JP6634742B2 - Imaging lens and imaging system - Google Patents

Description

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

  In recent years, various imaging lenses that have been made smaller have been devised (for example, see Patent Document 1). Such an imaging lens has a large F number and is dark. Therefore, there is a demand for an imaging lens having a simple configuration and a small (bright) F-number.

JP 2000-292688 A

The imaging lens according to the first aspect of the present invention is an imaging lens having a spherical image surface with a concave surface facing the object side, the second lens having a positive refractive power arranged in order from the object side along the optical axis. It has one lens component, a second lens component having a negative refractive power, and a third lens component having a positive refractive power, and satisfies the following conditional expression.
0.88 <(N1 + N3) / (2 × N2) <1.00
1.79 <Nm <2.30
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;
Nm: average value of the average refractive index of the first lens component, the average refractive index of the second lens component, and the average refractive index of the third lens component.

An imaging lens according to a second aspect of the present invention is an imaging lens having a spherical image surface with a concave surface facing the object side, the second lens having a positive refractive power arranged in order from the object side along the optical axis. It has one lens component, a second lens component having a negative refractive power, and a third lens component having a positive refractive power, and satisfies the following conditional expression.
0.88 <(N1 + N3) / (2 × N2) <1.00
0.050 <d2 / d3 <0.440
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 ;
d2: center thickness of the second lens component,
d3: center thickness of the third lens component.

An imaging lens according to a third aspect of the present invention is an imaging lens having a spherical image surface with a concave surface facing the object side, having a positive refractive power arranged in order from the object side along the optical axis. A first lens component, a second lens component having a negative refractive power, and a third lens component having a positive refractive power, wherein the first lens component, the second lens component, and the third lens component are provided. Are all spherical, satisfying the following condition:
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 system according to the present invention includes an imaging lens that forms an image of an object on an imaging surface, and an imaging device that captures an image of the object that is formed on the imaging surface, wherein the imaging lens An imaging lens according to the present invention, which 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.

FIG. 3 is a lens configuration diagram of an imaging lens according to a first example. 6A is a diagram illustrating various aberrations of the imaging lens according to the first example in a state of focusing on infinity, and FIG. FIG. 7 is a lens configuration diagram of an imaging lens according to a second example. (A) is an aberration diagram of the imaging lens according to Example 2 in an infinity in-focus state, and (b) is an aberration diagram in a short-distance in-focus state. FIG. 13 is a lens configuration diagram of an imaging lens according to a third example. (A) is an aberration diagram of the imaging lens according to Example 3 in an infinity in-focus state, and (b) is an aberration diagram in a short-distance in-focus state. It is a lens block diagram of the imaging lens concerning 4th Example. (A) is an aberration diagram in an infinity in-focus condition of the imaging lens according to Example 4, and (b) is an aberration diagram in a short-distance in-focus condition. It is a lens block diagram of the imaging lens concerning 5th Example. (A) is an aberration diagram in an infinity in-focus condition of the imaging lens according to Example 5, and (b) is an aberration diagram in a short-distance in-focus condition. It is sectional drawing of a digital still camera.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 11 illustrates a digital still camera CAM 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 is arranged on the image plane I. The image is formed on the image pickup device C. The subject image formed on the image sensor C is displayed on a liquid crystal monitor M disposed behind the imaging lens PL. After deciding the composition of the subject image while looking at the liquid crystal monitor M, the photographer 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 on which pixels (photoelectric converters) are two-dimensionally arranged is formed. The imaging surface Ci is curved (for example, spherical) so that the concave surface faces the object side, and the image plane I of the imaging lens PL is formed to be 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) that emits auxiliary light when a subject is dark, and for setting various conditions of the digital still camera CAM. A function button (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, which are 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, the lens having the minimum configuration capable of correcting Seidel's five aberrations is a triplet type lens. Further, in order to reduce the Petzval sum for the purpose of ensuring the flatness of the image plane, a Tessar type lens in which one concave lens is added to a triplet type lens has been put to practical use.

