Imaging lens and imaging device

Abstract

An imaging lens (10) is formed by disposing, in order from an object side, a front group having negative power, an aperture, and a rear group having positive power. In the front group, a first lens surface has a convex shape toward the object side. In the rear group, a second lens surface has a convex shape toward the object side, a third lens surface has a convex shape toward an image side, and the third lens surface is provided with an infrared cut coating. If the radius of curvature of the second lens surface is Rr, the radius of curvature of the third lens surface is Re, and the distance on the optical axis from the second lens surface to the third lens surface is Da, then 1.6<(Rr+|Re|) / Da<2.3 is satisfied.

Description

[Technical field]

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

[0002] In recent years, surveillance cameras, vehicle-mounted cameras, etc. have become widespread. As surveillance cameras and vehicle-mounted cameras (hereinafter referred to as vehicle-mounted cameras, etc.) become widespread, imaging lenses equipped with such cameras are required to have simpler configurations and higher performance. The performance of vehicle-mounted cameras, etc., includes a wide angle of view, good image quality, no deterioration in performance even with temperature changes, and small size.

[0003] As an on-vehicle imaging lens, an imaging lens of five lenses in four groups in which a concave surface is formed on the lens surface facing the object side has been disclosed (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-145828 A Summary of the Invention

[0005] The imaging device of the present disclosure includes an imaging lens and a flat cover glass, arranged in order from the object side. The imaging lens includes, arranged in order from the object side, a front group having negative power, an aperture stop, and a rear group having positive power. The front group has a first lens surface closest to the object side that is convex toward the object side. The rear group has a second lens surface closest to the object side that is convex toward the object side, and a third lens surface closest to the image side that is convex toward the image side, and the third lens surface is provided with an infrared cut coating. The imaging lens also satisfies the following conditional formula (1). The imaging device also satisfies the following conditional formula (3). 1.6<(Rr+|Re|) / Da<2.3 (1) where Rr is the radius of curvature of the second lens surface, Re is the radius of curvature of the third lens surface, and Da is the distance from the second lens surface to the third lens surface on the optical axis. 0.50≦R1 / (Dt+Db)≦0.52 (3) where R1 is the radius of curvature of the first lens surface, Dt is the distance from the first lens surface to the third lens surface on the optical axis, and Db is the distance from the third lens surface to the object side surface of the cover glass on the optical axis. 。 [Brief description of the drawings]

[0006] [Figure 1] FIG. 2 is a cross-sectional view of an imaging lens and an imaging device. [Diagram 2] FIG. 11 is an explanatory diagram for explaining a model of a ghost that occurs due to re-reflection on the second lens surface (surface S6). [Diagram 3] FIG. 1 is an explanatory diagram illustrating a model of a ghost that occurs due to re-reflection on a first lens surface (surface S1). [Figure 4] FIG. 11 is an explanatory diagram for explaining a model of a ghost that occurs due to re-reflection on the second lens surface (surface S6). [Diagram 5] FIG. 11 is an explanatory diagram illustrating a model of a ghost that occurs due to re-reflection on the third lens surface (surface S12). [Figure 6] FIG. 1 is a cross-sectional view of an imaging lens according to a first embodiment. [Figure 7] 4 is a graph showing (A) spherical aberration, (B) astigmatism, and (C) distortion in Example 1. [Figure 8] 1 is a graph showing the MTF of Example 1. [Figure 9] 6 is a graph showing (A) spherical aberration, (B) astigmatism, and (C) distortion of Example 2. [Figure 10] 13 is a graph showing the MTF of Example 2. [Figure 11] 11 is a graph showing (A) spherical aberration, (B) astigmatism, and (C) distortion of Example 3. [Figure 12] 13 is a graph showing the MTF of Example 3. [Figure 13] 11 is a graph showing (A) spherical aberration, (B) astigmatism, and (C) distortion of Example 4. [Figure 14] 13 is a graph showing the MTF of Example 4. [Figure 15] 11 is a graph showing (A) spherical aberration, (B) astigmatism, and (C) distortion of Example 5. [Figure 16] 13 is a graph showing the MTF of Example 5. [Figure 17] 11 is a graph showing (A) spherical aberration, (B) astigmatism, and (C) distortion of Example 6. [Figure 18] 13 is a graph showing the MTF of Example 6. [Figure 19] 13 is a graph showing (A) spherical aberration, (B) astigmatism, and (C) distortion of Example 7. [Figure 20] 13 is a graph showing the MTF of Example 7. [Figure 21] 13 is a graph showing (A) spherical aberration, (B) astigmatism, and (C) distortion of Example 8. [Figure 22] 13 is a graph showing the MTF of Example 8. [Figure 23] 13 is a graph showing (A) spherical aberration, (B) astigmatism, and (C) distortion of Example 9. [Figure 24] 13 is a graph showing the MTF of Example 9. [Diagram 25] 13 is a graph showing (A) spherical aberration, (B) astigmatism, and (C) distortion of Example 10. [Figure 26] 13 is a graph showing the MTF of Example 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] In-vehicle cameras and the like are provided with an imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor). In-vehicle cameras and the like are provided with a function for preventing unnecessary light that causes deterioration of image quality from being incident on these imaging elements, thereby preventing deterioration of image quality and the like. Hereinafter, an imaging lens and an imaging device according to the present disclosure that suppress deterioration of image quality with a simple configuration will be described.

