JP2016061902A - Imaging lens and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new imaging lens composed of two lens groups and having less variation of performance in association with focusing.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. During focusing from an object at infinity to an object at a close distance, the second lens group G2 is fixed to an image surface Im, and the first lens group G1 moves to the object side as a unit. A focal length f1 of the first lens group and a focal length f of an entire system in a state of focusing on the object at infinity satisfy a conditional expression: (1) 0.50<f1/f<0.90.SELECTED DRAWING: Figure 1

Description

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

  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.

  It is important that an imaging lens used in an image input apparatus for machine vision is stable with little change in lens performance due to focusing.

  An optical system described in Patent Document 1 is known as an optical system that suppresses fluctuations in lens performance caused by focusing.

  The optical system (lens system) described in Patent Document 1 includes a first lens unit having a positive refractive power and a second lens unit having a positive or negative refractive power.

Then, in order from the object side to the image side, the first lens unit including the lens unit 1a having a positive refractive power, the aperture stop, and the lens unit 1b having a positive refractive power moves to the object side.
Focusing from an infinite object to a close object is performed.

  It is an object of the present invention to realize a novel imaging lens having a two-lens group configuration and little change in performance due to focusing.

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 first lens group, and the second lens group is fixed with respect to the image plane during focusing from an object at infinity to a short distance object. Moves as a unit to the object side, the focal length of the first lens unit is f1, and the focal length of the entire system in a state of focusing on an object at infinity: f is a conditional expression:
(1) 0.50 <f1 / f <0.90
Satisfied.

  According to the present invention, it is possible to realize a novel imaging lens having a two-lens group configuration and little change in performance due to focusing.

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.
In “focusing from an infinitely distant object to a close object”, the second lens group G2 is fixed with respect to the image plane Im, and the first lens group G1 is moved integrally to the object side.

  That is, at the time of focusing, the “positional relationship between the second lens group G2 and the image plane Im” is kept unchanged, and the distance between the first lens group G1 and the second lens group G2 changes.

  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.

  In addition, when focusing from an infinite object to a short-distance object is performed simply by “total extension” on the object side with positive refractive power, various aberrations will occur due to changes in the object distance of the object to be focused. Will occur.

  That is, in the telephoto type imaging lens, the lens performance is likely to change with focusing.

  The inventor has found that the above-mentioned “difficulty of aberration correction” and “variation in lens performance due to focusing” can be effectively reduced by devising the configuration of the imaging lens.

  In the imaging lens of the present invention, as described above, the first lens group having a positive refractive power is sequentially moved from the object side to the image side, the first positive lens L11, the second positive lens L12, the negative lens L13, A third positive lens L14 is arranged.

  By configuring the first lens group in this way, it is possible to sufficiently correct “spherical aberration, coma aberration, and axial chromatic aberration” that occur when the positive lens L11 has a large aperture.

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

  By configuring the second lens group in such a manner, “sufficient correction of various aberrations while reducing the incident angle to the image plane” becomes possible.

  When focusing from an object at infinity to a near object, the second lens group is fixed with respect to the image plane, and the first lens group is moved to the object side.

  In such a configuration, the amount of movement of the first lens group by focusing can be reduced by shortening the focal length f1 of the first lens group, and focusing can be achieved by fixing the second lens group with respect to the image plane. The mechanism for can be simplified.

  Conditional expression (1) is a condition under which various aberrations can be corrected satisfactorily and fluctuations in lens performance accompanying focusing can be effectively suppressed.

  When the parameter of conditional expression (1) is 0.5 or less, the positive refractive power of the first lens group becomes excessive, and large aberrations are likely to occur in the first lens group, and the aberrations generated in the first lens group are the first. Since the magnification is increased by the two lens groups, it is difficult to correct aberrations of the entire system.

  When the parameter of the conditional expression (1) is 0.9 or more, the entire system of the imaging lens is easily increased in size to achieve focusing up to a high magnification.

The parameter of the conditional expression (1) is more preferably the following conditional expression that is slightly narrower than the conditional expression (1):
(1A) 0.55 <f1 / f <0.75
Good to be satisfied.

  The aperture stop disposed between the first and second lens groups can realize sufficient performance even when “moving integrally with the first lens group” or “fixed to the image plane” during focusing.

  However, when focusing from an object at infinity to an object at close distance, if the aperture stop is "fixed to the image plane together with the second lens group", the focusing mechanism can be simplified and the feed amount can be easily secured. become.

