JP2010145648A - Imaging lens constituted of three groups and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make an imaging lens compact, reduce the cost of the lens, and also, achieve brighter and higher imaging performance than the conventional one. <P>SOLUTION: The imaging lens includes: a first lens group G1 having positive power as a whole, wherein the surface closest to the object side is a convex surface; a second meniscus lens group G2, wherein the shape near the optical axis is a convex surface facing the object side as a whole; and a third lens group G3, wherein the surface closest to the object side is a convex surface near the optical axis, the surface closest to the object side or the surface closest to the image side has a shape to be a convex surface facing the image side between the peripheral part and the surface apex position. The imaging lens also satisfies the following conditional expressions (1) to (4): (1) 0.19≤CA/TL≤0.6, (2) 0.5≤D12a/f≤1.2, (3) 1.2≤TL/f≤1.7, (4) BF/TL≤0.35, wherein CA is an incident pupil diameter, TL is a total length, D12a is an on-axis distance between the surface closest to the object side in the first lens group and the surface closest to the image side in the second lens group, (f) is the entire on-axis focal length, and BF is a back focus. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging lens that forms an optical image of a subject on an imaging element such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), and a digital still camera that mounts the imaging lens to perform photography. The present invention relates to an imaging device such as a camera-equipped mobile phone and an information portable terminal (PDA: Personal Digital Assistance).

  In recent years, with the spread of personal computers to ordinary homes and the like, digital still cameras that can input image information such as photographed landscapes and human images to personal computers are rapidly spreading. In addition, camera modules for image input are often mounted on mobile phones. An image sensor such as a CCD or a CMOS is used for a device having such an image capturing function. In recent years, these image pickup devices have been made more compact, and the entire image pickup apparatus and the image pickup lens mounted thereon are also required to be compact. At the same time, the number of pixels of the image sensor is increasing, and there is a demand for higher resolution and higher performance of the imaging lens. For example, performance corresponding to a high pixel of 2 megapixels or more, more preferably 5 megapixels or more is required.

  In order to meet such demands, for example, the overall configuration of the lens is a three-group configuration in which there are six surfaces in contact with air, thereby achieving compactness and low cost, and in order to achieve high performance, It is conceivable to use an aspherical surface actively (see Patent Documents 1 to 4). In this case, the aspherical surface contributes to compactness and high performance. However, it is desirable that the use of the aspherical surface fully considers manufacturability in order to maximize the effect. Patent Document 5 discloses an imaging lens using a compound lens in each of the first group to the third group.

JP 2007-86485 A Japanese Patent Laid-Open No. 2005-17440 JP 2005-17439 A JP 2002-228922 A Japanese Patent No. 3977782

  By the way, in the imaging apparatus, brightening the lens system contributes to acquisition of a high dynamic range, photography in a low-luminance environment, and increase in light input conversion efficiency due to reduction in pixel pitch. Therefore, development of a bright and compact lens system is desired. However, the imaging lens described in each of the above-mentioned patent documents has a F-number of about 2.6 to 2.8, even if it is bright. The performance is insufficient to cope with (for example, F number 2.5 or less).

  The present invention has been made in view of such problems, and an object of the present invention is to provide a three-group imaging lens capable of realizing brighter and higher imaging performance as compared with the conventional one, while achieving compactness and low cost, and An object of the present invention is to provide an imaging device that can obtain a high-resolution captured image by mounting the imaging lens of the three-group configuration.

The imaging lens having a three-group structure according to the present invention has a first lens group having a positive power as a whole, and a shape near the optical axis as a whole on the object side. The second lens unit having a concave meniscus shape, the most object-side surface is convex in the vicinity of the optical axis, and the most object-side surface or most image-side surface is the periphery and surface apex. And a third lens group having a convex portion on the image side with respect to the position, and is configured to satisfy the following conditional expression.
0.19 ≦ CA / TL ≦ 0.6 (1)
0.5 ≦ D12a / f ≦ 1.2 (2)
1.2 ≦ TL / f ≦ 1.7 (3)
BF / TL ≦ 0.35 (4)
However,
CA: entrance pupil diameter (diameter)
TL: Full length (distance on the optical axis from the lens surface closest to the object side to the image plane. The length in terms of air on the image plane side from the third lens group)
BF: Back focus (distance on the optical axis from the vertex of the lens surface closest to the image side of the third lens unit to the image surface (air equivalent length))
D12a: Distance on the optical axis from the lens surface closest to the object side of the first lens group to the lens surface closest to the image side of the second lens group f: The entire paraxial focal length.

The imaging lens having a three-group configuration according to the present invention is configured by a relatively small number of lens groups of a three-group configuration as a whole, thereby achieving compactness and low cost. In addition, by optimizing the configuration of each lens group, it is possible to obtain brighter and higher imaging performance than the conventional one while suppressing the overall length. For example, by optimizing the lens shape of the third lens unit closest to the image side, which is particularly advantageous for image plane correction, by using an aspheric surface efficiently, it is advantageous for widening the angle of view and ensuring brightness. Further, by satisfying a predetermined conditional expression advantageous for shortening the overall length and ensuring brightness, sufficient brightness is ensured as compared with the prior art while maintaining the high imaging performance while suppressing the overall length.
Furthermore, by adopting the following preferable configuration selectively as appropriate, it is possible to make the optical performance as a whole more advantageous including brightness and imaging performance.

In the three-group imaging lens of the present invention, it is preferable that the following conditions are selectively satisfied as appropriate.
D3g / f3 ≦ 0.65 (5)
0.7 ≦ f / YIM ≦ 4.0 (6)
0.65 ≦ D12a / f ≦ 1.0 (2 ′)
0.20 ≦ D1g / f1 ≦ 0.75 (7)
0.45 ≦ R1 / f ≦ 1.0 (8)
−0.5 ≦ f2 / f3 (45−νd2g) ≦ 3 (9)
0.03 ≦ BF / DL ≦ 0.5 (10)
1.6 ≦ N1 (11)
0.5 ≦ f / f1 ≦ 1.05 (12)
0.24 ≦ D1 g / f ≦ 0.9 (13)
However,
YIM: Maximum image height f1: Paraxial focal length of the first lens group D1g: Total center thickness of lenses in the first lens group D3g: Total center thickness of lenses in the third lens group R1: First lens group F2: paraxial focal length of the second lens group f3: paraxial focal length of the third lens group νd2g: Abbe of the thickest lens in the second lens group Number DL: Distance on the optical axis from the vertex of the lens surface closest to the object side of the first lens unit to the vertex of the lens surface closest to the image side of the third lens unit N1: The lens having the thickest center thickness in the first lens unit Refractive index f1: The paraxial focal length of the first lens unit.

