JP7003604B2 - Imaging lens system, imaging device - Google Patents

Description

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

As a method of using an image pickup device using an area sensor, a conventional compact camera, a single-lens reflex camera, a mirrorless camera, and the like for photographing a subject, an industrial camera, an in-vehicle camera, and the like are known.
Examples of industrial cameras include machine vision applications that allow industrial machines to recognize objects, and the imaging lens system used for such applications has lens performance associated with focusing as compared to conventional camera applications. It is important that there is little decrease in the amount and that it is stable.
In order to satisfy such optical characteristics, imaging optical systems having 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 that the peripheral illumination ratio cannot be sufficiently secured and the angle of incidence on the image plane becomes large.

The present invention has been made in view of the above, and is an imaging lens system in which the peripheral illumination ratio is sufficiently high and the angle of incidence on the image plane is kept small while suppressing fluctuations in lens performance during focusing. The purpose is to provide.

In the imaging lens system of the present invention, the first lens group and the positive second lens group are arranged in order from the object side, and the distance from the first lens group is reduced when focusing from infinity to a short distance. This is an imaging lens system in which the second lens group moves toward the object side, and the first lens group is a negative first a lens group and a positive first b lens group in order from the object side to the image side. The second lens group is composed of a positive second a lens group, an aperture, and a positive second b lens group in order from the object side, and the second a lens group is positive in order from the object side to the image side. It is composed of a second a junction lens in which a lens and a negative lens are joined, and the second b lens group is a second b junction lens L in which a negative lens L _2b1 and a positive lens L _2b2 are joined in order from the object side to the image side. It consists of _2b12 , a positive lens L _2b3 , a negative lens L _2b4 , and _a positive lens L _2b5 . , Conditional expression (1):
(1) Satisfy -0.20 <f / f ₁ <0.20.

According to the imaging lens system of the present invention, it is possible to suppress fluctuations in lens performance during focusing, while suppressing fluctuations in lens performance while suppressing the peripheral illumination ratio sufficiently high and reducing the angle of incidence on the image plane.

It is a schematic configuration of the image pickup apparatus which concerns on this invention. It is sectional drawing which shows the structure of the imaging lens of Example 1. FIG. It is an aberration curve diagram in the infinity focusing state of the imaging lens of Example 1. FIG. It is an aberration curve diagram in the state which focused on WD = 0.25m of the imaging lens of Example 1. FIG. It is an aberration curve diagram in the state which focused on WD = 0.10m of the imaging lens of Example 1. FIG. It is sectional drawing which shows the structure of the imaging lens of Example 2. FIG. It is an aberration curve diagram in the infinity focusing state of the imaging lens of Example 2. FIG. It is an aberration curve diagram in the state which focused on WD = 0.25m of the imaging lens of Example 2. FIG. It is an aberration curve diagram in the state which focused on WD = 0.10m of the imaging lens of Example 2. FIG. It is sectional drawing which shows the structure of the imaging lens of Example 3. FIG. It is an aberration curve diagram in the infinity focusing state of the imaging lens of Example 3. FIG. It is an aberration curve diagram in the state which focused on WD = 0.25m of the imaging lens of Example 3. FIG. It is an aberration curve diagram in the state which focused on WD = 0.10m of the imaging lens of Example 3. FIG. It is sectional drawing which shows the structure of the imaging lens of Example 4. FIG. It is an aberration curve diagram in the infinity focusing state of the imaging lens of Example 4. FIG. It is an aberration curve diagram in the state which focused on WD = 0.25m of the imaging lens of Example 4. FIG. It is an aberration curve diagram in the state which focused on WD = 0.10m of the imaging lens of Example 4. FIG. It is sectional drawing which shows the structure of the imaging lens of Reference Example 1. FIG. It is an aberration curve diagram in the infinity focusing state of the imaging lens of Reference Example 1. FIG. It is an aberration curve diagram in the state of focusing on WD = 0.25m of the imaging lens of Reference Example 1 . It is an aberration curve diagram in the state of focusing on WD = 0.10m of the imaging lens of Reference Example 1 .

