Patent Application
20180335604
The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2017-100396 filed on May 19, 2017. The above application is hereby expressly incorporated by reference, in its entirety, into the present application.
The present invention relates to a zoom lens suitable for electronic cameras such as movie imaging cameras, broadcast cameras, digital cameras, video cameras, and surveillance cameras, and to an imaging apparatus comprising the zoom lens.
As zoom lenses used in electronic cameras such as movie imaging cameras, broadcast cameras, digital cameras, video cameras, and surveillance cameras, zoom lenses disclosed in JP2016-71140A. JP2014-10282A, and JP2016-206409A have been proposed.
In imaging apparatuses such as movie imaging cameras and broadcast cameras, there is a demand for a zoom lens that has favorable optical performance with a high magnification while having a small size. In particular, reduction in size is strongly demanded for imaging modes focusing on maneuverability and operability.
In the zoom lenses of JP2016-71140A, JP2014-10282A, and JP2016-206409A, fluctuation in aberration caused by zooming is corrected by moving five or more lens groups and varying a plurality of group distances. However, magnifications of the zoom lenses of JP2016-71140A and JP2014-10282A are not sufficiently high. In addition, the zoom lens of JP2016-206409A has a short back focal length and can not be mounted on a mount-exchange type broadcast camera or a movie camera.
The present invention has been made in consideration of the above-mentioned situations, and it is an object of the present invention to provide a zoom lens, which has a favorable optical performance with a high magnification while maintaining a sufficient back focal length and having a small size, and an imaging apparatus comprising the zoom lens.
According to the present invention, there is provided a zoom lens consisting of, in order from an object side: a first lens group that remains stationary with respect to an image plane during zooming and has a positive refractive power; and a subsequent section that consists of five or more lens groups including at least four movable lens groups which are moved by changing distances between the movable lens groups and adjacent groups in a direction of an optical axis during zooming. the first lens group is set as an A constituent section, and a lens closest to the object side in the A constituent section has a negative refractive power. the subsequent section includes a lens group having a stop, the lens group having the stop is set as a C constituent section, and the C constituent section moves to the object side during zooming from a wide-angle end to a telephoto end, and then moves toward an image side. a spacing between the A constituent section and the C constituent section is set as a B constituent section, and the B constituent section consists of one or two the movable lens groups, and has a negative refractive power as a whole at the wide-angle end. In addition, assuming that a lateral magnification of the B constituent section at the telephoto end is βTB, a lateral magnification of the B constituent section at the wide-angle end is βWB, and a zoom magnification is Zr, Conditional Expression (1) is satisfied.
1.3<βTB/βWB/Zr<5 (1)
It is preferable that Conditional Expression (1-1) is satisfied.
1.5<βTB/βWB/Zr<4 (1-1)
In the zoom lens of the present invention, it is preferable that the C constituent section has a negative refractive power.
It is preferable that the subsequent section has the two or more movable lens groups having positive refractive powers on the image side of the C constituent section.
It is preferable that a lens group adjacent to the image side in the C constituent section is the movable lens group having a positive refractive power, and the movable lens group adjacent to the image side in the C constituent section is a D constituent section. Assuming that a gutter magnification of the D constituent section at the telephoto end is gtT, and a gutter magnification of the D constituent section at the wide-angle end is gtW, it is preferable that Conditional Expression (2) is satisfied, and it is more preferable that Conditional Expression (2-1) is satisfied.
1.2<gtT/gtW<3 (2)
1.5<gtT/gtW<2.5 (2-1)
Here, gtT and gtW are represented by the following expressions. It should be noted that a lateral magnification of the D constituent section at the telephoto end is βTD, a lateral magnification of the E constituent section at the telephoto end in a case where all the lens groups located to be closer to the image side than the D constituent section are combined to be set as an E constituent section is βTE, a lateral magnification of the D constituent section at the wide-angle end is βWD, and a lateral magnification of the E constituent section at the wide-angle end in a case where all the lens groups located to be closer to the image side than the D constituent section are combined to be set as an E constituent section is βWE.
gtT=(1−βTD2)×βTE2
gtW=(1−βWD2)×βWE2
It is preferable that the C constituent section is positioned to be closest to the object side at a position closer to a wide-angle side than a position where a lateral magnification βB of the B constituent section is −1.
