JPH09105863A - Variable power viewfinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a real-image type variable power viewfinder through which an excellent viewfinder image can be observed over the entire power variation range by correcting diopter scale variation accompanying power variation and providing an objective system with at least one aspherical surface. SOLUTION: An image inversion optical system P consists of a triangular prism P1 and a roof prism P2 and an object image formed by an objective system 10 at a position 4 between the triangular prism P1 and roof prism P2 is inverted upside down and between the right and left and converted into an erect image. This objective system 10 consists of four 1st-4th lens groups L1-L4 and at least one aspherical surface in a specific shape is provided. Then the object image is formed by the objective system 10 at the position between the triangular prism P1 and roof prism P2 to make it easy to correct aberrations, so that the excellent object image can be observed. Further, the 3rd group L3 is moved toward an object to vary the power, thereby effectively obtaining a specific power variation ratio.

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 variable power viewfinder, and more particularly, in an external viewfinder provided separately from a photographing system, the lens configuration of an objective lens system constituting the viewfinder is appropriately set. Thus, the present invention relates to a real image type variable magnification finder suitable for a still camera, a video camera or the like, which enables good observation of a finder image.

[0002]

2. Description of the Related Art Conventionally, in a camera in which a photographing system and a finder system are separately configured, when the photographing system is a variable magnification system, the finder system is also constituted by a variable magnification system, and the finder field magnification is changed according to the variation of the photographing system. Is configured to change. Generally, the variable magnification finder is required to have a small size because it is incorporated in a camera and a predetermined variable magnification ratio can be easily obtained.

The applicant of the present invention, in Japanese Patent Laid-Open No. 61-156018 and Japanese Patent Laid-Open No. 1-116616, configures the objective lens with a multi-lens group, and changes the air spacing of each lens group during zooming. The object image with various magnifications changed by the objective lens is made an erect image through an image inverting member such as a Porro prism, and the erect image is observed by an eyepiece lens. Proposing a variable magnification finder.

In Japanese Patent Laid-Open No. 5-203876, the first group constituting the objective lens in the variable power finder of this type is constructed by using two negative lenses and an aspherical surface, and the aberration correction of off-axis rays is excellent. We have proposed a variable-magnification viewfinder with a wide view angle.

[0005]

In the real image type finder, it is required to downsize the entire lens system, but recently, as the camera body is downsized, further downsizing of the finder is required. In order to reduce the size of the finder, for example, the method of proportionally multiplying the entire finder and reducing the size of the finder accordingly reduces the size of the eyepiece lens, resulting in an inconvenient finder with a small eyepiece pupil diameter.

On the other hand, if the focal length of the objective lens is shortened while maintaining the focal length of the eyepiece lens in order to secure the pupil diameter of the eyepiece lens, the viewfinder system becomes smaller but the viewfinder magnification becomes smaller and the viewfinder observation becomes easier. There is a problem that it becomes an invisible finder.

According to the present invention, by appropriately setting the lens configuration of the objective lens system having a variable power portion, a predetermined variable power ratio can be easily obtained while ensuring a sufficient eyepiece pupil diameter and a viewfinder magnification, and further, It is an object of the present invention to provide a real image type variable power viewfinder capable of observing a good viewfinder image over a variable power range.

[0008]

The variable power finder of the present invention makes an object image formed by an objective lens system having a positive refracting power in order from the object side, forms an erect image through an image inverting optical system, and forms the erect image. When observing with an eyepiece lens system, the objective lens system is composed of a positive or negative first lens group, a negative second lens group, a positive third lens group, and a meniscus positive 41st lens element having a concave surface facing the object side. The fourth lens group of the fourth lens group, the third lens group is moved on the optical axis for zooming, and the diopter change due to zooming is changed by the first lens group, the second lens group, or the fourth lens group. The objective lens system is characterized in that at least one aspherical surface is provided in the objective lens system so that the off-axis light flux emitted from the fourth lens unit is corrected and is substantially parallel to the optical axis.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of an essential part of a first embodiment of the present invention, and FIGS. 2 to 4 are sectional views of lenses when numerical paths 1 to 3 of the present invention are expanded.

In the figure, reference numeral 10 denotes an objective lens system having a positive refractive power having a zooming portion, which forms an object image (finder image) on a predetermined surface. Reference numeral P denotes an image inverting optical system, which includes a triangular prism P1 and a roof prism P2, and the objective lens system 10 allows the triangular prism P1 and the roof prism P.
The object image formed at the position 4 between 2 and 2 is inverted vertically and horizontally to be converted into an erect image.

