JP2881895B2 - Viewfinder optical system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a finder optical system.

2. Description of the Related Art A virtual image finder and a real image finder are known as a finder including an optical system different from an imaging optical system. The virtual image finder has been used more frequently than before because of its compact configuration.

However, in recent years, a finder that can be applied to various types of cameras and provides a high-quality finder image has been demanded, and therefore, a real image type finder has also been widely used. Since the real image type finder does not include a half mirror between the optical paths, there is an advantage that a clear and bright field of view can be obtained and the field frame can be clearly seen as compared with the virtual image type finder such as an albada type or a daylighting type.

On the other hand, since the image is inverted in the real image type viewfinder, an inversion optical system for returning to an erect image is required. This reversing optical system is roughly classified into one that re-images using a relay system and one that uses reflection. In the case of performing re-imaging using a relay system, the optical path length of the relay system is unnecessarily long, and therefore, lacks compactness. As a device using reflection, a device using a Porro mirror or a Porro prism is well known (US Pat. No. 4,545,655, Japanese Utility Model Publication No. 50-4326, etc.). Eleventh
As shown in the figure, when a porro mirror is used, light rays (two-dot chain lines) are routed up, down, left, and right, so that a large space is required up, down, left, and right.

The porro mirror shown in FIG. 11 includes a first mirror (1), a second mirror (2), a third mirror (3), and a fourth mirror (4). Objective lens (5)
Is reflected from the first mirror (1) to the second mirror (2), and the light reflected by the second mirror (2) passes through the condenser lens (6) and then passes from the third mirror to the fourth mirror. After being reflected by the mirror (4) and passing through the eyepiece (7), it reaches the pupil plane (8).

In addition, when the roof reflection section is used as the reversing optical system, one of the up, down, left, and right directions can be made compact. For example, the case where two plane mirrors (10a) and (10b) are used as shown in FIG.
As shown in i), the function relating to image reversal is the same as when the roof mirror (11) is used, but when the roof mirror (11) is used (FIG. 12 (ii)), the plane mirror (10a) is used. ) (10b) occupies about half the space as compared with the case of (FIG. 12 (i)). That is, in the roof mirror (11) of FIG. 12 (ii), the reflected image (16) is formed by inverting the incident image (15) at a time by two plane mirrors forming an angle of 90 ° with the ridge line interposed therebetween. On the other hand, the plane mirrors (10a) and (10b) shown in FIG.
The reflection image (14) is formed by reflecting the reflection image (13). 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) and (10b), the size of the image is about the size of each mirror. Space is required, and the space occupied is about twice that of the Dachmirror (11).

The finder described in the specification of Japanese Utility Model Application No. 63-54774 uses a roof mirror (21) and two plane mirrors (23) and (24) as shown in FIG. In this viewfinder, since the roof mirror (21) is used as the roof reflection section as described above,
It has a compact configuration in either one of the left and right directions. That is, when the ridge line of the roof mirror (21) is placed in the horizontal direction as shown in FIG. 13, the space above and below is about half as compared with the case where a porro prism or a porro mirror is used.

Thus, in the viewfinder of the type shown in FIG. 13, two flat reflecting portions (flat mirrors (23) and (24))
Since the light beam is bent to the object side by 270 °, the overall length is short and compact. However, since the two plane reflectors are disposed between the condenser lens (22) and the eyepiece (25), the focal length of the eyepiece (25) cannot be short, and as a result, , Cannot increase the finder magnification. Next, this point will be described in more detail.

The finder magnification is an important specification of the finder, and is approximately expressed by the following equation.

β ≒ f ₁ / f _2, where β: finder magnification f ₁ : focal length of objective lens f ₂ : focal length of eyepiece lens

As can be seen from the equation, a high magnification finder is realized by increasing the focal length (f ₁ ) of the objective lens or shortening the focal length (f ₂ ) of the eyepiece.
However, when the focal length (f ₁ ) of the objective lens is increased, the entire length of the objective lens is extended more than necessary, and a compact finder cannot be obtained. Therefore, a compact high-magnification finder requires an eyepiece having a short focal length.