Hereinafter, an imaging lens system for an imaging device and an embodiment of the 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 image pickup apparatus 100 is an industrial camera for photographing an object WK as a subject and specifying the position and shape of the object WK by image recognition.
The image pickup device 100 is a lens system 10 which is an imaging optical system composed of a plurality of lenses for forming an image of an object WK, and an image pickup element which recognizes the light formed by the lens system 10 as an image. It has an image pickup unit 20 and.
In the lens system 10, it is assumed that the image pickup unit 20 captures an image formed on the image plane Im, and in FIGS. 2, 6, 10, 14, and 18, the reference numeral CG is “cover of the image pickup element”. "Glass" is shown.
Further, in FIGS. 2, 6, 10, 14, and 18, the left direction in the figure is referred to as the "object side" on which the object WK is placed, and the right direction in the figure is referred to as the "image side".

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

The cover glass CG has a "parallel flat plate shape", and the light receiving surface of the image pickup unit 20 matches the image plane Im.

The cover glass CG has a function of shielding and protecting the light receiving surface of the image pickup unit 20, but may also have a function of an infrared cut filter or the like.

The lens system 10 is a lens group in which a first lens group G1 and a second lens group G2 are arranged in order from the object side.
The lens system 10 adjusts the focus by moving the second lens group G2 toward the object during focusing from infinity to a short distance.

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

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

The second a lens group G2a is composed of a second a junction lens L _2a12 in which a positive lens L _2a1 and a negative lens L _2a2 are joined in order from the object side to the image side, and the second b lens group G2b is from the object side to the image side. It is a lens group composed of a second b-junction lens L _2b12 in which a negative lens L _2b1 and a positive lens L _2b2 are joined in this order, a positive lens L _2b3 , a negative lens L _2b4 , and a positive lens L _2b5 .
By arranging the lens on the most object side of the second b lens group G2b as a junction lens and the positive lens on the image side thereof in this way, the lens surface S _2b1 on the object side of the negative lens L _2b1 and the image side lens of the positive lens L _2b2 . The aberration generated between the surface S _2b2 and the lens surface on the object side of the positive lens L _2b3 can be appropriately exchanged, and particularly good correction can be performed for spherical aberration and coma.
Further, by constructing the second a junction lens L _{2a12 in which the second a lens group G2a is arranged in order from the object side with positive and negative refractive power arrangements, the second a junction lens L 2a12 and} the second b junction lens L, which are two junction lenses, are configured. An opening diaphragm 30 is arranged between the lens and the _{lens 2b12} .
That is, the arrangement of the refractive powers of the two bonded lenses is symmetrical with respect to the aperture diaphragm 30. With such a configuration, the color difference between coma aberration and coma aberration can be sufficiently corrected.
At this time, it is desirable that the positive lens L _2a1 of the second a junction lens L _2a12 is a convex lens having a convex surface on the image side, and the negative lens L _2a2 is a negative meniscus lens having a convex surface on the image side.
Further, it is more preferable that the junction surface of the second b junction lens L _2b12 has a concave surface facing the image side.
Further, by arranging the negative lens L _2b4 and the positive lens L _2b5 in this order on the image side of the positive lens L _2b3 , the residual aberration such as curvature of field and distortion is sufficiently corrected while sufficiently securing the exit pupil position. can.

By the way, in the image pickup lens system of the type in which the second b lens group G2b operates at the time of focusing in this way, if it is attempted to reduce the fluctuation of the lens performance at the time of focusing, the peripheral illumination ratio cannot be sufficiently secured and the image plane is affected. There was a problem that the incident angle of the lens became large.
Therefore, in the lens system 10 of the present embodiment, by satisfying the above-mentioned lens configuration and the following conditional equations (1) to (11), the peripheral light amount ratio is increased while suppressing the fluctuation of the lens performance during focusing. It is sufficiently high and the angle of incidence on the image plane can be kept small.

The lens system 10 in the present embodiment has a focal length of the entire lens system 10 including the first lens group G1 and the second lens group G2 in a state of being in focus on an infinite object: f, and the first lens group G1. When the focal length is f1, the following conditional expression (1) is satisfied.

