CN116203702A

CN116203702A - Optical system and imaging device

Info

Publication number: CN116203702A
Application number: CN202211292173.6A
Authority: CN
Inventors: 横田耕一郎; 高桥贤一
Original assignee: Tamron Co Ltd
Current assignee: Tamron Co Ltd
Priority date: 2021-11-30
Filing date: 2022-10-21
Publication date: 2023-06-02
Also published as: JP2023080533A

Abstract

The object is to provide a compact optical system and an imaging device having high optical performance. The optical system is composed of a 1 st lens group (G1) with positive focal power, a 2 nd lens group (G2) with positive focal power and a 3 rd lens group (G3) with negative focal power in order from an object side to an image side, wherein the 1 st lens group (G1) and the 3 rd lens group (G3) are fixed relative to an image plane in the optical axis direction during focusing, the 2 nd lens group (G2) moves along the optical axis, and the 1 st lens group (G1) is composed of a 1 st a group (G1 a) with negative focal power, an aperture diaphragm and a 1 st b group (G1 b) with positive focal power in order from the object side to the image side, and the prescribed mathematical formula is satisfied.

Description

Optical system and imaging device

Technical Field

The present invention relates to an optical system and an imaging apparatus.

Background

In recent years, imaging devices using solid-state imaging elements such as digital cameras have been increasingly popular. With this, the performance and miniaturization of optical systems have advanced, and small imaging device systems have been rapidly popularized. Among conventional lenses, particularly in monitoring lenses, video camera lenses, digital camera lenses, single-lens reflex camera lenses, mirror-less single-lens camera lenses, and the like, which are required to have a small overall length, the object is to miniaturize the optical system while maintaining high optical performance.

Patent document 1 discloses an invention of the following optical system: the lens group is composed of, in order from the object side, a 1 st lens group of positive optical power, a 2 nd lens group of positive optical power, and a 3 rd lens group of negative optical power, and the 2 nd lens group is moved in the optical axis direction at the time of focusing. However, in the lenses described in examples 2 to 5, the optical power of the lens group disposed on the object side of the aperture stop is weaker than the optical power of the 1 st lens group, and therefore the lens diameter becomes larger, which hinders downsizing of the lens barrel.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2015-001641

Disclosure of Invention

Problems to be solved by the invention

Accordingly, an object of the present invention is to provide a compact optical system having high optical performance.

Means for solving the problems

In order to solve the above-described problems, an optical system according to the present invention is configured by, in order from an object side to an image side, a 1 st lens group having positive optical power, a 2 nd lens group having positive optical power, and a 3 rd lens group having negative optical power, wherein the 1 st lens group and the 3 rd lens group are fixed in an optical axis direction with respect to an image plane during focusing, the 2 nd lens group moves along the optical axis, and the 1 st lens group is configured by, in order from the object side to the image side, a 1 st group having negative optical power, an aperture stop, and a 1b group having positive optical power, and satisfies the following formula.

-2.50≤f1a/f≤-0.05·····(1)

-3.45≤f3/f≤-1.35·····(2)

Wherein, the liquid crystal display device comprises a liquid crystal display device,

f1a: focal length of the 1 st group

f3: focal length of the 3 rd lens group

f: focal length of the optical system at infinity focusing

In order to solve the above problems, an imaging device according to the present invention includes: the optical system and an imaging element for converting an optical image formed by the optical system into an electrical signal.

Effects of the invention

According to the present invention, an optical system having high optical performance and being small can be provided.

Drawings

Fig. 1 is a sectional view of the optical system of embodiment 1.

Fig. 2 is a longitudinal aberration diagram in an infinity focusing state for the optical system of embodiment 1.

Fig. 3 is a cross-sectional view of the optical system of embodiment 2.

Fig. 4 is a longitudinal aberration diagram in an infinity focusing state for the optical system of embodiment 2.

Fig. 5 is a cross-sectional view of the optical system of embodiment 3.

Fig. 6 is a longitudinal aberration diagram in an infinity focusing state for the optical system of embodiment 3.

Fig. 7 is a cross-sectional view of the optical system of embodiment 4.

Fig. 8 is a longitudinal aberration diagram in an infinity focusing state for the optical system of embodiment 4.

Fig. 9 is a cross-sectional view of the optical system of embodiment 5.

Fig. 10 is an aberration diagram in an infinity focusing state for the optical system of embodiment 5.

Fig. 11 is a diagram schematically showing an example of the configuration of an imaging device according to an embodiment of the present invention.

