JPH08179400A - Finder optical system and reversal optical system thereof - Google Patents

Abstract

PURPOSE: To provide a compact finder optical system having a high finder magnification. CONSTITUTION: The real image type finder optical system using a roof prism 3 is constituted of an objective lens 1 having positive refractive power, the roof prism 3, a condenser lens 5, a 1st prism 8, a 2nd prism 9 and an ocular 15 in order from an object side. By such constitution, two prisms, that is, the 1st prism 8 and the 2nd prism 9 are used and a distance from the image surface 7 of the objective lens system to the ocular system is shortened in the reversal optical system constituted by using a pentagonal prism in the conventional manner, so that the compact finder optical system having high finder magnification is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finder optical system and its inverting optical system, and more particularly to a small finder optical system used for a lens shutter camera, a still video camera and the like and its inverting optical system.

[0002]

2. Description of the Related Art Conventionally, there are two types of finder optical systems, a real image type finder and a virtual image type finder. Compared to the virtual image finder, the real image finder
The field-of-view frame is clearly visible, and in the virtual image finder, the semi-transparent mirror necessary for splitting the luminous flux is not provided in the real image finder, so that there is an advantage that a bright field of view can be obtained.

Such a real image finder generally comprises an objective lens system, a reversing optical system, and an eyepiece lens system from the object side. The real image formed by the objective lens system is vertically and horizontally reversed by the reversing optical system. To obtain an upright image. As the reversing optical system, there are a reversing optical system and a re-imaging system using a relay system. However, when a relay system is used, the optical path length becomes long, so that compactness is lacking. Therefore, an inversion optical system based on a reflection optical system is often adopted.

As an inversion optical system using a reflection optical system, there are a type using a Porro prism and a type using a penta roof prism.

FIG. 20 is a perspective view showing a conventional example of a finder optical system using the Porro prism 116 as an inverting optical system. The finder optical system comprises, in order from the object side, an objective lens system 111 having a positive refractive power as a whole, a Porro prism 116, an eyepiece lens 117 having a positive refractive power, and a pupil plane 118. Porro prism 116 is the first
Reflective surface 112, second reflective surface 113, third reflective surface 114,
It has a fourth reflecting surface 115. Here, in the coordinate system, the direction in which the light beam enters the objective lens is the X direction, the upper direction is the Y direction when viewed from the object side in a plane perpendicular to X, and Y is 9 clockwise.
The direction rotated by 0 ° is defined as the X direction.

From objective lens 111 to Porro prism 116
The light flux incident on the positive X direction is reflected by the first reflecting surface 112 in the negative Y direction, by the second reflecting surface 113 in the negative Z direction, and by the third reflecting surface 114 in the positive Y direction. The light is reflected by the four-reflecting surface 115 in the same positive X direction as the incident direction, passes through the eyepiece lens 117, and reaches the pupil plane 118.

Therefore, the viewfinder optical system using the Porro prism requires a large space in both the YZ direction, and therefore has a layout limitation of the viewfinder and has a great influence on the camera size.

FIG. 21 shows a conventional example of a finder optical system using a penta roof prism as an inverting optical system.
1 (a) is a perspective view and FIG. 21 (b) is a top view. The finder optical system includes an objective lens system 121 having a positive refractive power as a whole from the object side, a roof prism 123 having a roof reflecting surface 122, a first prism 126 having a first reflecting surface 124, and a second reflecting surface 125, and an eyepiece lens. 12
7, pupil plane 128. In addition, the same coordinate system as that described in the conventional example using the Porro prism is defined.

From objective lens 121 to roof prism 123
The light beam incident on the X-positive direction is inverted and reflected in the X-positive direction by the roof reflection surface 122, forms an image on the image surface 129 once, and is then rotated counterclockwise in the X-direction by the first reflection surface 124 in the XZ plane. It is reflected in the direction rotated by 135 ° to the second reflection surface 1
The light is reflected in the positive X direction at 25, passes through the eyepiece lens 127, and reaches the pupil plane 128. Therefore, the luminous flux is all X
Proceed in the Z plane.

In such a finder optical system using the penta roof prism, the reflecting directions of the respective reflecting surfaces are on the same plane, so that it can be made compact in either YZ direction. Therefore, it is suitable for a camera that is required to be downsized.

By the way, in recent cameras, in order to achieve high quality and high quality, a viewfinder having a high magnification even with a compact body is desired. Here, the finder magnification of the real image formula is approximately the following formula (A)
Is represented by .GAMMA..apprxeq.fo / fe (A) where: .GAMMA .: real image finder magnification, fo: focal length of objective lens system, fe: focal length of eyepiece system.

From the formula (A), in order to realize a high-magnification viewfinder optical system, the focal length of the objective lens system must be increased,
Alternatively, it is necessary to shorten the focal length of the eyepiece lens system.

However, if the focal length of the objective lens system is lengthened, the total length of the objective lens system becomes longer and the finder optical system becomes larger. Therefore, in order to achieve a compact viewfinder with high magnification, the focal length of the eyepiece lens system must be shortened. The focal length of the eyepiece lens system is described by the following equation (B). fe≈ (1000 × S) / (S × λ−1000) (B) where S: distance between the principal point of the eyepiece lens system and the objective image plane, λ: diopter, fe: focal length of the eyepiece lens system Therefore, in order to shorten the focal length of the eyepiece lens system, as can be seen from the above equation (B), the distance between the eyepoint lens system principal point position and the image plane of the objective lens system may be shortened.

[0014]

However, in the conventional penta roof prism type, the two plane reflecting portions are arranged between the roof reflecting surface and the eyepiece lens, and the light flux is bent by 270 °. The distance between the image planes of the objective lens system could not be shortened, and a finder optical system with high magnification could not be realized.

An object of the present invention is to solve the above problems and provide a compact finder optical system having a high finder magnification and its inverting optical system.

[0016]

In order to achieve the above object, therefore, in the inverting optical system of the finder optical system according to the invention described in claim 1, the light beams from the object side are arranged in order from the object side. To the object side, and a first reflecting surface for temporarily reflecting the light flux from the roof reflecting surface toward the object side, and the first reflecting surface are arranged at an acute angle, and the light flux from the first reflecting surface is reflected. A second reflecting surface for reflecting the light toward the pupil surface side;
A prism and a first reflecting surface of the first prism, which are arranged substantially parallel to each other, and a first transmitting surface which transmits a light beam reflected by the second reflecting surface of the first prism and emitted from the first reflecting surface; A second prism having a second transmitting surface which is arranged at an acute angle to the first transmitting surface and which transmits a light beam parallel to the light beam incident on the roof reflecting surface is provided.

The reversing optical system of the finder optical system according to a second aspect of the present invention is the reversing optical system of the finder optical system according to the first aspect, which comprises a light beam incident on the roof reflecting surface and a light beam reflected by the roof reflecting surface. The angle θ and the angle χ formed by the first transmitting surface and the second transmitting surface of the second prism satisfy the following expression. 125 ≦ θ + χ ≦ 180-arc sin (NA / N
1) χ <arc sin (NA / N) Further, in the inverting optical system of the finder optical system according to the invention of claim 3, in the inverting optical system of the finder optical system of claim 1, the roof reflection surface is It is a reflecting surface of a roof prism.

The inverting optical system of the finder optical system according to the invention of claim 4 is the inverting optical system of the finder optical system of claim 1, wherein the first reflecting surface of the first prism and the second prism are It is characterized in that the distance d between the first transmitting surfaces satisfies the following relationship. 0 <d ≦ 0.05 However, the unit is mm.

According to a fifth aspect of the present invention, there is provided an inverting optical system of the finder optical system according to the fourth aspect, wherein the first reflecting surface of the first prism and the second prism are the same as the first reflecting surface of the first prism. It is characterized in that the member is coated to a thickness d at a position where the effective light flux does not pass through on one of the peripheral edges of the first transmitting surface.