It is preferable that the C constituent section has a stop at a position closest to the object side.
It is preferable that the C constituent section consists of a stop, a positive lens, and a negative lens.
Assuming that a focal length of the B constituent section is fB and a focal length of the A constituent section is fA, it is preferable that Conditional Expression (3) is satisfied, and it is more preferable that Conditional Expression (3-1) is satisfied.
−1<fB/fA<0 (3)
−0.5<fB/fA<−0.1 (3-1)
Assuming that a focal length of the C constituent section is fC, and a focal length of the B constituent section is fB, it is preferable that Conditional Expression (4) is satisfied, and it is more preferable that Conditional Expression (4-1) is satisfied.
2<fC/fB<4 (4)
2.5<fC/fB<3.7 (4-1)
Assuming that an Abbe number at a d line is vd, and a partial dispersion ratio is θgF, it is preferable that the A constituent section has two or more positive lenses satisfying Conditional Expressions (5) and (6), and it is more preferable that the positive lenses satisfying Conditional Expressions (5) and (6) satisfy at least one of Conditional Expressions (5-1) or (6-1).
70<vd (5)
90<vd<99 (5-1)
0.64<θgF+0.001625×vd<0.71 (6)
0.65<θgF+0.001625×vd<0.70 (6-1)
It is preferable that the B constituent section consists of, in order from the object side, the movable lens group having a negative refractive power, and the movable lens group having a positive refractive power.
In this case, assuming that a focal length of the movable lens group having a negative refractive power in the B constituent section is fB1, and a focal length of the movable lens group having a positive refractive power in the B constituent section is fB2, it is preferable that Conditional Expression (7) is satisfied, and it is more preferable that Conditional Expression (7-1) is satisfied.
−1<fB1/fB2<0 (7)
−0.5<fB1/fB2<−0.05 (7-1)
It is preferable that an image side part of the C constituent section of the subsequent section consists of, in order from the object side, the two movable lens groups that have positive refractive powers, and a stationary lens group that remains stationary with respect to the image plane during zooming and has a positive refractive power.
An imaging apparatus of the present invention comprises the above-mentioned zoom lens of the present invention.
It should be noted that the term “consists of ˜” means that the imaging lens may include not only the above-mentioned elements but also lenses substantially having no powers, optical elements, which are not lenses, such as a stop, a mask, a cover glass, and a filter, and mechanism parts such as a lens flange, a lens barrel, an imaging element, and a camera shaking correction mechanism.
Further, surface shapes, signs of refractive powers, radii of curvature of the lenses are assumed as those in paraxial regions in a case where some lenses have aspheric surfaces.
The zoom lens of the present invention consists of, in order from an object side: a first lens group that remains stationary with respect to an image plane during zooming and has a positive refractive power; and a subsequent section that consists of five or more lens groups including at least four movable lens groups which are moved by changing distances between the movable lens groups and adjacent groups in a direction of an optical axis during zooming. the first lens group is set as an A constituent section, and a lens closest to the object side in the A constituent section has a negative refractive power. the subsequent section includes a lens group having a stop, the lens group having the stop is set as a C constituent section, and the C constituent section moves to the object side during zooming from a wide-angle end to a telephoto end, and then moves toward an image side. A spacing between the A constituent section and the C constituent section is set as a B constituent section, and the B constituent section consists of one or two the movable lens groups, and has a negative refractive power as a whole at the wide-angle end. In addition, assuming that a lateral magnification of the B constituent section at the telephoto end is βTB, a lateral magnification of the B constituent section at the wide-angle end is βWB, and a zoom magnification is Zr, Conditional Expression (1) is satisfied. Therefore, it is possible to provide a zoom lens, which has favorable optical performance with a high magnification while maintaining a sufficient back focal length and having a small size, and an imaging apparatus comprising the zoom lens.
