JP2649574B2 - Optical system for distance measurement - Google Patents

Description

The present invention relates to a distance measuring optical system suitable for use in a portable camera, a video camera, and the like.

[Problems to be solved by conventional technology and invention]

2. Description of the Related Art Conventionally, a camera having a distance measuring means is provided with a means for automatically adjusting a focus according to a measured distance of a subject in order to enhance operability. Various means have been proposed. For example, as disclosed in Japanese Patent Publication No. 46-28500, of the light beams projected from the camera toward the subject, the light reflected by the subject and returned is received and measured. Do the distance,
There is known a technique for adjusting the amount of extension of a photographic lens so as to focus on the subject whose distance has been measured. This type of system generally uses the principle of triangulation. Accordingly, a light-emitting unit including a light-emitting optical system (hereinafter, referred to as a light-emitting lens) that emits a light beam toward a subject and a light-emitting element, and a light-receiving optical system (hereinafter, referred to as a light-receiving lens) that receives light reflected by the subject. And a light-receiving unit composed of a light-receiving element are made independent, and both are arranged at an interval. In other words, a certain distance is required to measure the distance from the angle of the reflected light beam from the subject that enters the light receiving element.

Hereinafter, such a conventional automatic distance measuring apparatus will be specifically described with reference to FIG. In FIG. 3, 1 is a light emitting side lens,
Reference numeral 2 denotes a light emitting element, 3 denotes a light receiving side lens, 4 denotes a light receiving element, 5 denotes a focus ring, 6 denotes a cam, 7 denotes a link mechanism, and 8 denotes a fulcrum of the link mechanism 7.

This automatic distance measuring device includes a light emitting section including a light emitting side lens 1 and a light emitting element 2, a light receiving section including a light receiving side lens 3 and a light receiving element 4 having a two-divided light receiving sensor, and a focus ring having a focus cam 6. 5 and a light-receiving-element drive unit including a link mechanism 7. The light emitting section and the light receiving section are arranged such that the optical axes of the light emitting side lens 1 and the light receiving side lens 3 are at a predetermined interval L and are parallel to each other.
The focus ring 5 is driven to rotate by a motor (not shown), and the rotation of the focus ring 5 is transmitted to the light receiving element 4 and is linked between the focus ring 5 and the light receiving element 4 so that the focus ring 5 can move in the direction of arrow y. A mechanism 7 is provided. The link mechanism 7 is of length p ₁ lever and length p ₂
Lever becomes linked via the fulcrum 8 of the end portion of the lever length p ₁ to the cam 6 provided on the focus ring 5, the end portion of the lever of Matanaga of p ₂ one of the light receiving element 4 Contacting the department. Light-receiving element 4 is urged by an elastic member not shown, whereby the ends of the lever length p ₂ of the link mechanism 7 is in contact with a portion of the light receiving element 4.

With this configuration, the rotational movement of the focus ring 5 is converted into a linear movement in the direction of the arrow x by the cam 6 and the link mechanism 7, whereby the light receiving element 4 linearly moves in the direction of the arrow y. In addition, the rotation of the focus ring 5 is expanded by the cam 6, thereby improving the positioning accuracy of the light receiving element.

Next, the operation of this prior art will be described.
Is emitted to the subject (not shown) located at the distance l via the light emitting side lens 1. The reflected light from the subject passes through the light receiving side lens 3 and forms an image on a two-divided light receiving sensor on the light receiving element 4. At this time, when the reflected light is not uniformly incident on each of the divided screens of the two-divided light receiving sensor, the focus ring is rotated by the motor so that the reflected light is uniformly incident on each of the divided screens. Move in the direction of arrow y. Then, when the reflected light is evenly incident on the screen for each minute, the rotation of the motor is stopped. With the rotation of the focus ring 5, the taking lens (not shown) of the optical system of the camera moves in the direction of the optical axis, and the reflected light is evenly incident on the respective divided screens of the two-part light receiving sensor of the light receiving element 4. In the state,
The camera will be in the correct range and focus state.

