Image forming lens, interchangeable lens, imaging device, and information processing device

Abstract

The invention relates to an image forming lens, an interchangeable lens, an imaging apparatus, and an information processing apparatus. The image forming lens includes, in order from an object side, a first lens group; an aperture stop; a second lens group; and a third lens group in which 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 when an aperture stop is inserted. And / or the surface on the image side of the lens closest to the image side in the first lens group and the surface on the object side of the lens closest to the object side in the second lens group have a symmetrical concave-convex surface shape when the aperture stop is inserted.

Description

Technical Field

[0001] The present invention relates to an image-forming lens, an interchangeable lens, an imaging device and an information processing device. Background Art

[0002] As the type of image forming lens, for example, a retro-focus type, a telephoto type, and a front focus type are known. In the retro-focus type, a lens group having a negative refractive power is arranged on the object side, and a lens group having a positive refractive power is arranged on the image side. The telephoto type is known as a lens type more suitable for miniaturization than the retro-focus type, and the telephoto type is a substantially symmetrical type or a type in which a lens group having a negative refractive power is arranged on the image side.

[0003] In addition, for example, Japanese Patent No. 5962744, Japanese Patent No. 7152823, and Japanese Patent No. 7234859 are called front focus types. The front focus type is a lens type that does not require a moving space for a focusing group in an optical system and does not require control of the ratio of the movement amounts of a plurality of groups such as floating, and moves only the front of the optical system during focusing. The front focus type can improve the longitudinal magnification of the focusing group while suppressing an increase in the size of the optical system, and is advantageous in accelerating autofocusing.

[0004] However, according to intensive studies by the present inventors, Japanese Patent No. 5962744, Japanese Patent No. 7152823, and Japanese Patent No. 7234859 have room for improvement from the standpoint of achieving a wide angle and a large diameter and achieving reduction in size and weight that facilitates contrast autofocus (AF).

[0005] The present invention has been made in view of the above-mentioned viewpoints, and an object of the present invention is to provide an image forming lens, an interchangeable lens, an imaging device, and an information processing device capable of achieving a wide angle and a large diameter and achieving a reduction in size and weight that is advantageous for contrast AF. Summary of the invention

[0006] The imaging forming lens according to the embodiment includes a first lens group, an aperture stop, a second lens group, and a third lens group in order from the object side. During focusing from infinity to a short distance, the first lens group and the second lens group are configured to move, and the third lens group is configured not to move. The first lens group includes a negative lens closest to the object side. 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 when an aperture stop is inserted, and / or the surface on the image side of the lens closest to the image side in the first lens group and the surface on the object side of the lens closest to the object side in the second lens group have symmetrical concave-convex surface shapes when an aperture stop is inserted. The following conditional expressions (1) and (2) are satisfied:

[0007] (1) 0.35 <Ds3 / Dsi<0.75

[0008] (2) 1.00 <D23 / D3<7.50

[0009] in,

[0010] Ds3: the on-axis distance between the aperture stop and the surface of the third lens group closest to the object side in infinity focus,

[0011] Dsi: the on-axis distance between the aperture stop and the image surface in infinity focus,

[0012] D23: the axial distance between the image-side surface of the second lens group and the object-side surface of the third lens group at infinity focus, and

[0013] D3: The axial distance between the surface closest to the object side and the surface closest to the image side in the third lens group.

[0014] According to the present embodiment, it is possible to provide an image forming lens, an interchangeable lens, an imaging device, and an information processing device capable of achieving a wide angle and a large diameter and achieving reduction in size and weight which is advantageous for contrast AF. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a lens configuration diagram of an infinite focus imaging forming lens according to Numerical Example 1;

[0016] Figure 2 is a lens configuration diagram of an infinite focus imaging forming lens according to Numerical Example 2;

[0017] Figure 3 is a lens configuration diagram of an infinite focus imaging forming lens according to Numerical Example 3;

[0018] Figure 4is a lens configuration diagram of an infinite focus imaging forming lens according to Numerical Example 4;

[0019] Figure 5 is a lens configuration diagram of an infinite focus imaging forming lens according to Numerical Example 5;

[0020] Figure 6 is a lens configuration diagram of an infinite focus imaging forming lens according to Numerical Example 6;

[0021] Figure 7 is a lens configuration diagram of an infinite focus imaging forming lens according to Numerical Example 7;

[0022] Figure 8 is a lens configuration diagram of an infinite focus imaging forming lens according to Numerical Example 8;

[0023] Fig. 9 is an aberration curve diagram of the imaging lens according to Numerical Example 1;

[0024] Fig.10 is an aberration curve diagram of the imaging lens according to Numerical Example 2;

[0025] Fig.11 is an aberration curve diagram of the imaging lens according to Numerical Example 3;

[0026] Fig.12 is an aberration curve diagram of the imaging lens according to Numerical Example 4;

[0027] Fig.13 is an aberration curve diagram of the imaging lens according to Numerical Example 5;

[0028] Fig.14 is an aberration curve diagram of the imaging lens according to Numerical Example 6;

[0029] Fig.15 is an aberration curve diagram of the imaging lens according to Numerical Example 7;

[0030] Fig.16 is an aberration curve diagram of the imaging lens according to Numerical Example 8;

[0031] Fig.17 is a first diagram showing an example of an imaging device on which the image forming lens of the present embodiment is mounted;

[0032] Fig.18 is a second diagram showing an example of an imaging device on which the image-forming lens of the present embodiment is mounted; and

[0033] Fig.19 is an external perspective view showing an example of an interchangeable lens according to the present embodiment.

[0034] The accompanying drawings are intended to depict exemplary embodiments of the present invention and should not be interpreted as limiting its scope.In the various drawings, the same or similar reference numerals represent the same or similar components. DETAILED DESCRIPTION

[0035] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0036] As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0037] In describing the preferred embodiments shown in the accompanying drawings, specific terms may be used for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terms so selected, and it should be understood that each specific element includes all technical equivalents having the same function, operating in a similar manner and achieving similar results.

[0038] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0039] The image forming lens according to the present embodiment is preferably mounted on an imaging optical system in, for example, an imaging device such as a digital SLR camera, an interchangeable lens used in an imaging device, or an information processing device. The image forming lens (imaging optical system) can also be applied to a digital camera, an interchangeable lens camera, an information terminal device, a video camera, a silver halide camera, an optical sensor, and a projection optical system (projector).

[0040] The image-forming lens may be replaced by an image-forming lens, a single focus lens or a wide-angle single focus lens. Imaging and videography may be understood as one another (may be synonymous). Distance and on-axis distance may be understood as one another (when simply referred to as distance, the term may represent on-axis distance). Radius of curvature and paraxial radius of curvature may be understood as one another (when simply referred to as radius of curvature, the term may represent paraxial radius of curvature).

[0041] The image-forming lens according to the present embodiment is a wide-angle single-focus lens having a focal length of 28 mm with respect to a 35 mm silver halide camera (so-called Leica plate) and having a wide angle and a large diameter (for example, an F number of about 2.8), wherein the purpose of the image-forming lens is to realize a small and light optical system that is advantageous for contrast AF.

[0042] As shown in each lens configuration diagram of Numerical Examples 1 to 8 ( Figures 1 to 8), the imaging forming lens according to the present embodiment includes, in order from the object side, a first lens group G1 having positive refractive power, an aperture stop SP for adjusting the amount of light, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. Filters F1 and F2 are provided between the third lens group G3 and the image surface (designed image surface) I. The filters F1 and F2 include, for example, a low-pass filter, an infrared cut filter, and a cover glass of the imaging element.

[0043] In Numerical Examples 1 to 5 and Numerical Examples 8 ( Figures 1 to 5 and Figure 8 ), the first lens group G1 includes, in order from the object side, a negative lens 11, a negative lens 12, and a positive lens 13. A biconvex air lens AL1 is formed between the negative lens 11 and the negative lens 12.

[0044] In Numerical Examples 6 and 7 ( Figure 6 and Figure 7 ), the first lens group G1 includes: a negative lens 11', a negative lens 12', a negative lens 13' and a positive lens 14' in order from the object side. A biconvex air lens AL1 is formed between the negative lens 11' and the negative lens 12'.

