Optical system, distance measuring device including the same, and imaging system

Abstract

To provide an optical system that has a sufficiently small F value and can well correct aberrations, a distance measuring device including the same, and an on-vehicle system.SOLUTION: An optical system has a first lens L1 having a positive refractive power, a second lens L2 having a negative refractive power, and a third lens L3 having a positive refractive power, which are arranged in order from an object side to an image side. At least one of the first lens L1 and the third lens L3 is formed of a chalcogenide material. When the refractive index at a wavelength of 0.9 μm of the lens formed of the chalcogenide material is defined as Np, and the refractive index at a wavelength of 0.9 μm of the second lens L2 as Nn, the conditional expression of 0.75<Np-Nn is satisfied.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system corresponding to infrared light, and is suitable for a distance measuring device such as an in-vehicle system or a monitoring system.

Background Art

[0002] As a distance measuring device for measuring the distance to an object (body), there is known a device that illuminates the object with a lighting device and calculates the distance to the object based on the time from when the reflected light from the object is received or the phase of the reflected light. In such a distance measuring device, it is required to use infrared light (infrared rays) that is less affected by obstacles such as fog on the distance measuring performance and less affected by the human eye.

[0003] Patent Document 1 describes a distance measuring device including an optical system using a lens made of chalcogenide having a high transmittance for infrared light.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Generally, since an infrared sensor corresponding to infrared light has lower sensitivity compared to a visible light sensor, in a distance measuring device using infrared light, it is required to adopt an optical system with a sufficiently small F value (bright). However, in Patent Document 1, the F value of the optical system is not considered, and there is no description at all about the configuration of the optical system for satisfactorily correcting various aberrations such as spherical aberration and field curvature while making the F value sufficiently small.

[0006] An object of the present invention is to provide an optical system that has a sufficiently small F-number and can effectively correct various aberrations, and a distance measuring device and an on-board system that include the same. [Means for solving the problem]

[0007] In order to achieve the above object, an optical system according to one aspect of the present invention includes a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power, which are arranged in this order from an object side to an image side, and at least one of the first lens and the third lens is is KA Consists of rucogenide material, The second lens is made of a glass material, When the refractive index of the lens made of the chalcogenide material at a wavelength of 0.9 μm is Np and the refractive index of the second lens at a wavelength of 0.9 μm is Nn, 0.75 <Np-Nnなる条件式を満足することを特徴とする。 [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an optical system that has a sufficiently small F-number and is capable of correcting various aberrations well, as well as a distance measuring device and an on-board system that include the same. [Brief explanation of the drawings]

[0009]

Figure 1

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Mode for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that each drawing may be drawn at a scale different from the actual for convenience. Also, in each drawing, the same members are denoted by the same reference numerals, and duplicate explanations are omitted.

[0011] [Example 1] FIG. 1 is a schematic diagram of the main part in a cross section including the optical axis of the optical system according to Example 1 of the present invention. In FIG. 1, the left side is the object side (front), and the right side is the image side (rear). Also, in FIG. 1, only the marginal rays of the on-axis light beam condensed at the on-axis image height and the marginal rays of the most off-axis light beam condensed at one of the most off-axis image heights are shown, and other rays are omitted.

[0012] The optical system according to this example is an imaging optical system that forms an image of an object on the image plane IM1 by condensing light from an object (not shown). That is, the optical system according to this example has a positive refractive power throughout the system. When the optical system according to this example is applied to an imaging device or a distance measuring device, the light receiving surface (imaging surface) of a light receiving element (imaging element) is arranged at the position of the image plane IM1.

[0013] The optical system according to this embodiment includes a first lens L11 with a positive refractive power (power), a second lens L12 with a negative refractive power, and a third lens L13 with a positive refractive power, which are arranged in order from the object side to the image side. On the object side of the first lens, there is an aperture S1 (aperture stop) that determines the F-number (Fno) of the optical system by restricting the light from the object. In this embodiment, the first lens L11 and the third lens L13 are made of chalcogenide material, and the second lens L12 is made of S-FPL53 (Ohara Corporation).

[0014] Here, the chalcogenide material refers to a material mainly composed of chalcogenide (chalcogenide). Chalcogenide is a compound containing chalcogen elements such as sulfur (S), selenium (Se), and tellurium (Te). In addition to the chalcogen elements, those containing germanium (Ge), antimony (Sb), phosphorus (P), arsenic (As), etc. are known. The chalcogenide material here is not limited to those consisting only of chalcogenide, but also includes those containing a small amount of substances (impurities) other than chalcogenide.

[0015] Note that the refractive index of the chalcogenide material may vary depending on the mixing ratio of the chalcogen element and other elements contained in the chalcogenide, the manufacturing method, the manufacturer, etc. However, at least by adopting the chalcogenide material, the same effects as in this embodiment can be obtained. Also, the material of the second lens L12 is not limited to S-FPL53, and the same effects as in this embodiment can be obtained as long as the material satisfies the conditional formula (1) described later.

[0016] Thus, in the optical system, by configuring at least one positive lens with a chalcogenide material and at least one negative lens with a material having a lower refractive index than the chalcogenide material, the F-number can be made sufficiently small while correcting various aberrations well. This will be described in detail below.