The inversion optical system of the finder optical system according to the invention of claim 6 is the inversion optical system of the finder optical system according to claim 4, wherein the first reflecting surface of the first prism and the second prism are A spacer member having a thickness d is provided on the peripheral portion between the first transmitting surfaces where the effective light flux does not pass,
It is characterized by.

The inversion optical system of the finder optical system according to the invention of claim 7 is the inversion optical system of the finder optical system according to claim 4, wherein the first reflecting surface of the first prism and the second prism are It is characterized in that a protrusion having a thickness d is provided at a position where an effective light beam does not pass through the peripheral portion of any one of the first transmitting surfaces.

According to an eighth aspect of the present invention, there is provided the inverting optical system of the finder optical system according to the first aspect, wherein the first reflecting surface of the first prism or the second prism is the inverting optical system of the finder optical system. Of at least two layers having the uppermost layer made of silicon dioxide and the lowermost layer made of a dielectric material are added to at least one of the first transmission surfaces of the above.

According to a ninth aspect of the present invention, there is provided the inverting optical system of the finder optical system according to the first aspect, wherein the first prism is on the second reflecting surface of the first prism. Is provided with a notch at a position farthest from the surface on which the luminous flux is incident and where the effective luminous flux is not reflected.

The inversion optical system of the finder optical system according to the invention of claim 10 is the inversion optical system of the finder optical system according to claim 1, wherein
It is characterized in that a projection is provided at a position on the reflection surface that is farthest from the surface on which the light beam enters the first prism and the effective light beam is not reflected, and a light-shielding member is applied to an end surface of the projection.

The inverting optical system of the finder optical system according to the present invention is characterized in that the second reflecting surface of the first prism has an optical film for correcting the color of the image of the finder. To do.

The inversion optical system of the finder optical system according to the invention of claim 12 is the inversion optical system of the finder optical system according to claim 1, wherein the first and second prisms both have a refractive index of 1. It is 6 or less.

The finder optical system according to a thirteenth aspect of the invention is an objective lens system having a positive refracting power as a whole from the object side, and a roof prism for reflecting the first light flux from the objective lens system. A first reflecting surface for temporarily reflecting the light beam from the roof prism toward the object side;
A first prism of a substantially triangular prism shape having a side surface of a second reflecting surface, which is arranged at an acute angle with the reflecting surface and reflects the light flux from the first reflecting surface toward the pupil surface, and a first prism of the first prism. 1
The second prism of the first prism is arranged substantially parallel to the reflecting surface.
The first transmission surface that transmits the light flux that has passed through the first reflection surface after being reflected by the reflection surface and the first transmission surface are arranged at an acute angle, and the light flux that is parallel to the light flux that is incident on the roof prism is transmitted. It is characterized by comprising a second prism having a substantially triangular prism shape having a second transmitting surface to be a side surface, and an eyepiece system having a positive refracting power as a whole.

A finder optical system according to a fourteenth aspect of the present invention is the finder optical system according to the thirteenth aspect, wherein the second transmitting surface of the second prism has a positive refracting power. To do.

A finder optical system according to a fifteenth aspect of the present invention is characterized in that, in the finder optical system according to the thirteenth aspect, a surface of the first prism on which a light beam enters has a positive refractive power. And

A finder optical system according to a sixteenth aspect of the present invention is the finder optical system according to the thirteenth aspect, wherein the exit surface of the roof prism has a positive refracting power.

A finder optical system according to a seventeenth aspect of the present invention is the finder optical system according to the thirteenth aspect, wherein the finder optical system is provided between the roof prism and the first prism and has a positive refractive power in order from the object side. A first surface having
A condenser lens having a flat second surface, a light emitting element provided opposite to the edge surface of the condenser lens, and an incident light formed at a position facing the light emitting element on the edge surface of the condenser lens. Surface and a peripheral edge portion of the first surface of the condenser lens where the first light flux does not pass, the second light flux incident from the light emitting element through the entrance surface is provided at a position facing the entrance surface, and the roof light is reflected by the roof light. A reflecting surface for reflecting the first light flux reflected by the surface substantially parallel to the first light flux, and a peripheral portion of the second surface of the condenser lens where the first light flux does not pass, and have a positive refracting power provided so as to face the reflecting surface. And a lens portion.

The finder optical system according to the invention of claim 18 is the finder optical system according to claim 13, which is provided between the roof prism and the first prism and has a positive refractive power in order from the object side. A first surface having
A condenser lens having a flat second surface, and between the condenser lens and the first prism, in a peripheral portion where the first light flux emitted from the second surface of the condenser lens does not pass, and toward the first light flux. The second luminous flux is provided between the condenser lens and the first prism at a peripheral portion between the condenser lens and the first prism where the first luminous flux emitted from the second surface of the condenser lens does not pass through. And a reflecting surface that reflects the first light flux emitted from the surface substantially in parallel with the first light flux.

A finder optical system according to a nineteenth aspect of the present invention is the finder optical system according to the thirteenth aspect, wherein the finder optical system is in the vicinity of the second reflecting surface of the first prism,
A light emitting element that emits a second light flux, and a first light from the light emitting element.
A reflecting surface that reflects the light beam and that is incident substantially parallel to the first light beam reflected by the second reflecting surface of the first prism on the peripheral portion of the first prism where the first light beam does not pass. Characterize.

Further, in the finder optical system according to the invention of claim 20, in order from the object side, an objective lens system having a positive refracting power as a whole, and a roof reflecting surface for reflecting the light flux from the objective lens system. , A first reflecting surface that temporarily reflects the light beam from the roof reflecting surface toward the object side, and the first reflecting surface are arranged at an acute angle, and reflect the light beam from the first reflecting surface toward the pupil plane side. A second prism that allows a part of the light flux to pass therethrough;
Is arranged substantially parallel to the first reflecting surface of the first prism,
The first transmission surface, which transmits the light flux reflected by the second reflection surface of the first prism and transmitted through the first reflection surface, and the first transmission surface are arranged at an acute angle, and are incident on the roof reflection surface. A second transmission surface that transmits a light beam parallel to the light beam, a second prism having a substantially triangular prism shape having a side surface, and an eyepiece system having a positive refracting power as a whole are provided. It is characterized in that a condenser lens having a positive refractive power and a photometric element are provided in this order from the side closer to the second reflecting surface on the optical axis of the emitted light flux.

A finder optical system according to a twenty-first aspect of the present invention is the finder optical system according to the twentieth aspect, which is provided so as to face the second reflecting surface of the first prism and is in the vicinity of the condenser lens. And a light emitting element that emits a second light flux that is incident on a peripheral portion of the first prism where the first light flux does not pass, in substantially parallel to the first light flux that is reflected by the second reflecting surface of the first prism. It is characterized by having.

Further, in the finder optical system according to the twenty-second aspect of the present invention, a roof reflection surface for reflecting a light beam from the object side and a light beam from the roof reflection surface are totally reflected to the object side in order from the object side. An inversion optical system of a finder optical system, comprising: a first surface; and a second surface that reflects the light flux from the first surface toward a pupil plane, wherein the light flux reflected by the second surface is It is characterized by transmitting through one surface.

[0037]

In the reversing optical system of the finder optical system according to claim 1 configured as described above, the light beam incident on the roof reflecting surface is reflected in one direction by the roof reflecting surface and is incident on the first prism. Then, the light is reflected by the first reflecting surface, further reflected by the second reflecting surface, and is sequentially transmitted through the first transmitting surface and the second transmitting surface of the second prism to be emitted, so that the roof reflecting surface and the first prism When used in a real image finder optical system in which a light beam is once formed, the light beam emitted from the second prism is an erect image having the same direction as the light beam incident on the roof reflection surface.