[0045] In Numerical Examples 1 to 8 ( Figures 1 to 8 ), the second lens group G2 includes: a positive lens 21, a negative lens 22 and a positive lens 23 in order from the object side. A biconvex air lens AL2 is formed between the negative lens 22 and the positive lens 23.

[0046] In Numerical Examples 1 to 3 and Numerical Examples 5 to 8 ( Figures 1 to 3 and Figures 5 to 8 ), the third lens group G3 includes a negative lens 31.

[0047] In Numerical Example 4 ( Figure 4 ), the third lens group G3 includes: a negative lens 31' and a positive lens 32' in order from the object side.

[0048] The digital camera market is spreading all over the world, and the needs of users for digital cameras are also diverse. Among them, a class of compact cameras that are small but high quality and equipped with a high-performance single focus lens (image forming lens) has been unanimously supported by users and maintains high expectations. As user needs, in addition to high performance, a small F number, that is, when the diameter is large, a small size, a light weight, and a fast focusing operation (autofocus) are also required.

[0049] Here, in terms of high performance, in addition to having a resolution corresponding to an imaging element having at least 20 to 40 million pixels, it is also necessary that frame flicker starting from the aperture opening is small, there is no collapse of the point image to the peripheral parts of the viewing angle in high contrast, there is no unnecessary coloring even in parts with small chromatic aberration and large brightness difference, and straight lines with small distortion aberration can be drawn as straight lines.

[0050] In terms of a large diameter, an F number of about 2.8 or less is desirable from the standpoint of differentiation from an ordinary compact camera mounted with a zoom lens.

[0051] In terms of miniaturization, it is necessary to minimize the overall optical length and diameter of the lens. In addition, in terms of miniaturization during non-photography, it is necessary to have a mechanism called a foldable type that shortens the air space on the optical axis in the photographic optical system, such as before and after the aperture and back focus, to shorten the overall lens length during non-photography.

[0052] In terms of speeding up automatic focusing, improving the longitudinal magnification of the focusing group to reduce the amount of movement during focusing is effective as one of the optical means.

[0053] Regarding the angle of view of a photographic lens, there are a wide range of users who strongly desire a wide angle, and desire an angle of view of 75 degrees or more, that is, a half angle of view of 37.5 degrees or more, corresponding to a 28 mm focal length of a 35 mm silver halide camera (so-called Leica plate).

[0054] There are many types of image-forming lenses for digital cameras, but the typical configuration of wide-angle single-focus lenses is the so-called retrofocus type, in which a lens group with negative refractive power is arranged on the object side, and a lens group with positive refractive power is arranged on the image side. Due to the characteristics of an area sensor having a color filter or a microlens in each pixel, it is necessary to move the exit pupil position away from the image surface so that the ambient light flux enters the sensor at an angle close to a vertical angle, which is the main reason for adopting the retrofocus type. However, as can be seen from the fact that the retrofocus type was originally intended to use a wide-angle lens as an interchangeable lens for a single-lens reflex camera to ensure back focus, the total lens length (the distance from the lens surface closest to the object side to the image surface) tends to become long.

[0055] On the other hand, in recent imaging elements, due to improvements and optimization of on-chip microlenses, advances in image processing, etc., there is a situation where no major problem occurs even if the ambient light flux is incident on the sensor at an angle to a certain extent, and a lens type suitable for further miniaturization can be selected, rather than insisting on vertical incidence of the ambient light flux as before.

[0056] As a lens type more suitable for miniaturization than the retrofocus type, a telephoto type which is a substantially symmetrical type or a type in which a lens group having a negative refractive power is provided on the image side has been proposed.

[0057] However, although the telephoto type image forming optical system is a relatively small wide-angle lens having a configuration close to a symmetrical system in which the negative force is arranged closest to the object side and closest to the image side, there are many internal focus types in which the F number is slightly dark to about 3.6, and the middle part of the lens system is used as a focusing group, so there is a problem that it is necessary to ensure a moving space for the focusing group, which causes the overall lens length to become long. Although the telephoto type image forming optical system has been reduced in size and increased in diameter with a configuration close to a symmetrical system in which the negative force is arranged closest to the object side and closest to the image side, the telephoto type image forming optical system is designed to take into account internal focusing (in which the middle part of the lens is used as a focusing group) and floating (in which multiple focusing groups move in different trajectories), and there are problems that the overall lens length tends to become long, the mechanism structure for holding the lens becomes complicated, and the camera tends to become large. In addition, when the telephoto type image forming optical system has a full-element focusing configuration, the amount of movement during focusing is relatively large, and there is a problem in accelerating contrast AF.

[0058] As a lens type that does not require a moving space for the focusing group in the optical system and does not require control of the ratio of the movement amounts of multiple groups such as floating, there is a front focus type that moves only the front part of the optical system during focusing. The front focus type can improve the longitudinal magnification of the focusing group while suppressing an increase in the size of the lens system, and is advantageous for accelerating autofocusing.

[0059] As a front focus type image forming lens, for example, the lenses described in the above-mentioned Japanese Patent No. 5962744, Japanese Patent No. 7152823, and Japanese Patent No. 7234859 are known. However, in Japanese Patent No. 5962744, the image forming lens is relatively small and has a bright F number of about 2.5, but has a total viewing angle of about 70 degrees at maximum, so there is room for improvement from the standpoint of widening the angle. In Japanese Patent No. 7152823, the image forming lens also has a bright F number of about 2.8 or less, but has a total viewing angle of about 50 degrees at maximum, so there is room for improvement from the standpoint of widening the angle. In addition, in Japanese Patent No. 7234859, the image forming lens also has a bright F number of about 2.8 or less, but has a total viewing angle of about 54 degrees at maximum, so there is room for improvement from the standpoint of widening the angle.

[0060] The present invention has been proposed in view of the above-mentioned viewpoints, and an object of the present invention is to provide a compact and lightweight image-forming lens (imaging optical system) having a high-performance wide-angle lens having a wide viewing angle of about 75° or more and a large diameter of about F-number 2.8, and being conducive to autofocusing.

[0061] Generally, when the angle is widened, coma, astigmatism, magnification chromatic aberration, field curvature, distortion, etc. may increase, and in addition to aberration control, the optical system tends to become larger in both the radial direction and the optical axis direction to pass light with a wide angle of view. When the longitudinal magnification of the focusing group is improved to speed up autofocusing, there is a characteristic (disadvantage) that even if the size and movement amount of the focusing group itself can be reduced, the fixed group that does not move during focusing tends to become larger.

[0062] The image forming lens according to the present embodiment is realized by finding that the problem in correcting aberrations and the problem of large size can be solved by adopting the following configuration.

[0063] The image forming lens according to the present embodiment includes: a first lens group G1, an aperture stop SP, a second lens group G2, and a third lens group G3 in order from the object side. During focusing from infinity to a short distance, the first lens group G1 and the second lens group G2 move, and the third lens group G3 does not move (is fixed on the image surface I). The first lens group G1 and the second lens group G2 may move integrally (may focus to the object side), or may move slightly different amounts of movement (may focus to the object side). The first lens group G1 includes a negative lens 11 or 11' closest to the object side.

[0064] The lens 13 or 14' closest to the image side in the first lens group G1 and the lens 21 closest to the object side in the second lens group G2 have refractive powers of the same sign with an aperture stop SP inserted therebetween, and / or the surface on the image side of the lens 13 or 14' closest to the image side in the first lens group G1 and the surface on the object side of the lens 21 closest to the object side in the second lens group G2 have symmetrical (near-axis symmetrical) concave-convex surface shapes with an aperture stop SP inserted therebetween.

[0065] More specifically, the lens 13 or 14' closest to the image side in the first lens group G1 and the lens 21 closest to the object side in the second lens group G2 both have positive refractive power, and the surface on the image side of the lens 13 or 14' closest to the image side in the first lens group G1 and the surface on the object side of the lens 21 closest to the object side in the second lens group G2 both have convex surfaces facing the aperture stop SP. In Numerical Examples 1 to 8, the lens 13 or 14' closest to the image side in the first lens group G1 and the lens 21 closest to the object side in the second lens group G2 both include biconvex positive lenses.

