JP2016061926A - Imaging lens and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new imaging lens that enables high performance and an increase in diameter.SOLUTION: An imaging lens comprises a first lens group G1 having positive refractive power, an aperture diaphragm S, and a second lens group G2 having positive or negative refractive power, which are arranged in order from an object side toward an image side. The first lens group G1 includes a first positive lens L11, a second positive lens L12, a negative lens L13, and a third positive lens L14, which are arranged in order from the object side toward the image side. The second lens group G2 includes a negative lens group G2N and a positive lens group G2P which are arranged in order from the object side toward the image side. An air space D1a between the first positive lens L11 and the second positive lens L12 of the first lens group G1 and a distance D1 on an optical axis from an object side lens surface of the first positive lens L11 to an image side lens surface of the third positive lens L14 of the first lens group satisfy a conditional expression: (1) 0.15<D1a/D1<0.50.SELECTED DRAWING: Figure 1

Description

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

  A so-called “industrial camera” has been widely put into practical use, and for example, development of an image input device for machine vision or the like is progressing.

  An imaging lens used in an image input device for machine vision is important to be able to form a high-definition image of an object (also called “work”) to be imaged for image input, and has excellent aberrations. It is desired to have high performance after being corrected.

  Further, it is desirable that the imaging lens is a “lens with a large aperture” so that a bright image is formed even when the “working distance” to the workpiece is large.

  This invention makes it a subject to implement | achieve the novel imaging lens which enabled high performance and large aperture.

The imaging lens according to the present invention includes, in order from the object side to the image side, a first lens group having a positive refractive power, an aperture stop, and a second lens group having a positive or negative refractive power, The first lens group includes, in order from the object side to the image side, a first positive lens, a second positive lens, a negative lens, and a third positive lens. The second lens group is arranged from the object side to the image side. The negative lens group and the positive lens group are arranged in order toward the air space between the first positive lens and the second positive lens of the first lens group: D1a, the object of the first positive lens of the first lens group. The distance D1 on the optical axis from the side lens surface to the image side lens surface of the third positive lens is a conditional expression:
(1) 0.15 <D1a / D1 <0.50
Satisfied.

  According to the present invention, it is possible to realize a novel imaging lens capable of high performance and a large aperture.

FIG. 3 is a diagram for explaining an imaging lens of Example 1. 6 is a diagram for explaining an imaging lens of Example 2. FIG. 6 is a diagram for explaining an imaging lens of Example 3. FIG. 6 is a diagram for explaining an imaging lens of Example 4. FIG. FIG. 6 is an aberration diagram in a state where the imaging lens of Example 1 is focused on an object at infinity. FIG. 6 is an aberration diagram in a state where focusing is performed on an object with an imaging magnification of −0.15 of the imaging lens of Example 1. FIG. 6 is an aberration diagram in a state in which an imaging lens of Example 1 is focused on an object with an imaging magnification of −0.3. FIG. 6 is an aberration diagram in a state where an imaging lens of Example 2 is focused on an object at infinity. FIG. 6 is an aberration diagram in a state in which an image forming magnification of the image forming lens of Example 2 is focused on an object of −0.15. FIG. 6 is an aberration diagram in a state in which an imaging lens of Example 2 focuses on an object with an imaging magnification of −0.3. FIG. 6 is an aberration diagram in a state where the imaging lens of Example 3 is focused on an object at infinity. FIG. 10 is an aberration diagram in a state in which an imaging lens of Example 3 is focused on an object with an imaging magnification of −0.15. FIG. 12 is an aberration diagram in a state where the imaging lens of Example 3 is focused on an object with an imaging magnification of −0.3. FIG. 10 is an aberration diagram in a state where the imaging lens of Example 4 is focused on an object at infinity. FIG. 12 is an aberration diagram in a state in which an imaging lens of Example 4 is focused on an object with an imaging magnification of −0.15. FIG. 10 is an aberration diagram in a state in which an imaging magnification of the imaging lens of Example 4 is focused on an object of −0.3. It is a figure for demonstrating the system of one Embodiment of an imaging device.