[0008] The imaging lens according to the embodiment includes, in order from the object side, a front group having negative power, an aperture stop, and a rear group having positive power. In the front group, a first lens surface closest to the object side has a convex shape toward the object side. In the rear group, a second lens surface closest to the object side has a convex shape toward the object side, and a third lens surface closest to the image side has a convex shape toward the image side, and the third lens surface is provided with an infrared cut coating. In addition, the imaging lens satisfies the following conditional formula (1). 1.6<(Rr+|Re|) / Da<2.3 (1) where Rr is the radius of curvature of the second lens surface, Re is the radius of curvature of the third lens surface, and Da is the distance from the second lens surface to the third lens surface on the optical axis.

[0009] The front group includes, from the object side, a first lens having a first lens surface and a concave meniscus shape, and a second lens having a concave meniscus shape. The second lens may be arranged with its convex surface facing the image side.

[0010] The rear group includes, in order from the object side, a third lens having a second lens surface, a fourth lens, and a cemented lens. The third lens, the fourth lens, and the cemented lens may all have positive power.

[0011] The cemented lens is made up of, in order from the object side, a fifth lens which is a concave lens and a sixth lens which is a convex lens. The sixth lens may have a third lens surface.

[0012] The following conditional expression (2) may be satisfied. 1.20≦(R1+|Re|) / Dt≦1.46 (2) where R1 is the radius of curvature of the first lens surface, Re is the radius of curvature of the third lens surface, and Dt is the distance from the first lens surface to the third lens surface on the optical axis.

[0013] An imaging device according to the embodiment includes, in order from the object side, any one of the imaging lenses described above and a flat cover glass.

[0014] The following conditional expression (3) may be satisfied. 0.50≦R1 / (Dt+Db)≦0.53 (3) where R1 is the radius of curvature of the first lens surface, Dt is the distance from the first lens surface to the third lens surface on the optical axis, and Db is the distance from the third lens surface to the object side surface of the cover glass on the optical axis.

[0015] The following conditional expression (4) may be satisfied. 0.66≦Rr / (Da+Db)≦0.83 (4) where Rr is the radius of curvature of the second lens surface, Da is the distance from the second lens surface to the third lens surface on the optical axis, and Db is the distance from the third lens surface to the object-side surface of the cover glass on the optical axis.

[0016] The following conditional expression (5) may be satisfied. 2.28≦|Re| / Db≦2.88 (5) where Re is the radius of curvature of the third lens surface, and Db is the distance on the optical axis from the third lens surface to the object-side surface of the cover glass.

[0017] The imaging lens and imaging device of the present disclosure will be described in detail below.

[0018] For example, when focusing on the infrared region, the imaging element is also sensitive to the infrared region. Therefore, the quality of the image may be degraded when infrared rays enter the imaging element. In-vehicle cameras and the like are provided with a function (infrared cut function) that prevents infrared rays from entering the imaging element, such as an infrared filter or an infrared cut coating on the lens, to prevent degradation of image quality caused by infrared rays.

