JPH03217831A - Finder optical system - Google Patents

Abstract

PURPOSE:To make one direction of this optical system short, to obtaine high magnification and to make the entire length of a finder short by bending a luminous flux from an objective lens with two plane reflection parts, transmitting the light through a condenser lens and then bending it further with a roof reflection part. CONSTITUTION:The luminous flux from an object is inverted in vertical and horizontal directions by the objective lens 31, bent by 1st and 2nd plane mirrors 32 and 33 and inverted in the vertical direction or the horizontal direction. After the luminous flux is formed into an image once in the vicinity of the condenser lens 34, bent by a roof mirror 35 and returns to an erected image, it is enlarged by an ocular lens 36 and arrives at a pupil surface 37. It is desirable that bending around the luminous flux by the mirrors 32 and 33 is <=270 deg., and it is preperable that the mirrors are the back surface reflection part of a prism integrally formed. Further, it is preferable that the surface of the mirror 35 is constituted integrally of the lens 34.

Description

[Detailed description of the invention] Peel millet kudzu group The present invention relates to a finder optical system.

Virtual image finders and real image finders are known as finders comprising an optical system separate from the photographic 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 applied to various types of cameras and provide high-quality finder images, and for this reason, real-image finders have come into widespread use.

A real image finder does not have a half mirror between the optical paths, so it uses an Albada type finder. Compared to virtual image finders such as daylight type finders, it has the advantage of providing a clearer and brighter field of view, as well as being able to clearly see the field of view.

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 Porro mirrors and Boro prisms (
(U.S. Patent No. 4,545,655, Utility Model Publication No. 4326, 1983, etc.). As shown in FIG. 11, when a Porro 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 dark surface (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. 12 (1), there is a case where two plane mirrors (10a) (10b) are used;
As shown in Figure 2 (ii), the function regarding image reversal is the same as when using a roof mirror (11), but
When using a roof mirror (11) (Fig. 12 (ii))
This requires about half the space compared to the case where the plane mirrors (10a) and (10b) are used (FIG. 12(i)). That is, Dahamira (11) in Figure 12 (ii)
In this case, the incident image (15) is inverted at once to form a reflected image (16) using two plane mirrors that form an angle of 90 degrees with the ridge line in between.
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 (11) is sufficient to be about the size of the incident image (15), but
With two plane mirrors (10a) (10b), a space about the size of the image is required for each mirror,
It occupies approximately twice the space compared to a roof mirror (1l). The finder described in Utility Model Application No. 1983-54774 is a Dahamira (2l) as shown in Figure 13.
This type uses a mirror and two flat mirrors (23) and (24). As mentioned above, this finder uses the roof mirror (21) as the roof reflection section, so it can be used both top and bottom. It becomes a compact configuration in either the left or right direction and becomes 1/ν. That is, when the edge 1 of the roof mirror (21) is placed in the horizontal direction as shown in FIG. 13, the vertical space is approximately half that of when using a Boro prism or a Boro prism.

In this way, in the finder of the type shown in FIG.
4)) bends the light ray toward the object side by 270'', resulting in a short overall length and compact configuration.However, these two plane reflecting parts are condenser lenses (22).
and the eyepiece lens (25), the focal length of the eyepiece lens (25) cannot be shortened, and as a result, the finder magnification cannot be increased. Next, this point will be explained in more detail.

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

βζf+/ft −−−−−−−−'−'−”−・−
(2) However, β: finder magnification f,: focal length of objective lens f2: focal length of eyepiece lens.

As can be seen from equation (2), a finder with high magnification is realized by increasing the focal length (r+) of the objective lens or shortening the focal length (f2) of the eyepiece lens. 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 lens, and is approximately expressed by the following 2).

However, S: distance between the image plane of the objective lens and the principal point position of the eyepiece; A: 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 of FIG. 13, two planar reflective parts are arranged between the condenser lens and the eyepiece lens provided near the image plane of the objective lens, so the distance (S) is shortened. As a result, it is not possible to increase the magnification of the finder and shorten the overall length of the finder.

Therefore, an object of the present invention is to provide a finder optical system that is compact, has high magnification in either the vertical or horizontal directions, and has a short overall length.

