JP2019101229A - Image forming lens system, imaging apparatus - Google Patents

Abstract

To provide an image forming lens system in which variation in lens performance upon focusing is suppressed and furthermore which has a sufficiently high peripheral light quantity ratio and suppresses angle of incidence to an image plane to be low.SOLUTION: The image forming lens system is provided that comprises a first lens group G1 and a positive second lens group G2 which are arranged in order from the object side, and that is configured in such a manner that the second lens group G2 moves toward the object side so that a distance between the first lens group G1 and the second lens group G2 is reduced when focusing from infinity to a short distance. The first lens group G1 comprises a negative 1a-th lens group G1a and a positive 1b-th lens group G1b in order from the object side to the image side. The second lens group G2 comprises a positive 2a-th lens group G2a, a diaphragm 30, and a positive 2b-th lens group G2b in order from the object side. The image forming lens system satisfies the following conditional expression: -0.20<f/f<0.20, where f and frespectively represent a focal length of the entire system and a focal length of the first lens group when focused on an object at infinity.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an imaging lens system used in an imaging device.

As a method of using an imaging device using an area sensor, in addition to conventional compact cameras, single-lens reflex cameras, mirrorless cameras, etc. for photographing an object, industrial cameras, in-vehicle cameras, etc. are known.
Industrial cameras include, for example, machine vision applications that cause industrial machines to recognize objects, but the imaging lens system used for such applications has lens performance associated with focusing compared to conventional camera applications and the like. It is important that the decrease in
In order to satisfy such optical characteristics, imaging optical systems of various lens group configurations are known (see, for example, Patent Documents 1 and 2).

  However, in the conventional method, when trying to reduce the fluctuation of the lens performance at the time of focusing, there are problems such that the peripheral light amount ratio can not be sufficiently secured and the incident angle to the image surface becomes large.

  The present invention has been made in view of the above, and it is an imaging lens system in which the peripheral light amount ratio is sufficiently high and the incident angle to the image plane is suppressed small while suppressing the fluctuation of the lens performance during focusing. The purpose is to provide.

The imaging lens system according to the present invention has the first lens unit and the second positive lens unit arranged in order from the object side, and the distance from the first lens unit decreases during focusing from infinity to near distance. The second lens group is an imaging lens system that moves to the object side, and the first lens group is a negative 1a lens group and a positive 1b lens group in order from the object side to the image side. The second lens group is composed of, in order from the object side, a positive 2a lens group, an aperture stop, and a positive 2b lens group, and the 2a lens group is positive in order from the object side to the image side lens and the negative lens is composed of the 2a cemented lens cemented, the 2b cemented lens and the 2b lens group negative lens L _2b1 order from the object side to the image side and a positive lens L _2b2 are bonded L _2B12, a positive lens _{L 2b3,} a negative lens _{L 2b4,} is a positive lens _{L 2b5} When the focal length of the entire system in a state in which the object is at infinity is f: f and the focal length of the first lens group: f ₁ , conditional expression (1):
(1)-0.20 <f / f ₁ <0.20 is satisfied.

  According to the imaging lens system of the present invention, the peripheral light amount ratio can be sufficiently high and the incident angle to the image plane can be suppressed small, while suppressing the fluctuation of the lens performance at the time of focusing.