Description of the reference numerals

S.aperture stop

CG & · & protective glass

IP & gtimage plane

G1.1 st lens group

G2.2 nd lens group

G3.3 rd lens group

G1a.cndot.cndot.1a group

G1b.1 b group

1-camera device

2.Camera

3- & lens

21-CCD sensor for detecting a position of a body or CMOS sensor

22-protective glass or IR cut filter

Detailed Description

Embodiments of an optical system and an imaging device according to the present invention are described below. The optical system and the imaging device described below are one embodiment of the optical system and the imaging device according to the present invention, and the optical system and the imaging device according to the present invention are not limited to the following embodiments.

1. Optical system

1-1 optical constitution

The optical system according to the present invention is composed of, in order from the object side, a 1 st lens group having positive optical power, a 2 nd lens group having positive optical power, and a 3 rd lens group having negative optical power. With this configuration, miniaturization is easy to achieve.

(1) 1 st lens group

The 1 st lens group is not particularly limited as long as it has positive optical power and is fixed with respect to the image plane at the time of focusing. The 1 st lens group is composed of a 1 st a group having negative optical power, an aperture stop, and a 1 st b group having positive optical power in order from the object side to the image side. By providing this configuration, particularly, the configuration in which the 1 st group (i.e., all lenses disposed further forward than the aperture stop among lenses included in the 1 st lens group) has negative optical power, it is easy to suppress each aberration and to realize miniaturization.

Here, the "lens group" is composed of 1 lens or a plurality of lenses adjacent to each other, and the interval between the lens groups adjacent to each other along the optical axis varies at the time of focusing. In the case where one lens group is constituted by a plurality of lenses, it is assumed that the distance on the optical axis between the lenses included in the one lens group does not change at the time of focusing.

The 1 st group 1a of the 1 st lens group is not particularly limited as long as it has negative optical power, and a lens element disposed closest to the object side of the 1 st group (hereinafter also referred to as "object side lens element") preferably has negative optical power. The term "lens element" as used herein refers to 1 single lens, a bonded lens formed by integrating a plurality of single lenses without air gaps, or a composite lens formed by integrating 1 single lens and resin without air gaps. In the case where the most object side lens element is a cemented lens or a compound lens, the configuration is not particularly limited as long as the cemented lens or the compound lens has negative optical power as a whole.

(2) Lens group 2

The specific configuration of the 2 nd lens group is not particularly limited as long as it is a lens group having positive optical power and moving along the optical axis at the time of focusing. In terms of high-speed movement on the optical axis at the time of focusing, the 2 nd lens group is preferably constituted by 1 lens element. In addition, the 2 nd lens group preferably has a biconvex lens on the most image side. With this configuration, aberration can be easily corrected and miniaturization can be achieved.

(3) 3 rd lens group

The 3 rd lens group is not particularly limited as long as it has positive optical power and is fixed with respect to the image plane at the time of focusing. The 3 rd lens group preferably includes a biconcave lens on the most image side. With this configuration, distortion aberration can be easily corrected and the overall length can be suppressed. In addition, in terms of miniaturization, the 3 rd lens group is preferably constituted by only 1 lens element.

(4) Aperture diaphragm

In this optical system, the specific configuration of the aperture stop is not particularly limited as long as it is disposed in the 1 st lens group. By disposing the aperture stop in the 1 st lens group, aberration can be effectively offset before and after the aperture stop, and it is preferable to obtain an optical system having high optical performance.

1-2. Action

(1) Focusing

In the optical system, the specific operation is not particularly limited as long as the 2 nd lens group is operated on the optical axis at the time of focusing from infinity to a close distance. In addition, in focusing from infinity to a close distance, it is preferable that the 2 nd lens group is configured to move toward the object side on the optical axis.

1-3. Math

The optical system preferably has the above-described configuration, and satisfies at least 1 or more of the following equations.

1-3-1. Formula (1)

-2.50≤f1a/f≤-0.05·····(1)

f1a: focal length of group 1a

f: focal length of the optical system at infinity focusing

Equation (1) is an equation for defining a ratio of a focal length of the 1 st lens group to a focal length of the 1 st a group disposed on the object side of the aperture stop. By satisfying the formula (1), it is easy to correct each aberration well and achieve miniaturization.

If the value is less than the lower limit value of expression (1), the optical power of group 1a becomes weak, and the diameter of the lens group disposed on the object side of the aperture stop is not sufficiently reduced. In addition, miniaturization of the lens barrel is hampered. On the other hand, if the upper limit value of the formula (1) is exceeded, the optical power of the 1 st group becomes strong, and it is difficult to correct each aberration such as coma and distortion.

In order to obtain the above-mentioned effects, the lower limit value of the formula (1) is preferably-2.40, more preferably-2.30. The upper limit of the formula (1) is preferably-0.10, more preferably-0.20. In the case where these preferable lower limit or upper limit are used, the inequality sign (. Ltoreq.) with the equal sign may be replaced with the inequality sign (. <) in the formula (1). The same applies to other formulas as the principle.

