効果】
上述のように、本発明によれば、２倍を越える変倍比を有しながらも、簡易な構成で且つ良好な収差補正機能を備えた、安価な小型の実像式ズームファインダーを提供することができる。
【図面の簡単な説明】
【図１】第１実施例にかかる実像式ズームファインダーの構成を示す光軸に沿う断面図であり、夫々（ａ）は広角端、（ｂ）は中間倍率、（ｃ）は望遠端での状態を示す図である。
【図２】第１実施例にかかる実像式ズームファインダーの収差曲線図であり、夫々（ａ）は広角端、（ｂ）は中間倍率、（ｃ）は望遠端での状態を示す図である。
【図３】第２実施例にかかる実像式ズームファインダーの構成を示す光軸に沿う断面図であり、夫々（ａ）は広角端、（ｂ）は中間倍率、（ｃ）は望遠端での状態を示す図である。
【図４】第３実施例にかかる実像式ズームファインダーの構成を示す光軸に沿う断面図であり、夫々（ａ）は広角端、（ｂ）は中間倍率、（ｃ）は望遠端での状態を示す図である。
【図５】第４実施例にかかる実像式ズームファインダーの構成を示す光軸に沿う断面図であり、夫々（ａ）は広角端、（ｂ）は中間倍率、（ｃ）は望遠端での状態を示す図である。
【符号の説明】
１ 対物光学系
２ 接眼光学系
Ｌ₁ 第１群
Ｌ₂ 第２群
Ｌ₃ 第３群
Ｌ₄ 第４群
Ｌ₅ プリズム
Ｌ₆ 接眼レンズ
Ｌ_C 光軸[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a real image zoom finder suitable for a lens shutter camera, a still camera, or the like in which a photographing lens and a finder lens are configured separately.
[0002]
[Prior art]
In general, a finder optical system configured separately from a photographing optical system used in a lens shutter camera or the like is roughly classified into a virtual image type finder and a real image type finder.
[0003]
In the case of the virtual image type finder, when the zoom ratio is increased, the diameter of the front lens is increased, and the downsizing is hindered. In addition, this type of finder optical system has a problem that the field frame is not clearly visible.
On the other hand, since the real image type finder can arrange the entrance pupil position in front of the finder, the front lens diameter can be reduced. In addition, since the image formed by the objective lens system can be observed through the eyepiece lens system, the drawbacks of the virtual image type finder as described above are almost eliminated, and a finder with a good view of the field frame can be realized. .
Furthermore, in the real image type finder, it is possible to realize a smaller finder by devising the configuration of a prism or the like constituting the erect image system. The reason why the real-image finder is currently used in many lens shutter cameras equipped with a zooming function is as described above.
[0004]
In recent years, there has been a demand for further downsizing and higher zooming of cameras.
In the real image type finder, as a finder having a zoom ratio of about 2 times, a two-group zoom type and a three-group zoom type have been proposed. However, in order to further increase the zoom ratio, it is necessary to increase the zooming action of each lens constituting the viewfinder. Accordingly, the refracting power of each lens group of the finder is also increased, and aberration fluctuation due to zooming is increased. Further, since it is necessary to secure a movable space for each lens group in order to change the magnification, the entire length of the finder is increased, which increases the thickness of the camera.
If the total length of the viewfinder is shortened while maintaining the same zoom ratio, the movable space required for zooming will be reduced, so it will be necessary to increase the refractive power of each lens group. The aberration generated in the lens group to be performed increases.
[0005]
As described above, when the zoom ratio of the real image type finder having the two-group or three-group configuration is increased, aberrations generated in the lens group that performs zooming in particular increase, so that aberration fluctuations due to zooming become significant. In the two-group or three-group zoom type, since the number of lens groups is small, it is difficult to correct aberrations if there is even one lens group that has a significant amount of aberration.
However, these problems can be solved by making the finder zoom group into four groups. According to the four-group type, the zooming action and the aberration correcting action can be successfully distributed to each group. In addition, when the first group closest to the object side among the four groups is provided with a negative refractive power, the back focus of the objective lens system can be long, and in particular, a part of the image inverting member is included in the objective lens system. In such a case, it is extremely advantageous for downsizing. Further, when the fourth lens group has a negative refractive power, it is advantageous for shortening the overall length of the objective lens system particularly on the long focal point side.