In addition, the focal length (f ₂ ) of the eyepiece is the diopter (usually −
If 1) is determined, it is uniquely determined by the distance between the image plane of the objective lens and the principal point position of the eyepiece, and is approximately expressed by the following equation.

Here, S: distance between the image plane of the objective lens and the principal point of the eyepiece A: diopter.

Therefore, if the distance (S) between the image plane of the objective lens and the principal point of the eyepiece becomes longer according to the equation, the focal length (f ₂ ) of the eyepiece also becomes longer, and as a result, the finder magnification (β) becomes larger. Drops. That is, in the finder shown in FIG. 13, since the two plane reflecting portions are arranged between the condenser lens provided near the image plane of the objective lens and the eyepiece, the distance (S) is shortened. As a result, it is impossible to increase the magnification of the finder and shorten the entire length of the finder.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a finder optical system that is compact in one of the vertical and horizontal directions and has a high magnification and a short overall length.

Means for Solving the Problems To achieve the above object, a finder optical system of the present invention includes an objective lens having a positive power as a whole,
In a finder optical system including a condenser lens provided in the vicinity of an image plane of the objective lens and an eyepiece having a positive power as a whole and enlarging an image of the objective lens, a finder optical system including the objective lens and the condenser lens A first planar reflecting portion for temporarily bending the light beam from the objective lens toward the object side and a second planar reflecting portion for bending the light beam from the first planar reflecting portion so as to intersect the optical axis of the objective lens; A roof reflecting portion for bending the light beam reflected by the second plane reflecting portion toward the pupil side is provided in the curve between the condenser lens and the eyepiece.

It is preferable that the light flux routed by the first and second flat reflecting portions is 270 ° or less. Further, the first plane reflecting section and the second plane reflecting section may be constituted by a plane mirror, or may be a back reflecting section of an integrally formed prism. Further, the surface of the prism on the roof reflecting portion side may be formed integrally with the condenser lens.

Further, the roof reflecting portion may be a surface reflecting portion of a roof mirror integrally formed of resin, or the roof reflecting portion may be a back reflecting portion of a roof prism integrally formed. Further, the surface of the roof prism on the side of the second plane reflecting portion may be formed integrally with the condenser lens.

According to the configuration described above, the light beam is bent toward the object side by the first flat reflecting portion, and the light beam from the first flat reflecting portion is bent by the second flat reflecting portion so as to intersect with the optical axis of the objective lens. The finder is short and compact. Also, since the luminous flux is bent toward the pupil side by the roof reflecting portion provided between the condenser lens and the eyepiece, one of the upper, lower, left and right directions can be made compact, and the image plane of the objective lens and the eyepiece can be reduced. The distance from the principal point position can be shortened. As a result, an eyepiece having a short focal length can be used, so that the magnification of the viewfinder can be increased.

Embodiments Hereinafter, embodiments of the present invention will be described 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, an orthogonal arrow (30) indicates a state of image reversal in the optical path. Objective lens with positive power (3
The light flux from the subject that has been inverted in the vertical and horizontal directions by 1) is bent to the object side by the first flat mirror (32). The light beam reflected by the first plane mirror (32) is bent by the second plane mirror (33) so as to intersect the optical axis of the objective lens (31). As a result, the objective lens (31) is formed by the first and second plane mirrors (32) and (33).
Is inverted in the vertical or horizontal direction. 1st, 2nd
When the plane mirrors (32) and (33) are arranged in the horizontal direction, the horizontal direction is reversed. When the plane mirrors (32) and (33) are arranged in the vertical direction, the vertical direction is reversed. FIG. 1 shows the first and second
This shows a case where the plane mirrors (32) and (33) are arranged in the horizontal direction.

