JP2017053887A - Imaging lens and imaging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small F-number (high-speed) imaging lens even with a simple configuration.SOLUTION: An imaging lens PL includes, arranged in order from an object side along an optical axis, a first lens component L1 that has positive refractive power; a second lens component L2 that has negative refractive power, and a third lens component L3 that has the positive refractive power. When an average refractive index of the first lens component L1 is denoted as N1, an average refractive index of the second lens component L2 is denoted as N2, and an average refractive index of the third lens component L3 is denoted as N3, the imaging lens satisfies a conditional expression expressed by 0.88<(N1+N3)/(2×N2)<1.00.SELECTED DRAWING: Figure 1

Description

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

  In recent years, various imaging lenses with a further reduced size have been devised (see, for example, Patent Document 1). Such an imaging lens has a large F number and is dark. For this reason, there is a demand for an imaging lens having a small F number but a simple configuration.

JP 2000-292688 A

  An imaging lens according to the present invention includes a first lens component having a positive refractive power, a second lens component having a negative refractive power, and a first lens having a positive refractive power, arranged in order from the object side along the optical axis. It has three lens components and satisfies the following conditional expression.

0.88 <(N1 + N3) / (2 × N2) <1.00
However,
N1: Average refractive index of the first lens component,
N2: average refractive index of the second lens component,
N3: Average refractive index of the third lens component.

  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, and an imaging element that images the image of the object formed on the imaging surface. The imaging lens according to the present invention satisfies the following conditional expression.

0.3 <{f × (N2-N1-N3)} / R <1.0
However,
f: focal length of the imaging lens,
R: radius of curvature of the imaging surface.

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.

  For example, as shown in FIG. 1, the imaging lens PL includes a first lens component L1 having a positive refractive power and a second lens component L2 having a negative refractive power arranged in order from the object side along the optical axis. And a third lens component L3 having a positive refractive power.

  In aberration correction, a lens having a minimum configuration capable of correcting Seidel's five aberrations is a triplet type lens. In order to reduce the Petzval sum for the purpose of ensuring flatness of the image surface, a Tesser type lens in which a single concave lens is added to a triplet type lens has been put into practical use.

  In the present embodiment, it is preferable that the image plane I of the imaging lens PL is curved so that the concave surface faces the object side. If a subject image is formed on the imaging surface Ci of the imaging device C that is curved so that the concave surface is directed toward the object side, even if a triplet type lens is used as the imaging lens PL, the minus direction of the meridional image plane (image Since the astigmatic difference can be corrected with priority over the field curvature in the direction from the side toward the object side, good imaging performance can be obtained. However, when correcting the curvature of field of the sagittal image surface curved so that the concave surface faces the image side, it is preferable to use a Tesser type lens.

  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 lens component having negative refractive power included in the triplet type or Tesser type lens, that is, the second lens component L2 in the imaging lens PL of the present embodiment. . The degree of increase in the refractive index of the second lens component L2 is defined by the following conditional expression (1).

0.88 <(N1 + N3) / (2 × N2) <1.00 (1)
However,
N1: Average refractive index of the first lens component L1,
N2: average refractive index of the second lens component L2,
N3: Average refractive index of the third lens component L3.

  By satisfying the condition represented by the conditional expression (1), it is possible to obtain an imaging lens PL having a small F number (bright). When the condition is less than the lower limit value of the conditional expression (1), it is necessary to select an optical material having a small Abbe number as the optical material of the second lens component L2, which is not preferable because it is difficult to correct axial chromatic aberration. On the other hand, when the condition exceeds the upper limit value of conditional expression (1), 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 (1) to 0.90. 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 0.99.

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

1.79 <Nm <2.30 (2)
However,
Nm: Average refractive index of the first lens component L1, the second lens component L2, and the third lens component L3.

