JP2001194705A - Real image type finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a real image type finder which can restrain the occurrence of decentration aberration such as astigmatism and coma aberration caused by a minute distance and ghost to the utmost and with which an excellent finder mage with high magnification and at a wide viewing angle can be observed despite of the miniaturized finder. SOLUTION: In this real image type finder where an object image formed by an objective lens is observed as an erect normal image with an eyepiece through a 1st prism and a 2nd prism, the light beam emitting surface of the 1st prism and the light beam incident surface of the 2nd prism are arranged by leaving the wedged minute gap whose one end is made narrower than the other end.

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 for an erect erect image using an image inverting means which appropriately sets a finder image (object image) of an inverted real image formed by an objective lens. The present invention relates to a real image type finder to be observed as an image.

[0002]

2. Description of the Related Art Various finder optical systems of the real image type, in which a real image formed on a primary image forming surface is observed through an eyepiece lens among finder systems such as a photographic camera and a video camera, have been proposed. ing.

The real image type finder optical system is easily used in cameras with a zoom lens recently because the size of the entire optical system can be easily reduced as compared with the virtual image type finder optical system. There is a real image type finder system using a Porro prism for an upright positive image. However, due to the outer shape of the Porro prism, a part thereof projects in the vertical and horizontal directions, and the entire finder system tends to be large.

Since this tendency is contrary to the recent demands for miniaturization and thinning of the entire camera, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 6-167739 that the entire length of the lens of the finder optical system is reduced. For this purpose, the optical path to the primary image forming surface on which the object image is formed by the objective lens is bent by the reflecting surfaces of the first prism and the second prism, and
There has been proposed a small finder optical system in which the next image plane is formed inside the image reversing means.

In order to increase the viewing angle in this viewfinder optical system, the size of the second prism must be increased, which tends to increase the thickness of the camera in the thickness direction.

In the finder optical system, the focal length fe of the eyepiece corresponds to the length from the image forming position to the eyepiece. If the finder magnification is γ and the focal length of the objective lens is fo, then γ = fo / fe. Therefore, when the second prism is enlarged to increase the viewing angle, the optical path from the image forming position to the eyepiece becomes longer, that is, the focal length fe of the eyepiece becomes longer, and the finder magnification γ decreases. Observing a good viewfinder image becomes difficult.

Therefore, Japanese Patent Application Laid-Open No. Hei 8-179400 discloses
Japanese Patent Application Laid-Open No. H10-206933 discloses a real image having a structure in which image reversing means capable of increasing a viewing angle and a finder magnification while having a small size is provided, and first and second prisms are arranged with a small air gap. An expression finder is disclosed.

FIGS. 8 and 9 show Japanese Patent Application Laid-Open No. 10-20693.
3 shows a basic configuration of a real image finder using a prism and a roof prism that bends an optical path to a primary image forming surface and has a configuration substantially the same as that disclosed in Japanese Patent Application Laid-Open No. 3 (1993) -316. In the figure, OL denotes an objective lens, P denotes an erecting erect image prism, and a first prism P11 and a second prism (parallel to the exit surface 111) with a small air gap d. Dach prism) P12. S is a field frame that limits the viewfinder field,
Near the exit surface 123 of the second prism P12 (primary imaging surface)
It is provided in. The finder image of the inverted real image by the objective lens OL is the roof reflection surface 1 of the second prism P12.
The image is inverted via the image 22 to form an erect image near the field frame S. EL denotes an eyepiece, which converts a finder image of an erect erect image formed near the field frame S into a second prism P.
Observed via 12.

In the above configuration, as shown in FIG. 8, a light beam passing through the objective lens OL is transmitted to the exit surface 111 of the first prism P11 and the entrance surface 121 of the second prism P12.
And the image is inverted on the roof reflecting surface 122, is once reflected toward the object side, is totally reflected by the incident surface 121 of the second prism 12, and is reflected on the primary image forming surface near the exit surface 123 of the second prism. Form a finder image. The reflection member M1 is 1
The light beam from the next imaging surface is reflected and guided to the eyepiece EL.