In order to achieve the above-mentioned object of "helping the mother," the finder optical system of the present invention includes an objective lens having an overall positive power, a condenser lens provided near the image plane of the objective lens, and an overall positive power. In a finder optical system, the finder optical system includes an eyepiece lens that has a positive power and magnifies the image of the objective lens. A planar reflecting section and a second planar reflecting section that bends the light beam from the first planar reflecting section so as to intersect with the optical axis of the objective lens are provided, and the second planar reflecting section is provided between the condenser lens and the eyepiece. The structure includes a roof reflection section that bends the reflected light beam toward the pupil.

It is preferable that the luminous flux distribution by the first plane reflection part and the second plane reflection part is 270 degrees or less.

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

Further, the roof reflecting portion may be a surface reflecting portion of a roof mirror integrally molded with resin, or the roof reflecting portion may be a back reflecting portion 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.

According to the above configuration, the first plane reflection section bends the light beam toward the object side, and the second plane reflection section bends the light beam from the first plane reflection section so that it intersects with the optical axis of the objective lens. ,
The overall length of the finder is short and compact. Also,
The roof reflector installed between the condenser lens and the eyepiece bends the light beam toward the pupil, making it more compact in either the vertical or horizontal direction, and the image plane of the objective lens and the principal point of the eyepiece. The distance between the two positions can be shortened. As a result, an eyepiece with a short focal length can be used, making it possible to increase the magnification of the finder.

Embodiments of the present invention will be described below with reference to 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 by step 1) is bent toward the object side by the first plane mirror (32). The light beam reflected by the first plane mirror (32) is bent by the second plane mirror (33) so as to intersect with the optical axis of the objective lens (31). As a result, the light beam from the objective lens (31) is reversed vertically or horizontally by the first and second plane mirrors (32) and (33). First and second plane mirrors (32) (33)
When they are arranged horizontally, the horizontal direction is reversed, and when they are arranged vertically, the vertical direction is reversed. In addition, Figure 1 is 1. Second plane mirror (32)
(33) are arranged horizontally.

The light beam bent by 270 degrees by the first plane mirror (32) and the second plane mirror (33) forms an image near a condenser lens (34), and then a roof mirror (35) integrally molded with resin. It is bent toward the pupil by After the image is vertically inverted and returned to an erect image by the roof mirror (35), it passes through the eyepiece (36) and reaches the pupil plane (37). The eyepiece (36) has positive power and magnifies the image formed by the objective lens (31). In addition, 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, the light beam from the objective lens (31) is bent toward the object side by the first plane mirror (32) used as the first plane reflection part, and the light beam from the objective lens (31) is bent toward the object side by the first plane mirror (32) used as the first plane reflection part. The first
The light beam from the plane mirror (32) is bent so as to intersect with the optical axis of the objective lens (31).

And the roof mirror (which is used as a roof reflection part)
The light beam is bent toward the pupil by the surface reflection section 35). That is, by reducing the angle of incidence on the roof mirror (35), high magnification of the finder is achieved. This point will be explained in more detail below.

FIGS. 10(a) to (c) show optical paths (solid lines) when a luminous flux of a certain width is reflected by the roof reflection section (41). Figure 10 (a) shows the optical path when the angle of incidence (α) is 45° without a groove, Figure 10 (b) shows the optical path when the angle of incidence (α) is 45°, and Figure 10 (c) shows the optical path when the angle of incidence (α) is 45°. It shows the optical path when the angle (α) exceeds 45°. 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 roof reflector (41) can be extracted as the corresponding parallel light flux after reflection, and the light within this range is Axis length (thick line)
indicates the required optical path length.

As shown in the figure, the angle of incidence (
The smaller α), the shorter the required optical path length.

Also, the smaller the incident angle (α) is, the smaller the roof reflection part (4
) can be used.

Furthermore, as shown in Figure 10(c), the angle of incidence (α
) is larger than 45°, the required optical path length becomes particularly long. In the present invention, in order to reduce the angle of incidence (α) of the light beam on the roof reflection portion (41), it is necessary to make the bending of the light beam by the plane reflection portion 270° or less. As a result, S (the distance between the principal point of the eyepiece and the image plane of the objective lens) in the above formula (2) can be made small, so that a finder with high magnification can be realized as described above.

