JPH11242258A - Finder optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently observe a finder image by providing an optical member having plural optical elements including rotationally asymmetric surface in an optical path and moving the optical element in a direction perpendicular to an optical axis so that optical characteristic may be adjusted. SOLUTION: An objective lens OL is provided with the optical member 1 consisting of two optical elements 1a and 1b having the rotationally asymmetric surface, a lens group 2 having negative refractive power, a lens group 3 having positive refractive power and a lens group 4 having positive refractive power in order from an object side. The lens group 2 constituting the lens OL is moved while holding a locus projecting to an image surface side and the lens group 3 is moved to the object side as shown by arrows. Furthermore, the optical elements 1a and 1b are moved in the direction perpendicular to the optical axis and in a reverse direction to each other, so that their synthetic power is changed to perform veriable power from a wide angle end to a telephoto end, and diopter change associated with the variable power is corrected. Thus, at least either of the plural optical elements 1a and 1b is moved in the direction perpendicular to the optical axis so as to adjust the optical characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a viewfinder optical system, and more particularly to a viewfinder image (object image) of an inverted real image formed by an objective lens, which is observed by an eyepiece as a viewfinder image of an erect image using an image inverting means. When doing
The present invention relates to a finder optical system capable of easily adjusting a finder diopter.

[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, Japanese Patent Application Laid-Open Nos. H7-172070 and H6-214159 disclose an object image (finder image) formed on a primary imaging surface by an objective lens, such as a Porro prism. The image is converted into an erect finder image via an image inverting means and observed with an eyepiece.

In general, when the taking lens is a zoom lens and the objective lens of the finder optical system is an optical system different from the taking lens, the objective lens of the finder optical system is also part of a lens group in synchronization with the zooming of the taking lens. Is moved by moving the lens in the optical axis direction.

In Japanese Patent Application Laid-Open No. Hei 7-152070, etc., a predetermined optical performance is obtained by using an aspherical lens as an objective lens, and the aspherical lens is manufactured from a plastic material because of its economical aspect. I have. Other eyepiece optical systems and image reversing means are made of plastic materials for the same reason.

[0006]

In order to observe a good finder image in a finder system, it is necessary to appropriately and appropriately configure an objective lens, an image inverting means, an eyepiece, and the like.

In a finder optical system that frequently uses an optical element made of a plastic material as a finder system,
These optical elements are usually manufactured by injection molding. For this reason, due to variations in molding conditions, shrinkage, and the like, there is a tendency that variations in the surface, outer shape, and the like, are greater than in optical elements made of glass materials. That is, there is a problem that the power (refractive power) varies, so that in a finder optical system, the diopter (finder diopter) varies due to a manufacturing error.

[0008] Such variations in the manufacturing of the surface and the outer shape are particularly large in a real image type finder in which the individual power of the lens is strong, and further, in the case of a variable magnification finder, at the telephoto end where the sensitivity of the manufacturing error increases. There is a problem that the diopter shifts greatly.

Conventionally, in order to correct such a diopter shift, an objective lens having a slightly different power is prepared, and the diopter variation is changed by replacing the objective lens according to the overall condition of the finder optical system. Is adjusted to fall within a predetermined range. In addition, as an adjustment mechanism, a part of the objective lens can be moved back and forth on the optical axis to continuously adjust the diopter due to a manufacturing error. However, in the above method, since the number of components to be prepared is large, management is difficult, and as a result, the cost is increased. In addition, in the adjustment method of moving the lens back and forth on the optical axis, there is a problem that the entire apparatus becomes large in view of securing this space.

A diopter adjustment method for replacing a part of the eyepiece or for moving the entire or part of the eyepiece in accordance with the diopter of the user's eyes is generally performed. These have the same problems as described above.

According to the present invention, there is provided an optical element having a rotationally asymmetric surface in an optical path when an object image formed on a primary image forming surface by an objective lens is observed as an erect erect image using an image inverting means by an eyepiece. By providing at least a plurality of optical elements, at least one of the optical elements is moved in a direction perpendicular to the optical axis, thereby changing (correcting) the diopter (finder diopter) so that a good finder image can be observed. The objective is to provide a finder optical system.