  By satisfying the condition expressed by the conditional expression (2), higher-order spherical aberration generated on each lens surface of the imaging lens PL can be reduced, and spherical aberration can be corrected more satisfactorily. Become. When the condition is lower than the lower limit value of the conditional expression (2), higher-order spherical aberration generated on each lens surface of the imaging lens PL becomes large, and correction of spherical aberration becomes difficult, which is not preferable. On the other hand, when the condition exceeds the upper limit value of the conditional expression (2), it is a range indicating the upper limit of the refractive index in the current optical material. Therefore, a difference in refractive index cannot be provided between a lens component having a positive refractive power and a lens component having a negative refractive power, and correction of spherical aberration becomes difficult, 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 1.82. 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 1.95.

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

0.050 <d2 / d3 <0.440 (3)
However,
d2: center thickness of the second lens component L2,
d3: Center thickness of the third lens component L3.

  When the condition expressed by conditional expression (3) is satisfied, the astigmatic difference can be kept within a favorable range without increasing the number of lenses, and the condition is below the lower limit of conditional expression (3). This is not preferable because the center thickness d3 of the third lens component L3 becomes too large and the entire length of the imaging lens PL becomes large. On the other hand, when the condition exceeds the upper limit value of conditional expression (3), it is difficult to correct the astigmatic difference, 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 0.070. 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 0.438.

  In the present embodiment, all the lens surfaces in the first lens component L1, the second lens component L2, and the third lens component L3 may be spherical. With this configuration, the first lens component L1, the second lens component L2, and the third lens component L3 can be easily manufactured, so that the manufacturing cost of the imaging lens PL can be reduced. Also in this configuration, the F number of the imaging lens PL can be reduced (brighter) to about 2.8.

  In the present embodiment, at least one lens surface in the first lens component L1 may be an aspheric surface, and at least one lens surface in the third lens component L3 may be an aspheric surface. With such a configuration, the image plane I of the imaging lens PL can be flattened. Further, it can contribute to widening the angle of the imaging lens PL.

  In the present embodiment, at least one of the lens surfaces in the second lens component L2 may be an aspherical surface. With such a configuration, it is possible to correct spherical aberration well and make the F number of the imaging lens PL smaller (brighter) than 2.8.

  In the present embodiment, it is preferable that the aperture stop S1 is disposed closer to the image side than the third lens component L3. With such a configuration, since the lens barrel portion to which each lens component is assembled and the mechanism portion of the aperture stop S1 are separated, the structure of the lens barrel can be simplified.

  In the present embodiment, it is preferable that the field stop is disposed on the image side with respect to the aperture stop S1. When the aperture stop S1 is disposed closest to the image side of the image pickup lens PL and a part of the upper light bundle becomes a flare component, the field stop is disposed closer to the image side than the aperture stop S1, so that the flare is generated by the field stop. Can block ingredients.

  In the present embodiment, the first lens component L1 is composed of one positive lens, the second lens component L2 is composed of one negative lens, and the third lens component L3 is composed of one positive lens. May be configured. Thus, the configuration of the imaging lens PL can be simplified by making the imaging lens PL a triplet type lens.

  In the present embodiment, the first lens component L1 is composed of one positive lens, the second lens component L2 is composed of one negative lens, and the third lens component L3 is composed of one positive lens and one lens. You may comprise so that it may consist of a negative lens. In this way, by using the imaging lens PL as a Tesser type lens, it is possible to satisfactorily correct the field curvature of the sagittal image plane.

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

0.3 <{f × (N2-N1-N3)} / Rc <1.0 (4)
However,
f: focal length of the imaging lens PL,
Rc: radius of curvature of the imaging surface Ci.

  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 expressed by the conditional expression (4), the shape of the imaging surface Ci of the imaging element C and the shape of the image surface I of the imaging lens PL (field curvature) can be made uniform. When the condition is lower than the lower limit value of the conditional expression (4), 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 (4), correction of field curvature 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 (4) to 0.4. 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 0.8.