[0010]

However, in the conventional real image finder, the first prism P1
1 and the entrance surface 1 of the second prism P12
Reference numeral 21 designates an arrangement that is decentered with respect to the optical axis of the objective lens OL or the eyepiece EL, so that light rays reflected on the roof reflection surface 122 of the second prism P12 are totally reflected on the incident surface 121 of the second prism. In other words, since the incident surface 121 of the second prism P12 is used for both transmission and reflection, as shown in FIG. 9, the transmission surface 111 of the first prism P11 and the incident surface 121 of the second prism P12 are substantially They are arranged in parallel with a small air gap d.

For this reason, as shown in FIG. 1, the refraction angle of the light beam indicated by the solid line differs depending on the position where the light beam passes to the exit surface 111 of the first prism P11 and the incident angle.
Accordingly, the optical path length within the minute air interval d is as a1 or a2 (a1 <a2). For this reason, astigmatism, coma aberration, and the like fluctuate between the left and right fields of view, making it difficult to observe a good finder image when the eyes are shaken.

Further, as shown by a light ray indicated by a broken line, surface reflection occurs on the exit surface 111 of the first prism P11 and the entrance surface 121 of the second prism P12. As shown by the path of this light beam, the light beam reflected on the entrance surface 121 of the second prism P12 is reflected on the exit surface 111 of the first prism P11,
When the light is incident on the incident surface 121 of the second prism P12, it becomes a ghost of a light ray shown by a normal solid line, and a double image is formed. Therefore, there is a problem that the optical performance of the finder is reduced.

Further, this ghost is caused by the first prism P1.
T1 and t1 depending on the angle of incidence of the light beam on the exit surface 111
2 (t1 <t2), the width of the double image is different.
For example, since the air gap d is very small, even if the ghost image having the double image width t1 is within the allowable range, the ghost image having the double image width t2 is conspicuous. There was a problem.

The present invention solves the above-mentioned conventional problems, and can minimize ghosts and various aberrations generated at a minute air gap between the first prism and the second prism. It is an object of the present invention to provide a small real image type viewfinder which can observe a good viewfinder image while being excellent.

[0015]

In order to achieve the above object, an object of the present invention is to provide an object image formed by an objective lens as an erect image through a first prism and a second prism. In a real image type viewfinder to be observed with a lens, a light exit surface of the first prism and a light incident surface of the second prism have a wedge-shaped minute shape in which one end is narrower than the other end. It is characterized by being arranged at air intervals.

According to a second aspect of the present invention, in the first aspect, one of the first prism and the second prism has a function as an image inverting means.

According to a third aspect of the present invention, in the first aspect of the present invention, an image inverting means is arranged in an optical path between the objective lens and the eyepiece, separately from the first prism and the second prism. It is characterized by.

According to a fourth aspect of the present invention, in the first aspect, the wedge-shaped minute air gap is formed.
The two surfaces are characterized by being in contact with each other outside of the light beam.

According to a fifth aspect of the present invention, in the first or the fourth aspect of the present invention, the wedge-shaped minute air spacing is such that a direction of a reference axis ray is a Z axis, and a plane perpendicular to the Z axis is the object side. Assuming that the upward direction is the Y axis as viewed from above, the interval on the side of the larger incident angle out of the incident angles of the reference axis ray to the air interval in the YZ plane is set to be narrow. It is characterized by.

The invention according to claim 6 is the invention according to claim 1, 4, or 5.
In the invention, the wedge-shaped minute air spacing is:
It is wedge-shaped in the YZ plane.

According to a seventh aspect of the present invention, in the first, fourth, fifth, or sixth aspect, the wedge-shaped surface is provided on the light exit surface of the first prism or the light incident surface of the second prism. A projection or a spacer member for setting a minute air gap is provided outside the effective light beam.

