Imaging lens, interchangeable lens, imaging apparatus, and information processing apparatus

Abstract

To achieve an increase in angle and diameter and realize a reduction in size and weight advantageous for auto-focusing.SOLUTION: An imaging lens comprises, in order from an object side, a first lens group, an aperture stop, a second lens group, and a third lens group. In focusing from infinity to a close range, the first lens group and the second lens group move, and the third lens group does not move. The first lens group has a negative lens on the most object side. The first lens group has a biconvex air lens. The second lens group has a biconvex air lens.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an imaging lens, an interchangeable lens, an imaging device, and an information processing device. [Background technology]

[0002] Known types of imaging lenses include, for example, retrofocus, telephoto, and front focus types. The retrofocus type has a lens group with negative refractive power arranged on the object side and a lens group with positive refractive power arranged on the image side. The telephoto type is known as a lens type that is more suitable for miniaturization than the retrofocus type, and is an approximately symmetrical type or has a lens group with negative refractive power arranged on the image side.

[0003] Furthermore, for example, Patent Documents 1 to 3 are known as front focus types. The front focus type is a lens type that does not require space for the focusing group to move within the optical system, and does not require control of the ratio of the amount of movement of multiple groups, such as floating, and moves only the front part of the optical system when focusing. The front focus type can improve the longitudinal magnification of the focusing group while preventing the optical system from becoming large, and is advantageous for speeding up autofocusing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5962744 [Patent Document 2] Patent No. 7152823 [Patent Document 3] Patent No. 7234859 Summary of the Invention [Problem to be solved by the invention]

[0005] However, according to the inventors' intensive research, Patent Documents 1 to 3 have room for improvement in terms of achieving a wider angle and a larger aperture, as well as realizing a smaller and lighter size that is advantageous for autofocus.

[0006] The present invention has been made in consideration of the above points, and aims to provide an imaging lens, an interchangeable lens, an imaging device, and an information processing device that can achieve a wider angle and a larger aperture, while also being compact and lightweight, which is advantageous for autofocus. [Means for solving the problem]

[0007] The imaging lens of this embodiment is composed of, in order from the object side, a first lens group, an aperture stop, a second lens group, and a third lens group, and is characterized in that when focusing from infinity to a close distance, the first lens group and the second lens group move, while the third lens group does not move, the first lens group has a negative lens closest to the object, the first lens group has an air lens with a biconvex shape, and the second lens group has an air lens with a biconvex shape. Effect of the Invention

[0008] According to the present invention, it is possible to provide an imaging lens, an interchangeable lens, an imaging device, and an information processing device that are capable of achieving a wider angle and a larger aperture while also achieving a smaller and lighter size that is advantageous for autofocusing. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a lens configuration diagram of the imaging lens of Numerical Example 1 when focused on an object at infinity. [Diagram 2] FIG. 11 is a lens configuration diagram of an imaging lens according to Numerical Example 2 when focused on an object at infinity. [Diagram 3] FIG. 11 is a lens configuration diagram of an imaging lens according to Numerical Example 3 when focused on an object at infinity. [Figure 4] FIG. 13 is a lens configuration diagram of an imaging lens according to Numerical Example 4 when focused on an object at infinity. [Diagram 5] FIG. 13 is a lens configuration diagram of an imaging lens according to Numerical Example 5 when focused on an object at infinity. [Figure 6] FIG. 13 is a lens configuration diagram of an imaging lens according to Numerical Example 6 when focused on an object at infinity. [Figure 7] FIG. 13 is a lens configuration diagram of an imaging lens according to Numerical Example 7 when focused on an object at infinity. [Figure 8] FIG. 13 is a lens configuration diagram of an imaging lens according to Numerical Example 8 when focused on an object at infinity. [Figure 9] FIG. 4 is an aberration curve diagram of the imaging lens of Numerical Example 1. [Figure 10] FIG. 11 is an aberration curve diagram of the imaging lens of Numerical Example 2. [Figure 11] FIG. 11 is an aberration curve diagram of the imaging lens of Numerical Example 3. [Figure 12] FIG. 11 is an aberration curve diagram of the imaging lens of Numerical Example 4. [Figure 13] FIG. 11 is an aberration curve diagram of the imaging lens of Numerical Example 5. [Figure 14] FIG. 13 is an aberration curve diagram of the imaging lens of Numerical Example 6. [Figure 15] FIG. 13 is an aberration curve diagram of the imaging lens of Numerical Example 7. [Figure 16] FIG. 13 is an aberration curve diagram of the imaging lens of Numerical Example 8. [Figure 17] FIG. 1 is a first diagram showing an example of an imaging device equipped with the imaging lens of the present embodiment. [Figure 18] FIG. 2 is a second diagram showing an example of an imaging device equipped with the imaging lens of the present embodiment. [Figure 19] FIG. 1 is an external perspective view showing an example of an interchangeable lens of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The imaging lens of the present embodiment is suitable for mounting on an imaging optical system in an imaging device such as a digital single-lens reflex camera, an interchangeable lens used in the imaging device, or an information processing device. The imaging lens (imaging optical system) can also be applied to digital cameras, interchangeable lens cameras, information terminal devices, video cameras, silver halide cameras, optical sensors, and projection optical systems (projectors).

[0011] The imaging lens may be read as an imaging lens, a prime lens, or a wide-angle prime lens. Furthermore, imaging and photography may be read as interchangeable (may be synonymous). Furthermore, distance and axial distance may be read as interchangeable (when simply referred to as distance, it may mean axial distance). Furthermore, radius of curvature and paraxial radius of curvature may be read as interchangeable (when simply referred to as radius of curvature, it may mean paraxial radius of curvature).

[0012] The imaging lens of this embodiment is a wide-angle prime lens with a focal length of 28 mm converted into a 35 mm film camera (the so-called Leica version), and has a wide angle and a large aperture (for example, an F-number of about 2.8), with one of the objectives being to realize a small, lightweight optical system that is advantageous for autofocus.

[0013] As shown in the lens configuration diagrams of Numerical Examples 1-8 (FIGS. 1-8), the imaging lens of this embodiment is composed of, in order from the object side, a first lens group G1 with positive refractive power, an aperture stop SP for adjusting the amount of light, a second lens group G2 with positive refractive power, and a third lens group G3 with negative refractive power. Filters F1 and F2 are disposed between the third lens group G3 and an image surface (designed image surface) I. The filters F1 and F2 are composed of, for example, a low-pass filter, an infrared cut filter, a cover glass of an image sensor, or the like.

[0014] In Numerical Examples 1-5 and 8 (FIGS. 1-5 and 8), the first lens group G1 is composed of, in order from the object side, a negative lens 11, a negative lens 12, and a positive lens 13. Between the negative lens 11 and the negative lens 12, a biconvex air lens AL1 is formed. In Numerical Examples 6 and 7 (FIGS. 6 and 7), the first lens group G1 is composed of, in order from the object side, a negative lens 11', a negative lens 12', a negative lens 13', and a positive lens 14'. A biconvex air lens AL1 is formed between the negative lens 11' and the negative lens 12'.

[0015] In Numerical Examples 1 to 8 (FIGS. 1 to 8), the second lens group G2 is composed of, in order from the object side, a positive lens 21, a negative lens 22, and a positive lens 23. Between the negative lens 22 and the positive lens 23, a biconvex air lens AL2 is formed.

[0016] The third lens group G3 is composed of a negative lens 31 in Numerical Examples 1-3 and 5-8 (FIGS. 1 to 3 and 5 to 8). In Numerical Example 4 (FIG. 4), the third lens group G3 is composed of, in order from the object side, a negative lens 31' and a positive lens 32'.

[0017] The digital camera market has penetrated deeply into the world, and users have a wide range of requirements for digital cameras. Among them, the category of small, high-image-quality compact cameras equipped with high-performance fixed-focus lenses (imaging lenses) has gained a certain amount of support from users, and expectations are high. In addition to high performance, users are looking for cameras with small F-numbers, meaning that they have a large aperture, but are also small, lightweight, and have high-speed focusing (autofocusing).

[0018] Here, in terms of high performance, in addition to having a resolution corresponding to an image sensor with at least 20 to 40 million pixels, it is necessary to have little coma flare even at full aperture, high contrast, and no distortion of point images even at the periphery of the angle of view, little chromatic aberration so that unnecessary coloring does not occur even in areas with large differences in brightness, and little distortion aberration so that straight lines can be depicted as straight lines.

[0019] In terms of increasing the aperture, an F-number of around 2.8 or less is desirable in order to differentiate it from ordinary compact cameras equipped with zoom lenses.

[0020] In terms of compactness, it is necessary to keep the total optical length and lens diameter small. Furthermore, in terms of compactness when not taking pictures, it is necessary to have a mechanism called a collapsible type that shortens the total lens length by shortening the air space on the optical axis in the photographic optical system, such as before and after the aperture and back focus, when not taking pictures.

[0021] In terms of increasing the speed of autofocusing, one effective optical measure is to increase the longitudinal magnification of the focusing group to reduce the amount of movement during focusing.

[0022] Regarding the angle of view of the photographic lens, there is a wide range of users who strongly desire a wide angle, so it is desirable for the angle of view to be 75 degrees or more, which is equivalent to a focal length of 28 mm in a 35 mm film camera (the so-called Leica version), or a half angle of view of about 37.5 degrees or more.

[0023] There are many types of imaging lenses for digital cameras, but a typical configuration of a wide-angle prime lens is the so-called retrofocus type, which has a lens group with negative refractive power on the object side and a lens group with positive refractive power on the image side. The main reason for adopting the retrofocus type is the requirement to move the exit pupil position away from the image plane and make the peripheral light beam enter the sensor at an angle close to perpendicular, due to the characteristics of an area sensor with a color filter and microlens for each pixel. However, as can be seen from the fact that the retrofocus type was originally intended to ensure back focus for using a wide-angle lens as an interchangeable lens for a single-lens reflex camera, the total lens length (the distance from the surface closest to the object to the image plane) tends to be large.

