Patent Grant
11662560
The present invention relates to a zoom lens suitable for an image pickup apparatus.
Japanese Patent Laid-Open No. (“JP”) 2014-178388 discloses a negative lead type zoom lens, which includes a lens unit that is closest to an object and has a negative refractive power, and serves as a zoom lens used for an image pickup apparatus, such as a still camera, a video camera, and a surveillance camera.
However, weight saving of the zoom lens is insufficient because structures and power arrangement of the plurality of lens units in the zoom lens disclosed in JP 2014-178388 are improper.
The present invention provides a lightweight zoom lens.
A zoom lens according to one aspect of the present invention includes, in order from an object side to an image side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a rear unit including one or more lens units. Distances between adjacent lens units change during zooming. The first lens unit and the second lens unit move during zooming. The first lens unit includes a negative lens made of resin. The rear unit includes a positive lens made of resin. The following conditions are satisfied:
40.0≤νd_NL
0.005≤θgF_NL−0.6438+0.001682×νd_NL
40.0≤νd_PL
0.005≤θgF_PL−0.6438+0.001682×νd_PL
0.1≤f_PL/fT≤2.0
0.9≤LPT/fT≤5.0
where νd_NL is an Abbe number of the negative lens for d-line, θgF_NL is a partial dispersion ratio of the negative lens for g-line and F-line, νd_PL is an Abbe number of the positive lens for the d-line, θgF_PL is a partial dispersion ratio of the positive lens for the g-line and the F-lines, f_PL is a focal length of the positive lens, fT is a focal length at a telephoto end of the zoom lens, and LPT is a distance from the positive lens to an image plane at the telephoto end.
An image pickup apparatus having the above zoom lens also constitutes another aspect of the present invention.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Referring now to the accompanying drawings, a description will be given of examples according to the present invention. A zoom lens according to each example is usable for an imaging optical system in an image pickup apparatus such as a still camera, a video camera, a television camera, and a surveillance camera, and is also usable for a projection optical system in an image projection apparatus (projector). In the description of each example, it is used for the imaging optical system.
When the zoom lens according to each example is used for the imaging optical system, an imaging plane of a solid-state image sensor (photoelectric conversion element), such as a CCD sensor and a CMOS sensor, or a film plane is disposed on an image plane IP. The “wide-angle end” and the “telephoto end” mean zoom positions when each lens unit is located at both ends of the movable range. During zooming from the wide-angle end to the telephoto end, each lens unit moves in the optical axis direction so as to draw a locus indicated by a solid arrow in each figure.
The zoom lens according to each example includes, in order from the object side to the image side, a first lens unit B1 having a negative refractive power, a second lens unit B2 having a positive refractive power, and a rear unit having a positive or negative refractive power. The rear unit includes at least one lens unit. The zoom lens according to each example provides a magnification variation (zooming) between the wide-angle end and the telephoto end, as a result of that at least the first lens unit B1 and the second lens unit B2 move on the optical axis and a distance between adjacent lens units changes.
The first lens unit includes a negative lens NL, and the rear unit includes a positive lens PL. Both the negative lens NL and the positive lens PL are resin lenses, which facilitates weight saving of the zoom lens.
The zoom lens according to each example satisfies the following conditional expressions (1) to (6):
40.0≤νd_NL (1)
0.005≤θgF_NL−0.6438+0.001682×νd_NL (2)
40.0≤νd_PL (3)
0.005≤θgF_PL-0.6438+0.001682×νd_PL (4)
0.1≤f_PL/fT≤2.0 (5)
0.9≤LPT/fT≤5.0 (6)
wherein νd_NL is an Abbe number of the negative lens NL for the d-line, θgF_NL is a partial dispersion ratio of the negative lens NL for the g-line and the F-line, νd_PL is an Abbe number of the positive lens PL for the d-line, θgF_PL is a partial dispersion ratio of the positive lens PL for the g-line and the F-line, f_PL is a focal length of the positive lens PL, fT is a focal length at the telephoto end of the zoom lens, and LPT is a distance from the positive lens PL of the zoom lens at the telephoto end to the image plane IP.