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

  As described above, the priority for correcting the curvature of field in the minus direction of the meridional image plane is reduced, so that it is not necessary to reduce the Petzval sum. Therefore, it is possible to use an optical material having a high refractive index for a lens component having a negative refractive power included in a triplet type or a Tessar type lens, that is, the second lens component L2 in the imaging lens PL of the present embodiment. . The degree of increasing 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 (bright) F-number. If the condition is below the lower limit value of 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 becomes difficult to correct axial chromatic aberration. On the other hand, if the condition exceeds the upper limit value of the conditional expression (1), it is not preferable because it becomes difficult to correct spherical aberration in a state where the F-number of the imaging lens PL is small.

  In order to sufficiently exhibit the effect of the present embodiment, it is desirable to set the lower limit of conditional expression (1) to 0.90. On the other hand, in order to sufficiently exhibit the effect of the present embodiment, 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 represented by the conditional expression (2), high-order spherical aberration generated on each lens surface of the imaging lens PL can be reduced, and the spherical aberration can be more favorably corrected. Become. If the condition is below the lower limit value of the conditional expression (2), high-order spherical aberration generated on each lens surface of the imaging lens PL increases, which makes it difficult to correct spherical aberration, which is not preferable. On the other hand, when the condition exceeds the upper limit value of the conditional expression (2), the range becomes the 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, which makes correction of spherical aberration difficult, which is not preferable.

  In order to properly achieve the effect of the present embodiment, it is desirable to set the lower limit of conditional expression (2) to 1.82. On the other hand, in order to sufficiently exhibit the effect of the present embodiment, 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.

  By satisfying the condition represented by conditional expression (3), the astigmatic difference can be suppressed to a favorable range without increasing the number of lenses, and the condition is below the lower limit of conditional expression (3). In addition, the center thickness d3 of the third lens component L3 becomes too large, and the overall length of the imaging lens PL is undesirably increased. On the other hand, if the condition exceeds the upper limit value of the conditional expression (3), it is difficult to correct the astigmatic difference, which is not preferable.

  In order to properly achieve the effect of the present embodiment, it is desirable to set the lower limit of conditional expression (3) to 0.070. On the other hand, in order to sufficiently exhibit the effect of the present embodiment, it is desirable to set the upper limit of conditional expression (3) to 0.438.

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

  In the present embodiment, at least one of the lens surfaces of the first lens component L1 may be aspherical, and at least one of the lens surfaces of the third lens component L3 may be aspherical. 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 of the second lens component L2 may be aspheric. With such a configuration, the spherical aberration can be satisfactorily corrected, and the F-number of the imaging lens PL can be made 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, the lens barrel portion to which each lens component is assembled is separated from the mechanical portion of the aperture stop S1, so that the structure of the lens barrel can be simplified.

  In the present embodiment, it is preferable that the field stop is arranged on the image side of the aperture stop S1. When the aperture stop S1 is arranged closest to the image side of the imaging lens PL and a part of the upper light beam becomes a flare component, the field stop is arranged on the image side of the aperture stop S1 so that the flare is caused by the field stop. Ingredients can be blocked.

  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. As described above, 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. And a negative lens. In this way, by using the imaging lens PL as a Tessar type lens, the field curvature of the sagittal image plane can be favorably corrected.

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

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 radius of curvature Rc of the imaging surface Ci of the imaging device C curved so that the concave surface is directed toward the object side is a predetermined apex position from the vertex position which is the origin of rotational symmetry 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 passing through two points separated by a distance. When the shape of the imaging surface Ci is spherical, the radius of curvature Rc of the imaging surface Ci is the radius of curvature of the spherical surface along the imaging surface Ci.

By satisfying the condition represented by the conditional expression (4), it is possible to make the shape of the imaging surface Ci of the imaging device C and the shape (field curvature) of the image plane I of the imaging lens PL uniform. If the condition is below the lower limit value of the conditional expression (4), the correction of the field curvature is insufficient, which is not preferable. On the other hand, if the condition exceeds the upper limit value of the conditional expression (4), the correction of the curvature of field becomes excessive, which is not preferable.