  Therefore, it becomes easy to achieve both miniaturization of the imaging lens and “focusing to a high magnification”.

The imaging lens has a conditional expression (1) in the above configuration in order to more effectively suppress the “change in lens performance due to focusing” in a relatively low magnification region where the imaging magnification is about −0.15 times. Conditional expression:
(2) 0.03 <M1 / f <0.10
Good to be satisfied.

  “M1” in the parameter of the conditional expression (2) is an amount of movement of the first lens unit when focusing from an object at infinity to an “object whose imaging magnification is −0.15 times”, and “f” is This is the focal length of the entire system when focusing on an object at infinity.

  When the parameter of the conditional expression (2) is 0.03 or less, the refractive power of the first lens group becomes relatively excessive with respect to the refractive power of the entire system, and a large aberration tends to occur in the first lens group. Since the generated aberration is magnified by the second lens group, it is difficult to satisfactorily correct the aberration of the entire system.

  If the parameter of the conditional expression (2) exceeds 0.10, the “movement distance of the first lens unit accompanying focusing” becomes large in the low magnification region, the focusing mechanism becomes large, and the imaging lens tends to be large. .

The parameter of the conditional expression (2) is more preferably the following conditional expression that is slightly narrower than the conditional expression (2):
(2A) 0.04 <M1 / f <0.08
Good to be satisfied.

The imaging lens has a conditional expression (1) in the above configuration in order to more effectively suppress the “change in lens performance due to focusing” in a relatively high magnification region where the imaging magnification is about −0.3 times. Or conditional expressions (1) and (2) together with conditional expressions:
(3) 0.10 <M2 / f <0.15
Good to be satisfied.

  “M2” in the parameter of the conditional expression (3) is a moving amount of the first lens unit when focusing from an object at infinity to an “object whose imaging magnification is −0.3 times”, and “f” is This is the focal length of the entire system when focusing on an object at infinity.

  When the parameter of the conditional expression (3) is 0.10 or less, the refractive power of the first lens group becomes relatively excessive with respect to the refractive power of the entire system, and a large aberration tends to occur in the first lens group. Since the generated aberration is magnified by the second lens group, it is difficult to satisfactorily correct the aberration of the entire system.

  If the parameter of the conditional expression (3) exceeds 0.15, the “movement distance of the first lens unit accompanying focusing” becomes large in a high magnification region, the focusing mechanism becomes large, and the imaging lens tends to be large. .

  If conditional expressions (2) and (3) are satisfied together with conditional expression (1), imaging magnification: from a low magnification region of about -0.15 times to imaging magnification: about -0.3 times It is possible to perform favorable focusing while suppressing fluctuations in lens performance up to the region.

  The imaging lens preferably satisfies the following conditional expression (4) together with conditional expression (1) or conditional expression (1) and “at least one of conditional expressions (2) and (3)”.

(4) 0.4 <D2a / D2 <0.7
In the parameter of the conditional expression (4), “D2a” is an air space between the negative lens group and the positive lens group constituting the second lens group, and “D2” is “most object side of the negative lens group in the second lens group”. Is the distance on the optical axis from the lens surface to the most image side lens surface of the positive lens unit.

  Hereinafter, this distance: D2 is also referred to as “thickness of the second lens group”.

  Within the range of conditional expression (4), 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 constituted by one positive lens L23 as in the embodiment of FIGS. 1 to 4, but it is of course not limited thereto.

  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 (5) to (7).

_{(5) 1.45 <n d <} 1.65
(6) 60.0 <ν _d <95.0
(7) 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

  In the first positive lens and the second positive lens of the first lens group, “the axial marginal ray passes through a high position”, it is an important lens for correcting the longitudinal chromatic aberration, and satisfies the conditions (5) to (7). By using such “glass type having anomalous dispersion”, sufficient correction of axial chromatic aberration is facilitated.

The imaging lens preferably satisfies the following conditional expression (8) in any of the various cases described above.
(8) 0.2 <D1a / D1 <0.5.

  “D1a” in the parameters is the air space between the first positive lens and the second positive lens, and “D1” is the distance from the object side surface of the first positive lens to the image side surface of the third positive lens in the first lens group. The distance on the optical axis, and this distance is also referred to as “the thickness of the first lens group” below.

  In the first lens group, aberration is exchanged between the object side surface of the first positive lens and the image side surface of the negative lens.

