JPH03217830A - Finder optical system - Google Patents

Abstract

PURPOSE:To make one direction of this optical system compact, to obtain high magnification and to make the entire length of a finder long by bending a luminous flux from a roof reflection part by a 1st plane reflection part so that it may pass through a condenser lens and bending it by a 2nd plane reflection part. CONSTITUTION:The luminous flux from an object is inverted in up-vertical and horizontal directions by an objective lens 31 and inverted in the vertical direction or the horizontal direction by a roof mirror 32. After the luminous flux bent to an object side by the mirror 32 is reflected to a pupil side by a 1st plane mirror 33 and formed into an image once in the vicinity of the condenser lens 34, it is bent to the pupil side further by a 2nd plane mirror 35 and returns to an erected image, then it passes through an ocular lens 36 to reach a pupil surface 37. Since the necessary optical path lengths of the mirrors 32, 33 and 35 are made short in such a manner, any one direction of the optical system of the vertical and the horizontal directions is made compact, a distance between the image surface of the lens 31 and the principal point position of the lens 36 is also made short and finder magnification is made high, then the position of the lens 36 and an eye point is extended backward.

Description

[Detailed description of the invention] skin presentation The present invention relates to a finder optical system.

Virtual image finders and real image finders are known as finders comprising an optical system different from the photographic optical system. Virtual image finders have a convection structure, so they are more widely used than conventional viewfinders.

However, in recent years, there has been a demand for finders that can be applied to various types of cameras and provide high-quality finder images, and for this reason, real-image finders have also come into widespread use.

Since a real image finder does not include a half mirror between the optical paths, it has the advantage that it provides a clearer and brighter field of view and the field frame is clearly visible compared to virtual image finders such as the Albada type and daylight type. Further, the real image finder can be configured to have a longer overall length so that it can be adapted to a camera format such as an SVC (still video camera), which has a longer overall length than a conventional lens shutter camera.

On the other hand, in a real-image finder, the image is inverted, so an inversion optical system is required to return it to an erect image. These inverting optical systems can be roughly divided into those that re-image using a relay system and those that use reflection. Those that re-image using a relay system lack compactness because the optical path length of the relay system becomes longer than necessary. Well-known methods that use reflection include those using Boro mirrors and Porro prisms (
(U.S. Patent No. 4,545,655, Utility Model Publication No. 4326, 1983, etc.). As shown in FIG. 13, when a boro mirror is used, the light beams (double-dashed lines) are routed vertically and horizontally, so a large space is required vertically and horizontally.

Note that the boro mirror shown in FIG. 13 is the first mirror (
1), a second mirror (2), a third mirror (3), and a fourth mirror (4). The light beam that passed through the objective lens (5) is reflected from the first mirror (1) to the second mirror (2), and the light beam reflected by the second mirror (2) passes through the condenser lens (6) and then the light beam is reflected from the first mirror (1) to the second mirror (2). 3rd mirror to 4th
After being reflected by the mirror (4) and passing through the eyepiece (7), it reaches the pupil plane (8).

In addition, when a roof reflection section is used as an inversion optical system,
It can be made more compact in either the vertical or horizontal direction. For example, as shown in FIG. 14(1), two plane mirrors (10a) (10b) are used, and
As shown in Figure 4 (ii), the function regarding image reversal is the same as when using the Dahmirror (11), but
When using a roof mirror (1l) (Fig. 14 (ii))
This requires about half the space compared to the case where the plane mirrors (10a) and (10b) are used (FIG. 14(i)). That is, the roof mirror (l1) in Figure 14 (ii)
In this case, the incident image (l5) is inverted at once using two plane mirrors that form an angle of 90° with the ridge line in between to form a reflected image (16).
a) In (10b), each mirror creates an incident image (1
By reflecting the reflected image (2) and the reflected image (13), the reflected image (
14). Therefore, the size of the roof mirror (1l) is sufficient to be about the size of the incident image (l5), but
With two plane mirrors (10a) (10b), a space about the size of the image is required for each mirror,
The space occupied is approximately twice that of the Dahamira (l1).

The finder described in Utility Model Application No. 1983-54774 is a roof mirror (21) as shown in Figure 15.
This type uses a mirror and two plane mirrors (23) and (24). As described above, this finder uses the roof mirror (21) as the roof reflection section, so it has a compact structure in either the vertical or horizontal direction. That is, when the ridgeline of the roof mirror (2l) is placed in the horizontal direction as shown in FIG. 15, the vertical space is approximately half that of the case where a Boro prism or a Boro mirror is used.