[0024] On the other hand, in recent image sensors, due to improvements and optimization of on-chip microlenses, advances in image processing, and the like, a situation has arisen in which even if peripheral light flux is incident on the sensor at a certain angle, it does not cause a major problem. Therefore, it is now possible to select a lens type that is more suitable for miniaturization without being as concerned as before about the perpendicular incidence of peripheral light flux.

[0025] Lens types that are more suitable for size reduction than the retrofocus type include a substantially symmetrical type and a telephoto type in which a lens group with negative refractive power is disposed on the image side.

[0026] However, telephoto type imaging optical systems are relatively small wide-angle lenses with a configuration close to a symmetrical system with negative powers on the most object side and the most image side, but they have a somewhat dark F-number of about 3.6, and many of them are inner focus types with the focusing group in the middle of the lens system, so there is a problem that the total lens length tends to be large because it is necessary to secure space for the focusing group to move. Telephoto type imaging optical systems are small and have a large aperture with a configuration close to a symmetrical system with negative powers on the most object side and the most image side, but they are designed with inner focus with the focusing group in the middle of the lens and floating that moves multiple focusing groups on different trajectories in mind, so the total lens length tends to be large and the mechanical structure that holds the lens becomes complex, which tends to make the camera large. Furthermore, in a telephoto type imaging optical system, if the entire system is extended, the amount of movement during focusing is relatively large, leaving a problem in increasing the speed of autofocus.

[0027] A front focus type lens, in which only the front portion of the optical system moves during focusing, is a lens type that does not require space for the focusing group to move within the optical system and does not require control of the ratio of the amount of movement of multiple groups, as is the case with floating lenses. The front focus type lens can improve the longitudinal magnification of the focusing group while preventing the lens system from becoming larger, which is advantageous for speeding up autofocusing.

[0028] As front focus type imaging lenses, for example, those described in the above-mentioned Patent Documents 1 to 3 are known. However, Patent Document 1 is relatively small and bright with an F-number of about 2.5, but has a maximum total angle of view of about 70 degrees, leaving room for improvement in terms of widening the angle. Patent Document 2 is also bright with an F-number of about 2.8 or less, but has a maximum total angle of view of about 50 degrees, leaving room for improvement in terms of widening the angle. Furthermore, Patent Document 3 is also bright with an F-number of about 2.8 or less, but has a maximum total angle of view of about 54 degrees, leaving room for improvement in terms of widening the angle.

[0029] The present invention has been made in consideration of the above points, and aims to provide a small, lightweight imaging lens (imaging optical system) that has high performance, a wide angle of view of about 75° or more, and a large aperture lens with an F-number of about 2.8, and is advantageous for autofocusing.

[0030] In general, as the angle of view is increased, coma, astigmatism, chromatic aberration of magnification, curvature of field, distortion, etc. tend to increase, and in addition to controlling these aberrations, the optical system tends to become longer both in the radial direction and in the optical axis direction in order to transmit light rays with a wide angle of view. Also, when the longitudinal magnification of the focusing group is improved to speed up autofocusing, the size and amount of movement of the focusing group itself can be reduced, but there is a characteristic (disadvantage) that the fixed group that does not move during focusing tends to become longer.

[0031] The imaging lens of this embodiment has been completed based on the discovery that the problems in correcting aberrations and the problem of increased size can be solved by adopting the following configuration.

[0032] The imaging lens of this embodiment is composed of, in order from the object side, a first lens group G1, an aperture stop SP, a second lens group G2, and a third lens group G3. When focusing from infinity to a close distance, the first lens group G1 and the second lens group G2 move, but the third lens group G3 does not move (it is fixed with respect to the image surface I). The first lens group G1 and the second lens group G2 may move together (may be extended toward the object side), or may move with slightly different amounts of movement (may be extended toward the object side). The first lens group G1 has a negative lens 11 or 11' closest to the object side.

[0033] In this specification, an "air lens" is defined as follows: An air gap between the image side surface of the object-side lens and the object side surface of the image-side lens that face each other of two adjacent lenses arranged at a distance from each other is called an air lens. In addition, the shape of the air lens is defined by taking the image side surface of the object-side lens as the object side surface of the air lens, and the object side surface of the image-side lens as the image side surface of the air lens.

[0034] In the imaging lens of this embodiment, the first lens group G1 has a biconvex air lens AL1 (an air lens formed between lens 11 or 11' and lens 12), and the second lens group has a biconvex air lens AL2 (an air lens formed between lens 22 and lens 23).

[0035] The imaging lens of this embodiment employs a front-focus type configuration in which a third lens group G3 does not move during focusing, and a first lens group G1 and a second lens group G2 that move during focusing (for example, are extended toward the object side as a unit) are arranged on the object side of the third lens group G3. This eliminates the need to create space within the optical system for movement of the focusing group, thereby preventing the lens system from becoming too long.

[0036] As mentioned above, the focusing groups (first and second lens groups) have a "substantially symmetrical power arrangement" to improve the ability to correct aberrations that become more difficult to correct as the angle of view becomes wider. By configuring both the air lens AL1 located in the first lens group G1 and the air lens AL2 located in the second lens group G2 to have a biconvex shape, it is possible to correct various aberrations at a higher level. In other words, it is easier to correct coma, distortion, and chromatic aberration of magnification, which become more difficult to correct as the angle of view becomes wider.

[0037] In other words, this corresponds to making all four surfaces, i.e., the object side surface of the air lens AL1 located in the first lens group G1, the image side surface of the air lens AL1 located in the first lens group G1, the object side surface of the air lens AL2 located in the second lens group G2, and the image side surface of the air lens AL2 located in the second lens group G2, concave.

[0038] Making the object side surface of the air lens AL1 located in the first lens group G1 a concave surface has the effect of appropriately controlling spherical aberration and facilitating correction of mainly astigmatism. Making the image side surface of the air lens AL2 located in the second lens group G2 a concave surface has the effect of controlling the exit pupil distance, making it possible to appropriately set the angle of incidence of the chief ray to the image plane at the peripheral image height, and facilitating correction of mainly coma and distortion.

[0039] Furthermore, making the image side surface of the air lens AL1 located in the first lens group G1 a concave surface has the effect of realizing a reduction in the diameter of the lens closest to the object side of the lens system and facilitating coma aberration correction for the lower ray. Making the object side surface of the air lens AL2 located in the second lens group G2 a concave surface has the effect of realizing a reduction in the diameter of the lens closest to the image side and facilitating coma aberration correction for the upper ray, which is advantageous for achieving both compactness and high performance.

[0040] In this way, in a front-focus type lens that is advantageous for compactness, by providing a biconvex air lens in each of the focusing groups (first and second lens groups), it is possible to obtain a high-performance imaging lens with sufficient aberration correction capability.

[0041] It is preferable that only one biconvex air lens AL1 is provided in the first lens group G1, and only one biconvex air lens AL2 is provided in the second lens group G2.

[0042] In order to maintain a "substantially symmetrical power arrangement" in the focusing group, it is desirable that the number of air lenses of similar shapes (biconvex shapes) in the first lens group and the second lens group be the same. However, because biconvex air lenses have a high ability to correct aberrations at each surface as described above, by adopting a configuration in which one each is placed in the first and second lens groups, it is possible to minimize the number of biconvex air lenses, which have concave surfaces facing each other, and thus reduce the thickness of the entire lens system.

[0043] It is preferable that the biconvex air lens AL1 of the first lens group G1 is formed closest to the object side of the first lens group G1, and the biconvex air lens AL2 of the second lens group G2 is formed closest to the image side of the second lens group G2.

[0044] By making the object side surface of the air lens AL1, which is the closest to the object in the first lens group G1, a concave surface, it is possible to improve the ability to correct aberrations, particularly astigmatism, and by making the image side surface of the air lens AL2, which is the closest to the image in the second lens group G2, a concave surface, it is possible to improve the ability to correct aberrations, particularly coma and distortion.

[0045] It is preferable that the imaging lens of this embodiment satisfies the following conditional expressions (1) and (2). (1)-0.90<(r1o+r2o) / (r1o-r2o)<0.00 (2)-0.45<(r1i+r2i) / (r1i-r2i)<0.40 however, r1o: radius of curvature of the object side surface of the biconvex air lens in the first lens group, r2o: radius of curvature of the image-side surface of the biconvex air lens in the first lens group, r1i: radius of curvature of the object side surface of the biconvex air lens in the second lens group, r2i: radius of curvature of the image-side surface of the biconvex air lens in the second lens group.

[0046] Conditional formula (1) indicates an appropriate range for the shape of the air lens AL1 positioned in the first lens group G1. If the upper limit value of conditional expression (1) is exceeded, the refractive power of the image side surface of the air lens AL1 located in the first lens group G1 becomes relatively too strong, which undesirably makes it easier for significant spherical aberration to occur in the over direction, makes it easier for the field curvature to tilt significantly to the positive side in the peripheral area, and makes it easier for coma aberration to remain. If the lower limit of conditional formula (1) is exceeded, the refractive power of the object-side surface of the air lens AL1 located in the first lens group G1 becomes relatively too strong, which undesirably causes significant spherical aberration in the under direction or causes the field curvature to be significantly displaced to the negative side at intermediate image heights.

[0047] Conditional expression (2) indicates an appropriate range for the shape of the air lens AL2 positioned in the second lens group G2. If the upper limit value of conditional expression (2) is exceeded, the refractive power of the image side surface of the air lens AL2 located in the second lens group G2 becomes relatively too strong, making it easier for astigmatism to occur and for coma aberration to become disturbed in the peripheral part of the pupil, which is not preferable. If the lower limit of conditional formula (2) is not reached, the refractive power of the object side surface of the air lens AL2 located in the second lens group G2 becomes relatively too strong, which undesirably makes it easier for large spherical aberration to occur in the over direction or makes it easier for inward coma aberration to remain.