1 is a schematic configuration of an imaging device according to the present invention. FIG. 2 is a cross-sectional view showing the configuration of the imaging lens of Example 1; 5 is an aberration curve diagram of the imaging lens of Embodiment 1 in an infinity in-focus condition. FIG. 5 is an aberration curve diagram of the imaging lens of Example 1 in a state of being focused on WD = 0.25 m. FIG. 5 is an aberration curve diagram of the imaging lens of Example 1 in a focused state at WD = 0.10 m. FIG. FIG. 7 is a cross-sectional view showing the configuration of the imaging lens of Example 2; 5 is an aberration curve diagram of the imaging lens of Embodiment 2 in an infinity in-focus condition. FIG. FIG. 6 is an aberration curve diagram of the imaging lens of Example 2 in a focused state at WD = 0.25 m. FIG. 6 is an aberration curve diagram of the imaging lens of Example 2 in a focused state at WD = 0.10 m. FIG. 7 is a cross-sectional view showing the configuration of the imaging lens of Example 3; FIG. 7 is an aberration curve diagram of the imaging lens of Example 3 in an infinity in-focus condition. It is an aberrational curve figure in the state focused on WD = 0.25 m of the imaging lens of Example 3. It is an aberrational curve figure in the state focused on WD = 0.10 m of the imaging lens of Example 3. FIG. 18 is a cross-sectional view showing the configuration of the imaging lens of Example 4. FIG. 18 is an aberration curve diagram of the imaging lens of Example 4 in an infinity in-focus condition. FIG. 18 shows aberration curve diagrams of the image forming lens of Example 4 in a focused state at WD = 0.25 m. FIG. 16 is an aberration curve diagram of the imaging lens of Example 4 in a focused state at WD = 0.10 m. FIG. 18 is a cross-sectional view showing the configuration of the imaging lens of Example 5. FIG. 16 is an aberration curve diagram of the imaging lens of Example 5 in an infinity in-focus condition. It is an aberrational curve figure in the state focused on WD = 0.25 m of the imaging lens of Example 5. It is an aberrational curve figure in the state focused on WD = 0.10 m of the imaging lens of Example 5.

  Hereinafter, embodiments of an imaging lens system for an imaging device and an imaging device according to the present invention will be described with reference to the drawings.

First Embodiment Hereinafter, an embodiment of a lens system 10 which is an imaging lens system which is an imaging optical system according to the present invention will be described.
In the present embodiment, as shown in FIG. 1, the imaging device 100 is an industrial camera for photographing an object WK as a subject and specifying the position, the shape, and the like of the object WK by image recognition.
The image pickup apparatus 100 is an image pickup element that recognizes, as an image, a lens system 10 that is an imaging optical system configured of a plurality of lenses for forming an image of an object WK and light that is formed by the lens system 10. And an imaging unit 20.
In the lens system 10, it is assumed that the image formed on the image plane Im is captured by the imaging unit 20, and in FIGS. "Glass" is shown.
In FIGS. 2, 6, 10, 14 and 18, the left direction in the drawing is referred to as the “object side” on which the object WK is placed, and the right direction in the drawing is referred to as the “image side”.

  The imaging unit 20 is an imaging element disposed so that the light receiving surface is on the image plane Im of the lens system 10.

  The cover glass CG is “parallel plate-like”, and the light receiving surface of the imaging unit 20 matches the image plane Im.

  The cover glass CG has a function of shielding and protecting the light receiving surface of the imaging unit 20, but may have a function such as an infrared cut filter.

The lens system 10 is a lens group in which a first lens group G1 and a second lens group G2 are disposed in order from the object side.
The lens system 10 adjusts the focus by moving the second lens group G2 to the object side at the time of focusing from infinity to near distance.

  The first lens group G1 includes a first a lens group G1a having negative refractive power and a first b lens group G1b having positive refractive power in order from the object side to the image side.

  The second lens group G2 is composed of, in order from the object side, a lens group G2a having a positive refractive power, an aperture stop 30, and a lens group G2b having a positive refractive power.

The 2a lens group G2a is composed of the 2a cemented lens _{L 2A12} which a positive lens _{L 2a1} sequentially toward the image side from the object side and a negative lens _{L 2a2} are joined, the 2b lens group G2b the image side from the object side and the 2b cemented lens _{L 2B12} which headed sequentially negative lens _{L 2b1} and the positive lens _{L 2b2} is joined to the positive lens _{L 2b3,} a negative lens _{L 2b4,} a lens group including a positive lens _{L 2b5.}
Thus the most object side of the lens cemented lens of the 2b lens group G2b, the by arranging the positive lens on the image side, the object side lens surface S _2b1 positive lens image side lens L _2b2 of the negative lens L _2b1 made properly exchanging aberrations occurring between the surface S _2b2 and the positive lens L the object-side lens surface of _2b3, it is possible to perform good correction especially for spherical aberration and coma.
Further, by forming the 2a-a cemented lens _L2a12 with the 2a-th lens group G2a arranged in order of positive and negative refractive power from the object side, the 2a-a cemented lens _L2a12 and the 2b-b cemented lens L are two cemented lenses _The aperture stop 30 is disposed between the light _source and the _{lens 2b12} .
That is, the arrangement of the refractive powers of the two cemented lenses is symmetrical with respect to the aperture stop 30. With this configuration, coma and coma aberration can be sufficiently corrected.
At this time, the positive lens _{L 2a1} convex surface of the convex lens on the image side of the 2a cemented lens _{L 2A12,} it is desirable negative lens _{L 2a2} is a negative meniscus lens having a convex surface directed toward the image side.
Further, it is more preferable that the cemented surface of the 2b-b cemented lens L ₂ b 12 have a concave surface facing the image side.
Further, the positive lens L _2b3 negative lens L _2b4 on the image side _of, by arranging the order of the positive lens L _2b5, while sufficiently securing the exit pupil position, sufficiently correct residual aberrations such as curvature of field and distortion it can.

