JP2005134887A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a lens system whose chromatic aberration is satisfactorily corrected from a visible region to a near infrared region and which is compact, has a large aperture ratio and is bright. <P>SOLUTION: The zoom lens is equipped with a 1st lens group G1 having negative refractive power and a 2nd lens group G2 having positive refractive power in order from an object side. Power is varied from a wide angle end to a telephoto end by moving the 2nd lens group G2 to the object side on an optical axis, and an image surface is corrected according as the power is varied by moving the 1st lens group G1 to the image side on the optical axis. The zoom lens satisfies conditional expressions (1) 0.5<¾f1/f2¾<0.8 and (2) 2.6<str/z<2.9. In expression (1), f1 shows the focal length of the 1st lens group G1, and f2 shows the focal length of the 2nd lens group G2. In expression (2), (str) shows moving amount(mm) associated with varying of the power of the 2nd lens group G2 and (z) shows a zoom ratio. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a zoom lens mainly used for monitoring, and more particularly to a zoom lens that can be used in both the visible range and the near infrared range.

  For surveillance cameras such as CCTV (Closed Circuit TeleVision), it is desired to develop a lens system that can be used day and night. In particular, surveillance cameras used outdoors usually shoot with visible light in the daytime and shoot with near-infrared light at night, so the lens system has a wide range from the visible range to the near-infrared range. What corresponds to the wavelength range is required.

  In a general lens system designed for the visible range, chromatic aberration occurs particularly in the near infrared region, and a focus shift occurs during photographing in the near infrared region at night. For this reason, in the lens system for surveillance cameras, it is particularly necessary that the chromatic aberration is corrected well from the visible range to the near infrared range.

Conventionally, zoom lenses in which chromatic aberration is corrected from the visible region to the near infrared region include, for example, those described in the following patent documents. The zoom lens described in Patent Document 1 is a two-group type zoom lens composed of a negative front group and a positive rear group in order from the object side. An example of a two-group three-element configuration as the front group and a five-group six-element configuration as the rear group is described.
JP 2002-207166 A

  As described above, in the lens system for the surveillance camera, it is necessary that chromatic aberration is particularly well corrected from the visible region to the near infrared region. For surveillance cameras, there is a further demand for a lens system that is bright and has a large aperture ratio that can be used even under low illumination. Therefore, it is desired to develop a lens system that satisfies these various requirements.

The present invention has been made in view of such problems, and a first object of the invention is to provide a zoom lens that can realize a small and bright lens system with a large aperture ratio.
A second object of the present invention is to provide a zoom lens capable of correcting chromatic aberration satisfactorily from the visible region to the near infrared region.

  The zoom lens according to the first aspect of the present invention includes, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power. The zooming is performed from the wide-angle end to the telephoto end by moving the object side on the axis, and the image plane correction accompanying the zooming is performed by moving the first lens group to the image side on the optical axis. And is configured so as to satisfy the following conditional expressions (1) and (2).

0.5 <| f1 / f2 | <0.8 (1)
2.6 <str / z <2.9 (2)
Here, f1 represents the focal length of the first lens group, and f2 represents the focal length of the second lens group. str represents the amount of movement (mm) from the wide-angle end to the telephoto end accompanying zooming of the second lens group, and z represents the zoom ratio.

  In the zoom lens according to the first aspect, the first lens group includes, for example, in order from the object side, a 1-1 lens having negative refractive power, a 1-2 lens having negative refractive power, It is preferable to have a three-group four-lens configuration in which a cemented lens including a first lens having negative refractive power and a first lens having positive refractive power is arranged. In this case, it is more preferable that the first lens 1-1 and the first lens 1-2 are negative meniscus lenses having a convex surface facing the object side, and the first lens-3 is a biconcave lens.

  The second lens group includes, for example, in order from the object side, a 2-1 lens having a positive refractive power, a 2-2 lens having a positive refractive power, and a second 2-3 having a negative refractive power. It is preferable that the lens and the second-fourth lens having a positive refractive power are arranged in a four-group four-lens configuration, and that at least one surface of the second-2-1 lens is aspherical. . In this case, it is more preferable that the 2-3 lens is a negative meniscus lens having a convex surface facing the object side.

