JPH03217829A - Finder optical system - Google Patents

Abstract

PURPOSE:To make one direction of this finder optical system compact, to obtain high magnification and to make an entier length long by bending a luminous flux which is bent to an object side by a roof reflection part to a pupil side with a plane reflection part. CONSTITUTION:The luminous flux from an object is inverted by an objective lens 31 and inverted by the roof reflection part consisting of a roof mirror 32 which is integrally formed of resin. After the luminous flux bent by the mirror 32 is formed into an image in the vicinity of a condenser lens 33, it is bent to the pupil side by the two plane reflection parts consisting of plane mirrors 34a and 34b and returns to an erected image and passes through an ocular 35 to reach a pupil surface 36. It is desirable that the roof reflection part is the back surface reflection part of an integrally formed roof prism and the surface on the back surface reflection part side is integrally constituted of the lens 33. Then, it is also desirable that two plane reflection parts are the back surface reflection part of the integrally formed prism.

Description

[Detailed description of the invention] Leather chestnut epidermis ■Public corporation The present invention relates to a finder optical system.

BACKGROUND OF THE INVENTION Virtual-image finders and real-image finders are known as conventional finders comprising an optical system different from a photographing optical system. Virtual image finders are more commonly used than before because they have a compact configuration.

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

A real-image type finder has the advantage of providing a clearer and brighter field of view and clearly seeing the field frame compared to virtual image type finders such as the Alhada 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. 11, 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.

Incidentally, the boromirror shown in FIG. 11 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,
Up and down. It can be made compact in either the left or right direction. For example, as shown in FIG. 12(i), there is a case where two plane mirrors (10a) (10b) are used;
As shown in Fig. 2 (ii), the function regarding image reversal is the same as when using the roof mirror (I1), but when using the roof mirror (1l) (Fig. 12 (ii)), the plane is better. The space required is approximately half that of the case where mirrors (10a) and (10b) are used (FIG. 12(i)).

That is, in the roof mirror (11) in Fig. 12 (ii), the incident image (I5) is inverted at once using two plane mirrors that form an angle of 90 degrees with the ridge line in between to form a reflected image (16). On the other hand, the plane mirror (10a) in FIG. 12(i)
(fob), each mirror creates an incident image (l2)
By reflecting the reflected image (l3), the reflected image (14
) is formed. Therefore, the size of the roof mirror (11) is sufficient to be about the size of the incident image (15), but with the two plane mirrors (10a) (10b), each mirror is about the size of the image. The space required is approximately twice that of the roof mirror (11).

The finder described in Utility Model Application No. 1983-54774 is a roof mirror (21) as shown in Fig. 13.
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 (21) is placed in the horizontal direction as shown in FIG. 13, the vertical space is approximately half that of the case where a Porro prism or Boro mirror is used.

As mentioned above, for long-length cameras such as SVC and Blu-ray cameras, it is necessary to have a finder with a longer overall length with the eyepiece position and eye point extended backwards, depending on the arrangement of peripheral equipment. . but,
In the finder of the type shown in Fig. 13, two plane reflection parts (plane mirrors (23) and (24)) between the condenser lens (22) and the eyepiece (25) bend the light beam 2706 toward the object side. Therefore, the eyepiece position and the eyepoint (26) cannot be extended rearward without reducing the viewfinder magnification. Next, this point will be explained in more detail.

The finder magnification is an important feature of the finder, and is approximately expressed by the following formula (2).

βζf + / f z −・・1・1−−−−−1−−・1・−・1−−−−■ However, β: Finder magnification f1: Focal length of objective lens fz: Focal length of eyepiece lens It is.

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 lens, and is approximately expressed by the following equation (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 it (f 2 ) of the eyepiece also increases, and as a result, according to formula (■), the finder magnification (β) decreases. In other words, the first
In the finder shown in Figure 3, the finder magnification (β)
Since 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 a high
As mentioned above, the position of the finder eyepiece and the eye point cannot be extended to the rear.

Therefore, an object of the present invention is to provide a finder optical system that is compact, has high magnification, and has a long overall length in either the vertical or horizontal direction. In order to achieve the above object, 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 finder optical system having positive power as a whole. In a finder optical system comprising an eyepiece that magnifies the image of the objective lens, a roof reflection section is provided between the objective lens and the condenser lens to once bend the light beam from the objective lens toward the object side, and the condenser lens The structure is such that two planar reflecting parts are provided between the roof reflecting part and the eyepiece to bend the light beam, which has been bent towards the object side by the roof reflecting part, back towards the pupil.

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

The two planar reflecting parts may be integrally formed rear reflecting parts of a prism, and furthermore, the surface of the prism on the side of the roof reflecting part may be formed integrally with the condenser lens. Moreover, the two planar reflection sections may be composed of two planar mirrors.

According to Yu Kazutomo and Tarunari mentioned above, the roof reflection section bends the light beam toward the object, and the two plane reflection sections bend the light flux toward the pupil, so the required optical path length of the roof reflection section and the plane reflection section is It becomes shorter. Therefore, the distance between the image plane of the objective lens and the principal point position of the eyepiece is shortened, and the viewfinder magnification becomes high, but the eyepiece position and eye point are rearward. Extend to.