  In the imaging lens having a three-group structure according to the present invention, the first lens group may be formed of a glass lens. By using the first lens group closest to the object side as a glass lens, it is advantageous for use in a high temperature and high humidity environment, for example.

In the imaging lens having a three-group structure according to the present invention, at least one of the first lens group, the second lens group, and the third lens group may be a composite aspheric lens. The composite aspherical lens includes a flat lens substrate, an object-side aspherical lens portion formed on the object-side surface side of the lens substrate, and an image-side surface formed on the image-side surface side of the lens substrate. The difference between the Abbe number between the lens substrate and the object-side aspherical lens unit and the difference between the Abbe number between the lens substrate and the image-side aspherical lens unit are respectively expressed by the following conditional expression (14). The Abbe number difference Δν (Abbe number difference with respect to the d-line) is satisfied, the difference in refractive index between the lens substrate and the object-side aspherical lens unit, and the refractive index between the lens substrate and the image-side aspherical lens unit. May be a refractive index difference ΔN (a refractive index difference with respect to the d-line) that satisfies the following conditional expression (15).
| Δν | ≦ 10 (14)
| ΔN | ≦ 0.1 (15)

  Further, the three-group imaging lens of the present invention may further include a stop. In this case, it is preferable that the stop is disposed so that the position on the optical axis is closer to the object side than the position of the center of gravity of the first lens group. More preferably, the position on the optical axis is disposed on the object side with respect to the position of the center of gravity of the first lens group and on the image side with respect to the surface vertex position on the most object side of the first lens group. Good to be.

An imaging device according to the present invention includes an imaging lens having a three-group configuration according to the present invention and an imaging element that outputs an imaging signal corresponding to an optical image formed by the imaging lens.
In the imaging apparatus according to the present invention, a high-resolution imaging signal is obtained based on the high-resolution optical image obtained by the imaging lens of the present invention.

  According to the imaging lens having the three-group configuration of the present invention, the aspherical surface is efficiently used with a relatively small number of lens groups of the three-group configuration as a whole, and the predetermined lens is advantageous for shortening the overall length and ensuring the brightness. Since the entire lens configuration is optimized while satisfying the conditions, it is possible to realize a brighter and higher imaging performance as compared with the prior art while achieving compactness and low cost.

  Further, according to the imaging apparatus of the present invention, since the imaging signal corresponding to the optical image formed by the high-performance three-group imaging lens of the present invention is output, it is brightened based on the imaging signal. A high-resolution captured image can be obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a first configuration example of an imaging lens according to an embodiment of the present invention. This configuration example corresponds to the lens configuration of a first numerical example (FIGS. 15 and 29) described later. Similarly, cross-sectional configurations of second to fourteenth configuration examples corresponding to lens configurations of second to fourteenth numerical examples (FIGS. 16 to 28 and FIGS. 30 to 42) described later are shown in FIGS. As shown in FIG. 1 to 14, the symbol Ri is the curvature of the i-th surface that is numbered sequentially so as to increase toward the image side (imaging side), with the surface of the lens element closest to the object side being the first. Indicates the radius. The symbol Di indicates the surface interval on the optical axis Z1 between the i-th surface and the i + 1-th surface. Since the basic configuration is the same in each configuration example, the configuration example of the imaging lens shown in FIG. 1 will be basically described below, and the configuration examples in FIGS. explain.

  The imaging lens according to the present embodiment is used for various imaging devices using an imaging device such as a CCD or CMOS, particularly for relatively small portable terminal devices such as digital still cameras, camera-equipped mobile phones, and PDAs. Is preferred. The imaging lens includes a first lens group G1, a second lens group G2, and a third lens group G3 in order from the object side along the optical axis Z1.

  An imaging apparatus according to the present embodiment includes an imaging lens according to the present embodiment and an imaging element 100 such as a CCD that outputs an imaging signal corresponding to an optical image formed by the imaging lens. . The image sensor 100 is disposed on the imaging surface (imaging surface) of the imaging lens. Various optical members CG may be arranged between the third lens group G3 and the image sensor 100 according to the configuration on the camera side where the lens is mounted. For example, a flat optical member such as a cover glass for protecting the imaging surface or an infrared cut filter may be disposed. In this case, as the optical member CG, for example, a flat cover glass provided with a coating having a filter effect such as an infrared cut filter or an ND filter may be used.

  The imaging lens also has a diaphragm St as a light beam limiting unit. The stop St is an optical aperture stop (brightness stop), and is preferably disposed before and after the first lens group G1. For example, it is preferable that the diaphragm St is a so-called “front diaphragm” and is disposed so that the position on the optical axis Z1 is closer to the object side than the position of the center of gravity of the first lens group G1. More preferably, the position on the optical axis Z1 is closer to the object side than the position of the center of gravity of the first lens group G1, and closer to the image side than the vertex position of the lens surface closest to the object side of the first lens group G1. It is good to be arranged. In the present embodiment, the lenses (FIGS. 1 to 8) of the first to eighth configuration examples are configuration examples corresponding to the front diaphragm.

  Further, a configuration of a so-called “medium aperture” in which the diaphragm St is disposed between the first lens group G1 and the second lens group G2 may be used. In the present embodiment, the lenses of the ninth to fourteenth configuration examples (FIGS. 9 to 14) are configuration examples corresponding to an intermediate stop.

  Further, as a light beam limiting means, a light beam blocking stopper for cutting unnecessary incident light beam may be provided at the same position as the stop St.

  In order to improve the performance of this imaging lens, it is preferable to use an aspheric surface for at least one surface in each of the first lens group G1, the second lens group G2, and the third lens group G3.

In this imaging lens, the first lens group G1 as a whole has a positive power in the vicinity of the optical axis. The most object side surface of the first lens group G1 is a convex surface in the vicinity of the optical axis. The first lens group G1 can be constituted by, for example, a single meniscus first lens L1 whose shape near the optical axis has a convex surface facing the object side.
The first lens group G1 is also a cemented lens composed of, for example, a biconvex positive lens L11 and a biconcave negative lens L12 in order from the object side, as in the fourth configuration example shown in FIG. It is also possible to adopt the configuration.