  In the zoom lens according to the first aspect, when the first lens group and the second lens group are configured as described above, it is more preferable that the zoom lens is configured to satisfy the following conditional expression.

nd _L14 > 1.83 (3)
νd _L21 > 60 (4-1)
nd _L23 > 1.83 (5)
Where nd _L14 is the refractive index of the 1-4 lens in the first lens group with respect to the d-line, νd _L21 is the Abbe number of the 2-1 lens in the second lens group with respect to the d-line, and nd _L23 is in the second lens group. The refractive index for the d-line of the 2-3 lens is shown.

  A zoom lens according to a second aspect of the present invention includes, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power. The zooming is performed from the wide-angle end to the telephoto end by moving the object side on the axis, and the image plane correction accompanying the zooming is performed by moving the first lens group to the image side on the optical axis. Has been made. The first lens group includes, in order from the object side, a first lens having negative refractive power, a first lens having negative refractive power, a first lens having negative refractive power, and a positive lens. And a cemented lens composed of a first to fourth lens having a refractive power of 3 in 4 groups. The second lens group includes, in order from the object side, a second 2-1 lens having a positive refractive power A four-group four-lens configuration in which a No. 2-2 lens having a positive refractive power, a No. 2-3 lens having a negative refractive power, and a No. 2-4 lens having a positive refractive power are arranged. In addition, at least one surface of the 2-2nd lens has an aspherical shape. And it is comprised so that the following conditional expression (1), (2) may be satisfied.

0.5 <| f1 / f2 | <0.8 (1)
2.6 <str / z <2.9 (2)
Here, f1 represents the focal length of the first lens group, and f2 represents the focal length of the second lens group. str represents the amount of movement (mm) from the wide-angle end to the telephoto end accompanying zooming of the second lens group, and z represents the zoom ratio.

  In the zoom lens according to the second aspect, the first and second lenses in the first lens group are negative meniscus lenses having a convex surface facing the object side, and the first and third lenses are biconcave lenses. It is preferable that In addition, it is preferable that the 2-3 lens in the second lens group is a negative meniscus lens having a convex surface directed toward the object side.

  The zoom lens according to the second aspect is preferably configured so as to satisfy the following conditional expression.

nd _L14 > 1.83 (3)
νd _L22 > 60 (4-2)
nd _L23 > 1.83 (5)
Where nd _L14 is the refractive index of the 1-4 lens in the first lens group with respect to the d-line, νd _L22 is the Abbe number of the second lens in the second lens with respect to the d-line, and nd _L23 is the second lens group in the second lens group. The refractive index for d-line of a -3 lens is shown.

  In the zoom lens according to the first and second aspects of the present invention, the above-described preferable configuration is appropriately adopted in accordance with required specifications and the like, so that aberration correction is favorably performed from the visible range to the near infrared range. At the same time, it becomes easy to reduce the size and increase the aperture ratio. In particular, by satisfying conditional expressions (1) and (2), it becomes easy to reduce the size while suppressing the occurrence of various aberrations. In particular, when the conditional expressions (3) and (5) are satisfied, the size can be further reduced.

  In particular, the first lens group has a configuration of four elements in three groups, so that, for example, spherical aberration at the telephoto end can be reduced while achieving a reduction in size as compared with the case where the first lens group has a configuration of three elements in two groups. And chromatic aberration of magnification can be easily corrected. In this case, the 1-1st lens and the 1-2nd lens are negative meniscus lenses having a convex surface facing the object side, and the 1-3rd lens is a biconcave lens. The correction is advantageous.

  In particular, in the zoom lens according to the first aspect of the present invention, at least one surface of the second lens 2-1 in the second lens group has an aspherical shape, so that a spherical surface generated particularly as the aperture ratio increases. It becomes easier to correct aberrations. Further, by using an aspherical surface for the 2-1 lens closest to the object side in the second lens group, it is easy to suppress the eccentricity sensitivity. Further, by satisfying conditional expression (4-1) for the 2-1 lens, it becomes easy to correct chromatic aberration well up to the near infrared region.

  In particular, in the zoom lens according to the second aspect of the present invention, at least one or more surfaces of the second lens 2-2 in the second lens group have an aspherical shape, and this particularly occurs with a large aperture ratio. It becomes easy to correct spherical aberration. Furthermore, by satisfying conditional expression (4-2) for the 2-2nd lens, it becomes easy to correct chromatic aberration well up to the near infrared region.

  According to the zoom lens according to the first aspect of the present invention, an appropriate condition regarding the ratio of the focal lengths of the lens groups is satisfied, and an appropriate condition is satisfied regarding the amount of movement of the second lens group. It is easy to realize a small and bright lens system with a large aperture ratio.