HusbandJLfi 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 (32) integrally molded with resin. Dahamira (32)
When the ridgeline of the roof is placed in the horizontal direction, the vertical direction is reversed, and when 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) forms an image near the condenser lens (33), and then is bent toward the pupil side by the plane mirror (34a). The light beam reflected by the plane mirror (34a) is
Furthermore, it is bent toward the pupil by a plane mirror (34b). After the image is reversed horizontally and returned to an erect image by the plane mirrors (34a) and (34b), the eyepiece (35)
and reaches the pupil plane (36). The eyepiece (35) has positive power and magnifies the image formed by the objective lens (31). In addition, the condenser lens (
33) is always placed near the image plane of the objective lens (31) in order to prevent the light flux reaching the pupil plane (36) from being eclipsed.

In this example, the light beam is bent toward the object side by the roof mirror (32) used as the roof reflection section.
A plane mirror (34a) used as a plane reflection section
(34b) bends the light beam toward the pupil. That is, the light beam is bent by 90 degrees or more with respect to the direction of incidence on the roof mirror (32), and the plane mirror (34a)
By setting the angle of incidence on (34b) to approximately 45°,
Roof mirror (32) and plane mirror (34a) (34
The required optical path length of the inversion optical system consisting of b) is shortened. This point will be explained in more detail below.

Figures 8(a) to 8(c) show that a light beam of a certain width is transmitted to a plane reflecting part (
40) shows the optical path (solid line) when reflected.

In the figure, the range of the luminous flux indicated by the dotted line is the plane reflection part (
40) shows the range in which the parallel light beam incident on 40) can be taken out as the corresponding parallel light beam after reflection, and the length of the optical axis within this range (thick line) shows the required optical path length. As shown in the figure, even if the angle of incidence (θ) on the plane reflection part (40) is too large (Fig. 8(C)) or too small (Fig. 8(C)),
Figure (a)) The required optical path length is longer and the angle of incidence (θ) is 45
6 (FIG. 8(b)), the required optical path length is the shortest. In addition, the smaller the incident angle (θ) is, the smaller the planar reflection part (
40) can be used.

9(a) to 9(c) are shown in FIGS. 8(a) to 9(c) except that a roof reflecting portion (41) is used instead of the plane reflecting portion (40) in FIG. 8(a) to (c). It shows the optical path when the incident angle (α) is changed similarly to (c). Roof reflector (41)
When using a roof reflector (41
) The smaller the angle of incidence (α) with respect to ), 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 using the roof reflection section (4l) and the plane reflection section (40) in combination in the inversion optical system, the angle of incidence (α) of the light flux to the roof reflection section (41) 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's eyepiece position and the eye point backward, in the embodiment shown in FIG. As you fold it to the side, the eyepiece (
35) 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)
) in the eyepiece lens (
35) and the position of the pupil plane (36), that is, the eye point extends considerably backward.

On the other hand, in FIG. 2(b), the eye point cannot be extended backwards because the light beam is bent toward the object side.

Figures 10(a) and 10(b) show when the bending angle (A) of the luminous flux by the roof reflector (41) is large (Fig. 10(a)) and when it is small when reversing light rays with the same luminous flux width. (FIG. 10(b)) shows the optical path (dotted line). still,
The smaller the angle of incidence (α) of the light beam on the roof reflection section (41), the larger the bending angle (A) becomes. Figure 10 (
a) As can be seen from (b), in order to shorten the required optical path length of the planar reflection section (40), the roof should be designed so that the incident angle (α) of the light beam to the roof reflection section (41) is as small as possible. It is preferable to determine the arrangement of the reflecting section (4l).

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 (41) 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°. Therefore,
The inverted optical system shown in FIG. 10(a), in which the bending angle (A) of the light beam is large, is more effective than the inverted optical system shown in FIG. 10(b) because the focal length of the eyepiece can be made shorter. It can be used as a high magnification finder.

FIG. 3(a) is a lens configuration diagram showing another embodiment of the present invention, and FIG. 3(b) is a perspective view of a roof prism (52) used therein. This embodiment has the same structure as the embodiments shown in FIGS. 1 and 2(a), except that the back reflection part (50) of the roof prism (52) integrally molded is used as the roof reflection part. ing. That is, the luminous flux from the object that has been inverted both vertically and horizontally by the objective lens (51) having positive power as a whole is inverted vertically or horizontally by the roof prism (52). The light beam bent toward the object side by the roof prism (52) forms an image near the condenser lens (53), and then is bent toward the pupil side by the plane mirror (54). The light beam reflected by the plane mirror (54) is further bent toward the pupil by the plane mirror (55). Plane mirror (5
4) By (55), the image is reversed horizontally or vertically and returned to an erect image, and then passes through the eyepiece (56) and reaches the pupil plane (57).