The first lens group G1 may be configured as a composite aspheric lens as in the sixth and seventh configuration examples shown in FIGS. The compound aspheric lens is formed using, for example, WLC (wafer level camera) technology. 6 and 7, the first lens group G1 includes a parallel plane lens (lens substrate) L1b and a non-object-side lens formed of a resin material on one surface side (object side) of the lens substrate L1b. A spherical lens portion L1a and an image side aspherical lens portion L1c formed of a resin material on the other surface side (image side) of the lens substrate L1b. The lens substrate L1b, the object-side aspherical lens portion L1a, and the image-side aspherical lens portion L1c constitute a single composite aspherical lens as a whole. The object-side surface of the object-side aspheric lens unit L1a is a convex surface in the vicinity of the optical axis. The image side surface of the image side aspherical lens portion L1c is, for example, a concave surface in the vicinity of the optical axis.
Note that the adhesion between the lens substrate L1b and the object side aspherical lens portion L1a and the adhesion between the lens substrate L1b and the image side aspherical lens portion L1c may be performed using an adhesive material (via an adhesive material). Although it is good, it is also possible to adhere by adhering adjacent lens surfaces directly without using an adhesive material. Further, it may be adhered to the adjacent and opposing lens surfaces after applying a coating treatment such as an antireflection film.

  In addition, when it is set as structures other than a composite aspherical lens, the 1st lens group G1 may be comprised with the glass lens. By using the first lens group G1 closest to the object side as a glass lens, it is advantageous for use in a high temperature and high humidity environment, for example.

  The second lens group G2 as a whole has a meniscus shape in which the shape in the vicinity of the optical axis has a concave surface facing the object side. It is preferable that the most object side surface of the second lens group G2 has a shape in which the peripheral portion is located closer to the object side than the most object side surface vertex position of the second lens group G2. The most image side surface of the second lens group G2 also preferably has a shape such that the peripheral portion is located closer to the object side than the most image side surface vertex position of the second lens group G2. The second lens group G2 can be constituted by, for example, a single meniscus second lens L2 whose shape near the optical axis is concave on the object side.

  Further, the second lens group G2 can be configured as a composite aspherical lens in the same manner as in the case of the first lens group G1 described above. In the present embodiment, in the sixth to eighth configuration examples shown in FIGS. 6 to 8, the second lens group G2 is a compound aspherical lens. 6 to 8, the second lens group G2 includes a parallel plane lens (lens substrate) L2b and an object-side non-layer formed of a resin material on one surface side (object side) of the lens substrate L2b. A spherical lens portion L2a and an image side aspherical lens portion L2c formed of a resin material on the other surface side (image side) of the lens substrate L2b. The lens substrate L2b, the object-side aspherical lens portion L2a, and the image-side aspherical lens portion L2c, as a whole, have one compound aspherical lens having a meniscus shape with a concave surface facing the object side in the vicinity of the optical axis. It is configured.

  The third lens group G3 is a lens group particularly effective for field curvature correction, and the most object side surface is a convex surface in the vicinity of the optical axis. The third lens group G3 also has a shape portion in which the most object-side surface or most image-side surface is convex on the image side between the peripheral portion and the surface vertex position (intermediate portion of the surface). Yes. The third lens group G3 can be constituted by, for example, one third lens L3 having a meniscus shape in which the shape near the optical axis is convex toward the object side.

  Further, the third lens group G3 can be configured as a composite aspherical lens in the same manner as in the case of the first lens group G1 described above. In the present embodiment, in the sixth to eighth configuration examples shown in FIGS. 6 to 8, the third lens group G3 is a compound aspherical lens. 6 to 8, the third lens group G3 includes a parallel plane lens (lens substrate) L3b and a non-object-side lens formed of a resin material on one surface side (object side) of the lens substrate L3b. A spherical lens portion L3a and an image-side aspherical lens portion L3c formed of a resin material on the other surface side (image side) of the lens substrate L3b. The lens substrate L3b, the object-side aspherical lens portion L3a, and the image-side aspherical lens portion L3c, as a whole, have one composite aspherical surface whose shape near the optical axis is a meniscus shape with the convex surface facing the object side. A lens is configured.

This imaging lens preferably satisfies at least the following conditional expressions (1) to (2).
0.19 ≦ CA / TL ≦ 0.6 (1)
0.5 ≦ D12a / f ≦ 1.2 (2)
1.2 ≦ TL / f ≦ 1.7 (3)
BF / TL ≦ 0.35 (4)
However,
CA: entrance pupil diameter (diameter)
TL: Full length (distance on the optical axis from the lens surface closest to the object side to the image plane. The length in terms of air on the image plane side than the third lens group G3)
BF: Back focus (distance on the optical axis from the apex of the lens surface closest to the image side of the third lens group G3 to the image plane (air equivalent length))
D12a: Distance on the optical axis from the most object-side lens surface of the first lens group G1 to the most image-side lens surface of the second lens group G2. F: Overall paraxial focal length.

This imaging lens preferably further satisfies the following conditions as appropriate.
D3g / f3 ≦ 0.65 (5)
0.7 ≦ f / YIM ≦ 4.0 (6)
0.20 ≦ D1g / f1 ≦ 0.75 (7)
0.45 ≦ R1 / f ≦ 1.0 (8)
−0.5 ≦ f2 / f3 (45−νd2g) ≦ 3 (9)
0.03 ≦ BF / DL ≦ 0.5 (10)
1.6 ≦ N1 (11)
0.5 ≦ f / f1 ≦ 1.05 (12)
0.24 ≦ D1 g / f ≦ 0.9 (13)
However,
YIM: Maximum image height f1: Paraxial focal length of the first lens group G1 D1g: Total center thickness of lenses in the first lens group G1 D3g: Total center thickness of lenses in the third lens group G3 R1: No. Paraxial radius of curvature of the most object-side surface of one lens group G1 f2: Paraxial focal length of the second lens group G2 f3: Paraxial focal length of the third lens group G3 νd2g: Most central in the second lens group G2 Abbe number of thick lens DL: Distance on the optical axis from the most object-side lens surface vertex of the first lens group G1 to the most image-side lens surface vertex of the third lens group G3 (see FIG. 1)
N1: Refractive index of the lens with the thickest center thickness in the first lens group G1 f1: The paraxial focal length of the first lens group G1.