1-3-2. Formula (2)

-3.45≤f3/f≤-1.35·····(2)

f3: focal length of 3 rd lens group

f: focal length of the optical system at infinity focusing

Equation (2) is an equation for defining a ratio of a focal length of the 3 rd lens group to a focal length of the optical system at the time of infinity focusing. By satisfying the expression (2), it is easy to correct each aberration well, and miniaturization of the 3 rd lens group is achieved.

If the refractive power of the 3 rd lens group is lower than the lower limit value of the formula (2), the refractive power of the 3 rd lens group becomes weak, and the rear lens diameter of the 3 rd lens group is not sufficiently reduced. On the other hand, if the upper limit value of the formula (2) is exceeded, the optical power of the 3 rd lens group becomes strong, and it is difficult to correct astigmatism and chromatic aberration of magnification.

In order to obtain the above-mentioned effects, the lower limit value of the formula (2) is preferably-3.40, more preferably-3.30. The upper limit of the formula (2) is preferably-1.40, more preferably-1.50.

1-3-3. 1 (3)

0.05≤f1/f≤4.30·····(3)

f: focal length of the optical system at infinity focusing

Equation (3) is an equation for defining a ratio of a focal length of the 1 st lens group to a focal length of the optical system at the time of infinity focusing. By satisfying the expression (3), it is easy to correct each aberration well, and miniaturization of the 1 st lens group is achieved.

If the refractive power is lower than the lower limit value of the formula (3), the optical power of the 1 st lens group becomes strong, and it is difficult to correct aberrations such as spherical aberration and coma aberration. On the other hand, if the upper limit value of the formula (3) is exceeded, the optical power of the 1 st lens group becomes weak, and the diameter of the 2 nd lens group does not sufficiently become small. In addition, the drive unit is enlarged, and it is difficult to achieve miniaturization of the lens barrel.

In order to obtain the above-described effect, the lower limit value of the formula (3) is preferably 0.10, more preferably 0.20, and still more preferably 1.00. The upper limit of the formula (3) is preferably 4.00, more preferably 3.70.

1-3-4. 1 (4)

1.10≤(1-β2 ² )×β3 ² ≤5.00·····(4)

beta 2: lateral magnification of 2 nd lens group in infinity focusing

Beta 3: lateral magnification of 3 rd lens group during infinity focusing

Equation (4) is an equation for defining the absolute value of the focus sensitivity of the 2 nd lens group moving on the optical axis during focusing, that is, the image plane movement amount in the case where the 2 nd lens group moves by a unit amount. By satisfying the expression (4), the amount of movement during focusing can be suppressed, and downsizing of the lens barrel can be easily achieved.

On the other hand, if the value of expression (4) is lower than the lower limit value, the amount of movement of the 2 nd lens group moving on the optical axis during focusing becomes large, and thus it is difficult to achieve miniaturization of the optical overall length. On the other hand, if the upper limit value of the formula (4) is exceeded, the amount of movement of the 2 nd lens group for correcting the positional deviation of the focal position is too small, and thus high-precision control is required, which is not preferable.

In order to obtain the above-described effect, the lower limit value of the formula (4) is preferably 1.20, more preferably 1.30. The upper limit of the formula (4) is preferably 4.50, more preferably 4.00.

1-3-5. 1. 5)

1.60≤Nd11≤2.15·····(5)

nd11: refractive index at d-line of lens element disposed closest to object side of 1 st lens group

Equation (5) is an equation defining the refractive index of the lens element disposed closest to the object side at the d-line. By satisfying the expression (5), it is easy to correct each aberration well, and miniaturization is achieved.

If the refractive index of the 1 st lens element is smaller than the lower limit value of expression (5), the front lens diameter becomes larger, and it is difficult to achieve downsizing of the barrel diameter. On the other hand, if the upper limit value of the formula (5) is exceeded, it is difficult to correct curvature of field aberration, and it is difficult to achieve high optical performance. When the lens element is a bonded lens, 1 lens may be bonded, or 2 or more lenses may be bonded. In the case where the 1 st lens element is a cemented lens, the most object side lens preferably satisfies the formula (5).

In order to obtain the above-described effect, the lower limit value of the formula (5) is preferably 1.65, more preferably 1.70. The upper limit of the formula (5) is preferably 2.10, more preferably 2.05.

1-3-6. 1 (6)

0.50≤f11/f1a≤1.70·····(6)

f11: focal length of lens element of 1 st lens group disposed closest to object side

Equation (6) is an equation for defining a ratio of focal lengths of the 1 st lens element disposed on the most object side of the 1 st lens group to the 1 st group. By satisfying the expression (6), it is easy to correct each aberration well, and miniaturization is achieved.