  In the zoom lens according to the first aspect of the present invention, in particular, in the second lens group, in order from the object side, a 2-1 lens having a positive refractive power and a 2-2 lens having a positive refractive power A four-group, four-lens configuration in which a second lens having negative refractive power and a second lens having positive refractive power are arranged, and at least one surface of the second lens When the lens is aspherical, it is easy to correct spherical aberration, and it becomes easier to achieve a larger aperture ratio. Further, by satisfying the predetermined conditional expression (4-1) with respect to the Abbe number of the second lens 2-1 in the second lens group, it is possible to reduce the size and increase the aperture ratio while correcting chromatic aberration well to the near infrared region. Can be achieved.

  In the zoom lens according to the second aspect of the present invention, an appropriate condition is satisfied with respect to the ratio of the focal lengths of the lens groups, and an appropriate condition is satisfied with respect to the movement amount of the second lens group. It is easy to realize a small and bright lens system with a large aperture ratio. In particular, since at least one surface of the second lens 2-2 in the second lens group is configured to be aspherical, it becomes easy to correct spherical aberration and to increase the aperture ratio.

  In the zoom lens according to the second aspect of the present invention, in particular, when the predetermined conditional expression (4-2) is satisfied with respect to the Abbe number of the second lens 2-2 of the second lens group, it is good up to the near infrared region. In addition, it is possible to reduce the size and increase the aperture ratio while correcting chromatic aberration.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 shows a configuration example of a zoom lens according to the first embodiment of the present invention. This configuration example corresponds to the lens configuration of Numerical Example 1-1 (Tables 1 to 3) described later. FIG. 2 shows another configuration example of the zoom lens according to the present embodiment. The configuration example of FIG. 2 corresponds to the lens configuration of Numerical Example 1-2 (Tables 4 to 6) described later. 1 and 2 show the lens arrangement at the wide-angle end.

  In each figure, the reference symbol Ri is the i-th (i) (i) (i) (i) indicating that the surface of the constituent element closest to the object side including the aperture stop St is first, and increases sequentially toward the image side (imaging side). = 1 to 18) indicates the radius of curvature of the surface. The symbol Di indicates the surface interval on the optical axis Z1 between the i-th surface and the i + 1-th surface. Since the basic configuration is the same in each configuration example, the following description is based on the configuration of the zoom lens shown in FIG.

  This zoom lens can be used in both the visible range and the near-infrared range, and is suitable for mounting on, for example, a day-and-night surveillance camera. This zoom lens has a configuration in which a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power are sequentially arranged from the object side along the optical axis Z1. ing. For example, an image sensor using a CCD (Charge Coupled Device) or a CMOS (Complementary Mental-Oxide Semiconductor) (not shown) is disposed on the image plane (imaging surface) of the zoom lens. Various optical members may be disposed between the second lens group G2 and the imaging plane depending on the configuration of the camera side on which the lens is mounted. In the configuration example of FIG. 1, a cover glass GC for protecting the imaging surface is disposed. A diaphragm St is disposed between the first lens group G1 and the second lens group G2.

  This zoom lens is a two-group zoom system, and the second lens group G2 is moved from the wide-angle end to the telephoto end by moving the second lens group G2 to the object side on the optical axis. The correction is performed by moving the first lens group G1 to the image side on the optical axis. The first lens group G1 and the second lens group G2 move so as to draw a locus shown by a solid line in FIG. 1 as the magnification is changed from the wide-angle end to the telephoto end. The first lens group G1 also functions as a focus group.

This zoom lens is configured to satisfy the following conditional expressions (1) and (2). However, f1 shows the focal distance of the 1st lens group G1, and f2 shows the focal distance of the 2nd lens group G2. str represents a stroke amount (movement amount, unit mm) from the wide-angle end to the telephoto end associated with zooming of the second lens group G2, and z represents a zoom ratio.
0.5 <| f1 / f2 | <0.8 (1)
2.6 <str / z <2.9 (2)

  The first lens group G1, for example, in order from the object side, includes a first lens L11 having negative refractive power, a first lens L12 having negative refractive power, and a first lens having negative refractive power. -3 lens L13 and a cemented lens composed of a first lens L14 having positive refractive power are arranged in a three-group four-lens configuration.

