JP5546343B2 - Ranging device and optical apparatus having the same - Google Patents

Description

  The present invention relates to a distance measuring device and is suitable for optical equipment such as a digital still camera and a digital video camera.

  As a passive distance measuring device, for example, a device that captures an object image with a pair of left and right sensors and calculates a distance to the object from the amount of deviation of each image obtained by the left and right sensors is known.

Patent Document 1, the imaging lens for forming an object image on the sensor employs a positive Menisuka scan lens, a distance measuring device having improved positioning accuracy while suppressing an increase in size of the distance measuring device Disclosure.

  Patent Document 2 discloses a focus detection device in which a sub-aperture is arranged separately from an aperture stop, and the influence of curvature of field is suppressed by increasing the depth of focus of an off-axis light beam, and the decrease in distance measurement accuracy caused thereby is suppressed. Disclosure.

JP 2003-15029 A JP 2005-25140 A

  However, although the distance measuring apparatus of Patent Document 1 is smaller than the case where the imaging lens is configured by a plano-convex lens, there is room for improvement in terms of size because the focal length of the imaging lens is long.

  In Patent Document 2, since the off-axis light beam is limited by the sub-aperture to increase the depth of focus, the light amount difference between the on-axis light beam and the off-axis light beam becomes large, and the light amount distribution on the sensor becomes non-uniform. . For this reason, it is difficult to obtain high distance measurement accuracy using an off-axis light beam in an environment where a sufficient amount of light cannot be secured.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a distance measuring device that is more compact than the conventional one and has improved distance measuring accuracy.

In order to achieve the above object, an exemplary distance measuring device of the present invention includes a pair of imaging lenses in which the optical axes are arranged at a base line length, and a pair of apertures corresponding to the pair of imaging lenses. A distance measuring device having a diaphragm provided with a sensor that receives an image formed by the pair of imaging lenses and converts the image into an electrical signal;
The diaphragm is disposed between the imaging lens and the sensor;
Each of the pair of imaging lenses is composed of one aspherical lens, the radius of curvature of the object side surface of each imaging lens is R1, the radius of curvature of the image side surface of each imaging lens is R2, and each The length of the aperture in the baseline length direction is A, the focal length of each imaging lens is f 1 , the distance from the image side surface of each imaging lens to the corresponding aperture is dSP, and the object side of each imaging lens is on the object side When the distance from the surface to the sensor is TL ,
−0.4 <(R1 + R2) / (R1−R2) <− 0.1
5.0 <f / A <11.0
0.075 ≦ dSP / TL ≦ 0.146
It is characterized by satisfying the following conditions.

  According to the present invention, it is possible to obtain a distance measuring device that is improved in distance measuring accuracy while being smaller than the conventional one.

It is a schematic block diagram of the ranging device of this embodiment. It is a principle figure of triangulation. It is an example of the signal read from two sensors. 2 is a lens cross-sectional view and aberration diagrams of Example 1. FIG. FIG. 6 is a lens cross-sectional view and aberration diagrams of Example 2. FIG. 6 is a lens cross-sectional view and aberration diagrams of Example 3. It is a principal part schematic diagram of a digital video camera.

  Embodiments of a distance measuring device of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a distance measuring device 101 according to the present embodiment. In FIG. 1, reference numerals 102 and 104 denote a pair of imaging lenses. The imaging lenses 102 and 104 are lenses having the same focal length and arranged in parallel with their optical axes parallel to each other. The imaging lenses 102 and 104 are integrally formed by resin molding. Thereby, relative eccentricity can be reduced compared with the case where the imaging lenses 102 and 104 are separate members, and high positional accuracy can be achieved. The distance between the optical axes of the imaging lenses 102 and 104 is defined as the baseline length B.

  Reference numeral 106 denotes a stop provided with a pair of apertures corresponding to the imaging lenses 102 and 104, respectively. Reference numerals 103 and 105 denote a pair of sensors that are provided corresponding to the imaging lenses 102 and 104 and receive an image of an object formed by each of the imaging lenses 102 and 104 and convert them into electrical signals. As shown in FIG. 1, the stop 106 is arranged behind the imaging lenses 102 and 104 (image side) and in front of the sensors 103 and 105 (object side). The sensors 103 and 105 are arranged in the baseline length direction on the same plane orthogonal to the optical axis, and each sensor includes a plurality of pixels arranged in the baseline length direction. Reference numeral 107 denotes a distance calculation unit that calculates a distance to an object using a signal corresponding to an image formed on the sensors 103 and 105.