[0066] For the image forming lens according to the present embodiment, a front focus type configuration is adopted in which the third lens group G3 which does not move during focusing and the first lens group G1 and the second lens group G2 which move during focusing are arranged on the object side, and this configuration makes it possible to eliminate the need for a moving space for the focusing group in the optical system, and thus to suppress an increase in the length of the lens system. By providing the negative lens 11 or 11' which is closest to the object side in the first lens group G1, the entrance pupil position becomes shallow, an increase in the size of the lens in the radial direction due to an increase in the angle is suppressed, and coma aberration at a peripheral angle of view is easily corrected.

[0067] A concave-convex surface shape symmetrical to both surfaces of the insertion aperture stop is provided, and the inside of the focusing group is based on a "substantially symmetrical force arrangement" (the surface on the image side of the lens 13 or 14' closest to the image side in the first lens group G1 and the surface on the object side of the lens 21 closest to the object side in the second lens group G2 have a concave-convex surface shape symmetrical (paraxially symmetrical) to the insertion aperture stop SP), thereby facilitating correction of coma aberration, distortion aberration, and magnification chromatic aberration, in which the difficulty of correction increases due to the widening of the angle. By providing the surface shape symmetry, the effect of correcting coma aberration is easily exhibited, especially at the peripheral angle of view. Here, “a concave-convex surface shape symmetrical to two surfaces of the inserted aperture stop” indicates, for example, a state in which, when the paraxial shape of the end surface in the first lens group G1 is convex toward the aperture stop SP, the paraxial shape of the beginning surface in the second lens group G2 is also convex toward the aperture stop SP, and when the paraxial shape of the end surface in the first lens group G1 is concave toward the aperture stop SP, the paraxial shape of the beginning surface in the second lens group G2 is also concave toward the aperture stop SP.

[0068] The lenses facing each other (the last lens in the first lens group G1 and the first lens in the second lens group G2) with the aperture stop inserted therebetween have the same refractive power, and the inside of the focusing group is based on the "substantially symmetrical power arrangement" (the lens 13 or 14' closest to the image side in the first lens group G1 and the lens 21 closest to the object side in the second lens group G2 have the same refractive power with the aperture stop SP inserted), so it is easy to correct coma aberration, distortion aberration, and magnification chromatic aberration, in which the difficulty of correction increases due to the widening of the angle. By providing refractive symmetry, the effect of correcting magnification chromatic aberration and distortion aberration is easily exhibited, especially at the peripheral angle of view. Here, the "refractive power" of the "last lens in the first lens group G1 and the first lens in the second lens group G2" does not mean the refractive power of the entire bonded lens even when a plurality of lenses are bonded, but means the refractive power when both sides of the lens component closest to the aperture stop SP are in contact with the air.

[0069] The image forming lens according to the present embodiment preferably satisfies the following conditional expressions (1) and (2).

[0070] (1) 0.35 <Ds3 / Dsi<0.75

[0071] (2) 1.00 <D23 / D3<7.50

[0072] in,

[0073] Ds3: The on-axis distance between the aperture stop and the surface of the third lens group closest to the object side at infinity focus,

[0074] Dsi: the on-axis distance between the aperture stop and the image surface in infinity focus,

[0075] D23: the axial distance between the image-side surface of the second lens group and the object-side surface of the third lens group at infinity focus, and

[0076] D3: The axial distance between the surface closest to the object side and the surface closest to the image side in the third lens group.

[0077] In the focusing group providing a substantially symmetrical force arrangement, the aperture stop is located substantially at the center of the focusing group (the first and second lens groups), and the distance from the aperture stop to the image surface and the distance from the aperture stop to the opening surface in the fixed group (the third lens group) are defined by conditional expression (1), thereby indicating an appropriate range of the position of the fixed group (the third lens group) relative to the focusing group (the first and second lens groups) in the optical system.

[0078] When the range exceeds the upper limit of conditional expression (1), the fixed group (third lens group) is excessively separated from the focusing group (first and second lens groups), which is advantageous for correction of field curvature and distortion aberration, but the position of the light flux at the peripheral angle of view passing through the fixed group (third lens group) becomes high, so there is a problem that the size of the fixed group (third lens group) in the radial direction and the thickness direction increases excessively.

[0079] When the range is less than the lower limit of the conditional expression (1), the height of the light flux at the peripheral angle of view passing through the fixed group (third lens group) decreases, which is advantageous for downsizing, but the thickness of the light flux passing through the fixed group (third lens group) increases, which enhances the contribution to spherical aberration. When the focusing group (first and second lens groups) and the fixed group (third lens group) have a relationship held across the movable mechanism, errors tend to occur in the relative attitude and positional relationship, but if the contribution of the fixed group (third lens group) to spherical aberration becomes enhanced, imaging performance tends to deteriorate due to the error, and there is a problem of degradation of productivity or degradation of imaging performance in a mass production plant.

[0080] Conditional expression (2) defines a range of an appropriate thickness of the fixed group (third lens group) with respect to the air space between the focusing group (first and second lens groups) and the fixed group (third lens group) in infinity focus.

[0081] When the range exceeds the upper limit of conditional expression (2), the fixed group (third lens group) becomes thinner and is separated from the focusing group (first and second lens groups) excessively, which is advantageous for correction of curvature of field and distortion aberration, but the position of the light flux at the peripheral angle of view passing through the fixed group (third lens group) becomes higher, so there is a problem that the size of the fixed group (third lens group) in the radial direction increases excessively.

[0082] When the range is less than the lower limit of conditional expression (2), the fixed group (third lens group) becomes excessively close to the focusing group (first and second lens groups), and the contribution of the fixed group (third lens group) to spherical aberration increases, so that the productivity in a mass production plant is deteriorated due to manufacturing errors or imaging performance degradation. In addition, the fixed group (third lens group) may become thicker to reduce the exchange of spherical aberration between the fixed group (third lens group) and the focusing group (first and second lens groups), so there is a problem that the total length of the lens becomes longer.

[0083] In this way, the optimum position and thickness of the fixed group (the third lens group) relative to the focusing group (the first and second lens groups) are defined by conditional expressions (1) and (2), wherein the aberration correction capability is improved by providing a “substantially symmetrical force arrangement”, and thus it is possible to balance the optimum aberration correction taking into account the sensitivity to degradation of imaging performance and the miniaturization of the lens system with respect to manufacturing errors that tend to occur in the front focus type.

[0084] In order to significantly obtain the operational effects of the conditional expressions (1) and (2) (to further improve the performance thereof), it is preferable that the following conditional expressions (1A) and (2A) are satisfied.

[0085] (1A) 0.40 <Ds3 / Dsi<0.65

[0086] (2A) 1.00 <D23 / D3<6.50

[0087] The image forming lens according to the present embodiment preferably satisfies the following conditional expression (3).

[0088] (3) 1.50<|f3 / f|<5.50

[0089] in,

[0090] f3: the focal length of the third lens group, and

[0091] f: The focal length of the entire system in infinity focus.

[0092] Conditional Expression (3) indicates an appropriate range of the refractive power of the third lens group with respect to the focal length of the entire lens system.

[0093] When the range exceeds the upper limit of conditional expression (3), the refractive power of the third lens group becomes too weak and the longitudinal magnification of the focus group cannot be improved, so there is a problem that the movement amount of the focus group during focusing is not reduced and the effect of accelerating autofocusing is reduced.

[0094] When the range is smaller than the lower limit of conditional expression (3), the refractive power of the third lens group becomes too strong and aberration exchange with the focusing group becomes excessive, so performance degradation due to manufacturing errors tends to occur, and there is a risk that the entire lens system becomes longer due to an increase in the number of third lens groups or an increase in thickness to perform independent aberration correction in the third lens group.

[0095] In order to significantly obtain the operational effect of conditional expression (3) (to further improve its performance), it is preferable to satisfy the following conditional expression (3A).

[0096] (3A) 2.00<|f3 / f|<5.00

[0097] The image forming lens according to the present embodiment preferably satisfies the following conditional expression (4).

[0098] (4) 0.05 <D23 / f<0.35

[0099] in,

[0100] D23: the axial distance between the image-side surface of the second lens group and the object-side surface of the third lens group at infinity focus, and

[0101] f: The focal length of the entire system in infinity focus.

[0102] Conditional Expression (4) indicates an appropriate range of the air space between the focusing group (the first and second lens groups) and the fixed group (the third lens group) with respect to the focal length of the entire system in infinite focus.