2 to 4, the triangular prism P1 and the roof prism P2 are shown as two glass blocks whose optical paths are expanded for simplicity. Le is an eyepiece lens having a positive refractive power, and the object image formed at the position 4 is observed from the eyepoint E as an upright object image through the image inverting optical system P. At the position 4, a display member 5 having a frame 5a indicating the viewfinder field range and various information 5b is provided.

The objective lens system 10 is a positive or negative first lens unit L.
1, the negative second group L2, the positive third group L3, and the positive fourth group
It is composed of four lens groups of the group L4.

In the present embodiment, the third lens group is moved to the object side as indicated by the arrow to change the magnification, and the change in the finder diopter caused by the change is caused by the second lens group having a convex locus on the image plane side as shown by the arrow. While moving, it is corrected. The first and fourth groups are fixed during zooming.

In the present embodiment, the first group or the fourth group may be moved on the optical axis to correct the diopter associated with zooming.

In this embodiment, the first lens unit L1 is composed of a single positive or negative eleventh lens, and the second lens unit L2 is composed of a single negative twenty-first lens having a concave surface facing the object side. The group L3 is composed of a positive 31st lens whose both lens surfaces are convex surfaces,
The fourth unit L4 is composed of a positive meniscus fourth lens having a convex surface directed toward the image plane side (pupil side).

In the present embodiment, the objective lens system 10 is composed of four lens groups of first, second, third and fourth groups, and has at least one aspherical surface of a predetermined shape. . Then, the object image by the objective lens system 10 is formed at the position 4 between the triangular prism P1 and the roof prism P2, whereby the aberration correction is facilitated and a good object image can be observed. Further, by moving the third lens unit to the object side for zooming, a predetermined zoom ratio is effectively obtained.

In the present embodiment, the first prism P1 forming the image inverting optical system P makes the light beam from the objective lens 10 incident from the incident surface P1a. At this time, the objective lens 1
0 is set to be injection telecentric. Then, the light beam incident from the incident surface P1a is incident on the incident surface P1b on the surface P1b.
The light is reflected in the direction P1c on the same plane as 1a. The surface P1c totally reflects the light flux from the surface P1b, makes it vertically enter the surface (emission surface) P1d, and emits it to the outside.

The second prism P2 allows the light flux from the surface P1d of the first prism P1 to enter through the surface (incident surface) P2a. The surface P1d and the surface P2a are substantially parallel to each other. The light beam incident from the surface P2a is reflected by the optical axis 1 of the objective lens 10.
The light is totally reflected by the surface P2b provided substantially perpendicular to 0a and is incident on the surface P2c formed of the roof surface. The surface P2c is the surface P
The light flux from 2b is reflected and guided to the surface P2d on the same plane as the surface P2a. At this time, the surface P2c is incident at an angle such that the light flux incident on the surface P2d is totally reflected by the surface P2d in a direction parallel to the optical axis 10a.

The surface P2c, which is a roof surface, is folded back in the direction of the short side of the observation visual field (finder visual field), that is, in the vertical direction of a normal camera. Then, the light beam totally reflected by the surface P2d is vertically incident on the surface P2d on the same plane as the surface P2b, and is emitted to the outside from that.

A finder image (object image) is formed by the objective lens 10 in the vicinity of the exit surface P1d of the first prism P1, that is, in the vicinity of the field frame 5a. Then, the finder image of the inverted real image formed by the eyepiece lens Le in the vicinity of the field frame 5a is observed as the finder image of the erect real image through the second prism P2.

In this embodiment, by setting the respective elements such as the prism and the field frame in this way, the amount of vertical projection of the entire finder system is made smaller than in the case of using the Porro prism, and the space is effectively used. We are trying to use it to reduce the size of the entire finder system.

The eyepiece lens system Le is composed of a positive lens whose both lens surfaces are convex, and has an aspherical surface whose positive refractive power becomes weaker from the lens center toward the lens periphery. In the objective lens system of the variable-magnification viewfinder including the wide-angle range, the two-group zoom type of negative and positive refracting powers or its modified zoom type is suitable for downsizing of the optical system. With a two-group zoom lens having negative and positive refractive power, the diagonal angle of view on the wide-angle side is 6
When it reaches 0 degree, negative distortion becomes a problem.

Therefore, in this embodiment, the first objective lens system
In order to correct distortion on the wide-angle side, an aspherical surface with an infinite paraxial focal length and a strong positive refractive power from the lens center to the lens periphery is provided to correct distortion on the wide-angle side. Corrected well. In the present embodiment, the case where the paraxial refractive power of the first group is zero is shown, but it may have a weak positive or negative refractive power.