[0048] In order to obtain the effects of conditional expressions (1) and (2) significantly (to obtain even better performance), it is preferable to satisfy the following conditional expressions (1A) and (2A). (1A)-0.80<(r1o+r2o) / (r1o-r2o)<-0.15 (2A)-0.40<(r1i+r2i) / (r1i-r2i)<0.30

[0049] It should be noted that when calculating the numerical values ​​corresponding to conditional expressions (1), (2), (1A), and (2A), even if the target lens surface is aspheric, the calculation can be performed using the paraxial radius of curvature.

[0050] It is preferable that the imaging lens of this embodiment satisfies the following conditional expression (3). (3) 1.0 <TL / f<2.0 however, TL: The axial distance between the surface of the first lens group closest to the object and the image plane when focusing at infinity, f: The focal length of the entire system when focused at infinity.

[0051] Condition (3) indicates an appropriate range of the total optical length relative to the focal length of the entire system. By satisfying condition (3), it is possible to obtain a wide-angle lens that is small in all of the lens length, total lens thickness, and lens diameter, sufficiently reduces various aberrations, and provides high performance with a resolution compatible with an image sensor with a high pixel count.

[0052] In order to significantly obtain the effect of condition (3) (to obtain even better performance), it is preferable to satisfy the following condition (3A). (3A)1.4 <TL / f<2.0

[0053] In the imaging lens of this embodiment, the image side surface of the lens 13 or 14' closest to the image in the first lens group G1 and the object side surface of the lens 21 closest to the object in the second lens group G2 have symmetric (paraxially symmetric) concave-convex surface shapes sandwiching the aperture stop SP. More specifically, the image side surface of the lens 13 or 14' closest to the image in the first lens group G1 and the object side surface of the lens 21 closest to the object in the second lens group G2 both have convex surfaces facing the aperture stop SP. In Numerical Examples 1-8, the lens 13 or 14' closest to the image in the first lens group G1 and the lens 21 closest to the object in the second lens group G2 are both composed of biconvex positive lenses.

[0054] In the imaging lens of this embodiment, the lens 13 or 14' closest to the image in the first lens group G1 and the lens 21 closest to the object in the second lens group G2 have refractive powers of the same sign with the aperture stop SP in between. More specifically, the lens 13 or 14' closest to the image in the first lens group G1 and the lens 21 closest to the object in the second lens group G2 both have positive refractive power. In Numerical Examples 1-8, the lens 13 or 14' closest to the image in the first lens group G1 and the lens 21 closest to the object in the second lens group G2 are both composed of biconvex positive lenses.

[0055] The imaging lens of this embodiment adopts a front focus type configuration in which a third lens group G3 that does not move during focusing is disposed on the object side thereof, and a first lens group G1 and a second lens group G2 that move during focusing (for example, are moved toward the object side as a unit), eliminating the need to create a movement space for the focusing group within the optical system and suppressing the increase in the length of the lens system. In addition, by disposing a negative lens 11 or 11' on the most object side of the first lens group G1, the entrance pupil position is made shallow, suppressing the increase in the radial size of the lens due to the wide angle, and facilitating the correction of coma aberration at the peripheral angle of view.

[0056] In addition, by providing symmetrical concave-convex surface shapes on both sides sandwiching the aperture and based on a "substantially symmetrical power arrangement" within the focusing group (the image-side surface of the lens 13 or 14' closest to the image in the first lens group G1 and the object-side surface of the lens 21 closest to the object in the second lens group G2 have symmetrical (paraxially symmetrical) concave-convex surface shapes sandwiching the aperture aperture SP), it is made easier to correct coma, distortion, and chromatic aberration of magnification, which become more difficult to correct as the angle of view becomes wider. Providing symmetry in terms of surface shape makes it easier to effectively correct coma, especially at the peripheral angle of view. Here, "symmetrical concave-convex surface shapes on both sides of the aperture" refers to a state in which, for example, when the paraxial shape of the final surface of the first lens group G1 is convex toward the aperture stop SP, the paraxial shape of the leading surface of the second lens group G2 is also convex toward the aperture stop SP, and when the paraxial shape of the final surface of the first lens group G1 is concave toward the aperture stop SP, the paraxial shape of the leading surface of the second lens group G2 is also concave toward the aperture stop SP.

[0057] In addition, the lenses facing each other across the aperture (the final lens of the first lens group G1 and the first lens of the second lens group G2) have the same sign of refractive power, and the focusing group is based on a "substantially symmetrical power arrangement" (the lens 13 or 14' closest to the image side of the first lens group G1 and the lens 21 closest to the object side of the second lens group G2 have the same sign of refractive power sandwiching the aperture aperture SP), which makes it easier to correct coma, distortion, and lateral chromatic aberration, which become more difficult to correct with a wide angle. By providing symmetry in terms of refractive power, it becomes easier to effectively correct lateral chromatic aberration and distortion aberration, especially at the peripheral angle of view. Here, the "refractive power" of "the final lens of the first lens group G1 and the first lens of the second lens group G2" does not mean the refractive power of the entire cemented lens even if it is a cemented lens of multiple lenses, but means the refractive power of the lens component closest to the aperture aperture SP when both sides of the lens component are in contact with air.

[0058] It is preferable that the imaging lens of this embodiment satisfies the following conditional expressions (4) and (5). (4) 0.35 <Ds3 / Dsi<0.75 (5) 1.00 <D23 / D3<7.50 however, Ds3: The axial distance between the aperture stop and the surface of the third lens group closest to the object when focusing at infinity. Dsi: Axial distance between the aperture stop and the image plane when focused at infinity, D23: The axial distance between the surface of the second lens group closest to the image side and the surface of the third lens group closest to the object side when focusing at infinity. D3: The axial distance between the surface in the third lens group closest to the object and the surface closest to the image.

[0059] In the focusing group having a substantially symmetrical power arrangement, the aperture stop is located approximately in the center of the focusing group (first and second lens groups), and conditional formula (4) specifies the distance from the aperture stop to the image plane and the distance from the aperture stop to the leading surface of the fixed group (third lens group), thereby indicating an appropriate range for the position of the fixed group (third lens group) relative to the focusing group (first and second lens groups) in the optical system. If the upper limit of conditional expression (4) is exceeded, the fixed group (third lens group) will be too far away from the focusing group (first and second lens groups). This is advantageous for correcting field curvature and distortion, but it may result in the position of the light flux at the peripheral angle of view that passes through the fixed group (third lens group) being higher, causing the fixed group (third lens group) to become too large in the radial and thickness directions. If the lower limit of conditional formula (4) is exceeded, the height of the light beam at the peripheral angle of view that passes through the fixed group (third lens group) will be low, which is advantageous for size reduction, but the thickness of the light beam that passes through the fixed group (third lens group) will be thicker, which will contribute more to spherical aberration. When the focusing group (first and second lens groups) and the fixed group (third lens group) are held across a movable mechanism, errors are likely to occur in their relative attitude and positional relationship, and if the fixed group (third lens group) makes a large contribution to spherical aberration, this error will likely cause a deterioration in imaging performance, which may result in a decrease in productivity in mass production factories or a deterioration in imaging performance.

[0060] Conditional formula (5) defines the appropriate range of the thickness of the fixed group (third lens group) in relation to the air spacing between the focusing group (first and second lens groups) and the fixed group (third lens group) when focusing at infinity. If the upper limit of conditional expression (5) is exceeded, even if the fixed group (third lens group) is made thin, it will be too far away from the focusing group (first and second lens groups). This is advantageous for correcting field curvature and distortion, but the position of the light flux at the peripheral angle of view that passes through the fixed group (third lens group) will be high, and there is a risk that the fixed group (third lens group) will become too large in the radial direction. If the lower limit of conditional expression (5) is exceeded, the fixed group (third lens group) becomes too close to the focusing group (first and second lens groups), which increases the contribution of the fixed group (third lens group) to spherical aberration, resulting in reduced productivity in mass production factories due to manufacturing errors and reduced imaging performance. Also, in order to reduce the exchange of spherical aberration between the fixed group (third lens group) and the focusing group (first and second lens groups), the fixed group (third lens group) becomes thicker, which can increase the overall length of the lens.

[0061] In this way, by defining the optimal position and thickness of the fixed group (third lens group) using conditional expressions (4) and (5) in relation to the focusing group (first and second lens groups) which has been given a "substantially symmetrical power arrangement" and has improved aberration correction capability, it is possible to achieve a balance between optimal aberration correction which takes into account the sensitivity of imaging performance degradation to manufacturing errors which are likely to occur in front focus types, and the miniaturization of the lens system.

[0062] In order to obtain the effects of conditional expressions (4) and (5) significantly (to obtain even better performance), it is preferable to satisfy the following conditional expressions (4A) and (5A). (4A) 0.40 <Ds3 / Dsi<0.65 (5A) 1.00 <D23 / D3<6.50

[0063] It is preferable that the imaging lens of this embodiment satisfies the following conditional expression (6). (6) 1.50<|f3 / f|<5.50 however, f3: focal length of the third lens group, f: The focal length of the entire system when focused at infinity.

[0064] Condition (6) indicates an appropriate range of the refractive power of the third lens group relative to the focal length of the entire lens system. If the upper limit of conditional expression (6) is exceeded, the refractive power of the third lens group will be too weak, making it impossible to improve the longitudinal magnification of the focusing group. As a result, the amount of movement of the focusing group during focusing cannot be reduced, which may reduce the effect of increasing the speed of autofocusing. If the lower limit of condition (6) is exceeded, the refractive power of the third lens group will be too strong, and the exchange of aberrations with the focusing group will become excessive, making it more likely that performance will deteriorate due to manufacturing errors. Alternatively, in order to perform independent aberration correction within the third lens group, the number of lenses in the third lens group will increase or the thickness will increase, which could result in the overall lens system becoming longer and larger.