Now, in the imaging lens system of the type in which the second b lens group G2b operates at the time of focusing, if it is attempted to reduce the fluctuation of the lens performance at the time of focusing, the peripheral light amount ratio can not be sufficiently ensured. The problem is that the incident angle of
Therefore, in the lens system 10 according to the present embodiment, the peripheral light intensity ratio is reduced while the fluctuation of the lens performance at the time of focusing is suppressed by satisfying the above-described lens configuration and the conditional expressions (1) to (11) described below. The angle of incidence on the image plane can be suppressed to a sufficiently high level.

  The lens system 10 in this embodiment has a focal length f of the entire lens system 10 including the first lens group G1 and the second lens group G2 in a state in which an object at infinity is in focus, and f1 of the first lens group G1. Assuming that the focal length is f1, the following conditional expression (1) is satisfied.

The conditional expression (1) indicates that the refractive power of the first lens group G1 with respect to the entire lens system 10 is weak.
If the upper limit of the conditional expression (1) is exceeded, the positive power of the first lens group G1 becomes excessive, which makes it difficult to correct coma aberration during focusing of the second b lens group.
In addition, since the refractive power of the second lens group G2 is relatively weakened, the function of the second lens group G2 as a focusing group is reduced, and the amount of movement is increased. It also leads to
When the value goes below the lower limit, the refractive power of the first lens group G1 becomes excessive on the negative side, so it becomes difficult to sufficiently reduce curvature of field caused by a change in the object distance to the subject WK.

  The lens system 10 can suppress aberration variation during focusing by satisfying the conditional expression (1).

More preferably, conditional expression (1) is more preferably within the range of −0.15 <f / f1 <0.15.
As described above, by further suppressing the refractive power of the first lens group G1 with respect to the entire lens system 10, the fluctuation of the curvature of field aberration at the time of focusing is further reduced, and the aberration fluctuation at the focusing is suppressed.

Further, in the present embodiment, the lens system 10, the focal length of the negative lens _{L 2b4: f L2b4,} the focal length of the positive lens _{L 2b5:} when the _{f L2b5,} satisfies the following conditional expression (2).

Such conditional expression (2) shows a ratio of the refractive power between the positive lens L _2b5 and the negative lens L _2b4, the balance of the refractive power of the two lenses arranged on the image side of the lens system 10 By setting the value within the range of the conditional expression (2), it is possible to satisfactorily correct the remaining uncorrected aberration and to further improve the imaging performance.
In addition, when the value is out of the range of the conditional expression (2), it is difficult to particularly correct the curvature of field aberration, and it is difficult to achieve satisfactory imaging performance.

The lens system 10 is the focal length of the 2b cemented lens _{L 2b12: f L2b12,} the focal length of the 2b cemented lens _L positive lens _{L 2b3} arranged on the image side of the _2B12: when the _{f L2b3,} the following conditions Formula (3) is satisfied.

The conditional expression (3) defines the ratio of the refractive power of the 2b-b cemented lens _L2b12 and the positive lens _L2b3 .
That is, when the upper limit value of the conditional expression (3) is exceeded, the positive refractive power of the positive lens _L2b3 becomes excessively _small, and the balance of aberration correction between the 2b-b cemented lens _L2b12 and the positive lens _L2b3 is broken, which is favorable. It is difficult to obtain good imaging performance.
If the lower limit value of the conditional expression (3) is not _reached , the refractive power of the positive lens _L2b3 becomes large, so that the balance is lost and it becomes difficult to correct spherical aberration and coma.