The first prism P1 and the second prism of the image inverting optical system P
In order to form the primary image of the objective lens system 10 between the prisms P2, the objective lens system requires a long back focus. In order to secure a long back focus while maintaining the focal length of the objective lens system in order to obtain a sufficient finder magnification with the two-group zoom lens having negative and positive refracting power, a positive second lens is used.
The refractive power of the group must be strengthened. However, if the refractive power is increased, it becomes difficult to correct the aberration. In this embodiment, a positive meniscus 41st lens having a concave surface facing the object side is provided as a fourth lens group in the final lens group of the objective lens system,
The rear principal point of the objective lens system is brought closer to the primary imaging plane side, and the aberration is favorably corrected while ensuring a sufficient back focus.

Since the first and second prisms P1 and P2 of the image reversing optical system P are provided with total reflection surfaces, total reflection conditions are satisfied at all angles of view to prevent light rays from being vignetted. Therefore, the refractive power is arranged such that the off-axis chief ray that exits the fourth lens group is substantially parallel to the optical axis.

Further, the second lens unit is composed of a negative 21st lens element having a strong concave surface facing the object side, so that the occurrence of spherical aberration is reduced. The third lens group is a positive third lens element with convex lens surfaces.
It is composed of one lens, and mainly corrects axial and off-axis aberrations in good balance. In particular, various aberrations are satisfactorily corrected by making the lens surface on the eyepiece side have a stronger refracting power than the lens surface on the objective side. Furthermore, it is better to use an aspherical surface with a shape in which the positive refracting power becomes weaker from the lens center to the lens periphery. This makes it possible to enhance the refracting power while compensating for aberrations well and to facilitate downsizing of the finder system. There is.

Further, when the radii of curvature of the object-side and image-side lens surfaces of the 41st lens are R41a and R41b, respectively, the condition 0 <R41b / R41a <1 (1) should be satisfied. ing. As a result, high optical performance is obtained over the entire zoom range and over the entire viewfinder field.

Next, numerical examples of the present invention will be shown. In the numerical examples, 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 spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass. R9 ~ R22
Up to the above, the reflecting surface of each prism constituting the image inverting optical system is shown, and each is ∞. R25 is an eye point. The aspherical shape has an X axis in the optical axis direction, an H axis in the direction perpendicular to the optical axis, a light traveling direction is positive, and R is a paraxial radius of curvature,
When K, B, and C are aspherical coefficients, respectively

[0029]

(Equation 1) It is represented by the following expression. Further, "D-0X" means "10 ^-X ".

