JP6972994B2 - Imaging lens, imaging device - Google Patents

Description

The present invention relates to an imaging lens and 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 imaging lenses used in such applications have higher lens performance associated with focusing than conventional camera applications. It is important that there is little decline 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, the conventional method has problems such as large fluctuations in spherical aberration and coma during focusing, and large F-numbers.

The present invention has been made in view of the above, and an object of the present invention is to provide an imaging lens that is bright and can sufficiently suppress fluctuations in lens performance due to focusing.

The imaging lens of the present invention comprises a first lens group, an aperture, a second lens group having a positive refractive force, and a third lens group in order from the object side to the image side, and is arranged from infinity to near infinity. when focusing to a distance, the said first lens group and the aperture stop and the second lens group an imaging lens moves toward the object side so as to increase the distance between the third lens group integrally, wherein The first lens group is a four-lens group consisting of a negative lens arranged on the most object side, a negative lens arranged on the most image side of the first lens group and having a concave surface facing the image side, and the above. It has two positive lenses arranged between two negative lenses, and the second lens group is a negative lens having a concave surface facing the object side in order from the object side to the image side. It is composed of three lenses, a lens and a positive lens, and the third lens group is composed of a positive lens, a negative lens, and a positive lens having a convex surface facing the image side in order from the object side to the image side, and is infinite. focal length of the entire system in a state of focusing on distant object: f, the composite focal length of the first lens group and the second lens _group: f _1g2g, the focal length of the third lens group: f _{3 g,} of the third lens group Distance on the optical axis from the image side lens surface of the negative lens to the object side lens surface of the positive lens arranged on the image side of the negative lens: d, the object of the positive lens on the most object side of the third lens group When the distance on the optical axis from the side lens surface to the image side lens surface of the positive lens arranged on the image side is D _{3 g} , the following conditional equations (1) to (3): (1) 0. 80 <f _1g 2g _{/ f <1.20 (2) -0.15 <f / f 3g} <0.25 (3) 0.03 <d / D _3g <0.20 is satisfied.

According to the imaging lens of the present invention, it is bright and can sufficiently suppress fluctuations in lens performance due to focusing.

It is a schematic structure 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 Example 5. FIG. It is an aberration curve diagram in the infinity focusing state of the imaging lens of Example 5. FIG. It is an aberration curve diagram in the state which focused on WD = 0.25m of the imaging lens of Example 5. FIG. It is an aberration curve diagram in the state which focused on WD = 0.10m of the imaging lens of Example 5. FIG.

Hereinafter, an imaging lens 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 as an imaging lens, 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 uses a lens system 10 as an imaging lens, which is an imaging optical system composed of a plurality of lenses for forming an image of an object WK, and light formed by the lens system 10 as an image. It has an image pickup unit 20 which is an image pickup element for recognizing.
In the lens system 10, it is assumed that the image pickup unit 20 captures an image formed on the image plane Im, and the reference numeral CG in FIG. 2 indicates “cover glass of the image pickup element”.
Further, in FIG. 2, 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”. Such a reference numeral is also common to FIGS. 6, 10, 14, and 18 showing the lens configuration in other numerical examples described later.

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.

In the lens system 10, the first lens group G1 having a positive or negative refractive power, the aperture 30 having an aperture aperture, the second lens group G2 having a positive refractive power, and the positive or negative refraction, in order from the object side, It is a lens group in which a third lens group G3 having power is arranged.
In the lens system 10, when focusing from infinity to a short distance, the first lens group G1, the second lens group G2, and the aperture 30 move together toward the object side to increase the distance between the first lens group G1 and the third lens group G3. Adjust the focus with.

_{As shown in FIG. 2, the first lens group G1 is a negative lens L 11} and a second lens, which are first lenses having a negative refractive power and having a concave surface facing the image side in order from the object side to the image side. It is composed of a positive lens L ₁₂ , a positive lens L _{13 which is a third lens, and a negative lens L 14 which is} a fourth lens with a concave surface facing the image side.
That is, the first lens group G1 is composed of four lenses in the present embodiment, and the refractive power of each lens is arranged so as to be negative, positive, positive, and negative in order from the object side to the image side. Has been done.
As will be described later in Numerical Example 5, the first lens group G1 has a _{three-lens configuration in which the negative lens L 11} arranged on the object side is omitted and the positive, positive, and negative refractive power arrangements are used. It may be a lens group of.

