Image capturing lens and image capturing device having the same

Abstract

To provide an image capturing lens which is compact, has high resolution, and yet offers reduced manufacturing variations, and a ranging sensor.SOLUTION: An image capturing lens is provided, consisting of a first lens, a second lens, a third lens, and a fourth lens arranged in order from the object side. The first lens has negative refractive power and has a concave surface on the object side. The second lens has positive refractive power and has convex surfaces both on the object side and the imaging plane side. The third lens has positive refractive power and has a convex surface on the imaging plane side. The fourth lens has negative refractive power and has a concave surface on the imaging plane side. The lens system satisfies the following conditions: f1 / f<-4 ...(1), 0.8<f2 / f ...(2), where f represents a focal length of the lens system, f1 represents a focal length of the first lens, and f2 represents a focal length of the second lens.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an imaging lens and an imaging device including the same. [Background technology]

[0002] In recent years, as typified by the increasing performance of imaging devices mounted on mobile communication terminals such as smartphones, there has been a demand for smaller imaging lenses with higher resolution for imaging devices mounted on a wide range of electronic devices. For example, Patent Document 1 listed below discloses a proposal for a four-element imaging lens that is smaller and has higher resolution.

[0003] Recently, electronic devices equipped with distance measuring sensors such as ToF (Time Of Flight) sensors have been increasing. Such distance measuring sensors measure the distance to an object from the time it takes for light to be emitted from a light source and for the light reflected by the object to be received by a light receiving element. Such distance measuring sensors are also a type of imaging device, and the reflected light is received by a light receiving element through an imaging lens. There is a demand for imaging lenses that are smaller and have higher resolution for use in distance measuring sensors. Patent Document 2 listed below discloses a proposal for achieving stable resolution performance for an imaging lens that forms an image using near-infrared light. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6324824 [Patent Document 2] Patent No. 6718147 Summary of the Invention [Problem to be solved by the invention]

[0005] If an imaging lens is designed improperly, the performance values ​​of the lenses actually produced will vary greatly compared to the design values, and the overall performance of a lens system made up of multiple lenses will not be fully demonstrated. Patent Documents 1 and 2 mentioned above do not mention this point, and there is room for improvement in realizing an imaging lens that is small, has high resolution, and can reduce production variation.

[0006] In view of the above, an object of the present disclosure is to provide an imaging lens that is small and has high resolution, while being able to reduce production variations, and an imaging device including the same. [Means for solving the problem]

[0007] An imaging lens according to one embodiment of the present disclosure is configured as a lens system including, in order from the object side, a first lens, a second lens, a third lens, and a fourth lens, wherein the first lens has negative refractive power and its object side lens surface is convex, the second lens has positive refractive power and its object side lens surface is convex, the third lens has positive refractive power and its image plane side lens surface is convex, and the fourth lens has negative refractive power and its image plane side lens surface is concave, and the lens system satisfies the following conditions:

[0008] f1 / f<-4 (1) 0.8 <f2 / f ···(2) Here, f is the focal length of the lens system, f1 is the focal length of the first lens, and f2 is the focal length of the second lens.