6 to 8, when at least one of the first lens group G1, the second lens group G2, or the third lens group G3 is a compound aspheric lens, For the compound aspherical lenses in the group, the Abbe number difference Δν (the Abbe number difference with respect to the d line) is set such that the Abbe number difference between adjacent lenses in the compound aspherical lens satisfies the following conditional expression (14). At the same time, it is preferable that the refractive index difference between adjacent lenses in the composite aspheric lens is a refractive index difference ΔN (a refractive index difference with respect to the d-line) that satisfies the following conditional expression (15). For example, when the first lens group G1 is a compound aspherical lens as in the configuration examples shown in FIGS. 6 and 7, the Abbe number difference between the lens substrate L1b and the object-side aspherical lens portion L1a, and the lens The difference in Abbe number between the substrate L1b and the image side aspherical lens portion L1c is an Abbe number difference Δν that satisfies the following conditional expression (14), and the lens substrate L1b and the object side aspherical lens portion L1a are It is preferable that the difference in refractive index and the difference in refractive index between the lens substrate L1b and the image-side aspherical lens portion L1c are each a refractive index difference ΔN that satisfies the following conditional expression (15).
| Δν | ≦ 10 (14)
| ΔN | ≦ 0.1 (15)

  Next, operations and effects of the imaging lens configured as described above, particularly operations and effects related to conditional expressions, will be described in more detail.

  In the imaging lens according to the present embodiment, since it is configured by a relatively small number of lens groups of a three-group configuration as a whole, compactness and low cost can be achieved. In addition, by optimizing the configuration of each lens group, it is possible to obtain brighter and higher imaging performance than the conventional one while suppressing the overall length. In particular, by optimizing the lens shape of the third lens group G3 closest to the image plane, which is advantageous for image plane correction, by efficiently using an aspheric surface, it is advantageous for widening the angle of view and ensuring brightness. In addition, by satisfying predetermined conditional expressions such as conditional expressions (1) to (4) that are advantageous for shortening the overall length and ensuring brightness, it has been possible to reduce the overall length while maintaining high imaging performance. Sufficient brightness is ensured.

  Regarding the aspherical shape, in particular, the third lens group G3 has a configuration having a shape portion that is convex on the image side between the peripheral portion and the surface vertex position (intermediate portion of the surface). The field curvature is corrected well from the center to the periphery. In the third lens group G3, the luminous flux is separated for each angle of view as compared with the first lens group G1 and the second lens group G2. For this reason, in particular, by making the most image-side surface of the third lens group G3, which is a lens surface close to the image pickup device 100, have different concave and convex shapes from the vicinity of the optical axis to the peripheral portion, the aberration for each angle of view. Correction is appropriately performed, and the incident angle of the light flux on the image sensor 100 is controlled to be equal to or smaller than a certain angle (the telecentricity of the principal ray at each angle of view is kept good). Accordingly, unevenness in the amount of light in the entire image plane can be reduced, and it is advantageous for correcting curvature of field, distortion, and the like. Further, in this imaging lens, both the second lens group G2 and the third lens group G3 are aspherical lenses, so that the total length can be maintained while maintaining the same optical performance as compared with the case where they are constituted by spherical lenses. It can be made smaller. More specifically, suppose that the second lens group G2 and the third lens group G3 are composed of spherical lenses to improve the resolution performance, and to maintain the telecentricity of the principal ray at each angle of view on the imaging surface. When an aspheric lens is used, it is possible to achieve the same performance with the overall length being reduced by 30% or more.

  In general, in an imaging lens system, telecentricity, that is, the incident angle of the principal ray on the imaging element 100 is close to the optical axis (the incident angle on the imaging surface is close to zero with respect to the normal of the imaging surface). It is preferable to become. In order to ensure this telecentricity, it is preferable that the aperture stop St is disposed as far as possible on the object side, in front of and behind the first lens group G1. On the other hand, when the diaphragm St is arranged at a position further away from the lens surface closest to the object side in the object side direction, the corresponding amount (distance between the diaphragm St and the lens surface closest to the object side) is added as the optical path length. Therefore, it is disadvantageous in terms of downsizing the overall configuration. Therefore, for example, the position of the aperture stop St on the optical axis Z1 is closer to the object side than the position of the center of gravity of the first lens group G1, and closer to the image side than the surface vertex position of the first lens group G1 closest to the object side. By arranging in such a position, the telecentricity can be ensured while shortening the overall length.

  In this imaging lens, the light incident from the object side is reflected in the object side direction by the image side surface of the first lens group G1, and further reflected by the object side surface of the first lens group G1 to be reflected on the image surface. Such ghost light may be generated. Arranging the diaphragm St closer to the object side than the position of the center of gravity of the first lens group G1 is advantageous in suppressing the generation of such ghost light.

  Further, when the aperture stop St is disposed between the first lens group G1 and the second lens group G2, the effective area between the first lens group G1 and the second lens group G2 is reduced, so that the surface power is reduced. In general, performance change due to manufacturing variations is small. Further, since the first lens group G1 and the second lens group G2 are close to the stop, the spherical aberration can be kept good, which is advantageous for a bright lens. In addition, the high-grade lens has an appearance advantage that the first lens group G1 is intentionally arranged on the object side of the stop St so that the user can recognize the lens from the outside.

  Hereinafter, the specific significance of each conditional expression described above will be described.

Conditional expression (1) defines an appropriate value of the entrance pupil diameter CA. When the aperture stop St is in the vicinity of the surface position closest to the object side of the first lens group G1, the entrance pupil diameter CA defines the effective diameter of the axial ray. If the lower limit of conditional expression (1) is not reached, the entrance pupil diameter CA becomes too small and the lens system becomes dark. If the upper limit is exceeded, the entrance pupil diameter CA becomes too large, and various performances such as resolution performance become insufficient.
In order to obtain better performance, the numerical range of conditional expression (1) is
0.22 ≦ CA / TL ≦ 0.5 (1 ′)
It is preferable that More preferably,
0.28 ≦ CA / TL ≦ 0.5 (1 ″)
Good to be.

Conditional expression (2) relates to the on-axis distance D12a from the most object side surface of the first lens group to the most image side surface of the second lens group. In this imaging lens, the spherical aberration is balanced from the first lens group G1 to the second lens group G2 so as to be under, and the third lens group G3 is over. Below the lower limit of (2), the spherical aberration cannot be made sufficiently under. In this imaging lens, the incident light beam is separated from the first lens group G1 to the second lens group G2 for each field angle, and the separated light beam is corrected for each field angle by the third lens group G3. The field curvature is corrected well for each angle of view. If the lower limit of conditional expression (2) is not reached, it is insufficient to separate the light beam from the first lens group G1 to the second lens group G2, and the field curvature correction in the third lens group G3 is also insufficient. End up. If the lower limit of the third lens group G3 is not reached, the lens thickness in the peripheral portion of the first lens group G1 and the second lens group G2 and the air gap between the first lens group G1 and the second lens group G2 become small, and processing is performed. It is disadvantageous. On the other hand, if the upper limit of conditional expression (2) is exceeded, the spherical aberration will be too under from the first lens group G1 to the second lens group G2. In addition, it becomes difficult to reduce the overall length while reducing the curvature of field.
In order to obtain better performance, the numerical range of conditional expression (2) is
0.65 ≦ D12a / f ≦ 1.0 (2 ′)
It is preferable that More preferably,
0.70 ≦ D12a / f ≦ 1.0 (2 ″)
Good to be.

