JP2017125904A - Imaging lens and imaging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging lens that is a wide-angle lens with a small F-number (high speed) even though it is simply configured.SOLUTION: In an imaging lens PL configured to make an image of an object image-formed on a curved imaging plane with a concave surface directed towards an object side, a following expression is satisfied: 0.02<{f*(Nn1+Np2-Np1-Nn2)}/Rc<0.10, where f: a focal length of the imaging lens PL, Rc: a radius of curvature of the imaging plane, Nn1: an average refractive index of a negative lens in a first lens group G1, Np1: an average refractive index of a positive lens in the first lens group G1, Nn2: an average refractive index of the negative lens in the second lens group G2, and Np2: an average refractive index of the positive lens in the second lens group G2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging lens and an imaging system.

  In recent years, an imaging lens that forms an image of an object on an imaging surface curved with a concave surface facing the object side has been devised (see, for example, Patent Document 1). In such an imaging lens, when the curvature of field increases, it is necessary to reduce the radius of curvature of the imaging surface curved in a concave shape of the imaging device, which makes it difficult to manufacture the imaging device. Therefore, there is a demand for an imaging lens that has a simple configuration but has a wide angle of view and a small F number (bright).

JP2013-25202A

  An imaging lens according to the present invention is an imaging lens that forms an image of an object on an imaging surface curved with a concave surface facing the object side, and is a first lens having a positive refractive power arranged in order from the object side. And a second lens group having a positive refractive power, the first lens group having a negative refractive power and a first partial group arranged in order from the object side, and a positive refractive power The second lens group includes a negative lens and a positive lens, and satisfies the following conditional expression.

0.02 <{fx (Nn1 + Np2-Np1-Nn2)} / Rc <0.10
However,
f: focal length of the imaging lens,
Rc: radius of curvature of the imaging surface,
Nn1: Average refractive index of the negative lens in the first lens group,
Np1: Average refractive index of the positive lens in the first lens group,
Nn2: average refractive index of the negative lens in the second lens group,
Np2: Average refractive index of the positive lens in the second lens group.

  In addition, an imaging system according to the present invention includes an imaging lens that forms an image of an object on an imaging surface curved with a concave surface facing the object side, and an imaging that images the image of the object imaged on the imaging surface. The imaging lens is an imaging lens according to the present invention.

It is a lens block diagram of the imaging lens which concerns on 1st Example. (A) is various aberration diagrams in the infinite focus state of the imaging lens according to the first example, and (b) is various aberration diagrams in the short distance focus state. It is a lens block diagram of the imaging lens which concerns on 2nd Example. (A) is various aberration diagrams in the infinite focus state of the imaging lens according to the second example, and (b) is various aberration diagrams in the short distance focus state. It is a lens block diagram of the imaging lens which concerns on 3rd Example. (A) is various aberration diagrams in the infinite focus state of the imaging lens according to the third example, and (b) is various aberration diagrams in the short distance focus state. It is a lens block diagram of the imaging lens which concerns on 4th Example. (A) is various aberration diagrams in the infinite focus state of the imaging lens according to the fourth example, and (b) is various aberration diagrams in the short distance focus state. It is a lens block diagram of the imaging lens which concerns on 5th Example. (A) is various aberration diagrams in the infinite focus state of the imaging lens according to the fifth example, and (b) is various aberration diagrams in the short distance focus state. It is sectional drawing of a digital still camera.

  Hereinafter, preferred embodiments of the present application will be described with reference to the drawings. A digital still camera CAM is shown in FIG. 11 as an imaging system including the imaging lens PL according to the present application. FIG. 11 is a cross-sectional view of the digital still camera CAM.

  In the digital still camera CAM, when a power button (not shown) is pressed, a shutter (not shown) of the imaging lens PL is opened, and light from a subject (object) is condensed by the imaging lens PL and arranged on the image plane I. The image is formed on the image sensor C. The subject image formed on the image sensor C is displayed on the liquid crystal monitor M disposed behind the imaging lens PL. The photographer determines the composition of the subject image while looking at the liquid crystal monitor M, and then depresses the release button B1 to photograph the subject image with the image sensor C, and records and saves it in a memory (not shown).

  The image sensor C is configured using an image sensor such as a CCD or a CMOS. On the surface of the imaging device C, an imaging surface Ci in which pixels (photoelectric converters) are two-dimensionally arranged is formed. The imaging surface Ci is curved so that the concave surface is directed toward the object side (for example, in a spherical shape), and the image surface I of the imaging lens PL is curved along the imaging surface Ci. Although not shown in detail, the digital still camera CAM is used for an auxiliary light emitting unit (not shown) for emitting auxiliary light when the subject is dark, and for setting various conditions of the digital still camera CAM. Function buttons (not shown) and the like are arranged.

  The imaging lens PL includes, for example, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, arranged in order from the object side, as in the imaging lens PL (1) shown in FIG. And is configured. The first lens group G1 includes a first partial group Ga having negative refractive power and a second partial group Gb having positive refractive power, which are arranged in order from the object side. The second lens group G2 includes a negative lens and a positive lens. The imaging lens PL according to the present embodiment may be the imaging lens PL (2) shown in FIG. 3, the imaging lens PL (3) shown in FIG. 5, or the imaging lens PL (4) shown in FIG. The imaging lens PL (5) shown in FIG.

  In aberration correction, a lens having a minimum configuration capable of correcting Seidel's five aberrations is a triplet type lens. Attempts have been made to increase the angle of view by using a triplet type lens as a master lens and disposing a wide angle converter including a negative lens and a positive lens on the object side of the master lens. In addition, the structure of the wide-angle converter that is arranged on the object side of the master lens is a structure that mainly aims to correct aberrations associated with widening the angle of view, so that a doublet-type lens can be used instead of a triplet-type lens. It is also possible.

  The imaging lens PL of the present embodiment is curved so that the image plane I of the imaging lens PL has a concave surface facing the object side, and similarly, the subject is placed on the imaging surface Ci of the imaging element C that is curved so that the concave surface faces the object side. Configured to form an image. In this way, it is possible to correct the astigmatism prior to the curvature of field in the minus direction of the meridional image plane (the direction from the image side to the object side). Can be obtained. In this way, since the priority for correcting the field curvature in the negative direction of the meridional image plane is low, it is not necessary to reduce the Petzval sum. Therefore, it is possible to use an optical material having a high refractive index for the positive lens (the positive lens of the first lens group G1) constituting the wide angle converter.

  At this time, in order to align the concave shape of the imaging surface Ci of the imaging element C and the shape of the image plane I (field curvature) of the imaging lens PL, the condition represented by the following conditional expression (1) is satisfied.

0.02 <{fx (Nn1 + Np2-Np1-Nn2)} / Rc <0.10 (1)
However,
f: focal length of the imaging lens PL,
Rc: radius of curvature of imaging surface Ci,
Nn1: Average refractive index of the negative lens in the first lens group G1,
Np1: Average refractive index of the positive lens in the first lens group G1,
Nn2: average refractive index of the negative lens in the second lens group G2,
Np2: Average refractive index of the positive lens in the second lens group G2.

