JP2004212913A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens realizing a variable power ratio higher than heretofore and also excellently correcting aberration from a visible region to a near infrared region though it is the comparatively compact lens type one of a two-group zoom system. <P>SOLUTION: The zoom lens of the two-group zoom system is equipped with a 1st negative lens group G1 and a 2nd positive lens group G2 in order from an object side. Furthermore, the zoom lens satisfies conditional expressions; (1) -3.4<f1/fw<-3.0, (2) -1.6<mT<-1.4 and (3) 60<ν(G2+). Provided that f1 means the focal distance of the 1st lens group G1, fw means the focal distance of an entire system at a wide angle end, mT means the image forming magnification of the 2nd lens group G2 at a telephoto end, and ν(G2+) means the average of the Abbe number of a positive lens included in the 2nd lens group G2. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００３９】
図６は、上述の条件式（１）〜（３）に対応する値を、各実施例について示したものである。図６に示したように、各実施例の値が、条件式（１）〜（３）の範囲内となっている。
【００４０】
図７（Ａ）〜（Ｃ）は、実施例１のズームレンズにおける広角端での球面収差、非点収差、およびディストーション（歪曲収差）を示している。図８（Ａ）〜（Ｃ）は、望遠端での球面収差、非点収差、およびディストーション（歪曲収差）を示している。各収差図には、ｄ線を基準波長とした収差を示すが、球面収差については近赤外域（８８０ｎｍ）についての収差も同時に示す。非点収差図において、実線はサジタル方向、破線はタンジェンシャル方向の収差を示す。
【００４１】
同様に、実施例２についての諸収差を図９（Ａ）〜（Ｃ）（広角端）および図１０（Ａ）〜（Ｃ）（望遠端）に示し、実施例３についての諸収差を図１１（Ａ）〜（Ｃ）（広角端）および図１２（Ａ）〜（Ｃ）（望遠端）に示し、実施例４についての諸収差を図１３（Ａ）〜（Ｃ）（広角端）および図１４（Ａ）〜（Ｃ）（望遠端）に示す。
【００４２】
以上の各レンズデータおよび各収差図から分かるように、各実施例について、約４．７倍という従来よりも高い変倍比を実現できており、また、可視域から近赤外域まで良好に収差補正が行われている。
【００４３】
なお、本発明は、上記実施の形態および各実施例に限定されず種々の変形実施が可能である。例えば、各レンズ成分の曲率半径、面間隔および屈折率の値などは、上記各数値実施例で示した値に限定されず、他の値をとり得る。
【００４４】
【発明の効果】
以上説明したように、請求項１ないし３のいずれか１項に記載のズームレンズによれば、物体側から順に、負の第１レンズ群と正の第２レンズ群とを備えた２群ズーム方式のレンズであって、各条件式（１）〜（３）を満足して各群のレンズ配置と硝種の選択を適切に行うようにしたので、２群ズーム方式の比較的小型なレンズタイプでありながら、従来よりも高い変倍比を実現すると共に、可視域から近赤外域まで良好に収差補正を行うことができる。
【００４５】
特に、請求項２記載のズームレンズによれば、前記第２レンズ群中に、少なくとも１枚の非球面レンズを含めるようにしたので、変倍域全域にわたって球面収差を十分補正することができ、さらにレンズ枚数の削減が可能となる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係るズームレンズの構成例を示すものであり、実施例１に対応するレンズ断面図である。
【図２】本発明の実施例１に係るズームレンズのレンズデータを示す図である。
【図３】本発明の実施例２に係るズームレンズのレンズデータを示す図である。
【図４】本発明の実施例３に係るズームレンズのレンズデータを示す図である。
【図５】本発明の実施例４に係るズームレンズのレンズデータを示す図である。
【図６】実施例１〜４に係るズームレンズが満たす条件式の値を示す図である。
【図７】実施例１に係るズームレンズの広角端における球面収差、非点収差、およびディストーションを示す収差図である。
【図８】実施例１に係るズームレンズの望遠端における球面収差、非点収差、およびディストーションを示す収差図である。
【図９】実施例２に係るズームレンズの広角端における球面収差、非点収差、およびディストーションを示す収差図である。
【図１０】実施例２に係るズームレンズの望遠端における球面収差、非点収差、およびディストーションを示す収差図である。
【図１１】実施例３に係るズームレンズの広角端における球面収差、非点収差、およびディストーションを示す収差図である。
【図１２】実施例３に係るズームレンズの望遠端における球面収差、非点収差、およびディストーションを示す収差図である。
【図１３】実施例４に係るズームレンズの広角端における球面収差、非点収差、およびディストーションを示す収差図である。
【図１４】実施例４に係るズームレンズの望遠端における球面収差、非点収差、およびディストーションを示す収差図である。
【符号の説明】
Ｇ１…第１レンズ群、Ｇ２…第２レンズ群、Ｌｃ…カバーガラス、Ｚ１…光軸、Ｌ１〜Ｌ８…第１〜第８レンズ。[0001]
TECHNICAL FIELD OF THE INVENTION