[0103] When the range exceeds the upper limit of conditional expression (4), the fixed group (third lens group) is excessively separated from the focusing group (first and second lens groups), which is advantageous for correction of field curvature and distortion aberration, but the position of the light flux at the peripheral angle of view passing through the fixed group (third lens group) becomes high, so there is a problem that the size of the fixed group (third lens group) in the radial direction is excessively increased.

[0104] When the range is less than the lower limit of conditional expression (4), the fixed group (third lens group) becomes excessively close to the focusing group (first and second lens groups), and the contribution of the fixed group (third lens group) to spherical aberration increases, so that the productivity in a mass production factory is deteriorated due to manufacturing errors or imaging performance degradation. In addition, the fixed group (third lens group) may become thicker to reduce the exchange of spherical aberration between the fixed group (third lens group) and the focusing group (first and second lens groups), so there is a problem that the total length of the lens becomes longer.

[0105] In order to significantly obtain the operational effect of conditional expression (4) (to further improve its performance), it is preferable to satisfy the following conditional expression (4A).

[0106] (4A) 0.10 <D23 / f<0.30

[0107] The image forming lens according to the present embodiment preferably satisfies the following conditional expression (5).

[0108] (5)1.20<|(R1l-R2s) / (R1l+R2s)|

[0109] in,

[0110] R11: the radius of curvature of the surface on the image side of the lens closest to the image side in the first lens group, and

[0111] R2s: The radius of curvature of the surface on the object side of the lens closest to the object side in the second lens group.

[0112] Conditional Expression (5) indicates an appropriate range of the curvature radius of the final surface in the first lens group and the curvature radius of the initial surface in the second lens group, which face each other with the stop interposed therebetween.

[0113] When the range is less than the lower limit of conditional expression (5), the symmetry between the two surfaces facing each other with the stop interposed therebetween is destroyed, the characteristic of "substantially symmetrical force arrangement" in the focusing group is weakened, and therefore, there is a problem that correction of coma aberration becomes difficult, particularly at peripheral angles of view. Since conditional expression (5) takes an absolute value, it seems that only one side of conditional expression (5) is defined, and it is intended to avoid that the corresponding numerical value of conditional expression (5) is within the range of -1.2 to 1.2.

[0114] When calculating the corresponding numerical value of the conditional expression (5), even when the target lens surface is an aspherical surface, the calculation can be performed using the paraxial curvature radius.

[0115] Throughout Numerical Examples 1 to 8 ( Figures 1 to 8 ), the third lens group G3 has negative refractive power. By allowing the third lens group G3 to have negative power, by pairing the third lens group G3 with the lens 11 or 11' in the first lens group G1 having negative power closest to the object side, the entire lens system becomes closer to a "substantially symmetrical power arrangement", and it becomes easy to correct coma aberration, distortion aberration, and magnification chromatic aberration, in which the difficulty of correction increases due to the widening of the angle.

[0116] In Numerical Examples 1 to 3 and Numerical Examples 5 to 8 ( Figures 1 to 3 and Figures 5 to 8 ), the third lens group G3 includes a negative single lens 31. By allowing the third lens group G3 to have a negative power, the aberration correction load of the third lens group G3 can be appropriately set, and further, by using the third lens group G3 as a negative single lens (with the simplest single-component configuration), it can contribute to the miniaturization of the lens. The mechanical configuration for holding the lens can be simplified, and contributes to the miniaturization and weight reduction of the entire camera.

[0117] In this specification, "air lens" is defined as follows. In two adjacent lenses arranged apart from each other, the air space between the image side surface of the object side lens and the object side surface of the image side lens facing each other is called an air lens. The shape of the air lens is defined using the image side surface of the object side lens as the object side surface of the air lens and using the object side surface of the image side lens as the image side surface of the air lens.

[0118] Here, the air lens AL1 formed closest to the object side in the first lens group G1 (the air lens formed between the lens 11 or 11' and the lens 12) has a biconvex shape. The air lens AL2 formed closest to the image side in the second lens group G2 (the air lens formed between the lens 22 and the lens 23) has a biconvex shape. Thus, preferably, the air lens AL1 closest to the object side in the first lens group G1 and the air lens AL2 closest to the image side in the second lens group G2 both have a biconvex shape. Preferably, only one air lens is provided in the first lens group G1, and only one air lens is provided in the second lens group G2.

[0119] As described above, the focusing groups (first lens group and second lens group) are set to a "substantially symmetrical force arrangement", thereby improving the ability to correct aberrations, in which the difficulty of correction increases as the angle widens. By forming the air lens AL1 closest to the object side in the first lens group G1 and the air lens AL2 closest to the image side in the second lens group G2 into a biconvex shape, various aberrations can be corrected at a higher level.

[0120] In other words, all four surfaces of the object side surface of the air lens AL1 closest to the object side in the first lens group G1, the image side surface of the air lens AL1 closest to the object side in the first lens group G1, the object side surface of the air lens AL2 closest to the image side in the second lens group G2, and the image side surface of the air lens AL2 closest to the image side in the second lens group G2 are formed as concave surfaces.

[0121] When the object side surface of the air lens AL1 closest to the object side in the first lens group G1 is made concave, there is an effect of appropriately controlling spherical aberration and mainly promoting astigmatism correction. When the image side surface of the air lens AL2 closest to the image side in the second lens group G2 is made concave, there is an effect of controlling the exit pupil distance, setting the incident angle of the principal ray on the image surface at the peripheral image height to an appropriate state, and mainly promoting correction of coma aberration and distortion aberration.

[0122] When the image side surface of the air lens AL1 closest to the object side in the first lens group G1 is made concave, there is an effect of reducing the lens diameter of the lens system closest to the object side and facilitating coma correction of lower light rays. When the object side surface of the air lens AL2 closest to the image side in the second lens group G2 is made concave, there is an effect of reducing the diameter of the lens closest to the image side and facilitating coma correction of upper light rays, which is conducive to achieving miniaturization and high performance.

[0123] The image forming lens according to the present embodiment preferably satisfies the following conditional expressions (6) and (7).

[0124] (6)-0.90<(r1o+r2o) / (r1o-r2o)<0.00

[0125] (7)-0.45<(r1i+r2i) / (r1i-r2i)<0.40

[0126] in,

[0127] r1o: the radius of curvature of the surface on the object side of the air lens formed closest to the object side in the first lens group,

[0128] r2o: the radius of curvature of the surface on the image side of the air lens formed closest to the object side in the first lens group,

[0129] r1i: the radius of curvature of the surface on the object side of the air lens formed closest to the image side in the second lens group, and

[0130] r2i: The radius of curvature of the surface on the image side of the air lens formed closest to the image side in the second lens group.

[0131] Conditional Expression (6) indicates an appropriate range of the shape of the air lens AL1 on the most object side in the first lens group G1 .

[0132] When the range exceeds the upper limit value of the conditional expression (6), the refractive power of the image side surface of the air lens AL1 closest to the object side in the first lens group G1 becomes relatively too strong, so that spherical aberration tends to occur largely in the overdirection, field curvature tends to decrease largely on the plus side in the peripheral portion, and coma aberration tends to remain, which is not preferable.

[0133] When the range is smaller than the lower limit value of the conditional expression (6), the refractive power of the object side surface of the air lens AL1 closest to the object side in the first lens group G1 becomes relatively too strong, so that spherical aberration tends to occur largely in the underdirection, and field curvature tends to shift largely to the minus side at the intermediate image height, which is not preferable.

[0134] The conditional expression (7) indicates an appropriate range of the shape of the air lens AL2 located on the most image side in the second lens group G2 .

[0135] When the range exceeds the upper limit value of conditional expression (7), the refractive power of the image side surface of the air lens AL2 closest to the image side in the second lens group G2 becomes relatively too strong, so that astigmatism tends to occur, and coma aberration in the pupil peripheral portion tends to be disturbed, which is not preferable.

[0136] When the range is smaller than the lower limit value of the conditional expression (7), the refractive power of the object side surface of the air lens AL2 closest to the image side in the second lens group G2 becomes relatively too strong, so that spherical aberration tends to occur a lot in the over direction, and inward coma aberration tends to remain, which is not preferable.

[0137] In order to significantly obtain the operational effects of the conditional expressions (6) and (7) (to further improve the performance thereof), it is preferable that the following conditional expressions (6A) and (7A) are satisfied.