  By satisfying the conditional expression (3), the lens system 10 can further correct spherical aberration and coma aberration, and can be miniaturized.

Further, the lens system 10 of the present invention, the object-side lens surface _{S 2b1} of the negative lens _{L 2b1} curvature _{radius: R L2b1sur. 1,} the image-side lens surface _{S 2b2} of the positive lens _{L 2b2} curvature _{radius: R L2b2sur. When it is 2} , the following conditional expression (4) is satisfied.

  By satisfying the conditional expression (4), it is possible to perform better aberration correction, in particular, good correction of spherical aberration and coma.

The conditional expression (4) represents the ratio of the radius of curvature of the lens surface of the second b cemented lens L ₂ b _{12 on} the object side and the image side and both sides, and when taking values outside the range of the conditional expression (4), The balance between spherical aberration and coma aberration is lost, and it becomes difficult to obtain good imaging performance.

In this embodiment also, the lens system 10, the refractive index at the d-line of the positive lens _{L 2b3:} when a _{nd L2b3,} satisfies the following conditional expression (5).

If the positive lens L 2 _{b 3} is made of a material having a refractive index larger than the upper limit value of the conditional expression (5), the cost is drastically increased, which may increase the cost of the lens.
On the other hand, if a material having a refractive index smaller than the lower limit value of the conditional expression (5) is used, it will be difficult to secure the positive refractive power necessary for aberration correction, and the radius of curvature of the lens surface will be increased. Become. Such an increase in the radius of curvature of the lens surface may lead to an increase in the incident angle with respect to the lens surface, so that various aberrations such as spherical aberration, coma aberration, and curvature of field are easily generated, which is not preferable.
Furthermore, such an increase in the radius of curvature may increase the performance deterioration sensitivity to manufacturing errors.
By satisfying the conditional expression (5), the lens system 10 of the present embodiment can achieve downsizing and good aberration correction.

  Further, in the present embodiment, the lens system 10 is a distance on the optical axis from the object-side lens surface of the lens positioned closest to the object side in the lens system 10 to the aperture stop 30: Ls. When the distance L on the optical axis from the object side lens surface of the lens closest to the object side to the image side lens surface of the lens closest to the image side is satisfied, the following conditional expression (6) is satisfied.

  In the conditional expression (6), L represents a so-called total lens length, Ls represents the length of the object side portion of the lens system 10 up to the aperture stop 30, and the conditional expression (6) This defines the “distance on the optical axis from the object-side lens surface of the lens closest to the object side in the system to the aperture stop 30”.

If the upper limit value of the conditional expression (6) is exceeded, the position of the aperture stop 30 is too close to the image side with respect to the entire lens system, and the degree of freedom of the second b lens group G2b is reduced. Aberration correction in the second b lens group G2b, which occupies a relatively large proportion of refractive power, becomes difficult.
In addition, since the off-axis ray passing through the first lens group G1 and the second lens group G2a becomes high, the size of the first lens group G1 is undesirably increased.
If the lower limit value of the conditional expression (6) is not reached, the position of the aperture stop 30 is too close to the object side with respect to the entire lens system, and the enlargement of the aperture stop 30 is caused. Further, the off-axis ray passing through the 2b-th lens unit G2b is too high, which leads to an increase in the size of the 2b-th lens unit G2b, which is not preferable.

  In the present embodiment, downsizing and satisfactory aberration correction can be achieved by the configuration that satisfies the conditional expression (6).

Further, in the present embodiment, in the lens system 10, the position of the first lens group G1 is fixed to the image plane at the time of focusing.
With this configuration, the moving mechanism for focusing can be simplified, and the entire lens system 10 can be easily miniaturized.

Further, in the present embodiment, the lens system 10 includes the object side lens of the lens L positioned closest to the object side of the 1b-th lens group G1b from the image side lens surface of the lens positioned closest to the image side of the 1a-th lens group G1a. Distance to the surface: D _L1a-L1b , light from the object-side lens surface of the lens located closest to the object side in the first lens group G1 to the image-side lens surface of the lens located closest to the image side in the first lens group G1 When on-axis distance: L ₁ is satisfied, conditional expression (7) is satisfied.