The second lens group G2 consists of a negative lens L ₂₁ , which is a fifth lens, a positive lens L ₂₂ , which is a sixth lens, and a positive lens L _{23, which is a seventh lens, in order from the object side to the image side.} This is a lens group consisting of three lenses. _{Let the} radius of curvature of the object-side lens surface S _{21a of the negative lens L 21} of the second lens group G2 be RL 2 ga.
The second lens group G2 has a positive refractive power as a whole.

_{The third lens group G3 includes a positive lens L 31 as} an eighth lens, a negative lens L _{32 as} a ninth lens, and a positive lens L _{33 as a} tenth lens, in which the convex surface is directed toward the image side in order from the object side to the image side. This is a three-lens lens group composed of.
In this way, by forming the third lens group G3 into a lens group having three lenses, the aberration correction ability is improved, and by making the arrangement of the refractive power positive, negative, and positive, the so-called triplet type, the number of lenses is increased. It is possible to balance the fluctuations of various aberrations that occur during focusing from infinity to short distances, while minimizing the amount of noise.
A gap shown by d (≠ 0) in FIG. 2 is formed between _{the positive lens L 33} arranged on the image side of the third lens group and the negative lens L _{32 of the third lens group.} .. Such d is "the distance on the optical axis from the image side lens surface of _{the negative lens L 32} of the third lens group G3 to _{the object side lens surface of the positive lens L 33} ", and is the negative lens L ₃₂ and the positive lens L _33. The lens spacing between and.

In the lens system 10 having the configuration shown in the present embodiment, the lens system 10 satisfies the following conditional expressions (1) to (3). However, the focal distance of the entire system in the focused state at infinity: f, the combined focal distance of the first lens group and the second lens group: f _1g2g , the focal distance of the third lens group: f _3g , the third lens group. Distance on the optical axis from the image-side lens surface of the negative lens L _{32 of G3 to the object-side lens surface of the positive lens L 33} : d, the lens surface of the third lens group G3 from the most object-side lens surface to the most image-side lens surface Distance on the optical axis to: D _3g .

The conditional equation (1) defines the ratio of the combined focal lengths of the first lens group G1 and the second lens group G2 to the focal lengths of the entire system.
If the upper limit of the conditional expression (1) is exceeded, the combined power of the first lens group G1 and the second lens group G2 becomes too small with respect to the power of the entire system, so that the function as the focus group is weakened. Therefore, it is not preferable because it causes an increase in the amount of movement during focusing and an accompanying increase in the size of the lens.
Further, if it falls below the lower limit of the conditional equation (1), the combined power of the first lens group G1 and the second lens group G2 becomes excessive with respect to the power of the entire system, so that the first lens group G1 and the second lens Aberration is likely to occur in the group G2. Therefore, it becomes more difficult to correct the aberration at the time of focusing, and the fluctuation of the lens performance at the time of focusing tends to be large, which is not preferable.
In the present embodiment, if the lens system 10 satisfies the conditional expression (1), focusing can be performed with a small amount of movement while performing good aberration correction.

Further, the lens system 10 in the present embodiment satisfies the conditional expression (2).

The conditional expression (2) defines the ratio of the focal lengths of all the lens systems 10 to the focal lengths of the third lens group G3. The third lens group G3 plays a role of reducing the angle of incidence of off-axis light rays on the image plane, and improves imaging performance by satisfactorily correcting residual aberrations generated in the first lens group G1 and the second lens group G2. Has a role to play.
When it is out of the range of the conditional equation (2), the power of the third lens group G3 becomes excessive with respect to the power of the entire lens system 10, so that the first lens group G1 and the second lens group, which are the focus groups, are present. There is a problem that the exchange of aberrations with G2 cannot be well balanced, and the fluctuation of lens performance during focusing tends to be large.
In the present embodiment, by satisfying the conditional expression (2), fluctuations in aberration during focusing are suppressed while performing good aberration correction.

Further, the lens system 10 in the present embodiment satisfies the conditional expression (3).