[0017] In an optical system, when the F-number is decreased, the incident angle of the most off-axis ray with respect to the lens closest to the object side becomes larger. Therefore, in order to converge the most off-axis ray onto the light-receiving surface disposed on the image plane, it is necessary to greatly refract the most off-axis ray by each lens. In that case, as the refractive power of each lens increases, spherical aberration greatly occurs. Further, when the F-number of the optical system is decreased, particularly when the angle of view of the optical system is increased, field curvature is likely to occur.

[0018] Since the field curvature in an optical system is correlated with the Petzval sum, in order to well-correct the field curvature, it is necessary to sufficiently decrease the Petzval sum. Here, when the focal length and refractive index of the first lens L11 are f1 and n1, the focal length and refractive index of the second lens L12 are f2 and n2, and the focal length and refractive index of the third lens L13 are f3 and n3, the Petzval sum Psum is expressed by the following formula (A). However, each of the refractive indices n1, n2, and n3 here indicates the refractive index for the same wavelength. Psum = 1 / f1n1 + 1 / f2n2 + 1 / f3n3 (A)

[0019] Since the refractive index of the material used for the lens is positive, it can be seen from formula (A) that in order to decrease the Petzval sum, at least one lens may have a negative focal length. That is, it is desirable to configure an optical system by combining a positive lens having a positive focal length (positive refractive power) and a negative lens having a negative focal length (negative refractive power). Therefore, in the optical system according to the present embodiment, by setting the first lens L11 and the third lens L13 as positive lenses and the second lens L12 as a negative lens, the Petzval sum is sufficiently decreased.

[0020] In order to form an image of an object on the light-receiving surface, it is necessary to set the refractive power of the entire optical system to a positive value. In this configuration, in order to reduce the Petzval sum with as few lenses as possible, it is desirable to reduce the number of negative lenses. Further, in order to satisfactorily correct both spherical aberration and field curvature, it is desirable to use a plurality of positive lenses. Considering these factors, the optical system according to this embodiment is composed of two positive lenses and one negative lens. However, the optical system may be composed of four or more lenses as required, but for miniaturization of the entire system, it is more preferable to configure the optical system with three lenses as in this embodiment.

[0021] When the optical system is configured with such a small number of lenses, in order to sufficiently reduce the Petzval sum, it can be understood from Equation (A) that it is only necessary to sufficiently reduce the absolute value of the focal length of the negative lens and make it close to the combined focal length of the positive lenses. However, as described above, particularly when the F-number is reduced, it is required to reduce the absolute value of the refractive power of each lens in order to suppress the occurrence of spherical aberration. That is, in order to satisfactorily correct field curvature while suppressing the occurrence of spherical aberration, it is desirable to provide as large a refractive index difference as possible between the positive lens and the negative lens.

[0022] As in the above-described S-FPL53, the refractive index of a general glass material mainly used in the visible wavelength band at a wavelength of 0.9 μm is at least about 1.43 and at most about 1.97. Therefore, when each lens of the optical system is composed only of such a general glass material, the refractive index difference between the positive lens and the negative lens can only be ensured to be at most about 0.54, so it becomes difficult to satisfactorily correct field curvature while sufficiently reducing the F-number.

[0023] Therefore, in this embodiment, while the negative lens is made of a general optical material, at least one of the positive lenses is made of a chalcogenide material with a refractive index sufficiently higher than that of a general optical material. The chalcogenide material can transmit infrared light in the wavelength band of about 0.7 μm to about 14.0 μm, and has a very high refractive index at a wavelength of 0.9 μm compared with a general optical material. Specifically, the refractive index of the chalcogenide material adopted in this embodiment is about 2.75. As described above, since the refractive index of a general optical material at a wavelength of 0.9 μm is about 1.43 to 1.97, according to the optical system according to this embodiment, the refractive index difference between the positive lens and the negative lens can be sufficiently ensured to be at most about 0.78 to 1.32.

[0024] In other words, when the refractive index of the positive lens made of the chalcogenide material at a wavelength of 0.9 μm is Np and the refractive index of the negative lens at a wavelength of 0.9 μm is Nn, the optical system according to this embodiment satisfies the following conditional expression (1). 0.75 < Np - Nn (1)

[0025] Here, since it is assumed that the optical system is applied to a distance measuring device using infrared light, the reference wavelength for the refractive index is set to 0.9 μm. By forming the positive lens with a chalcogenide material and the negative lens with a material satisfying the conditional expression (1), the refractive index difference between the positive lens and the negative lens can be sufficiently ensured. As a result, the Petzval sum can be made sufficiently small while suppressing an increase in the refractive power of each lens, so that spherical aberration and field curvature can be well corrected even when the F-number of the optical system is reduced. When the value is below the lower limit of the conditional expression (1), the refractive index difference between the positive lens and the negative lens becomes insufficient, and it becomes difficult to well correct spherical aberration and field curvature when the F-number is reduced.