  In FIG. 1, the diaphragm 106 is drawn away from the imaging lenses 102 and 104, but the holding member of the imaging lenses 102 and 104 may have the function of the diaphragm 106. A configuration is also conceivable in which the sensors 103 and 105 are used as one sensor and images are formed by the imaging lenses 102 and 104 in different regions of the one sensor.

  Although not shown, an illumination unit including a light emitting element (light source) and an illumination lens that irradiates light from the light emitting element to the object side may be provided in the distance measuring apparatus 101 to illuminate the object. If light from an object illuminated by the illumination unit is detected by the sensors 103 and 105, a signal having a high S / N ratio can be obtained regardless of the environment.

Next, the principle of distance calculation by triangulation will be described with reference to FIGS.
In FIG. 2, 201 is an object (subject). Reference numerals 202 and 203 denote an imaging lens and a sensor for the first optical path, respectively. Reference numerals 204 and 205 denote an imaging lens and a sensor for the second optical path, respectively. The imaging lenses 202 and 204 are installed such that their optical axes are separated by a base line length B. Sensors 203 and 205 are line sensors. Of the light from the object 201, the light that has followed the first optical path by the imaging lens 202 forms an image on the sensor 203, and the light that has followed the second optical path by the imaging lens 204 forms an image on the sensor 205. To do.

Here, FIG. 3 shows an example of signals read from the sensors 203 and 205 that have received two images formed by following the first and second optical paths. Since the two sensors are separated by the baseline length B, the two signals S1 and S2 are shifted by the number of pixels X, as can be seen from FIG. Therefore, the correlation X between the two signals S1 and S2 is calculated while shifting the pixels, and the shift amount X between the two signals can be calculated by obtaining the position where the correlation is maximized. From this shift amount X, the base line length B, and the focal length f of the imaging lenses 202 and 204, the distance L to the object can be determined by the principle of triangulation.
L = B × f / X
Is required.

  The focal length f is defined when a light ray parallel to the optical axis is incident on the optical system, that is, for an infinite object distance. Therefore, strictly speaking, the distance L cannot be calculated using the focal length for an object of a finite distance, but for the sake of simplicity, the principle will be described instead of the focal length.

  In such a distance measuring device, in order to reduce the size of the device, it is necessary to increase the refractive power (the reciprocal of the focal length) of the imaging lens. Further, in order to improve the distance measurement accuracy, it is necessary to appropriately set the aperture shape. The present invention has been made to find the relationship between the shape of the imaging lens, the focal length, and the aperture shape necessary for obtaining a desired distance measurement accuracy while reducing the size of the distance measurement apparatus.

  In this embodiment, each of the pair of imaging lenses 102 and 104 is composed of one aspheric lens. The imaging lenses 102 and 104 were made to satisfy the following conditions.

−0.4 <(R1 + R2) / (R1−R2) <− 0.1 (1)
5.0 <f / A <11.0 (2)
here,
R1: radius of curvature of the object side surface of each imaging lens R2: radius of curvature of the image side surface of each imaging lens A: length of each aperture in the baseline length direction f: focal length of each imaging lens .

  By using an aspheric lens as the imaging lens, the entire system can be reduced in size while suppressing spherical aberration, coma aberration, and field curvature.

  Conditional expression (1) is an expression that prescribes a shape factor indicating a specific shape for obtaining small and good imaging performance. By satisfying conditional expression (1), the object side has a convex surface, and the curvature of the image side surface is relatively smaller than that of the object side surface. By forming the imaging lens in such a shape, it becomes possible to correct aberrations when the refractive power is increased. If the upper limit of conditional expression (1) is exceeded, the curvature of the image-side surface becomes large (the radius of curvature is small), and it becomes difficult to correct spherical aberration. Exceeding the lower limit of conditional expression (1) is advantageous for correcting spherical aberration and reducing the size, but increases off-axis coma. It should be noted that the radius of curvature of the aspheric surface is obtained from conditional expression (1) using the paraxial radius of curvature.