The luminous flux bent by 270 ° by the first plane mirror (32) and the second plane mirror (33) forms an image once near the condenser lens (34), and is then formed by a roof mirror (35) integrally formed of resin. It is bent to the pupil side.
The image is inverted up and down by the Dach mirror (35) and returned to an erect image, and then passes through the eyepiece (36) to reach the pupil plane (37). The eyepiece (36) has a positive power and magnifies the image formed by the objective (31). Further, the condenser lens (34) is connected to the pupil plane (3
In order to prevent the light flux reaching 7) from being vignetted, it is always placed near the image plane of the objective lens (31).

In the present 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 section, and the first plane mirror (32) is used as the second plane reflection section. The light beam from the first plane mirror (32) is bent by the two plane mirror (33) so as to cross the optical axis of the objective lens (31). Then, the light beam is bent toward the pupil by the surface reflecting portion of the roof mirror (35) used as the roof reflecting portion. That is, Dach Miller (35)
By reducing the incident angle of the finder, a higher magnification of the finder is achieved. Hereinafter, this point will be described in more detail.

FIGS. 10 (a) to (c) show optical paths (solid lines) when a light beam having a certain width is reflected by the roof reflecting portion (41).
FIG. 10 (a) shows an optical path when the incident angle (α) is less than 45 °,
FIG. 10 (b) shows an optical path when the incident angle (α) is 45 °, and FIG.
FIG. 3C shows the optical path when the incident angle (α) exceeds 45 °. In the drawing, the range of the luminous flux indicated by the dotted line indicates a range in which the parallel luminous flux incident on the roof reflecting portion (41) can be taken out as a corresponding parallel luminous flux after reflection, and the optical axis within the range is shown. (Bold line) indicates the required optical path length.

As shown in the figure, the smaller the angle of incidence (α) with respect to the roof reflection portion (41), the shorter the required optical path length. Also, the smaller the reflection angle (α), the smaller the roof reflection part (4) can be used.

As shown in FIG. 10 (c), when the incident angle (α) is larger than 45 °, the required optical path length becomes particularly long. In the present invention, in order to reduce the incident angle (α) of the light beam on the roof reflecting portion (41), the light beam bending by the flat reflecting portion needs to be 270 ° or less. Thereby, S (the distance between the principal point of the eyepiece lens and the image plane of the objective lens) in the above equation can be reduced, so that a high-magnification finder 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 development 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 development view of the eyepiece system. In the present embodiment shown in FIG. 2A, although the entire length of the viewfinder shown in FIG. 2A is the same as that of the viewfinder shown in FIG.
Since the required optical path length is shorter than the case where the plane mirrors (23) and (24) are used, S is small as can be seen from FIGS. 3 (a) and 3 (b). On the other hand, in FIG. 2 (b), two plane reflectors (plane mirrors (23) and (24)) for bending a light beam by 270 ° are arranged between the condenser lens (22) and the eyepiece (25). Therefore, the value of S is increased as shown in FIG. 3 (b). Therefore, in the embodiment of FIG. 2A, the focal length of the eyepiece (36) can be made short,
A higher magnification can be achieved as compared with the conventional example shown in FIG. 2 (b) without changing the entire length of the viewfinder.

FIG. 4 is a lens configuration diagram showing another embodiment of the present invention. In the present embodiment, the first back reflector (50a) and the second back reflector (50b) of the prism (52) integrally formed as the first plane reflector and the second plane reflector are used, respectively. 1 and FIG. 2 (a). That is, the luminous flux from the subject that has been inverted in the vertical and horizontal directions by the objective lens (51) having a positive power as a whole is inverted vertically or horizontally by the prism (52). The light beam 270 ° bent by the prism (52) forms an image near the condenser lens (54), and is then bent toward the pupil by the roof mirror (55). The image is inverted left and right or up and down by the Dach mirror (55) to return to an erect image, and then the eyepiece (5
It passes through 6) to the pupil plane (57).