  1 to 4 show four embodiments of the imaging lens. These embodiments correspond to specific examples 1 to 4 described later in this order.

1 to 4, the left side of the figure is the “object side” and the right side of the figure is the “image side”.
1 to 4 are lens configuration diagrams in a state where the imaging lens is “focused at infinity”.

  In order to avoid complication, the reference numerals are shared in FIGS.

  In these drawings, reference numeral G1 indicates a “first lens group”, reference numeral G2 indicates a “second lens group”, and reference numeral S indicates an “aperture stop”.

Reference sign Im indicates an “image plane”.
The imaging lenses of these embodiments are assumed to “capture an image formed with an image sensor”, and in FIG. 1 to FIG. 4, a symbol CG indicates “a cover glass of the image sensor”.

  The cover glass CG has a “parallel plate shape”, and the light receiving surface of the image sensor matches the image plane Im.

  The cover glass CG has a function of shielding and protecting the light receiving surface of the image sensor, but can also have various filter functions such as an infrared cut filter.

  The first lens group G1 has “positive refractive power”, and the second lens group G2 has “positive or negative refractive power”.

Accordingly, the imaging lens whose embodiment is shown in FIGS. 1 to 4 includes, in order from the object side to the image side, a first lens group G1 having a positive refractive power, an aperture stop S, a positive or negative value. A second lens group G2 having refractive power is arranged.
The first lens group G1 includes a first positive lens L11, a second positive lens L12, a negative lens L13, and a third positive lens L14 in order from the object side to the image side.

  The second lens group includes a negative lens group G2N and a positive lens group G2P in order from the object side to the image side.

  1 to 4, the negative lens group G2N is composed of “two lenses L21 and L22”, and the positive lens group G2P is composed of “one lens L23”. ing.

  An imaging lens having a positive refractive power on the object side and a negative refractive power on the image side is called a “telephoto type”.

  "Telephoto type imaging lens" is generally considered to be "difficult to correct aberrations" because the refractive power distribution is positive and negative from the object side to the image side and not symmetrical. ing.

  In particular, it is considered difficult to correct “spherical aberration, coma aberration, and longitudinal chromatic aberration” that occur with an increase in aperture.

  The inventor increases the diameter of the first lens group by sequentially configuring the first lens group from the object side to the image side as described above from the first positive lens, the second positive lens, the negative lens, and the third positive lens. Acquired knowledge that it is possible to sufficiently correct spherical aberration, coma and axial chromatic aberration.

  The first lens group is an important group for correcting spherical aberration and coma aberration that occur with an increase in aperture because “the axial light beam is thick”.

  “Aberration” of “the object side surface of the first positive lens (first positive lens L11 in FIGS. 1 to 4) and the image side surface of the negative lens (negative lens L13 in FIGS. 1 to 4)” of the first lens group. "Interaction" contributes to correction of spherical aberration and coma.

  In order to make this contribution effective, it is important to “set appropriately the air gap D1a between the first positive lens and the second positive lens”.

  Conditional expression (1) indicates that an appropriate range of the air distance: D1a is set on the optical axis “from the object-side lens surface of the first positive lens to the image-side lens surface of the third positive lens” of the first lens group. Distance: D1 ”.

  The distance “D1” is also referred to as “the thickness of the first lens group” below.

  When the parameter of the conditional expression (1) is 0.50 or more, the air interval: D1a is excessively large relative to the thickness of the first lens group: D1, and the thickness and interval of the negative lens and the third positive lens are excessively small. It becomes.

  If the parameter of the conditional expression (1) is 0.15 or less, “aberration correction by exchanging aberrations between the object side surface of the first positive lens and the image side surface of the negative lens” becomes difficult.

  Therefore, “aberration correction in the first lens group” becomes difficult outside the range of the conditional expression (1).

By satisfying conditional expression (1), “good aberration correction in the first lens group” becomes possible,
It is possible to correct spherical aberration and coma in the entire system.

  The imaging lens of the present invention satisfies the conditional expression (1) and any one or more of the following conditional expressions (2), (6), (7), (8), and (9) in the above configuration. It is preferable.