FIG. 2(a) shows a schematic configuration of the embodiment shown in FIG. 1, and FIG. 3(a) shows a developed view of the eyepiece system. FIG. 2(b) shows a schematic configuration of the conventional example shown in FIG. 13, and FIG. 3(b) shows a developed view of the eyepiece system. Although the total length of the finder in FIG. 2(a) is the same as the total length of the finder in FIG. 2(b), the roof mirror (35
) is shorter than when using plane mirrors (23) and (24), so the required optical path length in Figure 3(a) (
As can be seen from b), the above S is small. On the other hand, in Fig. 2(b), the condenser lens (
22) and the eyepiece (25), there are two plane reflecting parts (plane mirror (23) (2
4) ') is arranged, the above-mentioned S becomes large as shown in FIG. 3(b). Therefore, Fig. 2 (a
), the focal length of the eyepiece lens (36) can be shortened, so it is possible to achieve higher magnification than the conventional example shown in FIG. 2(b) without changing the overall length of the finder. can.

FIG. 4 is a lens configuration diagram showing another embodiment of the present invention. In this embodiment, the first back reflection part (50a) and the second back reflection part (50b) of the prism (52) integrally molded are used as the first plane reflection part and the second plane reflection part, respectively. , has the same structure as the embodiment shown in FIGS. 1 and 2(a). That is, the luminous flux from the object that has been inverted vertically and horizontally by the objective lens (51) having positive power as a whole is inverted vertically or horizontally by the prism (52). The light beam bent by 270 degrees by the prism (52) forms an image near the condenser lens (54), and is then bent toward the pupil by the roof mirror (55). After the image is reversed horizontally or vertically and returned to an erect image by the roof mirror (55), it passes through the eyepiece (56) and reaches the pupil plane (57).

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

When the prism (52) is used, the air-equivalent required optical path length (D) within the prism (52) is expressed by the following equation (2).

D=d/n −−−−−−−・−・−−−−
11--■ However, d: Optical path length within the prism (52) n:
This is the refractive index of the material that makes up the prism (52). Therefore, the required air-equivalent optical path length (D) within the prism (52) is shortened, and there is no need to increase the lens back of the objective lens (51), increasing the degree of freedom in objective system design.

FIG. 5(a) shows the prism (
52) is a lens configuration diagram showing an embodiment in which the surface on the roof mirror (55) side is integrated with a condenser lens (54), and FIG. 5(b) is a perspective view of a prism (58) used therein. It is. That is, in this embodiment, the prism (58) has a spherical surface (59) on the side of the roof mirror (55).
) is used. By using the 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 reflecting portion (68) of an integrally molded roof prism (65) is used as the roof reflecting portion. has the same structure as the embodiment shown in FIGS. 1 and 2(a). That is, the luminous flux from the object that has been inverted vertically and horizontally by the objective lens (6l) having positive power as a whole is inverted vertically or horizontally by the first plane mirror (62) and the second plane mirror (63). Ru. 2 by these plane mirrors (62) (63)
70＠The bent light beam is passed through a condenser lens (6
4) An image is formed in the vicinity and then bent toward the pupil by the back reflection section (68) of the roof prism (65). After the image is reversed horizontally or vertically by the roof prism (65) and returned to an erect image, it passes through the eyepiece (66) and reaches the pupil plane (67).

Note that the back reflection by the back reflection section (68) can be achieved by total reflection or by a layer of aluminum, silver, or the like. The roof prism (65) 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.

By using the roof prism (65), the air-equivalent required optical path length of the roof reflection section can be further shortened compared to when a roof mirror is used. As a result, the focal length of the eyepiece (66) can be shortened, so
Furthermore, it is possible to achieve a finder with a higher magnification.

FIG. 7(a) is a lens configuration diagram showing an embodiment in which the surface of the roof prism (65) on the second plane mirror (63) side is integrated with the condenser lens (64) in the embodiment of FIG. 7(b) is a perspective view of a roof prism (60) used therein. That is, in this embodiment, a roof prism (60) whose surface on the second plane mirror (63) side is a spherical surface (69) is used.

In this way, a roof prism containing a condenser lens (
60), 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.

