Patent Application
20230139677
The aspect of the embodiments relates to a zoom lens and the like and is suitable for an image capture apparatus, such as a digital camcorder, a digital still camera, a broadcast camera, and a silver-halide film camera.
Wide angle lenses are widely used for landscape photography, astronomical photography, and the like. Wide angle lenses are desired to have a wide view angle with high optical performance.
Japanese Patent Laid-Open No. 2015-203734 describes a zoom lens that provides a wide view angle with high performance by adopting a plurality of negative lenses into a first lens unit to gently deflect off-axis rays.
In the zoom lens described in Japanese Patent Laid-Open No. 2015-203734, the lens open angle of a first lens is large, and unnecessary light obliquely reflected on an object-side lens surface of a second lens with respect to the lens surface reflects on an image-side lens surface of the first lens and reaches an image plane. If such unnecessary light reaches an image plane, a ghost effect may undesirably occur on a photo.
A zoom lens includes a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and two or more additional lens units. The first lens unit, the second lens unit, and the two or more additional lens units are disposed in order from an object side toward an image side, and, in zooming, the first lens unit is arranged to move, and an interval between adjacent lens units changes. The refractive index of a negative lens A disposed on a most object side of negative lenses included in the first lens unit is higher than or equal to 1.89. Where the radius of curvature of an image-side lens surface of the negative lens A is Ra, the radius of curvature of an object-side lens surface of a lens B disposed adjacent to the image side of the negative lens A is Rb, an air gap between the negative lens A and the lens B is Da, and an air gap between the lens B and a lens disposed adjacent to an image side of the lens B is Db, inequalities
2.0<Ra/Da<100, and
10<Rb/Db<100
are satisfied.
Further features of the disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, embodiments of the zoom lens and the image capture apparatus according to the disclosure will be described with reference to the attached drawings.
In each lens sectional view, the left side is an object side, and the right side is an image side. The zoom lens L0 of each embodiment may be used as a projector lens. At this time, the left side is a screen side, and the right side is a projected image side.
The zoom lens L0 of each embodiment includes a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, and two or more additional lens units, disposed in order from the object side toward the image side. In each sectional view, Li represents an ith lens unit that is the ith from the object side (i is a natural number). In the specification, a lens unit is a set of lenses that integrally move or stand still in zooming. In other words, the interval between adjacent lens units changes in zooming. Each lens unit may be made up of a single lens or may be made up of a plurality of lenses. Each lens unit may include an aperture stop.
The arrows shown in each lens sectional view represent movement loci in zooming from a wide angle end to a telephoto end and movement loci in focusing from an infinite distance to a short range.
In each lens sectional view, SP indicates an aperture stop. IP indicates an image plane, and, when the zoom lens of each embodiment is used in a digital still camera or a digital camcorder, the image pickup surface of a solid-state image pickup device (photoelectric conversion device), such as a CCD sensor and a CMOS sensor, is disposed. When the zoom lens of each embodiment is used as a shooting zoom lens of a silver-halide film camera, a photo surface corresponding to a film surface is placed at the image plane IP.
In a spherical aberration chart, Fno is an F-number and represents a spherical aberration for d line (wavelength: 587.6 nm) and a spherical aberration for g line (wavelength: 435.8 nm). In an astigmatism chart, S represents an aberration at a sagittal image plane, and M represents an aberration at a meridional image plane. A distortion aberration chart represents a distortion aberration for d line. A chromatic aberration chart represents a lateral chromatic aberration for g line. ω is an image pickup half view angle (°).
Next, the characteristic configuration of the zoom lens of each embodiment will be described.
In the zoom lens of each embodiment, by setting the refractive power of the first lens unit L1 to a negative value, the entrance pupil position is shifted toward the object side to reduce the diameter of a front lens (lens disposed on the most object side).
By setting the refractive power of the second lens unit L2 to a positive value, an axial marginal ray diverged by the first lens unit L1 is converged so as to reduce the diameters of portions downstream of the second lens unit L2. In addition, by providing two or more additional lens units on the image side of the positive second lens unit L2 and moving the first lens unit L1 in zooming, aberration is favorably corrected within a wide zoom range.