Further, in the inverting optical system of the finder optical system described in claim 2, the angle θ formed by the light beam reflected by the roof reflecting surface is formed.
And the angle χ formed by the first transmitting surface and the second transmitting surface of the second prism.
Since the angle θ of deflection of the light beam on the roof reflecting surface becomes a value in the vicinity of 90 ° by defining the relationship of
When the incident angle α to the reflecting surface is a value in the vicinity of 45 ° and the light flux is first incident on the first reflecting surface of the first prism, it is totally reflected, and the light flux is incident on the first transmitting surface of the second prism. In the case where the above conditions are satisfied, each of the three prisms can be compactly arranged under the condition that the total reflection is not performed.

Further, in the inverting optical system of the finder optical system according to the third aspect, the roof reflecting surface is made compact by using the roof reflecting surface as the reflecting surface of the roof prism.

Further, in the inverting optical system of the finder optical system according to claim 4, since the range of the distance d between the second reflecting surface of the first prism and the first transmitting surface of the second prism is defined, the normal light flux The deviation of the ghost can be reduced, and the difference in the optical path length from the emission of the light flux from the second reflecting surface to the pupil surface can be reduced.

Further, in the inverting optical system of the finder optical system according to any one of claims 5 to 7, the first reflecting surface of the first prism and the first transmitting surface of the second prism are provided at their peripheral portions where the effective light beam does not pass. The inversion optical system of the finder optical system according to claim 5 is formed by coating a member, and the inversion optical system of the finder optical system according to claim 6 is held by a spacer member. In the inverting optical system of the finder optical system, by providing a protrusion on either one of the peripheral edge portions, the distance between the first reflecting surface of the first prism and the first transmitting surface of the second prism is set to a desirable range of d. Easy to hold.

Further, in the inversion optical system of the finder optical system according to claim 8, at least one of the first reflecting surface of the first prism and the first transmitting surface of the second prism has a top layer of silicon dioxide and a bottom layer. By adding at least two or more optical films made of a dielectric material, the reflectance of the light flux is reduced on the two surfaces.

In the reversing optical system of the finder optical system according to the ninth and tenth aspects, scratches and smears are applied on the second reflecting surface of the first prism at a position farthest from the surface on which the light beam is incident. By providing the projection, when the ghost light generated by the reflection inside the first prism reaches the sharpening and the smear-coated projection, the ghost light cannot be reflected in the effective optical path, so that the ghost light is reflected by the eyepiece lens system. Do not let it penetrate in the direction.

In the reversing optical system of the finder optical system according to the eleventh aspect, when the light flux is reflected by the second reflecting surface of the first prism, the color tone of the image can be corrected by the added optical film.

Further, in the inverting optical system of the finder optical system according to the twelfth aspect, since the refractive indexes of the first and second prisms are both 1.6 or less, refraction on each surface of each prism is achieved. The reflectance of the light flux can be reduced.

Further, in the finder optical system according to the thirteenth aspect, the light flux emitted from the objective lens system is incident on the roof reflecting surface and is reflected and reflected in one direction by the roof reflecting surface, so that the roof reflecting surface and the first prism are formed. In between, the luminous flux forms an image once and then the first
The light enters the prism, is reflected by the first reflecting surface, and then is reflected by the second
It has a function of being reflected by the reflecting surface, sequentially passing through the first transmitting surface and the second transmitting surface of the second prism, and then through the eyepiece lens system to reach the pupil plane. Therefore, the light beam emitted from the eyepiece lens system becomes an erect image having the same direction as the light beam incident on the objective lens.

Further, in the finder optical system according to claim 14, since the second transmitting surface of the second prism is a spherical surface or an aspherical surface having a positive refractive power, the function of the eyepiece lens system is added to the third transmitting surface. it can.

In the finder optical system according to the fifteenth and sixteenth aspects, since the first transmitting surface of the first prism or the exit surface of the roof prism is a spherical surface or an aspherical surface having a positive refractive power, the first prism It is possible to add the function of a condenser lens to the entrance surface of and the exit surface of the roof prism.

Further, in the finder optical system according to the seventeenth aspect, the luminous flux emitted from the light emitting element enters the inside of the lens through the incident portion provided on the edge surface of the condenser lens and is reflected by the reflecting surface. The light enters the prism, is reflected by the first reflection surface, is further reflected by the second reflection surface, is transmitted through the first transmission surface and the second transmission surface of the second prism in order, and is transmitted through the eyepiece lens system to the pupil surface. Reach

Further, in the finder optical system according to the eighteenth aspect, the light flux emitted from the light emitting element is deflected by the reflecting surface,
The light enters the first prism, is reflected by the first reflecting surface, is further reflected by the second reflecting surface, is transmitted through the first transmitting surface and the second transmitting surface of the second prism in order, and is transmitted through the eyepiece lens system to form the pupil. To the surface.

In the finder optical system according to the nineteenth aspect, the light flux emitted from the light emitting element is deflected by the reflecting surface,
The light enters the first prism from the second reflecting surface, sequentially passes through the first transmitting surface and the second transmitting surface of the second prism, passes through the eyepiece lens system, and reaches the pupil surface.

Further, in the finder optical system according to the twentieth aspect, after the light beam is reflected by the first reflecting surface of the first prism, the second reflecting surface has a semi-transmissive property. Is transmitted without being reflected by the second reflecting surface, and is condensed on the photometric element by the condenser lens having a positive refractive power.

Further, in the finder optical system according to the twenty-first aspect, since the light flux emitted from the light emitting element is semi-transparent on the second reflection surface, the light flux enters the inside of the first prism from the second reflection surface. Then, the light is transmitted through the first transmitting surface and the second transmitting surface of the second prism in order, and then through the eyepiece lens system to reach the pupil plane.

Further, in the inverting optical system of the finder optical system according to claim 22, the light beam incident on the roof reflecting surface is reflected in one direction by the roof reflecting surface, and then the first surface and the second surface are sequentially arranged. Since it is reflected, when used in a finder optical system that temporarily forms an image between the roof reflecting surface and the first surface, the light beam emitted from the second reflecting surface has the same direction as the light beam entering the roof reflecting surface. It becomes an erect image.

[0055]

EXAMPLE A finder optical system according to the present invention and a first example thereof will be described below.

FIG. 1 is a first viewfinder optical system of the present invention.
It is a top view which shows an Example. Here, in the coordinate system, the direction in which the light beam enters the objective lens is the X direction, the upward direction when viewed from the object side in the plane perpendicular to X is the Y direction, and Y is 90 ° clockwise.
The rotated direction is defined as the Z direction.

In FIG. 1, in order from the object side, the objective lens 1, the diaphragm 2, the roof prism 3, the condenser lens 5, the first prism 8 and the second prism 9, which have positive power as a whole, have positive power as a whole. Eyepiece 1
5, the pupil plane 18 is arranged. The symmetry line of the roof reflecting surface 4 in the roof prism 3 is arranged substantially parallel to the XZ plane,
The roof reflection surface 4 is arranged so that a light beam incident in the positive X direction is reflected in a direction forming an angle θ with the incident light beam in the XZ plane. Further, the condenser lens 5 has a first surface 17 having a positive refracting power in order from the object side and a second surface 18 which is a flat surface, and is arranged perpendicular to the optical axis of the light flux from the roof reflecting surface 4. . A field frame 6 is provided on the condenser lens 5, and an image plane 7 of the objective lens system is provided near the second surface 18. The first prism 8 is the second surface 1 of the condenser lens 5.
8, the incident surface 10 arranged substantially in parallel with the incident surface 10, the light flux incident on the incident surface 10 at an acute angle and the incident angle α
The first reflecting surface 11 and the first reflecting surface 1 arranged in a
1 is an acute angle, and the luminous flux reflected by the first reflecting surface 11 is X
Second reflecting surface 1 arranged so as to reflect in the positive direction
2 and has a substantially triangular prism shape having side surfaces of the first reflecting surface 11 and the second reflecting surface 12. The second prism 9 has a first transmitting surface 13 arranged substantially parallel to the first reflecting surface 11, and a second transmitting surface 14 forming an acute angle χ with the first transmitting surface 13 and parallel to the YZ plane. Having a first transparent surface 13 and a second transparent surface 1
It has a substantially triangular prism shape having 4 as a side surface. Table 1 shows values of the constants defined in the present invention in Example 1.