[0006]
Among the real image type viewfinders configured in such four groups, in particular, the zoom ratio is 2 times or more, and the objective lens system has negative, positive, positive, and negative refractive powers in order from the object side. For example, those disclosed in JP-A-5-164964, JP-A-7-128707, JP-A-8-240769, and the like.
[0007]
[Problems to be solved by the invention]
Among these, the finder shown as Example 1 in Japanese Patent Application Laid-Open No. 5-164964 can satisfactorily correct aberrations by configuring the second group having a large zooming action with a plurality of lenses. However, the number of lenses constituting the finder is large, and the size of the finder is increased. The finder shown as Example 2 in the same publication realizes a small finder by constituting each group with a single lens, but in the third group, it is not on the image side with strong refractive power but on the object side. Since an aspherical surface is arranged, there is room for improvement in aberration correction. Further, in this finder, the combined longitudinal magnification of the second lens unit and later of the objective lens system becomes large at the telephoto end. Therefore, since the influence on the diopter due to the assembly error becomes large, it is necessary to assemble with high accuracy, resulting in an increase in production cost.
[0008]
Japanese Patent Application Laid-Open No. 7-128707 discloses a small real-image finder having a wide angle of view and each group composed of a single lens. However, in this finder, since the entrance surface of the first group is formed as a convex surface, the entrance pupil position enters the finder, and the lens aperture of the first group becomes large.
[0009]
The viewfinder disclosed in Japanese Patent Application Laid-Open No. 8-240769 realizes a small and highly variable viewfinder having a zoom ratio of 3 times or more. However, at the telephoto end, the combined longitudinal magnification of the second lens unit and subsequent lenses of the objective lens system is large, so that the influence on the diopter due to the assembly error appears remarkably. Therefore, it is necessary to assemble the finder with high accuracy, resulting in an increase in production cost.
[0010]
Therefore, in view of the above-described problems of the prior art, the present invention is an inexpensive small-sized device having a simple configuration and a good aberration correction function while having a high zoom ratio exceeding 2 times. An object of the present invention is to provide a real image type zoom finder.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a compact real-image zoom finder according to the present invention has, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, and a positive refractive power. An objective optical system having a positive refractive power composed of a third group and a fourth group having a negative refractive power ; and an eyepiece optical system having a positive refractive power composed of a prism and an eyepiece ; and The fourth group and the prism each have two reflecting surfaces, and the fourth group and the prism constitute an erect image system, and the first group and the fourth group are fixed. The zooming is performed by moving the second group and the third group, or by fixing the fourth group and moving the first group, the second group, and the third group, each group of the objective optical system consists respectively single lens, the concave surface on the object side of the first group And, the surface on the image side of the third group is an aspherical surface, and is characterized in that so as to satisfy the condition shown below.
2.5 <α _{T (R2)} <5.7
4.7 <D _13W /γ<6.2
Where α _{T (R2)} is the combined longitudinal magnification from the second group to the intermediate image at the telephoto end of the objective optical system, and D _13W is the axial thickness at the wide-angle end from the first group to the third group , Γ indicate the zoom ratio of the real image type zoom finder .
[0012]
The real image type zoom finder of the present invention is characterized in that the first group image side surface, the second group object side surface, and the fourth group object side surface are aspherical surfaces. To do.
Further, the real image type zoom finder of the present invention is characterized in that the object side surface of the third group is an aspherical surface.
[0013]
Furthermore, the real image type zoom finder of the present invention is characterized in that the first lens group is fixed during zooming .
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In order to achieve downsizing of the real-image finder while maintaining a high zoom ratio, it is preferable that the objective optical system that controls the zooming function has a four-group zoom configuration. In addition, since the back focus of the objective optical system can be formed long by providing a negative refractive power in the first group closest to the object, when a part of the image inverting member is provided in the objective optical system, This is extremely advantageous for downsizing. This also has the effect of disposing the entrance pupil on the front side of the viewfinder, so that the aperture of the lens constituting the viewfinder, particularly the front lens diameter, can be reduced.
Therefore, the real image type zoom finder of the present invention has an objective optical system having positive refractive power and arranged in four groups in order from the object side, and an erecting erect image for converting an intermediate image by the objective optical system into an erecting erect image. An image system and an eyepiece optical system having a positive refractive power are arranged, and in particular, the first group of the objective optical system has a negative refractive power.