[0012]

According to the present invention, there is provided a finder optical system comprising: (1-1) a finder image formed by an objective lens is inverted through an image inverting optical system into an erect erect image, and then an eyepiece is used. In a viewfinder optical system to be observed, an optical member having a plurality of optical elements including a rotationally asymmetric surface is provided in an optical path, and at least one of the plurality of optical elements is moved in a direction perpendicular to an optical axis to improve optical characteristics. It is characterized by being adjusted.

In particular, (1-1-1) the optical element has one axis of symmetry and is moved in the direction of the axis of symmetry.

(1-1-2) The optical member has two optical elements having one symmetry axis, and the two optical elements are relatively moved in the direction of the symmetry axis.

(1-1-3) The optical member is orthogonal to the optical axis and has two rotationally asymmetric surfaces opposed to each other having an axis of symmetry in the vertical direction. And two opposing rotationally asymmetric surfaces having an axis of symmetry, and the two opposing rotationally asymmetric surfaces are respectively moved in the direction of the axis of symmetry.

(1-1-4) The finder optical system has a zooming portion, and at least one optical element constituting the optical member is moved in accordance with zooming of the zooming portion. thing.

(1-1-5) The optical member has at least three rotationally asymmetric surfaces, of which two opposing rotationally asymmetric surfaces are relatively moved.

(1-1-6) The optical member forms a part of the objective lens.

(1-1-7) The optical member forms a part of the eyepiece or is formed of the eyepiece.

(1-1-8) The objective lens, the image reversing means and the eyepiece are made of a plastic material.

[0021]

FIG. 1 is a sectional view of a main part of a first embodiment of the present invention, and shows a real image type variable magnification finder. In FIG. 1, OL denotes an objective lens having a positive refractive power, which has a zooming portion. P is an image inversion optical system, for example, 2
It comprises two prisms, a triangular prism having two reflecting surfaces and a roof prism having four reflecting surfaces including a roof surface. In the same figure, the two expanded glass blocks 5,
6 is shown.

In this embodiment, a case where a simple prism is used as the image inversion optical system P is shown, but various types such as a Porro prism and a roof prism can be applied as the image inversion optical system.

EL is an eyepiece having a positive refractive power and is shown as one lens 8 in FIG. E is an eye point (pupil plane) of the observer 9. Reference numeral 6 denotes a primary image forming surface on which an object image is formed by the objective lens OL, and a field frame is arranged at or near this position.

The objective lens OL includes, in order from the object side, an optical member 1 comprising two optical elements 1a and 1b having rotationally asymmetric surfaces, a lens group 2 having a negative refractive power, a lens group 3 having a positive refractive power, and a positive lens group 3. The lens group 4 has a refractive power.

In the present embodiment, all of the above components 1 to 8 are made of a plastic material.

In the present embodiment, various kinds of light beams from a subject (not shown) are condensed by the objective lens OL and the objective lens OL is zoomed to a predetermined position on the primary image forming plane 6 via the prism 5. A finder image having a magnification of? Then, the finder image is converted into an erect finder image through the prism 7 and observed from the eye point E via the eyepiece EL.

In this embodiment, as shown by the arrow, the lens group 2 constituting the objective lens OL is moved while having a convex locus on the image plane side, and the lens group 3 is moved to the object side. Then, the optical elements 1a and 1b are moved in the direction perpendicular to the optical axis and in the directions opposite to each other to change the combined power to change the magnification from the wide-angle end to the telephoto end, and the diopter accompanying the magnification. Changes are corrected. The lens group 4 is fixed during zooming.