This conditional expression (7) is on the optical axis from the object-side lens surface of the lens positioned closest to the object side in the first lens group G1 to the image-side lens surface of the lens positioned closest to the image side in the first lens group G1. Defines the ratio of the distance on the optical axis between the lens subunits G1a and G1b relative to the distance L1.
If the upper limit value of the conditional expression (7) is exceeded, the distance between the 1a lens group G1a and the 1b lens group G1b becomes too wide, and the 1a lens group G1a is enlarged.
Below the lower limit value of the conditional expression (7), the distance between the 1a lens group G1a and the 1b lens group G1b becomes too narrow, and the aberration generated in the 1a lens group G1a is corrected by the 1b lens group G1b. It becomes impossible to clear and it is easy to produce degradation of imaging performance.

  In the present embodiment, by the configuration that satisfies the conditional expression (7), better aberration correction and downsizing can be achieved.

In this embodiment, the lens system 10 is the lens on the optical axis _between the object-side lens surface of the 2b-b cemented lens _{L2b12 and} the image-side lens surface: D _L2b12 , and the lens located closest to the object side in the _2bb lens group G2b distance on the optical axis from the object-side lens surface _{S 2b1} of L _2b1 to the image side lens surface of the lens _{L 2b5} located on the most image _side: when the _{L 2b,} which satisfies the conditional expression (8).

The conditional expression (8) defines the ratio of the thickness of the second b cemented lens _{L2b12 to} the thickness of the second b lens group G2b on the optical axis.
If the upper limit value of conditional expression (8), the distance between the image side lens surface of the object-side lens surface and a positive lens L _2b2 of the negative lens L _2b1 becomes excessive, a positive lens L _2b3, a negative lens L _2b4, positive lens The degree of freedom of each lens of L 2 _{b 5} is reduced.
Therefore, downsizing of the lens system 10 becomes difficult, and furthermore, sufficient correction of monochromatic aberration becomes difficult.
_Below the lower limit value of conditional expression (8), the distance between the object-side lens surface of the negative lens _{L2b1 and} the image-side lens surface of the positive lens _L2b2 becomes too small, and it becomes difficult to sufficiently correct spherical aberration and coma. .
In the present embodiment, when the lens system 10 satisfies the conditional expression (8), it is possible to effectively achieve both downsizing of the imaging lens and high performance.

Furthermore, in the present embodiment, a negative lens L _2b1, the refractive index of the negative lens L _2b1 with respect to the d-line: nd _L2B1, Abbe number of the negative lens L _2b1 at the d-line: [nu] d _L2B1, g-line, F-line, C-line Partial dispersion ratio defined as ( _ng- n _F ) / (n _F- n _C ) using refractive indices n _g , n _F and n _C : θ _{g, F} , the following conditional expressions are satisfied Do.

The conditional expressions (9), (10) and (11) respectively define the refractive index, Abbe number and anomalous dispersion of the glass material.
By being a glass material that satisfies the conditional expressions (9) to (11), it is possible to have high dispersion and anomalous dispersion while having a high refractive index, and to sufficiently correct monochromatic aberration while having chromatic aberration. Can be corrected sufficiently.

Further, the lens system 10 of the present embodiment, the first lens group G1, a negative lens L _1a1, a negative lens L _1a2, are preferably composed of a positive lens L _1b1. By dividing the two negative lenses in this way and arranging them so as to have an air gap between the two lenses, they can be shared and refracted, and good aberration correction becomes possible.

  Furthermore, in the present embodiment, it is preferable that all lenses in the lens system 10 be spherical lenses. Although not limited to such a configuration, an increase in cost of, for example, a mold for molding can be avoided by not adopting a lens having an aspheric surface or a diffractive surface. This is advantageous in cost especially in the production of small lots.

  Furthermore, in the present embodiment, it is preferable that all lens materials constituting the first group lens group G1 and the second lens group G2 be inorganic solid materials. Lenses made of organic materials, organic-inorganic hybrid materials, etc. have large changes in characteristics due to environmental conditions such as temperature and humidity. By forming all the lenses constituting the lens system 10 of an inorganic solid material, it is possible to realize the lens system 10 that is not easily affected by changes in environmental conditions such as temperature and humidity.