[0026] Note that when the value of Np - Nn becomes too large, the degree of freedom in selecting the material for each lens decreases, making it difficult to configure an optical system having the desired performance of the material. Therefore, in order to improve the degree of freedom in material selection, it is desirable to set the range of the conditional expression (1) to the following conditional expression (1a). 0.75 < Np - Nn < 1.45 (1a)

[0027] Furthermore, it is preferable to satisfy the following conditional expression (1b), and it is more preferable to satisfy the conditional expression (1c). 0.80 < Np - Nn < 1.40 (1b) 0.90 < Np - Nn < 1.35 (1c)

[0028] In this embodiment, both the first lens L11 and the third lens L13 are made of a chalcogenide material. However, the effects of the present invention can be obtained as long as at least one of them is made of a chalcogenide material. That is, by converging the light rays incident on the optical system at a large incident angle with the chalcogenide material having a high refractive index, spherical aberration and field curvature can be corrected well. However, in an optical system with a particularly small F value, off-axis light rays enter at a large incident angle, so various aberrations are likely to occur. Therefore, in order to correct various aberrations better, it is desirable to configure at least the first lens L11 arranged on the object side most with a chalcogenide material, and it is more preferable to configure both the first lens L11 and the third lens L13 with a chalcogenide material.

[0029] As described above, in an optical system with a small F value, it is necessary to suppress the occurrence of spherical aberration and correct the field curvature well. At this time, since spherical aberration is likely to occur in a lens where the incident position of the off-axis light ray with respect to the optical axis is relatively high, it is desirable to appropriately set the value of the ratio of the focal lengths of the first lens L11 arranged on the object side most and the second lens L12 arranged on its image side. That is, it is desirable to satisfy the following conditional expression (2). -3.0 < f1 / f2 < -1. (2)

[0030] ]]By satisfying conditional expression (2), the focal lengths of the first lens L11 and the second lens L12 can be appropriately set, and it becomes possible to balance and correct spherical aberration and field curvature in an optical system with a small F value. When conditional expression (2) is not satisfied, the value of the focal length of the first lens L11 becomes too large or too small with respect to the absolute value of the focal length of the second lens L12, and the correction of either spherical aberration or field curvature becomes insufficient. Furthermore, it is preferable to satisfy the following conditional expression (2a), and more preferably to satisfy conditional expression (2b). -2.9 < f1 / f2 < -1.2 (2a) -2.8 < f1 / f2 < -1.5 (2b)

[0031] Also, when the combined focal length of the lenses arranged on the image side of the second lens L12 is fr, it is desirable to satisfy the following conditional expression (3). In this embodiment, since the lens arranged on the image side of the second lens L12 is only the third lens L13, fr = f3. -3.0 < f2 / fr < -0.5 (3)

[0032] By satisfying conditional expression (3), the focal lengths of the second lens L12 and the lens arranged on its image side can be appropriately set, and it becomes possible to better correct field curvature. When conditional expression (3) is not satisfied, the absolute value of the focal length of the second lens L12 becomes too large or too small with respect to the combined focal length fr, and it becomes difficult to better correct field curvature. Furthermore, it is preferable to satisfy the following conditional expression (3a), and more preferably to satisfy conditional expression (3b). -2.7 < f2 / fr < -1.0 (3a) -2.5 < f2 / fr < -1.2 (3b)

[0033] Also, it is desirable to satisfy the following conditional expression (4). 0.1 < fr / f1 < 1.0 (4)

[0034] By satisfying conditional expression (4), the focal length of the lens disposed on the image side of the first lens L11 and the second lens L12 can be appropriately set, and it becomes possible to better correct field curvature and spherical aberration. When exceeding the upper limit value of conditional expression (4), the combined focal length fr becomes larger than the focal length of the first lens L11, and the correction of spherical aberration or field curvature becomes insufficient. When falling below the lower limit value of conditional expression (4), the focal length of the first lens L11 becomes too large with respect to the combined focal length fr, and the correction of spherical aberration or field curvature becomes insufficient. Furthermore, it is preferable to satisfy the following conditional expression (4a), and more preferable to satisfy conditional expression (4b). 0.15 < fr / f1 < 0.80 (4a) 0.2 < fr / f1 < 0 / 5 (4b)

[0035] Also, when the focal length of the optical system (the entire system) according to the present embodiment is f, it is desirable to satisfy the following conditional expression (5). 0.1 < f1 / f < 3.0 (5)

[0036] By satisfying conditional expression (5), spherical aberration can be better corrected. When exceeding the upper limit value of conditional expression (5), the refractive power of the first lens L11 becomes too small, and it becomes difficult to well correct spherical aberration. When falling below the lower limit value of conditional expression (5), the refractive power of the first lens L11 becomes too large, and various aberrations are likely to occur. Furthermore, it is preferable to satisfy the following conditional expression (5a), and more preferable to satisfy conditional expression (5b). 1.0 < f1 / f < 2.7 (5a) 1.5 < f1 / f < 2.5 (5b)

[0037] Also, it is desirable to satisfy the following conditional expression (6). -3.0 < f2 / f < -0.1 (6)

[0038] By satisfying conditional expression (6), when reducing the F-number of the optical system, spherical aberration and field curvature can be corrected better. If conditional expression (6) is not satisfied, the absolute value of the refractive power of the second lens L12 becomes too large or too small, making it difficult to balance the correction of spherical aberration and field curvature. Furthermore, it is preferable to satisfy the following conditional expression (6a), and more preferably to satisfy conditional expression (6b). -2.5 < f2 / f < -0.3 (6a) -2.0 < f2 / f < -0.5 (6b)