[0015]
Furthermore, in a real image type zoom finder, in order to achieve both high zooming and miniaturization, it is necessary to give a strong refractive power to the lens unit having a zooming function. Become prominent. For this reason, in the real image type zoom finder of the present invention, the second group and the third group of the objective optical system mainly responsible for the zooming function are each provided with a positive refractive power, and the zooming function is shared. This suppresses the increase in refractive power and suppresses the amount of aberration generated.
However, with this configuration, at the telephoto end, the first group having negative refractive power, the second group having positive refractive power, and the third group having positive refractive power are configured as one block. . As a result, the total length of the objective optical system at the telephoto end becomes equal to the focal length at the telephoto end. Therefore, in the real image type zoom finder of the present invention, the total length of the objective optical system is shortened by providing the fourth lens unit with a negative refractive power.
[0016]
Furthermore, in the real image type zoom finder of the present invention, each of the first to fourth groups of the objective optical system is constituted by a single lens, so that each group is thinned and the total length of the objective optical system is shortened. Further, by configuring each group of the objective optical system with a single lens, the configuration of the objective optical system becomes simple, and it is easy to assemble and the production cost can be reduced. Furthermore, by making the object side surface of the first group of the objective optical system concave, the entrance pupil position can be moved to the front side of the viewfinder. Thereby, the lens aperture of each group which comprises an objective optical system can be made small. Also, due to the camera layout, even when the photographic optical system's lens frame protrudes from the viewfinder entrance window to the object side, the photographic optical system's lens frame can be seen in the viewfinder's field frame. Can be reduced.
[0017]
Considering the above, the real image zoom finder of the present invention satisfies the following conditional expression when the combined longitudinal magnification from the second group to the intermediate image at the telephoto end of the objective optical system is α _{T (R2).} It is preferable.
2.5 <α _{T (R2)} <5.7 (1)
[0018]
Conditional expression (1) relates to the effect on the diopter due to the error in the group distance between the first group and the second group at the telephoto end of the objective optical system. In the real image type zoom finder of the present invention, the diopter shift due to the assembly error particularly at the telephoto end becomes large at the time of high zooming, and the zoom ratio must be restricted because it is difficult to maintain good assembly accuracy. It can happen that nothing happens. In order to avoid such a problem, it is necessary to satisfy the conditional expression (1).
If the value of α _{T (R2)} exceeds the upper limit of the range of values that can be taken by the conditional expression (1), the influence on the diopter is increased, making it difficult to assemble the viewfinder and increasing the production cost. On the other hand, if the value of α _{T (R2)} falls below the lower limit of the range of values that can be taken by conditional expression (1), the zoom ratio of the finder cannot be maintained.
[0019]
In the present invention, in order to reduce the number of parts of the finder and reduce the cost, it is preferable to integrate the fourth group of the objective optical system with a part of the erect image system. Further, even in the group that mainly performs the zooming action of the objective optical system, especially on the most image side of the third group, the central light beam and the peripheral light beam are most separated from the entrance pupil. By arranging an aspherical surface on the surface, there is an effect in aberration correction, particularly correction of asphalt.
[0020]
Furthermore, it is preferable that the real image zoom finder of the present invention satisfies the following conditional expression.
_{4.7 <D 13W /γ<6.2 ···· (2} )
Here, D _13W is the axial thickness at the wide-angle end from the first group to the third group of the objective optical system of the real-image zoom finder of the present invention, and γ is the zoom ratio of the real-image zoom finder of the present invention. Show.
[0021]
In the real image zoom finder of the present invention, when the fourth group of the objective optical system is integrated with a part of the erect image system, the erect image system can be reduced in size by folding the optical path. Since the zoom unit of the objective optical system needs to secure a moving space for the lens group, it is difficult to reduce the size. For this reason, the value of D _13W greatly affects the determination of the overall length of the finder. Further, if it is intended to increase the zoom ratio of the finder in a limited space, it is necessary to increase the refractive power of the lens group that performs zooming as described above, and the amount of aberration generated also increases. That is, conditional expression (2) shows the conditions for making the finder compact and high zoom ratio compatible.