Generally, when performing distance measurement based on triangulation, a light emitting element or a light receiving element is moved in a direction perpendicular to the optical axis of a photographic lens of a camera. Regarding the method of moving the light receiving element, the principle of triangulation will be described with reference to FIG.

In FIG. 4, the light emitting side lens has a focal length f, the light receiving side lens 3 has a focal length of B, the light receiving element C has a focal length of 4 (in FIG. 3, 4). The distance between the optical axis and the optical axis of the light-receiving side lens 3, that is, the base line length is L, the distance from the light-emitting side lens 1 to the subject B is l, the moving amount accompanying the distance measurement of the light receiving element C is y, and the light is received from the subject B The incident angle of light incident on the front principal point of the side lens 3 is θ ₁ , and the exit angle of light emitted from the rear principal point is θ ₁ ′.

Now, assuming that the image forming position of the subject B by the light-receiving lens is a distance l 'from the light-receiving lens, and that the focal length f of the light-emitting lens is substantially equal to the focal length of the light-receiving lens, from the light-emitting lens 1 to the subject B When the distance l is sufficiently larger than the focal length f of the light-receiving side lens 1, l 'can be regarded as and the following equation is established.

Returning to FIG. 3, the following distances are set between the movement amount y of the light receiving element 4, the movement amount x of the cam 6 of the focus ring 5, and the lengths p ₁ and p ₂ of the levers of the link mechanism 7. The relational expression holds.

By the way, in order to reduce the size of the camera, it is necessary to reduce the size of the light-emitting unit and the light-receiving unit. To this end, it is necessary to reduce the base line length L. The movement amount y of the light receiving element 4 is also smaller than in (1). For this reason, it is necessary to reduce the lever length p ₂ or the moving amount x of the cam 6 in the equation (2) or increase the lever length p ₁ . However, the moving amount x of the cam 6 is a quantity determined by the optical design, to smaller lengths p ₂ of the lever is limited. Also the length of the lever
Increasing the p _1, will be receiving unit increasingly away from the taking lens has the disadvantage that the camera is increased as a whole.

Further, when the movement amount y of the light receiving element 4 is reduced, it is necessary to increase the accuracy of a component that causes an error in the movement amount y.

By the way, in the above-mentioned structure, rattling of the fulcrum 8 of the link mechanism 7 occurs due to movement of the cam, and this rattling prevents the light receiving element 4 from moving smoothly. Therefore, and so as to contact with the end portion of the length p ₂ lever of the link mechanism 7 to urge the light receiving element 4 by an elastic member such as a spring to eliminate backlash of the fulcrum 8. However, the result is not sufficient, and therefore, a high moving accuracy of the light receiving element 4 is required. That is, assuming that the accuracy of the components is constant, the smaller the amount of movement of the light receiving element 4 is, the smaller the amount of movement y of the light receiving element 4 is in order to shorten the base line length. Therefore, in order to keep the distance measurement accuracy constant, the accuracy of the components must be increased. Accordingly, there has been a problem that it is difficult to manufacture parts and the price increases.

The present invention has been made in view of the above-mentioned problems of the related art, and an object of the present invention is to provide a compact and highly accurate distance measuring optical system. Another object is to provide a highly reliable and inexpensive distance measuring optical system.

[Means for solving the problem]

In order to achieve the above object, in the distance measuring optical system of the present invention, an issuer that projects a distance measuring light beam toward an object,
A light receiving unit for receiving a reflected light beam from the object; a distance measuring optical system for measuring the distance to the object based on the principle of triangulation; a light emitting unit includes a light emitting optical system and a light emitting element; Is composed of a light receiving optical system, a light receiving element, and a deflection prism disposed between the light receiving optical system and the light receiving element, and the prism has a condition that 15 ° ≧ α ≧ 4 ° when its apex angle is α. When measuring the distance, the deflection prism is moved along the optical axis of the light receiving optical system in a direction approaching the light receiving optical system as the object moves from a long distance to a short distance. Good.

