JP3352308B2 - Viewfinder 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 finder optical system, and more particularly, to a finder image of an erect upright image (object image) formed on a primary image forming surface by an objective optical system via an image inverting means. The present invention relates to a finder optical system that is observed as an image with an eyepiece.

[0002]

2. Description of the Related Art Among finder systems such as photographic cameras and video cameras, there have been various real image finder optical systems for observing a finder image of a real image formed on a primary image forming surface through an eyepiece lens. It has been proposed.
Since the real image type finder optical system is easier to miniaturize the entire optical system than the virtual image type finder optical system,
Recently, it is frequently used in cameras with a zoom lens.

As a real image type finder optical system, for example, in Japanese Utility Model Application Laid-Open No. 58-62337, an object image (finder image) formed on a primary image forming surface by an objective lens is forwarded through an image reversing means such as a Porro prism. It is converted into a normal viewfinder image and observed with an eyepiece. In Japanese Utility Model Laid-Open Publication No. 1-160427, a roof reflecting member and two
A real image type finder optical system in which two mirrors and the like are arranged to invert the finder image is proposed.

[0004] The applicant of the present invention disclosed in Japanese Patent Application Laid-Open No. Hei 6-167739 that a primary image forming object image is formed by an objective lens in order to shorten the overall length of a lens of a finder optical system with the miniaturization and thinning of the whole camera. A small finder optical system has been proposed in which an optical path to an image plane is bent by a reflection surface to form a primary image formation plane inside the image inversion means.

[0005]

A conventional real image type finder optical system using an image inverting means such as a Porro prism for erecting an erect image has an objective lens and an image inverting means for forming an object image on a primary image forming surface. And the optical effect is clearly distinguished. For example, the image reversing means is configured so as not to have a refractive power when the object image is formed on the primary image forming surface.

For this reason, in a finder optical system in which a part of the image inverting means (for example, a prism member) is provided between the objective lens and the primary imaging surface, the objective lens is retrofocused in order to lengthen the back focus of the objective lens. Composed of molds,
At this time, it was necessary to increase the degree of retrofocus according to the length of the back focus. For this reason, the size of the objective lens tends to increase and the size of the entire finder optical system tends to increase.

Further, a part of the image reversing means exists between the objective lens and the primary image forming surface, and is located closer to the object image than the primary image forming surface.
In a finder optical system having a total reflection surface for bending the optical path, it is necessary to configure the objective lens with an exit-side telecentric system in order to efficiently totally reflect the entire light beam on the total reflection surface. As a result, the size of the objective lens tends to increase.

According to the present invention, when observing an object image formed on a primary image forming surface by an objective optical system as an erect erect image using an image inverting means by an eyepiece, the configuration of the objective optical system is appropriately set. Accordingly, an object of the present invention is to provide a real image type finder optical system capable of satisfactorily correcting various aberrations and observing a good finder image while reducing the size of the finder optical system.

[0009]

According to a first aspect of the present invention, there is provided a viewfinder optical system comprising: an objective optical system; and an object image formed by the objective optical system on a primary image forming surface is formed into an erect image by using a roof surface. In a finder optical system having an image reversing means and an eyepiece for observing the object image of the erect erect image, the objective optical system has an aspherical decentered mirror reflecting surface having no axis of rotational symmetry, and a refracting surface. And a prism having a positive refractive power including an aspherical eccentric total reflection surface having no rotational symmetry axis.

A second aspect of the present invention is characterized in that, in the first aspect of the present invention, the prism includes a reflecting surface having one symmetric surface. According to a third aspect of the present invention, in the first aspect, the objective optical system has a stop on the object side of the prism. According to a fourth aspect of the present invention, in the first aspect, the objective optical system includes a lens group having a positive refractive power on the object side of the prism.

According to a fifth aspect of the present invention, there is provided a camera including the finder optical system according to any one of the first to fourth aspects.

[0012]

[0013]

FIG. 1 is a sectional view of an essential part of an optical system according to a first embodiment of the present invention, and FIG. 2 is a sectional view of an essential part showing an optical path when an optical path of an image inverting means of FIG. 1 is developed. .

In FIG. 1, OL denotes an objective optical system, which has an aperture 1 and a prism 2 having a positive refractive power, and forms an object image on a primary imaging surface 3a. Reference numeral 3 denotes a field frame provided near the primary imaging surface 3a for limiting the field of view of the finder. 4
Denotes an image reversing means, which converts an object image formed on the primary image forming surface 3a into an erect image. Reference numeral 5 denotes an eyepiece lens for observing an object image formed on the primary imaging surface 3a as an erect image via the image reversing means 4. Reference numeral 6 denotes an eye point for observation.

Next, the configuration of the prism 2 having a positive refractive power and constituting the objective optical system OL of the present embodiment will be described.