[0022]
When the value of D _13W / γ exceeds the upper limit of the range of values that can be taken by conditional expression (2), aberration correction becomes easy, but it is difficult to shorten the overall length of the objective optical system or increase the zoom ratio. It becomes. On the other hand, if the value of D _13W / γ falls below the lower limit of the range of values that can be taken by conditional expression (2), the moving space of the lens group for zooming is reduced, so that the refractive power of each group is strengthened. Must-have. In addition, the number of lenses constituting the finder must be reduced in accordance with zooming in a reduced space, and the amount of aberration generated in each group of the objective optical system increases. Further, since the distance between the aspherical surface arranged on the most image side surface of the third group and the entrance pupil position is shortened, the central light beam and the peripheral light beam are not largely separated, and aberration correction by the aspherical surface, In particular, it is difficult to correct the ass at the wide-angle end.
[0023]
In addition, in the real image type zoom finder of the present invention, by fixing the first group of the objective optical system at the time of zooming, it is possible to further simplify the configuration and further reduce the production cost. Can do.
[0024]
Hereinafter, the present invention will be described in detail based on the illustrated embodiments.
[0025]
First Embodiment FIG. 1 is a cross-sectional view along the optical axis showing the configuration of a real image type zoom finder according to the present embodiment. In the figure, (a) shows the state at the wide-angle end, (b) shows the intermediate magnification, and (c) shows the state at the telephoto end. The real image type zoom finder of the present embodiment is configured by arranging an objective optical system 1 and an eyepiece optical system 2 in order from an object side (not shown). The objective optical system 1 includes, in order from the object side, a first group L ₁ having a negative refractive power, a second group L ₂ having a positive refractive power, a third group L ₃ having a positive refractive power, and a negative The fourth group L ₄ having a refractive power of 2 and also having a function as a reflecting member is arranged. The eyepiece optical system 2 includes a prism L ₅ and an eyepiece lens L ₆ that are reflecting members in order from the object side. Furthermore, the fourth group L ₄ and the prism L ₅ constitute an erect image system.
[0026]
In the real image type zoom finder of the present embodiment, among the groups constituting the objective optical system 1, the first group L ₁ and the fourth group L ₄ are fixed, and the second group L ₂ and the third group L ₃ are respectively fixed. zooming is performed by moving the optical axis L _C. The object side surface of the first lens unit L ₁ is concave. The fourth group L ₄ and the prism L ₅ each have two reflecting surfaces (not shown). The first group L ₁ , the second group L ₂ , the third group L ₃ , and the fourth group L ₄ are each composed of one lens. Further, aspherical surfaces are arranged on the light exit surfaces of the first group L ₁ and the third group L ₃ and the light incident surfaces of the second group L ₂ and the fourth group L ₄ , respectively.
[0027]
Various numerical data relating to the real image type zoom finder of the present embodiment will be described below.
[0028]
Finder magnification: 0.432 to 1.014 times Viewing angle (2ω): 51.9 to 20.8 °
Pupil diameter: 4mmφ
