JPH03235931A - Finder capable of switching of observing direction - Google Patents

Abstract

PURPOSE:To obtain this finder which is compact by arranging a lens whose rear surface is cylindrical in front of a 1st prism and providing a 1st prism and a 2nd prism rotatably. CONSTITUTION:Luminous flux which is incident from a photographic lens is made incident on the 1st lens 1 and then made incident on the cylindrical inci dence surface 2-1 of the 1st prism 2 form the cylindrical surface of the 1st lens. Then the luminous flux which is transmitted through the slanting surface 2-2 of the 1st prism is made incident on the slanting surface 3-1 of the 2nd prism and emitted from the 1st outgoing surface 3-2 to the ocular lens of, for example, eye level. Then when the 1st and 2nd prisms 2 and 3 are rotated by a fine angle, the luminous flux is all reflected by the slanting surface 2-2 of the 1st prism. Then the light is reflected again by the reflecting surface 2-3 of the 1st prism and made incident on the 2nd prism 3, and the light is emitted from the 2nd projection surface 3-3 to the ocular lens of, for example, waist level. Consequently, the compact finder is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to finders for optical equipment such as cameras and videos, and in particular to finders that can switch viewing directions, so-called eye-level and waist-level viewfinders. It is related to.

[Prior Art] The present applicant has proposed a light splitting device as a viewfinder with switchable observation direction for cameras, video cameras, etc.
No. 186673 (Japanese Unexamined Patent Publication No. 61-69022). The principle of this device will be explained with reference to FIG.

In FIG. 5, 21 indicates a first prism, and 22 indicates a second prism.

The first prism 21 has a spherical entrance surface 21-1. It has a slope 21-2 provided obliquely with respect to the light beam that transmits or totally reflects the incident light beam, and a reflective surface 21-3 that reflects the light beam that is totally reflected on the slope. The second prism 22 has a slope 22-1 that is obliquely arranged to face the surface 21-2 of the first prism, and exit surfaces 22-2 and 22-3 from which the light beam exits. Then, these two prisms are connected at an angle θ1 around the spherical center O of the entrance surface 21-1.
This is intended to switch the emission direction of the luminous flux by rotating the light beam by a certain amount and utilizing the switching between transmission and total reflection on the slope.

FIG. 5(a) is a diagram showing the eye level state, and the light beam incident on the first prism 21 from the incident surface 21-1 is
1-2, and exits through the slope 22-1 and the exit surface 22-2. FIG. 5(b) is a waist level state diagram.
is rotated, and the light beam incident from the entrance surface 21-1 is totally reflected by the slope 21-2. The luminous flux totally reflected by the surface 21-2 is reflected by the reflective surface 21-3, and is reflected by the slope 21-2, 22-
1 and exit surface 22-3, and is ejected upward.

[Problems to be Solved by the Invention] The above-mentioned light splitting device is characterized in that it is easy to use because the observation direction can be switched between two directions, for example, between eye level and waist level, by simply rotating the two prisms. However, there are difficulties in making the device compact.

That is, in order to construct a compact observation direction switching finder, it is necessary that the center of rotation 0 in FIG. 5 be relatively close to the entrance surface 21-1 of the first prism, that is, the radius of rotation must be small. be. This is because if the prism is large, the amount of rotation or oscillation of the entire prism becomes large, making it impossible to achieve compactness.

Furthermore, a small radius of rotation means that the radius of curvature of the entrance surface 21-1 is small.

In this case, in a finder with a square field of view, such as a camera finder, the edge thickness of the prism 21 in the diagonal direction of the screen cannot be taken, and the thickness of the prism 21 in the optical axis direction must be increased, resulting in a lack of compactness. A problem arises.

Therefore, an object of the present invention is to provide a compact viewing direction switching finder that overcomes the above-mentioned problems.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a first lens, a first prism, and a second prism, which are provided in order from the photographic lens side toward the eyepiece lens, These first and second prisms are rotatably provided, and the first lens has a cylindrical surface on its rear surface, and the first prism has a cylindrical shape on which the light beam enters. and the plane of incidence of
The second prism has at least a slope obliquely provided with respect to the light beam so as to transmit or totally reflect the incident light beam, and a reflective surface that reflects the light beam reflected by the slope, and the second prism The prism is configured to have a slope opposite to the slope of the first prism, a first exit surface through which the light beam transmitted by the first prism exits, and a second exit surface through which the total reflected light beam exits. .