  Conditional expression (3) relates to the total length TL of the lens system. If the upper limit of conditional expression (3) is exceeded, the total length TL becomes too large, which is disadvantageous for shortening the total length TL. Exceeding the lower limit is advantageous for shortening the total length TL, but causes a reduction in imaging performance. In the case of a bright lens having a small F number, such as the imaging lens according to the present embodiment, the resolution depth becomes narrow and the effective range of axial rays increases, so that an image of spherical aberration and peripheral image height is obtained. It becomes strict to have a well-balanced surface curvature. Therefore, in order to improve the balance of the Petzval sum, the total length needs to be an appropriate value. If the total length is too large, the angle of view and the angle of exit to the image plane will be too obtuse compared to the current general F-number lens.

Conditional expression (4) relates to the back focus BF and the total length TL of the lens system. In a bright lens with a small F-number, such as the imaging lens according to the present embodiment, the spherical aberration is mainly caused by the first lens group G1 when the diaphragm St is set to the front side and the overall length is shortened. Can make it smaller. On the other hand, the chromatic aberration of magnification, the field curvature correction, and the astigmatic difference correction are most effective when an aspheric surface having an inflection point is arranged in the final lens (third lens group G3). Further, if the position of the aspherical surface is arranged away from the aperture stop St, the effect is demonstrated as the distance increases. As a result of disposing the aspherical surface of the final lens away from the stop St, the back focus BF tends to be small. On the other hand, a bright lens has a wide effective diameter of light rays at each image height, so that it is not necessary to widen the back focus BF greatly from the viewpoint of appearance quality and standard for foreign object scratches. For this reason, it is possible to place the final lens at a position where the back focus BF becomes relatively small with priority given to performance. If the upper limit of conditional expression (4) is exceeded, the back focus BF can be lengthened, but the correction effect of the final lens described above is reduced.
In order to obtain better performance, the numerical range of conditional expression (4) is
BF / TL ≦ 0.18 (4 ')
It is preferable that More preferably,
BF / TL ≦ 0.12 (4 ″)
Good to be.

  Conditional expression (5) defines an appropriate relationship between the paraxial focal length f3 of the third lens group G3 and the total center thickness D3g of the lenses in the third lens group G3. In conditional expression (5), when D3g / f3 is a negative value, it is advantageous for field curvature correction and Petzval sum correction. When D3g / f3 is a positive value, if the value of D3g / f3 is too large beyond the upper limit of conditional expression (5), it is difficult to correct the image plane.

Conditional expression (6) relates to the maximum image height YIM. With this imaging lens, bright and high imaging performance can be realized under the condition of conditional expression (6). Below the lower limit of conditional expression (6), the angle of view becomes too wide. If the upper limit of conditional expression (6) is exceeded, the angle of view becomes too narrow.
In order to obtain better performance, the numerical range of conditional expression (6) is
1.0 ≦ f / YIM ≦ 3.5 (6 ′)
It is preferable that More preferably,
1.4 ≦ f / YIM ≦ 3.0 (6 ″)
Good to be.

Conditional expression (7) defines an appropriate relationship between the paraxial focal length f1 of the first lens group G1 and the total center thickness D1g of the lenses in the first lens group G1. If the lower limit of conditional expression (7) is not reached, the effective diameter of the first lens group G1 is large in this imaging lens, so that the thickness of the edge portion of the lens in the first lens group G1 cannot be secured sufficiently. If the upper limit of conditional expression (7) is exceeded, the total length cannot be reduced.
In order to obtain better performance, the numerical range of conditional expression (7) is
0.25 ≦ D1 g / f1 ≦ 0.60 (7 ′)
It is preferable that More preferably,
0.28 ≦ D1 g / f1 ≦ 0.55 (7 ″)
Good to be.

Conditional expression (8) relates to the shape of the most object-side surface of the first lens group G1. Below the lower limit of conditional expression (8), the spherical aberration and the curvature of field tend to be too under. In addition, the distortion becomes excessive, and sufficient correction by an aspherical surface cannot be performed. If the upper limit of conditional expression (8) is exceeded, the spherical aberration and the curvature of field will be excessive, and the distortion will tend to be excessive. Furthermore, the overall length is also relatively disadvantageous.
In order to obtain better performance, the numerical range of conditional expression (8) is
0.5 ≦ R1 / f ≦ 0.8 (8 ′)
It is preferable that

Conditional expression (9) relates to the Abbe number νd2g of the lens having the thickest center thickness in the second lens group G2. If the range of the conditional expression (9) is not satisfied, the curvature of field and the chromatic aberration of magnification cannot be kept good at the same time.
In order to obtain better performance, the numerical range of conditional expression (9) is
−0.2 ≦ f2 / f3 (45−νd2g) ≦ 2 (9 ′)
It is preferable that More preferably,
−0.1 ≦ f2 / f3 (45−νd2g) ≦ 1 (9 ″)
Good to be.

Conditional expression (10) relates to the back focus BF and the lens system thickness DL. In order to satisfy these two requirements, shortening the overall lens length and preventing the final lens surface closest to the image sensor 100 from being too close to the imaging surface, the lens system thickness DL and the back focus BF Needs to be in an appropriate range. If the lower limit of conditional expression (10) is not reached, the back focus BF becomes too small. If the upper limit is exceeded, the thickness DL of the entire lens becomes too small, and the aberration performance is deteriorated and the manufacturing and assembly sensitivity is rapidly lowered. Increasing the number of aspheric surfaces in this imaging lens increases the sensitivity of performance degradation to variations during manufacturing. If the thickness DL is made too small, the numerical range of the conditional expression (10) is:
0.05 ≦ BF / DL ≦ 0.42 (10 ′)
It is preferable that More preferably,
0.10 ≦ BF / DL ≦ 0.35 (10 ″)
Good to be.