[0019] However, when an infrared filter is used, the incident light, particularly from a high-brightness light source, is partially reflected by the incident side of the infrared filter (the object side of the imaging lens). Due to this reflected light, for example, it is re-reflected by the lens surface facing the infrared filter, and an image is formed on the light receiving surface of the imaging element, becoming a light image called a ghost, which may cause a decrease in image quality. In addition, when an infrared cut coating or the like is applied to a lens, etc., the anti-reflection performance may decrease because the infrared cut performance is generally prioritized. Therefore, even in a lens or the like that is applied with an infrared cut coating or the like, ghosts may occur due to the reflected light from the lens surface of the lens that is applied with an infrared cut coating or the like, as in the case of an infrared filter. Therefore, one embodiment of the present disclosure has the following configuration.

[0020] 1, the imaging device 20 includes an imaging lens 10 and an image sensor 11. The image sensor 11 has a cover glass CG that protects an imaging surface IP. Therefore, the imaging lens 10 is a lens that forms an image of a subject on the imaging surface IP through the cover glass CG and captures the subject.

[0021] The imaging lens 10 is configured by arranging, from the object side along the optical axis Z1, a front group G1 having negative power, an aperture stop ST, and a rear group G2 having positive power. The imaging lens 10 is a retrofocus type wide-angle lens. The angle of view is, for example, an ultra-wide-angle lens exceeding 100 degrees. The temperature environment in which the imaging lens is used is, for example, from about -40°C to about 120°C.

[0022] In this embodiment, the front group G1 is composed of a first lens L1 and a second lens L2 arranged in order from the object side. The rear group G2 is composed of a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6 arranged in order from the object side. The fifth lens L5 and the sixth lens L6 form a cemented lens CL. Therefore, the imaging lens 10 of this embodiment is composed of five groups and six lenses. In addition, an aperture stop ST is provided between the second lens L2 and the third lens L3. Each of the first lens to the sixth lens is formed using, for example, glass.

[0023] In the front group G1, the first lens surface (surface S1) closest to the object side has a convex shape toward the object side. In the rear group G2, the second lens surface (surface S6) closest to the object side has a convex shape toward the object side. In the rear group G2, the third lens surface (surface S12) closest to the image side has a convex shape toward the image side. Furthermore, in the rear group G2, the third lens surface (surface S12) is provided with an infrared cut coating IR. Note that the infrared cut coating IR and the like are shown diagrammatically in FIG. 1 and may differ from the actual dimensions.

[0024] Surface S1 may be formed in a convex shape on the object side so that the radius of curvature of the center portion near the optical axis Z1 is small. By forming it in this way, it is possible to suppress the occurrence of ghosts caused by surface S1 of imaging lens 10, such as ghosts caused by reflected light of incident light being re-reflected toward the image side.

[0025] The radius of curvature Rr of the surface S6, the absolute value |Re| of the radius of curvature Re of the surface S12, and the distance Da from the surface S6 to the surface S12 on the optical axis satisfy the following formula (1).

[0026] 1.6<(Rr+|Re|) / Da<2.3 (1)

[0027] As shown in Figures 2 and 4, by satisfying formula (1), when light reflected toward the object side by surface S12 is reflected again by surface S6 and focused on imaging surface IP, the reflected light is actively cross-diffused, and the focused light diameter is enlarged while maintaining the optical performance of imaging lens 10. Therefore, even if a ghost of a specific color, for example, red, occurs due to the reflected light from surface S12 having the infrared cut coating IR, the ghost image on imaging surface IP has an enlarged focused light diameter, so the luminance is sufficiently reduced, and a noticeable effect on image quality is suppressed. In this embodiment, by satisfying formula (1), for example, the luminance can be reduced to 1 / 10 of the incident light. 7 As described above, the imaging lens 10 has an infrared cutting function, but suppresses the occurrence of ghosts caused by reflected light with a simple configuration that does not incorporate any special elements such as an infrared filter. In addition, in formula (1), the lower limit value of 1.6 may be 1.7. In formula (1), the lower limit value of 1.6 may be 1.8. In formula (1), the upper limit value of 2.3 may be 2.1. In formula (1), the upper limit value of 2.3 may be 2.0.

