Imaging lens and imaging device
阅读说明：本技术 成像镜头及摄像装置 (Imaging lens and imaging device ) 是由 永见亮介 于 2019-08-26 设计创作，主要内容包括：本发明提供一种成像镜头及具备该成像镜头的摄像装置,该成像镜头能够实现小型化且高速的对焦,并具有有利于确保周边光量的结构,广角且包括像散及畸变像差的多种像差良好地得到抑制,从而具有高性能。成像镜头从物体侧起依次由正的第1透镜组、正的第2透镜组、负的第3透镜组构成。当对焦时,只有第2透镜组移动。第2透镜组中所包含的透镜的片数为两片以下。最靠物体侧的透镜是使凸面朝向物体侧的负透镜。最靠像侧的透镜面为凸面。第1透镜组包括光圈。满足与第1透镜组和第2透镜组有关的预先确定的条件式。(The invention provides an imaging lens and an imaging device having the same, wherein the imaging lens can realize miniaturization and high-speed focusing, has a structure favorable for ensuring the peripheral light quantity, has wide angle, well inhibits various aberrations including astigmatism and distortion aberration, and has high performance. The imaging lens is composed of a positive 1 st lens group, a positive 2 nd lens group, and a negative 3 rd lens group in this order from the object side. When focusing, only the 2 nd lens group moves. The number of lenses included in the 2 nd lens group is two or less. The most object-side lens is a negative lens with a convex surface facing the object side. The lens surface closest to the image side is a convex surface. The 1 st lens group includes an aperture stop. Predetermined conditional expressions with respect to the 1 st lens group and the 2 nd lens group are satisfied.)
1. An imaging lens is provided, which comprises a lens body,
the imaging lens is composed of a 1 st lens group with positive refractive power, a 2 nd lens group with positive refractive power and a 3 rd lens group with negative refractive power in sequence from the object side to the image side,
upon focusing from an infinity object to a closest object, the 1 st lens group and the 3 rd lens group are fixed with respect to an image plane, the 2 nd lens group moves along an optical axis,
the 1 st lens group is composed of a 1a lens group, a diaphragm and a 1b lens group in order from the object side to the image side,
the most object-side lens of the 1a lens group is a negative lens whose object-side surface is a convex surface,
the number of lenses included in the 2 nd lens group is two or less,
the lens surface of the 3 rd lens group closest to the image side is a convex surface,
the focal distance of the entire system in a state of focusing on an object at infinity is set to f,
setting the focal distance of the 2 nd lens group to f2,
setting the focal distance of the 1 st lens group to f1,
setting the focal distance of the 1a lens group to f1a,
when the focal length of the 1b lens group is f1b, conditional expressions (1), (2) and (3) represented by the following expressions are satisfied,
0.35＜f/f2＜0.75 (1)
-0.5＜f1/f1a＜0.3 (2)
0.4＜f1/f1b＜0.95 (3)。
2. the imaging lens according to claim 1,
the 1 st lens group includes at least one cemented lens in which at least one positive lens and at least one negative lens are cemented.
3. The imaging lens according to claim 2,
at least one of the cemented lenses is disposed within the 1b lens group,
the cemented lens closest to the object side in the 1b lens group is composed of a positive lens and a negative lens cemented in this order from the object side.
4. The imaging lens according to claim 2,
the 1 st lens group includes two cemented lenses.
5. The imaging lens according to claim 4,
two of the cemented lenses are disposed within the 1b lens group,
the cemented lens closest to the object side in the 1b lens group is composed of a positive lens and a negative lens cemented in this order from the object side, and the cemented lens 2 closest to the object side in the 1b lens group is composed of a negative lens and a positive lens cemented in this order from the object side.