[0039] Also, it is desirable to satisfy the following conditional expression (7). 0.1 < fr / f < 2.0 (7)

[0040] By satisfying conditional expression (7), field curvature can be corrected better. If the upper limit value of conditional expression (7) is exceeded, the refractive power of the combined system on the image side relative to the second lens L12 becomes too small, making it difficult to correct field curvature well. If the lower limit value of conditional expression (7) is not reached, the refractive power of the combined system on the image side relative to the second lens L12 becomes too large, making it easier for various aberrations to occur. Furthermore, it is preferable to satisfy the following conditional expression (7a), and more preferably to satisfy conditional expression (7b). 0.2 < fr / f < 1.5 (7a) 0.3 < fr / f < 1.0 (7b)

[0041] Also, when the F-number of the optical system according to this embodiment is Fno, it is desirable to satisfy the following conditional expression (8). 0.6 < Fno < 1.0 (8)

[0042] When the optical system is composed of only general optical materials, it is difficult to make the F number smaller than 1.0. On the other hand, in this embodiment, by configuring some of the lenses of the optical system with a chalcogenide material, it is possible to make the F number smaller than 1.0. Specifically, the F number of the optical system according to this embodiment is 0.80. Note that when the lower limit value of the conditional expression (8) is not reached, it becomes difficult to correct various aberrations well.

[0043] FIG. 2 is a diagram showing the MTF (Modulation Transfer Function) curve of the optical system according to this embodiment. In FIG. 2, the horizontal axis represents the spatial frequency [cycles / mm], and the vertical axis represents the MTF value (contrast value). In this embodiment, it is assumed that the optical system forms an image of an object with light having a wavelength of 0.9 μm. Since the pixel pitch of a general infrared sensor is several tens of μm, it can be said that good imaging performance is achieved if the MTF value is 30% or more at a spatial frequency of 10 cycles / mm. As shown in FIG. 2, in the optical system according to this embodiment, since the minimum value a1 of the MTF value for a spatial frequency of 10 cycles / mm is about 80%, good imaging performance can be achieved.

[0044] [Embodiment 2] Hereinafter, the optical system according to Embodiment 2 of the present invention will be described. Regarding the configuration equivalent to that of the optical system according to Embodiment 1 described above in the optical system according to this embodiment, the description will be omitted.

[0045] FIG. 3 is a schematic diagram of the main part in a cross section including the optical axis of the optical system according to this embodiment. The optical system according to this embodiment is an imaging optical system that condenses the light passing through the aperture S2 onto the image plane IM2. The difference between the optical system according to this embodiment and the optical system according to Embodiment 1 is the shape and arrangement of each lens surface.

[0046] Similar to the optical system according to Example 1, the optical system according to this example consists of a first lens L21 with positive refractive power, a second lens L22 with negative refractive power, and a third lens L23 with positive refractive power, which are arranged in order from the object side to the image side. Also, the first lens L21 and the third lens L23 are made of chalcogenide material, and the second lens L22 is made of S-NBH56 (Ohara Corporation).

[0047] Figure 4 is a diagram showing the MTF curve of the optical system according to this example. In this example, it is assumed that the optical system forms an image of an object with light of wavelength 0.9 μm. As shown in Figure 4, in the optical system according to this example, since the minimum value a2 of the MTF value for a spatial frequency of 10 lines / mm is about 90%, good imaging performance can be achieved.

[0048] [Example 3] Hereinafter, the optical system according to Example 3 of the present invention will be described. Regarding the configuration equivalent to the optical system according to Example 1 described above in the optical system according to this example, the description will be omitted.

[0049] Figure 5 is a schematic diagram of the main part in a cross-section including the optical axis of the optical system according to this example. The optical system according to this example is an imaging optical system that condenses the light passing through the aperture S3 onto the image plane IM3. The difference between the optical system according to this example and the optical system according to Example 1 is the shape and arrangement of each lens surface.

[0050] Similar to the optical system according to Example 1, the optical system according to this example consists of a first lens L31 with positive refractive power, a second lens L32 with negative refractive power, and a third lens L33 with positive refractive power, which are arranged in order from the object side to the image side. Also, the first lens L31 and the third lens L33 are made of chalcogenide material, and the second lens L32 is made of S-BSL7 (Ohara Corporation).

[0051] FIG. 6 is a diagram showing the MTF curve of the optical system according to this embodiment. In this embodiment, it is assumed that the optical system forms an image of an object with light having a wavelength of 2.0 μm. As shown in FIG. 6, in the optical system according to this embodiment, since the minimum value a3 of the MTF value for a spatial frequency of 10 lines / mm is about 72%, good imaging performance can be achieved. Thus, even when light having a long wavelength of 2.0 μm is used, if the wavelength is within the transmission wavelength range of each lens, the effect of the present invention can be obtained by satisfying the conditional expression (1).

[0052] [Embodiment 4] Hereinafter, the optical system according to Embodiment 4 of the present invention will be described. Regarding the configuration equivalent to the optical system according to Embodiment 1 described above in the optical system according to this embodiment, the description will be omitted.