α _{T (R2)} = 4.60
D _13W /γ=5.52
[0029]
r ₁ = -13.958
d ₁ = 0.70 nd ₁ = 1.58423 ν ₁ = 30.49
r ₂ = 9.072 (aspherical surface)
d ₂ = 6.80 (wide angle end), 3.59 (intermediate magnification), 0.85 (telephoto end)
r ₃ = 6.291 (aspherical surface)
d ₃ = 1.53 nd ₃ = 1.49241 ν ₃ = 57.66
r ₄ = −61.633
d ₄ = 2.59 (wide-angle end), 3.25 (intermediate magnification), 0.73 (telephoto end)
r ₅ = 16.055
d ₅ = 1.33 nd ₅ = 1.49241 ν ₅ = 57.66
[0030]
r ₆ = -14.618 (aspherical surface)
d ₆ = 2.46 (wide-angle end), 5.00 (intermediate magnification), 10.25 (telephoto end)
r ₇ = -24.541 (aspherical surface)
d ₇ = 13.00 nd ₇ = 1.52542 ν ₇ = 55.78
r ₈ = ∞
d ₈ = 1.50
r ₉ = 12.504
d ₉ = 26.50 nd ₉ = 1.52542 ν ₉ = 55.78
r ₁₀ = -124.987
d ₁₀ = 1.50
[0031]
r ₁₁ = 14.176
d ₁₁ = 4.75 nd ₁₁ = 1.52542 ν ₁₁ = 55.78
r ₁₂ = -47.882
d ₁₂ = 18.50
r ₁₃ = ∞ (eyepoint)
[0032]
Conic coefficient and aspheric coefficient second surface K = -17.4679
A ₄ = 2.3937 × 10 ^-3 , A ₆ = -2.4953 × 10 ^-4
A ₈ = 3.4063 × 10 ^-5 , A ₁₀ = -3.1907 × 10 ^-6
[0033]
Third side K = 1.3715
A ₄ = -1.3301 × 10 ^-3 , A ₆ = -2.2595 × 10 ^-5
A ₈ = -1.4247 × 10 ^-6 , A ₁₀ = -2.2948 × 10 ^-7
[0034]
6th surface K = -5.9176
A ₄ = 3.8448 × 10 ^-4 , A ₆ = 6.2037 × 10 ^-6
A ₈ = 1.3894 × 10 ^-6 , A ₁₀ = -1.6737 × 10 ^-7
[0035]
Surface 7 K = 21.8505
A ₄ = -6.9410 × 10 ^-4 , A ₆ = 1.1885 × 10 ^-4
A ₈ = -8.0697 × 10 ^-6
[0036]
11th surface K = 1.0224
A ₄ = -9.1751 × 10 ^-5 , A ₆ = -3.0775 × 10 ^-6
A ₈ = 8.4886 × 10 ^-8 , A ₁₀ = -1.1576 × 10 ^-9
[0037]
FIG. 2 is an aberration curve diagram according to the real image type zoom finder of the present example, in which (a) is a wide angle end, (b) is an intermediate magnification, and (c) is a state at a telephoto end. is there.
[0038]
Second Embodiment FIG. 3 is a cross-sectional view along the optical axis showing the configuration of the real image type zoom finder according to the present embodiment. In the figure, (a) shows the state at the wide-angle end, (b) shows the intermediate magnification, and (c) shows the state at the telephoto end. In the real-image zoom finder of the present embodiment, the configuration other than the point that an aspherical surface is disposed on the light incident surface of the third lens unit L ₃ of the objective optical system 1 is the same as that shown in the first embodiment. Therefore, detailed description is omitted.
[0039]
Various numerical data relating to the real image type zoom finder of the present embodiment will be described below.
Finder magnification: 0.431 to 1.145 times Viewing angle (2ω): 52.0 to 18.5 °
Pupil diameter: 4mmφ
α _{T (R2)} = 5.14
D _13W /γ=5.14
[0040]
r ₁ = -21.349
d ₁ = 0.70 nd ₁ = 1.58423 ν ₁ = 30.49
r ₂ = 8.095 (aspherical surface)
d ₂ = 7.47 (wide-angle end), 4.07 (intermediate magnification), 0.45 (telephoto end)
r ₃ = 6.906 (aspherical surface)
d ₃ = 1.53 nd ₃ = 1.49241 ν ₃ = 57.66
r ₄ = -26.237
d ₄ = 2.60 (wide-angle end), 3.73 (intermediate magnification), 0.45 (telephoto end)
r ₅ = 8.858 (aspherical surface)
d ₅ = 1.33 nd ₅ = 1.49241 ν ₅ = 57.66
[0041]
r ₆ = 310.759 (aspherical surface)
d ₆ = 1.97 (wide-angle end), 4.24 (intermediate magnification), 11.14 (telephoto end)
r ₇ = -24.869 (aspherical surface)
d ₇ = 13.00 nd ₇ = 1.52542 ν ₇ = 55.78
r ₈ = ∞
d ₈ = 1.50
r ₉ = 11.539
d ₉ = 26.90 nd ₉ = 1.52542 ν ₉ = 55.78
r ₁₀ = ∞
d ₁₀ = 1.50
[0042]
r ₁₁ = 12.836
d ₁₁ = 2.45 nd ₁₁ = 1.52542 ν ₁₁ = 55.78
r ₁₂ = -51.611
d ₁₂ = 18.50
r ₁₃ = ∞ (eyepoint)
[0043]
Conic coefficient and aspherical coefficient second surface K = -12.9994
A ₄ = 2.5881 × 10 ⁻³ , A ₆ = −2.9222 × 10 ⁻⁴
A ₈ = 3.1774 × 10 ⁻⁵ , A ₁₀ = −2.0197 × 10 ⁻⁶
[0044]