[0028] The radius of curvature Rr of the surface S6 and the radius of curvature Re of the surface S12 may satisfy the following formula (1a): When formula (1a) is satisfied, the occurrence of ghosts is suppressed while the optical performance of the imaging lens 10 is more favorably maintained.

[0029] -1.11≦Rr / Re≦-0.90 (1a)

[0030] The radius of curvature Re of the surface S12 and the distance Da from the surface S6 to the surface S12 on the optical axis Z1 may satisfy the following formula (1b): When formula (1b) is satisfied, the occurrence of ghosts is suppressed while the optical performance of the imaging lens 10 is more favorably maintained.

[0031] -1.13≦Re / Da≦-0.82 (1b)

[0032] The radius of curvature Rr of the surface S6 and the distance Da from the surface S6 to the surface S12 on the optical axis Z1 may satisfy the following formula (1c): When formula (1c) is satisfied, the occurrence of ghosts is suppressed while the optical performance of the imaging lens 10 is more favorably maintained.

[0033] 0.90≦Rr / Da≦1.21 (1c)

[0034] The imaging lens 10 has a focal length f 16 and a distance Dt from the surface S1 on the optical axis to the surface S12 may satisfy the following formula (1d): By satisfying formula (1d), the imaging lens has appropriate optical performance and can be made compact.

[0035] 3.93≦Dt / f 16 ≦4.56 (1d)

[0036] As shown in Fig. 1, in this embodiment, the front group G1 is composed of a first lens L1 and a second lens L2 arranged in order from the object side. The first lens L1 is a concave meniscus lens having a first lens surface (surface S1). The second lens L2 is a concave meniscus lens. The lenses included in the front group G1 (the first lens L1 and the second lens L2) may be formed of a glass material having excellent durability so that they may be exposed to the installation environment, for example.

[0037] The first lens L1 is an aspheric lens having a negative power. For example, the first lens L1 has a temperature coefficient dn / dt of the relative refractive index at 20° C. to 40° C. of 3.6 (10 -6 / °C). In this specification, the temperature coefficient dn / dt is a value measured in accordance with the Japan Optical Glass Industry Association standard, JOGIS J18-2008 "Method of measuring the temperature coefficient of refractive index of optical glass". In addition, the first lens L1 may suppress the occurrence of aberration by making the radius of curvature of the surface S1 small at the center near the optical axis Z1, while setting the radius of curvature of the peripheral portion to be relatively large.

[0038] The second lens L2 is an aspheric lens having negative power. Therefore, the first lens L1 and the second lens L2 suppress aberration in the imaging lens 10, and ensure high optical performance stably over the entire angle of view.

[0039] The second lens L2 is arranged with its convex surface facing the image side. The first lens L1 and the second lens L2 are arranged close to the aperture stop ST. This makes it possible to ensure a desired wide angle while keeping the effective diameter of the first lens L1 small. Furthermore, the second lens L2 has a relatively large effect on the MTF (Modulation Transfer Function) and aberration among the lenses constituting the imaging lens 10. Therefore, the second lens L2 contributes to the excellent optical performance of the imaging lens 10 as a whole. Furthermore, the second lens L2 formed with an aspheric surface is arranged immediately before the object side of the aperture stop ST. This makes it possible for the imaging lens 10 to prevent ghosts caused by the second lens L2.

[0040] The rear group is composed of, in order from the object side, a third lens L3, a fourth lens L4, and a cemented lens CL. The third lens L3 has a second lens surface (surface S6). The cemented lens CL has a third lens surface (surface S12). The surface S12 is provided with an infrared cut coating IR. The third lens L3, the fourth lens L4, and the cemented lens CL all have positive power.