The conditional expression (1) indicates a condition on the Abbe number of the negative lens NL. If the negative lens NL has a high dispersion so that νd_NL is lower than the lower limit in the conditional expression (1), it becomes difficult to correct the first-order lateral chromatic aberration at the wide-angle end. If νd_NL becomes too large, a material having a low refractive index will be selected, and the edge thickness will increase and hinder weight saving. Thus, an upper limit value may be set in the conditional expression (1) as described later.
The conditional expression (2) indicates a condition on the partial dispersion ratio of the negative lens NL. If θgF_NL−0.6438+0.001682×νd_NL is lower than the lower limit in the conditional expression (2), it becomes difficult to correct the second-order lateral chromatic aberration at the wide-angle end. If θgF_NL−0.6438+0.001682×νd_NL becomes too large, it becomes difficult to correct the second-order chromatic aberration at the wide-angle end. Thus, an upper limit value may be set in the conditional expression (2) as described later.
The conditional expression (3) indicates a condition on the Abbe number of the positive lens PL. If the positive lens PL has a high dispersion so that νd_PL is lower than the lower limit in the conditional expression (3), it becomes difficult to correct the first-order lateral chromatic aberration at the wide-angle end and the first-order longitudinal chromatic aberration at the telephoto end. If νd_PL becomes too large, a material having a low refractive index will be selected, and the edge thickness will increase and hinder weight saving. Therefore, an upper limit value may be set in the conditional expression (3) as described later . . . .
The conditional expression (4) indicates a condition on the partial dispersion ratio of the positive lens PL. If the value is lower than the lower limit in the conditional expression (4), it becomes difficult to correct the second-order lateral chromatic aberration at the wide-angle end and the second-order longitudinal chromatic aberration at the telephoto end. If the value of the conditional expression (4) becomes too large, it becomes difficult to correct the second-order lateral chromatic aberration at the wide-angle end and the second-order longitudinal chromatic aberration at the telephoto end. Therefore, an upper limit may be set as in the conditional expression (4) will be described later.
The conditional expression (5) indicates a condition on the refractive power of the positive lens PL. If the refractive power of the positive lens PL is weakened so that f_PL/fT is higher than the upper limit in the conditional expression (5), it becomes difficult to correct the lateral chromatic aberration at the wide-angle end and the longitudinal chromatic aberration at the telephoto end. If the refractive power of the positive lens PL becomes too strong so that f_PL/fT is lower than the lower limit in the conditional expression (5), the thickness of the positive lens PL and the sensitivity to the manufacturing error of the surface accuracy become too high.
The conditional expression (6) indicates a condition on the position of the positive lens PL at the telephoto end. If the positive lens PL is separated from the image plane IP so that LPT/fT is higher than the upper limit in the conditional expression (6), the thickness of the positive lens PL and the sensitivity to the manufacturing error of the surface accuracy become too high. If the positive lens PL becomes closer to the image plane IP so that the LPT/fT is lower than the lower limit in the conditional expression (6), it becomes difficult to correct the longitudinal chromatic aberration at the telephoto end.
Satisfying the conditional expressions (1) to (6) described above will be able to provide a lightweight zoom lens having a high optical performance. In calculating the distance LPT from the positive lens PL to the image plane IP, when an optical element (such as a prism, a cover glass, and a filter) having substantially no refractive power is disposed on the object side of the zoom lens, the distance LPT is calculated without the optical element.
The zoom lens according to each example may further satisfy at least one of the following conditional expressions (7) to (15), where D1 is a thickness of the first lens unit B1 on the optical axis, f1 is a focal length of the first lens unit B1, fW is a focal length at the wide-angle end of the zoom lens, and LPW is a distance from the positive lens PL at the wide-angle end to the image plane IP, Nd_NL is a refractive index of the negative lens NL with respect to the d line, Nd_PL is a refractive index of the positive lens PL for the d-line, d_NL is a specific gravity of the negative lens NL, d_NL is a specific gravity of the positive lens PL, and f2 is a focal length of the second lens unit B2.