Third side K = -1.7007
A ₄ = 4.0044 × 10 ⁻⁴ , A ₆ = 3.4302 × 10 ⁻⁶
A ₈ = -1.7264 × 10 ^-7 , A ₁₀ = -7.2403 × 10 ^-7
[0045]
5th surface K = -5.6505
A ₄ = 6.4996 × 10 ⁻⁴ , A ₆ = −2.4386 × 10 ⁻⁶
A ₈ = 1.6154 × 10 ^-6 , A ₁₀ = 1.8594 × 10 ^-6
[0046]
6th surface K = -8.6130
A ₄ = 4.7895 × 10 ^-4 , A ₆ = 5.9261 × 10 ^-6
A ₈ = 7.8671 × 10 ^-7 , A ₁₀ = 2.3078 × 10 ^-6
[0047]
Surface 7 K = 21.4820
A ₄ = -1.3453 × 10 ^-4 , A ₆ = -4.3803 × 10 ^-5
A ₈ = 4.8903 × 10 ^-6
[0048]
11th surface K = 1.1927
A ₄ = -1.8483 × 10 ^-4 , A ₆ = 5.8107 × 10 ^-8
A ₈ = -4.6551 × 10 ^-8 , A ₁₀ = 2.8071 × 10 ^-11
[0049]
Third Embodiment FIG. 4 is a cross-sectional view along the optical axis showing the configuration of the real image type zoom finder according to the present embodiment. In the figure, (a) shows the state at the wide-angle end, (b) shows the intermediate magnification, and (c) shows the state at the telephoto end. The real image type zoom finder of this embodiment, among the group of the objective optical system 1, the fourth group L ₄ is fixed, the first group L _1, a second group L _2, a third group L ₃ each zooming is performed by moving the optical axis L _C. Since other configurations are the same as those shown in the first embodiment, detailed description thereof is omitted.
[0050]
Various numerical data relating to the real image type zoom finder of the present embodiment will be described below.
Viewfinder magnification: 0.433 to 1.225 times Viewing angle (2ω): 51.9 to 17.2 °
Pupil diameter: 4mmφ
α _{T (R2)} = 5.52
D _13W /γ=4.86
[0051]
r ₁ = -35.626
d ₁ = 0.70 nd ₁ = 1.58423 ν ₁ = 30.49
r ₂ = 7.291 (aspherical surface)
d ₂ = 8.19 (wide-angle end), 4.45 (intermediate magnification), 0.45 (telephoto end)
r ₃ = 7.667 (aspherical surface)
d ₃ = 1.53 nd ₃ = 1.49241 ν ₃ = 57.66
r ₄ = -19.589
d ₄ = 2.00 (wide-angle end), 3.23 (intermediate magnification), 0.45 (telephoto end)
r ₅ = 6.529 (aspherical surface)
d ₅ = 1.33 nd ₅ = 1.49241 ν ₅ = 57.66
[0052]
r ₆ = 18.700 (aspherical surface)
d ₆ = 2.15 (wide-angle end), 4.32 (intermediate magnification), 11.54 (telephoto end)
r ₇ = -19.864 (aspherical surface)
d ₇ = 13.00 nd ₇ = 1.52542 ν ₇ = 55.78
r ₈ = ∞
d ₈ = 1.50
r ₉ = 11.539
d ₉ = 26.90 nd ₉ = 1.52542 ν ₉ = 55.78
r ₁₀ = ∞
d ₁₀ = 1.50
[0053]
r ₁₁ = 12.836 (Aspherical surface)
d ₁₁ = 2.45 nd ₁₁ = 1.52542 ν ₁₁ = 55.78
r ₁₂ = -51.611
d ₁₂ = 18.50
r ₁₃ = ∞ (eyepoint)
[0054]
Conic coefficient and aspheric coefficient second surface K = -9.9740
A ₄ = 2.6068 × 10 ^-3 , A ₆ = -2.3924 × 10 ^-4
A ₈ = 2.6501 × 10 ⁻⁵ , A ₁₀ = −2.0853 × 10 ⁻⁶
[0055]
Third side K = -1.7356
A ₄ = 3.2639 × 10 ⁻⁴ , A ₆ = 2.2984 × 10 ⁻⁵
A ₈ = 6.8580 × 10 ⁻⁷ , A ₁₀ = −1.3606 × 10 ⁻⁶
[0056]
Fifth side K = -6.9045
A ₄ = 2.7640 × 10 ⁻³ , A ₆ = −1.7735 × 10 ⁻⁴
A ₈ = 1.6551 × 10 ^-5 , A ₁₀ = 1.9078 × 10 ^-6
[0057]
6th surface K = -2.9646
A ₄ = 5.1040 × 10 ⁻⁴ , A ₆ = 7.2434 × 10 ⁻⁶
A ₈ = -7.5901 × 10 ^-7 , A ₁₀ = 3.8889 × 10 ^-6
[0058]
Surface 7 K = 18.7601
A ₄ = 3.6273 × 10 ^-4 , A ₆ = -1.7302 × 10 ^-4
A ₈ = 1.2017 × 10 ^-5
[0059]
11th surface K = 1.1927
A ₄ = -1.8483 × 10 ^-4 , A ₆ = 5.8107 × 10 ^-8
A ₈ = -4.6551 × 10 ^-8 , A ₁₀ = 2.8071 × 10 ^-11
[0060]
Fourth Embodiment FIG. 5 is a cross-sectional view along the optical axis showing the configuration of the real image type zoom finder according to the present embodiment. In the figure, (a) shows the state at the wide-angle end, (b) shows the intermediate magnification, and (c) shows the state at the telephoto end. Since the configuration of the real image type zoom finder of the present embodiment is the same as that of the first embodiment, detailed description thereof is omitted.