1.3<βTB/βWB/Zr<5 (1)
Hereinafter, embodiments of the present invention will be described with reference to drawings.
In
In order to mount the zoom lens on an imaging apparatus, it is preferable to provide various filters and/or a protective cover glass based on specification of the imaging apparatus. Thus,
The zoom lens of the present embodiment consists of, in order from the object side: a first lens group G1 that remains stationary with respect to an image plane Sim during zooming and has a positive refractive power; and a subsequent section that consists of five or more lens groups including at least four movable lens groups which are moved by changing distances between the movable lens groups and adjacent groups in the direction of the optical axis during zooming.
In such a manner, by forming the first lens group G1 closest to the object side as a lens group having a positive refractive power, it is possible to shorten the total length of the lens system, and this configuration is advantageous for reduction in size. Further, by making the lens group stationary with respect to the image plane Sim during zooming, it is possible to reduce movement of the barycenter caused by the zooming.
The first lens group G1 is set as an A constituent section SA, and a lens closest to the object side in the A constituent section SA has a negative refractive power. The subsequent section includes a lens group having an aperture stop St, the lens group having the aperture stop St is set as a C constituent section SC, and the C constituent section SC moves to the object side during zooming from a wide-angle end to a telephoto end, and then moves toward an image side. A spacing between the A constituent section SA and the C constituent section SC is set as a B constituent section SB, and the B constituent section SB consists of one or two the movable lens groups, and has a negative refractive power as a whole at the wide-angle end.
In the A constituent section SA, the negative lens is disposed to be closest to the object side. Thereby, it is possible to minimize the incidence angle of off-axis rays from the object side to the second and subsequent lenses, and there is an advantage in achieving the wide angle.
The B constituent section SB has a negative refractive power, and thus has a main function of the zooming.
The C constituent section SC moves toward the object side during zooming from the wide-angle end to the telephoto end, and then moves toward the image side. Thereby, the movement stroke of the B constituent section SB, which has the main function of the zooming at a position closer to the object side than the aperture stop St, and there is an advantage in achieving high magnification. Further, in a case where the aperture stop St is configured to move toward the object side at a position closer to the telephoto side than the wide-angle end, it is possible to minimize the incidence height of the off-axial rays. As a result, there is an advantage in reducing the size of the A constituent section SA (first lens group G1).
Assuming that a lateral magnification of the B constituent section SB at the telephoto end is βTB, a lateral magnification of the B constituent section SB at the wide-angle end is βWB, and a zoom magnification is Zr, Conditional Expression (1) is satisfied. By appropriately setting the zooming function of the B constituent section SB at a position closer to the object side than the C constituent section SC including the aperture stop St so as to satisfy Conditional Expression (1), it is possible to achieve both high magnification and high performance. By not allowing the result of Conditional Expression (1) to be equal to or less than the lower limit, a zooming efficiency of the B constituent section SB is ensured, and thus there is an advantage in achieving high magnification. Further, in order to increase the zooming efficiency, it is necessary to increase the amount of zoom movement or to strengthen the refractive power of the B constituent section SB as a variator group. However, in order to achieve both high magnification and compactness, it is necessary to strengthen the negative refractive power of the variator group while suppressing the amount of zoom movement. Thus, by not allowing the result of Conditional Expression (1) to be equal to or less than the lower limit, it becomes easy to ensure the back focal length while keeping the total length short. By not allowing the result of Conditional Expression (1) to be equal to or greater than the upper limit, it is possible to prevent the zooming function of the B constituent section SB from becoming excessively large, and there is an advantage in suppressing fluctuation in aberration during zooming. In addition, in a case where at least one of Conditional Expression (1-1) or (1-2) is satisfied, it is possible to obtain more favorable characteristics.
1.3<βTB/βWB/Zr<5 (1)
1.5<βTB/βWB/Zr<4 (1-1)
1.7<βTB/βWB/Zr<3.5 (1-2)
In the zoom lens of the present embodiment, it is preferable that the C constituent section SC has a negative refractive power. With such a configuration, it is possible to obtain the movement stroke of the B constituent section SB, which has the main zooming function, at a position closer to the object side than the aperture stop St, and there is an advantage in high magnification. There is an advantage in ensuring the back focal length of the whole system.