If the refractive power of the 1 st lens element is lower than the lower limit value of the formula (6), the optical power becomes strong, and it is difficult to correct various aberrations such as astigmatism and chromatic aberration of magnification. On the other hand, if the upper limit value of expression (6) is exceeded, the optical power of the 1 st lens element becomes weak, and the front lens diameter does not sufficiently become small. In addition, it is difficult to achieve miniaturization of the lens barrel.

In order to obtain the above-described effect, the lower limit value of the formula (6) is preferably 0.55, more preferably 0.60, and further preferably 0.80. The upper limit of the formula (6) is preferably 1.65, more preferably 1.60.

1-3-7. Formula (7)

-1.25≤f11/f1≤-0.35·····(7)

Equation (7) is an equation for defining a ratio of the 1 st lens element disposed on the most object side of the 1 st lens group to the focal length of the 1 st lens group. By satisfying the expression (7), it is easy to correct each aberration well, and miniaturization is achieved.

If the refractive power of the 1 st lens element is lower than the lower limit value of expression (7), the front lens diameter is not sufficiently reduced. In addition, it is difficult to achieve miniaturization of the lens barrel. On the other hand, if the upper limit value of the formula (7) is exceeded, the optical power of the 1 st lens element becomes strong, and it is difficult to correct various aberrations such as astigmatism and chromatic aberration of magnification.

In order to obtain the above-mentioned effects, the lower limit value of the formula (7) is preferably-1.20, more preferably-1.15. The upper limit of the formula (7) is preferably-0.40, more preferably-0.45.

1-3-8. 1 (8)

-1.10≤f1a/f1≤-0.05·····(8)

Equation (8) is an equation for defining a ratio of a focal length of the 1 st lens group to a focal length of the 1 st a group disposed on the object side of the aperture stop. By satisfying the expression (8), it is easy to correct each aberration well, and miniaturization is achieved.

If the value is less than the lower limit value of expression (8), the optical power of group 1a becomes weak, and the diameter of the lens group disposed on the object side of the aperture stop is not sufficiently reduced. In addition, miniaturization of the lens barrel is hampered. On the other hand, if the upper limit value of the formula (8) is exceeded, the optical power of the 1 st group becomes strong, and it is difficult to correct each aberration such as coma and distortion.

In order to obtain the above-mentioned effects, the lower limit value of the formula (8) is preferably-1.00, more preferably-0.90. The upper limit of the formula (8) is preferably-0.10, more preferably-0.20.

2. Image pickup apparatus

Next, an imaging device according to the present invention will be described. The imaging device according to the present invention is characterized by comprising the optical system according to the present invention and an imaging element for converting an optical image formed by the optical system into an electrical signal. Further, the image pickup element is preferably provided on the image side of the optical system.

Here, the image pickup device and the like are not particularly limited, and a solid-state image pickup device and the like such as a CCD (Charge Coupled Device: charge coupled device) sensor, a CMOS (Complementary Metal Oxide Semiconductor: complementary metal oxide semiconductor) sensor and the like can also be used. The imaging device according to the present invention is suitable for imaging devices such as digital cameras and video cameras using these solid-state imaging elements. The imaging device can be applied to various imaging devices such as a single-lens reflex camera, a mirror-less single-lens camera, a digital camera, a monitoring camera, a vehicle-mounted camera, and a unmanned aerial vehicle-mounted camera. The imaging device may be a lens-interchangeable imaging device or a fixed lens type imaging device in which a lens is fixed to a housing. The optical system according to the present invention is particularly suitable as an optical system of an imaging device mounted with an imaging element having a large size such as a full size. The optical system is compact and lightweight as a whole, and has high optical performance, so that a high-quality captured image can be obtained even when the optical system is used as an optical system for such an imaging device.

Fig. 11 is a diagram schematically showing an example of the configuration of the imaging device according to the present embodiment. As shown in fig. 11, the imaging device 1 includes a camera 2 and a lens 3 that is detachable from the camera 2. The imaging apparatus 1 is one embodiment of an imaging apparatus.

The camera 2 includes a CCD sensor 21 as an image pickup element, and a cover glass 22. The CCD sensor 21 is disposed in the camera 2 at a position where the optical axis of the optical system in the lens 3 mounted on the camera 2 becomes the center thereof. The camera 2 may also have an IR cut filter or the like instead of the cover glass 22.

Next, examples are shown and the present invention is specifically explained. However, the present invention is not limited to the following examples.

