WO2020039486A1

WO2020039486A1 - Wide-angle lens

Info

Publication number: WO2020039486A1
Application number: PCT/JP2018/030695
Authority: WO
Inventors: 花井　美喜雄
Original assignee: 株式会社トヨテック
Priority date: 2018-08-20
Filing date: 2018-08-20
Publication date: 2020-02-27

Abstract

Provided is a large-aperture wide-angle lens that can excellently correct aberration. A wide-angle lens (10) comprises a first group (G1) having a negative refractive power and a second group (G2) having a positive refractive power sequentially from the object side toward an image surface (13) side. The first group (G1) comprises a meniscus-shaped first lens (L11) that has a negative refractive power and that is convex to the object side, and one or two lenses (L12, L13), sequentially from the object side. The lens surface (R6) on the side of an image surface (13) of the one of the one or two lenses is an aspherical surface that is convex to the image surface (13) side near the optical axis (Ax) and that is concave to the image surface side at the effective-diameter peripheral edge. The second group (G2) comprises three lenses (L21, L22, L23) having a positive refractive power.

Description

Wide-angle lens

The present invention relates to a large-aperture wide-angle lens capable of favorably correcting aberration.

装置 There is a device that projects light from a light emitting element, receives light reflected by an object through a lens system, and measures the distance to the object and the position of the object. The lens system that receives the reflected light is required to be small in size while having a wide angle and good correction of aberrations. As such a lens system, Patent Literature 1 discloses a four-element wide-angle lens in which aberration is well corrected.

JP 2007-94032 A

However, the technique described in Patent Literature 1 has a problem that the lens system is dark due to a large F value of about 2.8 (a small aperture), and it is difficult to detect weak reflected light.

The present invention has been made to solve the above-described problems, and has as its object to provide a large-aperture wide-angle lens capable of favorably correcting aberration.

In order to achieve this object, the wide-angle lens according to the present invention comprises, in order from the object side to the image plane side, a first group having a negative refractive power and a second group having a positive refractive power. The first group includes, in order from the object side, a meniscus-shaped first lens having a negative refractive power and projecting toward the object side, and one or two lenses. The lens surface of one of the lenses on the image plane side is formed of an aspherical surface that is convex toward the image plane near the optical axis and concave toward the image plane at the periphery of the effective diameter. The group consists of three lenses having positive refractive power.

According to the wide-angle lens according to the first aspect, the lens system is configured by the negative first group having the meniscus-shaped negative first lens convex to the object side and the second group including three positive lenses. Large diameter and wide angle can be achieved. Further, the lens surface on the image surface side of the first group which is located on the image surface side with respect to the first lens has a convex shape on the image surface side near the optical axis and is concave on the image surface side on the periphery of the effective diameter. Since it is formed of an aspherical surface, it is possible to satisfactorily correct spherical aberration and field curvature of a large-aperture wide-angle lens.

According to the wide-angle lens described in claim 2, the distance on the optical axis from the object-side lens surface of the first lens to the image plane is defined as TT, and the second group is most distant from the object-side lens surface of the first lens. When the distance on the optical axis to the lens surface on the side is TA, the following conditional expression (1) is satisfied. Thereby, in addition to the effect of the first aspect, the outer diameter of the wide-angle lens whose brightness is ensured can be reduced.

According to the wide-angle lens according to the third aspect, when the combined focal length of the second group is F2G and the focal length of the entire system is f, the following conditional expression (2) is satisfied. Thus, in addition to the effects of the first and second aspects, it is possible to shorten the overall length of the wide-angle lens while sufficiently increasing the diameter of the wide-angle lens.

According to the wide-angle lens according to the fourth aspect, the first group includes the first lens and one lens. Since at least two of all lens surfaces of the second group are aspherical, in addition to the effects of any one of claims 1 to 3, aberrations can be favorably corrected while increasing the diameter of the five-element wide-angle lens. .

According to the wide-angle lens according to the fifth aspect, each of the three lenses in the second group is a glass lens having a d-line refractive index of 1.9 or more, or a resin lens having a d-line refractive index of 1.6 or more. Consists of Therefore, in addition to the effect of any one of the first to fourth aspects, the aperture of the wide-angle lens can be further increased.