  In the first lens group G1, the 1-1st lens L11 and the 1-2th lens L12 are preferably negative meniscus lenses having a convex surface facing the object side. The 1-3 lens L13 is preferably biconcave. The 1-4 lens L14 is, for example, a meniscus lens having a convex surface facing the object side.

  The second lens group G2, in order from the object side, includes a 2-1 lens L21 having a positive refractive power, a 2-2 lens L22 having a positive refractive power, and a second 2-3 having a negative refractive power. A four-group four-lens configuration in which a lens L23 and a 2-4 lens L24 having a positive refractive power are arranged, and at least one surface of the 2-1 lens L21 has an aspheric shape. It is preferable.

  In the second lens group G2, the 2-1st lens L21 has, for example, a biconvex shape in the vicinity of the paraxial region. The second 2-2 lens L22 and the second-4 lens L24 have, for example, a biconvex shape. The 2-3 lens L23 is preferably composed of a negative meniscus lens having a convex surface facing the object side.

More preferably, the zoom lens is configured to satisfy the following conditional expression. However, nd _L14 is the refractive index with respect to the d-line of the 1-4th lens L14 in the first lens group G1, νd _L21 is the Abbe number with respect to the d-line of the 2-1 lens L21 in the second lens group G2, and nd _L23 is the first The refractive index with respect to d line of the 2nd-3 lens L23 in 2 lens group G2 is shown.
nd _L14 > 1.83 (3)
νd _L21 > 60 (4-1)
nd _L23 > 1.83 (5)

  Next, operations and effects of the zoom lens configured as described above will be described.

  In this zoom lens, zooming is performed by moving the second lens group G2 in the optical axis direction, and correction of image plane variation accompanying the zooming moves the first lens group G1 in the optical axis direction. Is done. Focus adjustment is also performed by moving the first lens group G1 in the optical axis direction.

  In this zoom lens, the first lens group G1 has a configuration of four elements in three groups, for example, various aberrations, while achieving a reduction in size as compared with a case where the first lens group G1 has a configuration of three elements in two groups. In particular, it becomes easy to correct lateral chromatic aberration and spherical aberration at the telephoto end. In particular, the chromatic aberration can be easily corrected by using the first lens 1-3 and the lens 1-4 as cemented lenses. In particular, by disposing two negative meniscus lenses (first lens L11 and first lens L12) having a convex surface facing the object side closest to the object side, spherical aberration can be corrected at the telephoto end. It becomes easy to do.

  In this zoom lens, at least one surface of the 2-1 lens L21 in the second lens group G2 has an aspherical shape, so that it becomes easy to correct spherical aberration that occurs particularly with a large aperture ratio. Further, by using an aspherical surface for the 2-1st lens L21 closest to the object side of the second lens group G2, it is easy to suppress the decentering sensitivity. Further, by satisfying conditional expression (4-1) for the 2-1 lens L21, it becomes easy to correct chromatic aberration well up to the near infrared region.

  Conditional expression (1) defines an appropriate range of the ratio f1 / f2 between the focal length f1 of the first lens group G1 and the focal length f2 of the second lens group G2. By satisfying conditional expression (1), various aberrations can be easily corrected while downsizing. If the upper limit of conditional expression (1) is exceeded, the refractive power of the first lens group G1 becomes too weak, and the amount of movement of the first lens group G1 increases, making it impossible to achieve compactness. Below the lower limit, the refractive power of the first lens group G1 becomes too strong, and in particular, spherical aberration at the telephoto end is insufficiently corrected.

  Conditional expression (2) defines an appropriate stroke range of the second lens group G2 accompanying zooming. If the upper limit of conditional expression (2) is exceeded, the amount of movement of the second lens group G2 will increase, making it impossible to achieve compactness. Below the lower limit, correction of spherical aberration and coma particularly at the wide-angle end becomes difficult, which is not preferable.

  Conditional expression (3) defines an appropriate refractive index range of the first to fourth lens L14 in the first lens group G1. Conditional expression (5) defines an appropriate refractive index range of the second to third lens L23 in the second lens group G2. By selecting a glass type having a high refractive index so as to satisfy the conditional expressions (3) and (5), it becomes easy to loosen the spherical shape of each lens L14, L23 (increase the radius of curvature) and to achieve a compact size. It becomes easy. In particular, by satisfying the conditional expression (5) by using the second-third lens L23 as a negative meniscus lens having a convex surface facing the object side, it becomes easier to achieve a more compact size. If the values of conditional expressions (3) and (5) are not reached, it is difficult to achieve compactness, which is not preferable.