The light flux incident from the photographing lens is incident on the first lens via, for example, a quick return mirror, and then enters the cylindrical entrance surface of the first prism from the cylindrical surface thereof. The light flux that has passed through the slope of the first prism is incident on the slope of the second prism, and exits from the first exit surface to, for example, an eye-level eyepiece. Next, when the first and second prisms are rotated by a small angle, the entire luminous flux is reflected on the slope of the first prism, and then reflected again on the reflective surface of the first prism and enters the second prism,
It then exits from a second exit surface, for example into an eyepiece at waist level.

As described above, according to the present invention, the observation direction can be switched, and the second lens is added, and the rear surface of the lens is cylindrical, and the entrance surface of the first prism is also cylindrical. The edge thickness of the first prism can be small, and the viewfinder can be downsized in the optical axis direction.

[Made by [Implementation example] First, the principle of this embodiment will be explained with reference to FIG. 1.2.

In FIG. 1, reference numeral 1 denotes a first lens located on the photographing lens side, and behind it, a first prism 2 and a second prism 3 are arranged in order.

The entrance surface 1-1 of the first lens 1 has a planar shape, but the rear surface on the exit side is provided with a cylindrical surface 1-2. The first prism 2 has a cylindrical entrance surface 2-1 that is substantially similar to the rear surface of the first lens, and has an inclined surface 2-2 on the opposite surface that transmits or reflects light depending on the angle of incidence. There is.

The first prism further has a reflective surface 2-3 obliquely arranged with respect to the optical axis at an appropriate angle. This reflective surface is made into a total reflection surface by metal vapor deposition or the like.

The second prism 3 has a slope 3-1 opposite to the slope 2-2 of the first prism, and a first exit surface 3-2.3-3. One exit surface 3-2 becomes, for example, an eye level surface substantially perpendicular to the optical axis, and the other exit surface 3-3
has a predetermined angle with respect to the exit surface 3-2, and is, for example, a waist level surface. These 1st and 2nd prisms can be rotated by a minute angle.

FIG. 2 is a diagram showing the effect of prism rotation. FIG. 2(a) is a diagram showing the eye level state, in which the light flux that has passed through the entrance surface 1-1 and rear surface 1-2 of the first lens 1 enters from the entrance surface 2-1 of the second prism. and inclined slope 2-2
reach. As shown in FIG. 2(a), when the incident angle θ2 of the light beam on the slope 2-2 is smaller than the critical angle for total reflection, the light beam passes through the slope 2-2 and passes through the slope 3-1 of the second prism. The light enters from the exit surface 3-2 and exits from the exit surface 3-2.

On the other hand, FIG. 2(b) is a diagram showing the waist level state,
+8) in Fig. 2, both small angle prisms 2.3 are rotated, and the incident angle of the light beam on the slope 2-2 becomes larger than the critical angle of total reflection, and the light beam is completely reflected on the slope 2-2. It is reflected and enters the reflecting surface 2-3. The light beam is then totally reflected in the direction of the slope 2-2. The angle of incidence on the slope 2-2 can be made smaller than the critical angle for total reflection by providing the slope 2-2 obliquely, and the light beam passes through the slope 2-2 and is reflected on the slope 3- of the second prism.
1.

The light beam further advances inside the second prism and exits from the exit surface 3-3.
eject from.

The above switching to the states shown in FIG. 2(a) and FIG. 2(b) is possible by rotating the two prisms 2-3 by a small angle. Therefore, it is possible to switch the emission direction of the light beam without losing the amount of light, and by rotating the prism by a small angle, the light beam can be selectively emitted from different emission surfaces, which saves space and improves operability. A finder capable of switching good viewing directions is provided.

Next, the principle of switching between transmission and total reflection on the slope 2-2 of the first prism will be explained.

As shown in Figure 2, the angle of incidence of the light beam on the slope 2-2 is set to θ
2. If the refractive index of the material of the second prism 3 is n, the critical angle φ for total reflection is φ-5in-''', so when θz<5in-self, the transmission is transmitted, and when θ2≧5in-''L, total reflection occurs.

In this case, assuming that the rotation angle of the prism is 01, θ1 is required to be an angle at which the entire luminous flux is switched from transmission to total reflection.