The invention according to claim 8 is the invention according to claims 1, 4, 5, and 6.
Alternatively, in the invention according to the seventh aspect, assuming that the minute air gap between the surface vertices of the first prism and the second prism is Dg, the air gap Dg is 0 <Dg ≦ 0.1 (where,
The unit satisfies the range of mm). According to a ninth aspect of the present invention, in the first, fourth, fifth, sixth, seventh, or eighth aspect, the wedge-shaped minute air gap is formed between the first prism and the second prism. Assuming that the angle formed by the surface is θg, the angle θg is 0 ′ <θg
≦ 50 ′ [where 1 ′ is (1/60) °].

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

Before describing the embodiment, a description will be given of how to express the configuration data and common matters of the entire embodiment.
Since the optical system of the present invention is a decentered optical system, each surface constituting the optical system does not have a common optical axis.

Therefore, in the embodiment of the present invention, as shown in FIG. 3, the center of the effective beam diameter of the first surface R1 is set as the origin, and the path of the light beam passing through the origin and the center of the pupil is defined as a reference of the optical system. An axis (a reference axis ray L is defined as a reference axis ray L). Each axis of the coordinate system is defined as follows.

Z-axis: Reference axis direction toward the origin and second surface R2.

Y-axis: A direction that forms 90 ° counterclockwise with respect to the Z-axis in the tilt plane (in the plane of the paper) about the origin.

X axis: a direction passing through the origin and perpendicular to each of the Z and Y axes (a straight line perpendicular to the paper).

The reference axis and the i-th surface (i = 1, 2, 3,...)
・ The point where () intersects is the surface vertex. For example, in the drawing, the surface vertex of the first prism P1 is a point X 1 at which the exit surface 11 intersects with the reference axis. In the optical system according to the present invention, the optical system is arranged with a minute air gap arranged in the optical path.
The two prisms are the first prism, the second
It is called a prism.

FIG. 1 shows a real image type finder according to an embodiment of the present invention. In the figure, OL is an objective lens,
P is a prism for an erect image and a first prism P1
And a second prism (dach prism) P2 arranged with a small air gap with respect to the exit surface 11 thereof. S is a field frame for limiting the viewfinder field, and this field frame is desirably provided near the exit surface 23 (primary imaging surface) of the second prism P2, and may be a mechanical component or a light source such as a liquid crystal. What used the transmission restriction pattern formation means may be used. The shape of the second prism P2 is such that the light reflected by the roof reflecting surface 22 is incident on the incident surface 21 of the second prism 2.
Is incident at an angle that allows total reflection. EL denotes an eyepiece for observing a finder image of an erect erect image formed near the field frame S. M1
Is a reflecting member, which converts the light beam from the primary imaging surface into an eyepiece lens EL.
Guide light in the direction.

In this configuration, the light beam that has passed through the objective lens OL passes through the exit surface 11 of the first prism P1 and the second beam.
The light is transmitted through the incident surface 21 of the prism P2, is reflected by the roof reflecting surface 22, inverts the image, and is once reflected to the object side. The reflected light is totally reflected by the incident surface 21 of the second prism P2, and forms a finder image on the primary image forming surface near the exit surface 22 of the second prism P2. The finder image of the inverted real image by the objective lens OL is formed near the field frame S as a finder image of an upright positive image via the second prism P2. The light beam from the primary imaging surface is reflected by the reflecting member M1, and is guided to the eyepiece EL.

As shown in FIG. 2, the exit surface 11 of the first prism P1 and the entrance surface 21 of the second prism P2 are arranged so as to form a wedge-shaped small air gap. By arranging in this manner, the width t2 (see FIG. 9) of the double image is set to t as shown by the optical path indicated by the broken line in FIG.
2 ′ (t2≫t2 ′).