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

  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 an optical low-pass filter is arranged on the object side of the imaging device C whose imaging surface Ci is curved so that the concave surface faces the object side, it is necessary to curve the shape of the optical low-pass filter into a concave shape in accordance with 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 crystal, it is difficult to deform the optical low-pass filter in accordance with the shape of the imaging surface Ci, and it is very difficult to manufacture an optical low-pass filter curved into a concave shape. Have difficulty. Further, the shape of 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 integrally configured. If the optical axis of the imaging lens PL is shifted with respect to the rotationally symmetric axis of the imaging device C whose imaging surface Ci is curved so that the concave surface faces the object side, the image quality in the diagonal direction of the image captured and acquired by the imaging device C becomes poor. Become uniform. Therefore, the imaging lens PL and the imaging element C are integrally configured, and when assembling the imaging lens PL and the imaging element C, the axes are set so that the rotational symmetry axis of the imaging element C coincides with the optical axis of the imaging lens PL. 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 (focusing). You may. With such a configuration, it is possible to reduce the fluctuation of the peripheral light amount at the time of focusing on a short distance.

  In this embodiment, during focusing (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. It may be configured as follows. With such a configuration, it is possible to reduce the driving load of the lens at the time of focusing on a short distance.

  As described above, according to the present embodiment, it is possible to obtain an imaging lens PL having a small (bright) F number while having a simple configuration, and a digital still camera CAM (imaging system) including the imaging lens PL.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a lens configuration diagram of an imaging lens PL (PL1) according to Example 1 in an infinity in-focus 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. And a third lens component L3 having a refractive power of?

  Note that the imaging lens PL1 according to the first example is a single focus lens. The diagonal length IH from the center to the diagonal of the imaging device C corresponding to the imaging lens PL1 is 20.7 mm. Further, the radius of curvature Rc of the imaging surface Ci of the imaging element C that is curved spherically so that the concave surface faces the object side is -135 mm when the value of the direction in which the concave surface faces the image surface I is a positive value.

  The first lens component L1 is composed of a single meniscus positive lens with the convex surface facing the object side. The second lens component L2 is composed of a single biconcave negative lens. The third lens component L3 is composed of a single biconvex positive lens. All lens surfaces of the first lens component L1, the second lens component L2, and the third lens component L3 are spherical. The aperture stop S1 is arranged near the image side of the third lens component L3, and also has a function as a field stop.

  Focusing from an object at infinity to an object at a close distance (object at a finite distance) is performed by moving the first lens component L1, the second lens component L2, and the third lens component L3 integrally to the object side along the optical axis. This is done by moving. At the time of focusing, the aperture stop S1 is fixed. 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 are tables in which the values of the specifications of the imaging lens PL according to the first to fifth examples are listed. 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 photographing 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, respectively. 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 each lens surface, and νd is the d line (wavelength λ = 587. 6 nm), and nd indicates the refractive index for 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 to the right of the first column (surface number) indicates that the lens surface is aspheric. Further, the radius of curvature “を” indicates a plane, and the description of the refractive index nd of the air nd = 1.00000 is omitted.

The aspherical coefficient shown in [Aspherical surface data] is such that the height (annular 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 (near Assuming that the radius of curvature of the axis (r) is r, the conic constant is κ, and the nth order (n = 2, 4, 6, 8) aspherical coefficient is An, the following equation (A) is obtained. In [Aspherical surface 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 photographing magnification. The [variable interval data] includes a value of the distance D0 from the object to the first lens surface, a value of the variable surface interval D6, a value of the back focus Bf, and a total length corresponding to each of the focal lengths and the photographing magnification. TL value. [Conditional expression corresponding value] shows the corresponding value of each conditional expression.

  In addition, the unit of the focal length f, the radius of curvature R, and other lengths described in all of the following specification values are generally “mm”, but the optical system may be proportionally enlarged or proportionally reduced. The present invention is not limited to this, since equivalent optical performance can be obtained. Also, the same reference numerals as in the present embodiment are used for the specification values of the second to fifth embodiments described later.