0.00<D1/|f1|≤0.50 (7)
1.0≤LPW/fW≤2.2 (8)
0.00<LPW/LPT≤0.9 (9)
1.480≤Nd_NL (10)
1.480≤Nd_PL (11)
d_NL≤2.0 (12)
d_PL≤2.0 (13)
1.0≤|f1|/fW≤3.0 (14)
0.50≤f2/fW≤1.50 (15)
The conditional expression (7) indicates a condition on the thickness D1 of the first lens unit B1. If the thickness D1 of the first lens unit B1 is increased so that D1/|f1| is higher than the upper limit in the conditional expression (7), it becomes difficult to reduce the weight of the zoom lens. When D1/|f1| satisfies the conditional expression (7), the weight of the zoom lens can be easily reduced.
The conditional expression (8) indicates a condition on the position of the positive lens PL at the wide-angle end. If the positive lens PL is more distant from the image plane IP so that the LPW/fW is higher than the upper limit in the conditional expression (8), it becomes difficult to correct the lateral chromatic aberration at the wide-angle end. If the positive lens PL is closer to the image plane IP so that the LPW/fW is lower than the lower limit in the conditional expression (8), the lens diameter becomes large and it becomes difficult to reduce the weight of the zoom lens.
The conditional expression (9) indicates a condition on the position of the positive lens PL at the wide-angle end and the position of the positive lens PL at the telephoto end. When LPW/LPT satisfies the conditional expression (9), the lateral chromatic aberration at the wide-angle end and the longitudinal chromatic aberration at the telephoto end can be satisfactorily corrected.
The conditional expression (10) indicates a condition on the refractive index of the negative lens NL. If Nd_NL is lower than the lower limit in the conditional expression (10), the edge thickness of the negative lens NL becomes larger in order for the negative lens NL to have the required power, and it becomes difficult to reduce the weight of the zoom lens. If the value of Nd_NL becomes too large, a material having a low refractive index will be selected, and the edge thickness will increase and hinder weight saving. Therefore, the upper limit value may be set to the conditional expression (10) as described later.
The conditional expression (11) indicates a condition on the refractive index of the positive lens PL. When Nd_PL is lower than the lower limit in the conditional expression (11), the central thickness of the positive lens PL becomes large so as to maintain required power, and it becomes difficult to reduce the weight of the zoom lens. If the value of Nd_PL becomes too large, a material having a low refractive index will be selected, and the edge thickness will increase and hinder weight saving. Therefore, the upper limit value may be set to the conditional expression (11) as described later.
The conditional expression (12) indicates a condition on the specific gravity of the negative lens NL. When d_NL satisfies the conditional expression (12), the weight of the zoom lens can be easily reduced. If the value of d_NL becomes too small, the rigidity of the lens becomes weak and it becomes difficult to handle the lens. Therefore, the lower limit value may be set to the conditional expression (12) as described later.
The conditional expression (13) indicates a condition on the specific gravity of the positive lens PL. Satisfying the range of the d_PL conditional expression (13) facilitates weight saving of the optical system. If the value of d_PL becomes too small, the rigidity of the lens becomes weak and it becomes difficult to handle the lens. Therefore, the lower limit value may be set to the conditional expression (13) as described later.
The conditional expression (14) indicates a condition on a relationship between the focal length f1 of the first lens unit B1 and the focal length fW of the zoom lens at the wide-angle end. If the refractive power of the first lens unit B1 is weak so that |f1|/fW is higher than the upper limit in the conditional expression (14), it becomes difficult to make compact the zoom lens. If the refractive power of the first lens unit B1 is strong so that |f1|/fW is lower than the lower limit in the conditional expression (14), it becomes difficult to suppress fluctuations in coma during zooming.