In the zoom lens L0 of each embodiment, the refractive index of the most object-side negative lens A of the negative lenses in the first lens unit L1 is higher than or equal to 1.89. Furthermore, the following inequalities are satisfied. Here, Ra is the radius of curvature of the image-side lens surface of the negative lens A. Rb is the radius of curvature of the object-side lens surface of the lens B disposed adjacent to the image side of the negative lens A. Da is an air gap between the negative lens A and the lens B. Db is an air gap between the lens B and a lens disposed adjacent to the image side of the lens B.
2.0<Ra/Da<100 (1)
10<Rb/Db<100 (2)
A wide angle lens tends to have an increased diameter of a first lens disposed on the most object side in the first lens unit, and tends to have an increased lens open angle. At this time, as shown in
For this reason, in the zoom lens L0 of each embodiment, the refractive index of the negative lens A is set to 1.89 to impart a necessary refractive power to the negative lens A while increasing a lens open angle. By increasing the curvature of the image-side lens surface of the negative lens A and the curvature of the object-side lens surface of the lens B within the range in which the inequalities (1) and (2) are satisfied, off-axis rays reflect at an angle close to a right angle with respect to the lens surface, so the intensity of the ghosting effect is reduced. When any one of the curvatures exceeds the upper limit value of a corresponding one of the inequalities (1) and (2), it is difficult to impart a necessary refractive power to the negative lens A or the lens B.
With the above configuration, it is possible to achieve a zoom lens capable of reducing occurrence of ghost images while having high optical performance.
At least one of the upper limit value and the lower limit value of the numeric range of any one of the inequalities (1) and (2) is preferably set to the following inequality (1a) or inequality (2a).
2.3<Ra/Da<50 (1a)
11<Rb/Db<50 (2a)
More preferably, at least one of the upper limit value and the lower limit value of the numeric range of any one of the inequalities (1) and (2) is preferably set to the following inequality (1b) or inequality (2b).
2.6<Ra/Da<10 (1b)
11.5<Rb/Db<30 (2b)
By setting the refractive index of the negative lens A to a value higher than 1.89, the lens open angle of the negative lens A can be set more preferably from the viewpoint of reduction of ghost images.
Next, the configuration of the zoom lens L0 according to each embodiment will be described.
The lens B disposed adjacent to the image side of the negative lens A can be a negative lens. With this configuration, negative lenses including the negative lens A are successively disposed, so off-axis rays are able to be gently deflected. Thus, it is possible to favorably reduce particularly astigmatism and field curvature at the wide angle end.
The first lens unit L1 can be made up of three negative lenses and a positive lens, disposed in order from the object side toward the image side. By successively disposing three negative lenses, it is possible to reduce astigmatism and field curvature at the wide angle end. By disposing a positive lens at the most image side, it is possible to further reduce particularly lateral chromatic aberration at the wide angle end.
Next, inequalities that can be satisfied for the zoom lens L0 of each embodiment will be described.
The zoom lens L0 of each embodiment preferably satisfies one or more of the following inequalities.
1.80<NdB (3)
2.0<d/fw<15 (4)
1.5<d2/fw<5.0 (5)
0.15<GL/TL<0.30 (6)
−20<100×(y−y0)/y0<−8 (7)
−2.5<fl/fw<−0.8 (8)
−3.5<fa/fw<−1.5 (9)
−3.5<fb/fw<−0.8 (10)
1.2<ft/fw<2.1 (11)
Here, NdB is the refractive index of the lens B ford line. d is a distance from the image-side lens surface of the negative lens A to the aperture stop SP at the wide angle end. fw is the focal length of the entire system of the zoom lens L0 at the wide angle end. d2 is a distance from the image-side lens surface of the lens B to the aperture stop SP at the wide angle end. GL is a distance from the most object-side lens surface of the first lens unit L1 to the most image-side lens surface of the first lens unit L1. TL is a distance from the most object-side lens surface of the zoom lens L0 to the image plane IP (paraxial imaging plane) at the wide angle end. y is the maximum value of a real image height at the wide angle end. y0 is an ideal image height at a view angle associated with the maximum real image height y (maximum view angle) at the wide angle end. fl is the focal length of the first lens unit L1. fa is the focal length of the negative lens A. fb is the focal length of the lens B. ft is the focal length of the entire system of the zoom lens L0 at the telephoto end.