It is preferable that the subsequent section has the two or more movable lens groups having positive refractive powers on the image side of the C constituent section SC. With such a configuration, it is possible to satisfactorily correct fluctuations in spherical aberration, curvature of field, astigmatism, and lateral chromatic aberration caused by zooming while providing an image forming function with positive refractive power.
It is preferable that a lens group adjacent to the image side in the C constituent section SC is the movable lens group having a positive refractive power, and the movable lens group adjacent to the image side in the C constituent section SC is a D constituent section SD. Assuming that a gutter magnification of the D constituent section SD at the telephoto end is gtT, and a gutter magnification of the D constituent section SD at the wide-angle end is gtW, it is preferable that Conditional Expression (2) is satisfied. By not allowing the result of Conditional Expression (2) to be equal to or less than the lower limit, it is possible to prevent the correction effect of the image forming position on the telephoto side of the D constituent section SD from becoming excessively weak. Thus, by minimizing the amount of movement on the telephoto side, there is an advantage in achieving reduction in size of the whole system. By not allowing the result of Conditional Expression (2) to be equal to or greater than the upper limit, it is possible to prevent the correction effect of the image forming position on the telephoto side of the D constituent section SD from becoming excessively strong, and it becomes unnecessary to perform control with high accuracy. In addition, in a case where at least one of Conditional Expression (2-1) or (2-2) is satisfied, it is possible to obtain more favorable characteristics.
1.2<gtT/gtW<3 (2)
1.5<gtT/gtW<2.5 (2-1)
1.6<gtT/gtW<2.4 (2-2)
It is preferable that the C constituent section SC is positioned to be closest to the object side at a position closer to a wide-angle side than a position where a lateral magnification βB of the B constituent section SB is −1. In a case where the A constituent section SA consisting of the first lens group G1 having a positive refractive power at a position closest to the object side remains stationary with respect to the image plane Sim during zooming, the off-axis principal rays passing through the A constituent section SA are highest between the wide-angle end and the position at which the lateral magnification βB of the B constituent section SB is −1. Therefore, by positioning the C constituent section SC at a position closest to the object side between the wide-angle end and the position at which the lateral magnification βB of the B constituent section SB is −1, there is an advantage in achieving reduction in size of the A constituent section SA.
It is preferable that the C constituent section SC has the aperture stop St at a position closest to the object side. Since the aperture stop St is positioned to be closest to the object side of the C constituent section SC, it is possible to reduce the incidence height of the off-axial rays on the wide-angle side, and there is an advantage in achieving reduction in size of the A constituent section SA.
It is preferable that the C constituent section SC consists of the aperture stop St, a positive lens, and a negative lens. The C constituent section SC has a function of mainly correcting fluctuation in the image plane position caused by zooming, and comprises the positive lens and the negative lens in the C constituent section SC. Thereby, it is possible to satisfactorily correct spherical aberration and longitudinal chromatic aberration.
Assuming that a focal length of the B constituent section SB is fB and a focal length of the A constituent section SA is fA, it is preferable that Conditional Expression (3) is satisfied. By not allowing the result of Conditional Expression (3) to be equal to or less than the lower limit, the refractive power of the B constituent section SB having the zooming function is ensured. As a result, it is possible to easily achieve high magnification. By not allowing the result of Conditional Expression (3) to be equal to or greater than the upper limit, it is possible to prevent the zooming function of the B constituent section SB from becoming excessively large, and it is possible to easily suppress fluctuation in aberration during zooming. Alternatively, it is possible to prevent the refractive power of the A constituent section SA from becoming excessively weak, which contributes to reduction in size of the A constituent section SA. In addition, in a case where at least one of Conditional Expression (3-1) or (3-2) is satisfied, it is possible to obtain more favorable characteristics.