6. The imaging lens according to claim 3 or 5,
when the refractive index of the positive lens constituting the cemented lens on the most object side in the 1b lens group with respect to d-line is N1bp,
satisfies conditional expression (4) represented by the following expression,
1.8＜N1bp＜2.1 (4)。
7. the imaging lens according to claim 3 or 5,
the d-line reference dispersion coefficient of the positive lens constituting the cemented lens on the most object side in the 1 b-th lens group is set to v 1bp,
when the d-line reference dispersion coefficient of the negative lens constituting the cemented lens on the most object side in the 1b lens group is ν 1bn,
satisfies conditional expression (5) represented by the following expression,
-50＜ν1bp-ν1bn＜0 (5)。
8. the imaging lens according to claim 2,
when the d-line reference dispersion coefficient of the positive lens constituting the cemented lens is set to vp,
the partial dispersion ratio between the g-line and the F-line of the positive lens constituting the cemented lens is set to θ gFp,
the d-line reference dispersion coefficient of the negative lens constituting the cemented lens is set to vn,
when a partial dispersion ratio between g-line and F-line of the negative lens constituting the cemented lens is θ gFn, at least one of the positive lens and the negative lens satisfying conditional expressions (6) and (7) expressed by the following expressions are cemented to at least one of the cemented lenses,
0.645＜0.0018×νp+θgFp＜0.72 (6)
0.645＜0.0018×νn+θgFn＜0.72 (7)。
9. imaging lens according to any one of claims 1 to 5,
satisfies conditional expression (8) represented by the following expression,
0.4＜f/f1＜1 (8)。
10. imaging lens according to any one of claims 1 to 5,
when the distance on the optical axis between the most object side lens surface of the 1 st lens group and the most image side lens surface of the 1 st lens group is DG1,
satisfies conditional expression (9) represented by the following expression,
1.6＜DG1/f＜2.5 (9)。
11. imaging lens according to any one of claims 1 to 5,
in the case where the focal distance of the 3 rd lens group is set to f3,
satisfies the conditional expression (10) represented by the following expression,
-0.8＜f/f3＜-0.05 (10)。
12. imaging lens according to any one of claims 1 to 5,
the number of lenses included in the 3 rd lens group is two or less.
13. Imaging lens according to any one of claims 1 to 5,
DS represents the sum of the distance on the optical axis from the diaphragm to the lens surface closest to the image side of the 3 rd lens group and the air converted distance on the optical axis from the lens surface closest to the image side of the 3 rd lens group to the image side focal position of the whole system in a state of focusing on an infinite object,
in the case where the maximum half angle of view is set to ω,
satisfies a conditional expression (11) represented by the following expression,
2＜DS/(f×tan(ω))＜2.85 (11)。
14. the imaging lens according to claim 1,
satisfying conditional formula (1-1) represented by the following formula,
0.35＜f/f2＜0.65 (1-1)。
15. the imaging lens according to claim 1,
satisfies the conditional formula (2-1) represented by the following formula,
-0.4＜f1/f1a＜0.22 (2-1)。
16. the imaging lens according to claim 1,
satisfies the conditional formula (3-1) represented by the following formula,
0.5＜f1/f1b＜0.9 (3-1)。
17. the imaging lens according to claim 7,
satisfies the conditional formula (5-1) represented by the following formula,
-40＜ν1bp-ν1bn＜-5 (5-1)。
18. the imaging lens according to claim 9,
satisfies the conditional formula (8-1) represented by the following formula,
0.5＜f/f1＜1 (8-1)。
19. the imaging lens according to claim 11,
satisfies the conditional expression (10-1) represented by the following expression,
-0.5＜f/f3＜-0.2 (10-1)。
20. an imaging device provided with the imaging lens according to any one of claims 1 to 19.
Technical Field
The present invention relates to an imaging lens and an imaging apparatus.
Background
Conventionally, as an imaging lens applicable to an imaging device such as a digital camera, there has been proposed an inner focus lens system as described in
Patent document 1: japanese patent No. 6090650 Specification
Patent document 2: japanese patent No. 6064422 Specification
Patent document 3: japanese patent No. 5760192 Specification
An imaging lens used in the imaging device is required to be capable of focusing at high speed and to be compact so as to be excellent in portability. Further, it is also required to secure a peripheral light amount, suppress various aberrations including astigmatism and distortion at a wide angle, and have high optical performance.
However, the lens system described in
Disclosure of Invention
The present invention has been made in view of the above circumstances. An object of one embodiment of the present invention is to provide an imaging lens that can achieve compact and high-speed focusing, has a configuration advantageous for ensuring a peripheral light amount, has a wide angle, and has high optical performance over the entire shooting distance by suppressing various aberrations including astigmatism and distortion aberration well, and an imaging device including the imaging lens.
An imaging lens according to
0.35＜f/f2＜0.75 (1)
-0.5＜f1/f1a＜0.3 (2)
0.4＜f1/f1b＜0.95 (3)
In the imaging lens of the above-described aspect, it is preferable that at least 1 of the following conditional expressions (1-1), (2-1), and (3-1) is satisfied.
0.35＜f/f2＜0.65 (1-1)
-0.4＜f1/f1a＜0.22 (2-1)
0.5＜f1/f1b＜0.9 (3-1)
In the imaging lens of the above-described manner, the 1 st lens group preferably includes at least one cemented lens in which at least one positive lens and at least one negative lens are cemented.
At least one of the cemented lenses is disposed in the 1 b-th lens group, and the cemented lens closest to the object side in the 1 b-th lens group is preferably cemented with a positive lens and a negative lens in this order from the object side.