The back reflection by the first and second back reflection portions (50a) and (50b) can be achieved by total reflection or evaporation of aluminum or silver. The prism (52) is made of a material such as glass or transparent resin.

When the prism (52) is used, the required air path length (D) in the prism (52) is expressed by the following equation.

D = d / n where d: optical path length in prism (52) n: refractive index of the material constituting prism (52). Therefore, the required air equivalent optical path length (D) in the prism (52) is shortened, and it is not necessary to lengthen the lens back of the objective lens (51), so that the degree of freedom in designing the objective system is increased.

FIG. 5A is a lens configuration diagram showing an embodiment in which the surface of the prism (52) on the roof mirror (55) side is integrally formed with the condenser lens (54) in the embodiment of FIG. FIG. 5 (b) shows the prism (5
It is a perspective view of 8). That is, in this embodiment, the Dach mirror (5
5) A prism (58) having a spherical surface (59) on the side is used. By using a prism (58) including a condenser lens, the number of parts can be reduced,
It becomes 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 portion (68) of a roof prism (65) integrally formed is used as a roof reflection portion. Has the same configuration as the embodiment of FIGS. 1 and 2 (a). That is, the luminous flux from the subject that has been inverted in the vertical and horizontal directions by the objective lens (61) having a positive power as a whole is inverted vertically and horizontally by the first plane mirror (62) and the second plane mirror (63). You. The luminous flux bent by 270 ° by these plane mirrors (62) and (63) forms an image near the condenser lens (64), and is then bent toward the pupil by the back reflection part (68) of the roof prism (65). The image is inverted left and right or up and down by the roof prism (65) and returned to an erect image, and then passes through the eyepiece (66) to the pupil plane (67).

The back reflection by the back reflection section (68) can be achieved by total reflection or vapor deposition of aluminum, silver, or the like. The roof prism (65) is made of a material such as glass or transparent resin. When using glass,
It is possible to make the accuracy of the roof part very high.

By using the roof prism (65), the required optical path length of the roof reflecting portion in terms of air can be further shortened as compared with the case where a roof mirror is used. As a result, the focal length of the eyepiece (66) can be shortened, so that a higher magnification finder can be achieved.

FIG. 7A is a lens configuration diagram showing an embodiment in which the surface of the roof prism (65) on the side of the second flat mirror (63) is integrally formed with the condenser lens (64) in the embodiment of FIG. FIG. 7 (b) is a perspective view of a roof prism (60) used therein. That is, in this embodiment, a roof prism (60) having a spherical surface (69) on the side of the second flat mirror (63) is used. By using the roof prism (60) including the condenser lens in this way, the number of components can be reduced, and a finder optical system with high positional accuracy in a small space can be obtained.

FIG. 8 shows the first and second plane mirrors (3) disposed between the objective lens (31) and the condenser lens (34).
2) An embodiment having the same configuration as in FIGS. 1 and 2 (a) is shown, except that the light beam routing in (33) is inclined toward the object side. The Dach Miller (75) is the second
It has a shape corresponding to the inclination of the light beam from the plane mirror (33). The width (A) of the reversing optical system can be made more compact by inclining the light beam routing by the plane reflecting portion, that is, the first and second plane mirrors (32) and (33) to the object side.

FIG. 9 is a cross-sectional view of the embodiment shown in FIG.
The roof prism (70) with the surface on the side of the second flat mirror (32) integrated with the condenser lens (34) instead of 5)
Shows an example in which is used. That is, in the present embodiment, similarly to the embodiment of FIG. 7 (a), the second flat mirror (32)
Since the roof prism (70) having the spherical surface (79) on the side is used, the same effect as in the case of using the roof prism (60) in FIG. 7 (b) is obtained.