  Table 1 below shows each parameter in the first embodiment. Note that the radii of curvature R of the first to seventh surfaces in Table 1 correspond to reference signs R1 to R7 given to the first to seventh surfaces in FIG.

(Table 1)
[Specification data]
f = 51.6
Fno = 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]
Focus on infinity Focus on short distance
f = 51.6 β = -0.1000
D0 ∞ 558.0204
D6 1.50000 6.66000
Bf 38.67685 38.67685
TL 65.17685 70.33684
[Values for conditional expressions]
Conditional expression (1) (N1 + N3) / (2 × N2) = 0.555
Conditional expression (2) Nm = 1.86306
Conditional expression (3): d2 / d3 = 0.085
Conditional expression (4) {f × (N2-N1-N3)} / Rc = 0.668

  As described above, in the present embodiment, it is understood that all of 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. Here, FIG. 2A is a diagram of various aberrations of the imaging lens PL1 according to Example 1 in a state of focusing on infinity, and FIG. 2B is a state of focusing on a short distance of the imaging lens PL1 (closest shooting distance). (L = 628 mm). FIG. In each aberration diagram, FNO indicates an F number, A indicates a maximum photographing half angle of view, NA indicates a numerical aperture, and H0 indicates an object height. In each aberration diagram, d is d-line (λ = 587.6 nm), g is g-line (λ = 435.8 nm), C is C-line (wavelength λ = 656.3 nm), F is F-line (wavelength (λ = 486.1 nm). In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. The aberration diagram showing the chromatic aberration of magnification is shown on the basis of the d line. The description of the aberration diagrams is the same in the other embodiments.

  From each aberration diagram, it can be seen that in the first example, various aberrations are corrected well and that the first example has excellent imaging performance. As a result, by mounting the imaging lens PL1 of the first embodiment, excellent optical performance can be ensured even in the digital still camera CAM.

(Second embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a lens configuration diagram of an imaging lens PL (PL2) according to Example 2 in an infinity in-focus 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. , An aperture stop S1, and a field stop S2.

  Note that the imaging lens PL2 according to the second example is a single focus lens. The diagonal length IH from the center to the diagonal of the imaging device C corresponding to the imaging lens PL2 is 13.7 mm. Further, the radius of curvature Rc of the imaging surface Ci of the imaging device C curved spherically so that the concave surface faces the object side is −100 mm when the value of the direction in which the concave surface faces the image surface I is a positive value.

  The first lens component L1 is composed of a single meniscus positive lens with the convex surface facing the object side. The second lens component L2 is composed of a single biconcave negative lens. The third lens component L3 is composed of a single biconvex positive lens. All (both sides) lens surfaces of the second lens component L2 are aspherical. The aperture stop S1 is arranged near the image side of the third lens component L3. The field stop S2 is arranged near the image side of the aperture stop S1.

  Focusing from an object at infinity to an object at a close distance (object at a finite distance) is performed by using the first lens component L1, the second lens component L2, the third lens component L3, the aperture stop S1, and the field stop S2 along the optical axis. This is performed by moving the object integrally along the object. 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 each parameter in the second embodiment. Note that the radii of curvature R of the first to eighth surfaces in Table 2 correspond to reference signs R1 to R8 given to the first to eighth surfaces in FIG. In the second embodiment, each of the third and fourth lens surfaces is formed in an aspherical shape.