[0138] (6A)-0.80<(r1o+r2o) / (r1o-r2o)<-0.15

[0139] (7A)-0.40<(r1i+r2i) / (r1i-r2i)<0.30

[0140] When calculating the corresponding numerical values ​​of the conditional expressions (6), (7), (6A), and (7A), even when the target lens surface is an aspherical surface, the calculation can be performed using the paraxial curvature radius.

[0141] The image forming lens according to the present embodiment preferably satisfies the following conditional expression (8).

[0142] (8) 2.00<|f2i / f|<20.00

[0143] in,

[0144] f2i: the focal length of the image-side lens in the second lens group, and

[0145] f: The focal length of the entire system in infinity focus.

[0146] Conditional expression (8) indicates an appropriate range of the refractive power of the lens 23 closest to the image side in the second lens group G2 relative to the focal length of the entire system. The focusing groups (first and second lens groups) of the image forming lens according to the present embodiment are set to a "substantially symmetrical power arrangement", thereby improving the correction capability of aberrations that are more difficult to correct due to a wide angle. For the lens 23 closest to the image side in the second lens group G2, by allocating a function that contributes to aberration correction at a position close to the image surface while minimizing the influence on the "substantially symmetrical power arrangement", it is advantageous to achieve miniaturization and high performance of the image forming lens.

[0147] When the range exceeds the upper limit of conditional expression (8), there is a problem that the refractive power of the lens 23 closest to the image side in the second lens group G2 becomes too small, so that the basic aberration correction ability in the entire second lens group G2 is reduced and the entire lens system becomes long, or the aberration exchange with the first lens group G1 becomes excessive and the performance is deteriorated due to manufacturing errors.

[0148] When the range is smaller than the lower limit of conditional expression (8), the refractive power of the lens 23 closest to the image side in the second lens group G2 becomes too large, which affects the "basically symmetrical power arrangement" of the entire focusing group, and the advantage of aberration correction by a symmetrical system is reduced, so there is a problem that the entire lens system becomes longer.

[0149] In order to significantly obtain the operational effect of Conditional Expression (8) (to further improve its performance), it is preferable to satisfy the following Conditional Expression (8A).

[0150] (8A) 2.20<|f2i / f|<15.00

[0151] In the image forming lens according to the present embodiment, it is preferred that the first lens group G1 and the second lens group G2 each include more than two and less than four lenses. Since the air lens AL1 closest to the object side in the first lens group G1 and the air lens AL2 closest to the image side in the second lens group G2 both have a biconvex shape, the air lens has a relatively strong negative refractive power, and in order to make the entire lens system have a positive focal length as an image forming lens, it is necessary to set a strong positive refractive power before and after the aperture stop SP. In order to realize such a power arrangement without difficulty and to achieve good aberration correction, it is preferred to provide a positive lens before and after the aperture stop SP separately from the lenses configuring the air lenses AL1 and AL2. Since two lenses are required to configure the air lens, it is preferred that the first lens group G1 and the second lens group G2 each include more than two and less than four lenses.

[0152] The image forming lens according to the present embodiment preferably satisfies the following conditional expression (9).

[0153] (9) 0.10<|f1 / f2|<15.0

[0154] in,

[0155] f1: the focal length of the first lens group, and

[0156] f2: focal length of the second lens group.

[0157] Conditional expression (9) indicates an appropriate range of the refractive power balance between the lens groups with the stop inserted in the focusing group (i.e., between the first lens group and the second lens group). Since the focusing group has a “substantially symmetrical power arrangement”, it is important to appropriately set the refractive power of the lens groups (the first lens group and the second lens group) with the stop inserted therebetween.

[0158] When the range exceeds the upper limit of conditional expression (9), the refractive power of the second lens group on the rear side of the stop becomes relatively too strong, so that minus distortion aberration tends to occur, outward coma aberration tends to occur, and short-wavelength chromatic magnification aberration tends to occur toward the outside of the screen, which is not preferable.

[0159] When the range is less than the lower limit of conditional expression (9), the refractive power of the first lens group on the front side of the stop becomes relatively too strong, so that distortion aberration tends to bend toward the plus side in the peripheral portion, inward coma aberration tends to occur, and short-wavelength chromatic magnification aberration tends to occur toward the inside of the screen, which is not preferable.

[0160] In order to significantly obtain the operational effect of conditional expression (9) (to further improve its performance), it is preferable to satisfy the following conditional expression (9A).

[0161] (9A) 0.20<|f1 / f2|<15.0

[0162] The image forming lens according to the present embodiment preferably satisfies the following conditional expression (10).

[0163] (10) 1.0 <TL / f<2.0

[0164] in,

[0165] TL: the on-axis distance between the object-side surface of the first lens group and the image surface at infinity focus, and

[0166] f: The focal length of the entire system in infinity focus.

[0167] The image forming lens of the present embodiment preferably satisfies the following conditional expression (11).

[0168] (11) 0.8 <Dt / f<1.5

[0169] in,

[0170] Dt: the axial distance between the surface closest to the object side of the first lens group and the surface closest to the image side of the third lens group at infinity focus, and

[0171] f: The focal length of the entire system in infinity focus.

[0172] By satisfying the conditional expressions (10) and (11), the total lens length and the total lens thickness can be optimized to realize a high-performance image-forming lens. When the range exceeds the upper limit or the lower limit of the conditional expressions (10) and (11), the setting of the total lens length and the total lens thickness becomes insufficient, which may hinder the realization of a high-performance image-forming lens.

[0173] In order to significantly obtain the operational effect of conditional expression (10) (to further improve its performance), it is preferable to satisfy the following conditional expression (10A).

[0174] (10A) 1.4 <TL / f<2.0

[0175] The image forming lens according to the present embodiment preferably satisfies the following conditional expression (12).

[0176] (12) 1.1 <Mg3^2<2.0

[0177] in,

[0178] Mg3: The magnification of the third lens group in infinity focus.

[0179] Conditional Expression (12) indicates the movement sensitivity of the focus group (first and second lens groups), which shows how much the focus position moves when the focus group (first and second lens groups) moves a predetermined movement amount (unit movement amount).

[0180] When the range exceeds the upper limit of conditional expression (12), the movement amount of the focus group (first and second lens groups) is suppressed, but the refractive power of the third lens group becomes too strong, the aberration exchange with the focus group (first and second lens groups) becomes excessive, and performance degradation due to manufacturing errors tends to occur. Alternatively, the number of third lens groups may be increased, or the thickness of the third lens group may be increased to perform aberration correction independently in the third lens group, so there is a problem that the entire lens system becomes long.

[0181] When the range is smaller than the lower limit of conditional expression (12), focusing becomes similar to all-element focusing, and the movement amount of the focusing group (first and second lens groups) required for focusing increases, so it is difficult to increase the speed of automatic focusing.

[0182] Furthermore, it is desirable to provide at least one aspherical surface in the third lens group. Although the height of the light passing through the third lens group is easily changed by focusing the focusing group (the first and second lens groups), the variation of aberration correction due to the distance is easily suppressed by using an aspherical surface. It is desirable that both the surface closest to the object side and the surface closest to the image side in the third lens group are made aspherical surfaces. It becomes easier to correct the variation in aberration correction, and it is also possible to easily correct the mold in terms of manufacturing, improve the surface shape accuracy of the lens, and suppress the influence of the alignment error.

[0183] Preferably, the image forming lens according to the present embodiment satisfies the following conditional expressions (13) and (14).

[0184] (13) 0.7 <Y’ / f<0.95

[0185] (14) 0.7 <tan(θPmax)<1.0

[0186] in,

[0187] Y': maximum image height,

[0188] f: the focal length of the entire system in infinity focus, and

[0189] θPmax: The angle of incidence of the chief ray that reaches the maximum image height on the image surface.

[0190] Conditional expression (13) regulates (defines) the viewing angle of the image-forming lens, and conditional expression (14) regulates (defines) the off-axis light image surface incident angle of the image-forming lens on the image surface. When conditional expressions (13) and (14) are satisfied, a high-performance image-forming lens that achieves both angle widening and size reduction can be realized. The image-forming lens according to the present embodiment is intended to achieve miniaturization and high performance by appropriately controlling the incident angle, which is the principal ray that reaches the maximum image height on the image surface in a wide-angle lens having a half viewing angle of about 35 degrees or more, and in order to achieve this purpose, conditional expressions (13) and (14) are preferably satisfied.