_{The conditional equation (3) is a positive lens L 33} from the image side lens surface _{of the negative lens L 32} with respect to the distance from the most object side lens surface of the third lens group G3 to the most image side lens surface of the third lens group G3. It defines the ratio of the distance to the lens surface on the object side.
In other words, the conditional expression (3) is the ratio of the lens spacing between the _{negative lens L 32} and the positive lens L _{33 to the lens length of the third lens group G3.}
As is clear from the conditional expression (3), in this embodiment, d ≠ 0 in any numerical embodiment.
In this way, the interval between the negative lens L ₃₂ and the positive lens L ₃₃ has the value of finite space serves as an air lens between the negative lens L ₃₂ and the positive lens L _33, the first lens group G1 And the residual aberration generated in the second lens group G2 can be satisfactorily corrected.

If the upper limit of the conditional expression (3) is exceeded, the distance between the negative lens L ₃₂ and the positive lens L ₃₃ becomes excessive with respect to the lens length of the third lens group G3. _{Therefore, the shapes of the lenses L 31} , L ₃₂ , and L ₃₃ constituting the third lens group G3 are limited, and it becomes difficult to perform good aberration correction.
Further, if it falls below the lower limit of the conditional expression (3), _{the distance between the negative lens L 32} and the positive lens L ₃₃ becomes too small with respect to the total lens length of the third lens group G3. Therefore, the effect as an air lens cannot be sufficiently obtained, and particularly good aberration correction of spherical aberration and coma becomes difficult, which is not preferable.

In the present embodiment, by satisfying the conditional expressions (1) to (3), it is possible to sufficiently suppress fluctuations in lens performance during focusing.

The conditional expression (1) is more preferably in the range of _{0.80 <f 1g 2g / f <1.05.}
Within such a range, focusing can be performed with a small amount of movement while performing better aberration correction.
_{Further, it is desirable that the positive lens L 31} of the third lens group G3 and the negative lens L ₃₂ are integrally formed as a junction lens.
In the third lens group G3, _{aberrations are exchanged between the positive lens L 31} having a positive power and the negative lens L ₃₂ having a negative power, which particularly contributes to the reduction of coma aberration.
By using these two lenses as a bonded lens, it is less likely to be affected by manufacturing errors that occur during assembly, and stable performance can be ensured.

Further, in the positive lens L ₃₁ , it is preferable that the object-side lens surface S _31a has a concave surface facing the object side. Further, the positive lens _{L 33,} the radius of curvature _{R S31a} of the object side lens surface _{S 31a} is, it is preferably smaller than the absolute value of the curvature radius _{R S31b} of the image-side lens surface _{S 31b.}
By setting the lens surface that exchanges spherical aberration and coma as described above, fluctuations in spherical aberration and coma associated with focusing can be further suppressed.

Further, the lens system 10, the focal length of the positive lens _{L 31:} f _L31, the focal length of the positive lens _{L 33:} f _L33, and the time, satisfies the conditional expression (4).

The conditional expression (4) defines the ratio of the focal length of the positive lens L _{33 to the focal length of the positive lens L 31.}
By being within the range of the conditional expression (4), the distribution of positive power in the third lens group G3 is shared in a well-balanced manner within an appropriate range, so that the correction of spherical aberration and coma is particularly well corrected. be able to.
If it goes out of the range of the conditional expression (4), the balance of positive power in the third lens group G3 is biased to one side, so that the aberration balance is lost and the performance is likely to deteriorate.

Further, the lens system 10 satisfies the conditional equation (5) when _{the focal length of the negative lens L 32 is f L32} and the focal length of the positive lens L ₃₁ is f _L31.

Conditional expression (5) defines the ratio of the focal length of the negative lens L _{32 to the focal length of the positive lens L 31.}
When the upper limit of the conditional expression (5) is exceeded, _{the power of the negative lens L 32 becomes excessive and the aberration exchange with the positive lens L 33} located closest to the image side becomes excessive, resulting in good aberration correction. It will be difficult.
If it falls below the lower limit of the conditional expression (5), the negative power of the negative lens L ₃₂ becomes too small, and the aberration correction between the positive lens L 31 and the negative lens L ₃₃ becomes insufficient, which is not preferable.

By satisfying the conditional expression (5), the aberration correction of the third lens group G3 can be satisfactorily corrected.

Further, in the lens system 10, the conditional equation (6) is satisfied when the radius of curvature of the image side lens surface of _{the negative lens L 32 is RL 32b} and the radius of curvature of the object side lens surface of the positive lens L _{33 is RL 33a.} ..