  Here, the curvature radius Rc of the imaging surface Ci of the imaging device C curved so that the concave surface faces the object side is a predetermined position from the vertex position that is the rotationally symmetric origin on the imaging surface Ci and the vertex position on the imaging surface Ci. It is defined as the radius of curvature of a spherical surface that passes through two points separated by a distance. In addition, when the shape of the imaging surface Ci is spherical, the curvature radius Rc of the imaging surface Ci is the curvature radius of the spherical surface along the imaging surface Ci.

  By satisfying the condition represented by the conditional expression (1), the field curvature of the imaging lens PL can be set within an appropriate range. When the condition is lower than the lower limit value of the conditional expression (1), correction of field curvature is insufficient, which is not preferable. On the other hand, when the condition exceeds the upper limit value of the conditional expression (1), correction of curvature of field becomes excessive, which is not preferable.

  In order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the lower limit of conditional expression (1) to 0.03. In order to better exhibit the effect of the present embodiment, it is desirable to set the lower limit of conditional expression (1) to 0.04. On the other hand, in order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the upper limit of conditional expression (1) to 0.09. In order to exhibit the effect of this embodiment more satisfactorily, it is desirable to set the upper limit of conditional expression (1) to 0.08.

  In the present embodiment, it is preferable that the condition represented by the following conditional expression (2) is satisfied.

  0.75 <Nn1 / Np1 <1.00 (2)

  By satisfying the condition represented by the conditional expression (2), it is possible to obtain good optical performance in a state where the F number of the imaging lens PL is small (bright). When the condition is lower than the lower limit value of the conditional expression (2), it is necessary to select an optical material having a small Abbe number as the optical material of the positive lens of the first lens group G1, and it is difficult to correct axial chromatic aberration. It is not preferable. On the other hand, when the condition exceeds the upper limit value of conditional expression (2), it is difficult to correct spherical aberration when the F number of the imaging lens PL is small, which is not preferable.

  In order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the lower limit of conditional expression (2) to 0.84. In order to exhibit the effect of the present embodiment better, it is desirable to set the lower limit value of conditional expression (2) to 0.88. On the other hand, in order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the upper limit of conditional expression (2) to 0.97. In order to exhibit the effect of this embodiment more satisfactorily, it is desirable to set the upper limit of conditional expression (2) to 0.95.

  In the present embodiment, it is preferable that the condition represented by the following conditional expression (3) is satisfied.

0.100 <f2 / f1 <0.600 (3)
However,
f1: Focal length of the first lens group G1
f2: focal length of the second lens group G2.

  By satisfying the condition expressed by the conditional expression (3), the residual aberration of the second lens group G2 can be corrected by the first lens group G1, and the condition is lower than the lower limit value of the conditional expression (3). In this case, it is difficult to correct the astigmatic difference, which is not preferable. On the other hand, when the condition exceeds the upper limit value of the conditional expression (3), the number of lenses constituting the second subgroup Gb increases in order to correct spherical aberration, which is not preferable.

  In order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the lower limit of conditional expression (3) to 0.350. In order to exhibit the effect of this embodiment more satisfactorily, it is desirable to set the lower limit of conditional expression (3) to 0.355. On the other hand, in order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the upper limit of conditional expression (3) to 0.550. In order to exhibit the effect of this embodiment more satisfactorily, it is desirable to set the upper limit of conditional expression (3) to 0.500.

  In the present embodiment, it is preferable that the distance between the first lens group G1 and the second lens group G2 is increased when focusing from an object at infinity to an object at a finite distance (short-distance object). With such a configuration, compared to the case where the first lens group G1 and the second lens group G2 are integrally moved to perform focusing at a short distance, the minus direction (from the image side toward the object side) is obtained. Direction) of the field curvature aberration (aberration fluctuation at the time of focusing at a short distance) can be reduced.

  In this case, it is preferable that the condition represented by the following conditional expression (4) is satisfied.

0.3 <X2 / X1 <1.0 (4)
However,
X1: A movement amount of the first lens group G1 along the optical axis during focusing,
X2: Amount of movement along the optical axis of the second lens group G2 during focusing.

  By satisfying the condition represented by the conditional expression (4), it is possible to satisfactorily correct the curvature of field at the time of focusing at a short distance. When the condition is less than the lower limit value of the conditional expression (4), the distance between the first lens group G1 and the second lens group G2 is too wide, and correction of field curvature becomes excessive, which is not preferable. On the other hand, when the condition exceeds the upper limit value of the conditional expression (4), the distance between the first lens group G1 and the second lens group G2 is not sufficiently widened, and correction of field curvature is insufficient, which is not preferable. .

  In order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the lower limit of conditional expression (4) to 0.4. In order to exhibit the effect of this embodiment better, it is desirable to set the lower limit of conditional expression (4) to 0.5. On the other hand, in order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the upper limit of conditional expression (4) to 0.9. In order to exhibit the effect of this embodiment better, it is desirable to set the upper limit of conditional expression (4) to 0.8.

  In the present embodiment, it is preferable that the condition represented by the following conditional expression (5) is satisfied.

0.6 <(− f11 × Nn1) / (f12 × Np1) <1.2 (5)
However,
f11: focal length of the first subgroup Ga,
f12: Focal length of the second subgroup Gb.

By satisfying the condition represented by the conditional expression (5), it is possible to secure a wide field angle photographing range and obtain better imaging performance. When the condition is lower than the lower limit value of the conditional expression (5), it is not preferable because correction of higher-order field curvature becomes difficult. On the other hand, if the condition exceeds the upper limit value of the conditional expression (5), the number of lenses constituting the second subgroup Gb increases in order to correct spherical aberration, which is not preferable.

  In order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the lower limit of conditional expression (5) to 0.65. In order to exhibit the effect of this embodiment better, it is desirable to set the lower limit of conditional expression (5) to 0.75. On the other hand, in order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the upper limit of conditional expression (5) to 0.89. In order to exhibit the effect of this embodiment more satisfactorily, it is desirable to set the upper limit of conditional expression (5) to 0.85.

  In the present embodiment, it is preferable that the condition represented by the following conditional expression (6) is satisfied.

−15 <Rc / IH <−5 (6)
However,
IH: Maximum image height on the imaging surface Ci.

  Conditional expression (6) is a value obtained by normalizing the radius of curvature Rc of the imaging surface Ci with the maximum image height IH (distance on the normal to the optical axis) on the imaging surface Ci, and the degree of curvature of the imaging surface Ci substantially. Is shown. By satisfying the condition expressed by the conditional expression (6), the field curvature of the imaging lens PL can be set within an appropriate range. When the condition is less than the lower limit value of the conditional expression (6), the curvature radius Rc (in the minus direction) of the imaging surface Ci becomes too large, and the field curvature of the imaging lens PL becomes flat in order to flatten the image surface. Correction is necessary with the imaging lens PL, which is not preferable because the lens configuration of the imaging lens PL becomes complicated. On the other hand, if the condition exceeds the upper limit value of the conditional expression (6), the radius of curvature Rc (in the minus direction) of the imaging surface Ci becomes too small, which makes it difficult to manufacture the imaging element C, which is not preferable.