[0058]

[Table 1]

Here, θ: angle formed by the light beam incident on the roof reflecting surface and the light beam reflected by it, α: incident angle of the light beam on the first reflecting surface of the first prism, χ: first transmitting surface of the second prism And the second transmission surface, N1: refractive index of the first prism, N2: refractive index of the second prism, NA: refractive index of air, a: arc sin (NA / N), d: first prism 8 The first reflecting surface 11 and the second prism 9 of
The distance between the first transmitting surfaces 13 of

In FIG. 1, the light flux incident from the subject passes through the objective lens 1 having a positive power as a whole and is incident on the roof reflection surface 4 in the roof prism 3. The light flux is reflected by the roof prism 3 and is once focused on the image plane 7 near the second surface 18 of the condenser lens 5. Then, the light beam is incident on the incident surface 10 of the first prism 8 and the first reflecting surface 1
The light is reflected by the first and second reflection surfaces 12. Second of the first prism 8
The light flux reflected by the reflecting surface 12 is the first light beam of the first prism 8.
The first transmitting surface 1 of the second prism 9 is transmitted through the reflecting surface 11.
3, the light enters the third transmission surface 14, passes through the eyepiece lens 15, and reaches the pupil surface 16. The eyepiece lens 15 has a positive power as a whole and magnifies the image formed by the objective lens 1.

This embodiment is different from the conventional penta roof prism type shown in FIG. 21 in the image plane 7 of the objective lens system.
And the distance between the eyepieces can be reduced. Less than,
This point will be described in detail.

FIG. 2A is an enlarged view of the penta prism 126 showing how the light flux is reflected by the penta roof prism type shown in FIG. Penta prism 126
Is the incident surface 51, the first reflecting surface 124, the second reflecting surface 12
5, it has an emission surface 52. Inside the pentaprism 126, a light beam having a width a enters from the incident surface 51, is reflected in the order of the first reflecting surface 124 and the second reflecting surface 125, and is emitted from the emitting surface 52. In the case of FIG. 2A, the angle α at which the light flux enters the first reflecting surface 124 and the second reflecting surface 125 is approximately 22.5 °.
Becomes

On the other hand, FIG. 2B is an enlarged view of the first prism 8 and the second prism 9 showing how the light beam is reflected in the first embodiment shown in FIG. In the prism configuration using the first prism 8 and the second prism 9, the light flux having the width a is reflected in the order described with reference to FIG. In the above case, the angle α at which the light beam enters the first reflecting surface 11 is approximately 47.5 °.

FIGS. 3A to 3C show optical paths (solid lines) when a light beam having a constant width is incident on the plane reflecting portion 130 at various angles. In the figure, the range of the light flux indicated by the dotted line shows the range in which the parallel light flux incident on the plane reflecting portion 130 can be taken out as it is after being reflected, and the thick line indicates the optical axis within the above range. Shows. That is, the length of the thick line corresponds to the minimum required optical path length (required optical path length) for the flat reflecting portion. As shown in the figure, even if the incident angle α between the flat reflector 130 and the light flux is too large (see FIG.
(C)) Also, if it is too small (FIG. 3A), the required optical path length becomes long, and when the angle α is 45 ° (FIG. 3B), the required optical path length becomes the shortest. The above is not limited to the case of parallel light flux.

From this, the required optical path length of the first reflecting surface 11 of the present embodiment (FIG. 2B) where the incident angle α of the light flux with the first reflecting surface 11 is close to 45 ° is the same as that of the conventional example. First reflecting surface 12
It can be seen that it is shorter than the required optical path length of 4. Therefore,
The distance between the first reflecting surface 11 and the second reflecting surface 12 in this embodiment can be made shorter than the distance between the first reflecting surface 124 and the second reflecting surface 125 in the conventional example.

From the above description, comparing the conventional example shown in FIG. 21 with the finder optical system of the embodiment of the present invention shown in FIG. 1, the optical path length to the image plane of the objective lens system is the same as that of the conventional example. Since the example is almost the same, it is understood that the example in which the distance between the image plane 7 of the objective lens system and the eyepiece lens 15 can be shortened is a compact and high-magnification viewfinder optical system.

Next, desirable conditions for the roof reflecting surface, the first prism and the second prism will be described.

It is desirable that the angle θ formed by the light beam incident on and the light beam reflected by the roof reflection surface 4 and the angle χ formed by the second transmission surface and the third transmission surface of the second prism 9 satisfy the following conditions. .

125 ≦ θ + χ ≦ 180−arc sin (NA / N1) (1) χ <arc sin (NA / N) (2) Where, N1: refractive index of the first prism, N Is the refractive index value of the refractive index N1 of the first prism or the refractive index of the second prism N2, whichever is not larger, NA: the refractive index of air.

First, the upper limit of equation (1) will be described.

As shown in FIG. 2B, the first prism 8
The light beam that first enters the first reflecting surface 11 from the incident surface 10 of the above must be totally reflected by the first reflecting surface 11. First
The condition for total reflection of the light beam incident on the reflecting surface 11 at the incident angle α is expressed by the following equation. α ≧ arc sin (NA / N1) ... (c) Further, from the geometrical relation, if α is represented by θ and χ, α = 180−θ−χ ... (d), which is ( Substituting into equation (c), we obtain θ + χ ≦ 180−arc sin (NA / N1).

Therefore, the upper limit of θ + χ in the equation (1) indicates the condition that the light beam is totally reflected by the first reflecting surface 11 of the first prism 8. If the range exceeds this range, the light beam is reflected by the first reflecting surface 1
1 is transmitted.

Next, the lower limit of equation (1) will be described.

FIGS. 4A to 4C show optical paths (solid lines) when light beams having a constant width are made incident on the roof reflecting portion 140 at various angles. As in the case of FIG. 2, the thick line indicates the required optical path length. As shown in the figure, for parallel light fluxes in the same range, the angle of incidence β of the light flux on the roof reflector 140
Is 45 ° (when the angle θ between the incident light flux and the outgoing light flux at the roof reflector is 90 °) (FIG. 4B), the required optical path length is the shortest.

If the angle β is made larger than 45 °, in other words, if the angle θ is made larger than 90 °, the optical path length at the roof reflection surface becomes large, and the focal length of the objective lens 1 must be made long. If the focal length of the objective lens 1 becomes long, a compact viewfinder optical system cannot be realized.

On the other hand, if the angle θ is smaller than 90 °, the roof reflector 140 can be made smaller. FIG. 5 is an enlarged view of the roof prism 3, the first prism 8 and the second prism 9 when the angle θ is smaller than 90 ° in FIG. As shown in the figure, when the angle θ is smaller than 90 °, the incident angle α of the light flux with the first reflecting surface 11 of the first prism 8 becomes smaller than 45 °, so that the first prism 8 is enlarged in the Y direction. There must be. If the first prism 8 is large, a similarly compact finder optical system cannot be realized.

In order to prevent the first prism 8 from becoming too large in the Z direction, it is desirable that the angle α is not larger than 55 °. Therefore, α ≦ 55 (e). From this and the relationship of the equation (d), 125 ≦ θ + χ is obtained. Therefore, the lower limit of equation (1) is obtained.