  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 first lens component L1, the second lens component L2, the third lens component L3, and the aperture stop S1 are configured to move integrally along the optical axis during focusing. May be. 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, during focusing, the first lens component L1, the second lens component L2, and the third lens component L3 move integrally along the optical axis, and the aperture stop S1 is fixed. You may comprise as follows. 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 a (bright) imaging lens PL having a small F number and a digital still camera CAM (imaging system) including the imaging lens PL with a simple configuration.

(First embodiment)
Embodiments of the present application will be described below with reference to the accompanying drawings. 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 (PL1) according to the first example in an infinitely focused state. The imaging lens PL1 according to the first example includes a first lens component L1 having a positive refractive power, a second lens component L2 having a negative refractive power, and a positive lens arranged in order from the object side along the optical axis. The third lens component L3 having a refractive power of 1 and the aperture stop S1.

  The imaging lens PL1 according to the first example is a single focus lens. The diagonal length IH from the center of the imaging element C corresponding to the imaging lens PL1 to the diagonal is 20.7 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 −135 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 lens component L1 includes a single meniscus positive lens having a convex surface facing the object side. The second lens component L2 is composed of one negative lens having a biconcave shape. The third lens component L3 is composed of a single biconvex positive lens. All the lens surfaces in the first lens component L1, the second lens component L2, and the third lens component L3 are spherical. The aperture stop S1 is disposed in the vicinity of the image side of the third lens component L3, and also has a function as a field stop.

  Note that focusing from an object at infinity to an object at a close distance (a finite distance object) causes the first lens component L1, the second lens component L2, and the third lens component L3 to be integrally moved to the object side along the optical axis. This is done by moving it. Note that the aperture stop S1 is fixed during focusing. Further, the image plane I of the imaging lens PL1 is curved so that the concave surface faces the object side in accordance with the imaging plane Ci of the imaging element C.

Tables 1 to 5 are shown below, and these are values respectively showing the values of the specifications of the imaging lens PL according to the first to fifth examples. In [Specification Data] in each table, f is the focal length of the imaging lens PL, Fnо 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 indicate the inner diameter of the field stop S2. 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], D6 indicates a variable surface interval, and Bf indicates a back focus. In addition, * attached | subjected to the right of the 1st column (surface number) shows that the lens surface is an aspherical surface. Also, the curvature radius “∞” indicates a plane, and the refractive index nd = 1.00000 of air is omitted from the description.

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 D6, 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. In addition, the same reference numerals as those of the present embodiment are used in the specification values of the second to fifth embodiments described later.

  Table 1 below shows specifications in the first embodiment. In addition, the curvature radius R of the 1st surface-the 7th surface in Table 1 respond | corresponds to code | symbol R1-R7 attached | subjected to the 1st surface-the 7th surface in FIG.

(Table 1)
[Specification data]
f = 51.6
Fnо = 2.9
ω = 22.8 °
φ1 = 13.62
[Lens data]
Surface number R D νd nd
1 22.2581 6.5000 37.35 1.834000
2 50.3436 4.3000
3 -82.0899 1.0000 23.96 1.921190
4 20.2270 1.4000
5 30.3360 11.8000 37.35 1.834000
6 -36.3951 D6
7 ∞ Bf (Aperture stop)
[Variable interval data]
Infinite focus state Short range focus state
f = 51.6 β = -0.1000
D0 ∞ 558.0204
D6 1.50000 6.66000
Bf 38.67685 38.67685
TL 65.17685 70.33684
[Conditional expression values]
Conditional expression (1) (N1 + N3) / (2 × N2) = 0.955
Conditional expression (2) Nm = 1.86306
Conditional expression (3) d2 / d3 = 0.085
Conditional expression (4) {f × (N2-N1-N3)} / Rc = 0.668

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (4) are satisfied.