Figure 8 shows the objective lens (31) and condenser lens (
34) and the first and second plane mirrors (
32) This shows an embodiment having the same configuration as in FIGS. 1 and 2(a), except that the light flux routing according to (33) is tilted toward the object side. In addition, Dahamira (75)
has a shape corresponding to the inclination of the light beam from the second plane mirror (33). Planar reflective parts, i.e., first and second
By tilting the light beam routing by the plane mirrors (32) (33) toward the object side, the radiation (A) of the inversion optical system can be configured even more compactly.

FIG. 9 shows the example of FIG.
Instead of 5), a roof prism (
70) is used. That is, in this embodiment, similarly to the embodiment of FIG. 7(a), a roof prism (79) whose surface on the second plane mirror (32) side is a spherical surface (79) is used.
0) is used, the same effect as in the case of using the roof prism (60) in FIG. 7(b) is obtained.

As explained above, according to the finder optical system of the present invention, the first plane reflection section bends the light beam toward the object, and the second plane reflection section bends the light beam from the first plane reflection section toward the object. The beam is bent to intersect with the optical axis of the lens, and the beam is further bent toward the pupil at the roof reflector, thereby shortening the distance between the image plane of the objective lens and the principal point position of the eyepiece. It is possible to realize a finder optical system that is compact, has high magnification, and has a short overall length in either direction.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing an embodiment of the present invention, and Fig. 2 shows the difference between the embodiment of the present invention and the conventional example with respect to the distance between the image plane of the objective lens and the principal point position of the eyepiece and the overall length of the finder. FIG. 3, which is a diagram for explaining the differences, is a diagram showing a developed view of their eyepiece systems. FIG. 4 is a schematic configuration diagram showing an embodiment in which the first plane reflection section and the second plane reflection section are constituted by the back surface reflection section of a prism, and FIG. FIG. 3 is a schematic configuration diagram showing an embodiment in which the rear reflection section of a roof prism is integrated with a condenser lens. FIG. 6 is a schematic configuration diagram showing an embodiment in which the roof reflection section is composed of a roof prism, and FIG. 7 is a schematic diagram showing an embodiment in which the roof reflection section is composed of a roof prism integrally constructed with a condenser lens. FIG. FIG. 8 is a schematic configuration diagram showing an embodiment in which the luminous flux distribution by the first plane reflection section and the second plane reflection section is tilted toward the object side, and FIG. FIG. 2 is a schematic configuration diagram showing an example in which a roof prism configured as shown in FIG. FIG. 10 is a diagram for explaining the required optical path length of the roof reflection section used in the present invention. Fig. II is a schematic configuration diagram showing a conventional example in which the inversion optical system is composed of a Porro mirror, 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. (41)...Douche reflection part, (21) (35) (55) (75)-11 Roof mirror (60) (65) (70)...Dach prism, (23) (24) 1 Plane mirror (32) ) (62)-1 first plane mirror (33) (6
3) - one second plane mirror (52) (58) - prism, (68) - one back reflecting section, (50a) - first back reflecting section, (50b) - one 21st reflecting section. 2nd figure 1-1 21 Dahamira figure 3 (eyepiece system developed view) (a) (b) figure 8 figure 9 figure 11 figure 12 (1) (ii) figure 13

Claims (8)

[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, there is a first plane reflection section between the objective lens and the condenser lens, which once bends the light beam from the objective lens toward the object side; and a second plane reflection section that bends the light so as to intersect with the condenser lens, and a roof reflection section that bends the light beam reflected by the second plane reflection section toward the pupil between the condenser lens and the eyepiece. Finder optical system. (2) A first device characterized in that the luminous flux routing by the first planar reflecting section and the second planar reflecting section is 270 degrees or less.
A finder optical system according to the claims. (3) 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. (4) The finder optical system according to claim 1, wherein the first plane reflection section and the second plane reflection section are back reflection sections of an integrally molded prism. (5) The finder optical system according to claim 4, wherein the surface of the prism on the side of the roof reflection section is constructed integrally with the condenser lens. (6) 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. (7) The finder optical system according to claim 1, wherein the roof reflection section is a back reflection section of an integrally molded roof prism. (8) The finder optical system according to claim 7, wherein the surface of the roof prism on the second plane reflection section side is configured integrally with the condenser lens.