(2) 0.2 <D1b / D1 <0.6
(6) 0.25 <(R11−R32) / (R11 + R32) <0.45
(7) 0.1 <(R41−R32) / (R41 + R32) <0.3
(8) 0.1 <(R21−R32) / (R21 + R32) <0.3
(9) 0.4 <D2a / D2 <0.7
The meaning of each symbol of the parameter under these conditions is as follows.

  “D1b” is the distance between the object side surface of the second positive lens and the image side surface of the negative lens in the first lens group, and “D1” is the thickness of the first lens group.

  “R11” is the radius of curvature of the object side surface of the first positive lens of the first lens group, and “R32” is the radius of curvature of the image side lens surface of the negative lens of the first lens group.

  “R21” is the radius of curvature of the object side surface of the second positive lens of the first lens group, and “R41” is the radius of curvature of the object side surface of the third positive lens of the first lens group.

  “D2a” is an air space between the negative lens group and the positive lens group of the second lens group.

  “D2” is a distance on the optical axis from the most object side lens surface of the negative lens group to the most image side lens surface of the positive lens group in the second lens group. The distance: D2 is also referred to as “the thickness of the second lens group” below.

  The “object side surface of the second positive lens and the image side surface of the negative lens” of the first lens group also exchange aberrations, and an appropriate setting of the distance D1b between these surfaces is within the first lens group. This is important for aberration correction.

  When the parameter of the conditional expression (2) is 0.6 or more, the distance between the object side surface of the second positive lens and the image side surface of the negative lens becomes “relatively large” with respect to the thickness of the first lens group. The thickness of the first positive lens and the third positive lens and the distance between the lenses are too small.

  When the parameter of the conditional expression (2) is 0.2 or less, the contribution of “aberration correction by exchanging aberration between the object side surface of the second positive lens and the image side surface of the negative lens” becomes small.

  Therefore, outside the range of the conditional expression (2), the aberration correction at the “object side surface of the second positive lens and the image side surface of the negative lens” can be effectively contributed to “aberration correction in the first lens group”. It becomes difficult.

  By satisfying conditional expression (2), it becomes possible to perform better aberration correction in the first lens group.

The object side surface of the first positive lens and the image side surface of the negative lens also exchange aberrations.
By determining the magnitude relationship between the curvature radii of these surfaces so that the conditional expression (6) is satisfied, the exchange of aberrations between these surfaces can be effectively contributed to the aberration correction of the entire system.

  Outside the range of the conditional expression (6), the balance of the magnitude relationship between the curvature radii of the object side surface of the first positive lens and the image side surface of the negative lens is lost, and it is difficult to make an effective contribution to the aberration correction of the entire system.

  The image side surface of the negative lens and the object side surface of the third positive lens of the first lens group also contribute to aberration correction of the entire system through the exchange of aberrations.

  By determining the magnitude relationship between the radii of curvature of these surfaces so that the conditional expression (7) is satisfied, the exchange of aberrations between these surfaces can be effectively contributed to the aberration correction of the entire system.

  Outside the range of conditional expression (7), the balance of the magnitude relationship between the curvature radii of the object side surface of the third positive lens and the image side surface of the negative lens is lost, and it is difficult to make an effective contribution to the aberration correction of the entire system.

  The object side surface of the second positive lens and the image side surface of the negative lens in the first lens group also contribute to aberration correction of the entire system through the exchange of aberrations.

  By determining the magnitude relationship between the curvature radii of these surfaces so that the conditional expression (8) is satisfied, the exchange of aberrations between these surfaces can be effectively contributed to the aberration correction of the entire system.

  Outside the range of conditional expression (8), the balance of the magnitude relationship between the curvature radii of the object side surface of the second positive lens and the image side surface of the negative lens is lost, making it difficult to make an effective contribution to aberration correction of the entire system.

The above conditional expressions (1), (2), (6) to (8) are conditions related to the first lens group.
Conditional expression (9) relates to the second lens group, and a suitable magnitude relationship between the air gap: D2a between the negative lens group and the positive lens group of the second lens group: D2a and the thickness of the second lens group: D2. It stipulates.