[0009] An imaging device according to another aspect of the present disclosure includes the imaging lens having the above-described configuration. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide an imaging lens that is small, has high resolution, and can reduce production variations, and a distance measuring sensor including the same. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a distance measuring sensor to which an imaging lens according to an embodiment of the present disclosure is applied. [Figure 2] FIG. 2 is a configuration diagram of an imaging lens according to the first embodiment of the present disclosure. [Figure 3] FIG. 3 is an aberration diagram of the imaging lens shown in FIG. [Figure 4] FIG. 4 is a graph showing the relative light amount versus image height of the imaging lens shown in FIG. [Figure 5] FIG. 5 is a configuration diagram of an imaging lens according to a second embodiment of the present disclosure. [Figure 6] FIG. 6 is an aberration diagram of the imaging lens shown in FIG. [Figure 7] FIG. 7 is a graph showing the relative light amount versus image height of the imaging lens shown in FIG. [Figure 8] FIG. 8 is a configuration diagram of an imaging lens according to a third embodiment of the present disclosure. [Figure 9] FIG. 9 is an aberration diagram of the imaging lens shown in FIG. [Figure 10] FIG. 10 is a graph showing the relative light amount versus image height of the imaging lens shown in FIG. [Figure 11] FIG. 11 is a configuration diagram of an imaging lens according to a fourth embodiment of the present disclosure. [Figure 12] FIG. 12 is an aberration diagram of the imaging lens shown in FIG. [Figure 13] FIG. 13 is a graph showing the relative light amount versus image height of the imaging lens shown in FIG. [Figure 14] FIG. 14 is a configuration diagram of an imaging lens according to a fifth embodiment of the present disclosure. [Figure 15] FIG. 15 is an aberration diagram of the imaging lens shown in FIG. [Figure 16] FIG. 16 is a graph showing the relative light amount versus image height of the imaging lens shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment will be described below with reference to the drawings. Throughout the drawings, identical or corresponding elements are designated by the same reference numerals, and redundant detailed descriptions will be omitted. Below, an example will be given in which an imaging device to which an imaging lens according to the present disclosure is applied constitutes a distance measurement sensor.

[0013] [Example of a distance measurement sensor to which an imaging lens is applied] FIG. 1 is a diagram illustrating a schematic configuration of a distance measurement sensor to which an imaging lens according to an embodiment of the present disclosure is applied. As shown in FIG. 1, the distance measurement sensor 10 includes a light source 20, a light receiver 30, and a controller 40. The light source 20 is, for example, a laser diode or a light-emitting diode that emits near-infrared light. The wavelength of light emitted by the light source 20 is set within a range, for example, with a lower limit of 700 nm, preferably 800 nm, and an upper limit of 1100 nm, preferably 1000 nm. The light source 20 is connected to the controller 40 via a driver 21. The driver 21 causes the light source 20 to emit light in response to a drive signal from the controller 40.

[0014] The light receiver 30 includes an imaging lens 1 configured with a lens system 2 (described later), and an imaging element 3 including a plurality of light receiving elements arranged on an imaging plane IA of the imaging lens 1. The imaging lens 1 shown in FIG. 1 is the same as the imaging lens 1A of Example 1 (described later with reference to FIG. 2). The plurality of light receiving elements that configure the imaging element 3 include, for example, photodiodes. For example, the imaging element 3 is a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor.

[0015] The controller 40 includes a calculation unit 41, an input unit 42, an output unit 43, a signal transmission unit 44, a signal reception unit 45, and a storage unit 46. These components are configured to be able to transmit signals to each other via a bus 47. The controller 40 is configured as a computer including a CPU, a main memory (RAM), storage, a communication interface, etc. Therefore, the above components 41, 42, ..., 46 can be considered as processing circuits.

[0016] The input unit 42 receives a control signal from an external device. For example, if the distance measurement sensor 10 is mounted on a communication terminal such as a smartphone, it receives a distance measurement start signal from a higher-level processor in the communication terminal as a control signal. When the input unit 42 receives the control signal, the signal transmission unit 44 outputs a drive signal for turning on the light source 20. The light receiver 30 receives (image captures) light that is emitted from the light source 20 and reflected by the subject. The image sensor 3 (light receiving element) converts the reflected light received through the imaging lens 1 into an electrical signal (image capture signal) and transmits it to the controller 40. The signal reception unit 45 receives the image capture signal from the light receiver 30.

[0017] The calculation unit 41 measures the time from when light emitted by the light source 20 is emitted until it is received by the image sensor 3, calculates the distance between the distance measuring sensor 10 and the subject from that time and the speed of light, and generates distance measurement data. The calculation unit 41 calculates the distance for each light receiving element (pixel) that makes up the image sensor 3, and can output the distance measurement data as image data. The output unit 43 outputs the distance measurement data calculated by the calculation unit 41 to the outside. For example, when the distance measuring sensor 10 is installed in a communication terminal as described above, the distance measurement data is output to a higher-level processor in the communication terminal.