[0191] Specific numerical examples 1 to 8 will be described. The meanings of the symbols in numerical examples 1 to 8 are as follows. The glass materials in the examples are optical glass type names of HOYA Corporation (HOYA) and Ohara Corporation (OHARA). The unit of length is [mm]. Here, when the reciprocal of the paraxial curvature radius (paraxial curvature) is C and the height from the optical axis is H, the aspherical surface is defined by the following equation.

[0192] 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

[0193] f: focal length of the entire system

[0194] F: F number

[0195] : Half viewing angle

[0196] Ya: Maximum image height

[0197] R: Radius of curvature

[0198] D: Surface spacing

[0199] Nd: Refractive index at d line

[0200] : Abbe number at the d line

[0201] BF: Back Focus

[0202] K: Conic constant of the aspherical surface

[0203] A4: 4th order aspheric coefficient

[0204] A6: 6th order aspheric coefficient

[0205] A8: 8th order aspheric coefficient

[0206] A10: 10th order aspheric coefficient

[0207] A12: 12th order aspheric coefficient

[0208] A14: 14th order aspheric coefficient

[0209] Numerical Example 1

[0210] Figure 1 and Fig. 9 And Tables 1 to 4 show image forming lenses according to Numerical Example 1. Figure 1 is the lens configuration in infinity focus, and Fig. 9 TABLE 1 shows surface data, TABLE 2 shows aspherical surface data, TABLE 3 shows focal length data, and TABLE 4 shows numerical data corresponding to conditional expressions.

[0211] exist Fig. 9In the aberration curve diagram of , the solid line and the dashed line indicate the d line, and the one-dot chain line and the two-dot chain line indicate the g line. In astigmatism, the solid line and the one-dot chain line indicate the sagittal cross-sectional aberration, and the dashed line and the two-dot chain line indicate the meridional cross-sectional aberration. The same applies to the numerical examples 2 to 8 described below. Figures 10 to 16 Aberration curve diagram.

[0212] The image forming lens according to Numerical Example 1 includes, in order from the object side, a first lens group G1, an aperture stop SP for light amount adjustment, a second lens group G2, and a third lens group G3. Filters F1 and F2 are provided between the third lens group G3 and an image surface (designed image surface) I. The filters F1 and F2 include, for example, a low-pass filter, an infrared cut filter, and a cover glass of an imaging element. In the following surface data (lens data), the filter F1 is described as an optical filter, and the filter F2 is described as an optical glass.

[0213] The first lens group G1 has positive refractive power. The first lens group G1 includes: a negative meniscus lens 11, a double concave negative lens 12, and a double convex positive lens 13, which are convex toward the object side in order from the object side. The negative meniscus lens 11 has an aspherical surface on the surface on the image side. The double concave negative lens 12 and the double convex positive lens 13 are cemented. A double convex air lens AL1 is formed between the negative meniscus lens 11 and the double concave negative lens 12.

[0214] The second lens group G2 has positive refractive power. The second lens group G2 includes: a biconvex positive lens 21, a biconcave negative lens 22, and a positive meniscus lens 23 convex toward the image side in order from the object side. The biconvex positive lens 21 and the biconcave negative lens 22 are cemented together. The positive meniscus lens 23 has aspherical surfaces on both sides. A biconvex air lens AL2 is formed between the biconcave negative lens 22 and the positive meniscus lens 23.

[0215] The third lens group G3 has negative refractive power. The third lens group G3 includes a negative meniscus lens 31 convex toward the image side. The negative meniscus lens 31 has aspherical surfaces on both sides.

[0216] (Table 1)

[0217] f=18.35, F=2.87, w=37.9, Ya=14.13, BF=0.7

[0218]

[0219] * is a rotationally symmetric aspherical surface.

[0220] (Table 2)

[0221]

[0222] Numerical Example 2

[0223] Figure 2 and Fig.10 And Tables 5 to 8 show the image forming lenses according to Numerical Example 2. Figure 2 is the lens configuration diagram in infinity focus, and Fig.10 is an aberration curve graph. Table 5 shows surface data, Table 6 shows aspherical surface data, Table 7 shows focal length data, and Table 8 shows numerical data corresponding to conditional expressions.

[0224] The lens configuration of the image forming lens according to Numerical Example 2 is the same as (common to) the lens configuration of the image forming lens according to Numerical Example 1.

[0225] (Table 5)

[0226] f=18.35, F=2.89, w=38.0, Ya=14.13, BF=0.7

[0227]

[0228] * is a rotationally symmetric aspherical surface.

[0229] (Table 6)

[0230]

[0231] (Table 7)

[0232]

[0233] (Table 8)

[0234]

[0235] Numerical Example 3

[0236] Figure 3 and Fig.11 And Tables 9 to 12 show the image forming lenses according to Numerical Example 3. Figure 3 is a diagram of the lens configuration for focusing at infinity. Fig.11 TABLE 9 shows surface data, TABLE 10 shows aspherical surface data, TABLE 11 shows focal length data, and TABLE 12 shows numerical data corresponding to conditional expressions.

[0237] The lens configuration of the image forming lens according to Numerical Example 3 is the same as (common to) that of the image forming lens according to Numerical Example 1 except for the following contents.

[0238] (1) The third lens group G3 generally includes a double-sided aspherical negative single lens 31 , but the negative single lens 31 has a meniscus shape convex toward the object side on and near the paraxial side, and has a meniscus shape convex toward the image side (with an inflection point) at a peripheral portion away from the paraxial side.

[0239] (Table 9)

[0240] f=18.35, F=2.88, w=38.0, Ya=14.13, BF=0.7

[0241]

[0242] * is a rotationally symmetric aspherical surface.

[0243] (Table 10)

[0244]

[0245] (Table 11)

[0246]

[0247] (Table 12)

[0248]

[0249] Numerical Example 4

[0250] Figure 4 and Fig.12 And Tables 13 to 16 show the image forming lenses according to Numerical Example 4. Figure 4 is the lens configuration in infinity focus, and Fig.12 TABLE 13 shows surface data, TABLE 14 shows aspherical surface data, TABLE 15 shows focal length data, and TABLE 16 shows numerical data corresponding to conditional expressions.

[0251] The lens configuration of the image forming lens according to Numerical Example 4 is the same as (common to) that of the image forming lens according to Numerical Example 1 except for the following contents.

[0252] (1) The third lens group G3 includes: a negative meniscus lens 31' convex toward the image side and a positive meniscus lens 32' convex toward the image side in order from the object side. The negative meniscus lens 31' has an aspherical surface on the surface on the object side. The positive meniscus lens 32' has an aspherical surface on the surface on the image side. The negative meniscus lens 31' and the positive meniscus lens 32' are cemented.

[0253] (Table 13)

[0254] f=18.35, F=2.39, w=38.0, Ya=14.13, BF=0.7

[0255]

[0256] * is a rotationally symmetric aspherical surface.

[0257] (Table 14)

[0258]

[0259] (Table 15)

[0260]

[0261] (Table 16)

[0262]

[0263] Numerical Example 5

[0264] Figure 5 and Fig.13 And Tables 17 to 20 show the image forming lenses according to Numerical Example 5. Figure 5 is the lens configuration in infinity focus, and Fig.13 TABLE 17 shows surface data, TABLE 18 shows aspherical surface data, TABLE 19 shows focal length data, and TABLE 20 shows numerical data corresponding to conditional expressions.

[0265] The lens configuration of the image forming lens according to Numerical Example 5 is the same as (common to) the lens configuration of the image forming lens according to Numerical Example 3.

[0266] (Table 17)

[0267] f=15.70, F=2.88, w=42.4, Ya=14.13, BF=0.7

[0268]

[0269] * is a rotationally symmetric aspherical surface.

[0270] (Table 18)

[0271]

[0272] (Table 19)

[0273]

[0274] (Table 20)

[0275]

[0276] Numerical Example 6

[0277] Figure 6 and Fig.14 And Tables 21 to 24 show the image forming lenses according to Numerical Example 6. Figure 6 is the lens configuration in infinity focus, and Fig.14 TABLE 21 shows surface data, TABLE 22 shows aspherical surface data, TABLE 23 shows focal length data, and TABLE 24 shows numerical data corresponding to conditional expressions.