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 a visible region and a near-infrared region.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, day and night cameras have been developed mainly for monitoring. Along with this, the demand for a visible / near-infrared dual-use lens suitable for day and night cameras has been increasing. Conventionally, many lenses for the visible region have been designed, but conventional lens systems designed for the visible region cause chromatic aberration especially in the near-infrared region, and photograph in the near-infrared region at night. In this case, there is a problem that a focus shift occurs.
[0003]
As a conventional lens system that can be used in both the visible region and the near infrared region, there are lenses described in the following publications. The lenses described in these publications have a relatively small lens configuration of a two-group zoom system.
[0004]
[Patent Document 1]
JP 2002-196235 A [Patent Document 2]
JP 2002-207166 A [Patent Document 3]
JP-A-2002-244038
[Problems to be solved by the invention]
Each of the lenses described in these publications has a zoom ratio of only about 2.2. However, in order to respond to various demands of users, even a relatively small lens system is expected to have a higher zoom ratio.
[0006]
The present invention has been made in view of such a problem, and an object thereof is to realize a higher zoom ratio than before and achieve a near-infrared light from a visible range while using a relatively small lens type of a two-group zoom method. It is an object of the present invention to provide a zoom lens capable of favorably correcting aberrations up to an outer region.
[0007]
[Means for Solving the Problems]
The zoom lens according to the present invention includes, in order from the object side, a negative first lens group and a positive second lens group, and changes by moving the first lens group and the second lens group on the optical axis. It is configured to perform the doubling and satisfy the following conditional expressions (1), (2) and (3).
[0008]
-3.4 <f1 / fw <-3.0 (1)
-1.6 <mT <-1.4 (2)
60 <ν (G2 +) (3)
Where f1 is the focal length of the first lens group, fw is the focal length of the entire system at the wide-angle end, mT is the imaging magnification of the second lens group at the telephoto end, and ν (G2 +) is the second lens group. Shows the average of the Abbe numbers of the positive lenses included in the above.
[0009]
In the zoom lens according to the present invention, by adopting the above-described configuration, a higher zoom ratio than before can be realized, and aberration correction can be favorably performed from the visible region to the near infrared region. In particular, by satisfying conditional expressions (1) and (2), it becomes easier to suppress aberration fluctuations due to zooming. In particular, by satisfying conditional expression (3), it becomes easy to suppress the occurrence of axial chromatic aberration in the near infrared region.
[0010]
Here, in the zoom lens according to the present invention, it is preferable that at least one aspherical lens is included in the second lens group. Thereby, there is an advantage that spherical aberration can be easily corrected.