Conditional expression (11) relates to the refractive index N1 of the lens having the thickest center thickness in the first lens group G1. If the lower limit of conditional expression (11) is not reached, the lens thickness at the periphery of the lenses in the first lens group G1 cannot be maintained, and chipping or the like may occur during processing, or in the case of polishing, polishing may not be possible.
In order to obtain better performance, the numerical range of conditional expression (11) is
1.75 ≦ N1 ≦ 2.50 (11 ′)
It is preferable that Exceeding this upper limit is disadvantageous in terms of cost because many of the existing optical materials are expensive. More preferably,
1.79 ≦ N1 ≦ 2.15 (11 ″)
Good to be.

Conditional expression (12) relates to the focal length f1 of the first lens group G1. When the lower limit of conditional expression (12) is exceeded, the power of the first lens group G1 becomes too small, which is disadvantageous for widening the angle. If the upper limit is exceeded, the power of the first lens group G1 becomes too large, which is disadvantageous for correction of coma aberration, chromatic aberration of magnification, and image plane disparity at the peripheral field angle.
In order to obtain better performance, the numerical range of conditional expression (12) is
0.5 ≦ f / f1 ≦ 1.0 (12 ′)
It is preferable that More preferably,
0.5 ≦ f / f1 ≦ 0.95 (12 ″)
Good to be.

Conditional expression (13) defines an appropriate relationship between the overall paraxial focal length f and the total center thickness D1g of the lenses in the first lens group G1. If the lower limit of conditional expression (13) is not reached, the effective diameter of the first lens group G1 is large in this imaging lens, so that the thickness of the edge portion of the lens in the first lens group G1 cannot be secured sufficiently. If the upper limit is exceeded, the total length cannot be reduced while maintaining the back focus appropriately.
In order to obtain better performance, the numerical range of conditional expression (13) is
0.35 ≦ D1 g / f ≦ 0.7 (13 ′)
It is preferable that

  Conditional expressions (14) and (15) are the appropriate Abbe number differences between adjacent lenses in the composite aspheric lens when the composite aspheric lens is used as in the configuration examples of FIGS. Δν and refractive index difference ΔN are defined. By configuring the lens configuration in the composite aspherical lens with materials as homogeneous as possible so that the Abbe number difference Δν and the refractive index difference ΔN are small so as to satisfy the conditional expressions (14) and (15), Light reflection at the interface between adjacent lenses can be reduced.

  As described above, according to the imaging lens according to the present embodiment, the aspherical surface is efficiently used with a relatively small number of lens groups of a three-group configuration as a whole, and the overall length is shortened and the brightness is ensured. Therefore, the entire lens configuration is optimized while satisfying predetermined conditions that are advantageous to the above, so that it is possible to realize a brighter and higher imaging performance as compared with the prior art while achieving compactness and low cost. In addition, by satisfying the preferable conditions as appropriate, manufacturing aptitude is good and higher imaging performance can be realized. In addition, according to the imaging apparatus according to the present embodiment, since the imaging signal corresponding to the optical image formed by the high-performance imaging lens according to the present embodiment is output, bright and high-resolution imaging is performed. An image can be obtained.

  Next, specific numerical examples of the imaging lens according to the present embodiment will be described. Hereinafter, a plurality of numerical examples will be described together.

  15 and 29 show specific lens data corresponding to the configuration of the imaging lens shown in FIG. In particular, FIG. 15 shows basic lens data, and FIG. 29 shows data relating to an aspherical surface. In the field of the surface number Si in the lens data shown in FIG. 15, for the imaging lens according to Example 1, the surface of the lens element closest to the object side is the first, and the numbers are sequentially increased toward the image side. The number of the i-th surface marked with is shown. In the column of the curvature radius Ri, the value (mm) of the curvature radius of the i-th surface from the object side is shown in correspondence with the reference symbol Ri in FIG. Similarly, the column of the surface interval Di indicates the interval (mm) on the optical axis between the i-th surface Si and the i + 1-th surface Si + 1 from the object side. The Ndj column shows the refractive index for the d-line (587.6 nm) of the j-th optical element from the object side, and the N (945) j column shows the refractive index value for the near-infrared wavelength (945 nm). . The column of νdj shows the Abbe number value for the d-line of the j-th optical element from the object side. Outside the column of FIG. 15, the values of the focal length f (mm) of the entire system are shown as various data.

  In the imaging lens according to Example 1, both surfaces of the second lens group G2 and the third lens group G3 are all aspherical. The first lens group G1 is a spherical surface. The basic lens data in FIG. 15 shows numerical values of the curvature radius in the vicinity of the optical axis (paraxial curvature radius) as the curvature radius of these aspheric surfaces.

FIG. 29 shows aspherical data in the imaging lens of Example 1. In the numerical values shown as aspherical data, the symbol “E” indicates that the subsequent numerical value is a “power exponent” with a base of 10, and the numerical value represented by an exponential function with the base of 10 is Indicates that the value before “E” is multiplied. For example, “1.0E-02” indicates “1.0 × 10 ⁻² ”.

  As the aspheric surface data, the values of the coefficients Ai and K in the aspheric surface expression represented by the following expression (A) are described. More specifically, Z is the length (mm) of a perpendicular line drawn from a point on the aspheric surface at a height h from the optical axis to the tangential plane (plane perpendicular to the optical axis) of the apex of the aspheric surface. Show.

Z = C · h ² / {1+ (1−K · C ² · h ² ) ^1/2 } + ΣAi · h ⁱ (A)
However,
Z: Depth of aspheric surface (mm)
h: Distance from the optical axis to the lens surface (height) (mm)
K: eccentricity C: paraxial curvature = 1 / R
(R: paraxial radius of curvature)
Ai: i-th order (i is an integer of 3 or more) aspheric coefficient

  In the imaging lens of Example 1, each aspheric surface is represented as the aspheric coefficient Ai by effectively using the coefficients A3 to A10 up to the tenth order as necessary.

  Similar to the imaging lens of Example 1 described above, specific lens data corresponding to the configuration of the imaging lens shown in FIG. Similarly, specific lens data corresponding to the configuration of the imaging lens shown in FIGS. 3 to 14 is shown in FIGS. 17 to 28 and FIGS. 31 to 42 as Examples 3 to 14. FIG.

  In the imaging lenses according to Examples 5 to 6, both surfaces of the second lens group G2 and the third lens group G3 are all aspherical, and the most object side surface and the most object side of the first lens group G1 are used. The surface is aspherical. In the imaging lens according to the other examples, like the imaging lens according to Example 1, both surfaces of the second lens group G2 and the third lens group G3 are all aspherical, and the first lens group G1 is spherical. Yes.