  In order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the lower limit of conditional expression (6) to -13. In order to exhibit the effect of this embodiment more satisfactorily, it is desirable to set the lower limit of conditional expression (6) to -11. On the other hand, in order to exhibit the effect of this embodiment satisfactorily, it is desirable to set the upper limit of conditional expression (6) to -6. In order to exhibit the effect of this embodiment more satisfactorily, it is desirable to set the upper limit of conditional expression (6) to -7.

  In the present embodiment, at least one lens surface of the lens on the most object side in the first partial group Ga may be an aspherical surface. With such a configuration, the first partial group Ga can be a simple configuration.

  In the present embodiment, all the lens surfaces in the second lens group G2 may be spherical. With such a configuration, since the second lens group G2 can be easily manufactured, the manufacturing cost of the imaging lens PL can be reduced.

  In the present embodiment, at least one of the lens surfaces in the second lens group G2 may be an aspherical surface. With such a configuration, various aberrations can be favorably corrected in the second lens group G2. In addition, by making the lens surface of at least one of the negative lenses constituting the second lens group G2 aspherical, it is possible to achieve a large aperture ratio of the imaging lens PL.

  In the present embodiment, it is preferable that an aperture stop is disposed on the image side of the second lens group G2. With such a configuration, since the lens barrel portion to which each lens group is assembled and the mechanism portion of the aperture stop are separated, the structure of the lens barrel can be simplified.

  In the present embodiment, it is preferable that the (first) field stop is disposed on the image side of the aperture stop. When the aperture stop is disposed on the most image side of the imaging lens PL and a part of the upper light beam becomes a flare component, the (first) field stop is disposed closer to the image side than the aperture stop. The flare component can be blocked by the field stop of 1).

  In the present embodiment, the first field stop may be disposed on the image side of the aperture stop, and the second field stop may be disposed between the first partial group Ga and the second partial group Gb. When a part of the lower beam bundle becomes a flare component with the increase in the aperture ratio, the second field stop is arranged between the first partial group Ga and the second partial group Gb, so that the second The flare component can be blocked by the field stop.

  In the present embodiment, an optical low pass filter (OLPF) for reducing moire or false color is not arranged between the imaging lens PL and the imaging element C. When the optical low-pass filter is arranged on the object side of the imaging element C in which the imaging surface Ci is curved so that the concave surface is directed toward the object side, the shape of the optical low-pass filter needs to be curved in a concave shape according to the shape of the imaging surface Ci. is there. However, since the optical low-pass filter is formed using a crystal material such as quartz, it is difficult to deform in accordance with the shape of the imaging surface Ci, and it is very difficult to produce an optical low-pass filter curved in a concave shape. Have difficulty. Further, the optical low-pass filter can be made concave by lens processing using a CG machine (curve generator), but desired optical characteristics cannot be obtained.

  In the present embodiment, it is preferable that the imaging lens PL and the imaging element C are configured integrally. When the optical axis of the imaging lens PL deviates with respect to the rotational symmetry axis of the imaging device C whose imaging surface Ci is curved so that the concave surface is directed toward the object side, the image quality in the diagonal direction of the image acquired by the imaging device C is not good. It becomes uniform. Accordingly, the imaging lens PL and the imaging element C are integrally configured, and when the imaging lens PL and the imaging element C are assembled, the rotational symmetry axis of the imaging element C and the optical axis of the imaging lens PL are aligned with each other. By performing the adjustment, an image with uniform image quality can be obtained.

  In the present embodiment, the second lens group G2 and the aperture stop may be configured to move integrally along the optical axis during focusing. With such a configuration, it is possible to reduce fluctuations in the amount of peripheral light when focusing on a short distance.

  In the present embodiment, the aperture stop may be fixed with respect to the image plane I during focusing. With such a configuration, it is possible to reduce the driving load of the lens when focusing on a short distance.

  As described above, according to the present embodiment, it is possible to obtain an imaging lens PL having a wide field angle and a small F-number (light) and a digital still camera CAM (imaging system) including the imaging lens PL with a simple configuration. It becomes possible.

  In the above-described embodiment, instead of the conditional expression (1), only the conditional expression (6) may be satisfied. Even if it is such a structure, the effect similar to the above-mentioned embodiment can be acquired. In this case, in addition to the conditional expression (6), at least one of the conditional expressions (1) to (5) may be satisfied.

Embodiments of the present application will be described below with reference to the accompanying drawings. 1, FIG. 3, FIG. 5, FIG. 7, and FIG. 9 show the lens configuration and refractive power distribution of the imaging lenses PL {PL (1) to PL (5)} according to the first to fifth embodiments. The sign (+) or (-) attached to the symbol of each lens group indicates the refractive power of each lens group. In addition, the moving directions when the first lens group G1 and the second lens group G2 are focused from a infinity object to a close object (finite distance object) as a focusing lens group are “focus 1” and “focus”. It is indicated by an arrow together with the characters “2”.

  In FIG. 1, FIG. 3, FIG. 5, FIG. 7, and FIG. 9, each lens group is a combination of a symbol G and a number (or alphabet), and each lens is a combination of a symbol L and a number (or alphabet). The aperture is represented by a combination of a symbol S and a number. In this case, in order to prevent complications due to an increase in the types and numbers of codes and numbers, the lens groups and the like are represented using combinations of codes and numbers independently for each embodiment. For this reason, even if the combination of the same code | symbol and number is used between Examples, it does not mean that it is the same structure.

  Tables 1 to 5 are shown below. Of these, Table 1 is the first example, Table 2 is the second example, Table 3 is the third example, Table 4 is the fourth example, and Table 5 is the first. It is a table | surface which shows the value of the item in 5 Examples. In each embodiment, the calculation target of aberration characteristics is d-line (wavelength λ = 587.6 nm), g-line (wavelength λ = 435.8 nm), C-line (wavelength λ = 656.3 nm), F-line (wavelength λ = 486.1 nm).

In [Specification Data] in each table, f is the focal length of the imaging lens PL, FNO is the F number, ω is the maximum shooting half angle of view (unit is “°”), and φ1 is the inner diameter of the aperture stop S1. Φ2 represents the inner diameter of the (first) field stop S2, and φ2 represents the inner diameter of the second field stop S3. In [Lens data], the surface number is the number of each lens surface counted from the object side, R is the radius of curvature of each lens surface, D is the distance between the lens surfaces, and νd is the d-line (wavelength λ = 587. Abbe number with respect to 6 nm), and nd represents the refractive index with respect to d-line (wavelength λ = 587.6 nm). In [Lens Data], Dm (m: lens surface number) represents the distance between the variable surfaces, and Bf represents the back focus. In addition, * attached | subjected to the right of the 1st column (surface number) shows that the lens surface is an aspherical surface. Further, the curvature radius “∞” indicates a plane or an opening, and the description of the refractive index nd of air = 1.000000 is omitted.