The conditional expression (6) defines the optical shape of the lens surface formed by _{the negative lens L 32} and the positive lens L _33.
If the upper limit of the conditional equation (6) is exceeded, the radius of curvature of the image side lens surface of _{the negative lens L 32 and the radius of curvature of the object side lens surface of the positive lens L 31} become too close to each other, resulting in spherical aberration and an image. The correction of curvature of field becomes insufficient, and outward coma aberration is likely to occur.
On the contrary, when it is below the lower limit of the conditional expression (6), spherical aberration is likely to occur on the over side, or inward coma is likely to occur.

Further, in the lens system 10, it is desirable that the first lens group G1 is fixed to the image plane at the time of focusing.
With such a configuration, the moving mechanism for focusing is simplified, and the entire lens including the mechanism can be easily miniaturized.

Further, the first lens group G1 has a negative lens L ₁₄ having a concave surface facing the image side, and at least two positive lenses L ₁₂ and L ₁₃ arranged on the object side of the negative lens L ₁₄ and the most object side. It has a negative lens L ₁₁ arranged in.
Further, the second lens group G2 has a negative lens L ₂₁ having a concave surface facing the object side, a positive lens L ₂₂ and a positive lens L ₂₃ in order from the object side to the image side.
With such a configuration, the arrangement is close to the Gaussian type, which is symmetrical with respect to the aperture 30, so that various aberrations generated in the focus group can be suppressed to a sufficiently small value.

As described above, the first lens group G1 may have a three-lens configuration in which the refractive power is positive, positive, and negative in order from the object side to the image side.
With such a configuration, various aberrations can be suppressed to a sufficiently small value with a smaller number of lenses.

Lens system 10, the curvature of the image side lens surface of the negative lens _{L 14} disposed nearest to the image side of the first lens group G1 _{radius: R L1gb,} the object-side lens surface of the negative lens _{L 21} of the second lens group G2 S _{When the} radius of curvature of _{21a is RL2ga} , the conditional equation (7) is satisfied.

The conditional expression (7) regulates the shape of the "negative air lens" formed on the adjacent surface between the first lens group G1 and the second lens group G2 with the aperture in between.
If the upper limit of the conditional equation (7) is exceeded, the radius of curvature of the image-side lens surface S _{14b of the negative lens L 14 arranged on the image-most side of the first lens group G1 becomes excessive.}
On the other hand, if it falls below the lower limit of the conditional equation (7), the radius of curvature of the object-side lens surface S _{21a of the negative lens L 21 of the second lens group G2 becomes excessive.}

In the present embodiment, by keeping the condition within the range of the conditional expression (7), the power distribution between the concave surface on the object side and the concave surface on the image side sandwiching the diaphragm 30 is appropriately performed, and particularly good correction of coma aberration is performed. To facilitate.

Further, the lens system 10 satisfies the conditional equation (8), where the radius of curvature of the image-side lens surface of _{the positive lens L 22 is RL 22b} and the radius of curvature of the lens surface of the positive lens L _{23 on} the object side is _{RL 23a.}

The conditional expression (8) regulates the shape of the air lens by regulating the shape formed between _{the positive lens L 22} and the positive lens L _23.
If the upper limit of the conditional equation (8) is exceeded, the _{radius of curvature of the image side lens surface of the positive lens L 22} becomes excessive, so that inward coma is likely to occur or spherical aberration is likely to be corrected on the over side. ..
If it is below the lower limit of the conditional equation (8), the _{radius of curvature of the lens surface on the object side of the positive lens L 23} becomes excessive, so that outward coma aberration is likely to occur or spherical aberration is likely to occur on the under side.
As described above, by keeping the condition within the range of the conditional expression (8), the lens system 10 can satisfactorily correct the spherical aberration and the coma aberration.

Further, in the lens system 10, when the lens adjacent to the image side of the aperture 30 is a negative lens, the refractive index of the negative lens with respect to the d line: nd _n , the Abbe number with respect to the d line: ν d _n , g line. Partial dispersion ratio when the refractive index for the F line and C line is n _g , n _F , n _{c : θ g} , F (= ((n g -n _F ) / (n _F -n _c ))) , The following conditional equations (9) to (11) are satisfied.

The conditional expressions (9) to (11) all show the refractive index, Abbe number, and anomalous dispersibility of the glass material of _{the negative lens L 21 of the second lens group G2, and have a high refractive index but a high dispersion.} Moreover, since it has anomalous dispersibility, it is possible to sufficiently correct chromatic aberration while correcting monochromatic aberration.
Further, in the imaging lens of the present invention, it is desirable that all the lenses constituting the lens system 10 are spherical lenses.
A lens having an aspherical surface or a diffractive surface may be used, but by configuring the lens system 10 only with a spherical lens, it contributes to cost reduction of a mold for molding and the like.