The 1 st lens group more preferably includes two of the above cemented lenses. Preferably, two of the cemented lenses are disposed in the 1b lens group, the cemented lens closest to the object side in the 1b lens group is formed by joining a positive lens and a negative lens in this order from the object side, and the cemented
In the case where the cemented lens closest to the object side in the 1b lens group is composed of a positive lens and a negative lens cemented in this order from the object side, it is preferable that the following conditional expression (4) is satisfied when the refractive index of the positive lens constituting the cemented lens closest to the object side in the 1b lens group with respect to the d-line is N1 bp.
1.8＜N1bp＜2.1 (4)
In the case where the cemented lens closest to the object side in the 1b lens group is composed of a positive lens and a negative lens cemented in this order from the object side, when ν 1bp is the d-line reference dispersion coefficient of the positive lens constituting the cemented lens closest to the object side in the 1b lens group and ν 1bn is the d-line reference dispersion coefficient of the negative lens constituting the cemented lens closest to the object side in the 1b lens group, the following conditional expression (5) is preferably satisfied, and more preferably the following conditional expression (5-1) is satisfied.
--50＜ν1bp-ν1bn＜0 (5)
-40＜ν1bp-ν1bn＜-5 (5-1)
In the case where the 1 st lens group includes at least 1 cemented lens to which at least one positive lens and at least one negative lens are cemented, it is preferable that at least one positive lens and at least one negative lens satisfying the following conditional expressions (6) and (7) are cemented to at least one of the cemented lenses, where vp is a dispersion coefficient of a d-line reference of the positive lens constituting the cemented lens, θ gFp is a partial dispersion ratio between a g-line and an F-line of the positive lens constituting the cemented lens, vn is a dispersion coefficient of a d-line reference of the negative lens constituting the cemented lens, and θ gFn is a partial dispersion ratio between a g-line and an F-line of the negative lens constituting the cemented lens.
0.645＜0.0018×νp+θgFp＜0.72 (6)
0.645＜0.0018×νn+θgFn＜0.72 (7)
In the imaging lens of the above-described aspect, when the focal length of the entire system is f and the focal length of the 1 st lens group is f1, the following conditional expression (8) is preferably satisfied, and the following conditional expression (8-1) is more preferably satisfied.
0.4＜f/f1＜1 (8)
0.5＜f/f1＜1 (8-1)
In the imaging lens of the above-described aspect, it is preferable that the following conditional expression (9) is satisfied, where DG1 represents a distance on the optical axis between the most object-side lens surface of the 1 st lens group and the most image-side lens surface of the 1 st lens group, and f represents a focal length of the entire system in a state of focusing on an object at infinity.
1.6＜DG1/f＜2.5 (9)
In the imaging lens of the present invention, when the focal distance of the entire system in a state of focusing on an object at infinity is f and the focal distance of the 3 rd lens group is f3, the following conditional expression (10) is preferably satisfied, and the following conditional expression (10-1) is more preferably satisfied.
-0.8＜f/f3＜-0.05 (10)
-0.5＜f/f3＜-0.2 (10-1)
In the imaging lens of the above aspect, the number of lenses included in the 3 rd lens group is preferably two or less.
In the imaging lens of the above-described aspect, it is preferable that the following conditional expression (11) is satisfied, where DS is a sum of an optical-axis distance from the stop to the image-most lens surface of the 3 rd lens group and an optical-axis air-converted distance from the image-most lens surface of the 3 rd lens group to the image-side focal position of the entire system in a state of focusing on an object at infinity, f is a focal distance of the entire system in a state of focusing on an object at infinity, and ω is a maximum half angle of view.
2＜DS/(f×tan(ω))＜2.85 (11)
An imaging device according to
In addition, "consisting of" and "consisting of" in the present specification mean that, in addition to the components listed above, the following may be included: a lens having substantially no optical power; optical elements other than lenses, such as a diaphragm, a filter, and cover glass; lens flanges, lens barrels, imaging elements, and mechanism parts such as a handshake correction mechanism.
In the present specification, "group having positive refractive power" means that the group as a whole has positive refractive power. Similarly, "group having negative refractive power" means that the group as a whole has negative refractive power. The meaning of "lens having positive refractive power" and "positive lens" is the same. The "lens having negative refractive power" and the "negative lens" have the same meaning. The "lens group" is not limited to a configuration including a plurality of lenses, and may be a configuration including only one lens.
"singlet" refers to an unbonded piece of lens. However, a compound aspherical lens (a spherical lens and an aspherical film formed on the spherical lens are integrated, and the lens functioning as 1 aspherical lens as a whole) is treated as one lens instead of being regarded as a cemented lens. The sign of refractive power and the surface shape of the lens surface of a lens including an aspherical surface are considered in the paraxial region unless otherwise specified.