The prism 2 has an incident surface 2a made of an aspherical surface having no axis of rotational symmetry , into which a light beam from an object passing through the stop 1 is incident, and a rotation for condensing and reflecting the light beam from the incident surface 2a to the incident surface 2a side. An aspherical eccentric reflecting surface 2b having no axis of symmetry, a total reflecting surface 2c continuous with the incident surface 2a for totally reflecting the light beam from the eccentric reflecting surface 2b, and a plane or rotational symmetry for emitting the light beam from the total reflecting surface 2c And an exit surface 2d formed of an aspheric surface having no axis.

In the present embodiment, the prism 2 having a positive refractive power bears most of the positive refractive power on the eccentric reflecting surface 2b, and the refracting power of the eccentric reflecting surface 2b causes the object image to be formed on the primary imaging surface 3a. Is formed. Then, various aberrations such as coma, astigmatism, and distortion generated in the eccentric reflecting surface 2b are reduced to the incident surface 2a.
(2c) and the aspherical surface of the exit surface 2d are corrected in a well-balanced manner.

The image reflecting means 4 includes an incident surface 4a for receiving a light beam from an object image formed on the primary image forming surface 3a, and an incident surface 4a.
Total reflection surface 4b, total reflection surface 4b for totally reflecting light flux from
Surfaces 4c and 4d for reflecting light beams from
an incident surface 4a for totally reflecting the light beams from c and 4d, a total reflection surface 4e on the same plane as the total reflection surface 4b for emitting a light beam from the total reflection surface 4e, and an emission surface 4f on the same plane. The object image formed on the primary imaging surface 3a is guided to the eyepiece lens 5 as an erect image. Each of the surfaces 4a to 4f of the image reversing means 4 is constituted by a plane, but if necessary, some surfaces may be constituted by a spherical surface or an aspherical surface or an aspherical surface having no axis of rotational symmetry.

FIG. 3 is a sectional view of a main part of a second embodiment of the present invention.

This embodiment is different from the first embodiment in FIG.
The difference lies in that the objective optical system OL is composed of a lens group 7 having a positive or negative refractive power composed of a negative lens 7a and a positive lens 7b, a diaphragm 1, and a prism 4, and the other configurations are the same. In the present embodiment, by providing the lens group 7 in the objective optical system OL, the light flux from the object is condensed and guided to the prism 4, the burden of the positive refractive power of the prism 4 is reduced, and the primary imaging surface is reduced. 3a, a good object image is formed.

Next, numerical examples of each embodiment of the present invention will be described. The aspherical shape (free-form surface) having no rotationally symmetric axis provided in the prism 2 has a Z-axis in the optical axis direction and an X-axis and a Y-axis in a direction orthogonal to the optical axis.

[0022]

(Equation 1) It is represented by the following equation.

The rotationally symmetric aspherical surface is represented by the following polynomial.

[0024]

(Equation 2) Ri is the shape of the i-th lens surface in order from the object side, Di
Is the i-th lens thickness and air gap from the object side, and Ni is the refractive index of the i-th medium in order from the object side. “E-0X” means 10 ^−X .

[0025]

[Outside 1]

[0026]

[Outside 2]

[0027]

[Outside 3]

[0028]

[Outside 4]

[0029]

As described above, according to the present invention, when the object image formed on the primary image forming surface by the objective optical system is observed by the eyepiece as an erect image using the image inverting means, the objective optical system is used. By appropriately setting the configuration of the system, it is possible to achieve a real image type finder optical system capable of properly correcting various aberrations and observing a good finder image while reducing the size of the finder optical system.

In particular, by using a prism having an aspherical decentered reflecting mirror surface having no rotationally symmetric axis for the objective optical system, a real image type of compact, small number of parts and excellent finder image observation is made possible. A finder optical system can be achieved.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of a main part when an optical path according to the first embodiment of the present invention is developed.

FIG. 3 is a sectional view of a main part when an optical path according to a second embodiment of the present invention is developed.

[Explanation of symbols]

 OL Objective optical system 1 Aperture 2 Prism 3 Field frame 3a Primary imaging plane 4 Image reversing means 5 Eyepiece 6 Eye point

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-234139 (JP, A) JP-A-1-209432 (JP, A) JP-A-5-303056 (JP, A) JP-A-6-302 43389 (JP, A) JP-A-6-324285 (JP, A) JP-A-6-167739 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03B 13/00-13 / 28 G02B 25/00

Claims (5)

(57) [Claims] 1. An objective optical system , an image inverting means for converting an object image formed on a primary imaging surface by the objective optical system into an erect image using a roof surface, and observing the object image of the erect image. eyepiece to
In the finder optical system having bets, objective optical system includes a decentered mirror reflection surface of aspherical having no axis of rotational symmetry,
Of an aspherical surface without an axis of rotational symmetry that also acts as a refractive surface
A finder optical system comprising a prism having a positive refractive power including an eccentric total reflection surface . 2. The finder optical system according to claim 1, wherein said prism includes a reflecting surface having one symmetric surface. 3. The finder optical system according to claim 1, wherein said objective optical system has a stop on the object side of said prism. 4. The finder optical system according to claim 1 , wherein the objective optical system has a lens group having a positive refractive power on the object side of the prism. 5. A camera comprising the finder optical system according to claim 1.