  Further, in the present embodiment, the imaging device 100 includes the lens system 10. Use of such a lens system 10 makes it possible to provide a high-performance imaging device capable of performing aberration correction well from infinity to near distance without causing performance deterioration during focusing.

Examples 1 to 5 will be shown below as specific numerical examples of the present invention.
The meanings of symbols in the examples are as follows.

F: F number
Y ': Image height
R: radius of curvature
D: spacing
Refractive index d d for Nd: d line: Abbe number for d line
BF: back focus θg, F: partial dispersion ratio
WD: Working distance (distance from the object to the vertex of the object-side lens surface of the lens located closest to the object)

As shown in the aberration diagrams of the examples, in each example, the aberration is corrected at a high level, and the change in the curvature of field due to focusing is well suppressed. Spherical aberration, axial chromatic aberration, and magnification chromatic aberration are also small, and coma aberration is well suppressed to the outermost peripheral portion. In addition, distortion is also 0.8% or less in absolute value from close to infinity.
That is, each of the lens systems 10 shown in Examples 1 to 5 realizes an imaging lens in which various aberrations are sufficiently reduced. That is, it has a resolution corresponding to an image sensor of 8 million pixels with an angle of view of about 37 ° to 54 °, an F number of about 1.8, and a lens number of 10, and has a close distance of 0.1 m working distance from an infinite object Can be described as a straight line, and it has become a high-performance imaging lens with less change in performance associated with focusing.

(Numerical Example 1)
FIG. 2 shows an optical layout of the lens system 10 according to the first embodiment. The first lens L1 to the tenth lens L10 are arranged in order from the object side (the left side in the drawing), and the aperture stop 30 is disposed between L5 and L6.
In Example 1, the aberration diagram in a state of focusing at infinity is FIG. 3, the aberration diagram in a state of focusing at 0.25 m is FIG. 4, and the working distance is at 0.10 m. Aberrations in the state are shown in FIG.

The intervals A and B described in Table 2 are lens intervals corresponding to A and B shown in FIG. 1 when focusing is performed to the respective working distance values.
The numerical values regarding the conditional expressions (1) to (11) shown above are as shown in Table 3.

Focal length f: 11.99
F number: 1.84
Half angle of view ω: 24.7 °

(Numerical Example 2)
FIG. 6 shows an optical layout of the lens system 10 according to the second embodiment. The first lens L1 to the tenth lens L10 are arranged in order from the object side (the left side in the drawing), and the aperture stop 30 is disposed between L5 and L6.
In Example 2, the aberration diagram in a state of focusing at infinity is FIG. 7, the aberration diagram in a state of focusing at 0.25 m is FIG. 8, and the working distance is at 0.10 m. Aberrations in the state are shown in FIG.

The intervals A and B described in Table 5 are lens intervals corresponding to A and B shown in FIG. 1 when focusing is performed to the respective working distance values.
The numerical values regarding the conditional expressions (1) to (11) shown above are as shown in Table 6.

Focal length f: 11.99
F number: 1.84
Half angle of view ω: 24.7 °

(Numerical Example 3)
FIG. 10 shows an optical layout of the lens system 10 according to the third embodiment. The first lens L1 to the tenth lens L10 are arranged in order from the object side (the left side in the drawing), and the aperture stop 30 is disposed between L5 and L6.
In Example 3, the aberration diagram in a state of focusing at infinity was as shown in FIG. 11, and the aberration diagram in a state of focusing at 0.25 m was as in FIG. 12, and the working distance was as 0.10 m. Aberrations in the state are shown in FIG.

The intervals A and B described in Table 8 are lens intervals corresponding to A and B shown in FIG. 1 when focusing is performed to the respective working distance values.
The numerical values regarding the conditional expressions (1) to (11) shown above are as shown in Table 3.