[0041] The third lens L3 is a spherical lens. The third lens L3 is formed using a material whose temperature coefficient dn / dT is a negative value. For example, the third lens L3 has a temperature coefficient dn / dt of the relative refractive index at 20° C. to 40° C. of −5.6 (10 -6 / ° C.), the third lens L3 has anomalous dispersion. Furthermore, the third lens L3 has a relatively short focal length.

[0042] The fourth lens L4 is an aspheric lens. The fourth lens L4 is made of a glass material that has a large linear expansion coefficient and a negative temperature coefficient dn / dt compared to the materials of the other lenses that make up the imaging lens 10. For example, the fourth lens L4 has a temperature coefficient dn / dt of the relative refractive index at 20° C. to 40° C. of −8.5 (10 -6 / °C). The fourth lens L4 has anomalous dispersion. Furthermore, the fourth lens L4 has a relatively short focal length.

[0043] As described above, the third lens L3 and the fourth lens L4 provide a function of temperature compensation for the entire imaging lens 10. Therefore, for example, the imaging lens 10 also has a function of suppressing the focus movement amount to a small amount. In addition, since the third lens L3 and the fourth lens L4 are used in combination, the radius of curvature of the surface S6, which is the object side surface of the third lens L3, can be controlled and set so as to suppress ghosting to a high degree while maintaining the optical performance of the imaging lens 10. Therefore, for example, ghosting caused by light reflected from the surface S12, which is the image side surface of the cemented lens CL having an infrared cut coating IR, being re-reflected from the surface S6 can be suppressed to a high degree.

[0044] The cemented lens CL is composed of, in order from the object side, a fifth lens L5 and a sixth lens L6. The fifth lens L5 is a concave lens. The sixth lens L6 is a convex lens. The fifth lens L5 and the sixth lens L6 are spherical lenses. As the cemented lens CL, the imaging lens 10 as a whole has a function of improving optical performance such as chromatic aberration correction. In addition, by using the cemented lens CL, the decentering sensitivity of the imaging lens 10 is reduced, thereby improving productivity.

[0045] The sixth lens L6 has a third lens surface (surface S12). Surface S12 has a convex shape toward the image side. Surface S12 is provided with an infrared cut coating IR. The infrared cut coating IR is configured to transmit visible light and block transmission of near-infrared light, for example, from 700 nm to 1200 nm. The infrared cut coating IR is, for example, a vapor deposition film, and can be formed by a known method. By thus providing the lens with an infrared protection function, the imaging lens 10 can be made compact with a simple configuration.

[0046] In the cemented lens CL, the fifth lens may be a convex lens and the sixth lens may be a meniscus lens. In this case, the surface S12 has a convex shape toward the image side, and the convex surface S12 is provided with an infrared cut coating IR.

[0047] The focal length f of the imaging lens 10 16 and a distance Da from the surface S6 to the surface S12 on the optical axis may satisfy the following formula (1e): When formula (1e) is satisfied, the optical performance of the imaging lens 10 is better.

[0048] 2.74≦Da / f 16 <= 3.30 (1e)

[0049] The distance Df on the optical axis from the surface S1 to the aperture stop ST and the distance Dr on the optical axis from the aperture stop ST to the surface S12 may satisfy the following formula (1f). Formula (1f) defines the ratio between the total length of the front group and the total length of the rear group. When formula (1f) is satisfied, the optical performance of the imaging lens 10 is better.

[0050] 0.33≦Df / Dr≦0.42 (1f)

[0051] Next, in this embodiment, the radius of curvature R1 at the center near the optical axis Z1 of surface S1, the absolute value |Re| of the radius of curvature Re of surface S12, and the distance Dt from the first lens surface S1 to surface S12 on the optical axis Z1 may satisfy the following formula (2).

[0052] 1.20≦(R1+|Re|) / Dt≦1.46 (2)

[0053] As shown in FIG. 3, by satisfying formula (2), the optical performance of the imaging lens 10 is maintained, and the reflected light reflected toward the object side by the surface S12 is prevented from being re-reflected by the surface S1 to become a ghost. Therefore, by satisfying formula (2), the imaging lens 10 has an infrared cut function, but suppresses the occurrence of a ghost caused by the reflected light with a simple configuration without incorporating a separate element such as an infrared filter. Note that in formula (2), the lower limit value of 1.20 may be 1.25. In formula (2), the lower limit value of 1.20 may be 1.27. In formula (2), the upper limit value of 1.46 may be 1.40. In formula (2), the upper limit value of 1.46 may be 1.36.