  Within the range of conditional expression (9), it becomes easy to correct various aberrations while reducing the angle of incidence on the image plane.

  The second lens group includes a “negative lens group” disposed on the object side and a “positive lens group” disposed on the image side.

  The “negative lens group” can be composed of a single negative lens, but can also be composed of a plurality of lenses. The negative lens group can be composed of “two lenses, a positive lens and a negative lens”.

  In the embodiment shown in FIGS. 1 to 4, the negative lens group includes two lenses, a positive lens L21 and a negative lens L22, and the two lenses L21 and L22 are cemented.

  The “positive lens group” can be configured by one positive lens L23 as in the embodiment shown in FIGS. 1 to 4, but is not limited thereto.

  Also in the first lens group, the positive lens L12 and the negative lens L13 are cemented in the embodiment shown in FIGS. By joining these two lenses L12 and L13, the relative decentration of the positive lens L12 and the negative lens L13 can be suppressed.

  In any of the above cases, of the four lenses constituting the first lens group, at least one of the two positive lenses on the object side (first positive lens, second positive lens) It is preferable to use a material that satisfies the conditional expressions (3) to (5).

_{(3) 1.45 <n d <} 1.65
(4) 60.0 <ν _d <95.0
(5) 0.005 <P _{g, F} − (− 0.001802 × ν _d +0.6483)
<0.050.

“N _d ”, “ν _d ”, and “P _{g, F} ” are the refractive index, Abbe number, and partial dispersion ratio of the lens material with respect to the d-line, respectively.

Partial dispersion ratio, the lens material of the g-line, F-line, the refractive index for the C _line: n _g, n F, the _{n C,
P g, F = (n g} -n F) / (n F -n C)
Defined by

  The first positive lens and the second positive lens in the first lens group are lenses that are important for correcting axial chromatic aberration because “the axial marginal ray passes through a high position” and satisfy the conditions (3) to (5). By using such “glass type having anomalous dispersion”, sufficient correction of axial chromatic aberration is facilitated.

  Of course, one or more special surfaces such as an aspherical surface and a diffractive surface can be adopted for the imaging lens of the present invention, but all lens surfaces can be formed of spherical surfaces.

  By not using a special surface such as an aspherical surface or a diffractive surface, for example, it is possible to avoid the occurrence of a “large manufacturing cost” such as a mold for molding, and this is advantageous in terms of cost especially in the production of a small lot.

  In addition, it is preferable that the materials of the lenses constituting the imaging lens are all “inorganic solid materials”. Lenses made of organic materials or “organic-inorganic hybrid materials” have a large change in characteristics due to environmental conditions such as temperature and humidity.

By forming all the lenses that make up the imaging lens from an “inorganic solid material,” temperature and
An imaging lens that is less susceptible to changes in environmental conditions such as humidity can be realized.

"Example"
Examples 1 to 4 will be described below as specific examples of the imaging lens whose embodiments are shown in FIGS.

  The imaging lens of Examples 1 to 4 is assumed to be used in an “image input device for machine vision”, and is a telescopic imaging lens that is easy to secure a working distance and is not easily affected by a perspective. is there.

  The “working distance” is a working distance, and is a distance from the object surface of the “work” that is an object to be imaged for image input to the tip of the lens.

  As shown in FIGS. 1 to 4 in which the reference numerals are shared, the imaging lens includes a first lens group G1, an aperture stop S, and a second lens group G2 from the object side to the image side.

  The first lens group G1 is configured by sequentially arranging four lenses of a first positive lens L11, a second positive lens L12, a negative lens L13, and a third positive lens L14 from the object side to the image side.

  In all of Examples 1 to 4, the second positive lens L12 and the negative lens L13 are cemented.

  The second lens group G2 disposed on the image side of the aperture stop S includes a negative lens group G2N and a positive lens group G2P sequentially from the object side to the image side.

  The negative lens group G2N includes a positive lens L21 and a negative lens L22. In each of Examples 1 to 4, the positive lens L21 and the negative lens L22 are cemented.