  FIG. 43 and FIG. 44 show a summary of values relating to the above-described conditional expressions for each example. 43 and 44, the part marked with “*” in the numerical value indicates that it is out of the numerical value range of the conditional expression.

  45A to 45C respectively show spherical aberration, astigmatism (field curvature), and distortion (distortion aberration) in the imaging lens of Example 1. Each aberration diagram shows an aberration with the e-line (wavelength 546.07 nm) as a reference wavelength. The spherical aberration diagram and the astigmatism diagram also show aberrations for the near infrared ray (wavelength 945 nm) and the C line (wavelength 656.27 nm). In the astigmatism diagram, the solid line indicates the sagittal direction (S), and the broken line indicates the tangential direction (T). FNo. Indicates the F value, and Y indicates the image height.

  Similarly, various aberrations with respect to the imaging lens of Example 2 are shown in FIGS. Similarly, various aberrations of the imaging lenses of Examples 3 to 6 are shown in FIGS. 47 (A) to (C) to 58 (A) to (C).

  This embodiment is designed in consideration of the performance on the relatively near-infrared side with respect to spectroscopy, and is designed to withstand use in a relatively wide band. For this reason, the aberration diagram also shows an aberration of 945 nm as a representative example in the near infrared region. In recent years, for example, a camera mounted on a mobile body has a need in the near infrared wavelength region. For such needs, for example, the transmission wavelength range of the imaging lens of the present embodiment is extended from visible to near infrared, or used in a narrow range of only a part of the near infrared region. Is possible. Note that when using in a narrow wavelength region such as only a narrow region in the near infrared region or in a narrow region in the visible region, the axial chromatic aberration should not be considered as important as when using in a wide band. good.

  As can be seen from the above numerical data and aberration diagrams, each example achieves a bright and high imaging performance.

  In addition, this invention is not limited to the said embodiment and each Example, A various deformation | transformation implementation is possible. For example, the radius of curvature, the surface interval, and the refractive index of each lens component are not limited to the values shown in the above numerical examples, and may take other values.

  In each of the above embodiments, the description is based on the premise that the fixed focus is used. However, it is possible to adopt a configuration in which focus adjustment is possible. For example, the entire lens system can be extended, or a part of the lenses can be moved on the optical axis to enable autofocusing.

1 is a lens cross-sectional view illustrating a first configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 1; FIG. FIG. 2 is a lens cross-sectional view illustrating a second configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 2; 3 is a lens cross-sectional view illustrating a third configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 3. FIG. 4 is a lens cross-sectional view illustrating a fourth configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 4; FIG. 5 is a lens cross-sectional view illustrating a fifth configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 5. FIG. 6 is a lens cross-sectional view illustrating a sixth configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 6. FIG. 7 is a lens cross-sectional view illustrating a seventh configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 7. FIG. 8 shows an eighth configuration example of the imaging lens according to an embodiment of the present invention, and is a lens cross-sectional view corresponding to Example 8. FIG. 9 is a lens cross-sectional view illustrating a ninth configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 9. FIG. 10 is a lens cross-sectional view illustrating a tenth configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 10. FIG. 11 shows an eleventh configuration example of the imaging lens according to the embodiment of the invention, and is a lens cross-sectional view corresponding to Example 11. FIG. 12 is a lens cross-sectional view illustrating a twelfth configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 12. FIG. 14 is a lens cross-sectional view illustrating a thirteenth configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 13. FIG. 14 is a lens cross-sectional view illustrating a fourteenth configuration example of an imaging lens according to an embodiment of the present invention and corresponding to Example 14. FIG. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 1 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 2 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 3 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 4 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 5 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 6 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 7 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 8 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 9 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 10 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 11 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 12 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 13 of this invention. It is a figure which shows the basic lens data of the imaging lens which concerns on Example 14 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 1 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 2 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 3 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 4 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 5 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 6 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 7 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 8 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 9 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 10 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 11 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 12 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 13 of this invention. It is a figure which shows the data regarding the aspherical surface of the imaging lens which concerns on Example 14 of this invention. It is the figure which showed collectively the value regarding the conditional expression about Examples 1-7. It is the figure which showed collectively the value regarding the conditional expression about Examples 8-14. 4A and 4B are aberration diagrams illustrating various aberrations of the imaging lens according to Example 1 of the present invention, in which (A) shows spherical aberration, (B) shows astigmatism (field curvature), and (C) shows distortion. FIG. 6 is an aberration diagram showing various aberrations of the imaging lens according to Example 2 of the present invention, in which (A) shows spherical aberration, (B) shows astigmatism (field curvature), and (C) shows distortion. FIG. 6 is an aberration diagram showing various aberrations of the imaging lens according to Example 3 of the present invention, in which (A) shows spherical aberration, (B) shows astigmatism (field curvature), and (C) shows distortion. It is an aberration diagram which shows the various aberrations of the imaging lens which concerns on Example 4 of this invention, (A) shows spherical aberration, (B) shows astigmatism (field curvature), (C) shows distortion aberration. It is an aberration diagram which shows the various aberrations of the imaging lens which concerns on Example 5 of this invention, (A) shows spherical aberration, (B) shows astigmatism (field curvature), (C) shows distortion aberration. It is an aberration diagram which shows the various aberrations of the imaging lens which concerns on Example 6 of this invention, (A) shows spherical aberration, (B) shows astigmatism (field curvature), (C) shows distortion aberration. It is an aberration diagram which shows the various aberrations of the imaging lens which concerns on Example 7 of this invention, (A) shows spherical aberration, (B) shows astigmatism (field curvature), (C) shows distortion aberration. It is an aberration diagram which shows the various aberrations of the imaging lens which concerns on Example 8 of this invention, (A) shows spherical aberration, (B) shows astigmatism (field curvature), (C) shows distortion aberration. It is an aberration diagram which shows the various aberrations of the imaging lens which concerns on Example 9 of this invention, (A) shows spherical aberration, (B) shows astigmatism (field curvature), (C) shows distortion aberration. It is an aberration diagram which shows the various aberrations of the imaging lens which concerns on Example 10 of this invention, (A) shows spherical aberration, (B) shows astigmatism (field curvature), (C) shows distortion aberration. It is an aberration diagram which shows the various aberrations of the imaging lens which concerns on Example 11 of this invention, (A) shows spherical aberration, (B) shows astigmatism (field curvature), (C) shows distortion aberration. It is an aberration diagram which shows the various aberrations of the imaging lens which concerns on Example 12 of this invention, (A) shows spherical aberration, (B) shows astigmatism (field curvature), (C) shows distortion aberration. It is an aberration diagram which shows the various aberrations of the imaging lens which concerns on Example 13 of this invention, (A) shows spherical aberration, (B) shows astigmatism (field curvature), (C) shows distortion aberration. It is an aberration diagram which shows the various aberrations of the imaging lens which concerns on Example 14 of this invention, (A) shows spherical aberration, (B) shows astigmatism (field curvature), (C) shows distortion aberration.