The "focal distance" used in the conditional expression is a paraxial focal distance. The value used in the conditional expression is a value obtained when d-line is used as a reference in addition to the partial dispersion ratio. The partial dispersion ratio θ gF between g-line and F-line of a certain lens is defined by θ gF ═ (Ng-NF)/(NF-NC) when the refractive indices of the lens with respect to g-line, F-line, and C-line are Ng, NF, and NC, respectively. The "d line", "C line", "F line" and "g line" described in the present specification are bright lines, the wavelength of the d line is 587.56nm (nm), the wavelength of the C line is 656.27nm (nm), the wavelength of the F line is 486.13nm (nm), and the wavelength of the g line is 435.84nm (nm).
Effects of the invention
According to an embodiment of the present invention, it is possible to provide an imaging lens that can realize a compact and high-speed focusing, has a configuration advantageous for securing a peripheral light amount, has a wide angle, and has high optical performance over the entire photographing distance by suppressing a plurality of aberrations including astigmatism and distortion aberration well, and an imaging apparatus including the imaging lens.
Drawings
Fig. 1 is a cross-sectional view corresponding to an imaging lens according to example 1 of the present invention and showing a configuration of the imaging lens according to an embodiment of the present invention.
Fig. 2 is a sectional view showing the structure of an imaging lens of
Fig. 3 is a sectional view showing the structure of an imaging lens of
Fig. 4 is a sectional view showing the structure of an imaging lens of embodiment 4 of the present invention.
Fig. 5 is a sectional view showing the structure of an imaging lens of embodiment 5 of the present invention.
Fig. 6 is each aberration diagram of the imaging lens of
Fig. 7 is each aberration diagram of the imaging lens of
Fig. 8 is each aberration diagram of an imaging lens of
Fig. 9 is each aberration diagram of the imaging lens of embodiment 4 of the present invention.
Fig. 10 is each aberration diagram of the imaging lens of embodiment 5 of the present invention.
Fig. 11 is a front perspective view of an imaging device according to an embodiment of the present invention.
Fig. 12 is a perspective view of the back side of the imaging device according to the embodiment of the present invention.
Detailed Description
Hereinafter, embodiments of an imaging lens of the present invention will be described in detail with reference to the drawings. Fig. 1 is a cross-sectional view showing a structure of an imaging lens according to an embodiment of the present invention. The example shown in fig. 1 corresponds to an imaging lens of
In addition, fig. 1 shows the following example: assume that an imaging lens is applied to an image pickup apparatus, and an optical member PP in the form of a parallel flat plate is arranged between the imaging lens and an image plane Sim. The optical member PP is a member assuming various filters, cover glasses, and the like. Examples of the various filters include a low-pass filter, an infrared cut filter, and a filter that cuts a specific wavelength region. The optical member PP is a member having no optical power, and a configuration in which the optical member PP is omitted can be realized.
The imaging lens is composed of, in order from the object side toward the image side along the optical axis Z, a 1 st lens group G1 having positive refractive power, a 2 nd lens group G2 having positive refractive power, and a 3 rd lens group G3 having negative refractive power. The 1 St lens group G1 includes an aperture stop St therein. The 1 St lens group G1 is composed of, in order from the object side to the image side, a 1a lens group G1a, an aperture stop St, and a 1b lens group G1 b.
For example, the imaging lens shown in fig. 1 includes a 1 a-th lens group G1a, a 1 b-th lens group G1b, a 2 nd lens group G2, and a 3 rd lens group G3. The 1a lens group G1a is composed of three lenses L11 to L13 in order from the object side toward the image side, and the 1b lens group G1b is composed of five lenses L14 to L18 in order from the object side toward the image side. The 2 nd lens group G2 is composed of lens L21 by lens, and the 3 rd lens group G3 is composed of lens L31 by lens. However, as in the embodiment described later, the number of lenses constituting each lens group may be different from that in the embodiment shown in fig. 1. Note that the aperture stop St shown in fig. 1 does not indicate a shape, but indicates a position on the optical axis Z.
In the imaging lens of the present invention, when focusing from an infinity object to a closest object, the 1 st lens group G1 and the 3 rd lens group G3 are fixed with respect to the image plane Sim, and the 2 nd lens group G2 moves along the optical axis Z. That is, the focusing group is the 2 nd lens group G2. In the example shown in fig. 1, the 2 nd lens group G2 moves to the object side when focusing from an infinity object to a closest object. An arrow toward the left direction below the 2 nd lens group G2 shown in fig. 1 refers to a focusing group in which the 2 nd lens group G2 moves to the object side when focusing from an infinity object to a closest object.