[0278] The lens configuration of the image forming lens according to Numerical Example 6 is the same as (common to) that of the image forming lens according to Numerical Example 1 except for the following contents.

[0279] (1) The first lens group G1 includes, 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 aspherical surface on the 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'.

[0280] (2) The positive meniscus lens 23 in the second lens group G2 has aspherical surfaces not on both surfaces but on the surface on the image side.

[0281] (Table 21)

[0282] f=17.00, F=2.78, w=40.1, Ya=14.13, BF=0.7

[0283]

[0284] * is a rotationally symmetric aspherical surface.

[0285] (Table 22)

[0286]

[0287] (Table 23)

[0288]

[0289] (Table 24)

[0290]

[0291] Numerical Example 7

[0292] Figure 7 and Fig.15 And Tables 25 to 28 show the image-forming lenses of Numerical Example 7. Figure 7 is the lens configuration in infinity focus, and Fig.15 TABLE 25 shows surface data, TABLE 26 shows aspherical surface data, TABLE 27 shows focal length data, and TABLE 28 shows numerical data corresponding to conditional expressions.

[0293] The lens configuration of the image forming lens according to Numerical Example 7 is the same as (common to) that of the image forming lens according to Numerical Example 1 except for the following contents.

[0294] (1) The first lens group G1 includes, 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 aspherical surface on the 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'.

[0295] (2) The positive meniscus lens 23 in the second lens group G2 has aspherical surfaces not on both surfaces but on the surface on the image side.

[0296] (3) The third lens group G3 generally includes a double-sided aspherical negative single lens 31 , but the negative single lens 31 has a meniscus shape convex toward the object side on and near the paraxial side, and has a meniscus shape convex toward the image side (with an inflection point) at a peripheral portion away from the paraxial side.

[0297] (Table 25)

[0298] f=16.41, F=2.79, w=41.1, Ya=14.13, BF=0.7

[0299]

[0300] * is a rotationally symmetric aspherical surface.

[0301] (Table 26)

[0302]

[0303] (Table 27)

[0304]

[0305] (Table 28)

[0306]

[0307] Numerical Example 8

[0308] Figure 8 and Fig.16 And Tables 29 to 32 show the imaging forming lenses according to Numerical Example 8. Figure 8 is the lens configuration in infinity focus, and Fig.16 TABLE 29 shows surface data, TABLE 30 shows aspherical surface data, TABLE 31 shows focal length data, and TABLE 32 shows numerical data corresponding to conditional expressions.

[0309] The lens configuration of the image forming lens according to Numerical Example 8 is the same as (common to) that of the image forming lens according to Numerical Example 1 except for the following contents.

[0310] (1) The positive meniscus lens 23 in the second lens group G2 has aspherical surfaces not on both surfaces but on the surface on the image side.

[0311] (2) The third lens group G3 generally includes a double-sided aspherical negative single lens 31 , but the negative single lens 31 has a meniscus shape convex toward the object side on and near the paraxial side, and has a meniscus shape convex toward the image side (with an inflection point) at a peripheral portion away from the paraxial side.

[0312] (Table 29)

[0313] f=18.35, F=2.85, w=38.0, Ya=14.13, BF=0.7

[0314]

[0315] * is a rotationally symmetric aspherical surface.

[0316] (Table 30)

[0317]

[0318] (Table 31)

[0319]

[0320] (Table 32)

[0321]

[0322] Will refer to Fig.17 and Fig.18 A digital camera (imaging device) 100 on which the image forming lens according to the present embodiment is mounted is described.

[0323] The digital camera 100 includes a camera body (casing) 101 , a photographic 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 .

[0324] The camera body 101 houses components of the digital camera 100. For example, a photographic lens 102 is combined by incorporating an image-forming lens according to the present embodiment into a lens barrel and / or an interchangeable lens. The viewfinder 103 is an observation window for determining a subject and a composition. The flash 104 emits a flash during night photography or photography in a dark place. The shutter button 105 is a physical switch for performing photography of the digital camera 100. The power button 106 is a physical switch for turning the power of the digital camera 100 on and off. The LCD monitor 107 displays an image captured by the digital camera 100, etc. The operation button 108 is a physical switch for setting a photography mode of the digital camera 100, etc. The memory card slot 109 is a slot into which a memory card that stores images captured by the digital camera 100, etc. is inserted.

[0325] The digital camera 100 includes a central processing unit 111 , an image processing device 112 , a light receiving element 113 , a signal processing device 114 , a semiconductor memory 115 , and a communication card 116 as functional components within the camera body 101 .

[0326] The central processing unit 111 performs various types of arithmetic processing inside the digital camera 100. The image processing device 112 performs various types of image processing on the image captured by the digital camera 100. The light receiving element 113 receives external light for photometric processing. The signal processing device 114 performs various types of signal processing, such as a photography instruction signal and an image processing signal. The semiconductor memory 115 configures a temporary storage area for the image captured by the digital camera 100. The communication card 116 enables wireless communication with an external device such as a PC. The digital camera 100 is used as an information processing device, and various types of processing are performed on the captured image information.

[0327] Fig.19 1 is an external perspective view showing an example of an interchangeable lens (lens barrel) 102 according to the present embodiment. Fig.19 As shown, the interchangeable lens 102 includes a lens holding tube 102X and an image forming lens held by the lens holding tube 102X. Fig.19 The lens 11 or 11 ′ disposed in the first lens group G1 closest to the object side among the image forming lenses is shown.

[0328] The configuration of the digital camera 100 described here is merely exemplary, and various design changes may be made (there is a degree of freedom in specific aspects of the digital camera 100). The present invention can also be applied to an information processing apparatus having a photographing function.

[0329] In addition to the above-described digital camera 100 , the image forming lens according to the present embodiment can be applied to, for example, interchangeable lenses, portable information terminal devices, video cameras, silver halide cameras, optical sensors, projection optical systems (projectors), and the like.

[0330] Hereinafter, the invention described in the claims originally filed in this application will be additionally described.

[0331] Note 1

[0332] An image forming lens, comprising:

[0333] From the object side, the first lens group; the aperture stop; the second lens group; and the third lens group, wherein,

[0334] During focusing from infinity to a short distance, the first lens group and the second lens group are configured to move, and the third lens group is configured not to move,

[0335] The first lens group includes a negative lens closest to the object side,

[0336] 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 with an aperture stop inserted therein, and / or the surface on the image side of the lens closest to the image side in the first lens group and the surface on the object side of the lens closest to the object side in the second lens group have symmetrical concave and convex surface shapes with an aperture stop inserted therein, and

[0337] The following conditional expressions (1) and (2) are satisfied:

[0338] (1) 0.35 <Ds3 / Dsi<0.75

[0339] (2) 1.00 <D23 / D3<7.50

[0340] in,

[0341] Ds3: the on-axis distance between the aperture stop and the surface of the third lens group closest to the object side in infinity focus,

[0342] Dsi: the on-axis distance between the aperture stop and the image surface in infinity focus,

[0343] D23: the axial distance between the image-side surface of the second lens group and the object-side surface of the third lens group at infinity focus, and

[0344] D3: The axial distance between the surface closest to the object side and the surface closest to the image side in the third lens group.

[0345] Note 2

[0346] The image forming lens according to Supplementary Note 1,

[0347] Wherein, 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 both have positive refractive power.

[0348] Note 3

[0349] The image forming lens according to note 1 or 2,

[0350] Wherein, a surface on the image side of the lens closest to the image side in the first lens group and a surface on the object side of the lens closest to the object side in the second lens group both have convex surfaces facing the aperture stop.

[0351] Note 4

[0352] An image-forming lens according to any one of Notes 1 to 3,

[0353] Wherein, 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 both include biconvex positive lenses.

[0354] Note 5

[0355] An image forming lens according to any one of Notes 1 to 4, wherein

[0356] The following condition expression (3) is satisfied:

[0357] (3) 1.50<|f3 / f|<5.50

[0358] in,

[0359] f3: the focal length of the third lens group, and

[0360] f: The focal length of the entire system in infinity focus.