  FIG. 2 is a diagram illustrating various aberrations of the imaging lens PL1 according to the first example. 2A is a diagram illustrating various aberrations of the imaging lens PL1 according to the first example in an infinite focus state, and FIG. 2B is a short-distance focusing state (closest shooting distance) of the imaging lens PL1. It is an aberration diagram at L = 628 mm). In each aberration diagram, FNO represents the F number, A represents the maximum shooting half angle of view, 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 PL1 of the first embodiment, excellent optical performance can be secured even in the digital still camera CAM.

(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 (PL2) according to the second example in an infinitely focused state. The imaging lens PL2 according to the second example includes a first lens component L1 having a positive refractive power, a second lens component L2 having a negative refractive power, and a positive lens arranged in order from the object side along the optical axis. And a third lens component L3 having a refractive power of 1, an aperture stop S1, and a field stop S2.

  The imaging lens PL2 according to the second example is a single focus lens. The diagonal length IH from the center of the imaging element C corresponding to the imaging lens PL2 to the diagonal 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 −100 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 lens component L1 includes a single meniscus positive lens having a convex surface facing the object side. The second lens component L2 is composed of one negative lens having a biconcave shape. The third lens component L3 is composed of a single biconvex positive lens. All (on both sides) lens surfaces in the second lens component L2 are aspherical surfaces. The aperture stop S1 is disposed near the image side of the third lens component L3. The field stop S2 is disposed in the vicinity of the image side of the aperture stop S1.

  Note that focusing from an object at infinity to a close object (finite distance object) uses the first lens component L1, the second lens component L2, the third lens component L3, the aperture stop S1, and the field stop S2 as optical axes. This is performed by moving the object integrally along the line. Further, the image plane I of the imaging lens PL2 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. In addition, the curvature radius R of the 1st surface-8th surface in Table 2 respond | corresponds to code | symbol R1-R8 attached | subjected to the 1st surface-8th surface in FIG. In the second embodiment, the lens surfaces of the third surface and the fourth surface are formed in an aspheric shape.

(Table 2)
[Specification data]
f = 35.0
Fnо = 2.0
ω = 21.9 °
φ1 = 12.86
φ2 = 11.56
[Lens data]
Surface number R D νd nd
1 14.7951 4.5000 31.31 1.903660
2 49.5342 1.7000
3 * -167.6565 1.0000 19.32 2.001780
4 * 15.6740 1.6000
5 49.5887 7.8000 31.31 1.903660
6 -30.3329 1.2000
7 ∞ 2.5000 (aperture stop)
8 ∞ Bf (Field stop)
[Aspherical data]
3rd surface κ = 40.8289, A2 = 0.00000E + 00, A4 = -8.05370E-06, A6 = 3.96410E-08, A8 = 0.00000E + 00
4th surface κ = 0.4770, A2 = 0.00000E + 00, A4 = 2.32630E-05, A6 = -3.37950E-08, A8 = 0.00000E + 00
[Variable interval data]
Infinite focus state Short range focus state
f = 35.0 β = -0.1000
D0 ∞ 380.9963
Bf 22.33511 25.83511
TL 42.63511 46.13511
[Conditional expression values]
Conditional expression (1) (N1 + N3) / (2 × N2) = 0.951
Conditional expression (2) Nm = 1.93637
Conditional expression (3) d2 / d3 = 0.128
Conditional expression (4) {f × (N2-N1-N3)} / Rc = 0.632

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (4) are satisfied.

  FIG. 4 is a diagram illustrating various aberrations of the imaging lens PL2 according to the second example. 4A is a diagram illustrating various aberrations of the imaging lens PL2 according to the second example in the infinite focus state, and FIG. 4B is a short distance focusing state (closest shooting distance) of the imaging lens PL2. It is an aberration diagram at L = 427 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 PL2 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 (PL3) according to the third example in an infinitely focused state. The imaging lens PL3 according to the third example has the same configuration as that of the imaging lens PL2 according to the second example, except for an aspheric lens surface. Therefore, in the third embodiment, the same members as those in the imaging lens PL2 according to the second embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. In the imaging lens PL3 according to the third example, the object-side lens surface in the first lens component L1 and the image surface I-side lens surface in the third lens component L3 are aspheric.