[0054] Furthermore, the radius of curvature R1 of the center of surface S1 near the optical axis Z1 and the radius of curvature Re of surface S12 may satisfy the following formula (2a). Formula (2a) defines the ratio between the radius of curvature R1 and the radius of curvature Re. When formula (2a) is satisfied, the occurrence of ghosts is more effectively suppressed while maintaining the optical performance of the imaging lens 10.

[0055] -1.04≦R1 / Re≦-0.89 (2a)

[0056] As shown in Fig. 1, the imaging device 20 includes, in order from the object side, an imaging lens 10 and an image sensor 11. The image sensor 11 has a flat cover glass CG. The cover glass CG protects an imaging surface IP of the image sensor 11, and is arranged in this order from the object side, the cover glass CG and the imaging surface IP. Therefore, the object side surface S13 of the cover glass CG faces the surface S12.

[0057] In this embodiment, in the imaging device 20, the radius of curvature R1 at the center near the optical axis Z1 of the first lens surface, the distance Dt from the surface S1 to the surface S12 on the optical axis Z1, and the distance Db from the surface S12 on the optical axis Z1 to the object side surface S13 of the cover glass CG may satisfy the following formula (3).

[0058] 0.50≦R1 / (Dt+Db)≦0.53 (3)

[0059] By satisfying formula (3), the optical performance of the imaging lens 10 is maintained, while preventing the reflected light reflected toward the object side by surface S13 from being re-reflected by surface S1 and becoming a ghost. Therefore, by satisfying formula (3), the occurrence of ghosts due to the cover glass in the imaging lens 10 is more effectively suppressed. The lower limit of formula (3) may be 0.51. The upper limit of formula (3) may be 0.52.

[0060] In the present embodiment, in the imaging device 20, the radius of curvature Rr of the surface S6, the distance Da from the surface S6 to the surface S12 on the optical axis, and the distance Db from the surface S12 to the surface S13 on the optical axis may satisfy the following formula (4).

[0061] 0.66≦Rr / (Da+Db)≦0.83 (4)

[0062] Satisfying formula (4) prevents light reflected toward the object side by surface S13 from being re-reflected by surface S6 to become a ghost, while maintaining the optical performance of the imaging lens 10. Therefore, satisfying formula (4) better suppresses the occurrence of ghosts caused by the cover glass in the imaging lens 10. Note that the lower limit value of formula (4) may be 0.68. The lower limit value of formula (4) may be 0.70. The upper limit value of formula (4) may be 0.74. The lower limit value of formula (4) may be 0.72.

[0063] Furthermore, in the present embodiment, in the imaging device 20, the absolute value |Re| of the radius of curvature Re of the surface S12 and the distance Db from the surface S12 to the surface S13 on the optical axis may satisfy the following formula (5).

[0064] 2.28≦|Re| / Db≦2.88 (5)

[0065] Depending on the relationship between the distance from the surface S12 to the surface S13 and the value of the radius of curvature of the surface S12, a ghost may be formed near the imaging surface IP. However, by satisfying the formula (5), as shown in FIG. 5, the radius of curvature Re of the surface S12 has a constant value in relation to the distance Db from the surface S12 to the surface S13. As a result, a ghost is not formed near the imaging surface IP. Therefore, in the imaging lens 10, the occurrence of a ghost due to the cover glass CG or the surface S12 is more effectively suppressed. Note that the lower limit value of the formula (5) may be 2.31. The lower limit value of the formula (5) may be 2.35. The upper limit value of the formula (5) may be 2.71. The upper limit value of the formula (5) may be 2.64.