(Operation)

Even if the angle of incidence of reflected light from the subject changes according to the distance to the subject, the deflection prism moves along the optical axis to form the position of the incident light on the light receiving element at the same position. In addition, the moving amount of the deflected prism to be moved at the time of distance measurement can be much larger than the moving amount of the light receiving element in the conventional method of moving the light receiving element.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic sectional view of a main part of an embodiment of an automatic distance measuring apparatus incorporating a distance measuring optical system according to the present invention.
1 is a light-emitting optical system, 2 is a light-emitting element, 3 is a light-receiving optical system, 4 is a light-receiving element, 5 is a deflection prism, 6 is a spindle mounted on the side surface of the deflection prism 5, and 7 is a deflection prism sliding. The groove, 8 is the focus ring of the taking lens, and 9 is the focus ring 8.
The cam.

In FIG. 2, a light emitting section is constituted by a light emitting optical system 1 and a light emitting element (for example, an infrared light emitting diode) 2, and a light receiving optical system 3, a light receiving element (for example, a two-part pin photodiode) 4, and an optical axis. A support shaft 6 arranged to be orthogonal to the other
Deflector prism (made of glass or plastic) 5 supported by the lens and movable in the optical axis direction, and a cam 9 of a focus ring 8 for moving the deflector prism 5 for moving the taking lens
An elastic member (not shown) for contacting the light-receiving portion constitutes a light-receiving portion. Further, since the support shaft 6 is fitted in the deflection prism sliding groove 7, when the focus ring 8 rotates as the photographing lens moves, the support shaft 6 moves along the deflection prism sliding groove 7 in the optical axis direction. The deflection prism 5 also moves in the optical axis direction.

The light from the light emitting element 2 is projected on a subject (not shown) through the light emitting optical system 1, and reflected light from the subject is
The light reaches the light receiving element 4 via the light emitting optical system 3 and the deflection prism 5. At this time, when the reflected light is not uniformly incident on each screen of the two-divided light receiving sensor of the light receiving element 4, that is, at the time of out-of-focus, the focus ring 8 is rotated by a motor (not shown), and the focus The deflection prism 5 in contact with the cam 9 of the ring 8 via the support shaft 6 is guided by the deflection prism sliding groove 7 in which the support shaft 6 is fitted, and the reflected light is divided into two parts of the two-part light receiving sensor. It moves along the optical axis until it evenly enters the minute screen. Thereby, the distance measurement of the camera is completed, and the camera is brought into a focused state.

Next, the operation of the distance measuring optical system of the present invention will be described. In this optical system, a deflection prism movable along the optical axis is arranged between the light receiving optical system 3 and the light receiving element 4 in the optical arrangement shown in FIG. 4 for explaining the principle of triangulation. is there. This is shown in FIG. In FIG. 1, 3: light receiving optical system, 5: deflecting prism, 4: light receiving elements, a focal length of the light receiving optical system 3, S _1: at a long distance ranging, angle-deviating prism from the light-receiving optical system 35 Distance to, ₁ : the distance from the light receiving optical system 3 to the deflection prism 5 during short-distance ranging, α: apex angle of deflection prism 5, ε: ray deflection angle by deflection prism 5

Hereinafter, in order to clearly explain the effects of the present invention, it is assumed that the lens is a thin-walled lens and the deflection prism is a prism having a small ridge angle.

First, θ ₁ ′ is determined from the parameters listed above. Referring to FIG. 4, light emitted from light emitting optical system 1 is reflected at subject B. Part of the reflected light enters the light receiving optical system 3 and exits therefrom. Now, assuming that the incident light passes through the principal point of the light receiving optical system 3, the output angle θ ₁ ′ of the light receiving optical system is equal to the incident angle θ ₁ and is given by the following equation.

In the above equation (3), in FIG. 1, the angle between the light emitted from the light receiving optical system 3 and the optical axis is θ ₁ ′, and the distance l of the subject B is
It is shown that it changes according to.

