One of the aspects of the embodiments relates generally to an optical system, and more particularly to an optical system suitable for a digital video camera, a digital still camera, a broadcasting camera, a film-based camera, a surveillance camera, and the like.
A macro lens is known as a lens that can provide close-up imaging. The macro lens has recently been demanded to have high optical performance and few aberration fluctuations in the entire focusing area.
Each of Japanese Patent Laid-Open Nos. 2015-57662 and 2019-164277 discloses a macro lens that corrects aberration fluctuations during focusing by moving a large focus lens unit during focusing.
However, in each of the macro lenses described in Japanese Patent Laid-Open Nos. 2015-57662 and 2019-164277, an actuator configured to move the large focus lens unit becomes large, and the large focus lens causes the focusing stop accuracy to deteriorate and the focusing speed to decrease.
An optical system according to one aspect of the disclosure includes, in order from an object side to an image side, a first lens unit, a second lens unit, a third lens unit, and a fourth lens unit. Each distance changes between adjacent lens units during focusing from infinity to a close distance. The optical system further includes an aperture stop disposed on the image side of the second lens unit, a final lens unit disposed closest to an image plane in the optical system, the first lens unit and the final lens unit being fixed relative to the image plane during the focusing, and focus lens units disposed on the object side and the image side of the aperture stop and movable during the focusing. A focus lens unit closest to the image plane among the focus lens units moves toward the image side during the focusing. The optical system is configured to increase an absolute value of an imaging magnification at a shortest imaging distance to 0.5 times or higher. The final lens unit includes a positive lens and a negative lens. The following inequality is satisfied:
0.025<dF/L<0.099
where dF is a sum of distances on an optical axis from a lens surface closest to an object to a lens surface closest to the image plane in each of the focus lens units, and L is an overall lens length of the optical system. An image pickup apparatus and an optical system having the above optical system also constitute another aspect of the disclosure.
Further features of the disclosure will become apparent from the following description of embodiments with reference to the attached drawings.
Referring now to the accompanying drawings, a description will be given of an embodiment of an optical system and an image pickup apparatus having the optical system according to the present disclosure.
The optical system according to each example is an optical system that is used in an image pickup apparatus such as a digital video camera, a digital still camera, a broadcasting camera, a film-based camera, and a surveillance camera.
In each lens sectional view, a left side is an object side, and a right side is an image side. The optical system L0 according to each example includes a plurality of lens units. In this specification, a lens unit is a group of lenses that move together or stand still during focusing. That is, in the optical system L0 according to each example, a distance between adjacent lens units changes during focusing from infinity to a close distance (a short distance). The lens unit may include one or more lenses. The lens unit may include an aperture stop.
Li represents an i-th lens unit where i is order of the lens units counted from the object side (i is a natural number). The optical system L0 according to each example includes a plurality of lens units Li.
SP represents an aperture stop (diaphragm). IP is an image plane. In a case where the optical system L0 according to each example is used as an imaging optical system for a digital still camera or a digital video camera, an imaging plane of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is placed on the image plane IP. In a case where the optical system L0 according to each example is used as an imaging optical system for a film-based camera, a photosensitive plane corresponding to the film plane is placed on the image plane IP.
An arrow relating to “focus” illustrated in each lens sectional view indicates a moving direction of the lens unit during focusing from infinity to a close distance.
In a spherical aberration diagram, Fno represents an F-number. The spherical aberration diagram indicates spherical aberration amounts for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In an astigmatism diagram, dS indicates an astigmatism amount on a sagittal image plane, and dM indicates an astigmatism amount on a meridional image plane. A distortion diagram illustrates a distortion amount for the d-line. The distortion is expressed by a value for the d-line based on the equisolid angle projection method at the shortest and intermediate focal lengths, and a value for the d-line at the longest focal length based on the central projection method. A chromatic aberration diagram illustrates a chromatic aberration amount for the g-line. ω is a paraxial imaging half angle of view (°).
A description will now be given of a characteristic configuration of the optical system L0 according to each example.