[0065] In order to obtain the effect of condition (6) significantly (to obtain even better performance), it is preferable to satisfy the following condition (6A). (6A) 2.00<|f3 / f|<5.00

[0066] It is preferable that the imaging lens of this embodiment satisfies the following conditional expression (7). (7) 0.05 <D23 / f<0.35 however, D23: The axial distance between the surface of the second lens group closest to the image side and the surface of the third lens group closest to the object side when focusing at infinity. f: The focal length of the entire system when focused at infinity.

[0067] Condition (7) defines an appropriate range for the air spacing between the focusing group (first and second lens group) and the fixed group (third lens group) with respect to the focal length of the entire system when focusing at infinity. If the upper limit of condition (7) is exceeded, the fixed group (third lens group) will be too far away from the focusing groups (first and second lens groups). This is advantageous for correcting curvature of field and distortion, but the position of the light beam at the peripheral angle of view that passes through the fixed group (third lens group) will be high, and the fixed group (third lens group) may become too large in the radial direction. If the lower limit of conditional expression (7) is exceeded, the fixed group (third lens group) becomes too close to the focusing group (first and second lens groups), which increases the contribution of the fixed group (third lens group) to spherical aberration, resulting in reduced productivity in mass production factories due to manufacturing errors and reduced imaging performance. Also, in order to reduce the exchange of spherical aberration between the fixed group (third lens group) and the focusing group (first and second lens groups), the fixed group (third lens group) becomes thicker, which can increase the overall length of the lens.

[0068] To obtain the effect of condition (7) significantly (to obtain even better performance), it is preferable to satisfy the following condition (7A). (7A) 0.10 <D23 / f<0.30

[0069] The third lens group G3 has negative refractive power throughout Numerical Examples 1 to 8 (FIGS. 1 to 8). By giving the third lens group G3 negative power, it forms a pair with the lens 11 or 11' closest to the object in the first lens group G1, which also has negative power, and the lens system as a whole approaches a "substantially symmetrical power arrangement", which makes it easier to correct coma, distortion, and lateral chromatic aberration, which become more difficult to correct as the angle of view becomes wider.

[0070] In Numerical Examples 1-3 and 5-8 (FIGS. 1-3 and 5-8), the third lens group G3 is composed of a negative single lens 31. By giving the third lens group G3 negative power, the load of aberration correction of the third lens group G3 can be appropriately set, and furthermore, by making the third lens group G3 a negative single lens (the simplest one-element configuration), it is possible to contribute to the miniaturization of the lens. In addition, the mechanical configuration for holding the lens can be simplified, which contributes to the miniaturization and weight reduction of the entire camera.

[0071] In the imaging lens of this embodiment, it is preferable that both the first lens group G1 and the second lens group G2 are composed of two or more and four or less lenses. The air lens AL1 located closest to the object side of the first lens group G1 and the air lens AL2 located closest to the image side of the second lens group G2 are both biconvex in shape, and therefore have a relatively strong negative refractive power. In order for the entire lens system to have a positive focal length as an imaging lens, it is necessary to arrange a strong positive refractive power in front of and behind the aperture stop SP. In order to naturally establish such a power arrangement and achieve good aberration correction, it is preferable to provide a positive lens in front of and behind the aperture stop SP in addition to the lenses constituting the air lenses AL1 and AL2. Since two lenses are required to constitute an air lens, it is preferable that both the first lens group G1 and the second lens group G2 are composed of two or more and four or less lenses.

[0072] It is preferable that the imaging lens of this embodiment satisfies the following conditional expression (8). (8) 1.20<|(R1l-R2s) / (R1l+R2s)| however, R1l: radius of curvature of the image-side surface of the lens closest to the image side in the first lens group, R2s: Radius of curvature of the object-side surface of the lens in the second lens group closest to the object.

[0073] Conditional expression (8) defines an appropriate range for the radius of curvature of the final surface of the first lens group and the leading surface of the second lens group, which face each other across the diaphragm. If the lower limit of conditional formula (8) is exceeded, the symmetry between the two surfaces facing each other across the aperture is lost, weakening the characteristics of the "approximately symmetrical power arrangement" in the focusing group, which can make it difficult to correct coma aberration, particularly at the peripheral angles of view. Note that conditional formula (8) takes an absolute value and therefore appears to regulate only one side of conditional formula (8), but the intention is to avoid the corresponding numerical value of conditional formula (8) being in the range of -1.2 to 1.2.

[0074] When calculating the numerical value corresponding to condition (8), even if the target lens surface is aspheric, the calculation can be performed using the paraxial radius of curvature.

[0075] It is preferable that the imaging lens of this embodiment satisfies the following conditional expression (9). (9) 2.00<|f2i / f|<20.00 however, f2i: focal length of the lens closest to the image in the second lens group, f: The focal length of the entire system when focused at infinity.

[0076] Conditional formula (9) indicates an appropriate range of the refractive power of the lens 23 closest to the image side in the second lens group G2 with respect to the focal length of the entire system. The focusing groups (first and second lens groups) of the imaging lens of this embodiment have an "approximately symmetrical power arrangement", which improves the ability to correct aberrations that become more difficult to correct as the angle becomes wider. The lens 23 closest to the image side in the second lens group G2 is assigned a function that contributes to aberration correction at a position close to the image plane while minimizing the effect on this "approximately symmetrical power arrangement", which is advantageous for achieving both a compact imaging lens and high performance. If the upper limit of conditional expression (9) is exceeded, the refractive power of the lens 23 closest to the image in the second lens group G2 will become too small, reducing the basic aberration correction ability of the second lens group G2 as a whole and making the entire lens system longer. Alternatively, the exchange of aberrations with the first lens group G1 will become excessive, making performance degradation due to manufacturing errors more likely to occur. If the lower limit of condition (9) is exceeded, the refractive power of the lens 23 closest to the image in the second lens group G2 will become too large, which will affect the "substantially symmetrical power arrangement" of the entire focusing group, thereby reducing the benefits of aberration correction provided by a symmetrical system and causing the entire lens system to become longer and larger.

[0077] In order to significantly obtain the effect of condition (9) (to obtain even better performance), it is preferable to satisfy the following condition (9A). (9A) 2.20<|f2i / f|<15.00

[0078] It is preferable that the imaging lens of this embodiment satisfies the following condition (10). (10) 0.10<|f1 / f2|<15.0 however, f1: focal length of the first lens group, f2: The focal length of the second lens group.

[0079] Condition (10) indicates the appropriate range of the refractive power balance between the lens groups on either side of the aperture in the focusing group, i.e., the first and second lens groups. Because the focusing group has a "substantially symmetrical power arrangement," it is important to appropriately set the refractive power of the lens groups before and after the aperture (the first and second lens groups). If the upper limit of condition (10) is exceeded, the refractive power of the second lens group behind the aperture stop becomes relatively too strong, which undesirably causes negative distortion, outward coma, and short-wavelength lateral chromatic aberration to occur toward the outside of the image field. If the lower limit of condition (10) is exceeded, the refractive power of the first lens group located in front of the aperture stop becomes too strong relatively, causing distortion to bend in the positive direction at the periphery, inward coma to occur, and short-wavelength lateral chromatic aberration to occur toward the inside of the image plane, which are undesirable.

[0080] In order to significantly obtain the effect of condition (10) (to obtain even better performance), it is preferable to satisfy the following condition (10A). (10A) 0.20<|f1 / f2|<15.0

[0081] It is preferable that the imaging lens of this embodiment satisfies the following condition (11). (11)0.8 <Dt / f<1.5 however, Dt: the axial distance between the surface of the first lens group closest to the object and the surface of the third lens group closest to the image when focused at infinity, f: The focal length of the entire system when focused at infinity.

[0082] By satisfying conditional expression (11), the overall lens length and the overall lens thickness can be optimized to realize a high-performance tube lens. If the upper or lower limit of conditional expression (11) is exceeded, the overall lens length and the overall lens thickness cannot be set sufficiently, which may hinder the realization of a high-performance tube lens.

[0083] It is preferable that the imaging lens of this embodiment satisfies the following condition (12). (12)1.1 <Mg3^2<2.0 however, Mg3: Magnification of the third lens group when focused at infinity.

[0084] Condition (12) expresses the movement sensitivity of the focusing group (first and second lens groups), that is, how much the focus position moves when the focusing group (first and second lens groups) moves a predetermined movement amount (unit movement amount). If the upper limit of condition (12) is exceeded, the amount of movement of the focusing group (first and second lens groups) is reduced, but the refractive power of the third lens group becomes too strong, causing excessive exchange of aberration with the focusing group (first and second lens groups), which is likely to cause performance degradation due to manufacturing errors. Alternatively, the number of lenses in the third lens group may increase or the thickness may increase in order to perform independent aberration correction within the third lens group, which may result in the overall lens system becoming longer and larger. If the lower limit of condition (12) is exceeded, the entire lens system will move forward, and the amount of movement of the focusing group (first and second lens groups) required for focusing will increase, making it difficult to achieve high-speed autofocusing.

[0085] In addition, it is desirable to have at least one aspherical surface in the third lens group. The height of the light rays passing through the third lens group is likely to change as the focusing group (first and second lens groups) advances, but the use of an aspherical surface makes it easier to suppress changes in aberration correction due to distance. It is desirable to make both the surface closest to the object and the surface closest to the image in the third lens group aspherical. In addition to making it easier to correct changes in aberration correction, this makes it easier to correct the mold in manufacturing, improving the precision of the lens surface shape and suppressing the effects of alignment errors.

[0086] It is preferable that the imaging lens of this embodiment satisfies the following conditions (13) and (14). (13)0.7 <Y’ / f<0.95 (14)0.7 <tan(θPmax)<1.0 however, Y': Maximum image height, f: focal length of the entire system when focused at infinity, θPmax: The angle of incidence of the chief ray reaching the maximum image height on the image plane.