The conditional expression (1) shows that the refractive power of the first lens group G1 is weak with respect to the entire lens system 10.
If the upper limit of the conditional equation (1) is exceeded, the positive power of the first lens group G1 becomes excessive, and it becomes difficult to correct the coma aberration at the time of focusing the second b lens group.
Further, since the refractive force of the second lens group G2 is relatively weakened, the function of the second lens group G2 as the focus group is lowered and the amount of movement is increased, so that the entire lens system 10 is large. It also leads to the conversion.
On the other hand, if it falls below the lower limit, the refractive power of the first lens group G1 becomes excessive on the negative side, and it becomes difficult to sufficiently reduce the curvature of field caused by the change in the object distance to the subject WK.

By satisfying the conditional expression (1), the lens system 10 can suppress aberration fluctuations during focusing.

Further, more preferably, the conditional expression (1) is more preferably within the range of −0.15 <f / f1 <0.15.
In this way, 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 during focusing is further reduced, and the fluctuation of the aberration during focusing is suppressed.

Further, in the present embodiment, the lens system 10 satisfies the following conditional expression (2) when the focal length of the negative lens L _2b4 is f _L2b4 and the focal length of the positive lens L _2b5 is f _L2b5 .

The conditional expression (2) shows the ratio of the refractive powers between the positive lens L _2b5 and the negative lens L _2b4 , and balances the refractive powers of the two lenses arranged on the image side of the lens system 10. By setting it within the range of the conditional expression (2), the aberration that cannot be completely corrected and remains can be satisfactorily corrected, and the imaging performance can be further improved.
Further, when it is out of the range of the conditional expression (2), it is particularly difficult to correct the curvature of field aberration, so that it is difficult to achieve satisfactory imaging performance.

Further, the lens system 10 has the following conditions when the focal length of the second b-junction lens L _2b12 is f _L2b12 and the focal length of the positive lens L _2b3 arranged on the image side of the second b-junction lens L _2b12 is f _L2b3 . Equation (3) is satisfied.

The conditional expression (3) defines the ratio of the refractive powers of the second b junction lens L _2b12 and the positive lens L _2b3 .
That is, when the upper limit of the conditional expression (3) is exceeded, the positive refractive power of the positive lens L _2b3 becomes too small, and the balance of aberration correction between the second b junction lens L _2b12 and the positive lens L _2b3 is lost, which is good. It is difficult to obtain good imaging performance.
Further, when the value is lower than the lower limit of the conditional expression (3), the refractive power of the positive lens L _2b3 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 improve spherical aberration and coma aberration, and can be miniaturized.

Further, in the lens system 10 of the present invention, the radius of curvature of the object-side lens surface S _2b1 of the negative lens L _2b1 : _{RL2b1sur. 1.} Radius of curvature of the image-side lens surface S _2b2 of the positive lens L _2b2 : _RL2b2sur. When it is ₂ , the following conditional expression (4) is satisfied.

By satisfying the conditional equation (4), better aberration correction, particularly good correction of spherical aberration and coma, can be performed.

The conditional expression (4) represents the ratio of the radii of curvature of the lens surfaces on the object side, the image side, and both sides of the second b junction lens L _2b12 , and when the value outside the range of the conditional expression (4) is taken, The balance between spherical aberration and coma is lost, making it difficult to obtain good imaging performance.

Further, in the present embodiment, the lens system 10 satisfies the following conditional expression (5) when the refractive index of the positive lens L _2b3 with respect to the d line is nd _L2b3 .

If the positive lens L _2b3 is made of a substance having a refractive index larger than the upper limit of the conditional expression (5), the cost will increase sharply, which may lead to an increase in the cost of the lens.
On the other hand, if a material having a refractive index smaller than the lower limit of the conditional expression (5) is used, it becomes difficult to secure the positive refractive power required for aberration correction, and the radius of curvature of the lens surface becomes large. Become. Such an increase in the radius of curvature of the lens surface may lead to an increase in the angle of incidence on the lens surface, and thus various aberrations such as spherical aberration, coma aberration, and curvature of field are likely to occur, which is not preferable.
Further, such an increase in the radius of curvature may increase the sensitivity of performance deterioration to manufacturing errors.
The lens system 10 of the present embodiment can be miniaturized and good aberration correction can be achieved by satisfying the conditional expression (5).