The conditional expression (15) indicates a condition on a relationship between the focal length f2 of the second lens unit B2 and the focal length fW of the zoom lens at the wide-angle end. If the refractive power of the second lens unit B2 is weak so that f2/fW is higher than the upper limit in the conditional expression (15), it becomes difficult to make compact the zoom lens. If the refractive power of the second lens unit B2 is strong so that f2/fW is lower than the lower limit in the conditional expression (15), it becomes difficult to suppress the spherical aberration and coma aberration particularly at the telephoto end.
At least one of the negative lens NL and the positive lens PL may have an aspherical surface. When the negative lens NL has an aspherical surface, it becomes possible to suppress the curvature of field and astigmatism at the wide-angle end. When the positive lens PL has an aspherical surface, it becomes possible to suppress the curvature of field and astigmatism at the telephoto end.
The lens G1 closest to the object in the first lens unit B1 may be a glass lens. The lens G1 made of glass can secure sufficient robustness. When the lens G1 has a negative refractive power, the lens diameter of the lens G1 can be reduced, and the weight of the zoom lens can be easily reduced.
The numerical ranges of the conditional expressions (1) to (15) may be set as follows:
45.0≤νd_NL≤70.0 (1a)
0.007≤θgF_NL−0.6438+0.001682×νd_NL≤0.030 (2a)
40.0≤νd_PL≤70.0 (3a)
0.006≤θgF_PL−0.6438+0.001682×νd_PL≤0.030 (4a)
0.5≤f_PL/fT≤1.8 (5a)
1.0≤LPT/fT≤2.5 (6a)
0.00≤D1/|f1|≤0.46 (7a)
1.2≤LPW/fW≤2.0 (8a)
0.00<LPW/LPT≤0.8 (9a)
1.500≤Nd_NL≤1.650 (10a)
1.500≤Nd_PL≤1.650 (11a)
0.8≤d_NL≤1.5 (12a)
0.8≤d_PL≤1.5 (13a)
1.3≤|f1|/fw≤2.5 (14a)
0.65≤f2/fw≤1.25 (15a)
The numerical ranges of the conditional expressions (1) to (15) may be set as follows:
50.0≤νd_n1≤60.0 (1b)
0.010≤θgf_n1−0.6438+0.001682×νd_n1≤0.020 (2b)
40.0≤νd_p1≤60.0 (3b)
0.010≤θgf_p1−0.6438+0.001682×νd_p1≤0.020 (4b)
0.8≤f_p1/ft≤1.6 (5b)
1.1≤lpt/ft≤1.5 (6b)
0.00<d1/|f1|≤0.42 (7b)
1.4≤lpw/fw≤1.8 (8b)
0.00≤lpw/lpt≤0.7 (9b)
1.520≤nd_n1≤1.600 (10b)
1.520≤nd_p1≤1.600 (11b)
0.9≤d_n1≤1.3 (12b)
0.9≤d_p1≤1.3 (13b)
1.5≤|f1|/fw≤2.0 (14b)
0.75≤f2/fw≤1.00 (15b)
The zoom lens according to Example 1 illustrated in
In the zoom lens according to this example, the first lens unit B1 moves to the image side and the second lens unit B2 and the third lens unit B3 move to the object side during zooming from the wide-angle end to the telephoto end. At that time, the distance between the first lens unit B1 and the second lens unit B2 is narrowed, and the distance between the second lens unit B2 and the third lens unit B3 is also narrowed.
A subunit 2B in the second lens unit B2 is a focus lens unit that moves on the optical axis during focusing, and moves from the object side to the image side during focusing from an object at infinity (infinity object) to a close (or short-distance) object.
The zoom lens according to Example 2 illustrated in
In the zoom lens according to this example, the first lens unit B1 moves to the image side and the second lens unit B2 to the fourth lens unit B4 move to the object side during zooming from the wide-angle end to the telephoto end. At that time, the distance between the first lens unit B1 and the second lens unit B2 is narrowed, the distance between the second lens unit B2 and the third lens unit B3 is widened, and the distance between the third lens unit B3 and the fourth lens unit B4 is narrowed. The third lens unit B3 is a focus lens unit, and moves from the object side to the image side during focusing from the infinity object to the close object.