[0361] Note 6

[0362] An image forming lens according to any one of Notes 1 to 5, wherein

[0363] The following condition expression (4) is satisfied:

[0364] (4) 0.05 <D23 / f<0.35

[0365] in,

[0366] D23: the axial distance between the image-side surface of the second lens group and the object-side surface of the third lens group at infinity focus, and

[0367] f: The focal length of the entire system in infinity focus.

[0368] Note 7

[0369] An image forming lens according to any one of Notes 1 to 6, wherein

[0370] The following condition expression (5) is satisfied:

[0371] (5)1.20<|(R1l-R2s) / (R1l+R2s)|

[0372] in,

[0373] R11: the radius of curvature of the surface on the image side of the lens closest to the image side in the first lens group, and

[0374] R2s: The radius of curvature of the surface on the object side of the lens closest to the object side in the second lens group.

[0375] Note 8

[0376] An image-forming lens according to any one of supplementary notes 1 to 7,

[0377] The third lens group has negative refractive power.

[0378] Note 9

[0379] An image-forming lens according to any one of Notes 1 to 8,

[0380] The third lens group includes a negative single lens.

[0381] Note 10

[0382] An image forming lens according to any one of Notes 1 to 9, wherein

[0383] The air lens formed closest to the object side in the first lens group has a biconvex shape, and

[0384] The air lens formed most on the image side in the second lens group has a biconvex shape.

[0385] Note 11

[0386] An image forming lens according to any one of Notes 1 to 10, wherein

[0387] The following conditional expressions (6) and (7) are satisfied:

[0388] (6)-0.90<(r1o+r2o) / (r1o-r2o)<0.00

[0389] (7)-0.45<(r1i+r2i) / (r1i-r2i)<0.40

[0390] in,

[0391] r1o: the radius of curvature of the object-side surface of the air lens formed closest to the object side in the first lens group,

[0392] r2o: the radius of curvature of the surface on the image side of the air lens formed closest to the object side in the first lens group,

[0393] r1i: the radius of curvature of the surface on the object side of the air lens formed closest to the image side in the second lens group, and

[0394] r2i: The radius of curvature of the surface on the image side of the air lens formed closest to the image side in the second lens group.

[0395] Note 12

[0396] An image forming lens according to any one of Notes 1 to 11, wherein

[0397] The following condition expression (8) is satisfied:

[0398] (8) 2.00<|f2i / f|<20.00

[0399] in,

[0400] f2i: the focal length of the image-side lens in the second lens group, and

[0401] f: The focal length of the entire system in infinity focus.

[0402] Note 13

[0403] An interchangeable lens comprising an image forming lens according to any one of Notes 1 to 12.

[0404] Note 14

[0405] An imaging device comprising an image forming lens according to any one of Notes 1 to 12.

[0406] Note 15

[0407] An information processing device comprising an image forming lens according to any one of Notes 1 to 12.

[0408] The above embodiments are illustrative and do not limit the present invention. Therefore, many additional modifications and variations are possible based on the above teachings. For example, at least one element of the different illustrative and exemplary embodiments herein may be combined with or substituted for each other within the scope of the present disclosure and the appended claims. In addition, the features of the components of the embodiments (such as quantity, position, and shape) are not limited to the embodiments and may therefore be preferably set. Therefore, it should be understood that within the scope of the appended claims, the disclosure of the present invention may be implemented in a manner different from that specifically described herein.

[0409] The method steps, processes, or operations described herein should not be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance or clearly identified by context. It should also be understood that additional or alternative steps may be employed.

[0410] Furthermore, any of the above-mentioned means, devices or units may be implemented as a hardware device, such as a dedicated circuit or device, or as a hardware / software combination, such as a processor executing a software program.

[0411] In addition, as described above, any of the above methods and other methods of the present invention can be implemented in the form of a computer program stored in any type of storage medium. Examples of storage media include, but are not limited to, floppy disks, hard disks, optical disks, magneto-optical disks, magnetic tapes, non-volatile memories, semiconductor memories, read-only memories (ROMs), etc.

[0412] Alternatively, any of the above methods and other methods of the present invention may be implemented by an application specific integrated circuit (ASIC), a digital signal processor (DSP) or a field programmable gate array (FPGA), which is prepared by interconnecting an appropriate network of conventional component circuits or by combining them with one or more conventional general-purpose microprocessors or correspondingly programmed signal processors.

[0413] Each function of the described embodiments may be implemented by one or more processing circuits or processing circuit systems. Processing circuit systems include programmed processors because processors include circuit systems. Processing circuits also include devices such as application specific integrated circuits (ASICs), digital signal processors (DSPs), field programmable gate arrays (FPGAs), and conventional circuit components arranged to perform the described functions.

Claims

1. An imaging lens, comprising: The first lens group in order from the object side; Aperture diaphragm; A second lens group; and a third lens group, wherein, During focusing from infinity to a short distance, the first lens group and the second lens group are configured to move, and the third lens group is configured not to move, The first lens group includes a negative lens closest to the object side, 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 with the aperture stop inserted therein, and / or a surface on the image side of the lens closest to the image side in the first lens group and a surface on the object side of the lens closest to the object side in the second lens group have symmetrical concave-convex surface shapes with the aperture stop inserted therein, and The following conditional expressions (1) and (2) are satisfied: (1) 0.35 <Ds3 / Dsi<0.75 (2) 1.00 <D23 / D3<7.50 in, Ds3: the on-axis distance between the aperture stop and the surface of the third lens group closest to the object side in infinity focus, Dsi: the on-axis distance between the aperture stop and the image surface in infinite focus, 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 in infinity focusing, and D3: the on-axis distance between the surface closest to the object side and the surface closest to the image side in the third lens group.

2. The image-forming lens according to claim 1, in, 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 both have positive refractive power.

3. The image-forming lens according to claim 1 or 2, in, A surface on the image side of the lens closest to the image side in the first lens group and a surface on the object side of the lens closest to the object side in the second lens group both have convex surfaces facing the aperture stop.

4. The image-forming lens according to claim 1 or 2, in, 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 both include biconvex positive lenses.

5. The image forming lens according to claim 1 or 2, wherein: The following condition expression (3) is satisfied: (3) 1.50<|f3 / f|<5.50 in, f3: focal length of the third lens group, and f: The focal length of the entire system in infinity focus.

6. The image forming lens according to claim 1 or 2, wherein: The following condition expression (4) is satisfied: (4) 0.05 <D23 / f<0.35 in, 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 in infinity focusing, and f: The focal length of the entire system in infinity focus.

7. The image forming lens according to claim 1 or 2, wherein: The following condition expression (5) is satisfied: (5)1.20<|(R1l-R2s) / (R1l+R2s)| in, R11: the radius of curvature of the surface on the image side of the lens closest to the image side in the first lens group, and R2s: the radius of curvature of the surface on the object side of the lens closest to the object side in the second lens group.

8. The image-forming lens according to claim 1 or 2, in, The third lens group has negative refractive power.

9. The image-forming lens according to claim 1 or 2, in, The third lens group includes a negative single lens.

10. The image forming lens according to claim 1 or 2, wherein: The air lens formed closest to the object side in the first lens group has a biconvex shape, and The air lens formed closest to the image side in the second lens group has a biconvex shape.

11. The image forming lens according to claim 1 or 2, wherein: The following conditional expressions (6) and (7) are satisfied: (6)-0.90<(r1o+r2o) / (r1o-r2o)<0.00 (7)-0.45<(r1i+r2i) / (r1i-r2i)<0.40 in, r1o: the radius of curvature of the surface on the object side of the air lens formed closest to the object side in the first lens group, r2o: the radius of curvature of the surface on the image side of the air lens formed closest to the object side in the first lens group, r1i: the radius of curvature of the surface on the object side of the air lens formed closest to the image side in the second lens group, and r2i: The radius of curvature of the surface on the image side of the air lens formed closest to the image side in the second lens group.

12. The image forming lens according to claim 1 or 2, wherein: The following condition expression (8) is satisfied: (8) 2.00<|f2i / f|<20.00 in, f2i: the focal length of the lens closest to the image side in the second lens group, and f: The focal length of the entire system in infinity focus.

13. An interchangeable lens comprising an image-forming lens according to claim 1 or 2.

14. An imaging device comprising the image-forming lens according to claim 1 or 2.

15. An information processing device comprising the image forming lens according to claim 1 or 2.

Images