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

In the conditional formula (6), L represents the so-called total length of the lens, Ls represents the length of the object-side portion of the lens system 10 up to the aperture diaphragm 30, and the conditional formula (6) represents the "total length of the lens system 10" with respect to the total length of the lens system 10. It defines "the distance on the optical axis from the lens surface on the object side of the lens located closest to the object side in the system to the aperture stop 30".

If the upper limit of the conditional equation (6) is exceeded, the position of the aperture diaphragm 30 will be too close to the image side with respect to the entire lens system, the degree of freedom of the second b lens group G2b will be reduced, and the degree of freedom in the lens system 10 will be reduced. It becomes difficult to correct aberrations in the second b lens group G2b, which occupies a relatively large proportion of the refractive power.
Further, since the off-axis light rays passing through the first lens group G1 and the second a lens group G2a become high, it leads to an increase in the size of the first lens group G1, which is not preferable.
Further, if it is less than the lower limit of the conditional expression (6), the position of the aperture diaphragm 30 is too close to the object side with respect to the entire lens system, which leads to an increase in the size of the aperture diaphragm 30. Further, the off-axis light rays passing through the second b lens group G2b become too high, which leads to an increase in the size of the second b lens group G2b, which is not preferable.

In the present embodiment, the size can be reduced and good aberration correction can be achieved by the configuration satisfying the conditional expression (6).

Further, in the present embodiment, in the lens system 10, the position of the first lens group G1 is fixed with respect to the image plane at the time of focusing.
With such a 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 is a lens on the object side of the lens L located on the most object side of the first b lens group G1b from the image side lens surface of the lens located on the image side of the first a 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 of the first lens group G1 to the image-side lens surface of the lens located closest to the image side of the first lens group G1. When the distance on the axis is L ₁ , the conditional expression (7) is satisfied.

The conditional equation (7) is on the optical axis from the object-side lens surface of the lens located closest to the object side of the first lens group G1 to the image-side lens surface of the lens located closest to the image side of the first lens group G1. It defines the ratio of the distance on the optical axis between the first a lens group G1a and the first b lens group G1b with respect to the distance of.
If the upper limit of the conditional expression (7) is exceeded, the distance between the first a lens group G1a and the first b lens group G1b becomes too wide, and the first a lens group G1a becomes large.
If it falls below the lower limit of the conditional equation (7), the distance between the first a lens group G1a and the first b lens group G1b becomes too narrow, and the aberration generated in the first a lens group G1a is corrected by the first b lens group G1b. It becomes difficult to cut off, and deterioration of imaging performance is likely to occur.

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

In the present embodiment, the lens system 10 is the distance on the optical axis from the object-side lens surface of the second b-junction lens L _2b12 to the image-side lens surface: D _L2b12 , the lens located closest to the object side in the second b lens group G2b. Conditional expression (8) is satisfied when the distance on the optical axis from the lens surface S _2b1 on the object side of L _2b1 to the lens surface on the image side of the lens L _2b5 located closest to the image side: L _2b .

The conditional expression (8) defines the ratio of the wall thickness of the second b junction lens L _2b12 to the thickness on the optical axis of the second b lens group G2b.
When the upper limit of the conditional equation (8) is exceeded, the distance between the object-side lens surface of the negative lens L _2b1 and the image-side lens surface of the positive lens L _2b2 becomes excessive, and the positive lens L _2b3 , the negative lens L _2b4 , and the positive lens The degree of freedom of each lens of L _{2b 5} is reduced.
Therefore, it becomes difficult to reduce the size of the lens system 10, and further, it becomes difficult to sufficiently correct the monochromatic aberration.
If it falls below the lower limit of the conditional equation (8), the distance between the object-side lens surface of the negative lens L _2b1 and the image-side lens surface of the positive lens L _2b2 becomes too small, and it becomes difficult to sufficiently correct spherical aberration and coma. ..
In the present embodiment, if the lens system 10 satisfies the conditional expression (8), it is possible to effectively achieve both miniaturization and high performance of the imaging lens.