Numerical Example 1 f = 352 to 644 2ω = 60.8 ° to 34.6 ° R 1 = ∞ D 1 = 1.20 N 1 = 1.49171 ν 1 = 57.4 R 2 = ∞ D 2 = variable R 3 = -6.194 D 3 = 1.20 N 2 = 1.58306 ν 2 = 30.2 R 4 = -300.298 D 4 = Variable R 5 = 8.398 D 5 = 3.40 N 3 = 1.49171 ν 3 = 57.4 R 6 = -6.454 D 6 = Variable R 7 =- 9.172 D 7 = 1.90 N 4 = 1.49171 ν 4 = 57.4 R 8 = -6.145 D 8 = 0.20 R 9 = ∞ D 9 = 3.75 N 5 = 1.5709 ν 5 = 33.8 R10 = ∞ D10 = 5.30 N 6 = 1.5709 ν 6 = 33.8 R11 = ∞ D11 = 4.35 N 7 = 1.5709 ν 7 = 33.8 R12 = ∞ D12 0.00 N 8 = 1.5709 ν 8 = 33.8 R13 = ∞ D13 = 0.40 R14 = ∞ D14 = 0.40 N 9 = 1.5230 ν 9 = 58.6 R15 = ∞ D15 = 0.40 N10 = 1.5230 ν10 = 58.6 R16 = ∞ D16 = 0.40 R17 = ∞ D17 = 5.15 N11 = 1.5709 ν11 = 33.8 R18 = ∞ D18 = 6.78 N12 = 1.5709 ν12 = 33.8 R19 = ∞ D19 = 0.00 N13 = 1.5709 ν13 = 33.8 R20 = ∞ D20 = 7.28 N14 = 1.5709 ν14 = 33.8 R21 = ∞ D21 = 4.79 N15 = 1.5709 ν15 = 33.8 R22 = ∞ D22 = 0.20 R23 = 27.633 D23 = 2.50 N16 = 1.49171 ν16 = 57.4 R24 = -12.281 D24 = 15.00 R25 = Eye point R41b / R41a = 0.67 Asphere Coefficient No RK B C 1 0 0 8.121 D-04 1.881 D-05 3 -6.194 D + 00 -1.222 D-01 -7.540 D-04 -7.140 D-05 5 8.398 D + 00 -5.570 D-01 -6.369 D-04 9.271 D-06 6 -6.453 D + 00 -6.855 D-01 3.097 D-05 7.812 D-06 7 -9.172 D + 00 2.145 D + 00 -6.967 D-04 5.145 D-06 23 2.763 D + 01 0 -9.653 D-05 -9.117 D-08 Focal length Variable distance 352.28 489.73 643.91 D2 1.32 1.95 1.48 D4 5.67 2.94 1.33 D6 0.40 2.49 4.57 <Numerical example 2> f = 402 ~ 739 2ω = 60.8 ° ~ 34.6 ° R 1 = ∞ D 1 = 1.20 N 1 = 1.49171 ν 1 = 57.4 R 2 = ∞ D 2 = Variable R 3 = -5.779 D 3 = 1.20 N 2 = 1.58306 ν 2 = 30.2 R 4 = -95.787 D 4 = Variable R 5 = 8.488 D 5 = 3.66 N 3 = 1.49171 ν 3 = 57.4 R 6 = -6.438 D 6 = Variable R 7 = -32.832 D 7 = 1.50 N 4 = 1.49171 ν 4 = 57.4 R 8 = -12.646 D 8 = 0.20 R 9 = ∞ D 9 = 3.75 N 5 = 1.5709 ν 5 = 33.8 R10 = ∞ D10 = 5.30 N 6 = 1.5709 ν 6 = 33.8 R11 = ∞ D11 = 4.35 N 7 = 1.5709 ν 7 = 33.8 R12 = ∞ D12 0.00 N 8 = 1.5709 ν 8 = 33.8 R13 = ∞ D13 = 0.40 R14 = ∞ D14 = 0.40 N 9 = 1.5230 ν 9 = 58.6 R15 = ∞ D15 = 0.40 N10 = 1.5230 ν10 = 58.6 R16 = ∞ D16 = 0.40 R17 = ∞ D17 = 5.15 N11 = 1.5709 ν11 = 33.8 R18 = ∞ D18 = 6.78 N12 = 1.5709 ν12 = 33.8 R19 = ∞ D19 = 0.00 N13 = 1.5709 ν13 = 33.8 R20 = ∞ D20 = 7.28 N14 = 1.5709 ν14 = 33.8 R21 = ∞ D21 = 4.79 N15 = 1.5709 ν15 = 33.8 R22 = ∞ D22 = 0.20 R23 = 27.633 D23 = 2.50 N16 = 1.49171 ν16 = 57.4 R24 = -12.281 D24 = 15.00 R25 = Eyepoint R41b / R41a = 0.385 Aspheric coefficient No RK B C 1 0 0 9.756 D-04 3.418 D-05 3 -5.779 D + 00 -2.053 D-01 -8.940 D-04 -1.228 D-04 5 8.487 D + 00 -6.812 D-01 -4.957 D-04 4.527 D-06 6 -6.438 D + 00 -9.964 D-01 1.763 D-05 2.342 D-06 7 -3.283 D + 01 -3.742 D + 00 -4.419 D-04 7.522 D- 07 23 2.763 D + 01 0 -9.653 D-05 -9.117 D-08 Focal length Variable interval 402.45 559.69 738.56 D2 1.19 1.80 1.33 D4 5.87 3.17 1.56 D6 0.40 2.49 4.57 <Numerical example 3> f = 349 to 658 2ω = 60.8 ° ~ 34.6 ° R 1 = ∞ D 1 = 1.20 N 1 = 1.49171 ν 1 = 57.4 R 2 = ∞ D 2 = Variable R 3 = -5.266 D 3 = 1.20 N 2 = 1.58306 ν 2 = 30.2 R 4 = -807.090 D 4 = Yes Variable R 5 = 7.950 D 5 = 3.68 N 3 = 1.49171 ν 3 = 57.4 R 6 = -5.416 D 6 = Variable R 7 = -6.753 D 7 = 1.90 N 4 = 1.49171 ν 4 = 57.4 R 8 = -5.592 D 8 = 0.20 R 9 = ∞ D 9 = 3.75 N 5 = 1.5709 ν 5 = 33.8 R10 = ∞ D10 = 5.30 N 6 = 1.5709 ν 6 = 33.8 R11 = ∞ D11 = 4.35 N 7 = 1.5709 ν 7 = 33.8 R12 = ∞ D12 0.00 N 8 = 1.5709 ν 8 = 33.8 R13 = ∞ D13 = 0.40 R14 = ∞ D14 = 0.40 N 9 = 1.5230 ν 9 = 58.6 R15 = ∞ D15 = 0.40 N10 = 1.5230 ν10 = 58.6 R16 = ∞ D16 = 0.40 R17 = ∞ D17 = 5.15 N11 = 1.5709 ν11 = 33.8 R18 = ∞ D18 = 6.78 N12 = 1.5709 ν12 = 33.8 R19 = ∞ D19 = 0.00 N13 = 1.5709 ν13 = 33.8 R20 = ∞ D20 = 7.28 N14 = 1.5709 ν14 = 33.8 R21 = ∞ D21 = 4.79 N15 = 1.5709 ν15 = 33.8 R22 = ∞ D22 = 0.20 R23 = 27.633 D23 = 2.50 N16 = 1.49171 ν16 = 57.4 R24 = -12.281 D24 = 15.00 R25 = Eyepoint R41b / R41a = 0.828 Aspherical coefficient No R K B C 100 0 1.084 D-03 -1.732 D-05 3 -5.265 D + 00 -7.281 D-01 -1.085 D-03 -1.166 D-04 5 7.950 D + 00 -6.646 D-01 -8.297 D-04 7.275 D-06 6 -5.415 D + 00 -8.693 D-01 1.617 D-04 -4.008 D-06 7 -6.753 D + 00 9.278 D-01 -4.263 D-04 -6.244 D-06 23 2.763 D + 01 0 -9.653 D-05 -9.117 D-08 Focal length variable distance 348.85 494.16 658.47 D2 1.52 1.88 1.21 D4 4.89 2.44 1.03 D6 0.80 2.89 4.97