Next, the range of equation (2) will be described.

In the structure of the prism according to the present invention shown in FIG. 2B, the light flux is the first reflection surface 1 of the first prism 8.
When entering 1, the first reflection surface 11 should not be totally reflected. Since the light flux is incident on the first reflecting surface 11 at an angle χ, the condition for total reflection of the light flux is expressed by the following equation. χ <arc sin (NA / N1) (f) Therefore, the range of the equation (f) is the first reflection surface 1 of the first prism 8.
A value of 1 indicates that the light beam is not totally reflected. If the light beam exceeds this range, the light beam is reflected by the first reflecting surface 11. Further, when the light flux is incident on the first transmission surface 13 of the second prism 9, it must not be totally reflected by the first transmission surface 13. The condition for totally reflecting the light beam incident on the first transmission surface 13 at the incident angle α is expressed by the following equation. χ <arc sin (NA / N2) (g) Therefore, the range of the expression (g) is the first transmission surface 1 of the second prism 9.
3 shows the condition that the light beam is not totally reflected, and when it exceeds this range, the light beam is reflected by the first transmitting surface 13. Therefore, in order to satisfy both the expressions (f) and (g), the following expression (2) may be satisfied. χ <arc sin (NA / N) (2) Next, a desirable distance d between the first reflecting surface of the first prism and the first transmitting surface of the second prism, which are arranged substantially in parallel, will be described. .

It is desirable that the distance d between the first reflecting surface of the first prism and the first transmitting surface of the second prism satisfies the following expression (3). 0 <d ≦ 0.05 (3) However, the unit is mm.

In the prism structure of the present invention as shown in FIG. 2B, the first reflecting surface 1 of the first prism 8 is formed.
At 1, the light flux from the first transmission surface 10 must be totally reflected. Therefore, the first reflecting surface 11 of the first prism 8
Therefore, the distance d between the second transmitting surfaces 13 of the second prism 9 cannot be set to 0, and the lower limit of d in the equation (3) is defined.

The upper limit of equation (3) is defined as follows.

FIG. 6 shows a first prism 8 and a second prism 9.
FIG. 3 is a schematic diagram showing surface reflection and ghost light that occur at the surface spacing of FIG. In FIG. 6, a normal light beam is refracted when emitted from the first reflecting surface 11 of the first prism 8, and further refracted by air and the second transmitting surface 13 of the second prism 9, and travels in the second prism 9. To do. However, when a normal light beam enters the second prism 9, a part of the light beam is emitted from the first prism of the second prism 9.
The light is reflected on the transmitting surface 13 and becomes a ghost shown by a dotted line in the figure, and travels in the second prism 9. The ghost doubles the image, degrading the performance of the finder optics.
Therefore, in order not to separate the ghost and the ordinary light flux, the first reflecting surface 11 of the first prism 8 and the second prism 9
It is preferable that the distance d between the first transmission surfaces 13 of 1 is small.

In the prism structure of the present invention as shown in FIG. 1, the optical path length from the exit of the first reflecting surface 11 to the pupil surface 16 is different at the left and right ends of the light beam. Therefore, when the eyes are moved left and right on the pupil plane, the aberration of the finder optical system changes. Aberration fluctuations degrade the performance of the finder optical system. This variation in aberration is caused by the first reflection surface 11 of the first prism 8 and the first reflection surface 11 of the second prism 9.
The smaller the distance d between the transmitting surfaces 13, the smaller the distance.

From the above, the distance d must be smaller than the upper limit value 0.05 mm defined by the equation (3) in consideration of the influence of the ghost and the allowable fluctuation of the aberration.

FIG. 7 shows a first prism 8 and a second prism 9.
It is a figure which shows an example of the holding | maintenance method in the case of hold | maintaining at the said space | interval d. In the example of FIG. 7, a suitable material is applied to the area 20, which is the peripheral portion of either one of the first reflecting surface 11 of the first prism 8 and the first transmitting surface 13 of the second prism 9 that does not transmit the effective optical path. The coating is performed to a thickness within the range of the distance d. Such coating may be applied to either the first prism 8 or the second prism 9. Further, it may be held in the region 20 via a spacer member having a thickness within the range of the distance d. If the coating and the spacer member are made of a light-shielding material, the first reflecting surface and the second
Another ghost generated on the reflecting surface can be shielded.

FIG. 8 shows a first prism 8 and a second prism 9.
FIG. 8 is a diagram showing another example of a holding method in the case where is held at the interval d. In the example of FIG. 8, the height (3) is added to the peripheral portion of the first transmission surface 13 of the second prism 9 where the effective optical path does not pass.
The protrusion 21 which is the range of a formula is provided. And the protrusion 21
And the first reflecting surface 11 of the first prism 8 are in pressure contact with each other. In FIG. 8, the protrusion 21 is integrally formed with the second prism 9, but it may be provided on the first prism 8 or both the first prism 8 and the second prism 9.

Further, in order to prevent the above-mentioned ghost, at least one of the first reflecting surface 11 of the first prism 8 and the first transmitting surface 13 of the second prism 9 has the uppermost layer of silicon dioxide and the uppermost layer. It is effective to add at least two or more antireflection films whose lower layers are made of a dielectric material, because they prevent surface reflection.

In addition to the above-mentioned causes, the ghost is caused by reflected light from various surfaces. 9 (a)-(c)
FIG. 6 is a diagram showing an example in which a light blocking portion is provided on the first prism 8 in order to prevent a ghost that occurs on the second reflecting surface 12 of the first prism 8. In FIG. 9A, a V-groove notch 22 is provided at a position distant from the incident surface 10 where the effective light flux of the second reflecting surface 12 is not reflected. 9 (b) and 9
Similarly, (c) shows the projection 23 and the projection 23 ′ at positions apart from the incident surface 10 where the effective light flux of the second reflecting surface 12 is not reflected.
Is provided. The end face of the protrusion 23 parallel to the second reflecting surface 12 and the end face of the protrusion 23 'which is distant from the first transmitting surface 10 are smeared to have a light shielding function. In the three examples above,
It is possible to prevent unnecessary ghosts repeatedly reflected by the first reflecting surface 11 and the second reflecting surface 12 of the first prism 8 from entering the eyepiece lens system.

If an optical film for correcting the color of the finder image is added to the second reflecting surface 12 of the first prism 8, a preferable image can be obtained on the pupil plane 16.

Next, desirable refractive indexes of the first prism and the second prism will be described.

FIG. 10 is a graph showing the relationship between the surface reflectance and the incident angle of the light beam and the refractive index of the medium.
In the graph of FIG. 10, the horizontal axis represents the d-line refractive index Nd of the prism medium, and the vertical axis represents the surface reflectance of the incident light beam. In the graph, each line shown by a black square, a black rhombus, etc. The refractive index and the surface reflectance corresponding to the luminous flux incident at the angle A defined in FIG. 11 are represented.

As can be seen from the graph, the reflectance of the surface becomes higher as the refractive index of the medium becomes higher. Therefore, when the prism medium is selected, it is preferable to select a medium having a low reflectance and a low refractive index because the reflected light on the surface causes a ghost as described above. Considering the ghost that is allowed in the actual viewfinder optical system, the first and second
The refractive indices N1 and N2 of the prism are preferably such that the reflectance is 6 to 7% or less when the angle α is around 45 °. Therefore, N1 and N2 must have a value smaller than 1.6.

The second to the second aspects of the finder optical system of the present invention will be described below.
A ninth embodiment will be described. In these examples, the basic configuration and the operation of the optical system are the same as those in the first example, so only the parts different from the first example will be described, and the duplicate description will be omitted. Further, in each embodiment, the coordinate system is defined as in the first embodiment.