As mentioned above, for cameras such as SVC and bridge cameras that have a long overall length, a finder with a long overall length with an eyepiece position and an eye point extended backwards is required, depending on the arrangement of peripheral devices. However, in the finder of the type shown in FIG.
Since the light beam is bent by 270 degrees toward the rostral body side by the two plane reflecting parts (plane mirrors (23) and (24)), the eyepiece position and eyepoint (26) can be extended backwards without reducing the viewfinder magnification. Can not. next,
This point will be explained in more detail.

The finder magnification mentioned above is an important specification of the finder, and is approximately expressed by the following 2〇.

β−f1/fz −−−−・−−−−1−−−−
(2) However, β: finder magnification f, focal length of two objective lenses; 2: focal length of eyepiece.

As can be seen from 2), a high magnification finder is achieved by increasing the focal length (1) of the objective lens or shortening the focal length (f2) of the eyepiece. However, if the focal length (f1) of the objective lens is increased, the total length of the objective lens becomes longer than necessary, and a compact finder cannot be obtained. Therefore, a compact high-magnification finder requires an eyepiece with a short focal length.

Also, the focal length (f2) of the eyepiece lens is the diopter (usually -
1) is uniquely determined by the distance between the image plane of the objective lens and the position of the principal point of the eyepiece, and is approximately expressed by the following 2).

However, the distance A between the image plane of the S2 objective lens and the principal point position of the eyepiece is the diopter.

Therefore, according to formula (■), if the distance (S) between the image plane of the objective lens and the principal point position of the eyepiece increases, the focal length (f2) of the eyepiece also increases, and as a result, according to formula (■), the finder magnification (β ) decreases. In other words, in the finder shown in Fig. 15, it is not possible to increase the distance (S) between the image plane of the objective lens and the principal point position of the eyepiece while maintaining the finder magnification (β) high. The eyepiece position and eye point cannot be extended backwards.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a finder optical system that is compact and has high magnification in either the vertical or horizontal directions, and has a long overall length with the eyepiece position and eye point extending backward.

Means for Solving the Problems In order to achieve the above objects, the finder optical system of the present invention includes an objective lens having positive power as a whole, a condenser lens provided near the image plane of the objective lens, and a viewfinder optical system as a whole. In a finder optical system equipped with an eyepiece lens 7 that has a positive power and magnifies the image of the objective lens, the light beam from the objective lens is sent between the objective lens and the condenser lens in order from the object side. A roof reflection section that bends the light beam toward the pupil side, and a first plane reflection section that bends the light beam from the roof reflection section toward the pupil are provided between the condenser lens and the eyepiece, and a first plane reflection section that bends the light beam from the condenser lens toward the pupil side is provided between the condenser lens and the eyepiece lens. It has a configuration in which two planar reflection sections are provided.

The roof reflection section may be a surface reflection section of a roof mirror integrally molded with resin, or the roof reflection section and the first plane reflection section may be a back reflection section of a roof prism integrally molded. Furthermore, the surface of the roof prism on the second plane reflection section side may be integrally formed with the condenser lens.

The second planar reflecting section may be a back reflecting section of an integrally molded prism.Furthermore, the surface of this prism on the first planar reflecting section side may be integrally formed with the condenser lens. Further, the first plane reflection section and the second plane reflection section may be constituted by a plane mirror.

Effect According to the above configuration, the light beam is bent toward the object side by the roof reflection section, and the light beam is bent by the first plane reflection section and the second plane reflection section between the condenser lens and the eyepiece provided near the image plane of the objective lens. Since the beam is bent toward the pupil, the required optical path length of the roof reflection section and each plane reflection section is shortened. Therefore,
As it becomes more compact in either the vertical or horizontal direction, the distance between the image plane of the objective lens and the position of the principal point of the eyepiece becomes shorter, and the viewfinder magnification increases, but the position of the eyepiece and the eye point extend backwards. .

Back JLJL Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 1 is a perspective view showing a schematic configuration of an embodiment of the present invention. In the figure, orthogonal arrows (30) indicate image reversal in the optical path. Objective lens with positive power (3
The luminous flux from the subject that has been reversed in the vertical and horizontal directions in step 1) is reversed in the vertical or horizontal directions by a roof mirror (3'2) integrally molded with resin. Dahamira (32)
) If the ridgeline of the roof is placed in the horizontal direction, the vertical direction is reversed, and if the ridgeline of the roof is placed in the vertical direction, the horizontal direction is reversed. Note that FIG. 1 shows a case where the ridgeline of the roof is placed in the horizontal direction.