  Conditional expression (2) is an expression in which the focal length of the imaging lens is defined by the opening length in the baseline length direction. When the upper limit of conditional expression (2) is exceeded, the influence of diffraction becomes large, resulting in degradation of imaging performance, making it difficult to achieve high distance measurement accuracy. If the lower limit of conditional expression (2) is exceeded, the imaging performance at the sensor peripheral image height is degraded. In addition, when a single lens is used, it is difficult to ensure a sufficient depth of focus for inevitable field curvature.

  As described above, by defining the shape of the imaging lens, and the relationship between the focal length of the imaging lens and the aperture shape, it is smaller than the prior art, which is the initial object of the present invention, but has high ranging accuracy. A ranging device can be realized.

  Next, more preferable conditions for the distance measuring apparatus of the present invention will be described. By adopting a configuration that satisfies the following conditions, the effects described later can be additionally obtained.

First, when the thickness on the optical axis of each imaging lens is d and the distance from the object side surface of each imaging lens to the corresponding sensor (so-called “optical total length”) is TL,
0.35 <d / TL <0.7 (3)
It is desirable to satisfy the following conditions.

Conditional expression (3) is an expression in which the thickness of the imaging lens on the optical axis is defined by the total optical length. By satisfying conditional expression (3), it becomes possible to reduce the size of the entire system and sufficiently correct various aberrations. When the upper limit of conditional expression (3) is exceeded, it becomes difficult to secure a desired back focus. Moreover, since it exceeds a hemispherical shape (approaching a spherical shape), it becomes difficult to hold the lens, and it is difficult to incorporate the lens into the lens barrel. When the lower limit of conditional expression (3) is exceeded, the center thickness of the lens becomes small, and the imaging performance around the sensor is degraded.

Next, when the distance from the image side surface of each imaging lens to the corresponding aperture is dSP,
0.075 ≦ dSP / TL ≦ 0.146 (4)
It is also desirable to satisfy the following conditions.

  When the lower limit of conditional expression (4) is exceeded, the off-axis light beam of the imaging lens is separated from the optical axis, which increases the diameter of the imaging lens. If the upper limit of conditional expression (4) is exceeded, the change in the distance from the optical axis of the peripheral light beam incident on the sensor will increase, and the inner wall flare (reflected light) of the lens barrel will increase, making it difficult to achieve high distance measurement accuracy. Become.

Next , when the apparent pixel pitch of the sensor is p,
1600 ≦ f / p ≦ 2800 (5)
It is also desirable to satisfy the following conditions.

  Conditional expression (5) is a condition for extracting good distance measuring performance with respect to the lens shape defined in conditional expression (1) and the aperture length of the aperture defined in conditional expression (2). If the upper limit of conditional expression (5) is exceeded, high distance measurement accuracy can be obtained in principle, but the relative position sensitivity of the pair of imaging lens and sensor increases, leading to erroneous calculation due to manufacturing errors. If the lower limit of conditional expression (5) is exceeded, the sensitivity for specifying the object distance is low, and it becomes difficult to achieve high distance measurement accuracy.

By the way, the apparent pixel pitch p indicates the pixel pitch itself in a one-line line sensor. When the pixel shift is performed by a two-line line sensor as in the distance measuring apparatus shown in FIG. 1, it indicates half of the pixel pitch of one line sensor. The same applies to the case of shifting pixels at equal intervals with a line sensor of three or more lines.
In addition, it is more preferable that the conditional expressions (1) to ( 3 ) satisfy the following conditions.

−0.35 <(R1 + R2) / (R1−R2) <− 0.15 (1a)
6.0 <f / A <9.0 (2a)
0.35 <d / TL <0.6 (3a)
By satisfying conditional expression of (1a), the correction of the miniaturization and the spherical aberration can be both a higher level. By satisfying conditional expression (2a), it becomes more appropriate to ensure the depth of focus with respect to the influence of diffraction and curvature of field. By satisfying conditional expression (3a), it is possible to achieve both higher back focus and smaller size .