−1<fB/fA<0 (3)
−0.5<fB/fA<−0.1 (3-1)
−0.3<fB/fA<−0.15 (3-2)
Assuming that a focal length of the C constituent section SC is fC, and a focal length of the B constituent section SB is fB, it is preferable that Conditional Expression (4) is satisfied. By not allowing the result of Conditional Expression (4) to be equal to or less than the lower limit, the refractive power of the B constituent section SB having the zooming function is ensured. As a result, it is possible to easily achieve high magnification. By not allowing the result of Conditional Expression (4) to be equal to or greater than the upper limit, it is possible to prevent the zooming function of the B constituent section SB from becoming excessively large, and it is possible to easily suppress fluctuation in aberration during zooming. In addition, in a case where at least one of Conditional Expression (4-1) or (4-2) is satisfied, it is possible to obtain more favorable characteristics.
2<fC/fB<4 (4)
2.5<fC/fB<3.7 (4-1)
3<fC/fB<3.5 (4-2)
Assuming that an Abbe number at a d line is vd, and a partial dispersion ratio is θgF, it is preferable that the A constituent section SA has two or more positive lenses satisfying Conditional Expressions (5) and (6). By not allowing the result of Conditional Expression (5) to be equal to or less than the lower limit, it is possible to satisfactorily correct the lateral chromatic aberration on the wide-angle side and the longitudinal chromatic aberration on the telephoto side. By not allowing the result of Conditional Expression (5) to be equal to or greater than the upper limit, it is possible to satisfactorily correct various aberrations such as spherical aberration by ensuring a necessary refractive index while satisfactorily correcting longitudinal chromatic aberration. By satisfying Conditional Expression (6) together with Conditional Expression (5), it is possible to satisfactorily correct the secondary spectrum. In a case where the positive lenses satisfying the Conditional Expressions (5) and (6) satisfy at least one of Conditional Expression (5-1) or (6-1), it is possible to obtain more favorable characteristics.
70<vd (5)
90<vd<99 (5-1)
0.64<θgF+0.001625×vd<0.71 (6)
0.65<θgF+0.001625×vd<0.70 (6-1)
It is preferable that the B constituent section SB consists of, in order from the object side, the movable lens group having a negative refractive power, and the movable lens group having a positive refractive power. With such a configuration, it is possible to satisfactorily correct fluctuations in spherical aberration, curvature of field, astigmatism, and lateral chromatic aberration caused by zooming while providing the zooming function with negative refractive power.
In this case, assuming that a focal length of the movable lens group having a negative refractive power in the B constituent section SB is fB1, and a focal length of the movable lens group having a positive refractive power in the B constituent section SB is fB2, it is preferable that Conditional Expression (7) is satisfied. In Examples 1, 2, 4, and 5 to be described below, the second lens group G2 has a negative refractive power and the third lens group G3 has a positive refractive power in the B constituent section SB. By not allowing the result of Conditional Expression (7) to be equal to or less than the lower limit, it is possible to prevent the zooming function of the B constituent section SB from becoming excessively weak, and there is an advantage in high magnification. By not allowing the result of Conditional Expression (7) to be equal to or greater than the upper limit, it is possible to prevent the zooming function of the B constituent section SB from becoming excessively strong, and there is an advantage in suppressing fluctuation in aberration during zooming. In addition, in a case where at least one of Conditional Expression (7-1) or (7-2) is satisfied, it is possible to obtain more favorable characteristics.
−1<fB1/fB2<0 (7)
−0.5<fB1/fB2<−0.05 (7-1)
−0.2<fB1/fB2<−0.07 (7-2)
It is preferable that an image side part of the C constituent section SC of the subsequent section consists of, in order from the object side, the two movable lens groups that have positive refractive powers, and a stationary lens group that remains stationary with respect the image plane Sim during zooming and has a positive refractive power. With such a configuration, it is possible to satisfactorily correct fluctuations in spherical aberration, curvature of field, astigmatism, and lateral chromatic aberration caused by zooming while two positive movable lens groups have the image forming function with positive refractive power. By providing a positive stationary lens group closest to the image side, it is possible to effectively correct lateral chromatic aberration.