[0087] Conditional formula (13) restricts (specifies) the angle of view of the imaging lens, and conditional formula (14) restricts (specifies) the angle of incidence of off-axis rays of the imaging lens on the image plane. By satisfying conditional formulas (13) and (14), a high-performance imaging lens that is both wide-angle and compact can be realized. The imaging lens of this embodiment is a wide-angle lens with a half angle of view of about 35 degrees or more, and aims to achieve compactness and high performance by appropriately controlling the angle of incidence of the chief ray that reaches the maximum image height on the image plane. In order to achieve this aim, it is preferable to satisfy conditional formulas (13) and (14).

[0088] Specific numerical examples 1-8 are shown below. The meanings of the symbols in numerical examples 1-8 are as follows. The glass materials in the examples are optical glass type names of HOYA CORPORATION (HOYA) and OHARA INC. (OHARA). The unit of length is [mm]. Here, the aspheric surface is defined by the following formula, where C is the reciprocal of the paraxial curvature radius (paraxial curvature) and H is the height from the optical axis. x=CH 2 / [1+[1-(1+K)C 2 H 2 ] 1 / 2 ]+A4H 4 +A6H 6 +A8H 8 +A 10 H 10 +A 12 H 12 +A 14 H 14 f: focal length of the entire system F:F Number ω: Half angle of view Ya: Maximum image height R: radius of curvature D: Surface spacing Nd: Refractive index at the d line νd: Abbe number at d line BF: Back focus K: conic constant of aspheric surface A4: 4th order aspheric coefficient A6: 6th order aspheric coefficient A8: 8th order aspheric coefficient A10: 10th order aspheric coefficient A12: 12th order aspheric coefficient A14: 14th order aspheric coefficient

[0089] [Numerical Example 1] Fig. 1, Fig. 9 and Tables 1 to 4 show the imaging lens of Numerical Example 1. Fig. 1 is a lens configuration diagram when focusing on infinity, and Fig. 9 is an aberration curve diagram. Table 1 shows surface data, Table 2 shows aspheric surface data, Table 3 shows focal length data, and Table 4 shows numerical data corresponding to conditional expressions.

[0090] In the aberration curve diagram of Fig. 9, the solid line and the dashed line indicate the d-line, and the dashed line and the two-dot dashed line indicate the g-line. In astigmatism, the solid line and the dashed line indicate the sagittal section aberration, and the dashed line and the two-dot dashed line indicate the meridional section aberration. This explanation also applies to the aberration curve diagrams of Figs. 10 to 16 in Numerical Example 2-8 described later.

[0091] The imaging lens of Numerical Example 1 is composed of, in order from the object side, a first lens group G1, an aperture stop SP for adjusting the amount of light, a second lens group G2, and a third lens group G3. Filters F1 and F2 are arranged between the third lens group G3 and an image surface (designed image surface) I. The filters F1 and F2 are composed of, for example, a low-pass filter, an infrared cut filter, and a cover glass of an image sensor. In the following surface data (lens data), the filter F1 is described as an optical filter, and the filter F2 is described as optical glass.

[0092] The first lens group G1 has positive refractive power. The first lens group G1 is composed of, in order from the object side, a negative meniscus lens 11 convex toward the object side, a biconcave negative lens 12, and a biconvex positive lens 13. The negative meniscus lens 11 has an aspheric surface on the image side. The biconcave negative lens 12 and the biconvex positive lens 13 are cemented together. Between the negative meniscus lens 11 and the biconcave negative lens 12, a biconvex air lens AL1 is formed.

[0093] The second lens group G2 has positive refractive power. The second lens group G2 is composed of, in order from the object side, a biconvex positive lens 21, a biconcave negative lens 22, and a positive meniscus lens 23 convex toward the image side. The biconvex positive lens 21 and the biconcave negative lens 22 are cemented together. The positive meniscus lens 23 has aspheric surfaces on both sides. Between the biconcave negative lens 22 and the positive meniscus lens 23, a biconvex air lens AL2 is formed.

[0094] The third lens group G3 has negative refractive power and is composed of a negative meniscus lens 31 that is convex toward the image side. The negative meniscus lens 31 has aspheric surfaces on both sides.

[0095] (Table 1) f=18.35, F=2.87, w=37.9, Ya=14.13, BF=0.7 Surface number RD Glass type (glass material) Nd νd 1 13.163 0.70 L-BAL42(OHARA) 1.58313 59.38 2* 10.800 2.21 3 -37.730 0.60 S-TIM22(OHARA) 1.64769 33.79 4 6.645 2.94 S-LAH58(OHARA) 1.88300 40.76 5 -40.496 1.10 6 Aperture 1.21 7 16.251 2.23 S-LAH58(OHARA) 1.88300 40.76 8 -10.978 0.50 S-TIM28(OHARA) 1.68893 31.07 9 13.041 1.43 10* -20.013 1.33 MTAFD305(HOYA) 1.85135 40.10 11* -15.533 5.271 12* -20.015 0.85 L-BAL42(OHARA) 1.58313 59.38 13* -60.000 3.398 14 ∞ 0.77 Optical filter 1.56200 61.80 15∞1.30 16 ∞ 0.70 Optical glass 1.50000 64.00 17∞BF * is a rotationally symmetric aspheric surface. (Table 2) Surface number K A4 A6 A8 A10 A12 A14 2 0 2.6842E-04 1.9135E-06 2.0622E-07 -3.4685E-09 1.3440E-10 2.1535E-13 10 0 1.7845E-04 -7.6428E-06 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 11 1.60673 4.5363E-04 -1.8081E-06 5.4014E-08 2.7568E-10 0.0000E+00 0.0000E+00 12 3.72112 1.0709E-05 -4.9579E-06 7.9678E-08 0.0000E+00 0.0000E+00 0.0000E+00 13 24.10589 -1.1114E-04 -3.3387E-06 4.6772E-08 -5.7777E-11 -1.6059E-12 1.2206E-14 (Table 3) First lens group: 31.65 Second lens group: 29.44 Third lens group: -51.91 (Table 4) Conditional expression Corresponding value (1) -0.555 (2) -0.211 (3) 1.485 (4) 0.608 (5) 6.201 (6) 2.829 (7) 0.287 (8) 2.341 (9) 3.909 (10) 1.075 (11) 1.110 (12) 1.295 (13) 0.770 (14) 0.888

[0096] [Numerical Example 2] Fig. 2, Fig. 10 and Tables 5 to 8 show the imaging lens of Numerical Example 2. Fig. 2 is a lens configuration diagram when focusing on infinity, and Fig. 10 is an aberration curve diagram. Table 5 shows surface data, Table 6 shows aspheric surface data, Table 7 shows focal length data, and Table 8 shows numerical data corresponding to conditional expressions.

[0097] The lens configuration of the imaging lens in Numerical Example 2 is similar to (common to) the lens configuration of the imaging lens in Numerical Example 1.

[0098] (Table 5) f=18.35, F=2.89, w=38.0, Ya=14.13, BF=0.7 Surface number RD Glass type (glass material) Nd νd 1 13.353 0.70 L-TIM28 (OHARA) 1.68948 31.02 2* 11.258 2.40 3 -17.988 0.65 S-FTM16 (OHARA) 1.59270 35.31 4 7.957 2.64 S-LAH58 (OHARA) 1.88300 40.76 5 -29.283 1.14 6 Aperture 1.20 7 16.939 2.60 S-LAH58 (OHARA) 1.88300 40.76 8 -9.407 0.50 S-TIM35 (OHARA) 1.69895 30.13 9 17.906 1.55 10* -15.696 1.35 S-TIM35 (OHARA) 1.76802 49.24 11* -13.531 3.100 12* -26.270 0.75 M-TAF101(HOYA) 1.80139 45.45 13* -91.182 6.976 14 ∞ 0.77 Optical filter 1.56200 61.80 15∞0.30 16 ∞ 0.70 Optical glass 1.50000 64.00 17∞BF * is a rotationally symmetric aspheric surface. (Table 6) Surface number K A4 A6 A8 A10 A12 A14 2 0 1.6766E-04 6.0373E-06 -1.8145E-07 1.2627E-08 -2.8330E-10 5.1394E-12 10 0 -2.4437E-04 4.7283E-06 -2.0379E-07 2.4790E-09 0.0000E+00 0.0000E+00 11 0.31036 6.2559E-05 2.5442E-06 1.4919E-07 -2.1728E-09 0.0000E+00 0.0000E+00 12 8.82985 -5.7547E-04 5.3727E-06 3.7740E-08 0.0000E+00 0.0000E+00 0.0000E+00 13 0 -5.5557E-04 6.4933E-06 -1.5819E-08 2.7958E-11 -8.3479E-13 1.0084E-14 (Table 7) First lens group: 37.54 Second lens group: 23.90 Third lens group: -46.28 (Table 8) Conditional expression Corresponding value (1) -0.230 (2) 0.066 (3) 1.527 (4) 0.503 (5) 4.133 (6) 2.522 (7) 0.169 (8) 3.744 (9) 5.477 (10) 1.571 (11) 1.013 (12) 1.454 (13) 0.770 (14) 0.881

[0099] [Numerical Example 3] Fig. 3, Fig. 11 and Tables 9 to 12 show the imaging lens of Numerical Example 3. Fig. 3 is a lens configuration diagram when focusing on infinity, and Fig. 11 is an aberration curve diagram. Table 9 shows surface data, Table 10 shows aspheric surface data, Table 11 shows focal length data, and Table 12 shows numerical data corresponding to conditional expressions.

[0100] The lens configuration of the imaging lens in Numerical Example 3 is similar to (common with) the lens configuration of the imaging lens in Numerical Example 1, except for the following points. (1) In common with these, the third lens group G3 is composed of a negative single lens 31 that is aspheric on both sides. However, the negative single lens 31 has a meniscus shape that is convex toward the object side at and near the paraxial line, and has a meniscus shape that is convex toward the image side in the peripheral portion away from the paraxial line (has an inflection point).