FIG. 3 is a cross-sectional view of the wide-angle lens according to the first embodiment. It is a longitudinal aberration figure obtained from a wide-angle lens. It is a lateral aberration figure obtained from a wide-angle lens. It is sectional drawing of the wide-angle lens in 2nd Example. It is a longitudinal aberration figure obtained from a wide-angle lens. It is a lateral aberration figure obtained from a wide-angle lens. It is sectional drawing of the wide-angle lens in 3rd Example. It is a longitudinal aberration figure obtained from a wide-angle lens. It is a lateral aberration figure obtained from a wide-angle lens. It is sectional drawing of the wide-angle lens in 4th Example. It is a longitudinal aberration figure obtained from a wide-angle lens. It is a lateral aberration figure obtained from a wide-angle lens. It is sectional drawing of the wide-angle lens in 5th Example. It is a longitudinal aberration figure obtained from a wide-angle lens. It is a lateral aberration figure obtained from a wide-angle lens. It is sectional drawing of the wide-angle lens in 6th Example. It is a longitudinal aberration figure obtained from a wide-angle lens. It is a lateral aberration figure obtained from a wide-angle lens. It is sectional drawing of the wide-angle lens in 7th Example. It is a longitudinal aberration figure obtained from a wide-angle lens. It is a lateral aberration figure obtained from a wide-angle lens.

Hereinafter, preferred embodiments will be described with reference to the accompanying drawings. First, a wide-angle lens according to an embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view including an optical axis Ax of a wide-angle lens according to an embodiment (the wide-angle lens 10 of the first example). The left side of FIG. 1 is the object side, and the right side of FIG. 1 is the image plane 13 side.

As shown in FIG. 1, the wide-angle lens is an imaging lens for near-infrared light used in a vehicle-mounted camera, a surveillance camera, and the like, and has a maximum angle of view (all angles of view) of 120 ° or more. Since the wide-angle lens for near-infrared light does not require correction of chromatic aberration, the number of lenses constituting the wide-angle lens can be reduced. The wide-angle lens according to the present embodiment includes five or six lenses. Further, as a projection method of a wide-angle lens used for an in-vehicle camera for detecting an obstacle, an equidistant projection method in which an image size is uniform with respect to an azimuth angle is preferable. In this case, the resolution with respect to the direction of the obstacle and the distance to the obstacle can be increased.

{Circle around (3)} The image plane formed by the wide-angle lens when the object is at infinity is the image plane 13, and the parallel-plate glass filter 12 is disposed on the image plane 13 side of the wide-angle lens. The glass filter 12 has functions such as a visible light cut filter, a band pass filter, an ultraviolet cut filter, and a polarizing filter. Note that the glass filter 12 is not essential, and the glass filter 12 can be omitted.

The wide-angle lens includes, in order from the object side to the image plane 13 side, a first group G1 having a negative refractive power and a second group G2 having a positive refractive power. Each lens constituting the wide-angle lens is configured to be line-symmetric with respect to the optical axis Ax. That is, the intersection between each lens surface and the optical axis Ax is the vertex of each lens surface.

絞り The wide-angle lens is provided with an aperture 11. The diaphragm 11 is for appropriately cutting the light flux (light amount) at the periphery (a part distant from the optical axis Ax). If the peripheral light amount can be appropriately cut, the position of the aperture 11 can be set relatively freely.

The first group G1 includes, in order from the object side, a meniscus-shaped first lens L11 having a negative refractive power and projecting toward the object side, and one or two lenses. The second group G2 includes three lenses L21, L22, and L23 having a positive refractive power. The light is converged by the large positive refractive power of the second group G2 while taking in a wide range of light by the first group G1. As a result, the first group G1 and the second group G2 can increase the angle of view of the wide-angle lens and increase the diameter of the wide-angle lens (decrease the F value).

The lens surface (surface R6 in the first embodiment) on the image surface 13 side of the first group G1, which is located closer to the image surface 13 than the first lens L1, is closer to the image surface 13 at the center near the optical axis Ax. It is formed of an aspherical surface that is convex and concave on the image surface side at the periphery of the effective diameter. The aspherical surface changes from a convex shape to a concave shape as the inflection portion adjacent to the entire periphery of the central portion approaches the peripheral portion. With such an aspherical surface, spherical aberration and curvature of field, which tend to be problems when a wide-angle lens is made large in diameter, can be satisfactorily corrected.