The light beam bent toward the object side by the roof mirror (32) is bent toward the pupil side by the first plane mirror (33). The light beam reflected by the first plane mirror (33) forms an image near the condenser lens (34), and then is further bent toward the pupil by the second plane mirror (35). The image is laterally inverted and returned to an erect image by the plane mirrors (33) and (34), and then passes through the eyepiece (36) and reaches the pupil plane (37). The eyepiece (36) has positive power and the objective lens (31)
magnify the image formed by Further, the condenser lens (34) is always placed near the image plane of the objective lens (31) in order to prevent the light beam reaching the pupil plane (37) from being eclipsed.

In this embodiment, a roof mirror (32) used as a roof reflection section bends the light beam toward the object side.
The first plane mirror (
33) and a second plane mirror (35) used as a second plane reflection section, the light beam is bent toward the pupil. That is, 90 degrees with respect to the direction of incidence on the roof mirror (32)
'The first plane mirror (33
) and the second plane mirror (35) to approximately 45 degrees, the required optical path length of the inversion optical system consisting of the roof mirror (32) and each plane mirror (33) (35) is shortened. . This point will be explained in more detail below.

FIGS. IO (a) to (c) show the optical path (solid line) when a luminous flux of a certain width is reflected by the plane reflection section (40). In the figure, the range of the light flux indicated by the dotted line indicates the range in which the parallel light flux incident on the plane reflection part (40) can be extracted as the corresponding parallel light flux after reflection, and indicates the optical axis within that range. The length (thick line) indicates the required optical path length. As shown in the figure, the angle of incidence (θ) on the plane reflection section (40)
Even if it is too large (Fig. 10 (C)) or too small (
Figure 10 (a)) The required optical path length becomes longer and the angle of incidence (θ)
When is 45 degrees (FIG. 10(b)), the required optical path length is the shortest. Further, the smaller the incident angle (θ) is, the smaller the plane reflecting portion (4o) can be used.

Figures 11(a) to (c) are similar to Figures 10(a) to (c).
) roof reflective part (41) instead of the flat reflective part (40)
The optical path when the incident angle (α) is changed is shown in the same manner as in Figures 10 (a) to (c) except that . When the roof reflection section (41) is used, as shown in the figure, the smaller the incident angle (α) to the roof reflection section (41), the shorter the required optical path length. Furthermore, the smaller the incident angle (α) is, the smaller the roof reflecting portion (4) can be used.

Therefore, when the roof reflection section (41) and the plane reflection section (40) are used in combination in the inversion optical system, the incident angle (α) of the light beam to the roof reflection section (4l) is small, and the plane reflection section ( 40), the required optical path length of the inversion optical system is the shortest. If the required optical path length of the inversion optical system is short, S in the above formula (■)
(The distance between the principal point of the eyepiece and the image plane of the objective lens) can be made small, so a finder with high magnification can be realized as described above.

On the other hand, considering the usability of the finder configuration when used at eye level, the finder image needs to be a virtual image projected toward the object side. In order to extend the viewfinder eyepiece position and eye point backward, the first plane mirror (33
) and the bending of the light beam at the second plane mirror (35),
In both cases, the eyepiece (36) is bent toward the pupil side.
is placed behind the viewfinder.

FIG. 2(a) shows the schematic structure of the embodiment shown in FIG. 1, and FIG. 2(b) shows the schematic structure of the conventional example shown in FIG. The above S in Fig. 2(a) and Fig. 2(b)
), the position of the eyepiece (36) and the position of the dark surface (37), that is, the eye point, are It extends far back.

On the other hand, in FIG. 2(b), the light beam is bent toward the object side, so the eye point cannot be moved backward. In addition, Fig. 2(b) and Fig. 15
In the conventional example shown in the figure, a condenser lens (22) and an eyepiece lens (22) are provided near the image plane of an objective lens (20).
5), there are two plane mirrors (23) and (24) between them, requiring a long optical path length.

Figures 12(a) and 12(b) show when the bending angle (A) of the luminous flux by the roof reflector (4l) is large (Fig. 12(a)) and when it is small when reversing light rays with the same luminous flux width. (FIG. 12(b)) shows the optical path (dotted line). still,
The smaller the angle of incidence (α) of the light beam on the reflection part (41), the larger the bending angle (^) becomes. Figure 12 (a
) As can be seen from (b), in order to shorten the required optical path length of the planar reflection part (40), the roof reflection part (41) must be It is preferable to determine the arrangement of the portion (41).