The optical system L0 according to each example includes, in order from the object side, to the image side a first lens unit L1, a second lens unit L2, a third lens unit L3, and a fourth lens unit L4. A distance between adjacent lens units changes during focusing from infinity to a close. An aperture stop SP is disposed on the image side of the second lens unit L2. The first lens unit L1 and the final lens unit located closest to the image plane in the optical system L0 are fixed relative to the image plane IP during focusing from infinity to a close distance. Focus lens units are disposed on the object side and the image side of the aperture stop SP and configured to move during focusing from infinity to a close distance. A focus lens unit closest to the image plane among the focus lens units moves toward the image side during focusing from infinity to a close distance. The optical system L0 is configured to increase an absolute value of an imaging magnification at the shortest imaging distance to 0.5 times or higher. The final lens unit includes a positive lens and a negative lens.
The optical system L0 according to each example satisfies the following inequality (1):
0.025<dF/L<0.099 (1)
where dF is a sum of distances on the optical axis from a lens surface closest to the object to a lens surface closest to the image plane in each focus lens unit, and L is an overall lens length of the optical system L0.
Inequality (1) defines a ratio of an overall thickness dF1 of all the focus lens units to the overall lens length L of the optical system L0. In a case where the value dF/L is lower than the lower limit of inequality (1), the overall lens length L becomes too large. In a case where the overall thickness dF increases and the value dF/L is higher than the upper limit of inequality (1), the size of the focus lens unit increases, focusing speed decreases, and the size of the optical system L0 increases.
Inequality (1) may be replaced with inequality (1a) below:
0.026<dF/L<0.098 (1a)
Inequality (1) may be replaced with inequality (1b) below:
0.027<dF/L<0.097 (1b)
A description will now be given of a configuration that may be satisfied by the optical system L0 according to each example.
Each focus lens unit may consist of four lenses or less. This configuration can reduce the weight of each focus lens unit and provide quick focusing.
The final lens unit may consist of, in order from the object side to the image side, a positive subunit and a negative subunit. Thereby, the final lens unit has a telephoto arrangement, and the overall lens length of the optical system L0 can be restrained from increasing.
The first lens unit L1 may have positive refractive power. Thereby, the entire optical system L0 becomes closer to the telephoto arrangement, and the overall lens length of the optical system L0 can be restrained from increasing.
One focus lens unit may be disposed on each of the object side and the image side of the aperture stop SP. That is, the number of focus lens units disposed on the object side of the aperture stop SP may be one, and the number of focus lens units disposed on the image side of the aperture stop SP may be one. This configuration can simplify the focus driving unit, and restrain the optical system L0 from becoming large.
Among the focus lens units disposed on the image side of the aperture stop SP, the focus lens unit disposed closest to the object may have negative refractive power. Thereby, the focus lens unit can be restrained from becoming large. In addition, disposing a lens unit having negative refractive power near the aperture stop SP enables the curvature of field to be easily corrected.
The first lens unit L1 may include a subunit L1a configured to move in a direction including a component orthogonal to the optical axis during image stabilization. This configuration can suppress the influence of camera shake during imaging and provides high-resolution imaging.
A description will be given of conditions that the optical system L0 according to each example may satisfy. The optical system L0 according to each example may satisfy one or more of the following inequalities (2) to (9):
0.0<|f1/fL|<1.0 (2)
0.1<|(1−βf2)×βr2|<5.1 (3)
0.8<L/f<2.4 (4)
0.2<f1/f<1.3 (5)
0.1<|f2/f|<2.5 (6)
0.2<|f3/f|<0.8 (7)
0.1<|f4/f|<0.9 (8)
|β|≥0.5 (9)
Here, f1 is a focal length of the first lens unit L1. fL is a focal length of the final lens unit. βf is a lateral magnification of the focus lens unit closest to the image plane among the focus lens units. βr is a combined lateral magnification of all the lens units disposed on the image side of the focus lens unit closest to the image plane among the focus lens units. f is a focal length of the optical system L0. f2 is a focal length of the second lens unit. f3 is a focal length of the third lens unit. f4 is a focal length of the fourth lens unit. β is an imaging magnification at the shortest imaging distance of the optical system L0.