Also, as shown by the solid line in the figure, the optical path length a2 (see FIG. 9) within a minute air gap is a2 '.
Since (a2≫a2 ′) becomes smaller, the fluctuation of aberration on the finder pupil plane due to the fact that the optical path length from the light beam exiting the first prism P1 to the pupil plane differs between left and right is suppressed. And the finder visual field can be favorably observed. In particular, when the minute air gap is formed in a wedge shape, it is preferable to form the wedge shape in the eccentric YZ plane.

Further, it is preferable that the wedge-shaped minute air gap is set so that the gap on the side of the larger incident angle out of the incident angles of the light rays is narrowed, so that the decentering aberration is most effective. Can be corrected. In FIG. 2, the incident angle α on the exit surface 11 of the first prism P1,
Since the incident angle β on the negative side in the Y-axis direction of β is large, the first prism P1 is arranged such that the air gap on the vertex angle side of the first prism P1 is widened.

In the real image finder shown in FIG. 4, the image is inverted by the first prism P41. The luminous flux from the objective lens OL is incident on the first prism P41, is totally reflected by the exit surface 411 and bends the optical path downward, and the luminous flux reflected almost upward by the roof reflection surface 412 is the exit surface of the first prism P41. 411, the second prism P42 is arranged such that the apex side of the second prism P42 is narrowed, passes through the entrance surface 421 of the prism P42, which has a minute wedge-shaped air gap, and forms a primary connection near the exit surface 422. A finder image is formed on the image plane.

In this finder system, the incident angle α on the minus side in the Z-axis direction becomes larger among the incident angles α and β of the reference axis ray L with respect to the minute air gap, so that the above arrangement is made. Has taken.

In the real image type viewfinder shown in FIG. 5, the same incident angle relationship as in FIG.
Exit surface 511. In the figure, the objective lens OL
Is incident on the first prism P51, is totally reflected on the exit surface 511 thereof, bends the optical path downward, and the light beam that has been mirror-reflected substantially upward by the reflective surface 512 on which vapor deposition or the like has been applied is the first prism P51. The light exits from the exit surface 511 of P51, and a minute wedge-shaped air gap passes through the entrance surface 521 of the second prism P52 arranged so that the apex side is narrowed, and forms a primary connection near the exit surface 522. A finder image is formed on the image plane. The luminous flux of the finder image is reflected by the roof reflecting surface 531 of the penta roof prism 53 serving as an image inverting unit, and is guided to the eyepiece EL.

Here, in order to make the minute air gap wedge-shaped, as shown in FIG. 1, when the incident surface 12 of the first prism P1 is arranged perpendicular to the reference axis ray L, The angle between the surface 11 and the reference axis ray L is θ21,
Assuming that the angle between the incident surface 21 of the prism P2 and the reference axis ray L is θ22, the angles of the first prism P1 and the second prism P2 may be set so that θ21 ≠ θ22. The entire first prism P1 may be slightly decentered as long as the amount of eccentricity of the incident surface 21 of one prism P1 with respect to the optical axis allows eccentric aberration.

Next, another embodiment of the present invention will be described with reference to FIGS.

In the embodiments of FIGS. 1, 4 and 5,
The two first prisms and the second prism, which are arranged with a minute wedge-shaped air gap, are arranged on the object side with respect to the primary imaging plane,
In other words, in this embodiment, the eyepiece lens E is placed from the primary image forming surface in order to obtain a desired finder magnification and viewing angle, as shown in FIGS.
In order to set the optical path length up to L shorter, the first and second prisms arranged with a small wedge-shaped air gap are arranged closer to the pupil side, that is, to the eyepiece EL side than the primary imaging plane. ing.

In the embodiment shown in FIG. 6, the objective lens OL, the pentaprism 63, and the first prism P6 are sequentially arranged on the optical path.
1, a second prism P62 and an eyepiece EL are arranged.