The optical element 1a has a rotationally asymmetric surface on the pupil plane (image plane) side, and the optical element 1b has both rotationally asymmetric surfaces. The pupil-side surface of the optical element 1a and the object-side surface of the optical element 1b are rotationally asymmetric surfaces symmetric with respect to the X axis and asymmetric with respect to the Y axis as shown in FIG. The Z axis is the optical axis. Then, with the movement of the lens groups 2 and 3 accompanying the magnification change, the optical element 1a and the optical element 1b
In addition, they are relatively moved in opposite directions (X direction).

Thus, the diopter of the finder system is adjusted by changing the combined power (refractive power) of the optical elements 1a and 1b, and the optical performance accompanying zooming is improved.

Further, the parallax of the finder is corrected, the symmetry of the optical performance at the time of changing the magnification of the objective lens is maintained well, and the diopter shift due to a manufacturing error is corrected. In this embodiment, the surface on the pupil side of the optical element 1b is a rotationally asymmetric surface, and the asymmetric aberration generated on the two rotationally asymmetric surfaces on the object side is corrected.

The optical principle of changing the refractive power by moving the optical elements 1a and 1b in opposite directions in this embodiment is disclosed in, for example, Japanese Patent Publication No. 43-10034 and Japanese Patent Application Laid-Open No. 61-177411. ing. The variable magnification finder of the present invention can be similarly applied to a system in which a photographic objective lens of a lens shutter camera or a single-lens reflex camera and a finder objective lens are the same.

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

In this embodiment, the objective lens OL is composed of two lens groups, a lens group 21 having a negative refractive power and a lens group 22 having a positive refractive power. The objective lens OL has a single focal length or a variable power system. In the case of a variable power system, the lens group 22 is moved toward the object side while the lens group 21 has a convex locus on the image plane side, and zooming is performed from the wide-angle end to the telephoto end.

P is an image reversing means similar to that of the first embodiment shown in FIG. 1, and is represented by two optical blocks 23 and 25 in which the optical paths of two prisms are developed. The image-side surface of the prism 23 is formed of a curved surface having a positive refractive power. Reference numeral 24 denotes a primary image forming surface on which an object image is formed by the objective lens OL. Further, a field frame is arranged in the vicinity thereof.

An eyepiece 26 has two optical elements 26a and 26b including a rotationally asymmetric surface. The image-side surface of the optical element 26a and the object-side surface of the optical element 26b are constituted by rotationally asymmetric surfaces as shown in FIG. Then, the optical element 26a is moved in a direction perpendicular to the optical axis to change the refractive power of the eyepiece 26 to adjust the diopter suitable for the observer 27. The asymmetric aberration generated on the surfaces of the optical elements 26a and 26b facing each other is corrected by the rotationally asymmetric surface on the object side of the optical element 26a. The surface on the image plane side of the optical element 26b is a spherical surface or a rotationally asymmetric surface. 27 is the pupil of the observer, and E is the eye point.

FIG. 4 is a sectional view of a main part of a third embodiment of the present invention. 4A shows a vertical cross section, and FIG. 4B shows a horizontal cross section.

In the figure, 1 is an optical member comprising three optical elements 31a, 31b and 31c each including a rotationally asymmetric surface, 2 is a lens group having a negative refractive power, 3 is a lens group having a positive refractive power, and P is The image inverting means is the same as that of the first embodiment shown in FIG. 1 and includes two prisms, and is shown as two glass blocks 5 and 7 in which the optical path is developed in FIG. 6 is 1
This is the next image forming plane, on which an object image is formed by the objective lens OL. Further, a field frame is arranged in the vicinity thereof.
EL is an eyepiece having a positive refractive power, and one lens 8
As shown. E is an eye point.

In this embodiment, the objective lens OL has a single focal length or a variable power system. In the case of a variable power system, the lens unit 2 of the objective lens OL has a locus convex toward the image plane side, and the lens unit 3 is moved to the object side to perform zooming from the wide-angle end to the telephoto end. I have.