FIG. 12 is a top view showing a second embodiment of the finder optical system of the present invention. In the second embodiment, the second transmitting surface 24 of the second prism 9 is a lens surface having the function of an eyepiece lens having a positive refractive power. A spherical surface may be used as such a lens surface, but an aspherical surface can further improve optical performance. Second
In the embodiment, since the second transmitting surface 24 of the second prism 9 has the function of the eyepiece lens, the space required for the eyepiece lens can be omitted and a compact viewfinder optical system can be realized.

FIG. 13 is a top view showing a third embodiment of the finder optical system of the present invention. In the third embodiment, the entrance surface 25 of the first prism 8 is a lens surface added with the function of a condenser lens having a positive refractive power. A spherical surface may be used as such a lens surface, but an aspherical surface can further improve optical performance. In the third embodiment, since the entrance surface of the first prism 8 has the function of a condenser lens, the space required for the condenser lens can be omitted and a compact finder can be realized.

FIG. 14 is a top view showing a fourth embodiment of the finder optical system of the present invention. In the fourth embodiment, the exit surface 26 of the roof prism 3 is a lens surface added with the function of a condenser lens having a positive refractive power. A spherical surface may be used as such a lens surface, but an aspherical surface can further improve optical performance. In the fourth embodiment, since the exit surface of the roof prism 3 has the function of a condenser lens, the space required for the condenser lens becomes small and a compact finder can be realized.

FIG. 15 is a top view showing a fifth embodiment of the finder optical system of the present invention. In the fifth embodiment, the second reflecting surface 27 of the first prism 8 is semi-transparent. Then, on the optical axis of the transmitted light flux transmitted from the second reflecting surface 27,
A condenser lens 28 having a positive refractive power, a diaphragm 29, and a photometric element 30 are arranged in order from the side closer to the second reflecting surface 27.

In the fifth embodiment, as in the case of the first embodiment, the light flux reflected by the roof reflecting surface 4 enters the entrance surface 10 of the first prism 8, and the first reflecting surface 11 and the second reflecting surface After being reflected by 27, the X direction is inverted and corrected to an erect image, and thereafter, it is incident on the first transmission surface 13 of the second prism 9, transmitted from the second transmission surface 14 through the eyepiece lens 15, and then onto the pupil surface 16. Reach At this time, a part of the light flux incident on the second reflecting surface 27 is transmitted through the second reflecting surface 27, is condensed by the condenser lens 28, is transmitted through the diaphragm 29, and is incident on the photometric element 30.

Therefore, in the fifth embodiment, the finder optical system of the present invention can detect the brightness of the object (hereinafter referred to as TTF photometry) by using the light flux transmitted through the finder.

In the finder optical system, it is necessary to display various information in addition to the image on the finder. An example of performing such an finder display will be described below.

FIG. 16 is a top view showing a sixth embodiment of the finder optical system of the present invention. In the sixth embodiment, the light emitting element 31 is provided to face the edge surface of the condenser lens 5. The condenser lens 5 includes a light emitting element 31.
For reflecting the light flux (second light flux) from the incident surface 32 in a direction substantially parallel to the first light flux at a position where the light flux (first light flux) from the incident surface 32 and the roof prism 3 does not pass through the edge surface in the vicinity. A lens portion 34 is provided at a position facing the reflecting surface 33 and the reflecting surface 33 of the second surface 18, respectively.

In the sixth embodiment, the second light from the light emitting element 31 is used.
The light flux enters the inside of the condenser lens 5 from the incident surface 32, is reflected by the reflecting surface 33 substantially in parallel with the first light flux, passes through the lens portion 34, exits from the condenser lens 5, and enters the first prism 8. . After entering the first prism 8, it passes through the first prism 8, the second prism 9 and the eyepiece lens 15 and reaches the pupil plane 16 in the same manner as a light beam from a normal subject.

The light emitting element 31 can have various arrangements other than the arrangement shown in FIG.

The seventh to ninth embodiments described below are examples in which a light emitting element 31 is added to the finder optical system of the first or fifth embodiment.

FIG. 17 is a top view showing the seventh embodiment. In the seventh embodiment, the reflecting surface 35 and the light emitting element 31 are arranged in the peripheral portion between the condenser lens 5 and the first prism 8 so that the first light flux that passes through the condenser lens 5 does not pass therethrough in the substantially vertical direction from the first light flux. Are arranged.

In the case of the seventh embodiment, from the light emitting element 31 to the first
The second light flux emitted toward the optical axis of the light flux is reflected by the reflecting surface 35.
Is reflected in the direction of the first prism 8, and the first prism 8,
The light passes through the second prism 9 and the eyepiece lens 15 and reaches the pupil plane 16.

FIG. 18 is a top view showing the eighth embodiment. The eighth embodiment is an example in which the light emitting element 31 and the reflecting mirror 36 are arranged on the object side of the first prism 8. In the case of the eighth embodiment, the second light flux emitted from the light emitting element 31 is reflected by the reflecting surface 3
The light is reflected by the first prism 8 toward the first prism 8 and is transmitted through the peripheral portion of the second reflection surface 27 of the first prism 8 where the first light flux is not reflected. At this time, the second light flux travels inside the first prism 8 substantially in parallel with the first light flux. After that, the second light flux passes through the second prism 9 and the eyepiece lens 15 and reaches the pupil plane 16.

FIG. 19 is a top view showing the ninth embodiment. The eighth embodiment is an example in which the light emitting element 31 is arranged in the case of the fifth embodiment having a configuration for performing TTF photometry. In the ninth embodiment, the light emitting element 31 is provided near the condenser lens 28. The second light flux for performing the infinder display is emitted from the light emitting element 31 toward the first prism 8, and passes through the peripheral portion of the second reflecting surface 27 of the first prism 8 where the first light flux is not reflected. At this time, the second light flux travels inside the first prism 8 substantially in parallel with the first light flux. afterwards,
The second light flux passes through the second prism 9 and the eyepiece lens 15 and reaches the pupil plane 16.

As described above, in the sixth to ninth examples, even in the finder optical system using the first and second prisms, the members for performing the infinder display can be efficiently arranged. In the ninth embodiment, TTF photometry can also be performed.

[0111]

As is apparent from the above description, claim 1
The reversing optical system of the finder optical system described is compared with a reversing optical system using a conventional penta roof prism when used in a real image type finder optical system in which a light beam is once formed between the roof reflecting surface and the first prism. Then, it has the same function of making the light beam emitted from the second prism an erect image having the same direction as the light beam incident on the roof reflection surface, while the eyepiece is seen from the image plane of the objective lens system in the reversing optical system. Since the distance to the lens system can be reduced, a compact and high-magnification viewfinder optical system can be realized.

Further, in the inverting optical system of the finder optical system described in claim 2, the angle θ formed by the light beam reflected by the roof reflecting surface is set.
And the angle χ formed by the second transmitting surface and the third transmitting surface of the second prism.
Since the angle θ of deflection of the light flux on the roof reflection surface has a value near 90 ° and the incident angle α of the light flux on the first reflection surface has a value near 45 °, the light flux First
Each of the three prisms is compactly arranged under the condition that total reflection is performed when first entering the first reflecting surface of the prism, and total reflection is not performed when entering a second transmitting surface of the second prism. . Therefore, the entire reversing optical system can be made compact, and the distance from the image plane of the objective lens system to the eyepiece lens system in the reversing optical system can be reduced, so that a compact and high-magnification viewfinder optical system can be obtained. Can be realized.

In the inverting optical system of the finder optical system according to the third aspect, the roof reflecting surface is made compact by using the roof reflecting surface as the reflecting surface of the roof prism, and a compact finder optical system can be realized.