Focal length f: 12.01
F number: 1.84
Half angle of view ω: 24.7 °

Numerical Embodiment 4
FIG. 14 shows an optical layout of the lens system 10 according to the fourth embodiment. The first lens L1 to the tenth lens L10 are arranged in order from the object side (the left side in the drawing), and the aperture stop 30 is disposed between L5 and L6.
In Example 4, the aberration diagram in a state of focusing at infinity was as shown in FIG. 15, and the aberration diagram in a state of focusing at a distance of 0.25 m was as shown in FIG. Aberrations in the state are shown in FIG.

The intervals A and B described in Table 11 are lens intervals corresponding to A and B shown in FIG. 1 when focusing is performed to the respective working distance values.
The numerical values for the conditional expressions (1) to (11) shown above are as shown in Table 12.

Focal length f: 15.99
F number: 1.84
Half angle of view ω: 19.0 °

Numerical Embodiment 5
FIG. 18 shows an optical layout of the lens system 10 according to the fifth embodiment. The first lens L1 to the tenth lens L10 are arranged in order from the object side (the left side in the drawing), and the aperture stop 30 is disposed between L5 and L6.
In Example 5, the aberration diagram in a state of focusing at infinity is FIG. 19 and the aberration diagram in a state of focusing at a distance of 0.25 m is FIG. 20, and the working distance is at a focus of 0.10 m. Aberrations in the state are shown in FIG.

The intervals A and B described in Table 14 are lens intervals corresponding to A and B shown in FIG. 1 when focusing is performed to the respective working distance values.
The numerical values for the conditional expressions (1) to (11) shown above are as shown in Table 15.

Focal length f: 15.99
F number: 1.84
Half angle of view ω: 19.0 °

  As described above, in the imaging lens system according to the present invention, aberrations are sufficiently corrected in the specific configurations shown in Numerical Embodiments 1 to 5. It is clear from each example that good optical performance can be ensured.

  As mentioned above, although embodiment concerning this invention was described, this invention is not limited to the above-mentioned each embodiment as it is, In an execution phase, in the range which does not deviate from the summary, a component is changed and can be materialized. . In addition, various inventions can be formed by appropriate combinations of a plurality of components disclosed in the above-described embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, different embodiments and modifications may be combined as appropriate.

10 Imaging optical system (lens system)
20 Image pickup element 100 Image pickup apparatus f The focal length of the whole system in a state in which an object at infinity is in focus
f ₁ focal length of the first lens group
f _L2b4 focal length of the negative lens _{L 2b4}
f focal length of _L2b5 positive lens _L2b5
Refractive index for d-line of nd _L2b3 positive lens _L2b3
Curvature radius of object side lens surface of R _L2b1sur.1 negative lens L _2b1
R _L2b2sur.2 most position to the object side by a distance L entire system on the optical axis to the diaphragm from the object side lens surface of the lens positioned closest to the object side in the image-side lens surface curvature radius Ls entire system of the positive lens L _2b2 On the optical axis from the object-side lens surface of the moving lens to the image-side lens surface of the lens located closest to the image in the whole system

Unexamined-Japanese-Patent No. 2017-083770 JP, 2016-126277, A

Claims (14)