Inequality (2) defines a ratio of the focal length f1 of the first lens unit L1 to the focal length fL of the final lens unit. In a case where the focal length f1 of the first lens unit L1 becomes small and the value |f1/fL| becomes lower than the lower limit of inequality (2), the refractive power of the first lens unit becomes too strong, and a light ray converged or diverged by the first lens unit cause spherical aberration and coma significantly. It becomes thus difficult to correct aberrations in the subsequent lens units. In a case where the focal length f1 of the first lens unit increases and the value |f1/fL| becomes higher than the upper limit of inequality (2), which is beneficial to aberration correction, the overall lens length becomes long because the lens unit has no refractive power, and size and weight reductions are hindered.
Inequality (3) defines the focus sensitivity of the focus lens unit closest to the image plane among the focus lens units. In a case where the value |(1−βf2)×βr2| becomes lower than the lower limit of inequality (3), a moving amount of the focus lens unit closest to the image plane among the focus lens units increases, and the overall lens length of the optical system L0 increases. In a case where the value |(1−βf2)×βr2| becomes higher than the upper limit of inequality (3), the focusing stop accuracy of the focus lens unit closest to the image plane during focusing becomes low, and it becomes difficult to achieve proper focusing.
Inequality (4) defines a ratio of the overall lens length L of the optical system L0 to the focal length f of the optical system L0. In a case where the focal length f increases and the value L/f becomes lower than the lower limit of inequality (4), the overall lens length L of the optical system L0 undesirably increases. In a case where the focal length f becomes small and the value L/f becomes higher than the upper limit of inequality (4), it becomes difficult to correct various aberrations.
Inequality (5) defines a ratio of the focal length f1 of the first lens unit L1 to the focal length f of the optical system L0. In a case where the focal length f1 becomes so short that the value f1/f becomes lower than the lower limit of inequality (5), correction of various aberrations becomes difficult. In a case where the focal length f1 becomes so long that the value f1/f becomes higher than the upper limit of inequality (5), the overall lens length of the optical system L0 undesirably increases.
Inequality (6) defines a ratio of the focal length f2 of the second lens unit L2 to the focal length f of the optical system L0. Inequality (6) is to reduce the occurrence of spherical aberration, and in a case where the value |f2/f| is maintained within the range of inequality (6), correction of spherical aberration becomes easier.
Inequality (7) defines a ratio of the focal length f3 of the third lens unit L3 to the focal length f of the optical system L0. Inequality (7) is to reduce the occurrence of spherical aberration, and in a case where the value |f3/f| is maintained within the range of inequality (7), correction of spherical aberration becomes easier.
Inequality (8) defines a ratio of the focal length f4 of the fourth lens unit L4 to the focal length f of the optical system L0. Inequality (8) is to reduce the occurrence of curvature of field, and in a case where the value |f4/f| is maintained within the range of inequality (8), correction of field curvature becomes easier.
Inequality (9) defines the condition of the imaging magnification β at the shortest imaging distance of the optical system L0. In a case where the value |β| becomes lower than the lower limit of inequality (9), high-magnification imaging becomes difficult.
Inequalities (2) to (9) may be replaced with inequalities (2a) to (9a) below:
0.0<|f1/fL|<0.95 (2a)
0.2<|(1−βf2)×βr2|<5.0 (3a)
1.0<L/f<2.3 (4a)
0.3<f1/f<1.2 (5a)
0.2<|f2/f|<2.4 (6a)
0.3<|f3/f|<0.7 (7a)
0.2<|f4/f|<0.8 (8a)
|β|≥0.7 (9a)
Inequalities (2) to (9) may be replaced with inequalities (2b) to (9b) below:
0.0<|f1/fL|<0.9 (2b)
0.3<|(1−βf2)×βr2|<4.9 (3b)
1.05<L/f<2.22 (4b)
0.4<f1/f<1.1 (5b)
0.3<|f2/f|<2.3 (6b)
0.33<|f3/f|<0.65 (7b)
0.3<|f4/f|<0.7 (8b)
|β|≥1.0 (9b)
A detailed description will now be given of the optical system L0 according to each example.