  Conditional expression (4-1) defines an appropriate Abbe number range of the 2-1 lens L21 in the second lens group G2. For the 2-1st lens L21 using an aspherical surface, by appropriately selecting the glass type so as to satisfy the conditional expression (4-1), particularly the axial chromatic aberration is favorably corrected from the visible range to the near infrared range. can do. Thereby, a visible range / near-infrared range lens can be easily realized. If the value of conditional expression (4-1) is not reached, correction of chromatic aberration from the visible to the near-infrared region becomes difficult, which is not preferable.

  As described above, according to the zoom lens according to the present embodiment, by appropriately adopting the above-described preferable configuration in accordance with required specifications and the like, the aberration correction is favorably performed from the visible region to the near infrared region. Thus, it is possible to reduce the size and increase the aperture ratio, and it is possible to easily obtain performance suitable for a monitoring camera. For example, even when shooting from a bright environment to a low-light environment, or when shifting from shooting with visible light to shooting with near-infrared light, an easy-to-use lens system is achieved without refocusing. it can.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.

  FIG. 7 shows a configuration example of a zoom lens according to the second embodiment of the present invention. This configuration example corresponds to the lens configuration of Numerical Example 2-1 (Tables 8 to 10) described later. FIG. 8 shows another configuration example of the zoom lens according to the present embodiment. The configuration example of FIG. 8 corresponds to the lens configuration of Numerical Example 2-2 (Tables 11 to 13) described later. 7 and 8 show the lens arrangement at the wide angle end.

  In FIGS. 7 and 8, the reference symbol Ri is assigned i so as to increase sequentially toward the image side (imaging side) with the surface of the most object side component including the stop St as the first. The radius of curvature of the th (i = 1-18) surface is shown. The symbol Di indicates the surface interval on the optical axis Z1 between the i-th surface and the i + 1-th surface.

  Since the basic configuration of the zoom lens according to the present embodiment is the same as that of the zoom lens shown in FIGS. 1 and 2, the following description will focus on portions different from these.

  In this zoom lens, the first lens group G1 includes, for example, four lenses L11 to L14. The basic shape of each lens L11-L14 is substantially the same as the configuration of FIGS.

  The second lens group G2 includes, for example, four lenses L21 to L24. Among these, the basic shapes of the second-3 lens L23 and the second-4 lens L24 are substantially the same as the configurations in FIGS.

  In the zoom lens shown in FIGS. 1 and 2, an aspherical surface is used for the 2-1 lens L21 in the second lens group G2. In this embodiment, however, at least one surface of the 2-2 lens L22 is used. As described above, an aspheric surface is used. In the present embodiment, the 2-1 lens L21 has, for example, a biconvex shape. The 2-2nd lens L22 has, for example, a planoconvex shape with a convex surface facing the object side in the vicinity of the paraxial.

This zoom lens is configured to satisfy the following conditional expressions (1) and (2), similarly to the zoom lens shown in FIGS.
0.5 <| f1 / f2 | <0.8 (1)
2.6 <str / z <2.9 (2)

This zoom lens preferably satisfies the following conditional expression. Here, νd _L22 indicates the Abbe number with respect to the d line of the 2-2nd lens L22 in the second lens group G2.
nd _L14 > 1.83 (3)
νd _L22 > 60 (4-2)
nd _L23 > 1.83 (5)

  In this zoom lens, at least one or more surfaces of the 2-2nd lens L22 in the second lens group G2 have an aspherical shape, so that it becomes easy to correct spherical aberration that occurs particularly with a large aperture ratio. Further, by satisfying conditional expression (4-2) for the 2-2nd lens L22, it becomes easy to correct chromatic aberration well up to the near infrared region.

  Conditional expression (4-2) defines an appropriate Abbe number range of the 2-2nd lens L22 in the second lens group G2. For the 2-2nd lens L22 using an aspherical surface, by appropriately selecting the glass type so as to satisfy the conditional expression (4-2), particularly the axial chromatic aberration is favorably corrected from the visible range to the near infrared range. can do. Thereby, a visible range / near-infrared range lens can be easily realized. If the value is less than the value of conditional expression (4-2), it is difficult to correct chromatic aberration from the visible to the near infrared region.