[0018] [Overview of imaging lenses] The imaging lens 1 in this embodiment is composed of a lens system 2 in which, from the object side, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4 are arranged. In Fig. 1, the lens surfaces of the lens system 2 are denoted as S1, S2, ..., S8 in order from the object side. For example, lens surface S1 refers to the lens surface of the first lens L1 facing the object side, and lens surface S2 refers to the lens surface of the first lens L1 facing the imaging surface side.

[0019] The first lens L1 has negative refractive power and its object-side lens surface S1 is convex. The second lens L2 has positive refractive power and its object-side lens surface S3 and its image-side lens surface S4 are both convex. The third lens L3 has positive refractive power and its image-side lens surface S6 is convex. The fourth lens L4 has negative refractive power and its image-side lens surface S8 is concave.

[0020] 1, the lens surface S2 of the first lens L1 on the imaging surface side is concave, the lens surface S5 of the third lens L3 on the object side is concave, and the lens surface S7 of the fourth lens L4 on the object side is convex. A bandpass filter 4 for transmitting near-infrared light is provided between the fourth lens L4 and the imaging surface IA (image sensor 3). The bandpass filter 4 may be omitted. Alternatively, an optical member such as a seal glass for protecting the image sensor 3 may be disposed in the position of the bandpass filter 4.

[0021] In this embodiment, the lens system 2 satisfies the following conditional expressions (1) and (2). f1 / f<-4 (1) 0.8 <f2 / f ···(2) Here, f is the focal length of the lens system 2, f1 is the focal length of the first lens L1, and f2 is the focal length of the second lens L2.

[0022] Conditional formula (1) defines the negative refractive power of the first lens L1, which has negative refractive power. The larger the negative value of f1 / f (the smaller the absolute value), the stronger the negative refractive power of the first lens L1, and the smaller the value of f1 / f (the larger the absolute value), the weaker the negative refractive power of the first lens L1.

[0023] If the value of f1 / f exceeds the upper limit of conditional expression (1), the negative refractive power of the first lens L1 becomes too strong, making it difficult to reduce the overall length of the lens system 2 while suppressing aberrations. On the other hand, by setting the value of f1 / f to be less than the upper limit and satisfying conditional expression (1), the refractive power of the first lens L1 is appropriately defined, making it possible to reduce the overall length of the lens system 2. It is preferable to set the upper limit of conditional expression (1) to -6.

[0024] Conditional formula (2) defines the positive refractive power of the second lens L2, which has positive refractive power. The smaller the positive value of f2 / f, the stronger the positive refractive power of the second lens L2, and the larger the positive value of f2 / f, the weaker the positive refractive power of the second lens L2.

[0025] In the lens system 2 of this embodiment, the second lens L2 is a main lens that determines the refractive power of the entire lens system 2. When the refractive power of the second lens L2 becomes stronger as the value of f2 / f falls below the lower limit of conditional expression (2), the occurrence of on-axis aberration increases and performance degradation due to decentering error increases. As a result, the performance values ​​of the second lens L2 that are actually produced vary greatly from the performance design values ​​of the second lens L2, and the performance of the entire lens system 2 cannot be fully demonstrated.

[0026] In contrast, by satisfying the range of conditional expression (2), the overall length can be shortened, resolution can be increased, the occurrence of on-axis aberration can be suppressed, and performance degradation due to decentering error can be reduced. As a result, a lens system 2 can be realized that can reduce production variations. It is preferable that the lower limit of conditional expression (2) be set to 0.9.

[0027] Furthermore, an upper limit may be set in conditional expression (2). In this case, the upper limit of conditional expression (2) is preferably set to, for example, 2, and more preferably to 1.6. By setting the value of f2 / f to be smaller than the upper limit, it becomes easy to ensure the refractive power of the second lens L2 and to ensure the positive refractive power required for shortening the overall length and increasing the diameter of the lens system 2.

[0028] In this embodiment, the lens system 2 can further satisfy the following conditional expression (3). f / Epd<1.8 (3) where Epd is the entrance pupil diameter.