Hereinafter, the technical meaning of each inequality will be described.
When the value is lower than the lower limit value of the inequality (3), the lens open angle needed at the time of imparting a desired refractive power to the lens B reduces, so particularly reflection on the object-side lens surface of the lens B can be problematic.
The inequality (4) means the ratio of a distance from the image-side lens surface of the negative lens A to the aperture stop SP at the wide angle end to the focal length of the entire system at the wide angle end. When the value exceeds the upper limit value, the distance from the image-side lens surface of the negative lens A to the aperture stop SP at the wide angle end is too long, so the size of the negative lens A tends to increase. When the value is lower than the lower limit value, it is difficult to sufficiently reduce the intensity of ghost images due to unnecessary light that reflects between the negative lens A and the lens B.
The inequality (5) means the ratio of a distance from the image-side lens surface of the lens B to the aperture stop SP at the wide angle end to the focal length of the entire system at the wide angle end. When the value exceeds the upper limit value, the distance from the image-side lens surface of the lens B to the aperture stop SP at the wide angle end is too long, so the size of the lens B tends to increase. When the value is lower than the lower limit value, it is difficult to sufficiently reduce the intensity of ghost images due to unnecessary light that reflects between the negative lens A and the lens B.
The inequality (6) means the ratio of a distance from the most object-side lens surface of the first lens unit L1 to the most image-side lens surface of the first lens unit L1 to a distance from the most object-side lens surface of the entire system to the paraxial imaging plane at the wide angle end. When the value exceeds the upper limit value, the distance from the most object-side lens surface of the first lens unit L1 to the most image-side lens surface of the first lens unit L1 is too long, so the distance from the aperture stop SP to a first lens (lens disposed on the most object side) extends. As a result, the size of the first lens increases. When the value is lower than the lower limit value, the distance from the most object-side lens surface of the entire system to the paraxial imaging plane at the wide angle end is too long, so the size of the zoom lens L0 increases.
The inequality (7) means a distortion rate at the wide angle end. The ideal image height y0 is a value obtained from f×tan θ where the focal length of the entire system at the wide angle end is f and an angle formed between an optical axis and ray that enters from the object side associated with the maximum real image height y to the most object side of the entire system (half view angle) is θ. The real image height y can be determined by the maximum radius of an image circle of the zoom lens L0. When the value exceeds the upper limit value, the refractive power in the first lens unit L1 needs to be lowered to reduce the absolute value of the distortion rate, so the distance from the most object-side lens surface to the image plane IP extends, with the result that the size of the zoom lens L0 tends to increase. When the value is lower than the lower limit value, the absolute value of the distortion rate is too large, so a peripheral portion of an image is compressed by a large amount, with the result that it is difficult to obtain a sufficiently high-quality image.
The inequality (8) means the ratio of the focal length of the first lens unit L1 to the focal length of the entire system at the wide angle end. When the value exceeds the upper limit value, the absolute value of the focal length of the first lens unit L1 is too short, so the refractive power is too high, with the result that the astigmatism, field curvature, and lateral chromatic aberration at the wide angle end undesirably increase. When the value is lower than the lower limit value, the absolute value of the focal length of the first lens unit L1 is too long, so the distance from the most object-side lens surface to the image plane IP extends, and the size increases.
The inequality (9) means the ratio of the focal length of the negative lens A to the focal length of the entire system at the wide angle end. When the value exceeds the upper limit value, the absolute value of the focal length of the negative lens A is too short, so the refractive power is too high, with the result that particularly the lateral chromatic aberration at the wide angle end increases. When the value is lower than the lower limit value, the absolute value of the focal length of the negative lens A is too long, so the distance from the most object-side lens surface to the image plane IP extends, with the result that the diameter of the negative lens A increases.
The inequality (10) means the ratio of the focal length of the lens B to the focal length of the entire system at the wide angle end. When the value exceeds the upper limit value, the absolute value of the focal length of the lens B is too short, so the refractive power is too high, with the result that particularly the astigmatism and lateral chromatic aberration at the wide angle end increase. When the value is lower than the lower limit value, the absolute value of the focal length of the lens B is too long, so the distance from the most object-side lens surface to the image plane IP extends, with the result that the diameter of the lens B increases.