  Other operations and effects are the same as those of the zoom lens according to the first embodiment. As described above, in the zoom lens according to the present embodiment, it is possible to reduce the size and increase the aperture ratio while satisfactorily correcting aberrations from the visible range to the near infrared range, which is suitable for a monitoring camera. Performance can be easily obtained.

  Next, specific numerical examples of the zoom lens according to the present embodiment will be described.

[Examples 1-1 and 1-2]
First, numerical examples corresponding to the first embodiment will be described. In the following, two numerical examples 1-1 and 1-2 will be described together. Tables 1 to 3 show specific lens data (Example 1-1) corresponding to the configuration of the zoom lens shown in FIG. Tables 4 to 6 show specific lens data (Example 1-2) corresponding to the configuration of the zoom lens shown in FIG. Tables 1 and 4 show basic data portions of the lens data of the embodiment, and Tables 2 and 5 show data portions related to the aspherical shape of the lens data of the embodiments. Tables 3 and 6 show other data.

  In the column of surface number Si in the lens data shown in each table, with respect to the zoom lens of each example, the surface of the component closest to the object side including the diaphragm St and the cover glass GC is first, and the surface is directed to the image side. The numbers of the i-th (i = 1 to 18) planes that are sequentially numbered according to FIG. In the column of the curvature radius Ri, the value of the curvature radius of the i-th surface from the object side is shown in correspondence with the reference symbol Ri in FIG. Also in the column of the surface interval Di, the interval on the optical axis between the i-th surface Si and the i + 1-th surface Si + 1 from the object side is shown in correspondence with the reference numerals in FIG. The unit of the value of the curvature radius Ri and the surface interval Di is millimeter (mm). In the column of ndi, the value of the refractive index with respect to the d-line (587.6 nm) of the i-th lens element from the object side including the aperture stop St and the cover glass GC is shown. In the column of νdj, the Abbe number value with respect to the d-line of the jth lens element (j = 1 to 9) from the object side including the cover glass GC is shown.

  In each lens data of Table 1 and Table 4, the symbol “*” attached to the left side of the surface number indicates that the lens surface has an aspherical shape. In each embodiment, both surfaces S9 and S10 of the 2-1 lens L21 in the second lens group G2 are aspherical. In the basic lens data, the numerical value of the radius of curvature near the optical axis (near the paraxial axis) is shown as the radius of curvature of these aspheric surfaces.

In the numerical values of each aspherical data in Table 2 and Table 5, the symbol “E” indicates that the next numerical value is a “power exponent” with 10 as the base, and is an exponential function with 10 as the base. Indicates that the numerical value represented is multiplied by the numerical value before “E”. For example, “1.0E-02” indicates “1.0 × 10 ⁻² ”.

In each aspheric surface data, the values of the coefficients B _i and KA in the aspheric surface expression represented by the following expression (A) are described. More specifically, Z is the length (mm) of a perpendicular line drawn from a point on the aspheric surface at a height h from the optical axis to the tangential plane (plane perpendicular to the optical axis) of the apex of the aspheric surface. Show.

Z = C · h ² / {1+ (1−KA · C ² · h ² ) ^1/2 } + ΣB _i · h ⁱ (A)
However,
Z: Depth of aspheric surface (mm)
h: Distance from the optical axis to the lens surface (height) (mm)
KA: eccentricity C: paraxial curvature = 1 / R
(R: paraxial radius of curvature)
B _i : i-th (i = 3 to 10) aspheric coefficient

  In each of the zoom lenses of each of the embodiments, the first lens group G1 and the second lens group G2 move on the optical axis with zooming. Therefore, the front and rear surface distances D7, D8, and D16 of these groups are as follows. It is variable. Tables 3 and 6 show values of the respective examples at the wide-angle end and the telephoto end as data at the time of zooming of these surface distances D7, D8, and D16. Tables 3 and 6 also summarize the focal length, F number (FNO.), And half angle of view ω at the wide-angle end and the telephoto end for the zoom lenses of the respective examples.

  Table 7 summarizes the values related to the conditional expressions (1) to (3), (4-1), and (5) for each example. As shown in Table 7, the value of each example is within the numerical range of each conditional expression.

  3A to 3C show spherical aberration, astigmatism, and distortion (distortion aberration) at the wide-angle end in the zoom lens of Example 1-1. 4A to 4C show similar aberrations at the telephoto end. Each aberration diagram shows the aberration with the d-line as the reference wavelength, but the spherical aberration diagram also shows the aberration in the near infrared region (wavelength 880 nm). In the astigmatism diagram, the solid line indicates the sagittal direction and the broken line indicates the tangential direction. ω indicates a half angle of view.