The aspheric coefficient shown in [Aspherical data] is that the height (ring zone position) in the direction perpendicular to the optical axis is y, the sag amount in the optical axis direction is X (y), and the radius of curvature of the reference spherical surface (near) When the radius of curvature (axis curvature) is r, the conic constant is κ, and the n-th order (n = 2, 4, 6, 8) aspheric coefficient is An, it is expressed by the following equation (A). In [Aspherical data], “En” indicates “× 10 ⁻ⁿ ”. For example, “1.234E-05” indicates “1.234 × 10 ⁻⁵ ”.

X (y) = (y ² / r) / {1+ (1−κ × y ² / r ² ) ^1/2 }
+ A2 × y ² + A4 × y ⁴ + A6 × y ⁶ + A8 × y ⁸ (A)

  In [variable interval data], f indicates the focal length of the imaging lens PL, and β indicates the imaging magnification. The [variable interval data] includes the value of the distance D0 from the object to the first lens surface, the value of the variable surface interval Dm, the value of the back focus Bf, the total length, and the total length corresponding to each focal length and imaging magnification. TL value. [Conditional Expression Corresponding Value] indicates the corresponding value of each conditional expression.

  The focal length f, the radius of curvature R, and other length units listed in all the following specifications are generally “mm”, but the optical system may be proportionally enlarged or reduced. Since equivalent optical performance can be obtained, the present invention is not limited to this. The explanation of the table so far is common to all the embodiments, and the duplicate explanation below will be omitted.

(First embodiment)
First, a first embodiment of the present application will be described with reference to FIGS. FIG. 1 is a lens configuration diagram of the imaging lens PL (1) according to the first example in an infinitely focused state. The imaging lens PL (1) according to the first example includes a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side along the optical axis. And an aperture stop S1 and a first field stop S2. The first lens group G1 is arranged in order from the object side along the optical axis, the first partial group Ga having a negative refractive power, the second field stop S3, and the second partial group having a positive refractive power. Gb.

  The imaging lens PL (1) according to the first example is a single focus lens. The diagonal length from the center of the imaging element C corresponding to the imaging lens PL (1) to the diagonal (that is, the maximum image height on the imaging surface Ci) IH is 21.0 mm. Further, the radius of curvature Rc of the imaging surface Ci of the imaging element C curved in a spherical shape so that the concave surface is directed toward the object side is −180 mm, where the value in the direction in which the concave surface is directed toward the image surface I is a positive value.

  The first partial group Ga includes a first lens L1 that is a negative meniscus lens having a convex surface directed toward the object side. The lens surface on the image plane I side of the first lens L1 is an aspherical surface. The second partial group Gb includes a second lens L2 that is a biconvex positive lens arranged in order from the object side along the optical axis, and a third lens L3 that is a negative meniscus lens having a convex surface facing the object side. The fourth lens L4 is a negative meniscus lens having a convex surface facing the object side. The lens surfaces on both sides of the fourth lens L4 are aspheric. The second field stop S3 is disposed in the vicinity of the object side of the second partial group Gb in the first lens group G1.

  The second lens group G2 is a cemented positive lens in which, in order from the object side, a fifth lens L5 that is a negative meniscus lens having a convex surface directed toward the object side and a sixth lens L6 that is a biconvex positive lens are cemented. Consists of All lens surfaces of the fifth lens L5 and the sixth lens L6 are spherical. The aperture stop S1 is disposed in the vicinity of the image side of the second lens group G2. The first field stop S2 is disposed in the vicinity of the image side of the aperture stop S1.

  Note that the focusing (focusing) from the object at infinity to the object at a close distance (finite distance object) is performed so that the distance between the first lens group G1 and the second lens group G2 is increased. This is done by moving the lens group G2 to the object side along the optical axis. At the time of focusing, the aperture stop S1 and the first field stop S2 move integrally with the second lens group G2. The image plane I of the imaging lens PL (1) is curved so that the concave surface faces the object side in accordance with the imaging plane Ci of the imaging element C.

  Table 1 below shows specifications in the first embodiment.

(Table 1)
[Specification data]
f = 35.0
FNO = 2.0
ω = 35.0 °
φ1 = 23.15
φ2 = 19.27
φ3 = 28.06
[Lens data]
Surface number R D νd nd
1 1499.6670 3.0000 40.10 1.851350
2 * 23.7149 14.8000
3 ∞ 0.0000 (second field stop)
4 34.2670 6.7000 29.14 2.001000
5 -185.2841 0.7000
6 30.2697 2.2000 52.34 1.755000
7 26.1531 4.5000
8 * 877.6877 1.5000 19.32 2.001780
9 * 162.3523 D9
10 253.4708 1.5000 22.74 1.808090
11 22.5336 9.8000 67.90 1.593190
12 -26.0659 1.8000
13 ∞ 7.5000 (Aperture stop)
14 ∞ Bf (first field stop)
[Aspherical data]
Second side κ = 1.2421
A2 = 0.00000E + 00, A4 = 2.46370E-06, A6 = 0.00000E + 00, A8 = 0.00000E + 00
8th surface κ = -0.1019E + 05
A2 = 0.00000E + 00, A4 = -3.63880E-06, A6 = -2.58050E-08, A8 = 0.00000E + 00
Surface 9 κ = 0.4770
A2 = 0.00000E + 00, A4 = 6.89730E-06, A6 = -4.45530E-09, A8 = 0.00000E + 00
[Variable interval data]
Infinite focus state Short range focus state
f = 35.0 β = -0.10000
D0 ∞ 355.5619
D9 1.50000 2.09099
Bf 37.30108 40.77750
TL 92.80108 96.86849
[Conditional expression values]
Conditional expression (1) {f × (Nn1 + Np2−Np1−Nn2)} / Rc = 0.0674
Conditional expression (2) Nn1 / Np1 = 0.934
Conditional expression (3) f2 / f1 = 0.384
Conditional expression (4) X2 / X1 = 0.855
Conditional expression (5) (−f11 × Nn1) / (f12 × Np1) = 0.781
Conditional expression (6) Rc / IH = −8.57

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (6) are satisfied.

FIG. 2 is a diagram illustrating various aberrations of the imaging lens PL (1) according to the first example. Here, FIG. 2A is a diagram of various aberrations of the imaging lens PL (1) according to the first example in the infinite focus state, and FIG. 2B is a close-up graph of the imaging lens PL (1). FIG. 6 is a diagram showing various aberrations in a focal state (closest shooting distance L = 452 mm). In each aberration diagram, FNO represents the F number, A represents the maximum shooting half field angle in the negative direction, NA represents the numerical aperture, and H0 represents the object height. In each aberration diagram, d is a d-line (λ = 587.6 nm), g is a g-line (λ = 435.8 nm), C is a C-line (wavelength λ = 656.3 nm), and F is an F-line (wavelength). Aberration at λ = 486.1 nm) is shown. In the aberration diagram showing astigmatism, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. An aberration diagram showing lateral chromatic aberration is shown with reference to the d-line. The description of the aberration diagrams is the same in the other examples.