The inequality (11) means a zoom ratio. When the value exceeds the upper limit value, the amount of movement of each lens unit tends to increase, so the size of the zoom lens L0 tends to increase to ensure space for movement. When the value is lower than the lower limit value, the zoom ratio is too small, so it is difficult to exert a sufficient function as a zoom lens.
At least one of the upper limit value and the lower limit value of each of the inequalities (3) to (11) is more preferably set as the following numeric ranges.
1.82<NdB (3a)
2.3<d/fw<10 (4a)
2.0<d2/fw<4.0 (5a)
0.17<GL/TL<0.27 (6a)
−19<100×(y−y0)/y0<−11 (7a)
−2.0<fl/fw<−1.0 (8a)
−3.1<fa/fw<−1.7 (9a)
−3.0<fb/fw<−1.0 (10a)
1.3<ft/fw<2.0 (11a)
At least one of the upper limit value and the lower limit value of each of the inequalities (3) to (11) is further preferably set as the following numeric ranges.
1.84<NdB (3b)
2.7<d/fw<5 (4b)
2.3<d2/fw<3.5 (5b)
0.19<GL/TL<0.24 (6b)
−18<100×(y−y0)/y0<−14 (7b)
−1.8<fl/fw<−1.2 (8b)
−2.8<fa/fw<−1.9 (9b)
−2.7<fb/fw<−1.2 (10b)
1.4<ft/fw<1.9 (11b)
Next, the detailed configuration of the zoom lens L0 according to each embodiment will be described.
The zoom lens L0 of the first embodiment includes a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, a third lens unit L3 having a negative refractive power, a fourth lens unit L4 having a positive refractive power, and a fifth lens unit L5 having a positive refractive power, disposed in order from the object side toward the image side. By alternately arranging a lens unit having a negative refractive power and a lens unit having a positive refractive power, a lateral chromatic aberration and a longitudinal chromatic aberration are appropriately corrected. By setting the fifth lens unit L5 having a positive refractive power, back focus is ensured with a wide view angle, it is possible to reduce ghost images due to unnecessary light reflected between the image plane IP (or a low-pass filter or an IR cut filter that can be disposed on the object side) and the fifth lens unit L5. The configuration to move the third lens unit L3 in focusing is adopted, and the third lens unit L3 has a concentric shape such that the object side of the third lens unit L3 has a concave surface facing the aperture stop SP. Thus, even when the third lens unit L3 moves in focusing, fluctuations in field curvature and astigmatism are reduced, so high performance is obtained over the entire screen. When the third lens unit L3 is made up of two lenses, that is, a positive lens and a negative lens, fluctuations in lateral chromatic aberration and longitudinal chromatic aberration are reduced even when the lenses are moved in an optical axis direction.
The locus of the first lens unit L1 at the time of zooming monotonously shifts toward the image side from the wide angle end to the telephoto end. Thus, the absolute value of the focal length of the first lens unit L1 is extended (the refractive power is reduced) to provide high performance of the zoom lens L0.
A second embodiment differs from the first embodiment in that the third lens unit L3 that is a focusing unit is made up of a single negative lens. Thus, the size of the third lens unit L3 that moves at the time of focusing is reduced.
The zoom lens L0 according to a third embodiment includes a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, a third lens unit L3 having a negative refractive power, a fourth lens unit L4 having a negative refractive power, and a fifth lens unit L5 having a positive refractive power, disposed in order from the object side toward the image side. By setting the fourth lens unit L4 having a negative refractive power, a lateral chromatic aberration that occurs in the fifth lens unit L5 having a positive refractive power is favorably corrected. By disposing a positive lens on the most object side, a negative distortion aberration that occurs in the first lens unit L1 is reduced to reduce a distortion rate, with the result that the compression ratio of a screen peripheral region is reduced to increase resolving power.
By joining the fourth lens unit L4 with the fifth lens unit L5, the intensity of unnecessary light that reflects between the fourth lens unit L4 and the fifth lens unit L5 is reduced to reduce ghost images.