The inflection portion has an inflection point at which the cross section including the optical axis Ax changes from a convex shape to a concave shape. This inflection point is preferably located at a position 70% to 85% of the effective diameter from the optical axis Ax. Thereby, the spherical aberration and the field curvature of the large-diameter wide-angle lens can be corrected more favorably.

When the first group G1 is composed of two lenses, the first lens L11 and one lens, and has five wide-angle lenses, at least two of the lens surfaces of the second group G2 are aspherical. Preferably, there is. In this case, aberrations that cannot be completely corrected by the two-group first group G1 can be satisfactorily corrected by the two aspheric surfaces of the second group G2. As a result, it is possible to satisfactorily correct aberrations while increasing the diameter of the five-element wide-angle lens.

The three lenses L21, L22, and L23 of the second group G2 are each made of a glass lens with a d-line refractive index of 1.9 or more, or a resin lens with a d-line refractive index of 1.6 or more. Thereby, the positive refractive power of the second group G2 can be further increased, so that the aperture of the wide-angle lens can be further increased.

樹脂 Because the resin lens is lighter than the glass lens, the weight of the wide-angle lens can be reduced by increasing the number of resin lenses. Also, providing an aspherical surface on a resin lens makes it easier to form an aspherical surface as compared with the case where an aspherical surface is provided on a glass lens, and can reduce the cost of forming an aspherical surface.

The wide-angle lens has a distance TT on the optical axis Ax from the object-side lens surface R1 of the first lens L11 to the image plane 13 (the total length of the wide-angle lens), and the first lens L11 has a distance from the object-side lens surface R1. Assuming that the distance on the optical axis Ax from the lens surface closest to the object side of the second group G2 (surface R7 in the first embodiment) is TA, it is preferable to satisfy the following conditional expression (1).

If the lower limit of conditional expression (1) is not exceeded, the overall length of the first unit G1 will be larger than the overall length of the wide-angle lens. Then, the outer diameter of the first lens L11 increases, and the outer diameter of the wide-angle lens whose brightness is ensured increases. On the other hand, by satisfying conditional expression (1), the outer diameter of the first lens L11 can be reduced. In order to capture a wide range of light, the outer diameter of the first lens L11 closest to the object is likely to be larger than the outer diameters of the other lenses. However, by reducing the outer diameter of the first lens L11, the brightness is reduced. The outer diameter of the wide-angle lens in which is secured can be reduced.

The wide-angle lens preferably satisfies the following conditional expression (2) when the combined focal length of the second group G2 is F2G and the focal length of the entire system is f. Note that the focal length in the present specification is a focal length at a wavelength (940 nm in the present embodiment) mainly received by a wide-angle lens.

では Below the lower limit of Conditional Expression (2), the spherical aberration generated in the second lens unit G2 tends to increase. In order to correct this spherical aberration, the second group G2 may require four or more lenses. In that case, the overall length of the wide-angle lens becomes longer. Above the upper limit of conditional expression (2), the overall length of the wide-angle lens becomes longer. By satisfying conditional expression (2), it is possible to shorten the overall length while sufficiently increasing the diameter of the wide-angle lens.

非 It is preferable that an aspherical surface that is convex near the optical axis Ax and concave at the periphery is disposed closest to the image plane 13 of the first lens unit G1. Thereby, the spherical aberration and the curvature of field of the large-diameter wide-angle lens can be favorably corrected.

It is preferable that an aspherical surface that is convex near the optical axis Ax and concave at the periphery is provided on the image plane 13 side of the meniscus lens that is convex on the image plane 13 side. As a result, the change in the lateral aberration in the tangential direction can be flattened, and the aperture of the wide-angle lens can be further increased. In particular, it is preferable that such a meniscus lens is located closest to the image plane 13 of the first group G1. As a result, the change in the lateral aberration in the tangential direction can be further flattened, and the aperture of the wide-angle lens can be further increased.

レンズ It is preferable that all lens surfaces of the first group G1 located closer to the image plane 13 than the first lens L1 are aspherical. Thereby, various aberrations such as spherical aberration, curvature of field, astigmatism, and distortion can be easily controlled, and various aberrations can be satisfactorily corrected.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. Note that the description common to each embodiment will be described only in the first embodiment, and the description in the other embodiments will be omitted.