  From the respective aberration diagrams, it can be seen that in the first example, various aberrations are corrected well and the imaging performance is excellent. As a result, by mounting the imaging lens PL (1) of the first embodiment, excellent optical performance can be ensured even in the digital still camera CAM.

In the first embodiment described above, the second part group Gb includes the second lens L2, the third lens L3, and the fourth lens L4. However, the present invention is not limited to this. The first part The group Ga may be composed of the first lens L1, and the second partial group Gb may be composed of the second lens L2. That is, the second lens group G2 is a cemented positive lens in which the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are cemented in order from the object side along the optical axis. May be configured. In this case, the conditional expression corresponding values of the conditional expressions (2) to (6) are the same as the conditional expression corresponding values of the first embodiment, but the conditional expression corresponding value of the conditional expression (1) is Instead of the value corresponding to the conditional expression of the first embodiment, it is expressed by the following expression.
Conditional expression (1) {f × (Nn1 + Np2-Np1-Nn2)} / Rc = 0.0800

(Second embodiment)
Hereinafter, a second embodiment of the present application will be described with reference to FIGS. FIG. 3 is a lens configuration diagram of the imaging lens PL (2) according to the second example in an infinitely focused state. The imaging lens PL (2) according to the second example includes a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side along the optical axis. And an aperture stop S1 and a field stop S2. The first lens group G1 includes a first partial group Ga having negative refractive power and a second partial group Gb having positive refractive power, which are arranged in order from the object side along the optical axis.

  The imaging lens PL (2) according to the second example is a single focus lens. The diagonal length from the center of the imaging element C corresponding to the imaging lens PL (2) to the diagonal (that is, the maximum image height on the imaging surface Ci) IH is 7.72 mm. Further, the curvature radius Rc of the imaging surface Ci of the imaging element C curved in a spherical shape so that the concave surface is directed toward the object side is −70 mm, with a value in the direction in which the concave surface is directed toward the image surface I being a positive value.

  The first partial group Ga includes a first lens L1 that is a negative meniscus lens having a convex surface directed toward the object side. The lens surface on the image plane I side of the first lens L1 is an aspherical surface. The second partial group Gb includes a second lens L2 that is a biconvex positive lens.

  The second lens group G2 is a third lens L3, which is a positive meniscus lens having a convex surface facing the object side, arranged in order from the object side along the optical axis, and a negative meniscus lens having a convex surface facing the object side. 4 lens L4 and the 5th lens L5 which is a biconvex positive lens. The lens surface on the image plane I side of the fourth lens L4 is an aspherical surface. The aperture stop S1 is disposed in the vicinity of the image side of the second lens group G2. The field stop S2 is disposed in the vicinity of the image side of the aperture stop S1.

  Note that the focusing (focusing) from the object at infinity to the object at a close distance (finite distance object) is performed so that the distance between the first lens group G1 and the second lens group G2 is increased. This is done by moving the lens group G2 to the object side along the optical axis. At the time of focusing, the aperture stop S1 and the field stop S2 move integrally with the second lens group G2. The image plane I of the imaging lens PL (2) is curved so that the concave surface faces the object side in accordance with the imaging plane Ci of the imaging element C.

  Table 2 below shows specifications in the second embodiment.

(Table 2)
[Specification data]
f = 13.0
FNO = 2.0
ω = 35.4 °
φ1 = 6.44
φ2 = 6.60
[Lens data]
Surface number R D νd nd
1 557.0191 1.0000 40.10 1.851350
2 * 18.4670 9.5000
3 37.9872 1.7000 29.14 2.001000
4 -59.4794 D4
5 10.5205 3.6000 40.66 1.883000
6 59.5132 0.5500
7 65.4878 0.5500 19.32 2.001780
8 * 8.4529 0.9000
9 29.2520 1.7000 52.34 1.755000
10 -19.4163 0.7000
11 ∞ 1.4000 (aperture stop)
12 ∞ Bf (Field stop)
[Aspherical data]
Second side κ = 4.3456
A2 = 0.00000E + 00, A4 = 3.67240E-05, A6 = 0.00000E + 00, A8 = 0.00000E + 00
8th surface κ = 1.2169
A2 = 0.00000E + 00, A4 = 8.09920E-07, A6 = -4.81970E-07, A8 = 0.00000E + 00
[Variable interval data]
Infinite focus state Short range focus state
f = 13.0 β = -0.10000
D0 ∞ 132.1854
D4 0.30194 1.06502
Bf 11.07817 12.34997
TL 32.98010 35.01498
[Conditional expression values]
Conditional expression (1) {f * (Nn1 + Np2-Np1-Nn2)} / Rc = 0.0617
Conditional expression (2) Nn1 / Np1 = 0.925
Conditional expression (3) f2 / f1 = 0.405
Conditional expression (4) X2 / X1 = 0.625
Conditional expression (5) (−f11 × Nn1) / (f12 × Np1) = 0.889
Conditional expression (6) Rc / IH = −9.07

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (6) are satisfied.

FIG. 4 is a diagram illustrating various aberrations of the imaging lens PL (2) according to the second example. Here, FIG. 4A is a diagram of various aberrations in the infinitely focused state of the imaging lens PL (2) according to the second example.
FIG. 4B is a diagram illustrating various aberrations when the imaging lens PL (2) is in a short distance in-focus state (closest photographing distance L = 167 mm). From the aberration diagrams, it can be seen that in the second example, various aberrations are corrected satisfactorily and the imaging performance is excellent. As a result, by mounting the imaging lens PL (2) of the second embodiment, excellent optical performance can be ensured even in the digital still camera CAM.

(Third embodiment)
Hereinafter, the third embodiment of the present application will be described with reference to FIGS. FIG. 5 is a lens configuration diagram of the imaging lens PL (3) according to the third example in an infinitely focused state. The imaging lens PL (3) according to the third example includes a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side along the optical axis. And an aperture stop S1 and a field stop S2. The first lens group G1 includes a first partial group Ga having negative refractive power and a second partial group Gb having positive refractive power, which are arranged in order from the object side along the optical axis.

  Note that the imaging lens PL (3) according to the third example is a single focus lens. The diagonal length from the center of the imaging element C corresponding to the imaging lens PL (3) to the diagonal (that is, the maximum image height on the imaging plane Ci) IH is 13.7 mm. Further, the radius of curvature Rc of the imaging surface Ci of the imaging element C curved in a spherical shape so that the concave surface is directed toward the object side is −125 mm with the value in the direction in which the concave surface is directed toward the image surface I being a positive value.

  The first partial group Ga includes a first lens L1 that is a negative meniscus lens having a convex surface directed toward the object side. The lens surface on the image plane I side of the first lens L1 is an aspherical surface. The second partial group Gb includes a second lens L2 that is a biconvex positive lens.

