JP2990974B2 - Zoom finder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable magnification finder suitable for a photographic camera, a video camera, and the like, and more particularly to a variable magnification finder capable of changing a finder magnification variously and observing a good finder image by removing a flare component. Things.

[0002]

2. Description of the Related Art In recent cameras, especially in compact cameras, the size of the entire camera is reduced and the photographing system is zoomed. As the finder system used for this, a variable-magnification finder for miniaturization and zooming is used.

For example, in Japanese Patent Application Laid-Open No. 61-156018, a variable magnification finder is configured by a secondary imaging system, and among these, an objective lens constituting a variable magnification finder is configured by a plurality of lens groups. A real image obtained by moving a predetermined lens group of the multiple lens groups on the optical axis to perform zooming, and arranging a Porro prism as an image inverting means behind the objective lens to obtain an erect normal image. A formula finder is proposed.

[0004]

When a reflecting member such as a Porro prism is used as an image inverting means in a real image type variable magnification finder as a finder system used in a finder device, total reflection is used in terms of reflection efficiency. This is preferable because evaporation materials (aluminum and silver) are not required.

[0005] However, in the method using total reflection, a light beam that does not satisfy the condition of total reflection passes through the reflecting surface, and a part of the light flux becomes stray light, reaches the eyepiece lens, and sometimes becomes ghost or flare.

FIGS. 4A and 4B are schematic views of a main part of the lens configuration at the wide-angle end and the telephoto end of a real image type variable magnification finder showing such a state.

In FIG. 1, reference numeral 91 denotes a first group having a negative refractive power;
Reference numeral 92 denotes a second group having a positive refractive power.
Is composed. Reference numeral 99 denotes a stop fixed to the first group 1; 90, a stop fixed to the second group 2;
Reference numeral 8 denotes a field frame for limiting the viewfinder field, which is provided near the image forming plane of the objective lens 100. Reference numeral 95 denotes an eyepiece.

In FIG. 1, both lens groups 9 of the objective lens 100 are shown.
1 and 92 are moved on the optical axis together with diaphragms 99 and 90 as indicated by arrows in FIG.
The finder image formed in the vicinity of the field frame 98 by 00 is observed by the eyepiece 95 via the prisms 96 and 97 as image reversing means.

At this time, the light beam width of the axial light beam on the wide-angle side shown in FIG. 4A is larger than the light beam width on the telephoto side of FIG. 10B. For this reason, on the wide-angle side, a part of the light beam does not satisfy the condition of total reflection on the total reflection surface provided in the prisms 96 and 97, passes without being totally reflected, becomes stray light, and a part of the light enters the eyepiece lens 95. As a result, there arises a problem that observation conditions of the finder image are deteriorated.

According to the present invention, by appropriately setting the lens configuration of the objective lens, it is possible to easily perform zooming while reducing the size of the entire lens system, and furthermore, a prism utilizing total reflection as an image inverting means. To effectively remove stray light that passes through the eyepiece and does not satisfy the conditions for total reflection when using a zoom lens, and to obtain a variable-magnification finder that can observe good finder images at various finder magnifications. Aim.

[0011]

SUMMARY OF THE INVENTION A variable magnification finder according to the present invention reverses a finder image formed using a variable magnification objective lens through an image inversion optical system having a total reflection surface. A variable magnification finder for observing with an eyepiece, wherein the objective lens includes, in order from the object side, a first group having a negative refractive power, a moving diaphragm, and a second group having a positive refractive power. While reducing the distance between the first lens unit and the movable aperture, and the distance between the movable aperture and the second lens unit, the first lens unit, the movable aperture, and the second lens unit are moved toward the object side, respectively. It is characterized in that zooming to the telephoto end is performed.

In particular, the image inversion optical system is characterized in that it has at least one total reflection surface.

[0013]

FIG. 1 shows a first embodiment of a variable magnification finder according to the present invention.
FIG. FIG. 2 is a schematic view of a main part when the optical system of the variable magnification finder of FIG. 1 is developed. FIG. 2 (A)
Indicates the wide-angle end, and FIG. 2B indicates the telephoto end.