  Similarly, various aberrations for Example 1-2 are shown in FIGS. 5A to 5C (wide-angle end) and FIGS. 6A to 6C (telephoto end).

  As can be seen from the numerical data and aberration diagrams described above, in each example, aberration correction is performed satisfactorily from the visible region to the near infrared region, and a small and large aperture ratio lens system can be realized.

[Examples 2-1 and 2-2]
Next, numerical examples corresponding to the second embodiment will be described. In the following, two numerical examples 2-1 and 2-2 will be described together. Tables 8 to 10 show specific lens data (Example 2-1) corresponding to the configuration of the zoom lens shown in FIG. Tables 11 to 13 show specific lens data (Example 2-2) corresponding to the configuration of the zoom lens shown in FIG. Tables 8 and 11 show basic data portions of the lens data of the example, and Tables 9 and 12 show data portions related to the aspherical shape of the lens data of the example. Tables 10 and 13 show other data. The meanings of symbols such as Ri and Di in each table are the same as those in Examples 1-1 and 1-2.

In each lens data of Table 8 and Table 11, the symbol “*” attached to the left side of the surface number indicates that the lens surface has an aspherical shape. In each embodiment, both surfaces S11 and S12 of the 2-2nd lens L22 in the second lens group G2 are aspherical. In the basic lens data, the numerical value of the radius of curvature near the optical axis (near the paraxial axis) is shown as the radius of curvature of these aspheric surfaces. In each aspheric data, the values of the coefficients B _i and KA in the aspherical shape expression expressed by the above-described expression (A) are described.

  In each of the zoom lenses of each of the embodiments, the first lens group G1 and the second lens group G2 move on the optical axis with zooming. Therefore, the front and rear surface distances D7, D8, and D16 of these groups are as follows. It is variable. Tables 10 and 13 show values of the respective examples at the wide-angle end and the telephoto end as data at the time of zooming of these surface distances D7, D8, D16. Tables 10 and 13 also collectively show the focal length, F number (FNO.), And half angle of view ω at the wide-angle end and the telephoto end for the zoom lenses of the respective examples.

  Table 14 summarizes the values related to the conditional expressions (1) to (3), (4-2), and (5) for each example. As shown in Table 14, the value of each example is within the numerical range of each conditional expression.

  FIGS. 9A to 9C show spherical aberration, astigmatism, and distortion (distortion aberration) at the wide angle end in the zoom lens of Example 2-1. 10A to 10C show similar aberrations at the telephoto end. Each aberration diagram shows the aberration with the d-line as the reference wavelength, but the spherical aberration diagram also shows the aberration in the near infrared region (wavelength 880 nm). In the astigmatism diagram, the solid line indicates the sagittal direction and the broken line indicates the tangential direction. ω indicates a half angle of view.

  Similarly, various aberrations for Example 2-2 are shown in FIGS. 11A to 11C (wide-angle end) and FIGS. 12A to 12C (telephoto end).

  As can be seen from the numerical data and aberration diagrams described above, in each example, aberration correction is performed satisfactorily from the visible region to the near infrared region, and a small and large aperture ratio lens system can be realized.

  The present invention is not limited to the above-described embodiments and examples, and various modifications can be made. For example, the radius of curvature, the surface interval, and the refractive index of each lens component are not limited to the values shown in the above numerical examples, and may take other values.

1 is a lens cross-sectional view illustrating an overall configuration of a zoom lens according to a first embodiment of the present invention and corresponding to Example 1-1. FIG. FIG. 2 is a lens cross-sectional view illustrating an overall configuration of another zoom lens according to the first embodiment of the present invention and corresponding to Example 1-2. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to Example 1-1. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens according to Example 1-1. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to Example 1-2. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at a telephoto end of a zoom lens according to Example 1-2. FIG. 2 is a lens cross-sectional view illustrating an overall configuration of a zoom lens according to a second embodiment of the present invention and corresponding to Example 2-1. FIG. 7 is a lens cross-sectional view illustrating an overall configuration of another zoom lens according to a second embodiment of the present invention and corresponding to Example 2-2. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to Example 2-1. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at a telephoto end of a zoom lens according to Example 2-1. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to Example 2-2. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at a telephoto end of a zoom lens according to Example 2-2.