  The positive lens group G2P is composed of one positive lens L23 in each of Examples 1 to 4.

  In each of Examples 1 to 4, the imaging lens is composed of seven lenses, and these seven lenses are all “spherical lenses” and are formed of “inorganic solid material”.

  In all of Examples 1 to 4, the “maximum image height is 8.0 mm”.

  In each embodiment, the parallel plate-like cover glass CG disposed on the image plane side of the second lens group G2 is disposed such that the image side surface is located at a position of about 1.0 mm from the image plane Im to the object side. Of course, this is not a limitation.

  In addition, in each of the imaging lenses of Examples 1 to 4, the first lens group G1 is moved toward the object side during focusing from an infinitely distant object to a close object, and the second lens group G2 is moved to the image plane Im. It is fixed against.

  At the time of focusing, the aperture stop S is also fixed with respect to the image plane Im.

  The aperture stop S may be moved integrally with the first lens group G1 during focusing. However, if the aperture stop S is fixed, the moving mechanism for focusing can be simplified, and the amount of extension of the first lens group can be easily reported. is there.

  The meanings of symbols in each embodiment are as follows.

f: Focal length of the entire system (focal length when focusing on an object at infinity)
F: F number
2ω: Angle of view (angle of view when focused at infinity)
R: radius of curvature
D: Face spacing
N: Refractive index (“n _d ” in the above description)
ν: Abbe number (“ν _d ” in the above explanation)
φ: Effective beam diameter.

  The unit of quantity having a length dimension is “mm” unless otherwise specified.

  The first example given first is a specific example of the imaging lens shown in FIG.

"Example 1"
f = 75.0mm, F = 2.83, 2ω = 12.2 degrees
The data of Example 1 is shown in Table 1.

  The left column of Table 1 shows the face plate numbers counted from the object side.

  Of course, the “aperture” in the above data is an “aperture stop”.

"Variable interval"
The variable interval is the interval between the first lens group and the aperture stop (“D7” in the above data).

  Focusing on an object at infinity (displayed as Inf), Focusing on an object (workpiece) whose imaging magnification is -0.15 times (displayed as x0.15), Imaging magnification is -0.3 times The value of “D7” in the state of focusing on the object (displayed as × 0.3) is shown.

  The same applies to the following other embodiments.

  Table 2 shows the variable interval data.

"Parameter values for conditional expressions"
Table 3 shows the parameter values of the conditional expressions in Example 1.

  In Table 3, “L1” indicates the first positive lens of the first lens group, and “L2” indicates the second positive lens. The same applies to Examples 2 to 4 below.

  The following Example 2 is a specific example of the imaging lens shown in FIG.

"Example 2"
f = 75.0mm, F = 2.80, 2ω = 12.2 degrees
The data of Example 2 is shown in Table 4.

"Variable interval"
Table 5 shows the variable interval data.

"Parameter values for conditional expressions"
Table 6 shows the parameter values of the conditional expressions in Example 2.

  The following Example 3 is a specific example of the imaging lens shown in FIG.

"Example 3"
f = 75.0mm, F = 2.85, 2ω = 12.2 degrees
The data of Example 3 is shown in Table 7.

"Variable interval"
Table 8 shows the variable interval data.

"Parameter values for conditional expressions"
Table 9 shows the parameter values of the conditional expressions in Example 3.

  Example 4 given at the end is a specific example of the imaging lens shown in FIG.

Example 4
f = 75.0mm, F = 2.82, 2ω = 12.2 degrees
The data of Example 4 is shown in Table 10.

"Variable interval"
Table 11 shows the variable interval data.

"Parameter values for conditional expressions"
Table 12 shows the parameter values of the conditional expressions in Example 4.

5 to 7 are aberration curve diagrams of the imaging lens of Example 1. FIG.
FIG. 5 is an aberration curve diagram in a state where the imaging lens of Example 1 is focused on an object at infinity.