Next, specific embodiments of the distance measuring device that satisfy the above-described conditions of the present invention and preferable conditions will be described.
FIGS. 4A and 4B are a lens cross-sectional view and an aberration diagram of the distance measuring apparatus of Embodiment 1, respectively. FIGS. 5A and 5B are a lens cross-sectional view and an aberration diagram of the distance measuring apparatus according to Embodiment 2, respectively. FIGS. 6A and 6B are a lens sectional view and an aberration diagram of the distance measuring apparatus according to the third embodiment, respectively.

  In the lens cross-sectional views shown in FIGS. 4A, 5A, and 6A, only elements corresponding to one of the imaging lenses are extracted and shown. . In each lens cross-sectional view, OL is an imaging lens, and SP is a stop provided with an aperture corresponding to the imaging lens. G is an optical block corresponding to an optical filter, a face plate, an infrared cut filter, or the like. IP is an image plane on which the sensor is arranged.

  In the aberration diagrams shown in FIGS. 4B, 5B, and 6B, d and g are the d-line and g-line, respectively, and ΔM and ΔS are the meridional image plane and the sagittal image plane. Lateral chromatic aberration is represented by the g-line. ω indicates a half angle of view, which is indicated by an angle of view obtained by paraxial calculation of focal length and image height.

  Example 1 is an imaging lens having a focal length of 4.0 mm, Example 2 is an imaging lens having a focal length of 3.2 mm, and Example 3 is an imaging lens having a focal length of 2.8 mm. In each of the imaging lenses of Examples 1 to 3, the object side surface is aspherical, but the image side surface or both surfaces may be aspherical.

  In each embodiment, the opening shape is rectangular. As a result, the light incident on the rectangular imaging lens is effectively used to secure the light quantity and maintain high distance measurement accuracy.

Hereinafter, numerical data (numerical examples) of Examples 1 to 3 are shown. In each numerical example, r is the radius of curvature, d is the distance between the i-th and (i + 1) -th surfaces from the object side, and the unit is (mm). Also, nd is the refractive index with respect to the d-line, νd is the Abbe number, and the Abbe number νd is defined by the following equation.
νd = (Nd−1) / (NF−NC)
Nd: Refractive index for d-line (wavelength 587.6 nm) NF: Refractive index for F-line (wavelength 486.1 nm) NC: Refractive index for C-line (wavelength 656.3 nm) * means a surface having an aspherical shape ing. The aspherical shape has an X axis in the optical axis direction, an H axis in the direction perpendicular to the optical axis, a positive light traveling direction, R is a paraxial radius of curvature, K is a conic constant, and A3 to A10 are aspheric coefficients. and when,

It is expressed by the following formula. It should be noted that the aspheric coefficient is 0 (zero) for terms that do not have an aspheric coefficient in the numerical examples. “E-x” means 10 ^−x .

(Numerical example 1)
Unit mm

Surface data surface number rd nd vd
1 * 2.910 2.00 1.52996 55.8
2 -5.950 0.40
3 (Aperture) ∞ 2.16
4 ∞ 0.30 1.52000 55.0
5 ∞ 0.45 1.51900 43.0
6 ∞ 0.00
Image plane ∞

Aperture stop 0.6 × 2.0 (rectangular)

Aspheric data 1st surface
K = 0.00000e + 000 A 4 = -6.11537e-003 A 6 = -1.03251e-003 A 8 = 4.12288e-005

Focal length 4.00
Angle of View 5.71
Statue height 0.40
Total lens length 5.05
Back focus 3.05

(Numerical example 2)
Unit mm

Surface data surface number rd nd vd
1 * 2.358 2.30 1.52996 55.8
2 -4.000 0.40
3 (Aperture) ∞ 1.23
4 ∞ 0.30 1.52000 55.0
5 ∞ 0.45 1.51900 43.0
6 ∞ 0.00
Image plane ∞

Aperture stop 0.4 × 1.4 (rectangular)

Aspheric data 1st surface
K = 0.00000e + 000 A 4 = -1.00451e-002 A 6 = -3.27096e-003 A 8 = -4.36807e-005

Focal length 3.20
Angle of View 7.13
Statue height 0.40
Total lens length 4.42
Back focus 2.12