The first lens group and the positive second lens group are disposed in order from the object side,
An imaging lens system in which the second lens unit moves to the object side so that the distance to the first lens unit decreases at the time of focusing from infinity to near distance;
The first lens group is composed of, in order from the object side to the image side, a negative first a lens group and a positive first b lens group.
The second lens group is composed of, in order from the object side, a positive 2a lens group, an aperture stop, and a positive 2b lens group.
The 2a lens group is composed of a 2a cemented lens in which a positive lens and a negative lens are cemented in order from the object side to the image side,
The 2b lens group 2b-th cemented lens L _2B12 and a negative lens L _2b1 order from the object side to the image side and a positive lens L _2b2 are bonded, a positive lens L _2b3, a negative lens L _2b4, a positive lens L _2b5 Configured and
Assuming that the focal length of the entire system in a state in which an object at infinity is in focus is f and the focal length of the first lens unit is f ₁ , conditional expression (1):
(1)-0.20 <f / f ₁ <0.20
An imaging lens system characterized by satisfying the above. In the imaging lens system according to claim 1,
Focal length of the negative lens L _2b4: f _L2b4, the focal length of the positive lens L _2b5: when the f _L2b5,
Conditional Expression (2):
(2) -1.55 <f _L2b4 / f _L2b5 <-0.90
An imaging lens system characterized by satisfying the above. The imaging lens system according to claim 1 or 2
Focal length of the 2b cemented lens: f _L2b12, the focal length of the positive lens _{L 2b3} of the 2b lens group, when the f _L2b3, conditional expression (3):
(3) -2.5 <f _L2b12 / f _L2b3 <-1.3
An imaging lens system characterized by satisfying the above. In the imaging lens system according to any one of claims 1 to 3,
Radius of curvature of the object side lens surface of the negative lens _{L 2b1:} R _L2b1sur.1, curvature of the image side lens surface of the positive lens _{L 2b2} radius: When the R _L2b2sur.2, conditional expression (4):
(4) 0.65 <R _L2b1sur.1 / R _L2b2sur.2 <0.90
An imaging lens system characterized by satisfying the above. In the imaging lens system according to any one of claims 1 to 4,
When the refractive index to the d-line of the positive lens L ₂ b ₃ is nd L ₂ b 3, conditional expression (5):
(5) 1.80 <nd _L2b3 <2.05
An imaging lens system characterized by satisfying the above. In the imaging lens system according to any one of claims 1 to 5,
Distance on the optical axis from the object-side lens surface of the lens located closest to the object in the whole system to the stop: Ls, from the object-side lens surface of the lens located closest to the object in the whole system to the image most Assuming that the distance on the optical axis to the image-side lens surface of the lens positioned is L, conditional expression (6):
(6) 0.48 <Ls / L <0.63
An imaging lens system characterized by satisfying the above. In the imaging lens system according to any one of claims 1 to 6,
An imaging lens system characterized in that the first lens group is fixed with respect to the image plane at the time of focusing. In the imaging lens system according to any one of claims 1 to 7,
Distance on the optical axis from the image side lens surface of the lens located closest to the image side of the 1a lens group to the object side lens surface of the lens located closest to the object side of the 1b lens group: D _L1a-L1b , 1st distance on the optical axis from the object side lens surface of the lens located closest to the object side in the lens group to the image side lens surface of the lens positioned closest to the image side of the first lens group when the L _1, condition ( 7):
(7) 0.15 <D _L1a-L1b / L ₁ <0.35
An imaging lens system characterized by satisfying the above. In the imaging lens system according to any one of claims 1 to 8,
Distance on the optical axis from the object-side lens surface of the 2b-b cemented lens to the image-side lens surface: D _L2 b 12 The image located closest to the image side from the object-side lens surface of the lens closest to the object side When the distance on the optical axis to the side lens surface is L 2 _b , the conditional expression (8):
(8) 0.40 <D _L2b12 / L _2b <0.60
An imaging lens system characterized by satisfying the above. The imaging lens system according to any one of claims 1 to 9.
refractive index of the negative lens _{L 2b1} with respect to the d-line: nd _L2B1,
Abbe number of the negative lens _{L 2b1} at the d-line: [nu] d _L2B1,
Partial dispersion ratio defined as ( _ng -n _F ) / (n _F -n _C ) by the refractive index n _g , n _F and n _C to the g-line, F-line and C-line of the negative lens L 2 _b 1: θ _{g And F} , conditional expressions (9), (10) and (11) respectively.
(9) 1.78 <nd _L2b1 <2.00
(10) 20.0 <d d _{L 2 b 1} <3 _2.0
(11) 0.005 <θ _{g, F} -(-0.001802 × _{d dL} 2 b ₁ + 0.6483) <0.009
An imaging lens system characterized by satisfying the above. In the imaging lens system according to any one of claims 1 to 10,
The first lens group, a negative lens L _1a1, a negative lens L _1a2, an imaging lens system, characterized in that it is a positive lens L _1b1. The imaging lens system according to any one of claims 1 to 11.
An imaging lens system characterized in that all lenses constituting the first lens group and the second lens group are spherical lenses. The imaging lens system according to any one of claims 1 to 12.
An imaging lens system characterized in that all lens materials constituting the first lens group and the second lens group are inorganic solid materials.   An imaging device having the imaging lens system according to any one of claims 1 to 13.

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