The optical system L0 according to Example 1 consists of, in order from the object side to the image side, a first lens unit L1 having positive refractive power, a second lens unit L2 having negative refractive power, a third lens unit L3 having positive refractive power, a fourth lens unit L4 having negative refractive power, and a fifth lens unit L5 having positive refractive power.
In the optical system L0 according to Example 1, the first lens unit L1, the third lens unit L3, and the fifth lens unit L5 are fixed relative to the image plane IP during focusing from infinity to a close distance. During focusing from infinity to a close distance, the second lens unit L2 and the fourth lens unit L4 move toward the image side. The third lens unit L3 includes an aperture stop SP, and the aperture stop SP is disposed closest to the object in the third lens unit L3.
The optical system L0 according to Example 2 consists of, in order from the object side to the image side, a first lens unit L1 having positive refractive power, a second lens unit L2 having positive refractive power, a third lens unit L3 having positive refractive power, a fourth lens unit L4 having negative refractive power, and a fifth lens unit L5 having positive refractive power.
In the optical system L0 according to Example 2, the first lens unit L1, the third lens unit L3, and the fifth lens unit L5 are fixed relative to the image plane IP during focusing from infinity to a close distance. During focusing from infinity to a close distance, the second lens unit L2 moves toward the object side, and the fourth lens unit L4 moves toward the image side. The third lens unit L3 includes an aperture stop SP, and the aperture stop SP is disposed closest to the object in the third lens unit L3.
The optical system L0 according to Example 3 consists of, in order from the object side to the image side, a first lens unit L1 having positive refractive power, a second lens unit L2 having negative refractive power, a third lens unit L3 having positive refractive power, a fourth lens unit L4 having negative refractive power, and a fifth lens unit L5 having positive refractive power.
The first lens unit L1, the third lens unit L3, and the fifth lens unit L5 are fixed relative to the image plane IP during focusing from infinity to a close distance. During focusing from infinity to a close distance, the second lens unit L2 and the fourth lens unit L4 move toward the image side. The third lens unit L3 includes an aperture stop SP, and the aperture stop SP is disposed closest to the object in the third lens unit L3.
The optical system L0 according to Example 4 consists of, in order from the object side to the image side, a first lens unit L1 having positive refractive power, a second lens unit L2 having negative refractive power, a third lens unit L3 having positive refractive power, a fourth lens unit L4 having negative refractive power, a fifth lens unit L5 having positive refractive power, and a sixth lens unit L6 having positive refractive power.
The first lens unit L1, the third lens unit L3, and the sixth lens unit L6 are fixed relative to the image plane IP during focusing from infinity to a close distance. The second lens unit L2, the fourth lens unit L4, and the fifth lens unit L5 move toward the image side during focusing from infinity to a close distance. The third lens unit L3 includes an aperture stop SP, and the aperture stop SP is disposed closest to the object in the third lens unit L3.
The optical system L0 according to Example 5 consists of, in order from the object side to the image side, a first lens unit L1 having positive refractive power, a second lens unit L2 having negative refractive power, a third lens unit L3 having positive refractive power, a fourth lens unit L4 having negative refractive power, and a fifth lens unit L5 having negative refractive power.
The first lens unit L1, the third lens unit L3, and the fifth lens unit L5 are fixed relative to the image plane IP during focusing from infinity to a close distance. During focusing from infinity to a close distance, the second lens unit L2 and the fourth lens unit L4 move toward the image side. The third lens unit L3 includes an aperture stop SP, and the aperture stop SP is disposed closest to the object in the third lens unit L3.
The optical system L0 according to Example 6 consists of, in order from the object side to the image side, a first lens unit L1 having positive refractive power, a second lens unit L2 having negative refractive power, an aperture stop SP, a third lens unit L3 having negative refractive power, and a fourth lens unit L4 having positive refractive power.
The first lens unit L1, the aperture stop SP, and the fourth lens unit L4 are fixed relative to the image plane IP during focusing from infinity to a close distance. During focusing from infinity to a close distance, the second lens unit L2 and the third lens unit L3 move toward the image side.