Example 1

(1) Optical structure

Fig. 1 is a cross-sectional view of an optical system of embodiment 1 of the present invention at the time of infinity focusing. The optical system is composed of, in order from the object side, a 1 st lens group G1 having positive optical power, a 2 nd lens group G2 having positive optical power, and a 3 rd lens group G3 having negative optical power.

The 2 nd lens group G2 moves from the image side to the object side along the optical axis upon focusing from an infinitely distant object to a close object.

The 1 st lens group G1 is constituted by a 1 st a group G1a, an aperture stop S, and a 1 st b group G1b in order from the object side. The 1 st group G1a is composed of, in order from the object side, a negative meniscus lens (the most object side lens element), a negative meniscus lens, and a junction lens formed by joining a biconcave lens and a biconvex lens, and the 1 st group G1b is composed of, in order from the object side, a junction lens formed by joining a negative meniscus lens and a biconvex lens, a positive meniscus lens, a biconvex lens, and a biconcave lens.

The 2 nd lens group G2 is constituted by only a biconvex lens.

The 3 rd lens group G3 is composed of only a biconcave compound aspherical lens having an aspherical surface on the object side.

In fig. 1, "IP" is an image plane, and specifically, indicates an image pickup plane of a solid-state image pickup device such as a CCD sensor or a CMOS sensor, a film plane of a silver halide film, or the like. The object side of the image plane IP is provided with a cover glass CG. This point is also the same in the cross-sectional views of the lenses shown in the other embodiments, and therefore, the description thereof will be omitted.

(2) Numerical examples

Next, a numerical example in which specific numerical values are applied to the optical system will be described. The following indicates "lens data", "various specifications", "variable interval", "aspherical coefficient", "focal length of each lens group". The values of the respective formulas (table 1) are summarized in example 5. In the numerical examples below, the units of length are all "mm" and the units of angle are all "°.

In (lens data), "surface No." denotes a number of a lens surface counted from the object side, "r" denotes a radius of curvature of the lens surface, "D" denotes a lens wall thickness or an air interval on the optical axis, "Nd" denotes a refractive index at D-line (wavelength λ=587.56 nm), and "vd" denotes an abbe number at D-line. In addition, the column "face No." indicates that the lens face is aspherical, and "S" indicates that the face is aperture stop S. In the column of "D", the meaning of "D (7)", "D (10)", etc. is that the interval on the optical axis of the lens surface is a variable interval that varies at the time of focusing. In addition, in the case of the optical fiber, "infinity" in the column of the radius of curvature means that the lens surface is a plane.

In (various specification tables), "F" is the focal length of the optical system, "fno" is the F value, and "ω" is the half field angle. The values at the time of infinity focusing and at the time of close focusing are shown, respectively.

In (variable interval), values at the time of infinity focusing and at the time of close focusing are respectively represented.

The (aspherical surface coefficient) means an aspherical surface coefficient when an aspherical surface shape is defined as follows. Where x is the displacement amount with respect to the reference plane in the optical axis direction, r is the paraxial radius of curvature, H is the height with respect to the optical axis in the direction perpendicular to the optical axis, K is the conic coefficient, and An is the aspherical coefficient n times. In the table of "aspherical coefficients", the "E.+ -. XX" represents an index mark, which means ". Times.10 ^±XX ”。

[ number 1]

The matters in each numerical embodiment are the same as those in other embodiments, and therefore, the explanation thereof will be omitted.

Fig. 2 shows a longitudinal aberration diagram of the optical system when an object at infinity is in focus. The longitudinal aberration diagrams shown in the respective figures are spherical aberration (mm), astigmatism (mm), and distortion aberration (%) in order from the left side of the figure. In the spherical aberration diagram, the solid line represents the spherical aberration at the d-line (wavelength 587.56 nm), the long-dashed line represents the spherical aberration at the F-line (wavelength 486.13 nm), and the short-dashed line represents the spherical aberration at the C-line (wavelength 656.28 nm). In the astigmatic diagram, the vertical axis is the half field angle (ω), the horizontal axis is defocus, the solid line represents the sagittal image plane (S) of the d-line, and the broken line represents the meridional image plane (T) of the d-line. In the distortion aberration diagram, the vertical axis is a half field angle (ω), and the horizontal axis is distortion aberration. These matters are the same in the aberration diagrams shown in other embodiments, and therefore, description thereof will be omitted later.

(lens data)

(various specification sheets)

f	16.4814	15.8322
			Fno.	2.8843	2.8961
ω	54.9227	54.8843

(variable spacing)

Multiplying power	∞	-0.1154
			D(17)	3.7929	2.7838
D(19)	2.4975	3.5066

(aspherical coefficient)

Surface NO.