Effect of the Invention As described above, according to the finder optical system of the present invention, the light beam is bent toward the object side by the first plane reflecting portion,
The light beam from the first flat reflecting portion is bent by the second flat reflecting portion so as to intersect with the optical axis of the objective lens, and the light beam is bent toward the pupil side by the roof reflecting portion. Since the distance from the principal point position is shortened, it is possible to realize a finder optical system which is compact in one of the vertical and horizontal directions and has a high magnification and a short overall length.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention, and FIG. 2 shows the distance between the image plane of the objective lens and the principal point of the eyepiece lens and the total length of the finder. FIG. 3 is a diagram for explaining the difference, and FIG. 3 is a diagram showing a development view of the eyepiece system. FIG. 4 is a schematic diagram showing an embodiment in which the first and second planar reflecting portions are constituted by a back surface reflecting portion of a prism, and FIG. 5 is a first and second planar reflecting portion. FIG. 3 is a schematic configuration diagram illustrating an example in which a unit is configured by a back surface reflection unit of a roof prism integrally configured with a condenser lens. FIG. 6 is a schematic configuration diagram showing an embodiment in which the roof reflecting portion is formed by a roof prism, and FIG. 7 is an embodiment in which the roof reflecting portion is formed by a roof prism integrally formed with a condenser lens. FIG. FIG. 8 is a schematic structural view showing an embodiment in which the light beam routing by the first and second flat reflecting portions is inclined toward the object side, and FIG. 9 further includes a roof reflecting portion integrated with a condenser lens. It is a schematic structure figure showing the example using the roof prism constituted. FIG. 10 is a diagram for explaining a required optical path length of the roof reflecting portion used in the present invention. FIG. 11 is a schematic configuration diagram showing a conventional example in which a reversing optical system is composed of a porro mirror, FIG. 12 is a diagram showing a difference in occupied space between two plane mirrors and one roof mirror, and FIG. FIG. 3 is a schematic configuration diagram showing a conventional example in which an optical system is configured by one sheet, a roof mirror, and two reflection mirrors. (41) ... Dach reflector, (21) (35) (55) (75) ... Dach mirror, (60) (65) (70) ... Dach prism, (23) (24) ... Plane mirror, ( 32) (62)… First plane mirror, (33) (63)… Second plane mirror, (52) (58)… Prism, (68)… Back reflection part, (50a)… 1st back reflection section, (50b) ... second back reflection section.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shigeto Omori 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Osaka International Building Minolta Camera Co., Ltd. (56) References JP-A-1-309020 (JP) , A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G03B 13/06

Claims (8)

(57) [Claims] An objective lens having an overall positive power, a condenser lens provided in the vicinity of an image plane of the objective lens, and an eyepiece having an overall positive power and enlarging an image of the objective lens. In a finder optical system comprising: a first flat reflecting portion for temporarily bending a light beam from the objective lens toward the object side between the objective lens and the condenser lens; and a light beam from the first flat reflecting portion to the objective lens. A second flat reflecting portion that bends so as to intersect with the optical axis; and a roof reflecting portion that bends the light beam reflected by the second flat reflecting portion to the pupil side between the condenser lens and the visible lens. A special finder optical system. 2. The finder optical system according to claim 1, wherein a light flux routed by said first plane reflection section and said second plane reflection section is 270 ° or less. 3. The finder optical system according to claim 1, wherein said first and second flat reflecting portions are formed of flat mirrors. 4. The finder optical system according to claim 1, wherein said first plane reflection section and said second plane reflection section are a back surface reflection section of an integrally formed prism. 5. The finder optical system according to claim 4, wherein a surface of the prism on the roof reflecting portion side is formed integrally with the condenser lens. 6. The finder optical system according to claim 1, wherein said roof reflecting portion is a surface reflecting portion of a roof mirror integrally formed of resin. 7. The finder optical system according to claim 1, wherein said roof reflecting section is a rear reflecting section of a roof prism integrally formed. 8. The finder optical system according to claim 7, wherein a surface of the roof prism on the side of the second flat reflecting portion is formed integrally with the condenser lens.