By configuring to move only the 2 nd lens group G2 during focusing, the focusing unit that moves during focusing can be made smaller and lighter, which is advantageous for speeding up focusing. Further, the present invention can contribute to downsizing of the lens system, and downsizing and weight reduction of the imaging device.
Since the 1 st lens group G1 has positive refractive power, the light flux emitted from the 1 st lens group G1 is converged and enters the 2 nd lens group G2, and therefore the diameter of the 2 nd lens group G2, which is a focusing group, can be reduced. This makes it possible to reduce the size and weight of the focus group, which is advantageous for speeding up the focusing.
Since the positive refractive power of the 2 nd lens group G2 can be enhanced by the 3 rd lens group G3 having a negative refractive power, it is possible to contribute to shortening the moving amount of the focus group at the time of focusing and speeding up the focusing. Further, the power arrangement of the 3 lens groups is made positive, and negative in order from the object side toward the image side, thereby achieving a telephoto type configuration, which is advantageous in shortening the total length of the lens system.
The most object-side lens in the 1 a-th lens group G1a is a negative lens having a convex surface on the object-side surface. The most image-side lens surface of the 3 rd lens group G3 is convex.
By setting the lens closest to the object side to a negative lens, the entrance pupil can be brought closer to the object side, and a wide angle of view and a reduction in diameter can be ensured. By making the most object side lens a negative meniscus lens with the convex surface facing the object side, it is advantageous to suppress astigmatism and distortion aberration and to secure the amount of peripheral light. In the 1 st lens group G1, a negative lens is disposed on the most object side, and the sign of the refractive power of the 1 st lens group G1 as a whole is positive, the sign of the refractive power of the 2 nd lens group G2 as a whole is positive, and the sign of the refractive power of the 3 rd lens group G3 as a whole is negative. Further, by making the lens surface closest to the object side and the lens surface closest to the image side of the imaging lens convex, the symmetry of the lens system can be improved, and the off-axis aberration can be corrected more effectively and favorably. Further, the 3 rd lens group G3 has a convex lens surface closest to the image side, which contributes to suppression of astigmatism and distortion aberration, and to suppression of the incident angle of the principal ray of the off-axis light flux with respect to the image plane Sim.
The number of lenses included in the 2 nd lens group G2 is set to two or less. This contributes to the reduction in size and weight of the lens system, and also contributes to the reduction in size and weight of the focusing unit.
The imaging lens is configured to satisfy the following conditional expression (1) when a focal distance of the entire system in a state of focusing on an infinite object is f, and a focal distance of the 2 nd lens group G2 is
0.35＜f/f2＜0.75 (1)
0.35＜f/f2＜0.65 (1-1)
The imaging lens is configured to satisfy the following conditional expression (2) when the focal distance of the 1 st lens group G1 is f1 and the focal distance of the 1 st a lens group G1a is f1 a. Since the aperture stop St is disposed adjacent to the image side of the 1a lens group G1a, the aperture stop St can be prevented from increasing in diameter by not being equal to or less than the lower limit of the conditional expression (2), which is advantageous for reducing the diameter of the lens. By not being equal to or more than the upper limit of conditional expression (2), the back focus can be easily secured. Further, a configuration satisfying the following conditional expression (2-1) can provide better characteristics.
-0.5＜f1/f1a＜0.3 (2)
-0.4＜f1/f1a＜0.22 (2-1)
The imaging lens is configured to satisfy the following conditional expression (3) when the focal distance of the 1 st lens group G1 is f1 and the focal distance of the 1b lens group G1b is f1 b. By setting the lower limit of conditional expression (3) or less, the back focus can be easily secured. The increase in the lens diameter of the 2 nd lens group G2 can be suppressed by setting the lens diameter not to be equal to or larger than the upper limit of the conditional expression (3). Further, a configuration satisfying the following conditional expression (3-1) can provide better characteristics.
0.4＜f1/f1b＜0.95 (3)
0.5＜f1/f1b＜0.9 (3-1)
By satisfying the conditional expressions (1), (2), and (3) at the same time, the power distribution in the 1 st lens group G1 can be set appropriately while maintaining the power of the focusing group in an appropriate range. This makes it possible to achieve both miniaturization, suppression of aberration variation during focusing, and securing of the back focus easily.
Next, a preferred structure and an achievable structure of the imaging lens of the present invention will be described. The 1 st lens group G1 preferably includes at least 1 cemented lens in which at least one positive lens and at least one negative lens are cemented. In this case, correction of chromatic aberration is facilitated. Since the 2 nd lens group G2 is formed with a small number of lenses and focusing is performed only with the 2 nd lens group G2, it is important to suppress chromatic aberration by the 1 st lens group G1 alone, and therefore, the 1 st lens group G1 preferably includes the above-described cemented lens.