Explanation of symbols

  G1 ... first lens group, G2 ... second lens group, G3 ... third lens group, L1 ... first lens, L2 ... second lens, L3 ... third lens, L1a, L2a, L3a ... object side aspherical lens , L1b, L2b, L3b ... Parallel plane lens (lens substrate), L11, L12 ... Joint lens, L1c, L2c, L3c ... Image side aspherical lens part, St ... Aperture stop, Ri ... Ith from the object side Radius of curvature of lens surface, Di... Surface distance between i-th and i + 1-th lens surfaces from the object side, Z1... Optical axis, 100.

Claims (16)

From the object side,
A first lens group having the most object side surface as a convex surface and having positive power as a whole;
A second lens group having a meniscus shape in which the shape near the optical axis as a whole is concave on the object side;
The most object side surface is a convex surface in the vicinity of the optical axis, and the most object side surface or the most image side surface has a shape portion that is convex on the image side between the peripheral portion and the surface vertex position. A third lens group,
An imaging lens having a three-group configuration, characterized in that the following conditional expression is satisfied.
0.19 ≦ CA / TL ≦ 0.6 (1)
0.5 ≦ D12a / f ≦ 1.2 (2)
1.2 ≦ TL / f ≦ 1.7 (3)
BF / TL ≦ 0.35 (4)
However,
CA: entrance pupil diameter (diameter)
TL: Full length (distance on the optical axis from the lens surface closest to the object side to the image plane. The length in terms of air on the image plane side from the third lens group)
BF: Back focus (distance on the optical axis from the vertex of the lens surface closest to the image side of the third lens unit to the image surface (air equivalent length))
D12a: Distance on the optical axis from the lens surface closest to the object side of the first lens group to the lens surface closest to the image side of the second lens group f: The entire paraxial focal length. Furthermore, the following conditional expression is satisfied. The imaging lens with a three-group configuration according to claim 1.
D3g / f3 ≦ 0.65 (5)
However,
f3: Paraxial focal length of the third lens group D3g: The sum of the center thicknesses of the lenses in the third lens group. The imaging lens having a three-group structure according to claim 1 or 2, further satisfying the following conditional expression.
0.7 ≦ f / YIM ≦ 4.0 (6)
However,
YIM: The maximum image height. The imaging lens having a three-group configuration according to any one of claims 1 to 3, further satisfying the following conditional expression.
0.65 ≦ D12a / f ≦ 1.0 (2 ′) Furthermore, the following conditional expressions are satisfied. The imaging lens of 3 groups composition given in any 1 paragraph of Claims 1 thru / or 4 characterized by things.
0.20 ≦ D1g / f1 ≦ 0.75 (7)
However,
f1: Paraxial focal length of the first lens group D1g: The sum of the center thicknesses of the lenses in the first lens group. Furthermore, the following conditional expression is satisfied. The imaging lens with a three-group configuration according to any one of claims 1 to 5.
0.45 ≦ R1 / f ≦ 1.0 (8)
However,
R1: The paraxial radius of curvature of the lens surface closest to the object side in the first lens unit is set. Furthermore, the following conditional expressions are satisfied. The imaging lens of 3 groups composition given in any 1 paragraph of Claims 1 thru / or 6 characterized by things.
−0.5 ≦ f2 / f3 (45−νd2g) ≦ 3 (9)
However,
f2: Paraxial focal length of the second lens group f3: Paraxial focal length of the third lens group νd2g: The Abbe number of the lens having the thickest center thickness in the second lens group. The three-group imaging lens according to any one of claims 1 to 7, wherein the following conditional expression is satisfied.
0.03 ≦ BF / DL ≦ 0.5 (10)
However,
DL: Distance on the optical axis from the most object-side lens surface vertex of the first lens unit to the most image-side lens surface vertex of the third lens unit. Furthermore, the following conditional expressions are satisfied. The imaging lens with a three-group configuration according to any one of claims 1 to 8.
1.6 ≦ N1 (11)
However,
N1: The refractive index of the lens having the thickest center thickness in the first lens group. The three-group imaging lens according to any one of claims 1 to 9, further satisfying the following conditional expression.
0.5 ≦ f / f1 ≦ 1.05 (12)
However,
f1: The paraxial focal length of the first lens unit is set. The imaging lens having a three-group configuration according to any one of claims 1 to 10, further satisfying the following conditional expression.
0.24 ≦ D1 g / f ≦ 0.9 (13) The imaging lens having a three-group configuration according to any one of claims 1 to 11, wherein the first lens group includes a glass lens. At least one of the first lens group, the second lens group, and the third lens group is a compound aspheric lens,
The composite aspheric lens includes a flat lens substrate, an object-side aspheric lens portion formed on the object-side surface side of the lens substrate, and an image side formed on the image-side surface side of the lens substrate. It consists of an aspheric lens part,
The difference in Abbe number between the lens substrate and the object-side aspheric lens unit and the difference in Abbe number between the lens substrate and the image-side aspheric lens unit satisfy the following conditional expression (14): Abbe number difference Δν (Abbe number difference with respect to d-line),
The difference in refractive index between the lens substrate and the object-side aspherical lens portion and the difference in refractive index between the lens substrate and the image-side aspherical lens portion each satisfy the following conditional expression (15): The imaging lens having a three-group configuration according to claim 1, wherein the imaging lens has a refractive index difference ΔN (a refractive index difference with respect to the d line).
| Δν | ≦ 10 (14)
| ΔN | ≦ 0.1 (15) In addition, with an aperture,
14. The diaphragm according to claim 1, wherein the stop is disposed such that a position on an optical axis is closer to an object side than a center of gravity position of the first lens group. A three-group imaging lens. The stop is disposed such that the position on the optical axis is closer to the object side than the position of the center of gravity of the first lens group and closer to the image side than the surface vertex position on the most object side of the first lens group. The imaging lens having a three-group configuration according to claim 14, wherein the imaging lens is configured as follows. The imaging lens according to any one of claims 1 to 15,
An imaging device comprising: an imaging element that outputs an imaging signal corresponding to an optical image formed by the imaging lens.

Images