[0053] FIG. 7 is a schematic diagram of a main part in a cross section including the optical axis of the optical system according to this embodiment. The optical system according to this embodiment is an imaging optical system that condenses the light passing through the aperture S4 onto the image plane IM4. Different from the optical system according to Embodiment 1, the optical system according to this embodiment is composed of four lenses.

[0054] Specifically, the optical system according to this embodiment is composed of a first lens L41 having a positive refractive power, a second lens L42 having a negative refractive power, a third lens L43 having a positive refractive power, and a fourth lens L44 having a positive refractive power, which are arranged in order from the object side to the image side. In this embodiment, the first lens L41, the third lens L43, and the fourth lens L44 are made of a chalcogenide material, and the second lens L42 is made of S-BSL7 (Ohara Corporation).

[0055] FIG. 8 is a diagram showing the MTF curve of the optical system according to this embodiment. In this embodiment, it is assumed that the optical system forms an image of an object with light having a wavelength of 0.9 μm. As shown in FIG. 8, in the optical system according to this embodiment, since the minimum value a4 of the MTF value for a spatial frequency of 10 lines / mm is about 88%, good imaging performance can be achieved. Thus, even when the optical system is composed of four or more lenses, the effect of the present invention can be obtained by satisfying the conditional expression (1).

[0056] [Numerical Example] Numerical Examples 1 to 4 corresponding to the above-described Examples 1 to 4 are shown below. In each numerical example, the surface number indicates the order of each optical surface when counted from the object surface. r [mm] indicates the radius of curvature of the i-th optical surface, and d [mm] indicates the distance between the i-th optical surface and the (i+1)-th optical surface. Note that aspheric surfaces are marked with an asterisk (*) next to the surface number.

[0057] The sag amount Z [mm] in the optical axis direction, which indicates the shape of each aspherical surface, is expressed by the following formula. Here, k is the conic constant (conic constant), h is the distance [mm] in the radial direction from the optical axis, and A to E are aspherical coefficients of fourth to twelfth order terms, respectively. Here, only aspherical coefficients of fourth to twelfth order terms are used, but aspherical coefficients of sixteenth order or higher terms may be used as necessary. The radius of curvature r of the aspherical surface indicates the value of the paraxial radius of curvature, and corresponds to the radius of curvature of the base spherical surface (reference spherical surface) that is the basis for the sag amount Z. Furthermore, "E±X" in the values ​​of the aspherical coefficients in each numerical example is expressed as "10 ±X " means.

[0058]

number

[0059] (Numerical Example 1) Surface number rd material Object plane 0 ∞ ∞ Aperture 1 ∞ 0.00 First lens 2* 15.97 2.61 Chalcogenide material 3 24.90 3.64 Second lens 4* -8.81 1.30 S-FPL53 5 15.45 0.88 Third lens 6* 17.14 5.76 Chalcogenide material 7 -29.47 5.81 Image plane 8 ∞ Face number 2 Face number 4 Face number 6 r 15.97 -8.81 17.14 k 0.00 0.00 0.00 A -1.60E-05 5.46E-04 -1.69E-04 B 3.50E-07 -1.20E-05 1.62E-06 C -2.01E-08 2.67E-07 -1.96E-08 D 4.40E-10 -2.57E-09 1.40E-10 E -5.24E-12 2.31E-11 -2.19E-13

[0060] (Numerical Example 2) Surface number r d Material Object surface 0 ∞ ∞ Aperture 1 ∞ 0.00 First lens 2* 14.20 2.50 Chalcogenide material 3 21.09 2.99 Second lens 4* -11.94 2.44 S-NBH56 5 15.02 0.50 Third lens 6* 12.55 5.21 Chalcogenide material 7 -31.61 6.36 Image surface 8 ∞ Surface number 2 Surface number 4 Surface number 6 r 14.20 -11.94 12.55 k 0.00 0.00 0.00 A -3.74E-05 8.35E-04 -3.62E-04 B -1.80E-07 -1.84E-05 5.07E-06 C -2.83E-08 4.48E-07 -8.34E-08 D 5.33E-10 -2.45E-09 7.39E-10 E -1.45E-11 -8.65E-12 -2.87E-12

[0061] (Numerical Example 3) Surface number rd material Object plane 0 ∞ ∞ Aperture 1 ∞ 0.00 First lens 2* 15.66 2.82 Chalcogenide material 3 29.39 3.59 Second lens 4* -8.64 1.30 S-BSL7 5 13.48 0.89 Third lens 6* 14.30 6.31 Chalcogenide material 7 -27.89 5.09 Image plane 8 ∞ Face number 2 Face number 4 Face number 6 r 15.66 -8.64 14.30 k 0.00 0.00 0.00 A -1.03E-05 1.04E-03 -2.91E-04 B 4.53E-07 -4.25E-05 5.17E-06 C -2.68E-08 1.52E-06 -1.08E-07 D 6.42E-10 -2.84E-08 1.30E-09 E -6.28E-12 2.24E-10 -6.14E-12