  The imaging lens PL3 according to the third example is a single focus lens. The diagonal length IH from the center of the imaging element C corresponding to the imaging lens PL3 to the diagonal is 7.7 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 −45 mm, with a value in the direction in which the concave surface is directed toward the image surface I being a positive value.

  Table 3 below shows specifications in the third embodiment. In addition, the curvature radius R of the 1st surface-8th surface in Table 3 respond | corresponds to code | symbol R1-R8 attached | subjected to the 1st surface-8th surface in FIG. In the third embodiment, the first and sixth lens surfaces are aspherical.

(Table 3)
[Specification data]
f = 20.0
Fnо = 2.9
ω = 21.5 °
φ1 = 5.68
φ2 = 5.60
[Lens data]
Surface number R D νd nd
1 * 8.0915 1.4000 42.71 1.820800
2 34.0711 1.6000
3 -12.6882 0.4000 25.46 2.000690
4 24.0806 1.7000
5 26.0695 2.1000 40.10 1.851350
6 * -17.3600 0.7000
7 ∞ 1.0000 (aperture stop)
8 ∞ Bf (Field stop)
[Aspherical data]
1st surface κ = 2.1946, A2 = 0.00000E + 00, A4 = -1.07890E-04, A6 = -1.72950E-06, A8 = 0.00000E + 00
6th surface κ = -15.3673, A2 = 0.00000E + 00, A4 = -1.15350E-04, A6 = 1.41900E-05, A8 = 0.00000E + 00
[Variable interval data]
Infinite focus state Short range focus state
f = 20.0 β = -0.1000
D0 ∞ 617.1110
Bf 14.46107 16.46089
TL 23.36107 25.36089
[Conditional expression values]
Conditional expression (1) (N1 + N3) / (2 × N2) = 0.918
Conditional expression (2) Nm = 1.90995
Conditional expression (3) d2 / d3 = 0.190
Conditional expression (4) {f × (N2-N1-N3)} / Rc = 0.743

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (4) are satisfied.

  FIG. 6 is a diagram illustrating various aberrations of the imaging lens PL3 according to the third example. Here, FIG. 6A is a diagram of various aberrations in the infinite focus state of the imaging lens PL3 according to the third example, and FIG. 6B is a short-distance focusing state (closest shooting distance) of the imaging lens PL3. It is an aberration diagram at L = 242 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 PL3 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 (PL4) according to the fourth example in an infinitely focused state. The imaging lens PL4 according to the fourth example includes a first lens component L1 having a positive refractive power, a second lens component L2 having a negative refractive power, and a positive lens arranged in order from the object side along the optical axis. The third lens component L3 having a refractive power of 1 and the aperture stop S1.

  The imaging lens PL4 according to the fourth example is a single focus lens. The diagonal length IH from the center of the imaging element C corresponding to the imaging lens PL4 to the diagonal is 3.92 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 −33 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 lens component L1 includes a single meniscus positive lens having a convex surface facing the object side. The second lens component L2 is composed of one negative lens having a biconcave shape. The third lens component L3 is composed of a single biconvex positive lens. The aperture stop S1 is disposed in the vicinity of the image side of the third lens component L3, and also has a function as a field stop.

  Note that focusing from an infinitely distant object to a close object (finite distance object) is performed by integrating the first lens component L1, the second lens component L2, the third lens component L3, and the aperture stop S1 along the optical axis. By moving it to the object side. The image plane I of the imaging lens PL4 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. In addition, the curvature radius R of the 1st surface-the 7th surface in Table 4 respond | corresponds to code | symbol R1-R7 attached | subjected to the 1st surface-the 7th surface in FIG. In the fourth embodiment, the first and sixth lens surfaces are aspherical.