(First embodiment)
As shown in FIG. 1, the wide-angle lens 10 in the first embodiment is composed of six lenses. The first group G1 of the wide-angle lens 10 includes, in order from the object side, a first lens L11, a meniscus-shaped second lens L12 having a negative refractive power and projecting toward the image plane 13 side, and a positive refractive power. And a third lens L13 having a meniscus shape protruding toward the image surface 13 side. The second group G2 of the wide-angle lens 10 includes, in order from the object side, a meniscus-shaped fourth lens L21 having a positive refractive power and convex on the image surface 13 side, a biconvex fifth lens L22, and a biconvex lens. And the sixth lens L23. The diaphragm 11 is arranged between the second lens L12 and the third lens L13.

The first lens L11, fourth lens L21, fifth lens L22, and sixth lens L23 of the wide-angle lens 10 are glass lenses. The second lens L12 and the third lens L13 of the wide-angle lens 10 are resin lenses. The lens surfaces of the lenses L11 to L23 are surfaces R1 to R12 in order from the object side. The object side of the glass filter 12 is a surface R13, and the image surface 13 side is a surface R14.

Table 1 shows optical values and lens data of the wide-angle lens 10. Note that the focal length f (940 nm) is the focal length of the entire wide-angle lens 10 when near-infrared light having a wavelength of 940 nm is used. The distance between the surfaces R1 to R14 and the upper surface of the stop 11 indicates the distance on the optical axis Ax between the surface and the surface on the image plane 13 side. The refractive index N940 is the refractive index of each of the lenses L11 to L23 when near infrared light having a wavelength of 940 nm is used. The refractive index nd (d-line refractive index) and Abbe number νd are the refractive index and Abbe number of each of the lenses L11 to L23 when a d-line having a wavelength of 587.56 nm is used.

The symbol * of the surface number in Table 1 indicates an aspheric surface. The surfaces R3 to R6 of the second lens L12 and the third lens L13 are all aspheric. Note that the shape of the aspheric surface is represented by the following equation (3).

However,
z: sag amount (distance in the optical axis Ax direction from an intersection with the optical axis Ax to a point on the aspheric surface)
c: curvature (curvature at the vertex of the lens surface)
r: distance from the optical axis Ax in the radial direction (perpendicular to the optical axis Ax) to a point on the aspherical surface k: conic constant A, B, C, D: aspherical coefficient (fourth order, sixth order, eighth order in order) 10th)

Tables 2 and 3 show the conic constants and aspheric coefficients of the surfaces R3 to R6. In this specification, a power of 10 is represented by using E (for example, 1.0 × 10 ⁻⁴ is 1.0E−4). In the wide-angle lens 10, the tenth-order aspherical surface coefficient D of the surfaces R3 to R6 is zero. The surface R6 is an aspheric surface that is convex near the optical axis Ax and concave at the periphery.

FIG. 2 shows a longitudinal aberration diagram obtained from the wide-angle lens 10 when near-infrared light having a wavelength of 940 nm is used, and a lateral aberration diagram obtained from the wide-angle lens 10 when using near-infrared light having a wavelength of 940 nm. 3 is shown. The horizontal axis of the spherical aberration diagram (LONGITUDINAL @ SPHERICAL @ ABER.) In FIG. 2 is the shift amount (FOCUS (mm)) in the direction of the optical axis Ax from the image plane 13 near the optical axis Ax. The vertical axis of the spherical aberration diagram is the entrance pupil coordinate (a value obtained by standardizing the height of incidence on the pupil with its maximum height).

The horizontal axis of the astigmatism diagram (ASTIGMATIC FIELD CURVES) in FIG. 2 is the shift amount (FOCUS (mm)) in the direction of the optical axis Ax from the image plane near the optical axis Ax. The vertical axis of the astigmatism diagram is a half angle of view (ANGLE (°)), which is an angle between the optical axis Ax and the principal ray. In the astigmatism diagram, the curvature S of the sagittal image surface is shown by a solid line, and the curvature T of the tangential image surface is shown by a broken line. Also, the astigmatism (astigmatic difference) can be read from the deviation between the two lines.

横 The horizontal axis of the distortion diagram (DISTORTION) in FIG. 2 is the distortion (DISTORTION (%)). The vertical axis of the distortion diagram is the half angle of view (ANGLE (°)), which is the angle between the optical axis Ax and the principal ray.