Next, regarding the light beam deflection angle ε, the subject distance l (see FIG. 4) is sufficiently larger than the base line length L under normal distance measurement conditions. Optics (1st volume), written by Kogoro Yamada, p126, “Prism with Small Edge Angle”, when the vertex angle of the prism 5 is α and the refractive index is N, the ray deflection angle ε is (N−1). It is given by α.

Returning to FIG. 1, the light reflected by a long-distance subject (not shown) is emitted at an angle θ _i ′ with respect to the optical axis of the light receiving optical system 3. This light enters the deflection prism 5, and after being refracted, on the light receiving element 4 placed on the focal plane of the light receiving optical system 3.
Reaches a height [Delta] y ₁ and marked position. Δy ₁ is easily obtained from the figure, and Δy ₁ = S ₁ tan θ ₁ ′ − (− S ₁ ) tan (ε−θ ₁ ′)
(4) The subject distance changes, and the emission angle of the light emitted from the light receiving optical system 3 becomes Let's say In this case, the light receiving optical system 3 and the light receiving element 4
Assuming that the position of the deflection prism 5 used between
The imaging position delta ₁ on the light receiving element 4 in (4), theta
₁ ' Is obtained by replacing Becomes

Now, if the deviation prism 5 from the position S ₁ by moving to _1, that can be matched delta ₁ of the image forming point on the image forming point of [Delta] y _1, the position of the deflecting prism P at that time ₁ Is obtained by solving the equation obtained by equalizing the above equations (4) and (4) ′ with respect to ₁ , and Becomes The deflection prism 5 at this time is shown by a broken line.

Equation (5) is an emission angle of light exiting the light receiving optical system 3. The position of the deflection prism 5 provided between the light receiving optical system 3 and the light receiving element 4 is changed in accordance with the change of the object distance l, so that the light receiving element 4 of the light emitted from the light receiving optical system 3 is changed. This shows that the upper imaging position can be maintained at a constant height (Δy ₁ ).

Equation (5) gives the distance ₁ from the light receiving optical system 3 to the deflection prism 5 when measuring the distance of the subject B at a short distance. In equation (5), And L is the base line length, ε = (N−1) α, is the focal length of the light receiving optical system 3, and Δy ₁ is kept constant. Therefore, by setting this equal to the constant Δy, Δy ₁ = Δy. Therefore, the position ₁ of the deflection prism P at the time of short distance measurement is α,
; L, N ,, ₁ = S (α,; L, N,
, Δy).

Next, the distance S ₁ from the light receiving optical system 3 to the deflection prism 5 at the time of distance measurement of the subject B at a long distance l is Given by In equation (9) ', Where L is the base line length, ε = (N−1) α, and the light receiving optical system 3
Focal length, and Δy ₁ = Δy. Therefore, the position S ₁ of the angle-deviating prism 5 at the time of long distance range finding, alpha, l; is given by; (L, N ,, Δy α , l) L, as a function of N ,, Δy S ₁ = S .

Assuming that the distance the deflector prism 5 has moved along with the switching from the long distance measurement to the short distance measurement is ΔS, ΔS = ₁₋ S ₁ = (α,; L, N ,, Δy) −S (α, l; L, N ,, Δy) (6) In the equation (6), ΔS ,, l, L, N ,, Δy are parameters to be determined when designing the distance measuring optical system.
If these parameters are determined, the value of the vertex angle α of the deflection prism 5 is also determined. The empirically obtained acceptable values of α are in the following ranges.

15 ° ≧ α ≧ 4 ° (7) That is, when the apex angle α of the deflection prism 5 exceeds the upper limit (15 °), the moving amount of the deflection prism 5 to be moved according to the change in the subject distance becomes small. However, the movement at this time is not preferable because the operation becomes unstable. On the other hand, when the apex angle α of the deflection prism 5 falls below the lower limit (4 °), the amount of movement of the deflection prism 5 to be moved increases in accordance with the change in the subject distance, and the range is within the light receiving optical system 3. And light receiving element 4
Which is not feasible.

 Next, two specific examples will be given.