In the vertical section of FIG. 4A, the image-side surface of the optical element 31a and the object-side surface of the optical element 31b are constituted by rotationally asymmetric surfaces. In the horizontal cross section of FIG. 4B, the surface on the image plane side of the optical element 31b and the optical element 31
The object-side surface of c is composed of a rotationally asymmetric surface. Of the optical elements 31a, 31b, 31c, the rotationally asymmetric surfaces facing each other are symmetric with respect to the X axis and asymmetric with respect to the Y axis as shown in FIG. The Z axis is the optical axis.

In the vertical section of FIG. 4A, the optical element 31a is moved in a direction perpendicular to the optical axis (X direction in FIG. 5) to change the refractive power (power) in the vertical section. or,
In the horizontal section of FIG. 4B, the optical element 31c is moved in a direction perpendicular to the optical axis (X direction in FIG. 5) to change the refractive power in the horizontal section.

In the present embodiment, the refractive power in two directions is independently changed, and the diopter deviation due to a manufacturing error is satisfactorily adjusted independently in the vertical and horizontal directions. Further, the degree of freedom of the asymmetric surface shape is increased to reduce the absolute amount of aberration, and good optical performance is obtained over the entire finder field.

In this embodiment, three or more optical elements 2 may be provided, and at least two of them may be moved in the same manner as described above.

[0043]

As described above, according to the present invention, when the object image formed on the primary image forming surface by the objective lens is observed as an erect image by using the image inverting means by the eyepiece, the object image is formed in the optical path. By providing a plurality of optical elements having a rotationally asymmetric surface, at least one of the optical elements is moved in a direction perpendicular to the optical axis, thereby changing (correcting) the diopter (finder diopter), thereby obtaining a good finder. A real image type finder optical system capable of observing an image can be achieved.

[Brief description of the drawings]

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

FIG. 2 is a perspective view of a main part of a part of FIG. 1;

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

FIG. 4 is a sectional view of a main part of an optical system according to a third embodiment of the present invention.

FIG. 5 is a perspective view of a main part of a part of FIG.

[Explanation of symbols]

OL Objective lens P Image reversing means EL Eyepiece E Eye point 1, 26, 31 Optical member 1a, 1b, 26a, 26b, 31a, 31b, 31c
Optical element 5, 7, 23, 25 Prism 6 Primary imaging plane

Claims (9)

[Claims] 1. A viewfinder optical system which inverts a finder image formed by an objective lens through an image inverting optical system to form an erect image and then observes the image with an eyepiece, wherein a plurality of optical elements including a rotationally asymmetric surface are provided. A finder optical system comprising: an optical member provided in an optical path; and at least one of the plurality of optical elements is moved in a direction perpendicular to an optical axis to adjust optical characteristics. 2. The optical element according to claim 1, wherein the optical element has one axis of symmetry and is moved in the direction of the axis of symmetry.
Viewfinder optical system. 3. The optical member according to claim 2, wherein the optical member has one axis of symmetry.
2. The finder optical system according to claim 1, comprising two optical elements, wherein said two optical elements are relatively moved in the direction of said symmetry axis. 4. The optical member has two opposing rotationally asymmetric surfaces orthogonal to the optical axis and having an axis of symmetry in the vertical direction, and an axis of symmetry orthogonal to the optical axis and in the horizontal direction. 2. The finder optical system according to claim 1, wherein the finder optical system has two opposing rotationally asymmetric surfaces, and the two opposing rotationally asymmetric surfaces are respectively moved in a symmetric axis direction. 5. The optical system according to claim 1, wherein the finder optical system has a zooming unit, and at least one optical element forming the optical member is moved in accordance with zooming of the zooming unit. The finder optical system according to claim 1, 2, 3, or 4. 6. The optical member according to claim 1, wherein the optical member has at least three rotationally asymmetric surfaces, of which two opposing rotationally asymmetric surfaces are relatively moved. 5 finder optical system. 7. The finder optical system according to claim 1, wherein said optical member forms a part of said objective lens. 8. The finder optical system according to claim 1, wherein the optical member forms a part of the eyepiece, or comprises the eyepiece. 9. The finder optical system according to claim 1, wherein said objective lens, said image reversing means and said eyepiece are made of a plastic material.