  Therefore, by appropriately setting the distance between the first positive lens and the second positive lens (= D1a), it becomes easy to sufficiently correct spherical aberration and coma aberration that occur with an increase in the diameter of the imaging lens.

  When the parameter of the conditional expression (8) is 0.2 or less, it is difficult to correct aberrations on the object side surface of the first positive lens and the image side surface of the negative lens L that are performing “aberration exchange”. Intragroup aberration correction tends to be difficult.

  When the parameter of the conditional expression (8) is 0.5 or more, the interval between the first positive lens and the second positive lens is increased, and the thickness and the interval of the other lenses are decreased. The aberration correction is likely to be difficult.

  As the imaging lens used in the above-mentioned “image input apparatus for machine vision”, a working distance of about 10 degrees is conceivable as a telephoto lens that is easy to secure a working distance and is not easily influenced by the perspective.

  Conditional expressions (5) to (7) are effective in suppressing the occurrence of chromatic aberration in such an imaging lens having an angle of view of about 10 degrees.

  The “working distance” is a working distance, which is a distance from an object plane of a target object (also referred to as “work”) to be imaged for image input to the tip of the lens.

  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 molding die.

  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 constituting the imaging lens from an “inorganic solid material”, it is possible to realize an imaging lens that is not easily affected by changes in environmental conditions such as temperature and humidity.

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

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

  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.

  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 in Table 1 is the surface number counted from the object side. The same applies to Examples 2 and below. 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.

  “L1” in Table 3 represents the first positive lens L11 in the first lens group, and “L2” represents the second positive lens L12 in the first lens group. The same applies to the following embodiments.

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

"Example 2"
f = 75.0mm, F = F2.80, 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 = F2.82, 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 when the imaging lens of Example 1 is focused on an object at infinity, and FIG. 6 is an aberration diagram when the imaging lens is focused on an object with an imaging magnification of −0.15 times. FIG. 7 is an aberration diagram in a state where focusing is performed on an object whose imaging magnification is −0.3 times.

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, and FIG. 9 is an aberration diagram when the imaging lens is focused on an object with an imaging magnification of −0.15 times. FIG. 10 is an aberration diagram in a state where focusing is performed on an object whose imaging magnification is −0.3 times.

11 to 13 show aberration curve diagrams of the imaging lens of Example 3. FIG.
11 is an aberration curve diagram when the imaging lens of Example 3 is focused on an object at infinity, and FIG. 12 is an aberration diagram when the imaging lens is focused on an object whose imaging magnification is −0.15 times. FIG. 13 is an aberration diagram in a state where focusing is performed on an object whose imaging magnification is −0.3 times.

FIGS. 14 to 16 show aberration curve diagrams of the imaging lens of Example 4. FIGS.
FIG. 14 is an aberration curve diagram when the imaging lens of Example 4 is focused on an object at infinity, and FIG. 15 is an aberration diagram when focused on an object whose imaging magnification is −0.15 times. FIG. 16 is an aberration diagram in a state where focusing is performed on an object whose imaging magnification is −0.3 times.

  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, the variation of the aberration diagram in the state of focusing on an object at infinity, the state of focusing on an object with an imaging magnification of -0.15 times, and the state of focusing on an object with an imaging magnification of -0.3 times is extremely large. small.

  In other words, each of the imaging lenses of Examples 1 to 4 has a two-lens group configuration and realizes a novel 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 has a resolution that is compatible with an image sensor with 6 to 10 million pixels, and it can draw a straight line with no distortion from the full aperture to the high contrast and the periphery of the angle of view. With a simple configuration, it is possible to realize a high-performance imaging lens from an object at infinity to a short distance object with a magnification of 0.3 times or more.

  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.

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

  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 12 and performs “focusing of the imaging lens and image acquisition by the imaging device” in the imaging device 10. Control.

  Products of various sizes are to be inspected as the workpiece WK, and the control means 20 identifies an appropriate working distance (imaging magnification) according to the size of the workpiece WK, and forms an image according to the identified working distance. Controls the focusing of the lens.

  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 G2 includes an image from the object side. The negative lens group G2N and the positive lens group G2P are arranged in order toward the side, and the second lens group G2 is fixed with respect to the image plane Im during focusing from an object at infinity to a short distance object. The first lens group G1 moves as a unit to the object side, the focal length of the first lens group G1 is f1, and the focal length of the entire system in a state of focusing on an object at infinity: f is a conditional expression:
(1) 0.50 <f1 / f <0.90
An imaging lens that satisfies the requirements.