  FIG. 6 is an aberration diagram in a state where focusing is performed on an “object whose imaging magnification is −0.15 times”, and FIG. 7 is an aberration in a state where focusing is performed on an “object whose imaging magnification is −0.3 times”. FIG.

8 to 10 are aberration curve diagrams of the imaging lens of Example 2. FIG.
FIG. 8 is an aberration curve diagram when the imaging lens of Example 2 is “focused on an object at infinity”.

  FIG. 9 is an aberration diagram in a state of focusing on an “object whose imaging magnification is −0.15 times”, and FIG. 10 is an aberration in a state of focusing on an “object whose imaging magnification is −0.3 times”. FIG.

11 to 13 show aberration curve diagrams of the imaging lens of Example 3. FIG.
FIG. 11 is an aberration curve diagram of the imaging lens of Example 3 in a “state focused on an object at infinity”.

  FIG. 12 is an aberration diagram in a state where focusing is performed on an “object whose imaging magnification is −0.15 times”, and FIG. 13 is an aberration in a state where focusing is performed on an “object whose imaging magnification is −0.3 times”. FIG.

FIGS. 14 to 16 show aberration curve diagrams of the imaging lens of Example 4. FIGS.
FIG. 14 is an aberration curve diagram of the imaging lens of Example 4 in a “state focused on an object at infinity”.

  FIG. 15 is an aberration diagram in a state of focusing on an “object whose imaging magnification is −0.15 times”, and FIG. 16 is an aberration in a state of focusing on an “object whose imaging magnification is −0.3 times”. FIG.

  In these aberration diagrams, the broken line in the “spherical aberration” diagram represents the “sine condition”, the solid line in the “astigmatism” diagram represents “sagittal”, and the broken line represents “meridional”.

  The thin line is an aberration curve with respect to “d line” and the thick line is “g line”.

  In each embodiment, the aberration is corrected at a high level, and the spherical aberration and the longitudinal chromatic aberration are so small as not to be a problem. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion is 0.5% or less in absolute value.

  In addition, “aberration fluctuation” in a state in which an object at infinity is focused, an object in which the imaging magnification is −0.15 times, an object in which the imaging magnification is −0.3 times is focused Very small.

  In other words, each of the imaging lenses of Examples 1 to 4 has a two-lens group configuration and realizes an imaging lens with little change in performance due to focusing.

  That is, according to the present invention, astigmatism, curvature of field, lateral chromatic aberration, color difference of coma aberration, distortion, etc. are sufficient with an angle of view of about 12 degrees, an F number of about 2.8, and a number of lenses of about 7. It is possible to realize an imaging lens reduced to a very low level.

  This imaging lens has “resolving power corresponding to an image sensor with 6 to 10 million pixels” and does not cause point image distortion from the full aperture to the periphery of the angle of view with high contrast.

  Therefore, this imaging lens is “capable of describing straight lines as straight lines without distortion”, and has high performance from a infinity object to a short distance object with a magnification of 0.3 times or more with a simple configuration.

  An example of a “machine vision image input device” system using an imaging device will be described with reference to FIG.

  This “system” performs product inspection. The workpiece WK as an inspection target is conveyed to the right side of the drawing by the conveyor 30, and the workpiece WK is imaged by the imaging device 10 and an image is input.

  The imaging device 10 uses the imaging lens according to any one of claims 1 to 10, specifically, for example, one shown in any one of the first to fourth embodiments.

  The control means 20 configured as a computer or a CPU controls the driving of the conveyor 30 and the blinking of the illumination device 20, and also controls the focusing of the imaging lens and the acquisition of an image by the imaging device.

Products of various sizes are inspected as workpieces WK.
The control unit 20 specifies an appropriate working distance (imaging magnification) according to the size of the workpiece WK, and controls focusing of the imaging lens according to the specified working distance.

  As described above, according to the present invention, a novel imaging lens and an imaging apparatus using the same can be realized as follows.