In the example shown in
Next, numerical examples of the zoom lens of the present invention will be described. First, a zoom lens of Example 1 will be described.
The zoom lens of Example 1 is composed of, in order from the object side, a first lens group G1 composed of five lenses L1a to L1e, a second lens group G2 composed of four lenses L2a to L2d, a third lens group G3 composed of two lenses L3a and L3b, a fourth lens group G4 composed of an aperture stop St and two lenses L4a and L4b, a fifth lens group G5 composed of four lenses L5a to L5d, a sixth lens group G6 composed of four lenses L6a to L6d, and a seventh lens group G7 composed of one lens L7a.
The A constituent section SA is composed of only the first lens group G1, the B constituent section SB is composed of the second lens group G2 and the third lens group G3, and the C constituent section SC is composed of only the fourth lens group G4, The D constituent section SD is composed of only the fifth lens group G5, and the E constituent section SE is composed of the sixth lens group G6 and the seventh lens group G7.
Table 1 shows basic lens data of the zoom lens of Example 1, Table 2 shows data about specification, Table 3 shows data about variable surface distances, and Table 4 shows data about aspheric coefficients. Hereinafter, meanings of the reference signs in the tables are, for example, as described in Example 1, and are basically the same as those in Examples 2 to 5.
In the lens data of Table 1, the column of the surface number shows surface numbers. The surface of the elements closest to the object side is the first surface, and the surface numbers sequentially increase toward the image plane side. The column of the radius of curvature shows radii of curvature of the respective surfaces. The column of the surface distance shows distances on the optical axis Z between the respective surfaces and the subsequent surfaces. Further, the column of n shows a refractive index of each optical element at the d line (a wavelength of 587.6 nm (nanometers)), the column of v shows an Abbe number of each optical element at the d line (a wavelength of 587.6 nm (nanometers)), and the column of θgF shows a partial dispersion ratio of each optical element.
In addition, the partial dispersion ratio θgF is represented by the following expression.
θgF=(ng−nF)/(nF−nC)
Here, ng is a refractive index at the g line,
nF is a refractive index at the F line, and
nC is a refractive index at the C line.
In addition, the sign of the radius of curvature is positive in a case where a surface has a shape convex toward the object side, and is negative in a case where a surface has a shape convex toward the image plane side. In the basic lens data, the aperture stop St and the optical member PP are additionally noted. In a place of a surface number of a surface corresponding to the aperture stop St, the surface number and a term of (stop) are noted. Further, in the lens data of Table 1, in each place of the surface distance which is variable during zooming and focusing, DD[surface number] is noted. Numerical values each corresponding to the DD[surface number] are shown in Table 3.
In the data about the specification of Table 2, values of the zoom magnification, the focal length f′, the back focal length Bf′, the F number FNo., and the total angle of view 2ω(°) are noted.
In the lens data of Table 1, the reference sign * is attached to surface numbers of aspheric surfaces, and radii of curvature of the aspheric surfaces are represented by numerical values of paraxial radii of curvature. The data about aspheric coefficients of Table 4 shows the surface numbers of the aspheric surfaces and aspheric coefficients of the aspheric surfaces. The “E±n” (n: an integer) in numerical values of the aspheric coefficients of Table 4 indicates “×10±n”. The aspheric coefficients are values of the coefficients KA and Am in aspheric surface expression represented as the following expression.
Zd=C·h/{1+(1−KA·C2·h2)1/2}+ΣAm·hm
Here, Zd is an aspheric surface depth (a length of a perpendicular from a point on an aspheric surface at height h to a plane that is perpendicular to the optical axis and contacts with the vertex of the aspheric surface),
h is a height (a distance from the optical axis),
C is an inverse of a paraxial radius of curvature,
KA and Am are aspheric coefficients, and
Σ at the aspheric surface depth Zd means a sum with respect to m.
In the basic lens data, the data about specification, and the data about variable surface distances, a degree is used as a unit of an angle, and mm (millimeters) is used as a unit of a length, but appropriate different units may be used since the optical system can be used even in a case where the system is enlarged or reduced in proportion.