The optical system L0 according to Example 7 consists of, in order from the object side to the image side, a first lens unit L1 having positive refractive power, a second lens unit L2 having negative refractive power, a third lens unit L3 having positive refractive power, a fourth lens unit L4 having negative refractive power, and a fifth lens unit L5 having negative refractive power.
During focusing from infinity to a close distance, the first lens unit L1, the third lens unit L3, and the fifth lens unit L5 are fixed relative to the image plane IP. During focusing from infinity to a close distance, the second lens unit L2 and the fourth lens unit L4 move toward the image side. The third lens unit L3 includes an aperture stop SP, and the aperture stop SP is disposed closest to the object in the third lens unit L3.
The optical system L0 according to Example 8 consists of, in order from the object side to the image side, a first lens unit L1 having positive refractive power, a second lens unit L2 having negative refractive power, a third lens unit L3 having positive refractive power, a fourth lens unit L4 having negative refractive power, and a fifth lens unit L5 having positive refractive power.
The first lens unit L1, the third lens unit L3, and the fifth lens unit L5 are fixed relative to the image plane IP during focusing from infinity to a close distance. During focusing from infinity to a close distance, the second lens unit L2 and the fourth lens unit L4 move toward the image side. The third lens unit L3 includes an aperture stop SP, and the aperture stop SP is disposed closest to the object in the third lens unit L3.
As described above, in the macro lens, each example can reduce the weight and size of the focus lens unit, improve the focusing stop accuracy, increase the focusing speed, and provide a compact and high-performance optical system.
Numerical examples 1 to 8 corresponding to examples 1 to 8 will be illustrated below.
In surface data in each numerical example, r represents a radius of curvature of each optical surface, and d (mm) represents an on-axis distance (distance on the optical axis) between an m-th surface and an (m+1)-th surface, where m is a surface number counted from the light incident side. nd represents a refractive index for the d-line of each optical element, and vd represents an Abbe number of the optical element. The Abbe number vd of a certain material is expressed as follows:
vd=(Nd−1)/(NF−NC)
where Nd, NF, and NC are refractive indices based on the d-line (587.6 nm), the F-line (486.1 nm), and the C-line (656.3 nm) in the Fraunhofer line, respectively. An effective diameter means a diameter of an area (effective area) of the lens surface through which an effective light beam that contributes to imaging passes.
In each numerical example, values of d, focal length (mm), F-number, and half angle of view (°) are set in a case where the optical system according to each example is in an in-focus state on an infinity object. “Back focus BF” is a distance on the optical axis from the final lens surface (lens surface closest to the image plane) to the paraxial image plane expressed in air conversion length. An “overall lens length” is a length obtained by adding the back focus to a distance on the optical axis from the first lens surface (lens surface closest to the object) of the optical system L0 to the final lens surface. The term “lens unit” includes one or more lenses.
In a case where the optical surface is an aspherical surface, an asterisk * is attached to the right side of the surface number. The aspherical shape is expressed as follows:
X=(h2/R)/[1+{1−(1+k)(h/R)2}1/2]+A4×h4+A6×h6+A8×h8+A10×h10+A12×h12
where X is a displacement amount from a surface vertex in the optical axis direction, h is a height from the optical axis in a direction orthogonal to the optical axis, a light traveling direction is set positive, R is a paraxial radius of curvature, k is a conic constant, and A4, A6, A8, A10, and A12 are aspherical coefficients. “e±XX” in each aspheric coefficient means “×10±XX.”
Table 1 below summarizes various values in each numerical example.
Referring now to
Applying the optical system L0 according to each example to an image pickup apparatus such as a digital still camera can provide an image pickup apparatus having a compact lens.
In the macro lens, this embodiment can reduce the weight and size of the focus lens unit, improve the focusing stop accuracy, increase the focusing speed, and provide a compact and high-performance optical system.
While the disclosure has been described with reference to embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2022-111958, filed on Jul. 12, 2022, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2022-111958 | Jul 2022 | JP | national |