When the 1 st lens group G1 includes the cemented lens, when the d-line reference dispersion coefficient of the positive lens constituting the cemented lens is vp, the partial dispersion ratio between the G-line and the F-line of the positive lens constituting the cemented lens is θ gFp, the d-line reference dispersion coefficient of the negative lens constituting the cemented lens is vn, and the partial dispersion ratio between the G-line and the F-line of the negative lens constituting the cemented lens is θ gFn, it is preferable that at least 1 positive lens satisfying the following conditional expression (6) and at least 1 negative lens satisfying the following conditional expression (7) are cemented to at least 1 cemented lens. By satisfying both the conditional expression (6) and the conditional expression (7), the chromatic aberration 2-order spectrum can be easily corrected.
0.645＜0.0018×νp+θgFp＜0.72 (6)
0.645＜0.0018×νn+θgFn＜0.72 (7)
When the 1 st lens group G1 includes the cemented lens, at least 1 cemented lens is disposed in the 1b lens group G1b, and the cemented lens closest to the object side in the 1b lens group G1b is preferably cemented with a positive lens and a negative lens in this order from the object side. The most object-side cemented lens in the 1 b-th lens group G1b is located near the aperture stop St, and therefore the lens diameter can be reduced. Further, by disposing the positive lens on the most object side in the cemented lens, the diameter of the entire cemented lens can be reduced, which is advantageous for reducing the diameter.
The 1b lens group G1b includes the cemented lens, and when the cemented lens closest to the object side in the 1b lens group G1b is formed by joining a positive lens and a negative lens in this order from the object side, it is preferable that the following conditional expression (4) is satisfied when the refractive index of the positive lens constituting the cemented lens closest to the object side in the 1b lens group G1b with respect to the d-line is N1 bp. The lower limit of conditional expression (4) is not set to be lower than the lower limit, which is advantageous for downsizing. By setting the upper limit of conditional expression (4) or more, the dispersion of the material does not become excessively large, and therefore, correction of chromatic aberration is facilitated.
1.8＜N1bp＜2.1 (4)
The 1b lens group G1b preferably includes the cemented lens described above, the cemented lens closest to the object side in the 1b lens group G1b is configured by joining a positive lens and a negative lens in this order from the object side, and when the d-line reference abbe number of the positive lens configuring the cemented lens closest to the object side in the 1b lens group G1b is ν 1bp, and the d-line reference abbe number of the negative lens configuring the cemented lens closest to the object side in the 1b lens group G1b is ν 1bn, the following conditional expression (5) is satisfied. By setting the lower limit of conditional expression (5) or less, chromatic aberration on the axis can be easily corrected. By setting the upper limit of conditional expression (5) or more, chromatic aberration of magnification can be easily corrected. That is, chromatic aberration is easily corrected by satisfying the conditional expression (5). Further, a configuration satisfying the following conditional expression (5-1) can provide better characteristics.
-50＜ν1bp-ν1bn＜0 (5)
-40＜ν1bp-ν1bn＜-5 (5-1)
The 1 st lens group G1 preferably includes two cemented lenses to which at least one positive lens and at least one negative lens are cemented. In this case, correction of chromatic aberration is facilitated. These two cemented lenses are preferably disposed in the 1 b-th lens group G1 b. The cemented lens closest to the object side in the 1b lens group G1b is preferably formed by joining a positive lens and a negative lens in this order from the object side, and the 2 nd cemented lens from the object side in the 1b lens group G1b is preferably formed by joining a negative lens and a positive lens from the object side. In this case, the power arrangement of the lenses constituting the two cemented lenses becomes positive, negative, and positive in order from the object side toward the image side, and therefore, correction of the curvature of the image plane is also facilitated.
When the focal distance of the entire system in a state of focusing on an object at infinity is f and the focal distance of the 1 st lens group G1 is f1, the following conditional expression (8) is preferably satisfied. By setting the lower limit of conditional expression (8) or less, the lens diameter of the 2 nd lens group G2 after the 1 st lens group G1 can be suppressed from increasing, and the focus group can be reduced in size and weight, which is advantageous for increasing the speed of focusing. By setting the refractive power of the 2 nd lens group G2 after the 1 st lens group G1 to not less than the upper limit of the conditional expression (8), the moving amount of the focus group at the time of focusing can be advantageously shortened. Further, a configuration satisfying the following conditional expression (8-1) can provide better characteristics.