  The second lens group G2 is a third lens L3, which is a positive meniscus lens having a convex surface facing the object side, arranged in order from the object side along the optical axis, and a positive meniscus lens having a convex surface facing the object side. The lens includes a four lens L4, a fifth lens L5 that is a negative meniscus lens having a convex surface facing the object side, and a sixth lens L6 that is a biconvex positive lens. All the lens surfaces of the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are spherical. The aperture stop S1 is disposed in the vicinity of the image side of the second lens group G2. The field stop S2 is disposed in the vicinity of the image side of the aperture stop S1.

  Note that the focusing (focusing) from the object at infinity to the object at a close distance (finite distance object) is performed so that the distance between the first lens group G1 and the second lens group G2 is increased. This is done by moving the lens group G2 to the object side along the optical axis. At the time of focusing, the aperture stop S1 and the field stop S2 are fixed with respect to the image plane I (imaging plane Ci). Further, the image plane I of the imaging lens PL (3) is curved so that the concave surface faces the object side in accordance with the imaging plane Ci of the imaging element C.

  Table 3 below shows specifications in the third embodiment.

(Table 3)
[Specification data]
f = 23.0
FNO = 1.8
ω = 34.9 °
φ1 = 12.00
φ2 = 12.00
[Lens data]
Surface number R D νd nd
1 985.4960 2.0000 40.10 1.851350
2 * 32.6688 16.2000
3 50.2996 2.5000 29.14 2.001000
4 -234.2439 D4
5 20.0225 3.0000 52.34 1.755000
6 77.2987 0.5000
7 17.7523 2.0000 40.66 1.883000
8 25.2171 1.0000
9 40.0672 1.0000 19.32 2.001780
10 12.0756 2.0000
11 58.0664 3.0000 52.34 1.755000
12 -42.0884 D12
13 ∞ 2.5000 (Aperture stop)
14 ∞ Bf (field stop)
[Aspherical data]
Second side κ = 3.9100
A2 = 0.00000E + 00, A4 = 8.11580E-06, A6 = 0.00000E + 00, A8 = 0.00000E + 00
[Variable interval data]
Infinite focus state Short range focus state
f = 23.0 β = -0.10000
D0 ∞ 234.3062
D4 1.00000 2.13309
D12 1.20000 3.46617
Bf 18.23805 18.23805
TL 56.13805 59.53731
[Conditional expression values]
Conditional expression (1) {f × (Nn1 + Np2-Np1-Nn2)} / Rc = 0.0651
Conditional expression (2) Nn1 / Np1 = 0.925
Conditional expression (3) f2 / f1 = 0.358
Conditional expression (4) X2 / X1 = 0.667
Conditional expression (5) (−f11 × Nn1) / (f12 × Np1) = 0.85
Conditional expression (6) Rc / IH = −9.12

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (6) are satisfied.

  FIG. 6 is a diagram illustrating various aberrations of the imaging lens PL (3) according to the third example. Here, FIG. 6A is a diagram of various aberrations of the imaging lens PL (3) according to the third example in the infinite focus state, and FIG. 6B is a close-up graph of the imaging lens PL (3). It is an aberration diagram in the focus state (closest shooting distance L = 294 mm). From the aberration diagrams, it can be seen that in the third example, various aberrations are satisfactorily corrected and the imaging performance is excellent. As a result, by mounting the imaging lens PL (3) of the third embodiment, excellent optical performance can be ensured even in the digital still camera CAM.

(Fourth embodiment)
Hereinafter, a fourth embodiment of the present application will be described with reference to FIGS. FIG. 7 is a lens configuration diagram of the imaging lens PL (4) according to the fourth example in the infinitely focused state. The imaging lens PL (4) according to the fourth example includes a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side along the optical axis. And an aperture stop S1 and a field stop S2. The first lens group G1 includes a first partial group Ga having negative refractive power and a second partial group Gb having positive refractive power, which are arranged in order from the object side along the optical axis.

  The imaging lens PL (4) according to the fourth example is a single focus lens. The diagonal length from the center of the imaging element C corresponding to the imaging lens PL (4) to the diagonal (that is, the maximum image height on the imaging surface Ci) IH is 3.91 mm. Further, the curvature radius Rc of the imaging surface Ci of the imaging element C curved in a spherical shape so that the concave surface is directed toward the object side is −35 mm with a value in the direction in which the concave surface is directed toward the image surface I being a positive value.

  The first partial group Ga includes a first lens L1 that is a negative meniscus lens having a convex surface directed toward the object side. The second partial group Gb includes a second lens L2 that is a biconvex positive lens.

  The second lens group G2 is a third lens L3, which is a positive meniscus lens having a convex surface facing the object side, arranged in order from the object side along the optical axis, and a negative meniscus lens having a convex surface facing the object side. The lens includes a four lens L4, a fifth lens L5 that is a negative meniscus lens having a convex surface facing the object side, and a sixth lens L6 that is a biconvex positive lens. The fifth lens L5 and the sixth lens L6 are cemented to form a cemented positive lens. All the lens surfaces of the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are spherical. The aperture stop S1 is disposed in the vicinity of the image side of the second lens group G2. The field stop S2 is disposed in the vicinity of the image side of the aperture stop S1.

  Note that the focusing (focusing) from the object at infinity to the object at a close distance (finite distance object) is performed so that the distance between the first lens group G1 and the second lens group G2 is increased. This is done by moving the lens group G2 to the object side along the optical axis. At the time of focusing, the aperture stop S1 and the field stop S2 move integrally with the second lens group G2. Further, the image plane I of the imaging lens PL (4) is curved so that the concave surface faces the object side in accordance with the imaging plane Ci of the imaging element C.

  Table 4 below shows specifications in the fourth embodiment.

(Table 4)
[Specification data]
f = 6.5
FNO = 2.0
ω = 36.2 °
φ1 = 3.38
φ2 = 3.40
[Lens data]
Surface number R D νd nd
1 278.5095 0.5000 49.49 1.772500
2 8.4045 5.8000
3 16.9303 0.9000 32.31 1.953750
4 -43.0393 D4
5 5.6516 1.5000 40.66 1.883000
6 28.9723 0.3000
7 17.8656 0.5000 19.32 2.001780
8 4.5221 0.4000
9 16.0094 0.5000 25.26 1.902000
10 9.2235 0.9000 52.34 1.755000
11 -11.7719 0.4000
12 ∞ 0.7000 (aperture stop)
13 ∞ Bf (Field stop)
[Variable interval data]
Infinite focus state Short range focus state
f = 6.5 β = -0.10000
D0 ∞ 65.1876
D4 0.40695 0.91566
Bf 5.83081 6.46754
TL 18.63776 19.78319
[Conditional expression values]
Conditional expression (1) {f * (Nn1 + Np2-Np1-Nn2)} / Rc = 0.0583
Conditional expression (2) Nn1 / Np1 = 0.007
Conditional expression (3) f2 / f1 = 0.365
Conditional expression (4) X2 / X1 = 0.556
Conditional expression (5) (−f11 × Nn1) / (f12 × Np1) = 0.794
Conditional expression (6) Rc / IH = −8.95

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (6) are satisfied.