[0011]
In the zoom lens according to the present invention, for example, the first lens group includes, in order from the object side, a negative first meniscus lens having a convex surface facing the object side and a negative second meniscus lens having a convex surface facing the object side. It can be composed of a concave lens and a positive lens. With such a configuration, the negative power is dispersed to the three negative lenses. Therefore, even if the negative power of the entire first lens unit is increased in order to realize a wide angle, each negative lens has There is an advantage that the radius of curvature is prevented from becoming too small, and that the manufacturing qualities are excellent.
[0012]
The second lens group can be composed of, for example, in order from the object side, a positive lens, a cemented lens composed of a combination of a negative lens and a positive lens, and a negative meniscus lens having a convex surface facing the object side. By including a cemented lens in the second lens group, there is an advantage that it is particularly easy to correct axial chromatic aberration. Further, by arranging the positive lens, the cemented lens, and the negative meniscus lens in this order, there is an advantage that the outer diameter of each lens in the second lens group is easily prevented from increasing.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0014]
1A and 1B are configuration examples of a zoom lens according to an embodiment of the present invention. FIG. 1A shows a lens arrangement at a wide-angle end, and FIG. 3 shows the lens arrangement. This configuration example corresponds to a lens configuration of a first embodiment (FIG. 2) described later. In FIGS. 1 (A) and 1 (B), the reference numeral Ri is assigned such that the surface of the component closest to the object side is the first surface, and the Ri sequentially increases toward the image side (imaging side). It shows the radius of curvature of the i-th (i = 1 to 16) surface. The symbol Di indicates a surface interval on the optical axis between the i-th surface and the (i + 1) -th surface. Simg indicates an imaging position.
[0015]
This zoom lens can be used in both the visible region and the near-infrared region, and is suitably mounted on, for example, a day / night monitoring camera. This zoom lens includes a negative first lens group G1 and a positive second lens group G2 in order from the object side along the optical axis Z1. For example, an image pickup device (not shown) such as a CCD or a CMOS is arranged on an image forming surface Simg of the zoom lens. A cover glass Lc for protecting the imaging surface is disposed between the second lens group G2 and the imaging surface Simg. A stop St is arranged between the first lens group G1 and the positive second lens group G2.
[0016]
This zoom lens performs magnification by moving the first lens group G1 and the second lens group G2 on the optical axis. More specifically, as the magnification is changed from the wide-angle end to the telephoto end, the first lens group G1 moves to the image plane side, and the second lens group G2 moves to the object side.
[0017]
This zoom lens is configured to satisfy the following conditional expressions (1), (2) and (3). In each conditional expression, f1 is the focal length of the first lens group G1, fw is the focal length of the entire system at the wide-angle end, mT is the imaging magnification of the second lens group G2 at the telephoto end, and ν (G2 +) is And the average of the Abbe numbers of the positive lenses included in the second lens group G2.
[0018]
-3.4 <f1 / fw <-3.0 (1)
-1.6 <mT <-1.4 (2)
60 <ν (G2 +) (3)
[0019]
In this zoom lens, for example, the first lens group G1 includes, in order from the object side, a negative first meniscus lens (first lens L1) having a convex surface facing the object side and a negative first meniscus lens having a convex surface facing the object side. It comprises a two meniscus lens (second lens L2), a biconcave lens (third lens L3), and a positive lens (fourth lens L4). The fourth lens L4 is composed of, for example, a positive meniscus lens having a convex surface facing the object side, or a biconvex lens.
[0020]
The second lens group G2 includes, for example, in order from the object side, a cemented lens including a combination of a positive lens (fifth lens L5), a negative lens (sixth lens L6) and a positive lens (seventh lens L7), and a And a negative meniscus lens (eighth lens L8) having a convex surface facing the lens. The cemented lens including the sixth lens L6 and the seventh lens L7 has, for example, a positive power as a whole.
[0021]
It is desirable that the second lens group G2 includes at least one aspheric lens. For example, it is desirable that both surfaces of the fifth lens L5 closest to the object side in the second lens group have an aspheric shape. Further, the image-side surface of the seventh lens L7 may have an aspherical shape.