[1]
A first lens group G1 having a positive refractive power, an aperture stop S, and a second lens group G2 having a positive or negative refractive power are arranged in order from the object side to the image side. Includes a first positive lens L11, a second positive lens L12, a negative lens L13, and a third positive lens L14 in order from the object side to the image side, and the second lens group 2G has an image from the object side. A negative lens group G2N and a positive lens group G2P are arranged in order toward the side, and an air space between the first positive lens L11 and the second positive lens L12 of the first lens group G1: D1a, and the first lens group G1. The distance D1 on the optical axis from the object side lens surface of the first positive lens L11 to the image side lens surface of the third positive lens L14 is a conditional expression:
(1) 0.15 <D1a / D1 <0.50
An imaging lens that satisfies the requirements.

[2]
In the imaging lens according to [1], the distance between the object side surface of the second positive lens L12 and the image side surface of the negative lens L13 in the first lens group: D1b, and the third positive side from the object side lens surface of the first positive lens L11. The distance on the optical axis: D1 to the image side lens surface of the lens L14 is a conditional expression:
(2) 0.2 <D1b / D1 <0.6
An imaging lens that satisfies the requirements.

[3]
In the imaging lens according to [1] or [2], the refractive index of the lens material for d-line: n _d , Abbe number: ν _d , and the refractive index for g-line, F-line, and C-line: _ng By n _F and n _C , the following formula:
_{P g, F = (n g} -n F) / (n F -n C)
The partial dispersion ratio defined by: _{Pg, F} is a conditional expression for at least one of the first positive lens L11 and the second positive lens L12 of the first lens group:
_{(3) 1.45 <n d <} 1.65
(4) 60.0 <ν _d <95.0
(5) 0.005 <P _{g, F} − (− 0.001802 × ν _d +0.6483)
<0.050
An imaging lens that satisfies the requirements.

[4]
In the imaging lens according to any one of [1] to [3], the radius of curvature of the object side surface of the first positive lens L11 of the first lens group: R11, the image side lens of the negative lens L13 of the first lens group The radius of curvature of the surface: R32 is the conditional expression:
(6) 0.25 <(R11−R32) / (R11 + R32) <0.45
An imaging lens that satisfies the requirements.

[5]
In the imaging lens described in any one of [1] to [4], the radius of curvature of the image side surface of the negative lens L13 of the first lens group: R32, and the radius of curvature of the object side surface of the third positive lens L14: R41. Conditional expression:
(7) 0.1 <(R41−R32) / (R41 + R32) <0.3
An imaging lens that satisfies the requirements.

[6]
In the imaging lens according to any one of [1] to [5], the radius of curvature of the object side surface of the second positive lens L12 of the first lens group: R21, the image side surface of the negative lens L13 of the first lens group. Radius of curvature: R32 is a conditional expression:
(8) 0.1 <(R21−R32) / (R21 + R32) <0.3
An imaging lens that satisfies the requirements.

[7]
In the imaging lens according to any one of [1] to [6], an air space: D2a between the negative lens group G2N and the positive lens group G2P of the second lens group 2G, and the negative lens group G2N of the second lens group The distance D2 on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the positive lens group G2P is a conditional expression:
(9) 0.4 <D2a / D2 <0.7
An imaging lens that satisfies the requirements.

[8]
In the imaging lens according to any one of [1] to [7], the negative lens group G2N of the second lens group 2G is configured by a cemented lens of a positive lens L21 and a negative lens L22, and the positive lens group G2P is 1 An imaging lens composed of a single positive lens L23.

[9]
The imaging lens according to any one of [1] to [8], wherein all the lenses constituting the first lens group G1 and the second lens group G2 are spherical lenses.

[10]
The imaging lens according to any one of [1] to [9], wherein all lenses constituting the first lens group G1 and the second lens group G2 are made of an inorganic solid material.

[11]
[1] An imaging apparatus having the imaging lens according to any one of [10].

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above, and the invention described in the claims unless otherwise specified in the above description. Various modifications and changes are possible within the scope of the above.

  In other words, the imaging lens of the present invention can be used not only for the image input device for machine vision but also for a digital camera, a video camera, a surveillance camera, and the like.

  The effects described in the embodiments of the present invention are merely a list of suitable effects resulting from the invention, and the effects of the present invention are not limited to those described in the embodiments.