[0031]

As described above, according to the present invention, by appropriately setting the lens configuration of the objective lens system having the variable power portion, a predetermined variable power ratio can be obtained while ensuring a sufficient eyepiece pupil diameter and viewfinder magnification. It is possible to achieve a variable magnification finder of a real image type, which can easily obtain an image and can observe a good finder image over the entire magnification range.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part according to a first embodiment of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 4 is a lens cross-sectional view of Numerical Example 3 of the present invention.

FIG. 5 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 6 is an intermediate aberration diagram of Numerical example 1 of the present invention.

FIG. 7 is an aberration diagram at a telephoto end according to Numerical Example 1 of the present invention.

FIG. 8 is an aberration diagram at the wide-angle end according to Numerical Example 2 of the present invention.

FIG. 9 is an intermediate aberration diagram of Numerical example 2 of the present invention.

FIG. 10 is an aberration diagram at a telephoto end according to Numerical Example 2 of the present invention.

FIG. 11 is an aberration diagram at a wide-angle end according to Numerical Example 3 of the present invention.

FIG. 12 is an intermediate aberration diagram of Numerical example 3 of the present invention.

FIG. 13 is an aberration diagram at a telephoto end according to Numerical Example 3 of the present invention.

[Explanation of Codes] 10 Objective Lens System P Image Inversion Optical System Le Eyepiece Lens System L1 1st group L2 2nd group L3 3rd group L4 4th group E Eyepoint ΔS Sagittal image surface ΔM Meridional image surface

Claims (5)

[Claims] 1. An object image formed by an objective lens system having a positive refracting power in order from the object side is made into an erected image through an image inverting optical system, and when the erected image is observed by an eyepiece lens system, the objective lens system is used. Is a positive or negative first group, a negative second group, a positive third group
Group, and four lens groups of a fourth group consisting of a positive meniscus 41st lens with the concave surface facing the object side. The third group is moved along the optical axis to perform magnification change. Is corrected by the first group, the second group, or the fourth group, and the off-axis light beam emitted from the fourth group is made substantially parallel to the optical axis, and at least 1 is set in the objective lens system. Magnification finder featuring two aspherical surfaces. 2. The first group, the second group, the third group and the fourth group
2. The variable power viewfinder according to claim 1, wherein each group is composed of a single lens. 3. The condition of 0 <R41b / R41a <1 is satisfied when the radiuses of curvature of the object-side and image-side lens surfaces of the 41st lens are R41a and R41b, respectively. Magnification finder. 4. The third lens group is composed of a positive thirty-first lens element having convex lens surfaces on both sides, and has an aspherical surface whose positive refractive power becomes weaker from the lens center to the lens periphery. The variable magnification finder according to claim 1, wherein: 5. The first group is composed of a single eleventh lens having at least one aspherical surface, and the aspherical surface has a shape in which the positive refracting power becomes stronger from the lens center to the lens periphery. The variable magnification finder according to claim 1, wherein