[0022]
In the second lens group G2, the fifth lens L5 has a biconvex shape near the optical axis, for example. The sixth lens L6 has, for example, a negative meniscus shape with the convex surface facing the object side, and the seventh lens L7 has, for example, a biconvex shape.
[0023]
Next, the operation and effects of the zoom lens configured as described above will be described.
[0024]
This zoom lens is a two-group zoom system, and includes a negative first lens group G1 and a positive second lens group G2 in order from the object side, but the first lens group G1 is used to realize a wide angle. When the negative power of the first lens group G1 is increased, the radius of curvature of the negative lens included in the first lens group G1 decreases, and the suitability for manufacturing tends to deteriorate. Thus, in this zoom lens, the negative power of the entire first lens group is dispersed by dispersing the negative power to three negative lenses (first lens L1 to third lens L3) in the first lens group G1. Even if it is strengthened, the radius of curvature of each negative lens is prevented from becoming too small.
[0025]
In this zoom lens, the second lens group G2 is arranged in the order of a positive lens (fifth lens L5), a cemented lens (sixth lens L6 and seventh lens L7), and a negative meniscus lens (eighth lens L8). The configuration prevents the outer diameter of each lens in the second lens group from increasing.
[0026]
Further, in this zoom lens, since the cemented lens is included in the second lens group G2, longitudinal chromatic aberration can be favorably corrected. In the case where a cemented lens is used, if the radius of curvature of the cemented surface is too small, the suitability for production is deteriorated. Therefore, in this zoom lens, the negative power in the second lens group G2 is distributed to the sixth lens L6 and the eighth lens L8, so that the radius of curvature of the cemented surface is prevented from becoming too small, and deterioration in manufacturing suitability is prevented. In. At the same time, spherical aberration at the telephoto end is easily corrected.
[0027]
Further, in this zoom lens, by providing at least one aspherical lens at a portion where the ray height becomes high in the second lens group G2, spherical aberration can be sufficiently corrected over the entire zooming range, and the number of lenses can be further reduced. Reduction is also possible.
[0028]
Conditional expression (1) defines an appropriate range of a ratio f1 / fw between the focal length f1 of the first lens group G1 and the focal length fw of the entire system at the wide-angle end. When the value exceeds the upper limit of conditional expression (1), the negative power of the first lens group G1 becomes too strong, and it becomes difficult to correct spherical aberration. If the lower limit is exceeded, sufficient back focus cannot be obtained.
[0029]
Conditional expression (2) defines an appropriate range of the imaging magnification mT of the second lens group G2 at the telephoto end. If the upper limit of conditional expression (2) is exceeded, it will be difficult to sufficiently correct aberration fluctuations caused by zooming. If the lower limit is exceeded, distortion at the wide-angle end increases.
[0030]
Conditional expression (3) defines an appropriate range of the average Abbe number ν (G2 +) of the positive lenses included in the second lens group G2. If the lower limit of conditional expression (3) is exceeded, axial chromatic aberration will increase. By appropriately selecting the glass type so as to satisfy the conditional expression (3), it is possible to preferably correct axial chromatic aberration particularly from the visible region to the near infrared region. As a result, a lens for both visible and near-infrared regions can be easily realized.
[0031]
As described above, according to the zoom lens according to the present embodiment, particularly in the two-unit zoom system lens including the negative first lens unit G1 and the positive second lens unit G2 in order from the object side, By appropriately arranging the lenses of each group so as to satisfy the expressions (1) and (2), it is possible to obtain a lens system having a high zoom ratio and high performance over the entire zoom range, with a small number of components. Can be. In particular, by appropriately selecting the glass type so as to satisfy the conditional expression (3), longitudinal chromatic aberration can be favorably corrected from the visible region to the near infrared region. As a result, despite being a relatively small lens type of the two-unit zoom system, it is possible to realize a higher zoom ratio than before and to perform aberration correction satisfactorily from the visible region to the near infrared region.