[0066] [Example] Examples of the imaging lens 10 will be described below. Fig. 6 is a cross-sectional view of the imaging lens 10 of Example 1. Surface numbers are designated Si (i = 1 to 15) in order from the object side surface S1 of the first lens L1. S5 is an aperture stop ST. S13 is the object side surface of the cover glass CG. S14 is the image side surface of the cover glass CG. S15 is the imaging surface IP of the image sensor 11. The surface spacing Di (i = 1 to 14, unit mm) is the distance from surface Si to surface Si+1 along the optical axis Z1.

[0067] Lens data of Example 1 are shown in Tables 1 and 2 below. Table 1 shows the surface number "i" of each surface Si of the imaging lens 10 of Example 1, the radius of curvature Ri (i=1 to 12, unit mm) of each surface Si, the surface spacing Di, the refractive index nd for the d-line (wavelength 587.6 nm), and the Abbe number vd (=(nd-1) / (nF-nC); nF is the refractive index for the F-line (wavelength 486.1 nm), and nC is the refractive index for the C-line (wavelength 656.3 nm)). In addition, the "*" mark next to the surface number "i" indicates that the surface is aspheric. Surfaces without an "*" mark next to the surface number "i" are spherical. The temperature coefficients of the relative refractive index dn / dt(-20 / 0), dn / dt(20 / 40), and dn / dt(60 / 80) are the values ​​at temperatures ranging from -20°C to 0°C, from 20°C to 40°C, and from 60°C to 80°C. The unit of the temperature coefficient of the relative refractive index dn / dt is 10 -6 / ° C. In addition, "-" is entered where no numerical value is entered (the same applies to other examples described later).

[0068] [Table 1]

[0069] The aspheric surface is expressed by the aspheric formula (6) below. In the aspheric formula (1), "Z" is the depth of the aspheric surface (mm), "C" is the paraxial curvature (i.e., C=1 / R when the paraxial radius of curvature is R (mm)), "h" is the distance from the optical axis to the lens surface (mm), "K" is the conic constant, and "Ai" is the aspheric coefficient. Table 2 shows "K" and "Ai" for each aspheric surface in Example 1 (see Table 1 marked with *).

[0070]

number

[0071] [Table 2]

[0072] The imaging lens 10 of the first embodiment satisfies the conditions of formulas (1), (2), (3), (4), and (5) as shown in Table 3 below. Also, the imaging lens 10 satisfies the conditions of formulas (1a), (1b), (1c), (1d), (1e), (1f), and (2a). Da is the sum of D6 to D11. Dr is the sum of D5 to D11. Dt is the sum of D1 to D11. Db is D12. Df is the sum of D1 to D4. Also, Rr is the radius of curvature R6 of surface S6. Re is the radius of curvature R12 of surface S12.

[0073] [Table 3]

[0074] Table 4 shows the focal lengths (mm) of each lens, the front group, the rear group, and the entire imaging lens 10 of Example 1.

[0075] [Table 4]

[0076] FIG. 7(A) shows spherical aberrations for the d-line, F-line, and C-line of the imaging lens 10 of Example 1. FIG. 7(B) shows astigmatism S in the sagittal (radical) direction and astigmatism T in the tangential (meridional) direction of the d-line of the imaging lens 10 of Example 1. FIG. 7(C) shows distortion of the imaging lens 10 of Example 1. FIG. 8 shows MTF of Example 1 at 22° C. In FIG. 8, F1 is the MTF on the optical axis Z1. F2R is the MTF in the sagittal direction at a point 26 degrees from the optical axis Z1. F2T is the MTF in the tangential direction at a point 26 degrees from the optical axis Z1. Similarly, F3R is the MTF in the sagittal direction at a point 60 degrees from the optical axis Z1. F3T is the MTF in the tangential direction at a point 60 degrees from the optical axis Z1.

[0077] As shown in FIGS. 6 to 8, the imaging lens 10 of Example 1 has a simple configuration of six elements in five groups, and while it has an infrared cutting function due to an infrared cutting coating, it suppresses the occurrence of ghosts caused by reflected light and has excellent optical performance.

[0078] As in Example 1 above, various lens data for the imaging lens 10 of Examples 2 to 10 are shown in Tables 5 to 31, and (A) spherical aberration, (B) astigmatism, and (C) distortion and MTF are shown in FIGS. 9 to 26.