[0029] Conditional formula (3) defines the so-called F-number. By satisfying conditional formula (3) by setting the value of f / Epd to be less than the upper limit, it is possible to ensure the necessary amount of light with a short exposure time even for a compact, high-definition image sensor 3.

[0030] In this embodiment, the lens system 2 can further satisfy the following conditional expression (4). R1 / f<1.8 (4) Here, R1 is the radius of curvature of the object-side lens surface S1 of the first lens L1.

[0031] Conditional expression (4) defines the relationship between the radius of curvature of the object-side lens surface S1 of the first lens L1 and the focal length. By satisfying conditional expression (4) with the value of R1 / f being less than the upper limit, divergence of on-axis rays at the first lens L1 can be suppressed and the overall length of the lens system 2 can be shortened. Note that the upper limit of conditional expression (4) is preferably set to 1.6.

[0032] Furthermore, a lower limit may be set in conditional formula (4). In this case, the lower limit is preferably 0.5, and more preferably 0.7. By making the value of R1 / f greater than the lower limit, it is possible to prevent the refractive power of the object-side surface of the first lens L1 from becoming weak, and to shorten the overall length of the lens system 2.

[0033] In this embodiment, the lens system 2 can further satisfy the following conditional expression (5). nd2>1.57 (5) Here, nd2 is the refractive index of the second lens L2.

[0034] Conditional formula (5) defines the refractive index of second lens L2. As described above, second lens L2 is the main lens that determines the refractive power of the entire lens system 2. Therefore, if the refractive index nd2 of second lens L2 falls below the lower limit of conditional formula (5), the refractive power of the entire lens system 2 cannot be ensured, and the amount of aberration generated increases.

[0035] In contrast, by making the refractive index nd2 of the second lens L2 larger than the lower limit value and satisfying conditional expression (5), the refractive power of the second lens L2 can be ensured, and the amount of aberration generated in the entire lens system 2 can be suppressed.

[0036] In this embodiment, the lens system 2 can further satisfy the following conditional expression (6). D23 / f<0.2 (6) Here, D23 is the distance between the lens surface S2 of the first lens L1 on the imaging plane side and the lens surface S3 of the second lens L2 on the object side.

[0037] Conditional formula (6) defines the lens spacing between the first lens L1 and the second lens L2. If the value of D23 / f exceeds the upper limit of conditional formula (6), the spacing between the first lens L1 and the second lens L2 becomes large, and the height of off-axis rays passing through the second lens L2 and the third lens L3 becomes large, making it difficult to reduce the size of the lens system 2. In addition, the amount of off-axis aberrations generated increases, making it difficult to correct the aberrations.

[0038] In contrast, by making the value of D23 / f smaller than the upper limit and satisfying conditional expression (6), the effective diameters of the second lens L2 and the third lens L3 can be made smaller. Furthermore, the amount of aberration produced can be reduced, resulting in a high-resolution lens. The upper limit of conditional expression (6) is preferably set to 0.15, and more preferably to 0.12. A lower limit may also be set to conditional expression (6). In this case, the lower limit of conditional expression (6) is preferably set to 0.01, and more preferably to 0.03.

[0039] In this embodiment, the lens system 2 can further satisfy the following conditional expression (7). 1 <TTL / f<2 ···(7) However, TTL is the overall length of the lens system 2. More specifically, TTL is the length from the object-side lens surface S1 of the first lens L1 to the imaging plane IA.

[0040] Conditional expression (7) defines the overall length of the lens system 2. If the value of TTL / f exceeds the upper limit of conditional expression (7), the overall length of the lens system 2 becomes long, making it impossible to reduce the size of the lens system 2. Also, if the value of TTL / f falls below the lower limit of conditional expression (7), it is impossible to suppress the amount of aberration generated by the entire lens system 2.

[0041] On the other hand, by satisfying the value of TTL / f within the range of conditional expression (7), it is possible to reduce the size of the lens system 2 while suppressing the amount of aberration generated in the entire lens system 2. The upper limit of conditional expression (7) is preferably set to 1.8. The lower limit of conditional expression (7) is preferably set to 1.2.