Further, in the present embodiment, the negative lens L _2b1 has a refractive index of the negative lens L _2b1 with respect to the d line: nd _L2b1 , and an Abbe number of the negative lens L _2b1 with respect to the d line: νd _L2b1 , g line, F line, and C line. Partial dispersion ratio defined as (n _g -n _F ) / (n _F -n _C ) using refractive index n _g , n _F , n _C : θ _{g, F} , the following conditional expression is satisfied. do.

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

Further, in the lens system 10 of the present embodiment, it is preferable that the first lens group G1 is composed of a negative lens L _1a1 , a negative lens L _1a2 , and 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, refraction can be shared and good aberration correction becomes possible.

Further, in the present embodiment, it is preferable that all the lenses constituting the lens system 10 are spherical lenses. Although not limited to such a configuration, by not adopting a lens having an aspherical surface or a diffractive surface, it is possible to avoid an increase in cost of, for example, a molding die. It is particularly advantageous in terms of cost when producing small lots.

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

Further, in the present embodiment, the image pickup apparatus 100 has a lens system 10. By using such a lens system 10, a high-performance image pickup device capable of satisfactorily correcting aberrations from infinity to a short distance without causing performance deterioration during focusing becomes possible.

Hereinafter, Examples 1 to 4 will be shown as specific numerical examples of the present invention.
The meanings of the symbols in the examples are as follows.

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

As shown in the aberration diagram of each embodiment, the aberration is corrected at a high level in each embodiment, and the change in curvature of field due to focusing is well suppressed. Spherical aberration, axial chromatic aberration, and magnifying chromatic aberration are also small, and coma aberration is well suppressed to the outermost periphery. In addition, the distortion aberration is 0.8% or less in absolute value from close to infinity.
That is, all of the lens systems 10 shown in Examples 1 to 5 realize an imaging lens in which various aberrations are sufficiently reduced. That is, it has a resolving power corresponding to an image sensor with an angle of view of about 37 ° to 54 °, an F number of about 1.8, and an image sensor of 8 million pixels with 10 lenses, and a "straight line" with a working distance of 0.1 m from an infinite object. Can be depicted as a straight line ", and it is a high-performance image sensor with little change in performance due to focusing.

(Numerical Example 1)
FIG. 2 shows an optical layout of the lens system 10 according to the first embodiment. It is composed of the first lens L1 to the tenth lens L10 in order from the object side (left side of the paper surface), and the aperture stop 30 is installed between L5 and L6.
In the first embodiment, the aberration diagram in the state of being in focus at infinity is shown in FIG. 3, and the aberration diagram in the state of focusing in the working distance: 0.25 m is shown in FIG. 4, the working distance is focused in 0.10 m. The aberration diagram in the state is shown in FIG. 5, respectively.

The intervals A and B shown in Table 2 are lens intervals corresponding to A and B shown in FIG. 1 when focused to the respective working distance values.
The numerical values relating to each of 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. It is composed of the first lens L1 to the tenth lens L10 in order from the object side (left side of the paper surface), and the aperture stop 30 is installed between L5 and L6.
In the second embodiment, the aberration diagram in the state of being in focus at infinity is shown in FIG. 7, and the aberration diagram in the state of focusing in the working distance: 0.25 m is shown in FIG. 8, the working distance is focused in 0.10 m. The aberration diagram in the state is shown in FIG. 9, respectively.

The intervals A and B shown in Table 5 are lens intervals corresponding to A and B shown in FIG. 1 when focused to the respective working distance values.
The numerical values relating to each of 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. It is composed of the first lens L1 to the tenth lens L10 in order from the object side (left side of the paper surface), and the aperture stop 30 is installed between L5 and L6.
In the third embodiment, the aberration diagram in the state of being in focus at infinity is shown in FIG. 11, and the aberration diagram in the state of focusing in the working distance: 0.25 m is shown in FIG. 12, the working distance is focused in 0.10 m. The aberration diagram in the state is shown in FIG. 13, respectively.