0.4＜f/f1＜1 (8)
0.5＜f/f1＜1 (8-1)
When the distance on the optical axis between the most object side lens surface of the 1 st lens group G1 and the most image side lens surface of the 1 st lens group G1 is DG1, and the focal length of the entire system in a state of focusing on an object at infinity is f, the following conditional expression (9) is preferably satisfied. By setting the lower limit of conditional expression (9) or less, spherical aberration and astigmatism are easily balanced in the 1 st lens group G1. Further, the amount of aberration variation in focusing can be easily suppressed. The upper limit of conditional expression (9) is not exceeded, which contributes to downsizing of the lens system. Further, a configuration satisfying the following conditional expression (9-1) can provide better characteristics.
1.6＜DG1/f＜2.5 (9)
1.8＜DG1/f＜2.2 (9-1)
When the focal distance of the entire system in a state of focusing on an object at infinity is f and the focal distance of the 3 rd lens group G3 is f3, the following conditional expression (10) is preferably satisfied. By setting the refractive power of the 2 nd lens group G2 to be not less than the lower limit of the conditional expression (10), the amount of variation in aberration in focus can be easily suppressed. The image plane bowing is easily corrected by not being equal to or more than the upper limit of conditional expression (10). Further, a configuration satisfying the following conditional expression (10-1) can provide better characteristics.
-0.8＜f/f3＜-0.05 (10)
-0.5＜f/f3＜-0.2 (10-1)
When the sum of the distance on the optical axis from the aperture stop St to the most image-side lens surface of the 3 rd lens group G3 and the air-converted distance on the optical axis from the most image-side lens surface of the 3 rd lens group G3 to the image-side focal position of the entire system in a state focused on an infinitely distant object is DS, the focal distance of the entire system in a state focused on an infinitely distant object is f, and the maximum half angle of view is ω, the following conditional expression (11) is preferably satisfied. By setting the angle not to be lower than the lower limit of conditional expression (11), the incident angle of the principal ray of the off-axis light flux with respect to the image plane Sim can be easily included in an appropriate range. The upper limit of conditional expression (11) is not exceeded, which is advantageous for downsizing.
2＜DS/(f×tan(ω))＜2.85 (11)
When the sum of the distance on the optical axis from the most object side lens surface of the 1 st lens group G1 to the most image side lens surface of the 3 rd lens group G3 and the air converted distance on the optical axis from the most image side lens surface of the 3 rd lens group G3 to the image side focal position of the entire system in a state focused on an object at infinity is TL, the focal distance of the entire system in a state focused on an object at infinity is f, and the maximum half angle is ω, the following conditional expression (12) is preferably satisfied. By setting the lower limit of conditional expression (12) or less, the curvature of field and the distortion aberration are easily corrected. By setting the upper limit of conditional expression (12) or more, the total length of the lens system and the diameter of the lens system can be reduced. That is, by satisfying the conditional expression (12), miniaturization and favorable aberration correction can be easily achieved at the same time.
3＜TL/(f×tan(ω))＜4.5 (12)
When the air converted distance on the optical axis from the most image side lens surface of the 3 rd lens group G3 to the image side focal position of the entire system in a state focused on an object at infinity is Bf, the focal distance of the entire system in a state focused on an object at infinity is f, and the maximum half angle of view is ω, it is preferable that the following conditional expression (13) is satisfied. By setting the lower limit of conditional expression (13) or less, the lens closest to the image side is not excessively close to the image plane Sim, which is advantageous for reducing the diameter of the lens. The total length of the lens system is advantageously shortened by not being equal to or more than the upper limit of conditional expression (13).
0.8＜Bf/(f×tan(ω))＜1.1 (13)
Specifically, for example, each lens group can have the following structure. The 1a lens group G1a may be composed of two negative lenses and one positive lens. More specifically, the 1a lens group G1a may be configured by, in order from the object side to the image side, two negative meniscus lenses having a convex surface on the object side and one positive lens having a convex surface on the object side. In the case where the 1a lens group G1a is configured by the above-described three lenses, it may be a single lens in which all of the three lenses are not cemented.
The 1b lens group G1b may be configured to include, in order from the object side toward the image side, a 1 st cemented lens in which a positive lens and a negative lens are cemented, a positive lens that is a single lens, and a 2 nd cemented lens in which a negative lens and a positive lens are cemented. In this case, the incident angle of the principal ray at the peripheral angle of view to the cemented surface can be reduced, which is advantageous in suppressing the occurrence of astigmatism. Further, the cemented surface of the 2 nd cemented lens may be formed in a shape in which the convex surface faces the object side, in which case it is advantageous to correct chromatic aberration of magnification. In addition, in the case where the positive lens disposed between the 1 st cemented lens and the 2 nd cemented lens is a meniscus lens with a convex surface facing the image side, and the object-side surface of the negative lens of the 2 nd cemented lens may be formed as a concave surface, the miniaturization is facilitated.