When the angle of incidence (α) on the roof reflection part (41) is large, the angle of incidence (θ) on the flat reflection part (40) also becomes large.
The required optical path length becomes longer. Furthermore, the roof reflection section (4l) itself becomes larger, and the required optical path length of the roof reflection section (41) also becomes longer. In particular, the angle of incidence (α) on the roof reflection part (41) is 4
This tendency becomes noticeable when the angle exceeds 5° (that is, when the light beam bending angle at the roof reflecting portion (41) is 90° or less). Therefore, the 12th light beam has a larger bending angle (A).
In the inverted optical system shown in FIG. 12(a), the focal length of the eyepiece can be made shorter than in the inverted optical system shown in FIG. 12(b), so a finder with higher magnification can be obtained.

FIG. 3 is a lens configuration diagram showing another embodiment of the present invention. In this example, the first back reflection part (50a) of the roof prism (52) integrally molded is used as the roof reflection part, and the second back reflection part (50b) of the roof prism (52) is used as the first plane reflection part. Other than that, the structure is the same as that of the embodiment shown in FIGS. 1 and 2(a). That is,
The light flux from the object that has been vertically and horizontally reversed by the objective lens (5l) having a positive power as a whole is reversed vertically or horizontally by the first back reflection section (50a) of the roof prism (52). The light beam bent toward the object side by the first back reflection part (50a) of the roof prism (52) is transmitted to the second back reflection part (50a) of the roof prism (52).
50b) is bent toward the pupil. The light beam bent by the second back reflection section (50b) is imaged near the condenser lens (53), and then further bent toward the pupil by the plane mirror (55), which is the second plane reflection section.

The image is reversed horizontally or vertically by the second back reflection section (50b) and the plane mirror (55) and returned to an erect image, and then passes through the eyepiece (56) to the llt surface (57).
leading to.

In addition, the first and second back reflection parts (50a) (50b
) can be achieved by total internal reflection or by aluminum or silver vapor deposition. Roof prism (52)
) is constructed using materials such as glass and transparent resin.

Moreover, when glass is used, it is possible to make the roof part highly accurate.

When using the roof prism (52), the roof prism (52)
The air-equivalent required optical path length (D) in 2) is expressed by the following formula (■).

D=d/n
---■ However, d: Optical path length n in the roof prism (52)
; is the refractive index of the material forming the roof prism (52). Therefore, the required air-equivalent optical path length (D) in the roof prism (52) is shortened, and there is no need to increase the lens back of the objective lens (51), which increases the degree of freedom in designing the objective system.

Also, as shown in Fig. 9, the first roof prism (70)
Back reflection by the back reflection section (71) and the second back reflection section (72) can be achieved by utilizing the total reflection phenomenon as described above. Furthermore, a second back reflection section (72
) of each back surface reflection (
71) Further space saving can be achieved by adjusting the angle of (72) with respect to the light beam.

FIG. 4 shows a roof prism (5
2) shows an embodiment in which the surface on the plane mirror (55) side is integrated with a condenser lens (54), and FIG. 5 is a perspective view of a roof prism (58) used therein. That is, in this embodiment, a roof prism (58) whose surface on the plane mirror (55) side is a spherical surface (59) is used. By using the roof prism (58) including a condenser lens in this way, it is possible to reduce the number of parts, and it is possible to obtain a finder optical system with high positional accuracy in a small space.

FIG. 6 is a lens configuration diagram showing still another embodiment of the present invention. In this embodiment, a back reflection section (66) of an integrally molded prism (65) is used as the second plane reflection section. Other than that, the structure is the same as that of the embodiment shown in FIGS. 1 and 2(a). That is, the luminous flux from the object that has been vertically and horizontally reversed by the objective lens (61) having positive power as a whole is reversed vertically or horizontally by the roof mirror (62). The light beam bent toward the object side by the roof mirror (62) is bent toward the pupil side by a plane mirror (63), which is a first plane reflection section. The light beam reflected by the plane mirror (63) forms an image near the condenser lens (64), and is then bent toward the pupil by the back reflection section (66) of the prism (65). The back reflection part of the plane mirror (63) and prism (65) (
66), the image is reversed horizontally or vertically and returned to an erect image, and then passes through the eyepiece lens (67) to the pupil plane (66).
8).

Note that the back reflection by the back reflection section (66) can be achieved by total reflection or vapor deposition of aluminum, silver, or the like. The prism (65) is constructed using a material such as glass or transparent resin.

By using the prism (65), the air-equivalent required optical path length of the second plane reflection section can be further shortened compared to when it is configured with a plane mirror.

As a result, the focal length of the eyepiece (67) can be shortened, making it possible to achieve a finder with even higher magnification.