(Table 2)
[Specification data]
f = 35.0
Fno = 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 surface data]
Surface 3 κ = 40.8289, A2 = 0.00000E + 00, A4 = -8.05370E-06, A6 = 3.96410E-08, A8 = 0.00000E + 00
Surface 4 κ = 0.4770, A2 = 0.00000E + 00, A4 = 2.32630E-05, A6 = -3.37950E-08, A8 = 0.00000E + 00
[Variable interval data]
Focus on infinity Focus on short distance
f = 35.0 β = -0.1000
D0 ∞ 380.9963
Bf 22.33511 25.83511
TL 42.63511 46.13511
[Values for conditional expressions]
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

  As described above, in the present embodiment, it is understood that all of 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. Here, FIG. 4A is a diagram illustrating various aberrations of the imaging lens PL2 according to Example 2 in an infinity in-focus state, and FIG. 4B is a short-range in-focus state of the imaging lens PL2 (a close-up shooting distance). (L = 427 mm). From the aberration diagrams, it can be seen that in the second embodiment, various aberrations are corrected well, 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, a third embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a lens configuration diagram of an imaging lens PL (PL3) according to Example 3 in an infinity in-focus state. The imaging lens PL3 according to the third example has the same configuration as 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 of the imaging lens PL2 according to the second embodiment are denoted by the same reference numerals, and detailed description is omitted. In the imaging lens PL3 according to the third example, the lens surface on the object side in the first lens component L1 and the lens surface on the image plane I side in the third lens component L3 are aspherical.

  Note that the imaging lens PL3 according to the third example is a single focus lens. The diagonal length IH from the center to the diagonal of the imaging device C corresponding to the imaging lens PL3 is 7.7 mm. The radius of curvature Rc of the imaging surface Ci of the imaging device C curved spherically so that the concave surface faces the object side is −45 mm, with the value in the direction in which the concave surface faces the image surface I being a positive value.

  Table 3 below shows each parameter in the third embodiment. Note that the radii of curvature R of the first to eighth surfaces in Table 3 correspond to the reference signs R1 to R8 attached to the first to eighth surfaces in FIG. In the third embodiment, each of the first and sixth lens surfaces is formed in an aspherical shape.

(Table 3)
[Specification data]
f = 20.0
Fno = 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 surface data]
Surface 1 κ = 2.1946, A2 = 0.00000E + 00, A4 = -1.07890E-04, A6 = -1.72950E-06, A8 = 0.00000E + 00
Surface 6 κ = -15.3673, A2 = 0.00000E + 00, A4 = -1.15350E-04, A6 = 1.41900E-05, A8 = 0.00000E + 00
[Variable interval data]
Focus on infinity Focus on short distance
f = 20.0 β = -0.1000
D0 ∞ 617.1110
Bf 14.46107 16.46089
TL 23.36107 25.36089
[Values for conditional expressions]
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

  As described above, in the present embodiment, it is understood that all of 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 of the imaging lens PL3 according to Example 3 in an infinity in-focus state, and FIG. 6B is a short-distance in-focus state of the imaging lens PL3 (closest photographing distance). (L = 242 mm). From the aberration diagrams, it can be seen that in the third embodiment, various aberrations are satisfactorily corrected and have excellent imaging performance. 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 invention will be described with reference to FIGS. FIG. 7 is a lens configuration diagram of an imaging lens PL (PL4) according to Example 4 when focused on infinity. 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 component L1 arranged in order from the object side along the optical axis. And a third lens component L3 having a refractive power of?

  The imaging lens PL4 according to the fourth example is a single focus lens. The diagonal length IH from the center to the diagonal of the imaging device C corresponding to the imaging lens PL4 is 3.92 mm. The radius of curvature Rc of the imaging surface Ci of the imaging device C curved spherically so that the concave surface faces the object side is −33 mm when the value of the direction in which the concave surface faces the image surface I is a positive value.

The first lens component L1 is composed of a single meniscus positive lens with the convex surface facing the object side. The second lens component L2 is composed of a single biconcave negative lens. The third lens component L3 is composed of a single biconvex positive lens. The aperture stop S1 is arranged near the image side of the third lens component L3, and also has a function as a field stop.

  Focusing from an object at infinity to an object at a close distance (object at a finite distance) 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 each parameter in the fourth embodiment. Note that the radii of curvature R of the first to seventh surfaces in Table 4 correspond to reference signs R1 to R7 attached to the first to seventh surfaces in FIG. In the fourth embodiment, each of the first and sixth lens surfaces is formed in an aspherical shape.