By moving the fifth lens unit L5 toward the object side at the telephoto end, the fifth lens unit L5 is able to be disposed at a location at which off-axis ray height at the telephoto end is low, and the size is reduced.
The zoom lens L0 according to a fourth embodiment includes a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, a third lens unit L3 having a positive refractive power, a fourth lens unit L4 having a negative refractive power, a fifth lens unit L5 having a positive refractive power, and a sixth lens unit L6 having a positive refractive power. The positive refractive power before and behind the aperture stop SP is divided as two lens units, and the two lens units are moved independently at the time of zooming. Thus, a spherical aberration and a coma aberration are favorably corrected in a wide zoom range.
The zoom lens L0 according to a fifth embodiment includes a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, a third lens unit L3 having a negative refractive power, a fourth lens unit L4 having a positive refractive power, and a fifth lens unit L5 having a negative refractive power, arranged from the object side toward the image side. By setting the fourth lens unit L4 with a positive refractive power and setting the fifth lens unit L5 with a negative refractive power, a front principal point position in the combination of the fourth lens unit L4 and the fifth lens unit L5 is able to be moved to the object side, and back focus is able to be shortened, so the size of the zoom lens L0 is reduced.
The zoom lens L0 of a sixth embodiment includes a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, a third lens unit L3 having a negative refractive power, and a fourth lens unit L4 having a positive refractive power, disposed in order from the object side toward the image side. By providing one of each of a positive lens and a negative lens in the fourth lens unit L4, a lateral chromatic aberration is favorably corrected within a wide zoom range.
The zoom lens L0 of each of the above-described embodiments may be used in an image capture apparatus having an image processing function to correct an aberration (a distortion aberration and a lateral chromatic aberration).
Hereinafter, first to sixth numerical embodiments respectively corresponding to the first to sixth embodiments will be described.
In surface data of each numerical embodiment, r denotes the radius of curvature of each optical surface, and d (mm) denotes an on-axis interval (distance on the optical axis) between an mth surface and an (m+1)th surface. Here, m is a number assigned to a surface and counted from a light incident side. nd denotes the refractive index of each optical member for d line, and vd denotes the Abbe number of the optical member. The Abbe number vd of a material is, where the refractive indexes for d line (587.6 nm), F line (486.1 nm), C line (656.3 nm), and g line (435.8 nm) of Fraunhofer's line are respectively Nd, NF, NC, Ng, expressed by
vd=(Nd−1)/(NF−NC).
When the optical surface is an aspherical surface, the sign “*” is suffixed to the surface number. An aspherical shape is, where X is an amount of displacement from a surface vertex in the optical axis direction, h is a height from the optical axis in a direction perpendicular to the optical axis, R is a paraxial radius of curvature, k is a conic constant, and A4, A6, A8, A10, A12, . . . are aspherical coefficients for respective degrees, expressed by
x=(h2/R)/[1+{1−(1k)(h/R)2}1/2]+A4×h4+A6×h6+A8×h8+A10×h10.
In each aspherical coefficient, “e±XX” means “×10±XX”.
Various values in each embodiment are shown in the following table.
Next, an embodiment of a digital still camera (image capture apparatus) using the zoom lens according to the embodiments of the disclosure will be described with reference to
Reference sign 12 denotes a solid-state image pickup device (photoelectric conversion device), such as a CCD sensor and a CMOS sensor, that is incorporated in the camera body 10 and that receives and photoelectrically converts an optical image formed by the lens apparatus 11. The camera body 10 may be a so-called single-lens reflex camera that has a quick-turn mirror or may be a so-called mirrorless camera that has no quick-turn mirror.
In this way, by applying the zoom lens L0 according to the embodiments of the disclosure to the image capture apparatus, such as a digital still camera, it is possible to obtain a high-quality image with a low aberration and a reduced ghosting effect.
The embodiments of the disclosure have been described above; however, the disclosure is not limited to these embodiments. Various modifications and changes are possible within the scope of the disclosure.
While the disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary 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. 2021-176783 filed Oct. 28, 2021, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-176783 | Oct 2021 | JP | national |