[0032]
【Example】
Next, specific numerical examples of the zoom lens according to the present embodiment will be described. Hereinafter, first to fourth numerical examples (Examples 1 to 4) will be described together. 2A and 2B show specific lens data corresponding to the configuration of the zoom lens shown in FIG. FIGS. 3A, 3B to 5A and 5B show lens data according to Examples 2 to 4, and the basic configuration of the zoom lens according to Examples 2 to 4 is shown in FIG. Is the same as the zoom lens shown in FIG. FIGS. 2A to 5A show basic data portions of the lens data of the embodiment, and FIGS. 2B to 5B show data relating to the aspherical shape. Show.
[0033]
In the column of the surface number Si in the lens data shown in each figure, the zoom lens of each embodiment has a code such that the surface of the component closest to the object side is the first, and the number increases sequentially toward the image side. The number of the attached i-th (i = 1 to 16) surface is shown. In the column of the radius of curvature Ri, the value of the radius of curvature of the i-th surface from the object side is shown in association with the symbol Ri attached in FIG. The column of the surface distance Di also shows the distance on the optical axis between the i-th surface Si and the (i + 1) -th surface Si + 1 from the object side, corresponding to the reference numerals given in FIG. The units of the values of the radius of curvature Ri and the surface interval Di are millimeters (mm). The columns of Ndj and νdj show the values of the refractive index and Abbe number of the j-th (j = 1 to 9) lens element from the object side with respect to the d-line (587.6 nm). In the lens data, the value of the radius of curvature Ri is set to 0 in a portion having a flat surface shape.
[0034]
Each lens data also shows the focal length f (mm), F value (FNO.), And back focus Bf (mm) of the entire system from the wide-angle end to the telephoto end. In the zoom lens of each embodiment, the value of the surface distance D8 changes with the magnification. In each lens data, a value at the wide-angle end (WIDE) and the value at the telephoto end (TELE) are representatively shown as the surface distance D8.
[0035]
In each lens data, the symbol “*” attached to the left side of the surface number indicates that the lens surface is aspheric. In each embodiment, both surfaces (the ninth surface and the tenth surface) of the fifth lens L5 are aspherical. In the basic lens data, numerical values of the radius of curvature near the optical axis (paraxial region) are shown as the radius of curvature of these aspheric surfaces.
[0036]
In the numerical values of each aspherical surface data, the symbol “E” indicates that the following numerical value is a “power exponent” with a base of 10, and the numerical value represented by the exponential function with the base of 10 is “ Indicates that the value before E "is multiplied. For example, “1.0E-02” indicates “1.0 × 10 ⁻² ”.
[0037]
In each aspherical surface data, the value of each coefficient A _i , κ in the aspherical surface expression represented by the following expression (A) is described.
However,
h: Height in the direction perpendicular to the optical axis (mm)
X: length (mm) of a perpendicular line drawn from a point on the aspherical surface at a height h from the optical axis to a tangent plane (a plane perpendicular to the optical axis) of the apex of the aspherical surface
r: paraxial radius of curvature (mm)
κ: Conic coefficient A _i : i-th order (i = 4, 6, 8, 10) aspherical coefficient
(Equation 1)

[0039]
FIG. 6 shows values corresponding to the above-mentioned conditional expressions (1) to (3) for each embodiment. As shown in FIG. 6, the value of each embodiment is within the range of conditional expressions (1) to (3).
[0040]
FIGS. 7A to 7C show spherical aberration, astigmatism, and distortion (distortion) at the wide-angle end in the zoom lens according to the first embodiment. 8A to 8C show spherical aberration, astigmatism, and distortion at the telephoto end. Each aberration diagram shows the aberration with the d-line as the reference wavelength, but the spherical aberration also shows the aberration in the near infrared region (880 nm). In the astigmatism diagram, the solid line shows the aberration in the sagittal direction, and the broken line shows the aberration in the tangential direction.