(Table 4)
[Specification data]
f = 9.7
Fno = 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]
Focus on infinity Focus on short distance
f = 9.7 β = -0.1000
D0 ∞ 299.1737
Bf 7.55440 8.52440
TL 12.25440 13.22440
[Values for conditional expressions]
Conditional expression (1) (N1 + N3) / (2 × N2) = 0.889
Conditional expression (2) Nm = 1.90735
Conditional expression (3): d2 / d3 = 0.438
Conditional expression (4) {f × (N2-N1-N3)} / Rc = 0.553

  As described above, in the present embodiment, it is understood that all of the conditional expressions (1) to (4) are satisfied.

FIG. 8 is a diagram illustrating various 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 Example 4 in a state of focusing on infinity, and FIG. 8B is a state of focusing on a short distance of the imaging lens PL4 (closest shooting distance). (L = 299 mm). From the aberration diagrams, it can be seen that in the fourth example, various aberrations are satisfactorily corrected and have excellent imaging performance. 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.

(Fifth embodiment)
Hereinafter, a fifth embodiment of the present application will be described with reference to FIGS. FIG. 9 is a lens configuration diagram of an imaging lens PL (PL5) according to Example 5 in an infinity in-focus 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 component L1 arranged in order from the object side along the optical axis. And a third lens component L3 having a refractive power of?

  Note that the imaging lens PL5 according to the fifth example is a single focus lens. The diagonal length IH from the center to the diagonal of the imaging device C corresponding to the imaging lens PL5 is 20.7 mm. The radius of curvature Rc of the imaging surface Ci of the imaging device C curved spherically so that the concave surface faces the object side is -172 mm when the value of the direction in which the concave surface faces the image surface I is a positive value.

  The first lens component L1 is composed of a single meniscus positive lens with the convex surface facing the object side. The second lens component L2 is composed of a single biconcave negative lens. The third lens component L3 is composed of a cemented lens in which a biconvex positive lens and a meniscus-shaped negative lens whose concave surface faces the object side are cemented. The aperture stop S1 is arranged near the image side of the third lens component L3, and also has a function as a field stop.

  Focusing from an object at infinity to an object at a close distance (object at a finite distance) is performed by moving the first lens component L1, the second lens component L2, and the third lens component L3 integrally to the object side along the optical axis. This is done by moving. At the time of focusing, the aperture stop S1 is fixed. 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 each parameter in the fifth embodiment. Note that the radii of curvature R of the first to eighth surfaces in Table 5 correspond to reference symbols R1 to R8 attached to the first to eighth surfaces in FIG. In the fifth embodiment, the first lens surface is formed in an aspherical shape.

(Table 5)
[Specification data]
f = 51.6
Fno = 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]
Focus on infinity Focus on short distance
f = 51.6 β = -0.1000
D0 ∞ 559.6854
D6 1.50000 6.66002
Bf 39.45875 39.45875
TL 63.15875 68.31877
[Values for conditional expressions]
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

  As described above, in the present embodiment, it is understood that all of the conditional expressions (1) to (4) are satisfied.

  FIG. 10 is a diagram illustrating various aberrations of the imaging lens PL5 according to Example 5. Here, FIG. 10A is a diagram of various aberrations of the imaging lens PL5 according to Example 5 in an infinity in-focus state, and FIG. 10B is a short-distance in-focus state of the imaging lens PL5 (closest photographing distance). (L = 628 mm). FIG. From the aberration diagrams, it can be seen that in the fifth embodiment, various aberrations are satisfactorily corrected, and the imaging performance is excellent. As a result, by mounting the imaging lens PL5 of the fifth embodiment, excellent optical performance can be ensured even in the digital still camera CAM.

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

  Note that, in the above-described embodiment, the contents described below can be appropriately adopted without impairing the optical performance.

  In each of the above-described embodiments, the configuration including three lens components has been described as the imaging lens. However, the configuration is also applicable to other configurations such as a configuration including four lens components. For example, a configuration in which a weak power lens (for example, a negative lens) is added to the most object side or a configuration in which a weak power lens is added to the most image side may be used.