(Table 4)
[Specification data]
f = 9.7
Fnо = 3.5
ω = 22.8 °
φ1 = 2.18
[Lens data]
Surface number R D νd nd
1 * 4.3963 1.3000 37.38 1.900430
2 9.2451 0.4000
3 -12.6706 0.7000 23.96 1.921190
4 4.5676 0.3000
5 7.7896 1.6000 37.38 1.900430
6 * -6.9946 0.4000
7 ∞ Bf (Aperture stop)
[Variable interval data]
Infinite focus state Short range focus state
f = 9.7 β = -0.1000
D0 ∞ 299.1737
Bf 7.55440 8.52440
TL 12.25440 13.22440
[Conditional expression values]
Conditional expression (1) (N1 + N3) / (2 × N2) = 0.989
Conditional expression (2) Nm = 1.90735
Conditional expression (3) d2 / d3 = 0.438
Conditional expression (4) {f × (N2-N1-N3)} / Rc = 0.553

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (4) are satisfied.

FIG. 8 is a diagram illustrating all aberrations of the imaging lens PL4 according to the fourth example. Here, FIG. 8A is a diagram of various aberrations of the imaging lens PL4 according to the fourth example in the infinite focus state, and FIG. 8B is a short distance focusing state (closest shooting distance) of the imaging lens PL4. It is an aberration diagram at L = 299 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 PL4 of the fourth embodiment, excellent optical performance can be ensured even in the digital still camera CAM.

(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 (PL5) according to Example 5 in the infinitely focused state. The imaging lens PL5 according to the fifth example includes a first lens component L1 having a positive refractive power, a second lens component L2 having a negative refractive power, and a positive lens arranged in order from the object side along the optical axis. The third lens component L3 having a refractive power of 1 and the aperture stop S1.

  Note that the imaging lens PL5 according to Example 5 is a single focus lens. The diagonal length IH from the center of the imaging element C corresponding to the imaging lens PL5 to the diagonal is 20.7 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 −172 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 lens component L1 includes a single meniscus positive lens having a convex surface facing the object side. The second lens component L2 is composed of one negative lens having a biconcave shape. The third lens component L3 includes a cemented lens in which a biconvex positive lens and a meniscus negative lens having a concave surface facing the object side are cemented. The aperture stop S1 is disposed in the vicinity of the image side of the third lens component L3, and also has a function as a field stop.

  Note that focusing from an object at infinity to an object at a close distance (a finite distance object) causes the first lens component L1, the second lens component L2, and the third lens component L3 to be integrally moved to the object side along the optical axis. This is done by moving it. Note that the aperture stop S1 is fixed during focusing. The image plane I of the imaging lens PL5 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. In addition, the curvature radius R of the 1st surface-8th surface in Table 5 respond | corresponds to code | symbol R1-R8 attached | subjected to the 1st surface-8th surface in FIG. In the fifth embodiment, the lens surface of the first surface is formed in an aspheric shape.

(Table 5)
[Specification data]
f = 51.6
Fnо = 2.9
ω = 22.4 °
φ1 = 13.92
[Lens data]
Surface number R D νd nd
1 * 22.3152 6.5000 37.35 1.834000
2 53.0680 4.3000
3 -57.4174 1.0000 23.96 1.921190
4 22.7372 1.4000
5 38.7463 8.0000 37.38 1.900430
6 -32.0000 1.0000 17.02 2.104200
7 -34.4398 D6
8 ∞ Bf (Aperture stop)
[Variable interval data]
Infinite focus state Short range focus state
f = 51.6 β = -0.1000
D0 ∞ 559.6854
D6 1.50000 6.66002
Bf 39.45875 39.45875
TL 63.15875 68.31877
[Conditional expression values]
Conditional expression (1) (N1 + N3) / (2 × N2) = 0.990
Conditional expression (2) Nm = 1.90810
Conditional expression (3) d2 / d3 = 0.111
Conditional expression (4) {f × (N2-N1-N3)} / Rc = 0.565

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (4) are satisfied.