  FIG. 8 is a diagram illustrating various aberrations of the imaging lens PL (4) according to the fourth example. Here, FIG. 8A is a diagram illustrating various aberrations of the imaging lens PL (4) according to the fourth example in the infinite focus state, and FIG. It is an aberration diagram in the focus state (closest shooting distance L = 85 mm). From the aberration diagrams, it can be seen that in the fourth example, various aberrations are corrected satisfactorily and the imaging performance is excellent. As a result, by mounting the imaging lens PL (4) of the fourth embodiment, excellent optical performance can be ensured even in the digital still camera CAM.

In the above-described fourth example, the second partial group Gb is composed of the second lens L2. However, the present invention is not limited to this, and the first partial group Ga is composed of the first lens L1, and the second part. The group Gb may be configured by a second lens L2, a third lens L3, and a fourth lens L4 arranged in order from the object side along the optical axis. That is, the second lens group G2 may include a cemented positive lens in which the fifth lens L5 and the sixth lens L6 are cemented in order from the object side. In this case, the conditional expression corresponding values of the conditional expressions (2) to (6) are the same as the conditional expression corresponding values of the fourth embodiment, but the conditional expression corresponding value of the conditional expression (1) is Instead of the value corresponding to the conditional expression of the fourth embodiment, it is expressed by the following expression.
Conditional expression (1) {f * (Nn1 + Np2-Np1-Nn2)} / Rc = 0.0331

(5th Example)
Hereinafter, a fifth embodiment of the present application will be described with reference to FIGS. 9 to 10 and Table 5. FIG. FIG. 9 is a lens configuration diagram of the imaging lens PL (5) according to the fifth example in the infinitely focused state. The imaging lens PL (5) according to the fifth example includes a front lens group Gf having a small refractive power, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, It comprises an aperture stop S1 and a field stop S2. The first lens group G1 includes a first partial group Ga having negative refractive power and a second partial group Gb having positive refractive power, which are arranged in order from the object side along the optical axis.

  The imaging lens PL (5) according to the fifth example is a single focus lens. The diagonal length from the center of the imaging element C corresponding to the imaging lens PL (5) to the diagonal (that is, the maximum image height on the imaging surface Ci) IH is 7.72 mm. Further, the curvature radius Rc of the imaging surface Ci of the imaging element C curved in a spherical shape so that the concave surface is directed toward the object side is −70 mm, with a value in the direction in which the concave surface is directed toward the image surface I being a positive value.

  The front lens group Gf includes a front lens Lf that is a negative meniscus lens having a small refractive power and having a convex surface directed toward the object side. The first partial group Ga includes a first lens L1 that is a negative meniscus lens having a convex surface directed toward the object side. The lens surface on the image plane I side of the first lens L1 is an aspherical surface. The second partial group Gb includes a second lens L2 that is a biconvex positive lens.

  The second lens group G2 is a third lens L3, which is a positive meniscus lens having a convex surface facing the object side, arranged in order from the object side along the optical axis, and a negative meniscus lens having a convex surface facing the object side. 4 lens L4 and the 5th lens L5 which is a biconvex positive lens. The lens surface on the image plane I side of the fourth lens L4 is an aspherical surface. The aperture stop S1 is disposed in the vicinity of the image side of the second lens group G2. The field stop S2 is disposed in the vicinity of the image side of the aperture stop S1.

  Note that the focusing (focusing) from the object at infinity to the object at a close distance (finite distance object) is performed so that the distance between the first lens group G1 and the second lens group G2 is increased. This is done by moving the lens group G2 to the object side along the optical axis. During focusing, the aperture stop S1 moves integrally with the second lens group G2, and the front lens group Gf and the field stop S2 are fixed with respect to the image plane I (imaging plane Ci). The image plane I of the imaging lens PL (5) is curved so that the concave surface faces the object side in accordance with the imaging plane Ci of the imaging element C.

  Table 5 below shows specifications in the fifth embodiment.

(Table 5)
[Specification data]
f = 13.0
FNO = 2.0
ω = 35.8 °
φ1 = 6.42
φ2 = 6.80
[Lens data]
Surface number R D νd nd
1 423.9842 1.0000 40.66 1.883000
2 129.7135 D2
3 670.4259 1.0000 40.10 1.851350
4 * 22.2268 9.5000
5 60.3470 1.7000 29.14 2.001000
6 -47.5377 D6
7 10.1282 3.6000 40.66 1.883000
8 54.4342 0.5500
9 49.9222 0.5500 19.32 2.001780
10 * 8.4664 0.9000
11 26.0409 1.7000 52.34 1.755000
12 -22.7514 0.7000
13 ∞ D13 (Aperture stop)
14 ∞ Bf (field stop)
[Aspherical data]
4th surface κ = 5.7998
A2 = 0.00000E + 00, A4 = 3.71470E-05, A6 = 0.00000E + 00, A8 = 0.00000E + 00
10th surface κ = 1.3317
A2 = 0.00000E + 00, A4 = -1.16730E-05, A6 = -5.89930E-07, A8 = 0.00000E + 00
[Variable interval data]
Infinite focus state Short range focus state
f = 13.0 β = -0.10000
D0 ∞ 131.7056
D2 3.30617 1.03964
D6 0.97550 1.93190
D13 1.40000 2.71013
Bf 11.01101 11.01101
TL 37.89267 37.89267
[Conditional expression values]
Conditional expression (1) {f * (Nn1 + Np2-Np1-Nn2)} / Rc = 0.0617
Conditional expression (2) Nn1 / Np1 = 0.925
Conditional expression (3) f2 / f1 = 0.308
Conditional expression (4) X2 / X1 = 0.578
Conditional expression (5) (−f11 × Nn1) / (f12 × Np1) = 0.934
Conditional expression (6) Rc / IH = −9.07

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (6) are satisfied.

  FIG. 10 is a diagram illustrating all aberrations of the imaging lens PL (5) according to the fifth example. Here, FIG. 10A is a diagram illustrating various aberrations of the imaging lens PL (5) according to the fifth example in the infinite focus state, and FIG. It is an aberration diagram in the focus state (closest shooting distance L = 132 mm). From the aberration diagrams, it can be seen that in the fifth example, various aberrations are corrected well and the imaging performance is excellent. As a result, by mounting the imaging lens PL (5) of the fifth embodiment, excellent optical performance can be ensured even in the digital still camera CAM.

  In the fifth embodiment, the front lens group Gf is composed of a lens having a small negative refractive power (front lens Lf). However, the present invention is not limited to this, and a lens having a small positive refractive power. Or a no-power lens.

  As described above, according to each embodiment, an imaging lens having a wide angle of view and a small F number and a digital still camera (imaging system) including the same can be realized with a simple configuration.

  In the above-described embodiment, the following description can be appropriately adopted as long as the optical performance is not impaired.

In each of the above-described embodiments, a configuration including two lens groups as an imaging lens and a configuration including three lens groups in which a lens having a weak negative power is added to the most object side are shown. The present invention can also be applied to other configurations such as a configuration including three lens groups to which a lens having a high power and a lens having no power are added. Further, a configuration in which a lens having a weak negative power, a lens having a weak positive power, or a lens having no power is added to the most image side may be used.