Specific Example 1. Base line length L = 30 mm Focal length of light receiving optical system 3 = 26 mm Apex angle of deflected prism α = 10 ゜ Refractive index of deflected prism N = 1.51633 Subject distance l = 1.2 m to 20 m Subject under the above conditions Is placed at a distance of 20 m, and the deflection prism 5 is arranged at a position 21 mm away from the light receiving optical system 3, the height of the light imaged on the surface of the light receiving element 4 is Δy ₁ = −0.
42 mm. Next, when the subject moves from 20 m to a short distance of 1.2 m, the deflection prism 5 is moved from the above position by ΔS =
By moving 5.30 mm, light can be focused on the same position on the surface of the light receiving element 4. Thus, the subject can be measured in a short distance, and the photographing lens can be focused on this distance. did it.

Specific example 2. Base line length L30mm Focal length of light receiving optical system 3 = 26mm Apex angle of deflected prism α = 6 ゜ Refractive index of deflected prism N = 1.51633 Subject distance l = 1.2m to 20m Under the above conditions, subject is 20m When the deflection prism 5 is disposed at a position 21 mm away from the light receiving optical system 3, the height of the light imaged on the surface of the light receiving element 4 is Δy ₁ = −0.
It was 24 mm. Next, when the subject moves from 20 m to a short distance of 1.2 m, the deflection prism 5 is moved from the above position by ΔS =
By moving the lens by 9.01 mm, light can be imaged at the same position on the surface of the light receiving element 4. Thus, the subject can be measured in a short distance, and the photographing lens can be focused on this distance. did it.

By the way, when the distance measuring optical system is configured by the conventional method,
When the amount of movement of the light receiving element is determined by the equation (1) in the method of moving the light receiving element according to the subject distance, it is 0.57 mm. When the distance measuring optical system is configured according to the present invention, the moving amount of the deflection prism 5 is 5.30 mm in the first embodiment, and the movement amount of the second embodiment is 5.30 mm.
9.01 mm, which is much larger than the conventional method. Therefore, in the case of the present invention, a predetermined distance measurement accuracy can be obtained without increasing the movement accuracy.

〔The invention's effect〕

The present invention is configured as described above, and has the following effects.

A deflection prism is provided between the light receiving optical system and the light receiving element,
Since the amount of movement involved in the distance measurement can be significantly increased as compared with the conventional method, the distance measurement accuracy can be improved without significantly increasing the movement accuracy of the deflection prism.

Further, since a transmission mechanism for transmitting the rotational movement of the focus ring of the photographing lens to the deflection prism can have a very simple configuration, it is possible to improve the reliability and reduce the cost of the distance measuring optical system.

[Brief description of the drawings]

FIG. 1 is a partial arrangement diagram of an optical system according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional configuration view of a main part of an automatic distance measuring device incorporating a distance measuring optical system according to an embodiment of the present invention. FIG. 4 is a schematic explanatory diagram of a conventional distance measuring device, and FIG. 4 is a diagram illustrating the principle of triangulation. DESCRIPTION OF SYMBOLS 1 ... Light-emitting optical system 2 ... Light-emitting element 3 ... Light-receiving optical system 4 ... Light-receiving element 5 ... Deflected prism 6 ... Support shaft attached to the side surface of deflected prism 5 7 ... Deflected prism Sliding groove 8: Focus ring of photographing lens 9: Cam of focus ring 8

Claims (1)

(57) [Claims] 1. A light emitting unit for projecting a light beam for distance measurement toward an object, and a light receiving unit for receiving a light beam reflected from the object,
In a distance measuring optical system that measures the distance of the object based on the principle of triangulation, a light emitting unit includes a light emitting optical system and a light emitting element, and a light receiving unit includes a light receiving optical system, a light receiving element, and the light receiving optical system and the light receiving element. The prism consists of a deflector prism disposed between the light receiving element and the prism, which satisfies the condition of 15 ° ≧ α ≧ 4 ° when the apex angle is α. An optical system for distance measurement, wherein the deflection prism is moved in a direction approaching the light receiving optical system along the optical axis of the light receiving optical system with movement to a distance.