Further, in the inversion optical system of the finder optical system according to claim 4, the range of the distance d between the first reflecting surface of the first prism and the second transmitting surface of the second prism is defined. Due to the duplication of the image due to the reflection of the light beam on the first reflecting surface and the second transmitting surface, and the difference in the optical path length from the exit of the light beam from the second reflecting surface to the pupil surface on the left and right sides. The variation of aberration on the pupil plane of the viewfinder is within an allowable range. Therefore, the image in the viewfinder is 2
It is possible to realize a viewfinder optical system that does not overlap and the image does not change even when the eyes are moved left and right.

Further, in the inversion optical system of the finder optical system according to any one of claims 5 to 7, the peripheral portion where the effective light beam does not pass is defined by the first reflecting surface of the first prism and the second transmitting surface of the second prism. Since the distance of is stably maintained in the desired range of d and the effective light flux is transmitted, the image in the viewfinder is
It is possible to realize a stable viewfinder optical system in which the image does not change even when the eyes are moved to the left and right without overlapping.

Further, in the inverting optical system of the finder optical system according to claim 8, at least one of the first reflecting surface of the first prism and the second transmitting surface of the second prism has a top layer of silicon dioxide and a bottom layer. By adding at least two or more optical films made of a dielectric material, it is possible to realize a finder optical system in which the reflectance of the light flux is reduced on the two surfaces and the ghost image is appropriately reduced.

Further, in the inverting optical system of the finder optical system according to the ninth and tenth aspects, the notch and the smear coating are provided on the second reflecting surface of the first prism at a position farthest from the first transmitting surface. By providing the projection, when the ghost light generated by the reflection inside the first prism reaches the notch and the smeared projection by sequentially reflecting each surface, the ghost light is reflected in the effective optical path. In addition, the ghost light does not enter the eyepiece system direction. Therefore, it is possible to stably realize a finder optical system in which the images on the finder do not overlap.

In the reversing optical system of the finder optical system according to claim 11, when the light flux is reflected by the second reflecting surface of the first prism, the added optical film corrects the color tone of the image. An image with a good color tone can be obtained with the viewfinder.

Further, in the inverting optical system of the finder optical system according to claim 12, since the refractive indexes of the first and second prisms are both 1.6 or less, it is possible to achieve refraction on each surface of each prism. The reflectance of the light flux can be set to 6 to 7% or less, and a finder optical system in which the intensity of the ghost image is reduced can be realized.

Further, in the finder optical system according to the thirteenth aspect of the present invention, the luminous flux emitted from the second prism is directed in the same direction as the luminous flux incident on the roof reflecting surface, as compared with the conventional inverting optical system using the penta roof prism. While having the same function of making an erected image with the above, it is possible to make the entire inverting optical system compact, and to reduce the distance from the image plane of the objective lens system to the eyepiece system in the inverting optical system. Therefore, a compact and high-magnification viewfinder optical system can be realized.

Further, in the finder optical system according to the fourteenth aspect, since the second transmitting surface of the second prism has a positive refracting power, the light flux passes through the second transmitting surface and then is formed on the pupil plane. An image can be formed, and the function of the eyepiece lens system can be added to the second transmitting surface. Therefore, the space required for the eyepiece lens system can be omitted, so that a compact viewfinder optical system can be realized.

In the finder optical system according to the fifteenth and sixteenth aspects, the first transmission surface of the first prism and the exit surface of the roof prism have positive refracting power.
The function of a condenser lens can be added to the entrance surface of the prism and the exit surface of the roof prism. Therefore, the space required for the condenser lens can be omitted, and a compact viewfinder optical system can be realized.

In the finder optical system according to the seventeenth to nineteenth aspects, a member for displaying necessary information can be efficiently arranged inside the finder of the finder optical system.

Further, in the finder optical system according to claim 20, since the second reflecting surface is a semi-transparent mirror after being reflected by the first reflecting surface of the first prism, a part of the light beam is reflected by the second reflecting surface. It has a function of being transmitted without being reflected by the surface and being condensed on the photometric element by a condenser lens having a positive refractive power. Therefore, using the light flux that has passed through the viewfinder optical system, the TTF
The members for photometry can be arranged efficiently.

Further, in the finder optical system according to the twenty-first aspect, the member for displaying necessary information can be efficiently arranged inside the finder even in the structure capable of TTF photometry.

The inverting optical system of the finder optical system according to claim 22 is a conventional penta-dach prism when used in a real image type finder optical system in which a light beam is once formed between the roof reflecting surface and the first surface. Compared to the inversion optical system using
It has the same function of making the light beam emitted from the second surface an erect image having the same direction as the light beam incident on the roof reflection surface, while it also includes the reversing optical system from the image plane of the objective lens system to the eyepiece lens system. Since the distance can be reduced, a compact and high-magnification viewfinder optical system can be realized.

[Brief description of drawings]

FIG. 1 is a top view showing a first embodiment of a finder optical system according to the present invention.

FIG. 2 is an enlarged view for explaining the difference in optical path length between the conventional example and the reversing reflection section of the eyepiece lens system of the present invention.

FIG. 3 is a schematic diagram for explaining a required optical path length of a flat reflecting portion.

FIG. 4 is a schematic diagram for explaining a required optical path length of a roof reflector.

FIG. 5 is a top view for explaining the difference in size of the first prism depending on the reflection angle on the roof reflection surface.

FIG. 6 is a schematic diagram illustrating a ghost.

FIG. 7 is an enlarged view showing a method of holding the first prism and the second prism.

FIG. 8 is an enlarged view showing a method of holding the first prism and the second prism.

FIG. 9 is an enlarged view showing an example in which a light blocking portion is provided on the first prism.

FIG. 10 is a graph showing the relationship between the surface reflectance and the incident angle of a light beam and the refractive index of a medium.

FIG. 11 is a schematic view for defining the incident angle of FIG.

FIG. 12 is a second view of the finder optical system according to the present invention.
The top view which shows an Example.

FIG. 13 is a third viewfinder optical system of the present invention.
The top view which shows an Example.

FIG. 14 is a fourth viewfinder optical system of the present invention.
The top view which shows an Example.

FIG. 15 is a fifth view of the finder optical system of the present invention.
The top view which shows an Example.

FIG. 16 is a sixth viewfinder optical system of the present invention.
The top view which shows an Example.

FIG. 17 is a seventh view of a finder optical system according to the present invention.
The top view which shows an Example.

FIG. 18 is an eighth viewfinder optical system of the present invention.
The top view which shows an Example.

FIG. 19 is a ninth viewfinder optical system of the present invention.
The top view which shows an Example.

FIG. 20 is a perspective view showing a conventional example of a finder optical system using a Porro prism.

FIG. 21 is a perspective view and a top view showing a conventional example of a finder optical system using a penta roof prism.