  FIG. 10 is a diagram illustrating various aberrations of the imaging lens PL5 according to the fifth example. Here, FIG. 10A is a diagram of various aberrations of the imaging lens PL5 according to the fifth example in the infinite focus state, and FIG. 10B is a short distance focusing state (closest shooting distance) of the imaging lens PL5. It is an aberration diagram at L = 628 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 PL5 of the fifth embodiment, excellent optical performance can be secured even in the digital still camera CAM.

  As described above, according to each embodiment, it is possible to realize a (bright) imaging lens having a small F number with a simple configuration and a digital still camera (imaging system) including the imaging lens.

  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, the configuration including the three lens components is shown as the imaging lens, but the present invention can also be applied to other configurations such as a configuration including the four lens components. For example, a configuration in which a lens having a weak power (for example, a negative lens) is added to the most object side or a lens having a weak power being added to the most image side may be used.

  In each of the above-described embodiments, the first lens component L1 is a single lens, but is not limited thereto, and may be a cemented lens. In each of the above-described embodiments, the second lens component L2 is also a single lens, but is not limited to this, and may be a cemented lens.

  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 aperture stop S1 or the 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 third lens component L3. However, the role of the aperture stop S1 may be substituted by a lens frame without providing a member as an aperture stop. The field stop S2 is preferably arranged on the image side of the aperture stop S1, but the role may be substituted by an aperture stop or a lens frame without providing a member as a field stop.

  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 L1 first lens component L2 second lens component L3 third lens component S1 aperture stop S2 field stop I image plane

Claims (14)

A first lens component having a positive refractive power, a second lens component having a negative refractive power, and a third lens component having a positive refractive power, arranged in order from the object side along the optical axis. ,
An imaging lens satisfying the following conditional expression:
0.88 <(N1 + N3) / (2 × N2) <1.00
However,
N1: Average refractive index of the first lens component,
N2: average refractive index of the second lens component,
N3: Average refractive index of the third lens component. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
1.79 <Nm <2.30
However,
Nm: Average refractive index of the first lens component, the second lens component, and the third lens component. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
0.050 <d2 / d3 <0.440
However,
d2: center thickness of the second lens component,
d3: Center thickness of the third lens component.   4. The imaging lens according to claim 1, wherein all lens surfaces in the first lens component, the second lens component, and the third lens component are spherical surfaces. 5. At least one of the lens surfaces in the first lens component is an aspheric surface;
4. The imaging lens according to claim 1, wherein at least one lens surface of the third lens component is an aspherical surface. 5.   4. The imaging lens according to claim 1, wherein at least one of the lens surfaces of the second lens component is an aspherical surface. 5.   The imaging lens according to claim 1, wherein an aperture stop is disposed closer to the image side than the third lens component.   The imaging lens according to claim 7, wherein a field stop is disposed closer to the image side than the aperture stop. The first lens component is composed of one positive lens,
The second lens component consists of one negative lens,
The imaging lens according to any one of claims 1 to 8, wherein the third lens component includes one positive lens. The first lens component is composed of one positive lens,
The second lens component consists of one negative lens,
The imaging lens according to any one of claims 1 to 8, wherein the third lens component includes one positive lens and one negative lens.   The imaging lens according to claim 1, wherein the image plane is curved so that the concave surface is directed toward the object side. An imaging lens that forms an image of an object on an imaging surface;
An image sensor that captures an image of the object imaged on the imaging surface;
The imaging lens is the imaging lens according to any one of claims 1 to 11,
An imaging system characterized by satisfying the following conditional expression:
0.3 <{f × (N2-N1-N3)} / Rc <1.0
However,
f: focal length of the imaging lens,
Rc: radius of curvature of the imaging surface.   The imaging system according to claim 12, 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 12 or 13, wherein the imaging lens and the imaging device are integrally configured.

Images