[0062] (Numerical Example 4) Surface number rd material Object plane 0 ∞ ∞ Aperture 1 ∞ 0.00 First lens 2* 13.01 3.02 Chalcogenide material 3 18.73 2.50 Second lens 4* -13.48 1.30 S-BSL7 5 9.56 0.98 Third lens 6* 9.65 2.97 Chalcogenide material 7 15.69 1.96 4th lens 8 26.55 3.58 Chalcogenide material 9 -42.30 3.50 Image plane 10 ∞ Plane number 2 Plane number 4 Plane number 6 r 13.01 -13.48 9.65 k 0.00 0.00 0.00 A -1.08E-05 1.23E-03 -3.76E-04 B 5.01E-07 -5.12E-05 5.70E-06 C -2.34E-08 1.46E-06 -1.30E-07 D 6.66E-10 -2.55E-08 1.47E-09 E -6.13E-12 1.97E-10 -8.93E-12

[0063] The following table shows the values for each conditional expression regarding the optical systems according to the above-described embodiments. In the table, f4 represents the focal length of the fourth lens L44, and the unit of each focal length is [mm]. Also, the combined focal length fr in Embodiment 4 is the combined focal length of the third lens L43 and the fourth lens L44. As shown in Table 1, the optical systems according to any of the embodiments satisfy each conditional expression.

[0064]

Table I

[0065] [Imaging device] FIG . 9 is a schematic diagram of a main part of an imaging device 20 according to an embodiment of the present invention. The imaging device 20 according to the present embodiment includes an optical system (imaging optical system) 21 according to any of the above-described embodiments, a light receiving element 22 that photoelectrically converts an image of an object formed by the optical system 21, and a camera body (housing) 23 that holds the light receiving element 22. The optical system 21 is held by a lens barrel (holding member) and is connected to the camera body 23. A display unit 24 that displays an image acquired by the light receiving element 22 may be connected to the camera body 23.

[0066] As the light receiving element 22, an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor can be used. When applying the imaging device 20 to a distance measuring device, it is desirable to adopt an infrared sensor that can photoelectrically convert infrared light as the light receiving element 22. Note that the optical system 21 and the camera body 23 may be configured to be detachable from each other. That is, the optical system 21 and the lens barrel may be configured as an interchangeable lens (lens device).

[0067] In addition, the imaging device 20 according to the present embodiment may be provided on a movable moving body (moving device). Further, the optical systems according to the above-described embodiments are not limited to imaging devices such as digital still cameras, silver halide film cameras, video cameras, in-vehicle cameras, and surveillance cameras, but can be applied to various optical devices such as telescopes, binoculars, projectors, and digital copiers.

[0068] [Distance Measuring Device] FIG. 10 is a schematic view (schematic diagram) of a main part in a cross section including the optical axis of a distance measuring device 100 according to an embodiment of the present invention. The distance measuring device 100 according to the present embodiment uses a technology called LiDAR (Light Detection And Ranging) that calculates the distance to an object based on the time until the reflected light from the object (object) is received or the phase of the reflected light. In FIG. 10, it is assumed that an object not shown is arranged on the right side of the distance measuring device 100.

[0069] The distance measuring device 100 includes an illumination unit 1 and a light receiving unit (imaging unit) 2 that receives light (reflected light or scattered light) from an object illuminated by the illumination unit 1. The illumination unit 1 includes a light source unit 11 and an optical system (illumination optical system) 12 that guides (irradiates) the light from the light source unit 11 to the object. The light receiving unit 2 includes an optical system (light receiving optical system) 21 according to any of the above-described embodiments and a light receiving element 22 that receives the light from the optical system 21 and outputs a signal. That is, the above-described imaging device 20 may be used as the light receiving unit 2.

[0070] The light source unit 11 has at least a light source, and may include an optical element for guiding the light from the light source to the optical system 12 as needed, or a scanning unit that scans an object through the optical system 12 by deflecting the light from the light source. As the scanning unit, a movable mirror such as a galvanometer mirror or a MEMS mirror, or an optical element such as a crystal element or a liquid crystal element whose refractive index changes when a voltage is applied can be adopted. In particular, according to the latter optical element, there is no need to provide a mechanism (drive unit) for driving the mirror, so the miniaturization and cost reduction of the entire device can be achieved.

[0071] Further, the distance measuring device 100 includes a first control unit (lighting control unit) 31 that controls the illumination light emitted by the illumination unit 1, and a second control unit (distance calculation unit) 32 that acquires information (distance information) regarding the distance to the object based on the output of the light receiving element 22. The first control unit 31 can, for example, control the light source to make the illumination light into pulsed light or perform intensity modulation of the illumination light to generate signal light. The second control unit 32 can acquire the distance information of the object based on the time from the time when the illumination light is emitted from the light source of the illumination unit 1 to the time when the light receiving element 22 receives the light from the object.

[0072] Note that the distance information may be acquired based on the phase of the light from the object instead of the time until the light from the object is received. Specifically, the difference (phase difference) between the phase of the signal of the light source in the illumination unit 1 and the phase of the signal output from the light receiving element 22 may be obtained, and the distance information of the object may be obtained by multiplying the phase difference by the speed of light. Also, when used in an environment where sufficient illumination light such as sunlight can be obtained, the distance measuring device 100 may be configured only by the light receiving unit 2 and the second control unit 32.