The intervals A and B shown in Table 8 are lens intervals corresponding to A and B shown in FIG. 1 when focused to the respective working distance values.
The numerical values relating to each of 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 Example 4)
FIG. 14 shows an optical layout of the lens system 10 according to the fourth embodiment. It is composed of the first lens L1 to the tenth lens L10 in order from the object side (left side of the paper surface), and the aperture stop 30 is installed between L5 and L6.
In the fourth embodiment, the aberration diagram in the state of being in focus at infinity is shown in FIG. 15, and the aberration diagram in the state of being in focus at working distance: 0.25 m is shown in FIG. 16, and the working distance is focused on 0.10 m. The aberration diagram in the state is shown in FIG. 17, respectively.

The intervals A and B shown in Table 11 are lens intervals corresponding to A and B shown in FIG. 1 when focused to the respective working distance values.
The numerical values relating to each of 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 °

( Reference example 1 )
FIG. 18 shows an optical layout of the lens system 10 as Reference Example 1 . It is composed of the first lens L1 to the tenth lens L10 in order from the object side (left side of the paper surface), and the aperture stop 30 is installed between L5 and L6.
In Reference Example 1 , the aberration diagram in the state of focusing at infinity is shown in FIG. 19, and the aberration diagram in the state of focusing to working distance: 0.25 m is shown in FIG. 20, and the working distance is focused to 0.10 m. The aberration diagram in the state is shown in FIG. 21, respectively.

The intervals A and B shown in Table 14 are lens intervals corresponding to A and B shown in FIG. 1 when focused to the respective working distance values.
The numerical values relating to each of 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 the numerical examples 1 to 4 . It is clear from each embodiment that good optical performance can be ensured.

Although the embodiments according to the present invention have been described above, the present invention is not limited to the above-described embodiments as they are, and at the implementation stage, the components can be modified and embodied within a range that does not deviate from the gist thereof. .. In addition, various inventions can be formed by an appropriate combination of the plurality of components disclosed in the above-described embodiment. For example, some components may be removed from all the components shown in the embodiments. Further, different embodiments and modifications may be appropriately combined.

10 Imaging optical system (lens system)
20 Image sensor 100 Image sensor f Focal length of the entire system when focused on an infinite object
f ₁ Focal length of the first lens group
f _L2b4 Negative lens L _2b4 focal length
f _L2b5 Focal length of positive lens L _2b5
nd _L2b3 Refractive index of positive lens L _2b3 with respect to d line
R _{L2b1 sur.1} Negative lens L _2b1 Radius of curvature of the object side lens surface
R _L2b2sur.2 Positive lens L The radius of curvature of the image side lens surface of _2b2 Ls Distance on the optical axis from the object side lens surface of the lens located on the object side most in the whole system L Position on the object side most in the whole system Distance on the optical axis from the lens surface on the object side of the lens to the lens surface on the image side of the lens located on the image side most in the entire system

Japanese Unexamined Patent Publication No. 2017-083770 Japanese Unexamined Patent Publication No. 2016-126277

Claims (14)