Now, the refractive index of the prism is 1.55, and the angle of the luminous flux is ±4
Taking the case of 1° as an example, the critical angle φ is 1.
55% Therefore, if 02'=45° in the state shown in FIG. 2(b), the total luminous flux will be 45°±4'=41° to 49° and will be totally reflected.

In the state shown in FIG. 2(a), the angle of incidence of the total luminous flux onto the 2-2 surface must be less than 40.2° in order to transmit the light through the 2-2 surface. Therefore, θ2=40.2°−4@
It is sufficient to set the angle to ~36°. That is, θ1=9° (4
Transmission and total reflection can be switched by a slight rotation (5° - 36°).

Next, an embodiment in which the present invention is applied to a finder of a single-lens reflex camera will be described with reference to FIG. In the figure, 11 is a light beam from an object (not shown), 12 is a photographing lens, 13 is a quick return mirror, 14 is a focusing plate, 15 is a penta roof prism, 1 is a first lens, 2 is a first prism, and 3 is a first prism. Prism number 2, number 16, and number 1 each indicate an eyepiece. A light beam 11 from an object is converged by a photographing lens 12, reflected upward by a quick return mirror 13, and formed into an image on a focusing plate 14. Furthermore, the light beam 11 passes through a pentagonal roof prism 15 and passes through a first lens 1,
It enters the first prism 2, the second prism 3, and! By rotating the first prism and the second prism, the eyepiece 1
It is selectively ejected in the direction of 6 or 17.

In addition, in FIG. 3, the structures of the first lens, twelfth prisms 2, 3, etc. are the lenses described in connection with FIG. 1.2,
Since it has the same structure as a prism etc., the explanation will be omitted. Further, although the entrance surface of the first lens 1 is a convex surface, it is effective to make it a convex surface because it also shares the role of the eyepiece lenses 16 and 17.

FIG. 4 shows an embodiment in which the present invention is applied to a reverse Galilean off-winder. According to this embodiment, the objective lens 1
Other than 8, the objective lens 1 is almost the same as the embodiment shown in FIG.
The light beam 11 incident on the eyepiece 8 is diverged and enters the first lens 1, the first prism 2, and the second prism 3.
Alternatively, it is selectively ejected in 17 directions.

According to this embodiment, the entrance surface 1-1 of the first lens 1 is a concave surface, but making it concave in this way is effective because it also shares the role of the objective lens 18.

[Effects of the Invention] As described in detail above, according to the present invention, the first lens having a cylindrical rear surface is disposed in front of the 11 2 prism, and the first prism has a cylindrical shape into which the light beam enters. In addition to having a shaped entrance surface, the first and second prisms are rotatably provided, so a compact observation direction switching finder can be obtained in which the observation direction can be changed just by slightly rotating these prisms. .

[Brief explanation of drawings]

Figures 1 and 2 are diagrams for explaining the principle of the embodiment of the present invention, where (a) in Figure 1 is a plan view thereof, (b) is a side view thereof, and (a) in Figure 2 is a luminous flux. (b) in Figure i2 is a side view similar to (b) in Figure 1 showing the condition at waist level. Figure 3 is applied to the viewfinder of a single-lens reflex camera. FIG. 4 is a schematic side view showing an embodiment applied to a reverse Galilean off-finder, and FIG. 5 shows an example proposed by the applicant, in which (a) is an eye level , and (
b) is a side view showing the state at waist level. 1... First lens 2... First prism 2-2... Slope 3... Second prism 3-2... First exit surface 3-3... Second Exit surface 1-2...Rear surface 2-1...Incidence surface 2-3...Reflection surface 3-1...Slope and other 4 people 1st (a) 1st (0)

Claims (1)

[Claims] 1. A first lens, a first prism, and a second prism are provided in order from the photographic lens side toward the eyepiece lens, and these first and second prisms are rotatably provided, The first lens has a cylindrical surface on its rear surface, and the first prism has a cylindrical entrance surface on which the light beam is incident, and a cylindrical entrance surface on which the light beam enters, and a cylindrical entrance surface that is configured to transmit or totally reflect the incident light beam. The second prism has at least a slope that is obliquely provided, and a reflective surface that reflects the light beam reflected by the slope, and the second prism has a slope opposite to the slope of the first prism, and a reflection surface that reflects the light beam reflected by the slope. A finder in which the viewing direction can be switched, characterized by having a first exit surface through which a light beam transmitted by a prism exits, and a second exit surface through which a light beam totally reflected by the first prism exits.