Note that the back reflection by the back reflection section (50) can be achieved by total reflection or vapor deposition of aluminum or silver. The 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
(2) However, d: Optical path length within the roof prism (52) n: Refractive index of the material constituting 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 make the lens bank of the objective lens (51) long, which increases the degree of freedom in designing the objective system.

FIG. 4 shows an embodiment in which the surface of the roof prism (52) on the plane mirror (54) side is integrated with the condenser lens (53) in the embodiment of FIG. 3(a).

That is, in this embodiment, the surface on the plane mirror (54) side is a spherical surface (
A roof prism (58) which is 59) is used.

In this way, a roof prism containing a condenser lens (
58), it becomes possible to reduce the number of parts, and it becomes possible to obtain a finder optical system with high positional accuracy in a small space.

FIG. 5 is a lens configuration diagram showing still another embodiment of the present invention. In this embodiment, a rear reflecting portion (60) of a prism (64) integrally formed as two planar reflecting portions is used. Other than that, the structure is the same as that of the 11th ffi and the embodiment of FIG. 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). Dahamira (62)
The light beam bent toward the object side by
) is bent toward the pupil by the two back reflecting portions (60). After the image is reversed horizontally or vertically by the prism (64) and returned to an erect image, the eyepiece (65)
and reaches the pupil plane (66).

Note that the back reflection by the back reflection section (60) can be achieved by total reflection or vapor deposition of aluminum, silver, or the like. The prism (64) is constructed using a material such as glass or transparent resin.

By using the prism (64), the air-equivalent required optical path length of the two plane reflecting sections can be further shortened compared to when the plane mirrors are used.

As a result, the focal length of the eyepiece (65) can be shortened, making it possible to achieve a finder with even higher magnification.

FIG. 6(a) shows the prism (
64) in which the surface on the side of the roof mirror (62) is integrated with the condenser lens (63).
Figure (b) is a perspective view of the prism (67) used therein. That is, in this embodiment, a prism (67) whose surface on the roof mirror (62) side is a spherical surface (68) is used. By using the prism (67) that includes a condenser lens in this way, it is possible to reduce the number of parts,
It becomes possible to obtain a finder optical system with high positional accuracy in a small space.

In Fig. 7, the roof prism (52) of Fig. 3(b) is used as the roof reflection part, and the prism (67) of Fig. 6(b) is used as the two planar reflection parts and the condenser lens. An example is shown. Since the inverting optical system is entirely composed of prisms, the degree of freedom in designing the objective system increases and it becomes possible to realize a finder with high magnification.

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 by the two planar reflection sections, so that the required optical path is Since the length is short, it is possible to realize a finder optical system that is compact, has high magnification in either the vertical or horizontal direction, and has a long overall length.

[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 is constructed of a roof prism, and FIG. 4 is a schematic diagram showing an embodiment in which the roof reflection section is constructed of a roof prism integrally constructed with a condenser lens. FIG. Fig. 5 is a schematic configuration diagram showing an embodiment in which two planar reflecting sections are composed of prisms, and Fig. 6 is a schematic diagram showing an embodiment in which two planar reflecting sections are composed of a prism that is integrated with a condenser lens. FIG. FIG. 7 is a schematic diagram illustrating an embodiment in which the roof reflection section is constituted by a roof prism, and the two planar reflection sections are constituted by prisms integrally formed with a condenser lens. FIG. 8 is a diagram for explaining the required optical path length of the planar reflection section used in the present invention, FIG. 9 is a diagram for explaining the required optical path length of the roof reflection section used for the invention, and FIG. It is a figure for demonstrating the relationship between the magnitude|size of the bending angle of the light beam by the roof reflection part used for this invention, and the required optical path length of a roof reflection part and a plane reflection part. Fig. 11 is a schematic configuration diagram showing a conventional example in which the inversion optical system is composed of Boro mirrors, Fig. 12 is a diagram showing the difference in occupied space between two plane mirrors and one roof mirror, and Fig. 13
The figure is a schematic configuration diagram showing a conventional example in which an inversion optical system is composed of one roof mirror and two reflection mirrors. (40) - one-plane reflective section, (41) - roof reflective section (2
1) (32) (62) - Dach mirror <52) (
58) -- Roof prism (23) (24) (34a) (34b) (54
) (55) (64) (67) -- Prism. plane mirror

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 reflection section is provided between the objective lens and the condenser lens to once bend the light beam from the objective lens toward the object, and a roof reflection section is provided between the condenser lens and the eyepiece to bend the light beam from the objective lens toward the object. A finder optical system characterized by being provided with two planar reflection parts that bend a light beam that has been bent to the side toward the pupil again. (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 is a back reflection section of an integrally molded roof prism. (4) The finder optical system according to claim 3, wherein the surface of the roof prism on the plane reflection section side is constructed integrally with the condenser lens. (5) The finder optical system according to claim 1, wherein the two planar reflecting portions are back reflecting portions of an integrally molded prism. (6) The finder optical system according to claim 5, wherein a surface of the prism on the side of the roof reflection section is constructed integrally with the condenser lens. (7) The finder optical system according to claim 1, wherein the two plane reflection sections are composed of two plane mirrors.