FIG. 3 shows a lateral aberration diagram in a tangential (TANGENTIAL) direction at a predetermined image height ratio (RELATIVE / FIELD / HEIGHT) and a half angle of view on the left side of the drawing. The lateral aberration diagram in the direction ()) is shown on the right side of the drawing. In each lateral aberration diagram, the horizontal axis is the entrance pupil coordinate, and the vertical axis is the lateral aberration (mm). The image height ratio is a value obtained by standardizing the image height with the maximum image height.

(Second embodiment)
As shown in FIG. 4, the wide-angle lens 20 according to the second embodiment includes six lenses. The first group G1 of the wide-angle lens 20 includes, in order from the object side, a first lens L11, a meniscus-shaped second lens L12 that is convex on the image surface 13 side, and has a positive refractive power on the image surface 13 side. And a third lens L13 having a convex meniscus shape. The second group G2 of the wide-angle lens 20 includes, in order from the object side, a meniscus-shaped fourth lens L21 having a positive refractive power and convex on the image surface 13 side, a biconvex fifth lens L22, and an object-side lens. And a sixth lens L23 having a substantially plano-convex shape. The stop 11 is arranged between the third lens L13 and the fourth lens L21.

The first lens L11, the fourth lens L21, and the fifth lens L22 of the wide-angle lens 20 are glass lenses. The second lens L12, the third lens L13, and the sixth lens L23 of the wide-angle lens 20 are resin lenses.

Table 4 shows optical values and lens data of the wide-angle lens 20. The lens surfaces of the lenses L11 to L23 are surfaces R1 to R12 in order from the object side. The object side of the glass filter 12 is a surface R13, and the image surface 13 side is a surface R14.

The surfaces R3 to R6 of the second lens L12 and the third lens L13 are all aspheric. Tables 5 and 6 show the conic constants and aspheric coefficients of the surfaces R3 to R6. In the wide-angle lens 20, the tenth-order aspheric coefficient D of the surfaces R3 to R6 is zero. The surface R6 is an aspheric surface that is convex near the optical axis Ax and concave at the periphery.

FIG. 5 shows a longitudinal aberration diagram obtained from the wide-angle lens 20 when near-infrared light having a wavelength of 940 nm is used. FIG. 6 shows a lateral aberration diagram obtained from the wide-angle lens 20 when near-infrared light having a wavelength of 940 nm is used.

(Third embodiment)
As shown in FIG. 7, the wide-angle lens 30 in the third embodiment is composed of six lenses. The first group G1 of the wide-angle lens 30 includes, in order from the object side, a first lens L11, a meniscus-shaped second lens L12 having a negative refractive power and projecting toward the image plane 13 side, and a positive refractive power. And a third lens L13 having a meniscus shape protruding toward the image surface 13 side. The second group G2 of the wide-angle lens 30 includes, in order from the object side, a meniscus-shaped fourth lens L21 having a positive refractive power and projecting toward the image plane 13, a biconvex fifth lens L22, and a biconvex lens. And the sixth lens L23. The diaphragm 11 is arranged between the fourth lens L21 and the fifth lens L22.

第 The first lens L11 of the wide-angle lens 30 is a glass lens. The second lens L12, the third lens L13, the fourth lens L21, the fifth lens L22, and the sixth lens L23 of the wide-angle lens 30 are resin lenses.

Table 7 shows optical values and lens data of the wide-angle lens 30. The lens surfaces of the lenses L11 to L23 are surfaces R1 to R12 in order from the object side. The object side of the glass filter 12 is a surface R13, and the image surface 13 side is a surface R14.

The surfaces R3 to R10 of the second lens L12, the third lens L13, the fourth lens L21, and the fifth lens L22 are all aspheric. Tables 8 to 11 show the conic constants and aspherical coefficients of the surfaces R3 to R10. In the wide-angle lens 30, the 10th-order aspherical surface coefficient D of the surfaces R3 to R10 is 0, and the 8th-order aspherical surface coefficient C of the surfaces R7 to R10 is 0. The surface R6 is an aspheric surface that is convex near the optical axis Ax and concave at the periphery.