[0042] In this embodiment, the lens system 2 can further satisfy the following conditional expression (8). f4 / f<-2 (8) Here, f4 is the focal length of the fourth lens L4.

[0043] Conditional expression (8) defines the relationship between the focal length of the fourth lens L4, which has negative refractive power, and the lens system 2. If the value of f4 / f exceeds the upper limit of conditional expression (8), the refractive power of the fourth lens L4 becomes too strong, making aberration correction difficult and significantly degrading performance due to decentering error. Furthermore, the fourth lens L4 is located close to the imaging surface IA and is susceptible to the heat generated by the imaging element 3 (light receiving element). Plastic lenses, in particular, have larger linear expansion coefficients and refractive indices that change with temperature than glass lenses, so changes in refractive power due to temperature change become significant, resulting in focal position fluctuations, degradation of optical characteristics such as resolution, and so on.

[0044] In contrast, by making the value of f4 / f smaller than the upper limit and satisfying conditional expression (8), the refractive power of the fourth lens L4 can be set within an appropriate range, thereby suppressing performance degradation due to decentering error and also suppressing fluctuations in optical characteristics due to temperature changes. Note that it is preferable to set the upper limit of conditional expression (8) to -3.

[0045] In this embodiment, the lens system 2 can further satisfy the following conditional expression (9). (R1+R2) / (R1-R2)>6 (9) Here, R1 is the radius of curvature of the lens surface S1 of the first lens L1 on the object side, and R2 is the radius of curvature of the lens surface S2 of the first lens L1 on the imaging surface side.

[0046] Conditional formula (9) defines the shape of first lens L1. By making the value of (R1+R2) / (R1-R2) greater than the lower limit of conditional formula (9), it is possible to prevent the refractive power of first lens L1 from becoming too large, and to make it easier to reduce the amount of aberration generated by each surface of first lens L1.

[0047] As described above, according to this embodiment, it is possible to provide an imaging lens 1 that is small, has high resolution, and can reduce production variations. Moreover, by using a lens system 2 with a small F-number, it is possible to provide an imaging lens 1 that can ensure sufficient peripheral light even when the angle of view is large.

[0048] In Patent Document 1, the F-number is about 2.3, making it difficult to achieve a large-diameter lens with a small F-number. Also, in Patent Document 2, the F-number is 2.0 to 2.6, and the half angle of view is narrow, at around 30 degrees. In particular, when applying the imaging lens 1 to a distance measuring sensor 10 such as that shown in FIG. 1, a lens with a wide angle of view (for example, a half angle of view of 35 degrees or more) and a small F-number that can ensure sufficient peripheral light intensity is desired.

[0049] In contrast to this, according to this embodiment, it is possible to provide an imaging lens 1 that is configured with a lens system 2 that has a wide half angle of view of 35 degrees or more while having an F-number of less than 1.8. Moreover, even with this type of imaging lens 1, it is possible to reduce production variations while maintaining a small size and high resolution.

[0050] [Example] Below, examples of the imaging lens 1 of the present disclosure are shown. The parameters used in each example are as follows. In the lens data and lens system specification data tables, angles are measured in degrees and lengths in mm. The calculated focal length wavelength is 940 nm. f: focal length of lens system 2 (mm) Fno: F-number (=f / Epd) ω: Half angle of view ImgH: Maximum image height TTL: Total optical length of lens system 2 (the distance on the optical axis from the object-side lens surface S1 of the first lens L1 to the image plane IA) i: Lens surface number (i=1, 2, ..., 8) Ri: Radius of curvature of the i-th lens surface (mm) Dik: Center-to-center distance between the i-th lens surface Si and the k=i+1-th lens surface Sk nd: refractive index of the lens for the d line vd: Abbe number of the lens The notation (STO) in the lens surface number indicates that the diaphragm surface STO is located on the corresponding lens surface Si. The lens surface on the object side of the bandpass filter 4 is numbered 9, and the lens surface on the imaging surface side is numbered 10. "inf" indicates that the surface is flat.