The first lens group and the positive second lens group are arranged in order from the object side.
This is an imaging lens system in which the second lens group moves toward the object so that the distance from the first lens group decreases when focusing from infinity to a short distance.
The first lens group is composed of a negative first a lens group and a positive first b lens group in order from the object side to the image side.
The second lens group is composed of a positive second a lens group, an aperture, and a positive second b lens group in order from the object side.
The second a lens group is composed of a second a junction lens in which a positive lens and a negative lens are joined in order from the object side to the image side.
The second b lens group consists of a second b-junction lens L _2b12 , a positive lens L _2b3 , a negative lens L _2b4 , and a positive lens L _2b5 in which a negative lens L _2b1 and a positive lens L _2b2 are joined in order from the object side to the image side. Configured,
When the focal length of the entire system is f and the focal length of the _first lens group is f1 when the object is in focus at infinity, the conditional equation (1):
(1) -0.20 <f / f ₁ <0.20
An imaging lens system characterized by satisfying. In the imaging lens system according to claim 1,
When the focal length of the negative lens L _2b4 is f _L2b4 and the focal length of the positive lens L _2b5 is f _L2b5 ,
Conditional expression (2):
(2) -1.55 <f _L2b4 / f _L2b5 <-0.90
An imaging lens system characterized by satisfying. In the imaging lens system according to claim 1 or 2,
When the focal length of the second b junction lens is f _L2b12 and the focal length of the positive lens L _2b3 of the second b lens group is f _L2b3 , the conditional equation (3):
(3) -2.5 <f _L2b12 / f _L2b3 <-1.3
An imaging lens system characterized by satisfying. The imaging lens system according to any one of claims 1 to 3.
Conditional expression (4): When the radius of curvature of the lens surface on the object side of the negative lens L _2b1 is R _L2b1sur.1 and the radius of curvature of the lens surface on the image side of the positive lens L _2b2 is R _L2b2sur.2 .
(4) 0.65 <R _L2b1sur.1 / R _L2b2sur.2 <0.90
An imaging lens system characterized by satisfying. In the imaging lens system according to any one of claims 1 to 4.
When the refractive index of the positive lens L _2b3 with respect to the d line is nd _L2b3 , the conditional expression (5):
(5) 1.80 <nd _L2b3 <2.05
An imaging lens system characterized by satisfying. 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 on the object side of the entire system to the aperture: Ls, from the object side lens surface of the lens located on the object side of the entire system to the image side of the entire system Conditional expression (6): When the distance on the optical axis to the image side lens surface of the positioned lens is L:
(6) 0.48 <Ls / L <0.63
An imaging lens system characterized by satisfying. 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 to the image plane during 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 on the image side of the 1st a lens group to the object side lens surface of the lens located on the object side of the 1b lens group: D _L1a-L1b , 1st The distance on the optical axis from the object-side lens surface of the lens located on the most object side of the lens group to the image-side lens surface of the lens located on the image side of the _first lens group: Conditional expression (L1) 7):
(7) 0.15 <D _L1a-L1b / L ₁ <0.35
An imaging lens system characterized by satisfying. 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 junction lens to the image side lens surface: D _L2b12 , the image located most on the image side from the object side lens surface of the lens located on the object side of the 2b lens group. Conditional expression (8): When the distance on the optical axis to the side lens surface is L _2b :
(8) 0.40 <D _L2b12 / L _2b <0.60
An imaging lens system characterized by satisfying. The imaging lens system according to any one of claims 1 to 9.
Refractive index of negative lens L _2b1 with respect to d line: nd _L2b1 ,
Abbe number of negative lens L _2b1 for d line: νd _L2b1 ,
The partial dispersion ratio defined as (n _g --n _F ) / (n _F --n _C ) by the refractive indexes n _g , n _F , and n _C for the g-line, F-line, and C-line of the negative lens L _2b1 : θ _g . _{, F} , conditional expressions (9), (10), (11), respectively
(9) 1.78 <nd _L2b1 <2.00
(10) 20.0 <νd _L2b1 <32.0
(11) 0.005 <θ _{g, F} -(-0.001802 × ν _dL2b1 + 0.6483) <0.009
An imaging lens system characterized by satisfying. In the imaging lens system according to any one of claims 1 to 10.
An imaging lens system characterized in that the first lens group is composed of a negative lens L _1a1 , a negative lens L _1a2 , and a positive lens L _1b1 . In the imaging lens system according to any one of claims 1 to 11.
An imaging lens system characterized in that all the lenses constituting the first group lens group and the second lens group are spherical lenses. In the imaging lens system according to any one of claims 1 to 12,
An imaging lens system characterized in that all the lens materials constituting the first group lens group and the second lens group are inorganic solid materials. An image pickup apparatus having the imaging lens system according to any one of claims 1 to 13.

Images