FIG. 8 shows a longitudinal aberration diagram obtained from the wide-angle lens 30 when near-infrared light having a wavelength of 940 nm is used. FIG. 9 shows a lateral aberration diagram obtained from the wide-angle lens 30 when near-infrared light having a wavelength of 940 nm is used.

(Fourth embodiment)
As shown in FIG. 10, the wide-angle lens 40 in the fourth embodiment is composed of six lenses. The first group G1 of the wide-angle lens 40 includes, in order from the object side, a first lens L11, a meniscus-shaped second lens L12 having a negative refractive power and projecting toward the image surface 13 side, and a positive refractive power. And a third lens L13 having a meniscus shape protruding toward the image surface 13 side. The second group G2 of the wide-angle lens 40 includes, in order from the object side, a meniscus-shaped fourth lens L21 having a positive refractive power and projecting toward the image surface 13 side, and an image surface 13 having a positive refractive power. A fifth lens L22 having a convex meniscus shape on the side and a sixth lens L23 having a positive refractive power and having a convex meniscus shape on the object side. The stop 11 is arranged between the third lens L13 and the fourth lens L21.

The first lens L11, the fifth lens L22, and the sixth lens L23 of the wide-angle lens 40 are glass lenses. The second lens L12, the third lens L13, and the fourth lens L21 of the wide-angle lens 40 are resin lenses.

Table 12 shows optical values and lens data of the wide-angle lens 40. The lens surfaces of the lenses L11 to L23 are surfaces R1 to R12 in order from the object side. The object side of the glass filter 12 is a surface R13, and the image surface 13 side is a surface R14.

The surfaces R3 to R8 of the second lens L12, the third lens L13, and the fourth lens L21 are all aspherical. Tables 13 to 15 show the conic constants and aspheric coefficients of the surfaces R3 to R8. In the wide-angle lens 40, the 10th-order aspherical surface coefficient D of the surfaces R3 to R8 is 0, and the 8th-order aspherical surface coefficient C of the surfaces R7 and R8 is 0. The surface R6 is an aspheric surface that is convex near the optical axis Ax and concave at the periphery.

FIG. 11 shows a longitudinal aberration diagram obtained from the wide-angle lens 40 when near-infrared light having a wavelength of 940 nm is used. FIG. 12 shows a lateral aberration diagram obtained from the wide-angle lens 40 when near-infrared light having a wavelength of 940 nm is used.

(Fifth embodiment)
As shown in FIG. 13, the wide-angle lens 50 in the fifth embodiment is composed of six lenses. The first group G1 of the wide-angle lens 50 includes, in order from the object side, a first lens L11, a meniscus-shaped second lens L12 having a negative refractive power and projecting toward the image plane 13 side, and a positive refractive power. And a third lens L13 having a meniscus shape protruding toward the image surface 13 side. The second group G2 of the wide-angle lens 50 includes, in order from the object side, a meniscus-shaped fourth lens L21 having a positive refractive power and projecting toward the image surface 13 side, and an image surface 13 having a positive refractive power. A fifth lens L22 having a convex meniscus shape on the side and a sixth lens L23 having a positive refractive power and having a convex meniscus shape on the object side. The stop 11 is arranged between the third lens L13 and the fourth lens L21.

The first lens L11 and the fifth lens L22 of the wide-angle lens 50 are glass lenses. The second lens L12, the third lens L13, the fourth lens L21, and the sixth lens L23 of the wide-angle lens 50 are resin lenses.

Table 16 shows optical values and lens data of the wide-angle lens 50. The lens surfaces of the lenses L11 to L23 are surfaces R1 to R12 in order from the object side. The object side of the glass filter 12 is a surface R13, and the image surface 13 side is a surface R14.

The surfaces R3 to R8 of the second lens L12, the third lens L13, and the fourth lens L21 are all aspherical. Tables 17 to 19 show the conic constants and aspheric coefficients of the surfaces R3 to R8. In the wide-angle lens 50, the 10th-order aspherical surface coefficient D of the surfaces R3 to R8 is 0, and the 8th-order aspherical surface coefficient C of the surfaces R7 and R8 is 0. The surface R6 is an aspheric surface that is convex near the optical axis Ax and concave at the periphery.