[Explanation of symbols]

 1: Objective lens system 3: Roof prism 4: Roof reflection surface 5: Condenser lens 8: First prism 9: Second prism 10: Incident surface 11: First reflection surface 12, 27: Second reflection surface 13: First transmission Surface 14: Second transmission surface 15: Eyepiece lens system 17: First surface 18: Second surface 20: Coating and spacer member area 21: Protrusion 22: Notch 23, 23 ': Protrusion 24: Positive refractive power The 2nd transmission surface which it has 25: The entrance surface which has positive refracting power 26: The exit surface of the roof prism which has positive refracting power 28: Condensing lens 30: Photometric element 31: Light emitting element 32: Incident surface 33: Reflecting surface 34: Lens part 35, 36: reflective surface

Claims (22)

[Claims] 1. A roof reflecting surface for reflecting a light beam from the object side, a first reflecting surface for once reflecting the light beam from the roof reflecting surface to the object side, and the first reflecting surface, in order from the object side. Arranged at an acute angle,
A first prism having a second reflection surface that reflects the light flux from the first reflection surface toward the pupil surface, and a first reflection surface of the first prism are arranged substantially parallel to each other,
The first transmissive surface, which transmits the light beam reflected by the second reflective surface of the first prism and emitted from the first reflective surface, and the first transmissive surface are arranged at an acute angle and are incident on the roof reflective surface. An inversion optical system of a finder optical system, comprising: a second prism having a second transmitting surface that transmits a light beam parallel to the light beam. 2. An angle θ formed by a light beam incident on the roof reflecting surface and a light beam reflected by the roof reflecting surface and an angle χ formed by the first transmitting surface and the second transmitting surface of the second prism satisfy the following equation: The inverting optical system of the finder optical system according to claim 1. 125 ≦ θ + χ ≦ 180-arc sin (NA / N
1) χ <arc sin (NA / N) where N1: refractive index of the first prism, N: refractive index of the refractive index of the first prism and the refractive index of the second prism, whichever is smaller, NA: refractive index of air. 3. The inverting optical system of the finder optical system according to claim 1, wherein the roof reflecting surface is a reflecting surface of a roof prism. 4. The inverting optics of the finder optical system according to claim 1, wherein a distance d between the first reflecting surface of the first prism and the first transmitting surface of the second prism satisfies the following relationship. system. 0 <d ≦ 0.05 However, the unit is mm. 5. A member having a thickness d is coated at a position where an effective light beam is not transmitted on the first transmitting surface at the peripheral portion of one of the first reflecting surface of the first prism and the second prism. The inverting optical system of the finder optical system according to claim 4. 6. A spacer member having a thickness d is provided at a peripheral edge portion between the first reflecting surface of the first prism and the first transmitting surface of the second prism where an effective light beam is not transmitted. An inverting optical system of the finder optical system according to claim 4. 7. A protrusion having a thickness d is provided at a position where an effective light beam does not pass through a peripheral portion of one of the first reflecting surface of the first prism and the first transmitting surface of the second prism. The inverting optical system of the finder optical system according to claim 4. 8. An optical system having at least two layers in which an uppermost layer is made of silicon dioxide and a lowermost layer is made of a dielectric material on at least one of the first reflecting surface of the first prism and the first transmitting surface of the second prism. The inverting optical system of the finder optical system according to claim 1, wherein a film is added. 9. A first reflection element on the second reflection surface of the first prism.
2. The reversing optical system of the finder optical system according to claim 1, wherein a notch is provided at a position farthest from the surface on which the light beam is incident on the prism and at which the effective light beam is not reflected. 10. A projection is provided on the second reflection surface of the first prism at a position farthest from the surface where the light flux enters the first prism and the effective light flux is not reflected, and a light-shielding member is applied to the end surface of the projection. The inverting optical system of the finder optical system according to claim 1, wherein 11. The inverting optical system of the finder optical system according to claim 1, wherein the second reflecting surface of the first prism has an optical film that corrects the color of the image of the finder. 12. The reversing optical system for a finder optical system according to claim 1, wherein the refractive indexes of the first and second prisms are both 1.6 or less. 13. An objective lens system having a positive refracting power as a whole in order from the object side, a roof prism for reflecting a first light beam from the objective lens system, and a light beam from the roof prism for once reflecting to the object side. An approximately triangular prism-shaped first side surface having a first reflecting surface and a second reflecting surface that are arranged at an acute angle with respect to the first reflecting surface and that reflects the light flux from the first reflecting surface toward the pupil plane side. The prism and the first reflecting surface of the first prism are arranged substantially parallel to each other,
The first transmission surface, which transmits the light flux transmitted through the first reflection surface after being reflected by the second reflection surface of the first prism, and the first transmission surface are arranged at an acute angle and are incident on the roof prism. Finder optics including a second prism having a substantially triangular prism shape having a second transmitting surface that transmits a light beam parallel to the light beam as a side surface, and an eyepiece lens system having a positive refracting power as a whole system. 14. The finder optical system according to claim 13, wherein the second transmitting surface of the second prism has a positive refractive power. 15. The surface of the first prism on which the light beam enters has a positive refractive power.
Viewfinder optical system described. 16. The finder optical system according to claim 13, wherein the exit surface of the roof prism has a positive refractive power. 17. A condenser lens, which is provided between the roof prism and the first prism, has a first surface having a positive refracting power and a second surface which is a flat surface in order from the object side, and a condenser lens of the condenser lens. A light emitting element provided facing the edge surface, an incident surface formed on the edge surface of the condenser lens at a position facing the light emitting element, and a first light flux of the condenser lens first surface does not pass through. A reflecting surface which is provided at a position facing the incident surface at the peripheral portion and which reflects the second luminous flux incident from the light emitting element through the incident surface substantially in parallel with the first luminous flux reflected by the roof reflecting surface; A lens portion having a positive refracting power, which is provided at a peripheral portion of the second surface of the condenser lens through which the first light flux does not pass, and is provided so as to face the reflecting surface.
3. The finder optical system described in 3. 18. A condenser lens, which is provided between the roof prism and the first prism, has a first surface having a positive refractive power and a second surface which is a flat surface in order from the object side, and the condenser lens. Between the first prisms, a light emitting element that emits a second light beam toward the first light beam in a peripheral portion where the first light beam emitted from the second surface of the condenser lens does not pass, and the condenser lens and the first light beam. Between the 1 prisms, a reflecting surface is provided at a peripheral portion where the first light flux emitted from the second surface of the condenser lens does not pass through and reflects the second light flux substantially parallel to the first light flux emitted from the second surface of the condenser lens. ,
The finder optical system according to claim 13, further comprising: 19. A light emitting element, which emits a second light flux, is located in the vicinity of the second reflecting surface of the first prism, and reflects the first light flux from the light emitting element, and the second reflection of the first prism. 14. The finder optical system according to claim 13, further comprising: a reflection surface that is incident on a peripheral edge portion of the first prism where the first light flux is not transmitted substantially in parallel with the first light flux reflected by the surface. 20. An objective lens system having a positive refracting power as a whole in order from the object side, a roof reflecting surface for reflecting a light beam from the objective lens system, and a light beam from the roof reflecting surface to the object side once. The first reflecting surface to be reflected and the first reflecting surface are arranged at an acute angle,
A first prism having a substantially triangular prism shape having a side surface of a second reflecting surface that reflects the light flux from the first reflecting surface toward the pupil plane side and transmits a part of the light flux, and a first reflecting surface of the first prism. And are arranged almost in parallel,
The first transmission surface, which transmits the light flux reflected by the second reflection surface of the first prism and transmitted through the first reflection surface, and the first transmission surface are arranged at an acute angle, and are incident on the roof reflection surface. A second transmission surface that transmits a light flux parallel to the light flux; a second prism having a substantially triangular prism shape having a side surface; and an eyepiece system that has a positive refracting power as a whole, and from the second reflection surface A finder optical system comprising a condenser lens having a positive refractive power and a photometric element in order from the side closer to the second reflecting surface on the optical axis of the emitted light flux. 21. A first light flux that is provided so as to face the second reflecting surface of the first prism, is near the condenser lens, and is substantially parallel to the first light flux reflected by the second reflecting surface of the first prism. 21. The finder optical system according to claim 20, further comprising a light emitting element that emits a second light flux that is incident on a peripheral portion of the first prism where the first light flux does not pass. 22. In order from the object side, a roof reflecting surface that reflects a light beam from the object side, a first surface that totally reflects the light beam from the roof reflecting surface to the object side, and a light beam from the first surface are provided. A finder optical system including a second surface for reflecting light to the pupil surface side, wherein the light flux reflected by the second surface is transmitted through the first surface. Inversion optical system.