The zoom lens according to Example 3 illustrated in
In the zoom lens according to this example, the first lens unit B1 moves to the image side and the second lens unit B2 to the fourth lens unit B4 move to the object side during zooming from the wide-angle end to the telephoto end. At that time, the distance between the first lens unit B1 and the second lens unit B2 is narrowed, the distance between the second lens unit B2 and the third lens unit B3 is widened, and the distance between the third lens unit B3 and the fourth lens unit B4 is narrowed. The third lens unit B3 is a focus lens unit, and moves from the object side to the image side during focusing from the infinity object to the near object.
The zoom lens according to Example 4 illustrated in
In the zoom lens according to this example, the first lens unit B1 moves to the image side and the second lens unit B2 to the fourth lens unit B4 move to the object side during zooming from the wide-angle end to the telephoto end. At that time, the distance between the first lens unit B1 and the second lens unit B2 is narrowed, the distance between the second lens unit B2 and the third lens unit B3 is widened, and the distance between the third lens unit B3 and the fourth lens unit B4 is narrowed. The third lens unit B3 is a focus lens unit, and moves from the object side to the image side during focusing from the infinity object to the close object.
The zoom lens according to Example 5 illustrated in
In the zoom lens according to this example, the first lens unit B1 moves to the image side and the second lens unit B2 and the third lens unit B3 move to the object side during zooming from the wide-angle end to the telephoto end. At that time, the distance between the first lens unit B1 and the second lens unit B2 is narrowed, and the distance between the second lens unit B2 and the third lens unit B3 is widened.
The third lens unit B3 is a focus lens unit, and moves from the object side to the image side during focusing from the infinity object to the close object.
The zoom lens according to each example may be used for an image stabilizing unit that reduces (corrects) an image blur by shifting one or part of the lens unit in the zoom lens relative to the optical axis.
The zoom lens according to each example has one focus lens unit, but may include a plurality of focus lens units to perform floating type focusing. The zoom lens according to each example may include a diffractive optical element and a catoptric optical member.
Specific numerical examples 1 to 5 of the zoom lenses according to Examples 1 to 5 will be illustrated hereinafter. In each numerical example, ri represents a radius of curvature (mm) of an i-th surface from the object side, and di represents a lens thickness or air spacing (mm) between an i-th and (i+1)-th surfaces. ndi represents a refractive index of a material of the i-th optical member for the d-line. νdi represents an Abbe number of the material of the i-th optical member for the d-line. The Abbe number νd is expressed as νd=(Nd−1)/(NF−NC) where Nd, NF, and NC are refractive indexes for the d-line (587.6 nm), the F-line (486.1 nm), and the C-line (656.3 nm) in the Fraunhofer line.
BF represents a backfocus (mm). The backfocus is expressed by an air conversion length on the optical axis from the final surface of the zoom lens (the lens surface closest to the image) to the paraxial image plane. The overall length of the zoom lens is the length obtained by adding the backfocus to the distance on the optical axis from the frontmost surface (the lens surface closest to the object) to the final surface.
An asterisk “*” attached to the surface number means that the surface is aspherical. The shape of the aspherical surface shape is expressed as follows, where x is a displacement amount from the surface vertex in the optical axis direction, h is a height from the optical axis in the direction orthogonal to the optical axis, R is a paraxial radius of curvature, k is a conical constant, and A4, A6, A8, and A10 are aspherical coefficients.
x=(h2/R)/[1+{1−(1+k)(h/R)2/}1/2+A4×h4+A6×h6+A8×h8±A10×h10
“E±XX” in each aspherical coefficient means “×10±XX.”
Table 1 summarizes values corresponding to the conditional expressions (1) to (15) in Examples 1 to 5.