FIG. 14 shows a longitudinal aberration diagram obtained from the wide-angle lens 50 when near-infrared light having a wavelength of 940 nm is used. FIG. 15 shows a lateral aberration diagram obtained from the wide-angle lens 50 when near-infrared light having a wavelength of 940 nm is used.

(Sixth embodiment)
As shown in FIG. 16, the wide-angle lens 60 according to the sixth embodiment includes six lenses. The first group G1 of the wide-angle lens 60 includes, in order from the object side, a first lens L11, a biconvex second lens L12, and a third meniscus-shaped third lens having a positive refractive power and convex to the image plane 13 side. And a lens L13. The second group G2 of the wide-angle lens 60 includes, in order from the object side, a meniscus-shaped fourth lens L21 having a positive refractive power and projecting toward the image surface 13 side, and an image surface 13 having a positive refractive power. A fifth lens L22 having a convex meniscus shape on the side and a sixth lens L23 having a positive refractive power and having a convex meniscus shape on the object side. The stop 11 is arranged between the third lens L13 and the fourth lens L21.

The first lens L11, fourth lens L21, fifth lens L22, and sixth lens L23 of the wide-angle lens 60 are glass lenses. The second lens L12 and the third lens L13 of the wide-angle lens 60 are resin lenses.

Table 20 shows optical values and lens data of the wide-angle lens 60. The lens surfaces of the lenses L11 to L23 are surfaces R1 to R12 in order from the object side. The object side of the glass filter 12 is a surface R13, and the image surface 13 side is a surface R14.

The surfaces R3 to R6 of the second lens L12 and the third lens L13 are all aspherical. Tables 21 and 22 show the conic constants and aspherical coefficients of the surfaces R3 to R6. In the wide-angle lens 60, the tenth-order aspheric coefficient D of the surfaces R3 to R6 is zero. The surface R6 is an aspheric surface that is convex near the optical axis Ax and concave at the periphery.

FIG. 17 shows a longitudinal aberration diagram obtained from the wide-angle lens 60 when near-infrared light having a wavelength of 940 nm is used. FIG. 18 shows a lateral aberration diagram obtained from the wide-angle lens 60 when near-infrared light having a wavelength of 940 nm is used.

(Seventh embodiment)
As shown in FIG. 19, the wide-angle lens 70 in the seventh embodiment is composed of five lenses. The first group G1 of the wide-angle lens 70 includes, in order from the object side, a first lens L11 and a meniscus-shaped second lens L12 having a negative refractive power and projecting toward the image plane 13 side. The second group G2 of the wide-angle lens 70 includes, in order from the object side, a biconvex third lens L21, a biconvex fourth lens L22, and a biconvex fifth lens L23. The stop 11 is disposed between the second lens L12 and the third lens L21.

第 The fifth lens L23 of the wide-angle lens 70 is a glass lens. The first lens L11, the second lens L12, the third lens L21, and the fourth lens L22 of the wide-angle lens 70 are resin lenses.

Table 23 shows optical values and lens data of the wide-angle lens 70. The lens surfaces of the lenses L11 to L23 are surfaces R1 to R10 in order from the object side. The object side of the glass filter 12 is a surface R11, and the image surface 13 side is a surface R12.

The surfaces R3 to R8 of the second lens L12, the third lens L21, and the fourth lens L22 are all aspheric. Tables 24 to 26 show the conic constants and aspherical coefficients of the surfaces R3 to R8. In the wide-angle lens 70, the 10th-order aspherical surface coefficient D of the surfaces R4 to R8 is 0, and the 8th-order aspherical surface coefficient C of the surfaces R5 to R8 is 0. The surface R4 is an aspheric surface that is convex near the optical axis Ax and concave at the peripheral edge.

FIG. 20 shows a longitudinal aberration diagram obtained from the wide-angle lens 70 when near-infrared light having a wavelength of 940 nm is used. FIG. 21 shows a lateral aberration diagram obtained from the wide-angle lens 70 when near-infrared light having a wavelength of 940 nm is used.

The angle of view ω, the F value, the value of TT / TA in conditional expression (1), the value of F2G / f in conditional expression (2), and the position of the inflection point of the wide-angle lenses 10 to 70 in the above embodiments are shown. 27. Note that the inflection point position in Table 27 refers to an aspheric surface that is convex near the optical axis Ax and concave at the periphery of the second lens L12 or the third lens L13 of the first group G1. Is the ratio obtained by dividing the distance from the optical axis Ax in the direction perpendicular to the axis to the inflection point by the effective diameter.