Next, a zoom lens of Example 2 will be described.
Next, a zoom lens of Example 3 will be described.
The zoom lens of Example 3 is composed of, in order from the object side, a first lens group G1 composed of five lenses L1a to L1e, a second lens group G2 composed of six lenses L2a to L2f, a third lens group G3 composed of an aperture stop St and two lenses L3a and L3b, a fourth lens group G4 composed of four lenses L4a to L4d, a fifth lens group G5 composed of four lenses L5a to L5d, and a sixth lens group G6 composed of one lens L6a.
The A constituent section SA is composed of only the first lens group G1, the B constituent section SB is composed of only the second lens group G2, the C constituent section SC is composed of only the third lens group G3, the D constituent section SD is composed of only the fourth lens group G4, and the E constituent section SE is composed of the fifth lens group G5 and the sixth lens group G6.
Table 9 shows basic lens data of the zoom lens of Example 3, Table 10 shows data about specification, Table 11 shows data about surface distances which are variable, Table 12 shows data about aspheric coefficients thereof, and
Next, a zoom lens of Example 4 will be described.
The data about the diffractive optical surface coefficients in Table 17 shows the surface numbers of the diffractive optical surfaces and the diffractive optical surface coefficients of the diffractive optical surfaces. The “E±n” (n: an integer) in numerical values of the diffractive optical surface coefficients of Table 9 indicates “×10±n”. The diffractive optical surface applied to each lens is represented by a macroscopic lens shape as a basic shape and an optical path difference function Φ(h) where the addition amount of the optical path length which should be set for the diffractive optical surface is represented by a function of the height h from the optical axis Z. The diffractive optical surface coefficient is a value of each coefficient Pk in the optical path difference function Φ(h) represented by the following expression.
Φ(h)=λ/(2π)×ΣPk·hk
Here, Φ(h) is an optical path difference function (an amount of addition to the optical path length of the diffractive optical surface),
λ is a wavelength,
Pk is a diffractive optical surface coefficient,
h is a height (a distance from the optical axis to the lens surface), and
Σ in the optical path difference function Φ(h) means a sum with respect to k.
Next, a zoom lens of Example 5 will be described.
Table 23 shows values corresponding to Conditional Expressions (1) to (7) of the zoom lenses of Examples 1 to 5. It should be noted that, in the above-mentioned examples, the d line is set as the reference wavelength, and the values shown in Table 23 are values at the reference wavelength.
As can be seen from the above data, all the zoom lenses of Examples 1 to 5 are zoom lenses each of which satisfies Conditional Expressions (1) to (7) has a favorable optical performance with a high magnification of 30 times or more while maintaining a sufficient back focal length and having a small size.
Bfw/fw≥3
Here, Bfw is a back focal length (air conversion length) of the whole system at the wide-angle end, and
fw is a focal length of the whole system at the wide-angle end.
Next, an imaging apparatus according to an embodiment of the present invention will be described.
The imaging apparatus 10 comprises a zoom lens 1, a filter 2 which is disposed on the image side of the zoom lens 1, and an imaging element 3 which is disposed on the image side of the filter 2. In addition,
The imaging element 3 captures an optical image, which is formed through the zoom lens 1, and converts the image into an electrical signal. For example, charge coupled device (CCD), complementary metal oxide semiconductor (CMOS), or the like may be used. The imaging element 3 is disposed such that the imaging surface thereof is coplanar with the image plane of the zoom lens 1.
The imaging apparatus 10 also comprises a signal processing section 5 which performs calculation processing on an output signal from the imaging element 3, a display section 6 which displays an image formed by the signal processing section 5, and a zoom control section 7 which controls zooming of the zoom lens 1. It should be noted that
The present invention has been hitherto described through embodiments and examples, but the present invention is not limited to the above-mentioned embodiments and examples, and may be modified into various forms. For example, values such as the radius of curvature, the surface distance, the refractive index, and the Abbe number of each lens are not limited to the values shown in the numerical examples, and different values may be used therefor.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-100396 | May 2017 | JP | national |