The 2 nd lens group G2 can be configured by one or two lenses. When the number of lenses included in the 2 nd lens group G2 is only one, the size reduction is more facilitated. The 2 nd lens group G2 may be configured by one piece of biconvex lens, in which case the 2 nd lens group G2 can have a strong refractive power, which is advantageous for downsizing and speeding up of focusing. Alternatively, the 2 nd lens group G2 may be configured to be a cemented lens in which a negative lens and a positive lens are cemented, which is advantageous for downsizing and suppressing variation in chromatic aberration during focusing.
The number of lenses included in the 3 rd lens group G3 is preferably two or less. In this case, miniaturization is facilitated. When the number of lenses included in the 3 rd lens group G3 is set to one, it is more advantageous to reduce the size. The 3 rd lens group G3 may be configured by a single negative meniscus lens with the image side surface being convex. Alternatively, the 3 rd lens group G3 may be formed of two negative meniscus lenses having a convex image-side surface.
The above-described preferred configurations and realizable configurations can be arbitrarily combined, and are preferably selectively adopted as appropriate in accordance with the required specifications. According to the technique of the present invention, it is possible to realize a compact and high-speed focusing, and to realize an imaging lens having a configuration advantageous for securing the peripheral light amount, and having a wide angle and well suppressed various aberrations including astigmatism and distortion aberration, and having high optical performance over the entire imaging distance. The term "wide angle" as used herein means a total angle of view of 80 degrees or more.
Next, a numerical example of the imaging lens of the present invention will be explained.
[ example 1]
A cross-sectional view showing the structure of the imaging lens of
With respect to the imaging lens of example 1, basic lens data are shown in table 1, various factors are shown in table 2, variable surface intervals are shown in table 3, and aspherical surface coefficients are shown in table 4. In table 1, the column Sn shows the surface number in which the surface closest to the object side is the 1 st surface and the numbers are increased one by one toward the image side, the column R shows the radius of curvature of each surface, and the column D shows the surface interval on the optical axis between each surface and the surface adjacent to the image side. The refractive index of each component with respect to the d-line is shown in the Nd column, the d-line reference dispersion coefficient of each component is shown in the vd column, and the partial dispersion ratio between the g-line and the F-line of each component is shown in the θ gF column.
In table 1, the sign of the radius of curvature of the surface of the shape in which the convex surface faces the object side is positive, and the sign of the radius of curvature of the surface of the shape in which the convex surface faces the image side is negative. Table 1 also shows the aperture stop St, and the column of the surface number corresponding to the surface of the aperture stop St is provided with the term (surface number) and (St). The value in the lowermost column of D in table 1 is the distance between the image plane Sim and the surface closest to the image side in the table. In table 1, a sign DD [ ] is used for the variable surface interval in which the focus time interval changes in an increasing manner, and the object-side surface number of the interval is denoted by [ ] and is shown in column D.
In table 2, values of the focal length F of the imaging lens, the back focus Bf in the air-converted distance, the F number fno, and the maximum full-
In table 3, the value of the variable surface interval in a state of focusing on an object at infinity and the value of the variable surface interval in a state of focusing on an object at an object distance of 1m (meter) are shown in the columns expressed as "infinity" and "1 m", respectively.
In table 1, the numbers of the surfaces of the aspherical surfaces are denoted by x, and numerical values of paraxial radii of curvature are described in the column of radii of curvature of the aspherical surfaces. In table 4, the column Sn shows the surface number of the aspherical surface, and the columns KA and Am (m is 4, 6, 8, and 10) show the numerical values of the aspherical surface coefficients of the respective aspherical surfaces. "E. + -. n" (n: integer) of the numerical values of the aspherical surface coefficients of Table 4 represents ". times.10±n". KA and Am are aspheric coefficients in an aspheric expression represented by the following expression.
Zd＝C×h2/{1+(1-KA×C2×h2)1/2}+∑Am×hm
Wherein the content of the first and second substances,
and (d) is as follows: aspheric depth (length of perpendicular line from point on aspheric surface of height h to plane perpendicular to optical axis in contact with aspheric apex)
h: height (distance from optical axis to lens surface)
C: reciprocal of paraxial radius of curvature
KA. Am, and (2): the coefficient of the aspherical surface is,
the aspherical Σ refers to the sum of m.
In the data of each table, the degree is used as an angle unit and mm (millimeter) is used as a length unit, but other appropriate units can be used since an optical system can be used even if it is scaled up or down. Each table shown below shows numerical values rounded by a predetermined number of digits.
[ Table 1]
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