G1 first lens group
L11 1st positive lens
L12 2nd positive lens
L13 negative lens
L14 3rd positive lens
S Aperture stop
G2 second lens group
G2N negative lens group
G2P positive lens group
L21 positive lens
L22 negative lens
L23 positive lens
CG Photo detector cover glass
Im image plane
10 Imaging device
12 Lighting equipment
20 Control means
30 conveyor
WK work

Claims (11)

In order from the object side to the image side, a first lens group having a positive refractive power, an aperture stop, and a second lens group having a positive or negative refractive power are arranged.
The first lens group includes, in order from the object side to the image side, a first positive lens, a second positive lens, a negative lens, and a third positive lens.
The second lens group includes a negative lens group and a positive lens group in order from the object side to the image side.
Air distance between the first positive lens and the second positive lens of the first lens group: D1a, light from the object side lens surface of the first positive lens to the image side lens surface of the third positive lens of the first lens group The distance on the axis: D1 is the conditional expression:
(1) 0.15 <D1a / D1 <0.50
An imaging lens that satisfies the requirements. The imaging lens according to claim 1.
Distance between the object side surface of the second positive lens and the image side surface of the negative lens in the first lens group: D1b, on the optical axis from the object side lens surface of the first positive lens to the image side lens surface of the third positive lens Distance: D1 is a conditional expression:
(2) 0.2 <D1b / D1 <0.6
An imaging lens that satisfies the requirements. The imaging lens according to claim 1 or 2,
The refractive index of the lens material with respect to d-line: n _d , Abbe number: ν _d , and the refractive index with respect to g-line, F-line, and C-line: n _g , n _F , n _{C
P g, F = (n g} -n F) / (n F -n C)
The partial dispersion ratio defined by: _{Pg, F} is a conditional expression for at least one of the first positive lens and the second positive lens of the first lens group:
_{(3) 1.45 <n d <} 1.65
(4) 60.0 <ν _d <95.0
(5) 0.005 <P _{g, F} − (− 0.001802 × ν _d +0.6483)
<0.050
An imaging lens that satisfies the requirements. The imaging lens according to any one of claims 1 to 3,
The radius of curvature of the object side surface of the first positive lens of the first lens group: R11, and the radius of curvature of the image side lens surface of the negative lens of the first lens group: R32 are conditional expressions:
(6) 0.25 <(R11−R32) / (R11 + R32) <0.45
An imaging lens that satisfies the requirements. The imaging lens according to any one of claims 1 to 4,
The radius of curvature of the image side surface of the negative lens of the first lens group: R32, and the radius of curvature of the object side surface of the third positive lens: R41 are conditional expressions:
(7) 0.1 <(R41−R32) / (R41 + R32) <0.3
An imaging lens that satisfies the requirements. The imaging lens according to any one of claims 1 to 5,
The radius of curvature of the object side surface of the second positive lens of the first lens group: R21, and the radius of curvature of the image side surface of the negative lens of the first lens group: R32 are conditional expressions:
(8) 0.1 <(R21−R32) / (R21 + R32) <0.3
An imaging lens that satisfies the requirements. The imaging lens according to any one of claims 1 to 6,
Air distance between the negative lens group and the positive lens group of the second lens group: D2a, on the optical axis from the lens surface closest to the object side of the negative lens group to the lens surface closest to the image side of the positive lens group Distance D2 is a conditional expression:
(9) 0.4 <D2a / D2 <0.7
An imaging lens that satisfies the requirements. The imaging lens according to any one of claims 1 to 7,
An imaging lens in which the negative lens group of the second lens group is composed of a cemented lens of a positive lens and a negative lens, and the positive lens group is composed of one positive lens. The imaging lens according to any one of claims 1 to 8,
An imaging lens in which all lenses constituting the first lens group and the second lens group are spherical lenses. The imaging lens according to any one of claims 1 to 9,
An imaging lens in which the materials of all the lenses constituting the first lens group and the second lens group are inorganic solid materials.   An imaging apparatus having the imaging lens according to claim 1.

Images