As shown in Table 27 and FIGS. 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, 18, 20, and 21, according to the wide-angle lenses 10 to 70 of each embodiment, 5 Alternatively, it can be seen that in the six-lens configuration, the F-number can be increased to about 0.7 while widening the angle of view to 120 ° or more, and various aberrations (particularly, spherical aberration and curvature of field) can be corrected well. In addition, since the wide-angle lenses 10 to 70 of each embodiment satisfy the conditional expression (1), the outer diameter of the wide-angle lenses 10 to 70 whose brightness is ensured can be reduced. Further, since the wide-angle lenses 10 to 70 of each embodiment satisfy the conditional expression (2), the overall length can be reduced while the wide-angle lenses 10 to 70 have a sufficiently large aperture.

In addition, in the wide-angle lenses 10 to 70 of each embodiment, the inflection point of the aspheric surface having a convex shape near the optical axis Ax and a concave shape at the peripheral edge in the second lens L12 or the third lens L13 of the first group G1. Are located 70% to 85% of the effective diameter from the optical axis Ax. As a result, the spherical aberration and the field curvature of the large-aperture wide-angle lenses 10 to 70 are favorably corrected.

In the wide-angle lenses 10 to 60 of the first to sixth embodiments, the aspherical surface that is convex near the optical axis Ax and concave at the periphery is a meniscus shape convex to the image surface 13 side in the first group G1. The third lens L13 is provided on a surface R6 on the image plane 13 side. In the wide-angle lens 70 according to the seventh embodiment, the aspherical surface that is convex near the optical axis Ax and concave at the periphery is the second meniscus convex surface of the first group G1 that faces the image surface 13. It is provided on a surface R4 on the image plane 13 side of the lens L12. Thereby, the change of the lateral aberration in the tangential direction is flattened.

As described above, the present invention has been described based on the embodiments and the examples. However, the present invention is not limited to the above embodiments and the above examples, and various improvements and modifications may be made without departing from the spirit of the present invention. What is possible can easily be inferred. A lens having little refractive power (such as a cover glass) may be provided on the object side or the image plane 13 side of the wide-angle lenses 10 to 70. Further, the materials of the lenses L11 to L23 may be appropriately changed. An aspherical surface may be provided on the glass lens.

In the first to sixth embodiments, the case has been described where the surface R6 of the third lens L13 is a convex aspherical surface near the optical axis Ax and a concave aspherical surface at the periphery, but is not necessarily limited to this. Absent. The surface R4 of the second lens L12 may be an aspheric surface that is convex near the optical axis Ax and concave at the peripheral edge. Also in this case, the spherical aberration and the field curvature of the large-diameter wide-angle lens can be corrected well.

10, 20, 30, 40, 50, 60, 70 Wide-angle lens 13 Image plane G1 First group G2 Second group L11 First lens

Claims

A wide-angle lens including, in order from the object side to the image plane side, a first group having a negative refractive power and a second group having a positive refractive power,
The first group includes, in order from the object side, a meniscus-shaped first lens having a negative refractive power and projecting toward the object side;
Consisting of one or two lenses,
One of the one or two lenses has an image-side lens surface that is convex from the image surface near the optical axis and concave from the image surface at the periphery of the effective diameter. Become
The wide-angle lens according to claim 2, wherein the second group includes three lenses having a positive refractive power.
The distance on the optical axis from the object side lens surface of the first lens to the image plane is TT, and the distance from the object side lens surface of the first lens to the most object side lens surface of the second group is The wide-angle lens according to claim 1, wherein the following conditional expression (1) is satisfied when a distance on the optical axis is TA.
3. The wide-angle lens according to claim 1, wherein the following conditional expression (2) is satisfied, where F2G is a combined focal length of the second group and f is a focal length of the entire system. 4.
The first group includes the first lens and one lens,
The wide-angle lens according to any one of claims 1 to 3, wherein at least two surfaces of the second group are aspherical among all lens surfaces.
3. The three lenses of the second group are each made of a glass lens having a d-line refractive index of 1.9 or more, or a resin lens having a d-line refractive index of 1.6 or more. 5. The wide-angle lens according to any one of items 1 to 4.