Further, in the imaging lens of the present invention, it is desirable that all the lens materials constituting the first lens group G1 and the second lens group G2 are inorganic solid materials.
Organic materials and organic-inorganic hybrid materials are generally vulnerable to changes in temperature and humidity, which may lead to deterioration of optical performance.However, since inorganic solid materials are stable, deterioration of optical performance due to temperature, humidity, etc. Hard to receive.

With each of the above configurations, by using the imaging lens of the present invention, it is possible to obtain a high-performance image pickup apparatus capable of satisfactorily correcting aberrations from infinity to a short distance without causing deterioration in performance during focusing.

Hereinafter, as the imaging lens of the present invention, specific numerical examples of the lens system 10 will be shown. As shown in Examples 1 to 5, aberrations are sufficiently corrected in any of the lens systems 10, and very good image performance can be ensured.
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)

Further, in the aberration diagram shown below, the broken line in the figure of spherical aberration represents the sine and cosine condition.
The solid line in the figure of astigmatism shows sagittal, and the broken line shows meridional.

As shown in the aberration diagram of each embodiment, the aberration is corrected at a high level in each embodiment, and the spherical aberration due to focusing is sufficiently suppressed. Changes in coma aberration and curvature of field are also well suppressed up to the outermost periphery.
Distortion is also an absolute value of 0.8% when measured from close to infinite.
That is, in each of the lenses of Examples 1 to 5, various aberrations are sufficiently reduced, the angle of view is about 24 to 38 ° F-number 1.8, and the resolving power corresponding to an image sensor of about 8 million pixels is achieved. It has a high precision image sensor that can draw a straight line as a straight line at a close distance of 0.1 m from an infinite object and has little change in performance during focusing.
As described above, in the imaging lens according to the present invention, aberrations are sufficiently corrected in the specific configurations shown in the numerical examples 1 to 5. It is clear from each embodiment that good optical performance can be ensured.

(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 L 11} to the tenth lens L ₃₃ in order from the object side (left side of the paper), and the aperture 30 is installed between the _{negative lens L 14} which is the fourth lens and the negative lens L _{21 which is the fifth lens.} Will be done.
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 distance A shown in Table 2 is the lens distance corresponding to A shown in Table 1 when focusing on 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: 16.00
F number: 1.84
Half angle of view ω: 19.0

(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 L 11} to the tenth lens L ₃₃ in order from the object side (left side of the paper surface), and the diaphragm 30 is installed between _{the fourth lens L 14} and the fifth lens L _21.
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 distance A shown in Table 5 is the lens distance corresponding to A shown in Table 4 when focusing on 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: 16.01
F number: 1.84
Half angle of view ω: 19.0

(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 L 11} to the tenth lens L ₃₃ in order from the object side (left side of the paper surface), and the diaphragm 30 is installed between _{the fourth lens L 14} and the fifth lens L _21.
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 distance A shown in Table 8 is the lens distance corresponding to A shown in Table 7 when focusing to each working distance value.
The numerical values relating to each of the conditional expressions (1) to (11) shown above are as shown in Table 9.

Focal length f: 16.00
F number: 1.84
Half angle of view ω: 19.0

(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 L 11} to the tenth lens L ₃₃ in order from the object side (left side of the paper surface), and the diaphragm 30 is installed between _{the fourth lens L 14} and the fifth lens L _21.
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 distance A shown in Table 11 is the lens distance corresponding to A shown in Table 10 when focusing on 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: 16.00
F number: 1.84
Half angle of view ω: 19.0

(Numerical Example 5)
FIG. 18 shows an optical layout of the lens system 10 according to the fifth embodiment. _{It is composed of the first lens L 11} to the ninth lens L ₃₃ in order from the object side (left side of the paper surface), and the diaphragm 30 is installed between the third lens and the fourth lens.
In the fifth embodiment, the aberration diagram in the state of being in focus at infinity is shown in FIG. 19, and the aberration diagram in the state of focusing in the working distance: 0.25 m is shown in FIG. 20, and the working distance is focused in 0.10 m. The aberration diagram in the state is shown in FIG. 21, respectively.