K

A4

A6

A8

A10

3

0.00000E+00

6.82780E-05

-9.99113E-07

5.12613E-09

0.00000E+00

4

0.00000E+00

7.14175E-05

-1.14562E-06

-5.34864E-09

0.00000E+00

14

0.00000E+00

-2.92014E-05

-2.49463E-07

-6.03768E-11

0.00000E+00

15

0.00000E+00

9.17837E-05

-3.87076E-07

2.46877E-09

0.00000E+00

20

0.00000E+00

-3.02348E-05

-1.12435E-07

1.17164E-10

0.00000E+00

(focal Length of each lens group)

G1	30.706
		G2	28.103
G3	-44.933

Example 2

(1) Optical structure

Fig. 3 is a cross-sectional view of the optical system of embodiment 2 of the present invention at the time of infinity focusing. The optical system is composed of, in order from the object side, a 1 st lens group G1 having positive optical power, a 2 nd lens group G2 having positive optical power, and a 3 rd lens group G3 having negative optical power.

The 1 st lens group G1 is constituted by a 1 st a group G1a, an aperture stop S, and a 1 st b group G1b in order from the object side. The 1 st group G1a is composed of, in order from the object side, a negative meniscus lens (the most object side lens element), a negative meniscus lens, and a junction lens formed by joining a biconcave lens and a biconvex lens, and the 1 st group G1b is composed of, in order from the object side, a junction lens formed by joining a negative meniscus lens and a biconvex lens, and a biconcave lens.

The 2 nd lens group G2 is constituted by only a biconvex lens.

(2) Numerical examples

Next, a numerical example in which specific numerical values are applied to the optical system is shown. Fig. 4 shows a longitudinal aberration diagram at the time of infinity focusing of the optical system.

(lens data)

(various specification sheets)

f	15.8110	15.2446
			Fno.	2.8840	2.8995
ω	56.0468	56.1871

(variable spacing)

Multiplying power	∞	-0.1107
			D(17)	4.0290	3.0446
D(19)	2.5004	3.4848

(aspherical coefficient)

Surface NO.

K

A4

A6

A8

A10

3

0.00000E+00

7.26547E-05

-1.02670E-06

4.33587E-09

0.00000E+00

4

0.00000E+00

6.23251E-05

-1.15432E-06

-1.27734E-08

0.00000E+00

14

0.00000E+00

-2.26052E-05

-1.58588E-07

-8.32590E-10

0.00000E+00

15

0.00000E+00

8.36388E-05

-4.47202E-07

1.13438E-09

0.00000E+00

20

0.00000E+00

-3.87171E-05

-9.81562E-08

-3.87217E-10

0.00000E+00

(focal Length of each lens group)

G1	28.312
		G2	28.862
G3	-49.017

Example 3

(1) Optical structure

Fig. 5 is a cross-sectional view of the optical system of example 3 according to the present invention at the time of infinity focusing. The optical system is composed of, in order from the object side, a 1 st lens group G1 having positive optical power, a 2 nd lens group G2 having positive optical power, and a 3 rd lens group G3 having negative optical power.

The 1 st lens group G1 is constituted by a 1 st a group G1a, an aperture stop S, and a 1 st b group G1b in order from the object side. The 1 st group G1a is composed of, in order from the object side, a negative meniscus lens (the most object side lens element), a negative meniscus lens, and a junction lens formed by joining the negative meniscus lens and the positive meniscus lens, and the 1 st group G1b is composed of, in order from the object side, a junction lens formed by joining the negative meniscus lens and the biconvex lens, a biconcave lens, and a biconcave lens.

The 2 nd lens group G2 is constituted by only a biconvex lens.

(2) Numerical examples

Next, a numerical example in which specific numerical values are applied to the optical system is shown. Fig. 6 shows a longitudinal aberration diagram at the time of infinity focusing of the optical system.

(lens data)

(various specification sheets)

f	16.1597	15.6244
			Fno.	2.8840	2.9208
ω	55.2222	55.2293

(variable spacing)

Multiplying power	∞	-0.1154
			D(17)	3.6817	2.8587
D(19)	3.0869	3.9100

(aspherical coefficient)

Surface NO.

K

A4

A6

A8

A10

3

0.00000E+00

1.27560E-04

-8.33243E-07

-9.28556E-09

0.00000E+00

4

0.00000E+00

9.45114E-05

-5.25690E-07

-4.74923E-08

0.00000E+00

14

0.00000E+00

-4.15675E-05

-3.56142E-07

-9.80924E-10

0.00000E+00

15

0.00000E+00

2.82561E-05

-4.19613E-07

1.24271E-12

0.00000E+00

20

0.00000E+00

-6.36104E-05

-1.38232E-07

2.14449E-10

0.00000E+00

(focal Length of each lens group)

G1	42.008
		G2	25.149
G3	-43.721

Example 4

(1) Optical structure

Fig. 7 is a cross-sectional view of the optical system of embodiment 4 of the present invention at the time of infinity focusing. The optical system is composed of, in order from the object side, a 1 st lens group G1 having positive optical power, a 2 nd lens group G2 having positive optical power, and a 3 rd lens group G3 having negative optical power.