1 and 2, reference numeral 60 denotes an objective lens having a first group 61 having a negative refractive power, a movable stop 69, a fixed stop 70, and a second group 62 having a positive refractive power. .

Reference numerals 66 and 67 denote prisms each having a reflection surface and a total reflection surface as image inverting means. In FIG.

In the prism 66, an entrance surface 66a is formed by a lens surface having a positive refractive power. 66
b is a total reflection surface, 66c is a reflection surface on which a deposition film is applied, 66d
Is an exit surface on the same plane as the total reflection surface 66b.

In the prism 67, 67a is an incident surface, 6
7b is a total reflection surface, 67c is a roof reflection surface, 67d is a total reflection surface on the same plane as the incident surface 67a, and 67e is a total reflection surface 67.
The exit surface is on the same plane as b. The exit surface 66d of the prism 66 and the entrance surface 67a of the prism 67 are parallel to each other.

Reference numeral 68 denotes a field frame for limiting the field of view of the finder, which is provided near the image forming plane on which the finder image is formed by the objective lens 60. Reference numeral 65 denotes an eyepiece, which converts a finder image formed on a field frame 68 into a prism 6.
7 and is observed as an erect image.

In this embodiment, when zooming from the wide-angle end to the telephoto end, the first unit 61 and the second unit 62 are moved to the object side as indicated by arrows 61a and 62a so that the distance between both lens units is reduced. I have. Further, the movable stop 69 is moved toward the object side as indicated by an arrow 69a so that the distance between the lens units is reduced.
It is moved by less than two. In addition, fixed aperture 7
0 is moving integrally with the second group.

In this embodiment, as described above, each lens group 6
By moving the movable apertures 1 and 62 and the movable stop 69 on the optical axis, magnification is changed, and a real viewfinder image with various magnifications is formed near the field stop 68 via the prism 66.

At this time, the objective lens 60 and the lens surface 66a of the prism 66 constitute a substantially telecentric system, and the principal ray of the light beam passing through the lens surface 66a of the prism 66 is substantially parallel to the optical axis. I have to. Then, the finder image formed near the field stop 68 is observed through the prism 67 as an erect erect image from the eyepiece lens 65.

In general, a variable-magnification finder according to the present invention has sufficient axial luminous flux on the wide-angle side. For this reason, in the present embodiment, the movable stop 69 is positioned in the direction of the second lens group 62 on the wide-angle side, so that the off-axis light beam is not blocked as compared with the conventional variable magnification finder shown in FIG. Only the periphery is shielded from light.

Thus, the width of the on-axis light beam is reduced so that many on-axis light beams satisfy the total reflection condition on the total reflection surfaces (66b, 67b, 67d) provided on the prisms 66, 67. The generation of stray light that is totally reflected and passes through the total reflection surface is effectively prevented.

In this embodiment, the entrance surface 6 of the prism 66 is
The luminous flux having a full angle of view incident on 6a is totally reflected by the total reflection surface 66b, reflected by the reflection surface 66c, and then emitted from the exit surface 66d so that the principal ray of the full angle of view is emitted almost vertically. I have. Then, the light enters the incident surface 67a of the prism 67, is totally reflected by the total reflection surface 67b, and is reflected by the roof surface 67c.
When the light is totally reflected by the total reflection surface 67d and exits from the exit surface 67e, the principal ray at all angles of view exits substantially perpendicularly.

With such a configuration, the light beams at all angles of view are effectively totally reflected by the respective total reflection surfaces.

FIG. 3 is a perspective view of a main part of a variable magnification finder according to a second embodiment of the present invention.

In this embodiment, a Porro prism 80 is used as an image inverting means, and an objective lens 60 is used as compared with the first embodiment shown in FIG.
In that a field lens 81 is provided in the vicinity of an image forming plane on which a finder image is formed, and the other configuration is the same. In FIG. 3, the same elements as those shown in FIG. 1 are denoted by the same reference numerals.