The distance A shown in Table 14 is the lens distance corresponding to A shown in Table 13 when focusing to each working distance value.
The numerical values relating to each of the conditional expressions (1) to (11) shown above are as shown in Table 15.

Focal length f: 24.98
F number: 1.84
Half angle of view ω: 12.4

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) (imaging lens)
20 Image sensor 100 Image sensor f Focal length of the entire system
f _{1g 2g Combined} focal distance of the first lens group and the second lens group f _3g Focal distance of the third lens group f _L31 Focus distance of the positive lens placed closest to the object side of the third lens group _{f L32 Third lens group} Negative lens focal distance f _L33 Positive lens focal distance arranged on the most image side of the third lens group L ₂₁ Negative lens L of _{the second lens group 22 Positive lens L 23} arranged on the object side of the second lens group Positive lens arranged on the image side of the second lens group L ₃₁ Positive lens with a convex surface facing the image side (positive lens arranged on the most object side of the third lens group)
L ₃₂ Negative lens of _{the 3rd lens group L 33} Positive lens arranged on the most image side of the 3rd lens group _{L 1gb} Radius of curvature R of the image side lens surface of the negative lens arranged on the most image side of the 1st lens group _L2ga Radius of curvature of the lens surface of the negative lens of _{the second lens group on the object side RL22b Radiance} of curvature of the image side lens surface of the positive lens arranged on the object side of _{the second lens group RL23a Arranged on} the image side of the second lens group Radius of curvature of the lens surface on the object side of the positive lens

Japanese Unexamined Patent Publication No. 2016-61918 Japanese Patent No. 4361304

Claims (11)