[0061]
Various numerical data relating to the real image type zoom finder of the present embodiment will be described below. Viewfinder magnification: 0.432 to 1.009 times Viewing angle (2ω): 51.1 to 20.6 °
Pupil diameter: 4mmφ
α _{T (R2)} = 2.69
D _13W /γ=6.07
[0062]
r ₁ = -19.916
d ₁ = 0.80 nd ₁ = 1.58423 ν ₁ = 30.49
r ₂ = 11.127 (aspherical surface)
d ₂ = 8.54 (wide angle end), 4.63 (intermediate magnification), 0.80 (telephoto end)
r ₃ = 7.395 (aspherical surface)
d ₃ = 1.70 nd ₃ = 1.52542 ν ₃ = 55.78
r ₄ = -30.988
d ₄ = 1.82 (wide-angle end), 3.97 (intermediate magnification), 2.27 (telephoto end)
r ₅ = 21.281
d ₅ = 1.30 nd ₅ = 1.49241 ν ₅ = 57.66
[0063]
r ₆ = -26.915 (aspherical surface)
d ₆ = 2.04 (wide angle end), 3.80 (intermediate magnification), 9.33 (telephoto end)
r ₇ = -52.368 (aspherical surface)
d ₇ = 13.00 nd ₇ = 1.52542 ν ₇ = 55.78
r ₈ = ∞
d ₈ = 1.50
r ₉ = 12.504
d ₉ = 26.69 nd ₉ = 1.52542 ν ₉ = 55.78
r ₁₀ = ∞
d ₁₀ = 1.50
[0064]
r ₁₁ = 14.795 (aspherical surface)
d ₁₁ = 2.45 nd ₁₁ = 1.52542 ν ₁₁ = 55.78
r ₁₂ = -32.070
d ₁₂ = 18.50
r ₁₃ = ∞ (eyepoint)
[0065]
Conic coefficient and aspheric coefficient second surface K = -10.0850
A ₄ = 3.3985 × 10 ^-4 , A ₆ = 1.0964 × 10 ^-5
A ₈ = 2.9651 × 10 ^-6 , A ₁₀ = -4.0317 × 10 ^-7
[0066]
Third side K = 2.0347
A ₄ = -1.2911 × 10 ^-3 , A ₆ = 7.1069 × 10 ^-6
A ₈ = 4.9448 × 10 ⁻⁷ , A ₁₀ = −3.7711 × 10 ⁻⁷
[0067]
6th surface K = -5.0721
A ₄ = 3.0467 × 10 ⁻⁴ , A ₆ = 1.0782 × 10 ⁻⁵
A ₈ = 8.2483 × 10 ⁻⁷ , A ₁₀ = −2.1377 × 10 ⁻⁷
[0068]
7th surface K = -43.9144
A ₄ = -5.8891 × 10 ^-4 , A ₆ = 3.9137 × 10 ^-5
A ₈ = -1.6541 × 10 ^-6
[0069]
11th surface K = 0.7176
A ₄ = -9.4274 × 10 ^-5 , A ₆ = -2.1222 × 10 ^-6
A ₈ = 6.1948 × 10 ^-8 , A ₁₀ = -8.5431 × 10 ^-10
[0070]
However, in the various numerical data in the above-described embodiments, r ₁ , r ₂ ,... Are the curvature radii of the lens surfaces and the like, and d ₁ , d ₂ ,. ... Nd ₁ , nd ₂ ,... Represents the refractive index on the d-line of each lens, and ν ₁ , ν ₂ ,. Each of the aspheric shapes has a light traveling direction on the optical axis as the Z axis, a direction perpendicular to the optical axis as the Y axis, a conic coefficient as K, and an aspheric coefficient as A ₄ , A ₆ , A ₈ , When A ₁₀ is given, it is given by the following equation.