[2]
[1] The imaging lens according to [1], wherein the aperture stop S is fixed with respect to the image plane Im together with the second lens group G2 when focusing from an object at infinity to an object at a short distance.

[3]
In the imaging lens according to [1] or [2], the amount of movement of the first lens unit when focusing from an infinite object to an object having an imaging magnification of -0.15 times: M1, to an infinite object The focal length f of the entire system in the focused state is f:
(2) 0.03 <M1 / f <0.10
An imaging lens that satisfies the requirements.

[4]
In the imaging lens according to any one of [1] to [3], the amount of movement of the first lens group G1 when focusing from an object at infinity to an object with an imaging magnification of −0.3 times: M2, the focal length of the entire system in a state of focusing on an object at infinity: f is a conditional expression:
(3) 0.10 <M2 / f <0.15
An imaging lens that satisfies the requirements.

[5]
In the imaging lens according to any one of [1] to [4], the air space between the negative lens group G2N of the second lens group G2 and the positive lens group G2P: D2a, the negative lens group of the second lens group G2 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 unit is a conditional expression:
(4) 0.40 <D2a / D2 <0.70
An imaging lens that satisfies the requirements.

[6]
In the imaging lens according to any one of [1] to [5], the negative lens group G2N of the second lens group G2 is configured by a cemented lens of a positive lens L21 and a negative lens L22, and the positive lens group is 1 An imaging lens composed of a single positive lens L23.

[7]
In the imaging lens according to any one of [1] to [6], the refractive index of the lens material with respect to d-line: n _d , Abbe number: ν _d , and refraction with respect to g-line, F-line, and C-line Rate: 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 L11 and the second positive lens L12 of the first lens group G1:
_{(5) 1.45 <n d <} 1.65
(6) 60.0 <ν _d <95.0
(7) 0.005 <P _{g, F} − (− 0.001802 × ν _d +0.6483)
<0.050
An imaging lens that satisfies the requirements.

[8]
In the imaging lens according to any one of [1] to [7], an air space: D1a between the first positive lens L11 and the second positive lens L12 of the first lens group G1, and the first lens group G1 of the first lens group G1. The distance D1 on the optical axis from the object side surface of the first positive lens L11 to the image side surface of the third positive lens L14 is a conditional expression:
(8) 0.2 <D1a / D1 <0.5
An imaging lens that satisfies the requirements.

[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 device 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

JP 2013-2108015 A

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.
During focusing from an object at infinity to an object at a short distance, the second lens group is fixed with respect to the image plane, and the first lens group moves integrally to the object side,
The focal length of the first lens group: f1, the focal length of the entire system in a state of focusing on an object at infinity: f is a conditional expression:
(1) 0.50 <f1 / f <0.90
An imaging lens that satisfies the requirements. The imaging lens according to claim 1.
An imaging lens in which an aperture stop is fixed with respect to an image plane together with a second lens group during focusing from an object at infinity to an object at a short distance. The imaging lens according to claim 1 or 2,
Imaging magnification: The amount of movement of the first lens unit when focusing from an object at infinity to an object with a magnification of -0.15: M1, and the focal length of the entire system in a state of focusing on the object at infinity: f formula:
(2) 0.03 <M1 / f <0.10
An imaging lens that satisfies the requirements. The imaging lens according to any one of claims 1 to 3,
Imaging magnification: the amount of movement of the first lens unit when focusing from an object at infinity to an object having a magnification of -0.3 times: M2, and the focal length of the entire system in a state of focusing on the object at infinity: f formula:
(3) 0.10 <M2 / f <0.15
An imaging lens that satisfies the requirements. The imaging lens according to any one of claims 1 to 4,
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:
(4) 0.40 <D2a / D2 <0.70
An imaging lens that satisfies the requirements. The imaging lens according to any one of claims 1 to 5,
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 6,
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:
_{(5) 1.45 <n d <} 1.65
(6) 60.0 <ν _d <95.0
(7) 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 7,
Air distance between the first positive lens and the second positive lens in the first lens group: D1a, the distance on the optical axis from the object side surface of the first positive lens to the image side surface of the third positive lens in the first lens group : D1 is a conditional expression:
(8) 0.2 <D1a / D1 <0.5
An imaging lens that satisfies the requirements. 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.

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