[0051] In each example, all lens surfaces Si have an aspherical shape, which is expressed by the following equation, where X is the distance (sag) from the tangent plane of the surface vertex in the optical axis direction, H is the height from the optical axis, R is the radius of curvature, K is the conic constant, and Am is the m-th aspherical coefficient. X=(H 2 / R) / [1+{1-(1+K)H 2 / R 2} 1 / 2 ]+ΣAm·H m ···(10)

[0052] Therefore, in the following, the value of Am in the above formula (10) is shown to specify the aspherical shape. In the aspherical data table, the numerical values ​​of the aspherical coefficients "E±n" (n: natural number) are expressed as exponential expressions with base 10. In other words, "E±n" means "×10 ±n " means.

[0053] [Example 1] Fig. 2 is a configuration diagram of imaging lens 1A in Example 1 of the present disclosure. Fig. 3 is an aberration diagram of imaging lens 1A shown in Fig. 2 at a wavelength of 940 nm. Fig. 4 is a graph showing the relative light intensity versus image height of imaging lens 1A shown in Fig. 2. The relative light intensity indicates the proportion of the light intensity at an image height position when the light intensity at the optical axis position on imaging plane IA is set to 100%.

[0054] The imaging lens 1A of Example 1 is composed of, in order from the object side, a first lens L1 with negative refractive power, with a convex surface facing the object side and a concave surface facing the imaging surface side, an aperture stop STO, a positive second lens L2 with a biconvex shape, a positive third lens L3 with a concave surface facing the object side and a convex surface facing the imaging surface side, and a negative fourth lens L4 with a convex surface facing the object side and a concave surface facing the imaging surface side.

[0055] Table 1 below shows the lens data of the imaging lens 1A of Example 1.

[0056] [Table 1]

[0057] The conic constant K and the aspherical coefficient Am in Example 1 are shown in Tables 2 and 3 below.

[0058] [Table 2]

[0059] [Table 3]

[0060] The focal length f, F-number, half angle of view ω, maximum image height ImgH, and total optical length TTL of the imaging lens 1A in Example 1 are shown in Table 4 below.

[0061] [Table 4]

[0062] [Example 2] Fig. 5 is a configuration diagram of imaging lens 1B in Example 2 of the present disclosure. Fig. 6 is an aberration diagram of imaging lens 1B shown in Fig. 5. Fig. 7 is a graph showing the relative light intensity versus image height of imaging lens 1B shown in Fig. 5. The relative light intensity indicates the proportion of the light intensity at the image height position when the light intensity at the optical axis position on imaging plane IA is set to 100%.

[0063] The imaging lens 1B of Example 2 is composed of, in order from the object side, an aperture stop STO, a first lens L1 with negative refractive power and a convex surface facing the object side and a concave surface facing the imaging surface side, a positive second lens L2 with a biconvex shape, a positive third lens L3 with a concave surface facing the object side and a convex surface facing the imaging surface side, and a negative fourth lens L4 with a convex surface facing the object side and a concave surface facing the imaging surface side.

[0064] Table 5 below shows the lens data of the imaging lens 1B of Example 2.

[0065] [Table 5]

[0066] The conic constant K and the aspherical coefficient Am in Example 2 are shown in Tables 6 and 7 below.

[0067] [Table 6]

[0068] [Table 7]

[0069] The focal length f, F-number, half angle of view ω, maximum image height ImgH, and total optical length TTL of the imaging lens 1B in Example 2 are shown in Table 8 below.

[0070] [Table 8]

[0071] [Example 3] Fig. 8 is a configuration diagram of an imaging lens 1C according to a third embodiment of the present disclosure. Fig. 9 is an aberration diagram of the imaging lens 1C shown in Fig. 8. Fig. 10 is a graph showing the relative light intensity versus image height for the imaging lens 1C shown in Fig. 8. The relative light intensity indicates the proportion of the light intensity at an image height position when the light intensity at the optical axis position on the imaging plane IA is set to 100%.