The 1 st lens group G1 is constituted by a 1 st a group G1a, an aperture stop S, and a 1 st b group G1b in order from the object side. The 1 st group G1a is composed of, in order from the object side, a negative meniscus lens (the most object side lens element), a negative meniscus lens, and a biconvex compound aspherical lens having an aspherical surface on the object side, and the 1 st group G1b is composed of, in order from the object side, a biconvex lens, and a cemented lens formed by joining a positive meniscus lens and a negative meniscus lens.

The 2 nd lens group G2 is composed of a biconcave aspherical lens and a biconvex aspherical lens in order from the object side.

(2) Numerical examples

Next, a numerical example in which specific numerical values are applied to the optical system is shown. Fig. 8 shows a longitudinal aberration diagram at the time of infinity focusing of the optical system.

(lens data)

Surface NO.	r	D	Nd	vd
					1	19.8611	1.2000	1.88300	40.81
2	9.4923	5.8751
					3	156.9035	1.0000	1.49700	81.61
4	10.4878	2.6977
					5*	55.2977	0.2000	1.53610	41.21
6	29.4087	2.3472	1.91082	35.25
					7	-84.5403	6.0300
8S	∞	1.5000
					9	25.4275	3.7629	1.49700	81.61
10	-14.7214	0.6836
					11	-32.6671	4.0004	1.78590	43.93
12	-8.2866	0.7000	1.88100	40.13
					13	-30.6235	D(13)
14*	-64.1141	0.8000	1.80139	45.45
					15*	81.9216	0.7144
16*	29.8488	6.7390	1.49700	81.61
					17*	-10.1153	D(17)
18*	-53.8636	0.2000	1.53610	41.21
					19	-40.2005	1.0000	1.64769	33.84
20	23.5243	20.2092
					21	∞	2.5000	1.51680	64.20
22	∞	1.0000

(various specification sheets)

f	16.4811	15.8986
			Fno.	2.8878	2.9113
ω	54.3806	54.6280

(variable spacing)

Multiplying power	∞	-0.0905
			D(13)	2.6917	2.2614
D(17)	1.9992	2.4296

(aspherical coefficient)

Surface NO.	K	A4	A6	A8	A10
						5	0.00000E+00	4.45639E-05	8.12432E-07	-1.14394E-08	1.96460E-10
14	0.00000E+00	1.44370E-04	-2.84799E-06	-5.84227E-08	5.20571E-10
						15	0.00000E+00	1.85613E-04	1.88726E-06	-1.35773E-07	1.20959E-09
16	0.00000E+00	-1.27270E-04	5.40504E-06	-9.21760E-08	4.95535E-10
						17	0.00000E+00	9.44297E-05	-4.03657E-07	7.01258E-09	0.00000E+00
18	0.00000E+00	5.77689E-06	-4.71936E-07	0.00000E+00	0.00000E+00

(focal Length of each lens group)

G1	22.363
		G2	21.72
G3	-24.683

Example 5

(1) Optical structure

Fig. 9 is a cross-sectional view of the optical system of example 5 according to the present invention at the time of infinity focusing. The optical system is composed of, in order from the object side, a 1 st lens group G1 having positive optical power, a 2 nd lens group G2 having positive optical power, and a 3 rd lens group G3 having negative optical power.

The 1 st lens group G1 is constituted by a 1 st a group G1a, an aperture stop S, and a 1 st b group G1b in order from the object side. The 1 st group G1a is composed of, in order from the object side, a negative meniscus lens (the most object side lens element), a negative meniscus lens, and a biconvex compound aspherical lens having an aspherical surface on the object side, and the 1 st group G1b is composed of, in order from the object side, a biconvex lens, and a cemented lens formed by joining the biconvex lens and the biconcave lens.

(2) Numerical examples

Next, a numerical example in which specific numerical values are applied to the optical system is shown. Fig. 10 shows a longitudinal aberration diagram at the time of infinity focusing of the optical system.