[0079] In the examples, the spherical aberration, astigmatism, and distortion are all data at 22°C.

[0080] [Table 5]

[0081] [Table 6]

[0082] [Table 7]

[0083] [Table 8]

[0084] [Table 9]

[0085] [Table 10]

[0086] [Table 11]

[0087]

Table 12

[0088]

Table 13

[0089]

Table 14

[0090]

Table 15

[0091]

Table 16

[0092]

Table 17

[0093]

Table 18

[0094]

Table 19

[0095]

Table 20

[0096]

Table 21

[0097]

Table 22

[0098]

Table 23

[0099]

Table 24

[0100]

Table 25

[0101]

Table 26

[0102]

Table 27

[0103]

Table 28

[0104]

Table 29

[0105]

Table 30

[0106]

Table 31

[0107] It should be noted that the above-described embodiments and examples can be modified in various ways. For example, in addition to the imaging lens 10 described in the above examples, it is possible to configure an imaging lens having the same shape, arrangement, and imaging performance as the imaging lens 10 by changing the radius of curvature, the refractive index, the presence or absence of an infrared cut coating, the surfaces that are provided with an infrared cut coating, and other lens data. [Explanation of symbols]

[0108] 10 Imaging lens 20 Imaging device L1 First lens L2 Second lens L3 Third lens L4 4th lens L5 5th lens L6 6th lens ST aperture stop CG cover glass IP imaging surface LT Ray REF1 1st reflection REF2 Second reflection

Claims

1. The lens comprises, in order from the object side, a front group having negative power, a stop, and a rear group having positive power. the front group has a first lens surface closest to the object side that has a convex shape toward the object side; the rear group has a second lens surface closest to the object side that has a convex shape toward the object side, a third lens surface closest to the image side that has a convex shape toward the image side, and the third lens surface has an infrared-cut coating; an imaging lens that satisfies the following conditional expression (1); A flat cover glass is provided in this order from the object side. An imaging apparatus that satisfies the following conditional expression (3): 1.6<(Rr+|Re|) / Da<2.3 (1) Here, Rr is the radius of curvature of the second lens surface, Re is the radius of curvature of the third lens surface, and Da is the distance from the second lens surface to the third lens surface on the optical axis. 0.50≦R1 / (Dt+Db)≦0.52 (3) where R1 is the radius of curvature of the first lens surface, Dt is the distance from the first lens surface to the third lens surface on the optical axis, and Db is the distance from the third lens surface to the object side surface of the cover glass on the optical axis.

2. the front group includes, in order from the object side, a first lens having a concave meniscus shape and having the first lens surface, and a second lens having a concave meniscus shape, The imaging device according to claim 1 , wherein the second lens is disposed with a convex surface facing an image side.

3. the rear group includes, in order from the object side, a third lens having the second lens surface, a fourth lens, and a cemented lens, 3. The imaging device according to claim 1, wherein the third lens, the fourth lens and the cemented lens all have positive power.

4. the cemented lens includes, in order from the object side, a fifth lens which is a concave lens and a sixth lens which is a convex lens, The imaging device according to claim 3 , wherein the sixth lens has the third lens surface.

5. 5. The imaging apparatus according to claim 1, which satisfies the following conditional expression (2): 1.20≦(R1+|Re|) / Dt≦1.46 (2) Here, R1 is the radius of curvature of the first lens surface, Re is the radius of curvature of the third lens surface, and Dt is the distance from the first lens surface to the third lens surface on the optical axis.

6. 6. The imaging apparatus according to claim 1, which satisfies the following conditional expression (4): 0.66≦Rr / (Da+Db)≦0.83 (4) where Rr is the radius of curvature of the second lens surface, Da is the distance from the second lens surface to the third lens surface on the optical axis, and Db is the distance from the third lens surface to the object side surface of the cover glass on the optical axis.

7. 7. The imaging apparatus according to claim 1, which satisfies the following conditional expression (5): 2.28≦|Re| / Db≦2.88 (5) Here, Re is the radius of curvature of the third lens surface, and Db is the distance on the optical axis from the third lens surface to the object side surface of the cover glass.

Images