[0101] (Table 9) f=18.35, F=2.88, w=38.0, Ya=14.13, BF=0.7 Surface number RD Glass type (glass material) Nd νd 1 16.191 0.70 M-TAFD405 (HOYA) 1.95150 29.83 2* 13.225 1.78 3 -80.577 0.70 S-FTM16 (OHARA) 1.59270 35.31 4 6.802 3.22 S-LAH58 (OHARA) 1.88300 40.76 5 -36.700 1.10 6 Aperture 1.21 7 141.517 1.82 S-LAH58 (OHARA) 1.88300 40.76 8 -9.797 0.50 S-TIH10 (OHARA) 1.72825 28.46 9 28.777 1.15 10* -18.704 1.53 M-TAFD405 (HOYA) 1.95150 29.83 11* -13.814 5.411 12* 7.643 0.85 M-TAFD305 (HOYA) 1.85135 40.10 13* 6.252 4.463 14 ∞ 0.77 Optical filter 1.56200 61.80 15∞0.60 16 ∞ 0.70 Optical glass 1.50000 64.00 17∞BF * is a rotationally symmetric aspheric surface. (Table 10) Surface number K A4 A6 A8 A10 A12 A14 2 0 1.4967E-04 3.1039E-06 -3.9687E-08 4.1119E-09 -1.0024E-10 1.3324E-12 10 0 -2.3963E-04 -2.2297E-06 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 11 -9.11636 -5.3949E-04 1.0149E-05 -1.9908E-07 3.7252E-09 0.0000E+00 0.0000E+00 12 -9.62386 -7.6618E-04 4.3342E-06 -3.6841E-09 0.0000E+00 0.0000E+00 0.0000E+00 13 -6.98764 -6.4027E-04 4.0220E-06 9.6262E-09 -5.0637E-10 4.6727E-12 -1.4401E-14 (Table 11) First lens group: 21.15 Second lens group: 56.56 Third lens group: -56.12 (Table 12) Conditional expression Corresponding value (1) -0.718 (2) 0.212 (3) 1.483 (4) 0.590 (5) 6.366 (6) 3.059 (7) 0.295 (8) 1.700 (9) 2.626 (10) 0.374 (11) 1.088 (12) 1.142 (13) 0.770 (14) 0.871

[0102] [Numerical Example 4] Fig. 4, Fig. 12 and Tables 13 to 16 show the imaging lens of Numerical Example 4. Fig. 4 is a lens configuration diagram when focusing at infinity, and Fig. 12 is an aberration curve diagram. Table 13 shows surface data, Table 14 shows aspheric surface data, Table 15 shows focal length data, and Table 16 shows numerical data corresponding to conditional expressions.

[0103] The lens configuration of the imaging lens in Numerical Example 4 is similar to (common with) the lens configuration of the imaging lens in Numerical Example 1, except for the following points. (1) The third lens group G3 is composed of, in order from the object side, a negative meniscus lens 31' convex toward the image side, and a positive meniscus lens 32' convex toward the image side. The negative meniscus lens 31' has an aspheric surface on the object side. The positive meniscus lens 32' has an aspheric surface on the image side. The negative meniscus lens 31' and the positive meniscus lens 32' are cemented together.

[0104] (Table 13) f=18.35, F=2.39, w=38.0, Ya=14.13, BF=0.7 Surface number RD Glass type (glass material) Nd νd 1 11.784 0.85 L-TIM28 (OHARA) 1.68948 31.02 2* 10.509 2.92 3 -17.419 0.60 S-TIM22 (OHARA) 1.64769 33.79 4 8.412 2.76 S-LAH58 (OHARA) 1.88300 40.76 5 -25.393 0.67 6 Aperture 1.09 7 14.229 3.28 S-LAH58 (OHARA) 1.88300 40.76 8 -12.198 0.50 S-TIM28 (OHARA) 1.68893 31.07 9 15.221 1.40 10* -18.837 1.53 M-TAFD305 (HOYA) 1.85135 40.10 11* -14.155 3.10 12* -14.344 0.79 M-FD80 (HOYA) 1.68893 31.16 13 -54.738 1.710 M-FCD1 (HOYA) 1.49710 81.56 14* -27.436 4.70 15 ∞ 0.770 Optical filter 1.56200 61.80 16∞1.30 17 ∞ 0.70 Optical glass 1.50000 64.00 18∞BF * is a rotationally symmetric aspheric surface. (Table 14) Surface number K A4 A6 A8 A10 A12 A14 2 0 1.4247E-04 3.1997E-06 -1.0378E-07 1.2788E-08 -4.3667E-10 7.4784E-12 10 0 2.4860E-04 1.1427E-05 -5.6289E-08 -6.6160E-09 0.0000E+00 0.0000E+00 11 -6.23947 2.5727E-04 1.4791E-05 1.3672E-07 -7.9330E-09 0.0000E+00 0.0000E+00 12 -0.39395 2.0856E-04 -1.1851E-06 4.6871E-09 0.0000E+00 0.0000E+00 0.0000E+00 14 0 1.3458E-04 -1.8773E-06 8.6276E-09 -2.3810E-11 0.0000E+00 0.0000E+00 (Table 15) First lens group: 46.11 Second lens group: 20.36 Third lens group -40.00 (Table 16) Conditional expression Corresponding value (1) -0.247 (2) -0.106 (3) 1.600 (4) 0.505 (5) 1.240 (6) 2.180 (7) 0.169 (8) 3.549 (9) 3.169 (10) 2.265 (11) 1.155 (12) 1.599 (13) 0.770 (14) 0.884

[0105] [Numerical Example 5] Fig. 5, Fig. 13 and Tables 17 to 20 show the imaging lens of Numerical Example 5. Fig. 5 is a lens configuration diagram when focusing on infinity, and Fig. 13 is an aberration curve diagram. Table 17 shows surface data, Table 18 shows aspheric surface data, Table 19 shows focal length data, and Table 20 shows numerical data corresponding to conditional expressions.

[0106] The lens configuration of the imaging lens in Numerical Example 5 is similar to (common to) the lens configuration of the imaging lens in Numerical Example 3.

[0107] (Table 17) f=15.70, F=2.88, w=42.4, Ya=14.13, BF=0.7 Surface number RD Glass type (glass material) Nd νd 1 13.000 0.70 M-FCD1 (HOYA) 1.49710 81.56 2* 7.854 3.70 3 -15.464 0.65 S-FTM16 (OHARA) 1.59270 35.31 4 9.303 2.16 S-LAH58 (OHARA) 1.88300 40.76 5 -27.311 0.79 6 Aperture 1.00 7 13.084 2.69 S-LAH58 (OHARA) 1.88300 40.76 8 -10.903 1.48 S-TIH14 (OHARA) 1.76182 26.52 9 20.096 0.82 10* -36.694 1.80 M-TAFD305 (HOYA) 1.85135 40.10 11* -21.476 3.37 12* 17.885 0.70 M-TAFD305 (HOYA) 1.85135 40.10 13* 13.509 5.960 14 ∞ 0.77 Optical filter 1.56200 61.80 15∞1.300 16 ∞ 0.70 Optical glass 1.50000 64.00 17∞BF * is a rotationally symmetric aspheric surface. (Table 18) Surface number K A4 A6 A8 A10 A12 A14 2 0 1.6896E-04 1.0557E-05 -3.9814E-07 3.3212E-08 -1.0888E-09 2.2344E-11 10 0 3.8428E-04 1.4690E-05 -1.1886E-07 -6.0634E-09 0.0000E+00 0.0000E+00 11 -16.89557 3.8614E-04 1.2805E-05 5.0757E-07 -1.4438E-08 0.0000E+00 0.0000E+00 12 0 -1.2109E-03 7.9559E-06 -3.1767E-08 0.0000E+00 0.0000E+00 0.0000E+00 13 0 -1.2124E-03 1.1484E-05 -7.4258E-08 2.3540E-10 -1.5457E-12 1.3987E-14 (Table 19) First lens group: 169.79 Second lens group: 17.28 Third lens group -70.00 (Table 20) Conditional expression Corresponding value (1) -0.326 (2) -0.292 (3) 1.865 (4) 0.524 (5) 4.818 (6) 4.458 (7) 0.215 (8) 2.839 (9) 3.674 (10) 9.825 (11) 1.265 (12) 1.231 (13) 0.900 (14) 0.928

[0108] [Numerical Example 6] Fig. 6, Fig. 14 and Tables 21 to 24 show the imaging lens of Numerical Example 6. Fig. 6 is a lens configuration diagram when focusing on infinity, and Fig. 14 is an aberration curve diagram. Table 21 shows surface data, Table 22 shows aspheric surface data, Table 23 shows focal length data, and Table 24 shows numerical data corresponding to conditional expressions.

[0109] The lens configuration of the imaging lens in Numerical Example 6 is similar to (common with) the lens configuration of the imaging lens in Numerical Example 1, except for the following points. (1) The first lens group G1 is composed of, in order from the object side, a biconcave negative lens 11', a negative meniscus lens 12' convex toward the image side, a negative meniscus lens 13' convex toward the object side, and a biconvex positive lens 14'. The biconcave negative lens 11' has an aspheric surface on the image side. The negative meniscus lens 13' and the biconvex positive lens 14' are cemented together. A biconvex air lens AL1 is formed between the biconcave negative lens 11' and the negative meniscus lens 12'. (2) The positive meniscus lens 23 in the second lens group G2 has an aspheric surface on the image side, not on both sides.