(lens data)

Surface NO.	r	D	Nd	vd
					1	19.1175	1.2000	1.88300	40.81
2	9.1370	6.0287
					3	215.1384	1.0000	1.49700	81.61
4	10.9693	2.5426
					5*	59.9342	0.2000	1.53610	41.21
6	34.0236	2.3466	1.91082	35.25
					7	-59.3684	6.0321
8S	∞	1.5000
					9	35.1168	3.5416	1.49700	81.61
10	-14.9146	0.6046
					11	309.6062	4.9668	1.80611	40.73
12	-8.5126	0.7000	1.88202	37.22
					13	108.2794	D(13)
14*	-125.0396	0.8000	1.76802	49.24
					15*	115.7335	0.5563
16*	29.9394	6.8106	1.49700	81.61
					17*	-10.0903	D(17)
18*	-57.3545	0.2000	1.53610	41.21
					19	-41.4948	1.0000	1.64769	33.84
20	26.2967	19.6246
					21	∞	2.5000	1.51680	64.20
22	∞	1.0000

(various specification sheets)

f	16.4815	15.9592
			Fno.	2.8840	2.8956
ω	54.3231	54.4370

(variable spacing)

Multiplying power	∞	-0.0909
			D(13)	2.6973	2.2663
D(17)	1.9988	2.4298

(aspherical coefficient)

(focal Length of each lens group)

G1	42.848
		G2	18.932
G3	-27.115

(Table 1)

	Example 1	Example 2	Example 3	Example 4	Example 5
						(1) f3a/f	-1.268	-1.433	-0.780	-1.221	-1.300
(2) f3/f	-2.726	-3.100	-2.706	-1.498	-1.645
						(3) f1/f	1.863	1.791	2.600	1.357	2.600
(4) (1-. Beta.2) ² )×β3 ²	1.669	1.549	1.948	3.201	3.201
						Nd11 of (5)	1.697	1.697	1.773	1.883	1.883
Formula (6) f11/f1a	1.154	0.952	1.400	1.082	0.980
						(7) f11/f1	-0.785	-0.762	-0.420	-0.974	-0.490
Formula (8) f1a/f1	-0.681	-0.800	-0.300	-0.900	-0.500
						f	16.482	15.811	16.160	16.481	16.482
f1	30.706	28.312	42.008	22.363	42.848
						f1a	-20.899	-22.652	-12.604	-20.127	-21.424
f11	-24.118	-21.563	-17.645	-21.773	-21.005
						f3	-44.933	-49.017	-43.721	-24.683	-27.115
β2	0.384	0.409	0.266	0.381	0.210
						β3	1.399	1.364	1.448	1.935	1.830

Industrial applicability

The optical system according to the present invention can be suitably applied to an optical system of an imaging device such as a film camera, a digital camera, or a digital video camera.

Claims

1. An optical system is composed of a 1 st lens group with positive focal power, a 2 nd lens group with positive focal power, and a 3 rd lens group with negative focal power in order from an object side to an image side,

during focusing, the 1 st lens group and the 3 rd lens group are fixed relative to the image plane in the optical axis direction, the 2 nd lens group moves along the optical axis,

the 1 st lens group is composed of a 1 st a group with negative focal power, an aperture diaphragm and a 1 st b group with positive focal power in sequence from the object side to the image side,

and satisfies the following formula:

-2.50≤f1a/f≤-0.05·····(1)

-3.45≤f3/f≤-1.35·····(2)

f1a: focal length of the 1 st group

f3: focal length of the 3 rd lens group

f: focal length of the optical system at infinity focusing.

2. The optical system according to claim 1,

satisfies the following formula:

0.05≤f1/f≤4.30·····(3)

f1: focal length of the 1 st lens group.

3. The optical system according to claim 1 or claim 2,

satisfies the following formula:

1.10≤(1-β2 ² )×β3 ² ≤5.00·····(4)

beta 2: lateral magnification of the 2 nd lens group at the time of infinity focusing

Beta 3: and (3) the transverse magnification of the 3 rd lens group in infinite focusing.

4. The optical system according to claim 1 to 3,

the lens element of the 1 st lens group disposed at the most object side satisfies the following formula:

1.60≤Nd11≤2.15·····(5)

nd11: refractive index of the lens element disposed closest to the object side of the 1 st lens group at d-line.

5. The optical system according to claim 1 to 4,

0.50≤f11/f1a≤1.70·····(6)

f11: focal length of lens element disposed closest to object side of the 1 st lens group.

6. The optical system according to claim 1 to 5,

-1.25≤f11/f1≤-0.35·····(7)

f11: focal length of lens element of the 1 st lens group disposed closest to object side

f1: focal length of the 1 st lens group.

7. An optical system as claimed in any one of claims 1 to 6, characterized in that,

satisfies the following formula:

-1.10≤f1a/f1≤-0.05·····(8)

f1: focal length of the 1 st lens group.

8. An image pickup apparatus comprising the optical system according to any one of claims 1 to 7, and an image pickup element that converts an optical image formed by the optical system into an electrical signal on an image side of the optical system.