The first lens group, the diaphragm, the second lens group having a positive refractive power, and the third lens group are arranged in order from the object side to the image side.
An imaging lens that moves toward an object so as to increase the distance between the first lens group, the aperture, and the second lens group as a unit when focusing from infinity to a short distance. hand,
The first lens group is a four-lens group consisting of a negative lens arranged on the most object side and a negative lens arranged on the most image side of the first lens group and having a concave surface facing the image side. It has two positive lenses, which are arranged between the two negative lenses.
The second lens group is composed of three lenses, a negative lens, a positive lens, and a positive lens, in which the concave surface is directed toward the object side in order from the object side to the image side.
The third lens group is composed of a positive lens, a negative lens, and a positive lens having a convex surface facing the image side in order from the object side to the image side.
Infinity focal length of a state in which the zoom lens is focused on an object: f, the composite focal length of the first lens group and the second lens _group: f _1g2g, the focal length of the third lens group: f _{3 g,} the third lens group Distance on the optical axis from the image side lens surface of the negative lens to the object side lens surface of the positive lens arranged on the image side of the negative lens: d, of the positive lens on the most object side of the third lens group When the distance on the optical axis from the lens surface on the object side to the lens surface on the image side of the positive lens arranged on the image side is D _{3 g} , the following conditional equations (1) to (3):
(1) 0.80 <f _1g2g / f <1.20
(2) -0.15 <f / f _3g <0.25
(3) 0.03 <d / D _3g <0.20
An imaging lens characterized by satisfying. The first lens group, the diaphragm, the second lens group having a positive refractive power, and the third lens group are arranged in order from the object side to the image side.
An imaging lens that moves toward an object so as to increase the distance between the first lens group, the aperture, and the second lens group as a unit when focusing from infinity to a short distance. hand,
The first lens group has a negative lens arranged on the image side most and a concave surface facing the image side, and at least two positive lenses arranged on the object side of the negative lens.
The second lens group is composed of three lenses, a negative lens, a positive lens, and a positive lens, in which the concave surface is directed toward the object side in order from the object side to the image side.
The third lens group is composed of a positive lens, a negative lens, and a positive lens having a convex surface facing the image side in order from the object side to the image side.
Infinity focal length of a state in which the zoom lens is focused on an object: f, the composite focal length of the first lens group and the second lens _group: f _1g2g, the focal length of the third lens group: f _{3 g,} the third lens group Distance on the optical axis from the image side lens surface of the negative lens to the object side lens surface of the positive lens arranged on the image side of the negative lens: d, of the positive lens on the most object side of the third lens group The distance on the optical axis from the lens surface on the object side to the lens surface on the image side of the positive lens placed closest to the image side: D _{3 g} .
Of the two positive lenses arranged in the second lens group,
Radius of curvature of the image side lens surface of the positive lens placed on the object side: _RL22b,
Radius of curvature of the object-side lens surface of the positive lens placed on the image side: _RL23a,
Then, the following conditional expressions (1) to (3), and (8) :
(1) 0.80 <f _1g2g / f <1.20
(2) -0.15 <f / f _3g <0.25
(3) 0.03 <d / D _3g <0.20
(8) −0.65 <(R _L22b + R _L23a ) / (R _L22b −R _L23a ) <0.15
An imaging lens characterized by satisfying. The first lens group, the diaphragm, the second lens group having a positive refractive power, and the third lens group are arranged in order from the object side to the image side, and the lens adjacent to the image side of the diaphragm is arranged. It is a negative lens
An imaging lens that moves toward an object so as to increase the distance between the first lens group, the aperture, and the second lens group as a unit when focusing from infinity to a short distance. hand,
The third lens group is composed of a positive lens, a negative lens, and a positive lens having a convex surface facing the image side in order from the object side to the image side.
Infinity focal length of a state in which the zoom lens is focused on an object: f, the composite focal length of the first lens group and the second lens _group: f _1g2g, the focal length of the third lens group: f _{3 g,} the third lens group Of the negative lens
Distance on the optical axis from the image-side lens surface to the object-side lens surface of the positive lens arranged on the image side of the negative lens: d, the object-side lens surface of the most object-side positive lens in the third lens group Distance on the optical axis from to the image side lens surface of the positive lens placed closest to the image side: D _{3 g} , and the refractive index of the negative lens adjacent to the image side of the aperture with respect to the d line: nd _n , d line Abbe number of the negative lens which is adjacent to the image side of the aperture for: [nu] d _n, g-line, F-line, the refractive index n _g for the C line, n _F, the _{n C (n g -n F)} / (n F - When the partial dispersion ratio defined as _{n C ) is θ g, F} , the following conditional equations (1) to (3) and (9) to (11):
(1) 0.80 <f _1g2g / f <1.20
(2) -0.15 <f / f _3g <0.25
(3) 0.03 <d / D _3g <0.20
(9) 1.78 <nd _n <2.000
(10) 20.0 <νd _n <32.0
(11) 0.005 <θ _{g, F} -(-0.001802 × νd _n +0.6483) <0.009
An imaging lens characterized by satisfying. The imaging lens according to any one of claims 1 to 3.
When the focal length of the positive lens arranged on the most object side of the third lens group _{is f L31 and} the focal length of the positive lens arranged on the image side of the third lens group is f _L33 , the conditional equation ( 4):
(4) 0.75 <f _L33 / f _L31 <1.10
An imaging lens characterized by satisfying. The imaging lens according to any one of claims 1 to 4.
Conditional expression (5): When the focal length of the positive lens arranged on the most object side of the third lens group is f _{L31 and} the focal length of the negative lens of the third lens group is f _L32.
(5) -0.60 <f _L32 / f _L31 <-0.35
An imaging lens characterized by satisfying. The imaging lens according to any one of claims 1 to 5.
_{The condition is that} the radius of curvature of the image side lens surface of the negative lens of _{the third lens group: RL32b} , the radius of curvature of the object side lens surface of the positive lens arranged on the image side of the third lens group: RL33a. Equation (6):
(6) _{-0.30 <(RL32b-} R _L33a ) / ( _RL32b + R _L33a ) <-0.04
An imaging lens characterized by satisfying. The imaging lens according to any one of claims 1 to 6.
An imaging lens characterized in that the third lens group is fixed to an image plane during the focusing. In the imaging lens according to claim 1 or 2,
Radius of curvature of the image side lens surface of the negative lens arranged on the image side of the first lens group: _RL1gb,
Radius of curvature of the object-side lens surface of the negative lens of the second lens group: _RL2ga ,
Then, the following conditional expression (7):
(7) -0.65 <(R _L1gb + R _L2ga ) / (R _L1gb -R _L2ga ) <0.15
An imaging lens characterized by satisfying. The imaging lens according to any one of claims 1 to 8.
An imaging lens characterized in that the lenses constituting the first lens group, the second lens group, and the third lens group are all spherical lenses. The imaging lens according to any one of claims 1 to 9.
An imaging lens characterized in that the materials of the lenses constituting the first lens group, the second lens group, and the third lens group are all inorganic solid materials. An image pickup apparatus having the imaging lens according to any one of claims 1 to 10.

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