[0072] The imaging lens 1C of Example 3 is composed of, in order from the object side, a first lens L1 with negative refractive power, with a convex surface facing the object side and a concave surface facing the imaging plane side, an aperture stop STO, a positive second lens L2 with a biconvex shape, a positive third lens L3 with a concave surface facing the object side and a convex surface facing the imaging plane side, and a negative fourth lens L4 with a convex surface facing the object side and a concave surface facing the imaging plane side.

[0073] Table 9 below shows the lens data of the imaging lens 1C of Example 3.

[0074] [Table 9]

[0075] The conic constant K and the aspherical coefficient Am in Example 3 are shown in Tables 10 and 11 below.

[0076] [Table 10]

[0077] [Table 11]

[0078] The focal length f, F-number, half angle of view ω, maximum image height ImgH, and total optical length TTL of the imaging lens 1C in Example 3 are shown in Table 12 below.

[0079] [Table 12]

[0080] [Example 4] Fig. 11 is a configuration diagram of an imaging lens 1D according to a fourth embodiment of the present disclosure. Fig. 12 is an aberration diagram of the imaging lens 1D shown in Fig. 11. Fig. 13 is a graph showing the relative light intensity versus image height of the imaging lens 1D shown in Fig. 11. The relative light intensity indicates the proportion of the light intensity at the image height position when the light intensity at the optical axis position on the imaging plane IA is set to 100%.

[0081] The imaging lens 1D of Example 4 is composed of, in order from the object side, a first lens L1 with negative refractive power, with a convex surface facing the object side and a concave surface facing the imaging surface side, an aperture stop STO, a positive second lens L2 with a biconvex shape, a positive third lens L3 with a concave surface facing the object side and a convex surface facing the imaging surface side, and a negative fourth lens L4 with a convex surface facing the object side and a concave surface facing the imaging surface side.

[0082] Table 13 below shows the lens data of the imaging lens 1D of Example 4.

[0083] [Table 13]

[0084] The conic constant K and the aspherical coefficient Am in Example 4 are shown in Tables 14 and 15 below.

[0085] [Table 14]

[0086] [Table 15]

[0087] The focal length f, F-number, half angle of view ω, maximum image height ImgH, and total optical length TTL of the imaging lens 1D in Example 4 are shown in Table 16 below.

[0088] [Table 16]

[0089] [Example 5] Fig. 14 is a configuration diagram of an imaging lens 1E according to a fifth embodiment of the present disclosure. Fig. 15 is an aberration diagram of the imaging lens 1E shown in Fig. 14. Fig. 16 is a graph showing the relative light intensity versus image height for the imaging lens 1E shown in Fig. 14. The relative light intensity indicates the proportion of the light intensity at the image height position when the light intensity at the optical axis position on the imaging plane IA is set to 100%.

[0090] The imaging lens 1E of Example 5 is composed of, in order from the object side, a first lens L1 with negative refractive power, with a convex surface facing the object side and a concave surface facing the imaging surface side, an aperture stop STO, a positive second lens L2 with a biconvex shape, a positive third lens L3 with a concave surface facing the object side and a convex surface facing the imaging surface side, and a negative fourth lens L4 with a convex surface facing the object side and a concave surface facing the imaging surface side.

[0091] Table 17 below shows the lens data of the imaging lens 1E of Example 5.

[0092] [Table 17]

[0093] The conic constant K and the aspherical coefficient Am in Example 5 are shown in Tables 18 and 19 below.

[0094] [Table 18]

[0095] [Table 19]

[0096] The focal length f, F-number, half angle of view ω, maximum image height ImgH, and total optical length TTL of the imaging lens 1E in Example 5 are shown in Table 20 below.

[0097] [Table 20]

[0098] Table 21 shows the values ​​corresponding to conditional expressions (1) to (9) in the lens systems of Examples 1 to 5. Tables 22 and 23 show the numerical values ​​related to conditional expressions (1) to (9). As shown in Table 21, all of conditional expressions (1) to (9) are satisfied in each of the Examples.