In the optical system having this configuration, the objective lens O
The optical path of the light from L is bent by the pentaprism 63, and a finder image of an inverted real image is formed near the exit surface 631, and the light flux from the primary imaging surface incident on the first prism P 61 is totally transmitted through the transmission surface 611. The light is reflected and directed to the roof reflection surface 612, where the light is reflected and image inversion is performed.
From the transmission surface 611 of the first prism P61, the light is emitted into a small wedge-shaped air gap and transmitted through the second prism P62,
The light is guided to the eyepiece EL.

As described above, in the embodiment shown in FIGS. 1 and 6, the image inverting function is provided to the second prism P22 or the first prism P61 among the two wedge-shaped prisms arranged at an air gap. It is a configuration that it has.

In the embodiment shown in FIG. 7, an objective lens OL, a penta roof prism 53, a first prism P71, a second prism P72, and an eyepiece EL are arranged in this order on the optical path.

In the optical system having this configuration, the objective lens O
The light beam from L is inverted by the roof reflecting surface 531 of the penta roof prism 53 to form a finder image of an erect image near the exit surface 532. The luminous flux incident on the first prism P71 from the primary imaging surface is transmitted through the transmission surface 7
11, the light is returned to the object side once, and is reflected specularly on the reflecting surface 712 on which evaporation or the like has been performed. The light beam is bent toward the pupil side and heads for a minute wedge-shaped air gap. The light passes through P72 and is guided to the eyepiece EL.

As in the embodiments of FIGS. 7 and 5,
An image reversing means such as a penta roof prism 53 may be provided separately from the two prisms arranged with a minute wedge-shaped air gap.

In the embodiment of the present invention described above,
The exit surface of the first prism and one end of the entrance surface of the second prism do not necessarily have to be in contact with each other, and the effect of the present invention can be obtained as long as one of the intervals is narrower than the other as in a wedge shape. Can be expected.

However, as a practical problem, in order to form a small wedge-shaped air gap, it is easier to construct the case where the exit surface of the first prism and one end of the entrance surface of the second prism are in contact. In this case, the distance between the exit surface of the first prism and the entrance surface of the second prism becomes 0 outside the effective beam area,
That is, they need to be in contact.

In order to set the interval outside the effective light beam, a convex portion may be provided on the exit surface of the first prism or the entrance surface of the second prism to improve the positional accuracy. Further, when the first prism and the second prism are glass members, positioning may be performed with a spacer member or the like interposed therebetween. In this case, flare or the like can be effectively removed by configuring the spacer member so as to block light other than the effective light flux.

In the embodiment of the present invention, as shown in FIG. 2, the surface vertex X ₈ (see FIG. 3) of the exit surface of the first prism, which forms a minute air gap, and the surface of the entrance surface of the second prism. Assuming that the distance from the vertex X ₉ (see FIG. 3) is Dg, the distance Dg satisfies the range of the following expression.

0 <Dg ≦ 0.1 (unit: mm) When the interval Dg is larger than 0.1, image doubling (ghost) due to reflection of light rays in a minute air interval, and It becomes difficult to suppress the fluctuation of aberration on the finder pupil surface due to the difference in the optical path length from the ray exiting the first prism to the pupil surface on the left and right.

Further, in order to suppress ghost and aberration fluctuation and obtain a good visual field, the interval Dg is preferably 0.04 or less. When the first prism and the second prism are glass members, dew condensation becomes a problem if the minute air gap is too narrow, so that the gap Dg is 0.02 <Dg ≦ 0.04 (unit: mm) ).

In the embodiment of the present invention, as shown in FIG. 2, assuming that the angle between the exit surface of the first prism and the entrance surface of the second prism forming a minute air gap is θg, the angle θg is given by the following equation. Meets the range.

0 '<θg <50' [unit: minute]
1 ′ = (1/60) °] When the angle θg is larger than 50 ′, the air gap of the wider wedge becomes too large, and it becomes difficult to correct the eccentric aberration. When the distance Dg between the exit surface of the first prism and the apex of the entrance surface of the second prism is within the above range,
It is preferable that the angle θg satisfies the above range.