  In each of the above embodiments, the first lens component L1 is a single lens, but is not limited to this, and may be a cemented lens. Further, 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 is not limited thereto. 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 device C having the spherically curved imaging surface Ci so that the concave surface faces the object side is illustrated as the imaging device corresponding to the imaging lens PL, but the imaging device is not limited thereto. . For example, the imaging surface Ci of the imaging device C may be formed to be aspherically or elliptically curved so that the concave surface faces the object side.

  Further, each lens may be formed of a glass material, may be formed of a resin material, or may be 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 assembling adjustment are facilitated, and deterioration of optical performance due to errors in processing and assembling adjustment is prevented. Further, even when the image plane is displaced, it is preferable because there is little deterioration in the rendering performance. When the lens surface is aspherical, the aspherical surface is aspherical surface by grinding, a glass mold aspherical surface in which glass is formed into an aspherical shape with a mold, a composite type aspherical surface in which resin is formed in an aspherical shape on the surface of glass Any aspheric 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 arranged on the image side of the third lens component L3. However, the role 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.

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

  In the above-described embodiment, the digital still camera CAM in which the imaging lens PL and the camera body (the imaging device C) are integrally configured is used as the imaging system including the imaging lens PL. It is not something that can be done. 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 from each other may be used. Further, for example, a camera mounted on a portable terminal or the like may be used as an imaging system including the imaging lens PL. Further, 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 without using the liquid crystal monitor M or the operation member may be used.

CAM digital still camera (imaging system)
C imaging device (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)

An imaging lens having a spherical image surface curved with a concave surface facing the object side,
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 characterized by satisfying the following conditional expression.
0.88 <(N1 + N3) / (2 × N2) <1.00
1.79 <Nm <2.30
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 ;
Nm: average value of the average refractive index of the first lens component, the average refractive index of the second lens component, and the average refractive index of the third lens component. An imaging lens having a spherical image surface curved with a concave surface facing the object side,
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 characterized by satisfying the following conditional expression.
0.88 <(N1 + N3) / (2 × N2) <1.00
0.050 <d2 / d3 <0.440
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;
d2: center thickness of the second lens component,
d3: center thickness of the third lens component. An imaging lens having a spherical image surface curved with a concave surface facing the object side,
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. ,
All lens surfaces of the first lens component, the second lens component, and the third lens component are spherical,
An imaging lens characterized by 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.
0.050 <d2 / d3 <0.440
However,
d2: center thickness of the second lens component,
d3: center thickness of the third lens component. Said first lens component, said second lens component, and the claims 1 to all of the lens surface in the third lens component, characterized in that a spherical surface, in any one of claims 2, and claim 4 The imaging lens according to the above. At least one lens surface of the first lens component is an aspheric surface;
5. The imaging lens according to claim 1, wherein at least one lens surface in the third lens component is an aspheric surface. 6. 5. The imaging lens according to claim 1, wherein at least one of the lens surfaces of the second lens component is an aspherical surface. 6. The imaging lens according to any one of claims 1 to 7 , wherein an aperture stop is arranged on an image side of the third lens component. The imaging lens according to claim 8 , wherein a field stop is disposed on an image side of the aperture stop. The first lens component includes one positive lens,
The second lens component includes one negative lens,
The imaging lens according to any one of claims 1 to 9 , wherein the third lens component includes one positive lens. The first lens component includes one positive lens,
The second lens component includes one negative lens,
The imaging lens according to any one of claims 1 to 9 , wherein the third lens component includes one positive lens and one negative lens. An imaging lens that forms an image of an object on an imaging surface;
An imaging device that captures an image of the object formed 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.   13. The imaging system according to claim 12, wherein an optical low-pass filter for reducing moire or false color is not arranged between the imaging lens and the imaging device.   14. The imaging system according to claim 12, wherein the imaging lens and the imaging device are integrally formed.

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