FIG. 7 shows a prism (65) in the embodiment of FIG.
The plane mirror (63) side of the condenser lens (6
4) is shown. That is, in this embodiment, a prism (60) whose surface on the plane mirror (63) side is a spherical surface (69) is used. If the prism (60) including the condenser lens is used in this way,
The number of parts can be reduced, making it possible to obtain a finder optical system with high positional accuracy in a small space.

FIG. 8 shows an embodiment in which the roof prism (58) of FIG. 5 and the prism (65) of FIG. 6 are used. This example has the same configuration as each of the above examples except for the inversion optical system, but since the inversion optical system is entirely composed of prisms, the degree of freedom in objective system design is expanded and the high magnification finder It becomes possible to realize this.

Moreover, as explained above, according to the finder optical system of the present invention, the light beam is bent toward the object side by the roof reflection section, and the light beam is bent toward the pupil side by the first and second flat reflection sections. , because the required optical path length is shortened,
It is possible to realize a finder optical system that is compact in either the left or right direction, has high magnification, and has a long overall length with the eyepiece position and eye point extending backward.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, and FIG. 2 is a diagram for explaining the differences between the embodiment of the present invention and the conventional example regarding the position of the eyepiece and the eye point. FIG. 3 is a schematic configuration diagram showing an embodiment in which the roof reflection section and the first plane reflection section are constructed of a roof prism, and FIG. 4 is a schematic diagram showing an embodiment in which the roof reflection section and the first plane reflection section are constructed integrally with a condenser lens. FIG. 5 is a schematic configuration diagram showing an embodiment of the present invention, which is composed of a roof prism, and FIG. 5 is a perspective view showing the roof prism. FIG. 6 is a schematic configuration diagram showing an embodiment in which the second plane reflection section is composed of a prism, and FIG. 7 is a schematic diagram showing an embodiment in which the second plane reflection section is composed of a prism integrally constructed with a condenser lens. - is a schematic configuration diagram showing an example. FIG. 8 shows a roof prism in which the roof reflection part and the first plane reflection part are integrally molded with a condenser lens,
FIG. 6 is a schematic configuration diagram showing an embodiment in which the second plane reflecting section is formed of an integrally molded prism. FIG. 9 is a diagram for explaining the overlapping of the total reflection part and the transmission part of the roof prism. Figure 10 is a diagram for explaining the required optical path length of the planar reflection section used in the present invention, Figure 11 is a diagram for explaining the required optical path length of the roof reflection section used in the invention, and Figure 12. FIG. 2 is a diagram for explaining the relationship between the bending angle of a light beam by the roof reflection section used in the present invention and the required optical path length of the roof reflection section and the plane reflection section. Fig. 13 is a schematic configuration diagram showing a conventional example in which the inversion optical system is composed of porro mirrors, Fig. 14 is a diagram showing the difference in occupied space between two plane mirrors and one roof mirror, and Fig. 15
The figure is a schematic configuration diagram showing a conventional example in which an inversion optical system is formed by one roof mirror and two reflection mirrors. (41) - Roof reflecting section, (21) (32) - Roof mirror (52) (58) (70) --- Roof prism, (50a) (Tl) - First back reflecting section, (50
b) (72) one second back reflection section, (40) one plane reflection section, (33) one first plane mirror (35) - one second
Plane mirror (23) (24) (55) (63) Single plane mirror (60) (65) -- Prism.

Claims (7)

[Claims] (1) Comprising an objective lens that has positive power as a whole, a condenser lens provided near the image plane of the objective lens, and an eyepiece lens that has positive power as a whole and magnifies the image of the objective lens. In the finder optical system, a roof reflecting section is provided between the objective lens and the condenser lens to bend the light beam from the objective lens toward the object side in order from the object side, and a first roof reflecting section that bends the light beam from the roof reflecting section toward the pupil side. What is claimed is: 1. A finder optical system, comprising: a second flat reflecting section; the second flat reflecting section is provided between the condenser lens and the eyepiece, and further bends the light beam from the condenser lens toward the pupil. (2) The finder optical system according to claim 1, wherein the roof reflection section is a surface reflection section of a roof mirror integrally molded with resin. (3) The finder optical system according to claim 1, wherein the roof reflection section and the first plane reflection section are integrally molded back surface reflection sections of a roof prism. (4) The finder optical system according to claim 3, wherein the surface of the roof prism on the second plane reflection section side is configured integrally with the condenser lens. (5) The finder optical system according to claim 1, wherein the second plane reflecting section is a back reflecting section of an integrally molded prism. (6) The finder optical system according to claim 5, wherein the surface of the prism on the first plane reflecting section side is configured integrally with the condenser lens. (7) The finder optical system according to claim 1, wherein the first plane reflection section and the second plane reflection section are constituted by plane mirrors.