[0099] [Table 21]

[0100] [Table 22]

[0101] [Table 23]

[0102] Furthermore, as shown in the aberration diagrams of each example (FIGS. 3, 7, 11, 15, and 19), despite having a wide angle of view of 35 degrees or more half angle of view, it is possible to realize a lens system 2 in which the amount of transmitted light is secured and aberrations are well corrected. Furthermore, as shown in the graphs of peripheral illumination versus image height of the imaging lens of each example (FIGS. 4, 8, 12, 16, and 20), despite having a wide angle of view, it is possible to secure nearly 50% of the amount of light at positions with high image heights (peripheral illumination) as the amount of light at the optical axis position.

[0103] Although the embodiments of the present disclosure have been described above, the configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible as appropriate within the scope of the gist of the present disclosure. The present disclosure is not limited to the embodiments, but is limited only by the scope of the claims. [Industrial Applicability]

[0104] The present disclosure is useful for providing an imaging lens that is compact, has high resolution, and can reduce production variation. The imaging device to which the imaging lens of the present disclosure is applied is not limited to the distance measurement sensor exemplified in the above embodiment. For example, the imaging device may also be applied to a camera for photographing that forms an image using visible light. Furthermore, a distance measurement sensor to which the imaging lens of the present disclosure is applied is, for example, a distance measurement sensor that receives reflected light from a light source that emits single-wavelength light such as near-infrared light or visible light. A distance measurement sensor equipped with the imaging lens of the present disclosure is useful for providing, for example, photography assistance functions in imaging cameras such as background blurring and autofocus, autonomous driving technology for automatic vacuum cleaners and automobiles, face recognition technology, and AR space realization technology. [Explanation of symbols]

[0105] 1,1A,1B,1C,1D,1E Imaging lenses 2 Lens system 3. Image sensor (photodetector) 10. Distance sensor (imaging device) 20 light source L1 First lens L2 Second lens L3 Third lens L4 4th lens

Claims

1. A lens system including, in order from the object side, a first lens, a second lens, a third lens, and a fourth lens, the first lens has negative refractive power and has a convex lens surface on the object side; the second lens has a positive refractive power, and both its object side lens surface and its image pickup surface side lens surface are convex surfaces; the third lens has a positive refractive power and a lens surface on the imaging surface side thereof is a convex surface, the fourth lens has a negative refractive power and a lens surface on the imaging surface side thereof is a concave surface, The lens system is an imaging lens that satisfies the following conditions: f1 / f<-4...(1) 0.8<f2 / f...(2) Here, f is the focal length of the lens system, f1 is the focal length of the first lens, and f2 is the focal length of the second lens.

2. The imaging lens according to claim 1 , wherein the lens system further satisfies the following condition: f / Epd<1.8...(3) where Epd is the entrance pupil diameter.

3. The imaging lens according to claim 1 , wherein the lens system further satisfies the following condition: R1 / f<1.8...(4) Here, R1 is the radius of curvature of the lens surface on the object side of the first lens.

4. 4. The imaging lens according to claim 1, wherein the lens system further satisfies the following condition: nd2>1.57...(5) Here, nd2 is the refractive index of the second lens.

5. 5. The imaging lens according to claim 1, wherein the lens system further satisfies the following condition: D23 / f<0.2...(6) Here, D23 is the distance between the lens surface of the first lens on the image pickup surface side and the lens surface of the second lens on the object side.

6. 6. The imaging lens according to claim 1, wherein the lens system further satisfies the following condition: 1<TTL / f<2 (7) Here, TTL is the total length of the lens system.

7. 7. The imaging lens according to claim 1, wherein the lens system further satisfies the following condition: f4 / f<-2...(8) Here, f4 is the focal length of the fourth lens.

8. An imaging device comprising the imaging lens according to claim 1 .

9. A light source that irradiates light; a light receiving element that receives light reflected from the light source by a subject through the imaging lens, 9. The imaging device according to claim 8, configured as a distance measuring sensor that calculates a distance to the subject by measuring a time from when the light source emits light to when the reflected light is received.

Images