[0071]
As described above, it is preferable that the small real image type zoom finder according to the present invention has the following features (1) and (2) in addition to the features described in the claims.
[0072]
(1) The real image zoom finder according to claim 1, wherein the fourth group of the objective optical system is integrated with a part of the erect image system.
[0073]
(2) The real image zoom finder according to any one of claims 1 to 3 or (1), wherein the first group of the objective optical system is fixed during zooming.
[0074]
【The invention's effect】
As described above, according to the present invention, there is provided an inexpensive small real-image zoom finder having a simple configuration and a good aberration correction function while having a zoom ratio exceeding 2 times. Can do.
[Brief description of the drawings]
FIGS. 1A and 1B are cross-sectional views along the optical axis showing the configuration of a real image type zoom finder according to a first embodiment, where FIG. 1A is a wide angle end, FIG. 1B is an intermediate magnification, and FIG. 1C is a telephoto end; It is a figure which shows a state.
FIGS. 2A and 2B are aberration curve diagrams of the real-image zoom finder according to the first example, in which FIG. 2A shows a state at a wide angle end, FIG. 2B shows an intermediate magnification, and FIG. 2C shows a state at a telephoto end, respectively. .
FIGS. 3A and 3B are cross-sectional views along the optical axis showing the configuration of the real image type zoom finder according to the second embodiment, where FIG. 3A is a wide angle end, FIG. 3B is an intermediate magnification, and FIG. 3C is a telephoto end; It is a figure which shows a state.
FIGS. 4A and 4B are cross-sectional views along the optical axis showing the configuration of the real image type zoom finder according to the third embodiment, where FIG. 4A is a wide angle end, FIG. 4B is an intermediate magnification, and FIG. 4C is a telephoto end; It is a figure which shows a state.
FIGS. 5A and 5B are cross-sectional views along the optical axis showing a configuration of a real image type zoom finder according to a fourth embodiment, where FIG. 5A is a wide angle end, FIG. 5B is an intermediate magnification, and FIG. 5C is a telephoto end; It is a figure which shows a state.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Objective optical system 2 Eyepiece optical system L ₁ 1st group L ₂ 2nd group L ₃ 3rd group L ₄ 4th group L ₅ Prism L ₆ Eyepiece lens L _C Optical axis

Claims (4)

In order from the object side, a first lens unit having a negative refractive power, a second group having a positive refractive power, a third group having a positive refractive power, and positive refractive consisting fourth group having a negative refractive power An objective optical system having power, and an eyepiece optical system having positive refractive power composed of a prism and an eyepiece , and
The fourth group and the prism each have two reflecting surfaces, and the fourth group and the prism constitute an erect image system,
The first group and the fourth group are fixed, the second group and the third group are moved, or the fourth group is fixed, and the first group, the second group, and the third group are fixed. Scaling is done by moving the group,
Wherein each group of the objective optical system consists respectively single lens, the object-side surface of the first group is a concave surface, the image side surface of the third group is an aspherical surface, and the following conditions A real-image zoom finder characterized by satisfying the formula.
2.5 <α _{T (R2)} <5.7
4.7 <D _13W /γ<6.2
Where α _{T (R2)} is the combined longitudinal magnification from the second group to the intermediate image at the telephoto end of the objective optical system, and D _13W is the axial thickness at the wide-angle end from the first group to the third group , Γ indicate the zoom ratio of the real image type zoom finder . 2. The real image zoom finder according to claim 1, wherein the image-side surface of the first group, the object-side surface of the second group, and the object-side surface of the fourth group are aspherical surfaces. . 3. The real image zoom finder according to claim 2, wherein the object side surface of the third group is an aspherical surface . The real image zoom finder according to any one of claims 1 to 3 , wherein the first lens group is fixed during zooming.

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