[0041]
Similarly, FIGS. 9A to 9C (wide-angle end) and FIGS. 10A to 10C (telephoto end) show various aberrations in the second embodiment, and show various aberrations in the third embodiment. 11 (A) to 11 (C) (wide angle end) and FIGS. 12 (A) to 12 (C) (telephoto end). FIGS. 13 (A) to 13 (C) (wide angle end) 14 (A) to 14 (C) (telephoto end).
[0042]
As can be seen from the lens data and the aberration diagrams described above, in each example, a higher zoom ratio of about 4.7 times than that of the related art was realized, and the aberrations were excellent in the visible region to the near infrared region. Corrections have been made.
[0043]
The present invention is not limited to the above embodiment and each example, and various modifications can be made. For example, the values of the radius of curvature, the surface spacing, the refractive index, and the like of each lens component are not limited to the values shown in each of the numerical examples, and may take other values.
[0044]
【The invention's effect】
As described above, according to the zoom lens according to any one of claims 1 to 3, a two-unit zoom including the negative first lens unit and the positive second lens unit in order from the object side. Since the lens arrangement of each group and selection of the glass type are appropriately performed by satisfying the conditional expressions (1) to (3), a relatively small lens type of the two-group zoom system Nevertheless, it is possible to realize a higher zoom ratio than before and to perform aberration correction satisfactorily from the visible region to the near infrared region.
[0045]
In particular, according to the zoom lens of the second aspect, since at least one aspherical lens is included in the second lens group, spherical aberration can be sufficiently corrected over the entire zooming range, Further, the number of lenses can be reduced.
[Brief description of the drawings]
FIG. 1 illustrates a configuration example of a zoom lens according to an embodiment of the present invention, and is a lens cross-sectional view corresponding to Example 1.
FIG. 2 is a diagram showing lens data of a zoom lens according to Embodiment 1 of the present invention.
FIG. 3 is a diagram showing lens data of a zoom lens according to Embodiment 2 of the present invention.
FIG. 4 is a diagram showing lens data of a zoom lens according to Embodiment 3 of the present invention.
FIG. 5 is a diagram showing lens data of a zoom lens according to Embodiment 4 of the present invention.
FIG. 6 is a diagram illustrating values of conditional expressions satisfied by zoom lenses according to Examples 1 to 4.
FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to Example 1.
FIG. 8 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens according to Example 1.
FIG. 9 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion at a wide angle end of the zoom lens according to the second embodiment.
FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens according to Example 2.
FIG. 11 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion at a wide-angle end of the zoom lens according to Example 3;
FIG. 12 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens according to Example 3.
FIG. 13 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion at a wide-angle end of a zoom lens according to Example 4;
FIG. 14 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens according to Example 4.
[Explanation of symbols]
G1: first lens group, G2: second lens group, Lc: cover glass, Z1: optical axis, L1 to L8: first to eighth lenses.

Claims (3)

In order from the object side, a negative first lens group and a positive second lens group are provided.
Zooming is performed by moving the first lens group and the second lens group on the optical axis,
A zoom lens characterized by satisfying the following conditional expressions (1), (2) and (3).
-3.4 <f1 / fw <-3.0 (1)
-1.6 <mT <-1.4 (2)
60 <ν (G2 +) (3)
However,
f1: focal length fw of the first lens group: focal length mT of the entire system at the wide-angle end: imaging magnification ν (G2 +) of the second lens group at the telephoto end: Abbe number of the positive lens included in the second lens group average The zoom lens according to claim 1, wherein the second lens group includes at least one aspheric lens. The first lens group includes, in order from the object side, a negative first meniscus lens having a convex surface facing the object side, a negative second meniscus lens having a convex surface facing the object side, a biconcave lens, and a positive lens. Become
The second lens group includes, in order from the object side, a positive lens, a cemented lens composed of a combination of a negative lens and a positive lens, and a negative meniscus lens having a convex surface facing the object side. 3. The zoom lens according to 1 or 2.

Images