Explanation of symbols

GC ... cover glass, G1 ... first lens group, G2 ... second lens group, St ... stop, Ri ... radius of curvature of the i-th lens surface from the object side, Di ... i-th and i + 1-th from the object side The distance between the lens surface and Z1,.

Claims (9)

From the object side,
A first lens group having negative refractive power;
A second lens group having a positive refractive power,
By moving the second lens group to the object side on the optical axis, zooming from the wide-angle end to the telephoto end is performed, and image plane correction accompanying the zooming is performed on the image side of the first lens group on the optical axis. To be done by moving to
The zoom lens is configured to satisfy the following conditional expressions (1) and (2).
0.5 <| f1 / f2 | <0.8 (1)
2.6 <str / z <2.9 (2)
However,
f1: Focal length of the first lens group f2: Focal length of the second lens group str: Amount of movement (mm) from the wide-angle end to the telephoto end associated with zooming of the second lens group
z: Zoom ratio The first lens group includes:
In order from the object side, a first lens having a negative refractive power, a first lens having a negative refractive power, a first lens having a negative refractive power, and a first lens having a positive refractive power. It is composed of 4 elements in 3 groups in which a cemented lens consisting of 1-4 lenses is arranged,
The second lens group includes:
In order from the object side, a 2-1 lens having a positive refracting power, a 2-2 lens having a positive refracting power, a 2-3 lens having a negative refracting power, and a positive refracting power 2. The four-group four-lens configuration in which the second to fourth lenses are arranged, and at least one surface of the second to 2-1 lens is configured to be an aspherical shape. Zoom lens. In the first lens group,
The first lens 1-1 and the first lens 1-2 are negative meniscus lenses having a convex surface facing the object side, and the first lens-3 is a biconcave lens. Zoom lens. The zoom lens according to claim 2 or 3, wherein the 2-3 lens of the second lens group is a negative meniscus lens having a convex surface directed toward the object side. The zoom lens according to any one of claims 2 to 4, further configured to satisfy the following conditional expression.
nd _L14 > 1.83 (3)
νd _L21 > 60 (4-1)
nd _L23 > 1.83 (5)
However,
nd _L14 : Refractive index with respect to the d-line of the 1-4 lens in the first lens group νd _L21 : Abbe number with respect to the d-line of the 2-1 lens in the second lens group nd _L23 : 2-3 in the second lens group Refractive index for d-line of lens From the object side,
A first lens group having negative refractive power;
A second lens group having a positive refractive power,
By moving the second lens group to the object side on the optical axis, zooming from the wide-angle end to the telephoto end is performed, and image plane correction accompanying the zooming is performed on the image side of the first lens group on the optical axis. To be done by moving to
The first lens group is
In order from the object side, a first lens having a negative refractive power, a first lens having a negative refractive power, a first lens having a negative refractive power, and a first lens having a positive refractive power. It is composed of 4 elements in 3 groups in which a cemented lens consisting of 1-4 lenses is arranged,
The second lens group is
In order from the object side, a 2-1 lens having a positive refracting power, a 2-2 lens having a positive refracting power, a 2-3 lens having a negative refracting power, and a positive refracting power A four-group four-lens configuration in which second to fourth lenses are arranged, and at least one surface of the second to second lenses is configured to be aspheric.
The zoom lens is configured to satisfy the following conditional expressions (1) and (2).
0.5 <| f1 / f2 | <0.8 (1)
2.6 <str / z <2.9 (2)
However,
f1: Focal length of the first lens group f2: Focal length of the second lens group str: Amount of movement (mm) from the wide-angle end to the telephoto end associated with zooming of the second lens group
z: Zoom ratio In the first lens group,
The first 1-1 lens and the first 1-2 lens are negative meniscus lenses having a convex surface facing the object side, and the first-3 lens is a biconcave lens. Zoom lens. The zoom lens according to claim 6 or 7, wherein the 2-3 lens of the second lens group is a negative meniscus lens having a convex surface directed toward the object side. The zoom lens according to any one of claims 6 to 8, further configured to satisfy the following conditional expression.
nd _L14 > 1.83 (3)
νd _L22 > 60 (4-2)
nd _L23 > 1.83 (5)
However,
nd _L14 : Refractive index of the 1-4 lens in the first lens group with respect to the d-line νd _L22 : Abbe number of the 2-2 lens in the second lens group with respect to the d-line nd _L23 : 2-3 in the second lens group Refractive index for d-line of lens

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