  In each of the above-described embodiments, the first lens group G1 and the second lens group G2 are expanded so that the distance between the first lens group G1 and the second lens group G2 is increased during focusing from an object at infinity to an object at a close range (finite distance object). Although the lens group G1 and the second lens group G2 are moved to the object side along the optical axis, the present invention is not limited to this. For example, only the first lens group G1 may be moved to the object side along the optical axis so that the distance between the first lens group G1 and the second lens group G2 is increased. Further, for example, the first lens group G1 is moved to the object side along the optical axis so that the distance between the first lens group G1 and the second lens group G2 is increased, and the second lens group G2 is moved along the optical axis. You may move to the image surface I side.

  In each of the above-described embodiments, the distance between the first lens group G1 and the second lens group G2 is increased at the time of focusing from an object at infinity to an object at a close distance (finite distance object). However, the present invention is not limited to this. For example, as illustrated in the modifications of the first and fourth embodiments, the distance between the first lens group G1 and the second lens group G2 is fixed. May be configured. That is, as long as the first lens group G1 has a positive refractive power and the second lens group G2 has a positive refractive power, the division between the first lens group G1 and the second lens group G2 is any. It does not matter.

  In each of the above-described embodiments, a filter group such as an optical low-pass filter is not disposed on the image side of the (first) field stop S2 in the imaging lens PL, but the present invention is not limited to this. For example, an infrared cut filter may be arranged as a filter group excluding the optical low-pass filter.

  In each of the above-described embodiments, the imaging element C having the imaging surface Ci curved in a spherical shape so that the concave surface is directed toward the object side is illustrated as the imaging element corresponding to the imaging lens PL, but is not limited thereto. . For example, the imaging surface Ci of the imaging element C may be formed to be aspherical or elliptical so that the concave surface faces the object side.

  Each lens may be formed of a glass material, a resin material, or a composite of a glass material and a resin material.

  Further, the lens surface may be formed as a spherical surface, a flat surface, or an aspheric surface. When the lens surface is a spherical surface or a flat surface, lens processing and assembly adjustment are facilitated, and optical performance deterioration due to errors in processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance. When the lens surface is an aspheric surface, the aspheric surface is an aspheric surface by grinding, a glass mold aspheric surface made of glass with an aspheric shape, or a composite aspheric surface made of resin with an aspheric shape on the glass surface. Any aspherical surface may be used. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

  The aperture stop S1 is preferably disposed on the image side of the second lens group G2. However, the role of the aperture stop S1 may be substituted by a lens frame without providing a member as an aperture stop. The (first) field stop S2 is preferably arranged on the image side of the aperture stop S1, but instead of providing a member as a field stop, a role of a lens frame or a light shielding plate is used instead. Also good. The second field stop S3 is preferably arranged between the first partial group Ga and the second partial group Gb. However, the second field stop S3 is not provided with a member as a field stop, but is formed by a lens frame or a light shielding plate. A role may be substituted.

  In addition, each lens surface may be provided with an antireflection film in order to reduce flare and ghost and achieve high optical performance. The antireflection film can be appropriately selected, and may be an antireflection film having a multilayer coating or an ultra-low refractive index layer made of fine crystal particles. Further, the number of lens surfaces on which the antireflection film is applied is not particularly limited.

  In the above-described embodiment, the digital still camera CAM in which the imaging lens PL and the camera body (imaging device C) are integrally configured is used as the imaging system including the imaging lens PL. Is not something For example, as an imaging system including the imaging lens PL, a digital single-lens reflex camera in which the imaging lens PL and the camera body are configured to be detachable can be used. For example, a camera mounted on a portable terminal or the like may be used as an imaging system including the imaging lens PL. In addition, for example, as an imaging system including the imaging lens PL, an imaging apparatus including at least the imaging lens PL and the imaging element C may be used without including the liquid crystal monitor M and the operation member.

CAM digital still camera (imaging system)
C Image sensor (Ci imaging surface)
PL imaging lens G1 first lens group G2 second lens group Ga first partial group Gb second partial group S1 aperture stop S2 (first) field stop S3 second field stop I image plane

Claims (15)

An imaging lens that forms an image of an object on an imaging surface curved with a concave surface facing the object side,
A first lens group having a positive refractive power and a second lens group having a positive refractive power, arranged in order from the object side;
The first lens group includes a first partial group having a negative refractive power and a second partial group having a positive refractive power, which are arranged in order from the object side.
The second lens group includes a negative lens and a positive lens,
An imaging lens satisfying the following conditional expression:
0.02 <{fx (Nn1 + Np2-Np1-Nn2)} / Rc <0.10
However,
f: focal length of the imaging lens,
Rc: radius of curvature of the imaging surface,
Nn1: Average refractive index of the negative lens in the first lens group,
Np1: Average refractive index of the positive lens in the first lens group,
Nn2: average refractive index of the negative lens in the second lens group,
Np2: Average refractive index of the positive lens in the second lens group. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
0.75 <Nn1 / Np1 <1.00 The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
0.100 <f2 / f1 <0.600
However,
f1: the focal length of the first lens group,
f2: focal length of the second lens group.   The imaging lens according to any one of claims 1 to 3, wherein a distance between the first lens group and the second lens group is widened when focusing from an object at infinity to an object at a finite distance. . The imaging lens according to claim 4, wherein the following conditional expression is satisfied.
0.3 <X2 / X1 <1.0
However,
X1: the amount of movement along the optical axis of the first lens group at the time of focusing;
X2: The amount of movement along the optical axis of the second lens group at the time of focusing. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
0.6 <(− f11 × Nn1) / (f12 × Np1) <1.2
However,
f11: focal length of the first subgroup,
f12: Focal length of the second partial group.   The imaging lens according to any one of claims 1 to 6, wherein at least one lens surface of the lens on the most object side in the first partial group is an aspherical surface.   The imaging lens according to claim 1, wherein all lens surfaces in the second lens group are spherical surfaces. The imaging lens according to any one of claims 1 to 7, wherein at least one of the lens surfaces in the second lens group is an aspherical surface.   The imaging lens according to any one of claims 1 to 9, wherein an aperture stop is disposed on the image side of the second lens group.   The imaging lens according to claim 10, wherein a field stop is disposed on the image side of the aperture stop. A first field stop is disposed on the image side of the aperture stop;
The imaging lens according to claim 10 or 11, wherein a second field stop is disposed between the first partial group and the second partial group. An imaging lens that forms an image of an object on an imaging surface curved with a concave surface facing the object side;
An image sensor that captures an image of the object imaged on the imaging surface;
The imaging system according to claim 1, wherein the imaging lens is an imaging lens according to claim 1.   The imaging system according to claim 13, wherein an optical low-pass filter for reducing moire or false color is not disposed between the imaging lens and the imaging element.   The imaging system according to claim 13 or 14, wherein the imaging lens and the imaging device are integrally formed.

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