(Numerical Example 3)
Unit mm

Surface data surface number rd nd vd
1 * 2.168 2.00 1.52996 55.8
2 -3.200 0.60
3 (Aperture) ∞ 0.77
4 ∞ 0.30 1.52000 55.0
5 ∞ 0.45 1.51900 43.0
6 ∞ 0.00
Image plane ∞

Aperture stop 0.4 × 1.4 (rectangular)

Aspheric data 1st surface
K = 0.00000e + 000 A 4 = -1.72668e-002 A 6 = -4.50580e-003 A 8 = -4.91418e-004

Focal length 2.80
Angle of View 8.13
Statue height 0.40
Total lens length 3.91
Back focus 1.91

  The relationship between each conditional expression and each numerical example is shown in the following table.

Next, an embodiment of an optical apparatus using the distance measuring device of the present invention will be described. FIG. 7 is a schematic view of the main part of the digital video camera of this embodiment.

In FIG. 7 , reference numeral 10 denotes a camera body, and 11 denotes a photographing optical system. Reference numeral 12 denotes a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives an image of a subject formed by the photographing optical system 11 and is built in the camera body. Reference numeral 13 denotes a liquid crystal monitor. Reference numeral 14 denotes a distance measuring device of the present invention.

  The digital video camera of the present embodiment performs contrast detection type autofocus using a video signal output from the solid-state imaging device 12. The contrast detection method is a method in which the focus lens is finely driven to determine the direction of focus shift and search for the position of the focus lens at which the contrast reaches a peak. Therefore, it takes time to achieve focusing. On the other hand, by combining the distance measurement information obtained from the distance measuring device 14 and the position information of the focus lens, the drive direction and drive amount of the focus lens up to the in-focus position can be derived instantaneously. However, autofocus using distance measurement information of the distance measuring device 14 is inferior to the contrast detection method in terms of accuracy.

  The digital video camera of this embodiment performs fine adjustment of the focus lens by the contrast detection method after moving the focus lens to the vicinity of the in-focus position based on information from the distance measuring device 14. As a result, high-speed and high-precision autofocus is possible. In particular, since the distance measuring device 14 of the present invention achieves high distance measuring accuracy, the driving amount of the focus lens can be derived with high accuracy, and as a result, the time to focus on the contrast detection method can be shortened. Is possible. Furthermore, since the distance measuring device 14 of the present invention is small, it contributes to the miniaturization of the entire digital video camera and the freedom of design.

  In the above, an example of a digital video camera has been described as an optical device having the distance measuring device of the present invention. However, the present invention is also applied to other optical devices such as a liquid crystal projector equipped with a distance measuring device for measuring a distance to a screen. The distance measuring device of the invention is applicable.

102, 104 Imaging lens 106 Aperture 103, 104 Sensor

Claims (4)

An image formed by a pair of imaging lenses in which the optical axes of the optical axes are spaced apart from each other, a diaphragm provided with a pair of apertures corresponding to the pair of imaging lenses, and the pair of imaging lenses In a distance measuring device having a sensor that receives light and converts it into an electrical signal,
The diaphragm is disposed between the imaging lens and the sensor;
Each of the pair of imaging lenses is composed of one aspherical lens, the radius of curvature of the object side surface of each imaging lens is R1, the radius of curvature of the image side surface of each imaging lens is R2, and each The length of the aperture in the baseline length direction is A, the focal length of each imaging lens is f 1 , the distance from the image side surface of each imaging lens to the corresponding aperture is dSP, and the object side of each imaging lens is on the object side When the distance from the surface to the sensor is TL ,
−0.4 <(R1 + R2) / (R1−R2) <− 0.1
5.0 <f / A <11.0
0.075 ≦ dSP / TL ≦ 0.146
A distance measuring device satisfying the following condition: When the thickness on the optical axis of each imaging lens d, the distance from the object-side surface of each imaging lens to the sensor and TL,
0.35 <d / TL <0.7
The range finder according to claim 1, wherein the following condition is satisfied. When the apparent pixel pitch of the sensor is p,
1600 ≦ f / p ≦ 2800
Distance measuring apparatus according to claim 1 or 2, characterized by satisfying the following condition. An optical apparatus comprising the distance measuring device according to claim 1 .

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