[0055]

As described above, according to the present invention,
The light exit surface of the first prism and the light entrance surface of the second prism are arranged at a small wedge-shaped air gap, one end of which is narrower than the other end. In addition, eccentric aberrations such as astigmatism and coma due to minute air gaps and ghost can be suppressed as much as possible, and a good finder image can be observed.

In addition, one of the two prisms has the function of the image reversing means, or the image reversing means is disposed separately from the two prisms, so that the function from the primary image formation position to the eyepiece can be achieved. The optical path can be shortened, and not only can the device be miniaturized, but also a good finder image can be observed with a high magnification and a wide angle of view.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a real image type finder showing an embodiment of the present invention.

FIG. 2 is a sectional view showing an arrangement of two prisms of the real image type viewfinder of FIG. 1;

FIG. 3 is a sectional view of a main part showing a coordinate system in the real image type viewfinder of FIG. 1;

FIG. 4 is a sectional view of a main part showing an example in which the arrangement of two prisms in the embodiment of FIG. 1 is interchanged;

FIG. 5 is a sectional view of a main part showing an example in which the image reversing means is arranged separately from the prism in the embodiment of FIG. 4;

FIG. 6 is a cross-sectional view of a main part of a real image type finder showing another embodiment of the present invention.

FIG. 7 is a sectional view of a main part showing an example in which the image inverting means is arranged separately from the prism in the embodiment of FIG. 5;

FIG. 8 is a sectional view of a main part showing a conventional real image type viewfinder.

FIG. 9 is a cross-sectional view showing a difference between a ghost and an optical path length at a minute air gap in the conventional real image type viewfinder.

[Explanation of symbols]

 OL Objective lens EL Eyepiece S Field frame P1 First prism P2 Second prism M1 Reflecting member 53 Penta roof prism 63 Penta prism

Claims (9)

[Claims] 1. A real image finder for observing an object image formed by an objective lens as an erect erect image via an eyepiece via a first prism and a second prism, wherein a light exit surface of the first prism; A real image type finder, wherein a light incident surface of the second prism is arranged at a small wedge-shaped air gap, one end of which is narrower than the other end. 2. The real image type viewfinder according to claim 1, wherein one of the first prism and the second prism has a function as an image inverting unit. 3. The real image finder according to claim 1, wherein an image inverting means is arranged in an optical path between the objective lens and the eyepiece, separately from the first prism and the second prism. . 4. The real image type viewfinder according to claim 1, wherein the two surfaces forming the minute wedge-shaped air gap are in contact with each other outside the effective area of the light beam. 5. The wedge-shaped minute air gap is defined by a Z-axis in a direction of a reference axis ray and a Y-axis in a plane orthogonal to the Z-axis when viewed from the object side as a Y-axis. 5. The real image type finder according to claim 1, wherein the interval on the side of the larger incident angle out of the incident angles of the reference axis ray to the air interval is set to be narrow. . 6. The real image type finder according to claim 1, wherein said minute wedge-shaped air gap has a wedge shape in said YZ plane. 7. A wedge-shaped convex portion or a spacer member for setting a minute air gap is provided on a light exit surface of the first prism or a light incident surface of the second prism. 7. The real image finder according to claim 1, wherein the finder is provided outside. 8. When the minute air gap between the surface vertices of the first prism and the second prism is Dg,
The air gap Dg satisfies the range of 0 <Dg ≦ 0.1 (where the unit is mm).
6. The real image finder according to 6 or 7. 9. An angle θg defined by two surfaces of the first prism and the second prism forming the minute wedge-shaped air gap is defined as θg: 0 ′ <θg ≦ 50 ′ [However, 1 'is (1/6
0) °].
6. The real image type viewfinder according to 6, 7, or 8.