Aspheric Data
3rd Surface
K=0.00000e+000 A 4=−1.23443e−004 A 6=6.41187e−007 A 8=−8.76998e−010 A10=−5.29610e−012
4th Surface
K=0.00000e+000 A 4=−1.33781e−004 A 6=7.27864e−007 A 8=−1.61418e−009 A10=−3.49272e−012
14th Surface
K=0.00000e+000 A 4=−8.39279e−005 A 6=3.77559e−007 A 8=−6.11987e−009 A10=1.31773e−011
15th Surface
K=0.00000e+000 A 4=−3.02891e−005 A 6=1.92534e−007
Aspheric Data
3rd Surface
K=0 A 4=−1.41463e−004 A 6=7.66013e−007 A 8=−1.27190e−009 A10=−1.10963e−011
4th Surface
K=0 A 4=−1.69055e−004 A 6=8.63631e−007 A 8=−2.53183e−009 A10=−7.27576e−012
14th Surface
K=0 A 4=−9.44164e−006 A 6=5.54551e−007 A 8=−1.94972e−008 A10=2.35602e−010
15th Surface
K=0 A 4=3.12388e−005 A 6=2.31800e−007
Various Data
Zoom Ratio 2.35
Aspheric Data
3rd Surface
K=0.00000e+000 A 4=−1.06687e−005 A 6=−2.40190e−007 A 8=2.29892e−009 A10=−6.11185e−012
4th Surface
K=0.00000e+000 A 4=−9.59718e−006 A 6=−2.74436e−007 A 8=2.73461e−009 A10=−7.90906e−012
14th Surface
K=0.00000e+000 A 4=−1.65669e−004 A 6=−5.36961e−007 A 8=−3.86282e−008 A10=9.59619e−010
15th Surface
K=0.00000e+000 A 4=−7.58667e−005 A 6=−5.73278e−007
Aspheric Data
4th Surface
K=0 A 4=−4.47785e−006 A 6=4.80655e−008 A 8=−5.32262e−010 A10=1.27701e−012
8th Surface
K=0 A 4=−3.43112e−005 A 6=3.14927e−008 A 8=−2.95172e−009 A10=4.26192e−011
12th Surface
K=0 A 4=−3.22505e−005 A 6=1.56251e−007 A 8=−1.96015e−008 A10=3.12929e−010
Aspheric Data
3rd Surface
K=0 A 4=−1.24978e−004 A 6=2.71294e−007 A 8=1.41979e−009 A10=−9.72356e−012
4th Surface
K=0 A 4=−1.37193e−004 A 6=3.71703e−007 A 8=7.25801e−010 A10=−7.69387e−012
14th Surface
K=0 A 4=4.49135e−005 A 6=1.54680e−006 A 8=−2.35020e−008 A10=2.91319e−010
15th Surface
K=0 A 4=7.57248e−005 A 6=1.14052e−006
The camera body 10 may be a single-lens reflex camera having a quick turn mirror, or a mirrorless camera having no quick turn mirror.
Each of the above examples can provide a lightweight zoom lens.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention 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. 2020-067831, filed on Apr. 3, 2020 which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2020-067831 | Apr 2020 | JP | national |
| Number | Name | Date | Kind |
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| 20190094490 | Gyoda | Mar 2019 | A1 |
| 20190302430 | Ebe | Oct 2019 | A1 |
| 20200110251 | Gyoda | Apr 2020 | A1 |
| 20200257181 | Gyoda | Aug 2020 | A1 |
| 20210149165 | Saito et al. | May 2021 | A1 |
| Number | Date | Country |
|---|---|---|
| 101726842 | Jun 2010 | CN |
| 102331619 | Jan 2012 | CN |
| 105652423 | Jun 2016 | CN |
| H0961711 | Mar 1997 | JP |
| 2011017990 | Jan 2011 | JP |
| 2014-178388 | Sep 2014 | JP |
| 2018040948 | Mar 2018 | JP |
| Entry |
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| Notification of the First Office Action issued by the China National Intellectual Property Administration on Dec. 2, 2022 in corresponding CN Patent Application No. 202110348078.2, with English translation. |
| Number | Date | Country | |
|---|---|---|---|
| 20210311290 A1 | Oct 2021 | US |