[0073] Such a distance measuring device using LiDAR is suitable for an in-vehicle system that identifies vehicles, people, obstacles, etc. as objects and controls the host vehicle according to the distance information of the objects. As the distance measuring device using LiDAR, a coaxial system in which the optical axis of the illumination unit coincides with the optical axis of the light receiving unit, or a non-coaxial system in which the optical axis of the illumination unit does not coincide with the optical axis of the light receiving unit can be adopted. The optical system 21 according to the present embodiment is particularly suitable for a non-coaxial system as shown in FIG. 10.

[0074] Thus, by applying the optical system 21 according to each of the above-described embodiments to the distance measuring device 100, even when an infrared sensor having lower sensitivity than a visible light sensor is used as the light receiving element 22, distance information of an object can be acquired with high accuracy. Further, the optical system 21 according to each of the above-described embodiments is suitable even when the intensity of the reflected light from the object reaching the light receiving element 22 is weak, such as when the object is far away from the distance measuring device 100.

[0075] [In-vehicle system] FIG. 11 is a configuration diagram of a distance measuring device 100 and an in-vehicle system (driving support device) 600 including the same according to the present embodiment. The in-vehicle system 600 is held by a movable body (mobile device) such as an automobile (vehicle), and is a device for assisting the driving of the vehicle based on the distance information of an object (obstacle) around the vehicle acquired by the distance measuring device 100. FIG. 12 is a schematic diagram of a vehicle 700 including the in-vehicle system 600. In FIG. 12, a case where the distance measuring range 50 of the distance measuring device 100 is set in front of the vehicle 700 is shown, but the distance measuring range 50 may be set behind or on the side of the vehicle 700.

[0076] As shown in FIG. 11, the in-vehicle system 600 includes a distance measuring device 100, a vehicle information acquisition device 200, a control device (ECU: Electronic Control Unit) 300, and a warning device 400. The distance measuring device 100 includes the above-described illumination unit 1, light receiving unit 2, first control unit 31, and second control unit 32. The second control unit 32 according to the present embodiment has functions as a distance calculation unit and a collision determination unit.

[0077] FIG. 13 is a flowchart showing an operation example of the in-vehicle system 600 according to the present embodiment. Hereinafter, the operation of the in-vehicle system 600 will be described along this flowchart.

[0078] First, in step S1, the illumination unit 1 illuminates an object around the vehicle, and based on the signal output by the light receiving unit 2 by receiving the reflected light from the object, the second control unit 32 acquires the distance information of the object. Also, in step S2, vehicle information including the vehicle speed, yaw rate, steering angle, etc. of the vehicle is acquired from the vehicle information acquisition device 200. Then, in step S3, the second control unit 32 determines whether the distance information acquired in step S2 is within the range of a preset set distance.

[0079] Thereby, it can be determined whether there is an obstacle within the set distance around the vehicle, and the possibility of collision between the vehicle and the obstacle can be determined. Note that steps S1 and S2 may be processed in the reverse order of the above, or may be processed in parallel with each other. The second control unit 32 determines "collision possible" when there is an obstacle within the set distance (step S4), and determines "no collision possible" when there is no obstacle within the set distance (step S5).

[0080] Next, when the second control unit 32 determines "collision possible", it notifies the control device 300 and the warning device 400 of the determination result. At this time, the control device 300 controls the vehicle based on the determination result of the second control unit 32 (step S6), and the warning device 400 warns the driver based on the determination result of the second control unit 32 (step S7). Note that the notification of the determination result may be made to at least one of the control device 300 and the warning device 400.

[0081] The control device 300 performs control on the vehicle, such as applying brakes, releasing the accelerator, generating a control signal for generating braking force on each wheel to suppress the output of the engine or motor, etc. Further, the warning device 400 gives warnings to the user (driver) of the vehicle, such as emitting a warning sound, displaying warning information on the screen of a car navigation system, etc., or giving vibrations to the seat belt or steering wheel.

[0082] As described above, according to the in-vehicle system 600 according to this embodiment, an obstacle can be detected by the above-described processing, and a collision between the vehicle and the obstacle can be avoided. In particular, by applying the optical system according to each of the above-described embodiments to the in-vehicle system 600, high ranging accuracy can be realized, so that the detection of obstacles and the collision determination can be performed with high accuracy.

[0083] In this embodiment, the in-vehicle system 600 is applied to driving support (collision damage reduction), but it is not limited thereto, and the in-vehicle system 600 may be applied to cruise control (including the function of following the vehicle speed) or automatic driving. Further, the in-vehicle system 600 is not limited to vehicles such as automobiles, and can be applied to moving bodies such as ships, airplanes, and industrial robots. Further, not limited to moving bodies, it can be applied to various devices that utilize object recognition such as advanced road traffic systems (ITS) and monitoring systems.

[0084] Further, the in-vehicle system 600 or the moving device 700 may be provided with a notification device (notification unit) for notifying, in the event that the moving device 700 collides with an obstacle, the manufacturer (maker) of the in-vehicle system or the dealer of the moving device, etc. For example, as the notification device, one that transmits information (collision information) regarding the collision between the moving device 700 and the obstacle to a preset external notification destination by e-mail or the like can be adopted.