In this embodiment, a finder image is formed by the objective lens 60 on the image forming surface near the field lens 81 or near the entrance surface of the Porro prism 80. Then, the finder image formed on the image forming surface is reflected (total reflection) by the reflecting surfaces 80a, 80b, 80c, and 80d of the Porro prism 80 in order to form an erect erect image. I'm observing.

Also in this embodiment, the movable diaphragm 6 is changed with the magnification change.
9 is moved in the same manner as in the first embodiment of FIG.

Next, numerical examples of the variable magnification finder shown in FIG. 1 will be described. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, and Di is the i-th lens surface from the object side.
The second lens thickness, the air gap, and Ni and νi are the refractive index and Abbe number of the glass of the ith lens in order from the object side.

The aspheric surface has an X-axis in the optical axis direction, an H-axis in a direction perpendicular to the optical axis, a positive traveling direction of light, R is a paraxial radius of curvature,
When A, B, C, D, and E are each aspheric coefficients

[0032]

(Equation 1) It is represented by the following equation. Numerical example 2 ω = 27.5 ° to 50 ° R 1 = -15.61 D 1 = 1.29 N 1 = 1.58306 ν 1 = 30.2 R 2 = 29.67 D 2 = Variable R 3 = ∞ D 3 = Variable R 4 = 11.15 D 4 = 3.09 N 2 = 1.49171 ν 2 = 57.4 R 5 = Aspherical surface D 5 = Variable R 6 = 12.38 D 6 = 14.15 N 3 = 1.57090 ν 3 = 33.8 R 7 = ∞ D 7 = 0.63 R 8 = ∞ D 8 = 24.00 N 4 = 1.57090 ν 4 = 33.8 R 9 = ∞ D 9 = 0.20 R10 = Aspherical surface D10 = 3.20 N 5 = 1.49171 ν 5 = 57.4 R11 = -13.08 D11 = 14.00 R7: Exit surface of prism 66 R8, 9: Incident surface and exit surface of prism 67

[0033]

[Table 1] Aspheric surface R5: R = -10.76, A = 0, B = 4.1
× 10 ⁻⁴ C = −7.4 × 10 ⁻⁶ D = 5.97 × 10 ⁻⁷ R10: R = 21.82, A = 0, B = −1.
41 × 10 ⁻⁴ C = 1.17 × 10 ⁻⁶ , D = −1.7 × 10 ⁻⁸

[0034]

According to the present invention, by appropriately setting the lens configuration of the objective lens, it is possible to easily change the magnification while reducing the size of the entire lens system, and furthermore, as an image inverting means. When a prism that uses reflection is used, stray light that passes through without satisfying the conditions for total reflection and enters the eyepiece is effectively removed, and a viewfinder image that can be observed at various viewfinder magnifications is obtained. Achieve double viewfinder.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a variable magnification finder according to a first embodiment of the present invention.

FIG. 2 is an explanatory view when the optical path of FIG. 1 is developed.

FIG. 3 is a perspective view of a main part of a zoom finder according to a second embodiment of the present invention.

FIG. 4 is a schematic view of a main part when an optical path of a conventional zoom finder is developed.

[Explanation of symbols]

 Reference Signs List 60 Objective lens 61 First group 62 Second group 65 Eyepiece 66, 67 Image reversing prism 69 Moving diaphragm 70 Fixed diaphragm

Claims (1)

(57) [Claims] 1. A variable-magnification fine which is obtained by inverting a finder image formed by using a variable-magnification objective lens through an image inverting optical system having a total reflection surface and then observing the image with an eyepiece. a loaders, objective lens, in order from the object side, and a second group of the first group and the movable stop and the positive refractive power of the negative refractive power, the first group and the aperture stop the movement And the moving aperture
While Rito該 the interval between the second group is reduced respectively, said first
The group, the moving aperture, and the second group are moved to the object side, respectively .
A variable magnification finder that performs magnification from the wide-angle end to the telephoto end.