[0110] (Table 21) f=17.00, F=2.78, w=40.1, Ya=14.13, BF=0.7 Surface number RD Glass type (glass material) Nd νd 1 -80.000 0.80 L-BSL7 (OHARA) 1.51633 64.06 2* 14.772 1.95 3 -31.030 0.65 S-NPH4 (OHARA) 1.89286 20.36 4 -103.360 0.33 5 14.053 0.60 S-TIH6 (OHARA) 1.80518 25.42 6 11.016 2.37 S-LAH55VS (OHARA) 1.83481 42.74 7 -30.844 1.00 8 Aperture 1.38 9 16.051 2.26 S-LAH58 (OHARA) 1.88300 40.76 10 -8.665 1.39 S-TIM35 (OHARA) 1.69895 30.13 11 12.565 1.36 12 -13.482 1.30 L-LAH85V (OHARA) 1.85400 40.38 13* -12.639 2.512 14* -26.817 0.80 L-BAL43 (OHARA) 1.58573 59.70 15* -91.710 6.191 16 ∞ 0.77 Optical filter 1.56200 61.80 17∞1.30 18 ∞ 0.70 Optical glass 1.50000 64.00 19∞BF * is a rotationally symmetric aspheric surface. (Table 22) Surface number K A4 A6 A8 A10 A12 A14 2 0 3.1322E-04 3.6003E-06 3.2576E-08 8.5734E-10 0.0000E+00 0.0000E+00 13 -11.43563 -3.1898E-04 2.5767E-05 -4.0642E-07 7.4937E-09 0.0000E+00 0.0000E+00 14 -19.68936 -2.0081E-04 -1.4026E-07 -5.6689E-09 0.0000E+00 0.0000E+00 0.0000E+00 15 50.15571 -1.3211E-04 -1.1287E-06 2.1033E-08 -2.3688E-10 0.0000E+00 0.0000E+00 (Table 23) First lens group: 28.52 Second lens group: 32.15 Third lens group -65.00 (Table 24) Conditional expression Corresponding value (1) -0.355 (2) -0.035 (3) 1.668 (4) 0.494 (5) 3.140 (6) 3.823 (7) 0.148 (8) 3.170 (9) 8.138 (10) 0.887 (11) 1.100 (12) 1.327 (13) 0.831 (14) 0.906

[0111] [Numerical Example 7] Fig. 7, Fig. 15 and Tables 25 to 28 show the imaging lens of Numerical Example 7. Fig. 7 is a lens configuration diagram when focusing on infinity, and Fig. 15 is an aberration curve diagram. Table 25 shows surface data, Table 26 shows aspheric surface data, Table 27 shows focal length data, and Table 28 shows numerical data corresponding to conditional expressions.

[0112] The lens configuration of the imaging lens in Numerical Example 7 is similar to (common with) the lens configuration of the imaging lens in Numerical Example 1, except for the following points. (1) The first lens group G1 is composed of, in order from the object side, a biconcave negative lens 11', a negative meniscus lens 12' convex toward the image side, a negative meniscus lens 13' convex toward the object side, and a biconvex positive lens 14'. The biconcave negative lens 11' has an aspheric surface on the image side. The negative meniscus lens 13' and the biconvex positive lens 14' are cemented together. A biconvex air lens AL1 is formed between the biconcave negative lens 11' and the negative meniscus lens 12'. (2) The positive meniscus lens 23 in the second lens group G2 has an aspheric surface on the image side, not on both sides. (3) In common with these, the third lens group G3 is composed of a negative single lens 31 that is aspheric on both sides. However, the negative single lens 31 has a meniscus shape that is convex toward the object side at and near the paraxial line, and has a meniscus shape that is convex toward the image side in the peripheral portion away from the paraxial line (has an inflection point).

[0113] (Table 25) f=16.41, F=2.79, w=41.1, Ya=14.13, BF=0.7 Surface number RD Glass type (glass material) Nd νd 1 -80.000 0.80 FC5 (HOYA) 1.48749 70.44 2* 12.053 2.04 3 -31.030 0.65 FDS18 (HOYA) 1.94595 17.98 4 -72.997 0.28 5 12.977 0.76 S-TIH6 (OHARA) 1.80518 25.42 6 10.232 2.17 S-LAH55VS (OHARA) 1.83481 42.74 7 -76.735 1.00 8 Aperture 1.53 9 14.231 2.85 S-LAH58 (OHARA) 1.88300 40.76 10 -8.125 0.60 S-TIM35 (OHARA) 1.69895 30.13 11 14.370 1.14 12 -19.684 1.38 L-LAH85V (OHARA) 1.85400 40.38 13* -16.638 1.932 14* 16.027 0.80 L-BAL35 (OHARA) 1.58913 61.15 15* 10.683 7.306 16 ∞ 0.77 Optical filter 1.56200 61.80 17∞1.30 18 ∞ 0.70 Optical glass 1.50000 64.00 19∞BF * is a rotationally symmetric aspheric surface. (Table 26) Surface number K A4 A6 A8 A10 A12 A14 2 0 2.4660E-04 5.2159E-06 -7.4474E-08 3.1229E-09 0.0000E+00 0.0000E+00 13 -19.91623 -8.3660E-05 1.6650E-05 -1.7007E-07 3.8869E-09 0.0000E+00 0.0000E+00 14 0 -6.8855E-04 -1.1344E-07 4.8749E-08 0.0000E+00 0.0000E+00 0.0000E+00 15 0 -8.7242E-04 4.2843E-06 7.3713E-09 -3.6877E-10 2.1736E-12 0.0000E+00 (Table 27) First lens group: 47.64 Second lens group: 21.56 Third lens group: -57.58 (Table 28) Conditional expression Corresponding value (1) -0.440 (2) -0.156 (3) 1.750 (4) 0.449 (5) 2.415 (6) 3.510 (7) 0.118 (8) 1.455 (9) 6.349 (10) 2.209 (11) 1.093 (12) 1.345 (13) 0.861 (14) 0.950

[0114] [Numerical Example 8] Fig. 8, Fig. 16 and Tables 29 to 32 show the imaging lens of Numerical Example 8. Fig. 8 is a lens configuration diagram when focusing on infinity, and Fig. 16 is an aberration curve diagram. Table 29 shows surface data, Table 30 shows aspheric surface data, Table 31 shows focal length data, and Table 32 shows numerical data corresponding to conditional expressions.

[0115] The lens configuration of the imaging lens in Numerical Example 8 is similar to (common with) the lens configuration of the imaging lens in Numerical Example 1, except for the following points. (1) The positive meniscus lens 23 in the second lens group G2 has an aspheric surface on the image side, not on both sides. (2) Both of the third lens group G3 and the fourth lens group G4 have in common the feature that they are composed of a negative single lens 31 that is aspherical on both sides. However, the negative single lens 31 has a meniscus shape that is convex toward the object side at and near the paraxial line, and has a meniscus shape that is convex toward the image side in the peripheral portion away from the paraxial line (has an inflection point).

[0116] (Table 29) f=18.35, F=2.85, w=38.0, Ya=14.13, BF=0.7 Surface number RD Glass type (glass material) Nd νd 1 15.004 0.70 M-FDS910 (HOYA) 1.82115 24.06 2* 12.835 1.80 3 -80.449 0.70 S-FTM16 (OHARA) 1.59270 35.31 4 6.660 2.90 S-LAH58 (OHARA) 1.88300 40.76 5 -49.131 1.10 6 Aperture 1.21 7 44.820 1.68 S-LAH58 (OHARA) 1.88300 40.76 8 -14.486 0.50 S-TIH13 (OHARA) 1.74077 27.79 9 25.520 1.17 10 -20.474 1.44 L-LAH85V (OHARA) 1.85400 40.38 11* -14.672 5.000 12* 6.943 0.95 Plastic lens 1.53600 56.00 13* 5.302 3.580 14 ∞ 0.77 Optical filter 1.56200 61.80 15∞1.30 16 ∞ 0.70 Optical glass 1.50000 64.00 17∞BF * is a rotationally symmetric aspheric surface. (Table 30) Surface number K A4 A6 A8 A10 A12 A14 2 0 1.6452E-04 2.6096E-06 -8.0123E-09 3.9909E-09 -1.2922E-10 2.0291E-12 11 -10.12212 -3.2009E-04 1.4492E-05 -2.2620E-07 3.2798E-09 0.0000E+00 0.0000E+00 12 -12.52022 -1.0865E-03 8.5721E-06 -3.5148E-08 0.0000E+00 0.0000E+00 0.0000E+00 13 -7.22398 -7.5688E-04 5.8540E-06 -1.1243E-08 -5.0504E-10 5.5044E-12 -2.0244E-14 (Table 31) First lens group: 21.95 Second lens group: 52.90 Third lens group: -52.45 (Table 32) Conditional expression Corresponding value (1) -0.725 (2) 0.110 (3) 1.428 (4) 0.579 (5) 5.263 (6) 2.858 (7) 0.272 (8) 21.793 (9) 2.965 (10) 0.415 (11) 1.044 (12) 1.160 (13) 0.770 (14) 0.845

[0117] A digital camera (image capture device) 100 incorporating the imaging lens of this embodiment will be described with reference to FIGS.

[0118] The digital camera 100 has a camera body (housing) 101, a photographing lens 102, a viewfinder 103, a flash 104, a shutter button 105, a power button 106, a liquid crystal monitor 107, operation buttons 108, and a memory card slot 109.

[0119] The camera body 101 houses each component of the digital camera 100. The photographing lens 102 is, for example, a unit formed by incorporating the imaging lens of this embodiment into a lens barrel and / or an interchangeable lens. The viewfinder 103 is a viewing window for determining the subject and composition. The flash 104 emits a flash when photographing at night or in a dark place. The shutter button 105 is a physical switch for executing photographing with the digital camera 100. The power button 106 is a physical switch for switching the power of the digital camera 100 on and off. The liquid crystal monitor 107 displays images photographed by the digital camera 100, etc. The operation button 108 is a physical switch for setting the photographing mode of the digital camera 100, etc. The memory card slot 109 is a slot for inserting a memory card for storing images photographed by the digital camera 100, etc.

[0120] The digital camera 100 has, as internal functional components within the camera body 101, a central processing unit 111, an image processing unit 112, a light receiving element 113, a signal processing unit 114, a semiconductor memory 115, and a communication card .