[0085] By adopting a configuration in which the collision information is automatically notified by the notification device in this way, it is possible to promptly take measures such as inspection and repair after a collision occurs. Note that the notification destination of the collision information may be an insurance company, a medical institution, a police station, etc., or any arbitrary one set by the user. Further, not limited to the collision information, the notification device may be configured to notify the notification destination of the failure information of each part and the consumption information of consumables. Regarding the detection of the presence or absence of a collision, it may be performed using the distance information acquired based on the output from the light receiving unit 2 described above, or may be performed by another detection unit (sensor).

[0086] [Modified Example] As described above, the preferred embodiments and examples of the present invention have been described. However, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist thereof.

[0087] For example, in the optical system according to each embodiment, the aperture stop is arranged on the object side of the first lens. However, the position of the aperture stop is not limited to this, and for example, the aperture stop may be arranged between the first lens and the second lens. Further, in the optical system according to each embodiment, the lens surfaces on the object side of the first lens, the second lens, and the third lens are aspherical surfaces. However, other lens surfaces may be aspherical surfaces or all lens surfaces may be spherical surfaces as required.

[0088] In the above-described embodiment, the case where the second control unit has a function as a collision determination unit (determination unit) has been described. However, it is not limited to this. For example, in an in-vehicle system, a collision determination unit separate from the second control unit may be provided. That is, the second control unit only needs to have at least a function as a distance calculation unit (distance information acquisition unit). Further, if necessary, the first control unit and the second control unit may be provided outside the distance measuring device (for example, inside the vehicle). [Explanation of Reference Numerals]

[0089] L1 First lens L2 Second lens ​

Claims

1. It has a first lens with a positive refractive power, a second lens with a negative refractive power, and a third lens with a positive refractive power, which are arranged in order from the object side to the image side. At least one of the first lens and the third lens is made of a chalcogenide material, and the second lens is made of a glass material. When the refractive index of the lens made of the chalcogenide material at a wavelength of 0.9 μm is Np, and the refractive index of the second lens at a wavelength of 0.9 μm is Nn. 0.75 < Np - Nn An optical system characterized by satisfying the conditional expression.

2. 0.75 < Np - Nn < 1.45 The optical system according to claim 1, characterized by satisfying the conditional expression.

3. When the focal length of the first lens is f1 and the focal length of the second lens is f2. - / 3.0 < f1 / f2 < -1.0 The optical system according to claim 1 or 2, characterized by satisfying the conditional expression.

4. When the focal length of the second lens is f2 and the combined focal length of the lenses arranged on the image side of the second lens is fr. [[ID=]]-3.0 < f2 / fr < -.05 The optical system according to any one of claims 1 to 3, characterized by satisfying the conditional expression.

5. When the focal length of the first lens is f1 and the combined focal length of the lenses arranged on the image side of the second lens is fr. 0.1 < fr / f1 < 1.0 The optical system according to any one of claims 1 to 4, characterized by satisfying the conditional expression.

6. When the focal length of the first lens is f1 and the focal length of the optical system is f. 0.1 < f1 / f < 3.0 The optical system according to any one of claims 1 to 5, characterized by satisfying the conditional expression.

7. When the focal length of the second lens is f2 and the focal length of the optical system is f. -3.0 < f2 / f < -0.1 The optical system according to any one of claims 1 to 6, characterized by satisfying the conditional expression.

8. When the combined focal length of the lenses arranged on the image side of the second lens is fr and the focal length of the optical system is f. 0.1 < fr / f < 2.0 The optical system according to any one of claims 1 to 7, characterized by satisfying the conditional expression.

9. When the F-number of the optical system is Fno 0.6 < Fno < 1.0 The optical system according to any one of claims 1 to 8, characterized by satisfying the conditional expression.

10. The optical system according to any one of claims 1 to 9, wherein the first lens is made of a chalcogenide material.

11. The optical system according to claim 10, wherein the third lens is made of a chalcogenide material.

12. The optical system according to any one of claims 1 to 11, wherein an aperture is disposed on the object side of the first lens.

13. An imaging device comprising the optical system according to any one of claims 1 to 12, and a light receiving element that receives an image of an object formed by the optical system.

14. A distance measuring device comprising the imaging device according to claim 13, and a control unit that acquires distance information of the object based on an output of the light receiving element.

15. An imaging system comprising the imaging device according to claim 13, and a determination unit that determines a possibility of collision between the moving device and the object based on the distance information of the object.

16. The imaging system according to claim 15, further comprising a control device that outputs a control signal for generating a braking force to the moving device when it is determined that there is a possibility of collision between the moving device and the object.

17. The imaging system according to claim 15 or 16, further comprising a warning device that warns a user of the moving device when it is determined that there is a possibility of collision between the moving device and the object.

18. The imaging system according to any one of claims 15 to 17, further comprising a notification device that notifies external information regarding a collision between the moving device and the object.

19. A moving device comprising the imaging device according to claim 13, and being movable while holding the imaging device.

20. The moving device according to claim 19, further comprising a determination unit that determines a possibility of collision with the object based on the distance information of the object.

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