[0121] The central processing unit 111 performs various types of arithmetic processing within the digital camera 100. The image processing unit 112 performs various types of image processing on images captured by the digital camera 100. The light receiving element 113 takes in and receives external light used for photometry processing. The signal processing unit 114 performs various types of signal processing such as shooting instruction signals and image processing signals. The semiconductor memory 115 forms a temporary storage area for images captured by the digital camera 100. The communication card 116 enables wireless communication with external devices, etc. The digital camera 100 functions as an information processing unit that performs various types of processing on captured image information.

[0122] Fig. 19 is an external perspective view showing an example of an interchangeable lens (lens barrel) 102 of this embodiment. As shown in Fig. 19, the interchangeable lens 102 has a lens holding barrel 102X and an imaging lens held by this lens holding barrel 102X. Fig. 19 depicts lens 11 or 11', which is of the imaging lens and is disposed closest to the object side in first lens group G1.

[0123] According to the present embodiment, it is possible to provide an imaging lens, an interchangeable lens, an imaging device, and an information processing device that can achieve a wider angle and a larger aperture while also achieving a smaller and lighter size that is advantageous for autofocusing.

[0124] The configuration of the digital camera 100 described here is merely one example, and various design modifications are possible (there is a degree of freedom in the specific form of the digital camera 100). In addition, the digital camera 100 can also be applied to an information processing device equipped with a shooting function.

[0125] The imaging lens of this embodiment can be applied to devices other than the digital camera 100 described above, such as exchange lenses, portable information terminal devices, video cameras, silver halide cameras, optical sensors, and projection optical systems (projectors).

[0126] The invention as described in the claims of the original application is set forth below. [Appendix 1] The zoom lens is composed of, in order from the object side, a first lens group, an aperture stop, a second lens group, and a third lens group. When focusing from infinity to a close distance, the first and second lens groups move, but the third lens group does not move. the first lens group has a negative lens closest to the object; The first lens group includes a biconvex air lens, The second lens group has a biconvex air lens. An imaging lens characterized by: [Appendix 2] the first lens group has only one biconvex air lens; The second lens group has only one biconvex air lens. 2. The imaging lens according to claim 1, [Appendix 3] The biconvex air lens of the first lens group is formed closest to the object side of the first lens group, The biconvex air lens of the second lens group is formed closest to the image side of the second lens group. 3. The imaging lens according to claim 1 or 2, [Appendix 4] The following conditional expressions (1) and (2) are satisfied. 4. The imaging lens according to claim 1, (1)-0.90<(r1o+r2o) / (r1o-r2o)<0.00 (2)-0.45<(r1i+r2i) / (r1i-r2i)<0.40 however, r1o: radius of curvature of the object side surface of the biconvex air lens in the first lens group, r2o: radius of curvature of the image-side surface of the biconvex air lens in the first lens group, r1i: radius of curvature of the object side surface of the biconvex air lens in the second lens group, r2i: radius of curvature of the image-side surface of the biconvex air lens in the second lens group. [Appendix 5] The following condition (3) is satisfied: 5. The imaging lens according to claim 1, (3) 1.0 <TL / f<2.0 however, TL: The axial distance between the surface of the first lens group closest to the object and the image plane when focusing at infinity, f: The focal length of the entire system when focused at infinity. [Appendix 6] The lens closest to the image side in the first lens group and the lens closest to the object side in the second lens group have refractive powers of the same sign on both sides of the aperture stop. 6. The imaging lens according to claim 1, [Appendix 7] an image-side surface of the lens closest to the image side in the first lens group and an object-side surface of the lens closest to the object side in the second lens group have concave-convex surface shapes that are symmetrical with respect to an aperture stop; 7. The imaging lens according to claim 1, [Appendix 8] the lens in the first lens group closest to the image side and the lens in the second lens group closest to the object side both have positive refractive power; 8. The imaging lens according to claim 1, [Appendix 9] the image-side surface of the lens closest to the image side in the first lens group and the object-side surface of the lens closest to the object side in the second lens group both have convex surfaces facing the aperture stop; 9. The imaging lens according to claim 1, [Appendix 10] The lens closest to the image side in the first lens group and the lens closest to the object side in the second lens group are both composed of biconvex positive lenses. 10. The imaging lens according to claim 1, [Appendix 11] The following conditional expressions (4) and (5) are satisfied. 11. The imaging lens according to claim 1, (4) 0.35 <Ds3 / Dsi<0.75 (5) 1.00 <D23 / D3<7.50 however, Ds3: The axial distance between the aperture stop and the surface of the third lens group closest to the object when focusing at infinity. Dsi: Axial distance between the aperture stop and the image plane when focused at infinity, D23: The axial distance between the surface of the second lens group closest to the image side and the surface of the third lens group closest to the object side when focusing at infinity. D3: The axial distance between the surface in the third lens group closest to the object and the surface closest to the image. [Appendix 12] The following condition (6) is satisfied: 12. The imaging lens according to claim 1, (6) 1.50<|f3 / f|<5.50 however, f3: focal length of the third lens group, f: The focal length of the entire system when focused at infinity. [Appendix 13] The following condition (7) is satisfied: 13. The imaging lens according to claim 1, (7) 0.05 <D23 / f<0.35 however, D23: The axial distance between the surface of the second lens group closest to the image side and the surface of the third lens group closest to the object side when focusing at infinity. f: The focal length of the entire system when focused at infinity. [Appendix 14] the third lens group has negative refractive power; 14. The imaging lens according to claim 1, [Appendix 15] The third lens group is composed of a negative single lens. 15. The imaging lens according to claim 1, [Appendix 16] An interchangeable lens having an imaging lens according to any one of claims 1 to 15. [Appendix 17] An imaging device comprising the imaging lens according to any one of claims 1 to 15. [Appendix 18] 16. An information processing device comprising the imaging lens according to any one of claims 1 to 15. [Explanation of symbols]

[0127] G1 First lens group 11 Negative Lens 12 Negative Lens 13 Positive lens 11' negative lens 12' negative lens 13' negative lens 14' positive lens AL1 Air Lens G2 2nd lens group 21 Positive lens 22 Negative Lens 23 Positive lens AL2 Air Lens G3 3rd lens group 31 Negative Lens 31' Negative Lens 32' positive lens SP aperture stop F1 F2 Filter I image plane 100 Digital camera (imaging device, information processing device) 102 Photographic lenses (lens barrels, interchangeable lenses)

Claims

1. The zoom lens is composed of, in order from the object side, a first lens group, an aperture stop, a second lens group, and a third lens group. When focusing from infinity to a close distance, the first lens group and the second lens group move, but the third lens group does not move. The first lens group has a negative lens closest to the object, The first lens group includes a biconvex air lens, The second lens group includes a biconvex air lens. An imaging lens characterized by:

2. the first lens group has only one biconvex air lens; The second lens group has only one biconvex air lens.

2. The imaging lens according to claim 1,

3. The biconvex air lens of the first lens group is formed closest to the object side of the first lens group, the biconvex air lens of the second lens group is formed closest to the image side of the second lens group; 3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane.

4. The following conditional expressions (1) and (2) are satisfied:

3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane. (1) -0.90<(r1o+r2o) / (r1o-r2o)<0.00 (2) -0.45<(r1i+r2i) / (r1i-r2i)<0.40 however, r1o: radius of curvature of the object side surface of the biconvex air lens in the first lens group, r2o: radius of curvature of the image side surface of the biconvex air lens in the first lens group, r1i: radius of curvature of the object side surface of the biconvex air lens in the second lens group, r2i: radius of curvature of the image-side surface of the biconvex air lens in the second lens group.

5. The following condition (3) is satisfied:

3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane. (3) 1.0<TL / f<2.0 however, TL: the axial distance between the surface of the first lens group closest to the object and the image plane when focusing at infinity, f: focal length of the entire system when focused at infinity.

6. The lens closest to the image side in the first lens group and the lens closest to the object side in the second lens group have refractive powers of the same sign on both sides of the aperture stop.

3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane.

7. an image-side surface of the lens closest to the image side in the first lens group and an object-side surface of the lens closest to the object side in the second lens group have concave-convex surface shapes that are symmetrical with respect to an aperture stop; 3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane.

8. the lens in the first lens group closest to the image side and the lens in the second lens group closest to the object side both have positive refractive power; 3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane.

9. an image-side surface of the lens closest to the image side in the first lens group and an object-side surface of the lens closest to the object side in the second lens group both have convex surfaces facing the aperture stop; 3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane.

10. The lens closest to the image side in the first lens group and the lens closest to the object side in the second lens group are both composed of biconvex positive lenses.

3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane.

11. The following conditional expressions (4) and (5) are satisfied:

3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane. (4) 0.35<Ds3 / Dsi<0.75 (5) 1.00<D23 / D3<7.50 however, Ds3: the axial distance between the aperture stop and the surface of the third lens group closest to the object when focusing at infinity, Dsi: Axial distance between the aperture stop and the image plane when focused at infinity, D23: the axial distance between the surface of the second lens group closest to the image side and the surface of the third lens group closest to the object side when focusing at infinity, D3: The axial distance between the surface of the third lens group closest to the object and the surface of the third lens group closest to the image.

12. The following condition (6) is satisfied:

3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane. (6) 1.50<|f3 / f|<5.50 however, f3: focal length of the third lens group, f: focal length of the entire system when focused at infinity.

13. The following condition (7) is satisfied:

3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane. (7) 0.05<D23 / f<0.35 however, D23: the axial distance between the surface of the second lens group closest to the image side and the surface of the third lens group closest to the object side when focusing at infinity, f: focal length of the entire system when focused at infinity.

14. The third lens group has a negative refractive power.

3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane.

15. The third lens group is composed of a negative single lens.

3. The imaging lens according to claim 1, wherein the first and second lenses are arranged in a first plane.

16. An interchangeable lens comprising the imaging lens according to claim 1 or 2.

17. An imaging device comprising the imaging lens according to claim 1 or 2.

18. 3. An information processing device comprising the imaging lens according to claim 1.

Images