JP2005010623A - Zoom lens and imaging apparatus provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain a small-sized zoom lens while securing a desired zooming ratio and a desired telecentric performance. <P>SOLUTION: As for the zoom lens provided with a 1st lens group L1 having negative refractive power, a 2nd lens group L2 having positive refractive power and a 3rd lens group L3 having positive refractive power in this order from an object side to an image side, for zooming by shifting each lens group, the 1st lens group L1 is constituted of a negative lens 11 and a positive lens 12, the 2nd lens group L2 is constituted of a biconvex positive lens 21 and a negative lens 22 which has a concave face on the image side and which is constituted so that the absolute value of the refractive power of the face on the image side is larger than that on the object side. And the focal length of the 2nd lens group and a distance between the 2nd lens group and the 3rd lens group at a wide angle end are appropriately set. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

で表される。但しＲは近軸曲率半径、Ｂ，Ｃは非球面係数、ｋは円錐定数である。
【００５０】
又、「Ｄ−Ｘ」は「×１０^−Ｘ」を意味している。前述の各条件式と数値実施例における諸数値との関係を表−１に示す。
【００５１】
【外２】

【００５２】
【外３】

【００５３】
【外４】

【００５４】
【表１】

【００５５】
以上説明した本実施形態のズームレンズによれば、固体撮像素子を用いた撮影系に好適な、構成レンズ枚数が少なくコンパクトで、特に沈胴ズームレンズに適した、変倍比が２〜３倍程度の優れた光学性能を有するズームレンズが実現できる。
【００５６】
又、所定のレンズ群中に効果的に非球面を導入すること、特に第２レンズ群Ｌ２に２面以上の非球面を導入することによって軸外諸収差、特に非点収差・歪曲収差および大口径比化した際の球面収差の補正が効果的に行える。
【００５７】
更に本実施形態のズームレンズによれば、
（ａ）広角端の画角を大きくしながら、高性能、コンパクト化を図ることができる。
（ｂ）広角側での非点収差、歪曲収差を良好に補正することができる。
（ｃ）感度の低い高画素の固体撮像素子に好適なズームレンズとして、大口径比化を図ることができる。
（ｄ）構成枚数を最小としながら、固体撮像素子を用いた撮影系に好適な良好な像側テレセントリック結像をもたせることができる。
（ｅ）広角端のみならずズーム全域で歪曲収差を良好に補正することができる。（ｆ）像側テレセントリック結像のズーミングに伴う変動を小さくすることができる。
（ｇ）テレセントリック結像を保ったまま変倍レンズ群の移動量を減らし、小型化を達成することができる。
（ｆ）フォーカシング機構を簡素化することができる。
等の様々な効果が得られる。
【００５８】
次に本発明のズームレンズを撮影光学系として用いたデジタルスチルカメラの実施形態を図１３を用いて説明する。
【００５９】
図１３において、４０はカメラ本体、４１は本発明のズームレンズによって構成された撮影光学系、４２はカメラ本体に内蔵され、撮影光学系４１によって形成された被写体像を受光するＣＣＤセンサやＣＭＯＳセンサ等の固体撮像素子（光電変換素子）、４３は固体撮像素子４２によって光電変換された被写体像に対応する情報を記録するメモリ、４４は液晶ディスプレイパネル等によって構成され、固体撮像素子４２上に形成された被写体像を観察するためのファインダである。
【００６０】
このように本発明のズームレンズをデジタルスチルカメラ等の光学機器に適用することにより、小型で高い光学性能を有する光学機器が実現できる。
【００６１】
【発明の効果】
以上説明したように、本発明のズームレンズは、各レンズ群の構成枚数を削減すると共に、所望の変倍比を確保しつつ変倍レンズ群の移動量も減らして小型化を実現することができる。しかも所望のテレセントリック性も維持できる。
【図面の簡単な説明】
【図１】実施形態１のズームレンズのレンズ断面図である。
【図２】実施形態１のズームレンズの広角端における収差図である。
【図３】実施形態１のズームレンズの中間ズーム位置における収差図である。
【図４】実施形態１のズームレンズの望遠端における収差図である。
【図５】実施形態２のズームレンズのレンズ断面図である。
【図６】実施形態２のズームレンズの広角端における収差図である。
【図７】実施形態２のズームレンズの中間ズーム位置における収差図である。
【図８】実施形態２のズームレンズの望遠端における収差図である。
【図９】実施形態３のズームレンズのレンズ断面図である。
【図１０】実施形態３のズームレンズの広角端における収差図である。
【図１１】実施形態３のズームレンズの中間ズーム位置における収差図である。
【図１２】実施形態３のズームレンズの望遠端における収差図である。
【図１３】デジタルスチルカメラの要部概略図である。
【符号の説明】
Ｌ１ 第１レンズ群
Ｌ２ 第２レンズ群
Ｌ３ 第３レンズ群
ＳＰ 開口絞り
ＩＰ 像面
Ｇ ガラスブロック
ｄ ｄ線
ｇ ｇ線
ΔＳ サジタル像面
ΔＭ メリディオナル像面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens, and is particularly suitable for a photographing optical system such as a video camera or a digital still camera.
[0002]
[Prior art]
Recently, with the enhancement of functionality of imaging devices (cameras) such as video cameras and digital still cameras using solid-state imaging devices such as CCD sensors and CMOS sensors, the shooting optical system used for them has a large aperture that includes a wide angle of view. Ratio zoom lenses are needed.
[0003]
In this type of camera, various optical members such as an optical low-pass filter and a color correction filter are arranged between the rearmost part of the lens and the image sensor, so that the photographing optical system used therefor has a relatively long back focus. A lens system is required. Furthermore, in the case of a color camera using an image pickup device for color images, in order to avoid color shading, an optical system with good telecentric characteristics on the image side is desired.
[0004]
Conventionally, a two-group zoom of a so-called short zoom type, which is composed of two lens groups, a first lens group having a negative refractive power and a second lens group having a positive refractive power, and performing zooming by changing the distance between the two lenses. Various lenses have been proposed. In these short zoom type zoom lenses, zooming is performed by moving the second lens unit having a positive refractive power, and image point positions associated with zooming are moved by moving the first lens unit having a negative refractive power. Correction is performed. In the lens configuration composed of these two lens groups, the zoom magnification is about twice.
[0005]
Further, in order to collect the entire lens into a compact shape while having a high zoom ratio of 2 times or more, for example, in Patent Document 1 and Patent Document 2, the negative or positive refractive power on the image side of the two-group zoom lens is A so-called three-group zoom lens has been proposed in which a three-lens group is arranged and various aberrations that occur as the magnification increases are corrected.
[0006]
For example, Patent Document 3 and Patent Document 4 propose a three-group zoom lens that satisfies back focus and telecentric characteristics. Further, in Patent Document 5, the first lens group having a negative refractive power is fixed in the three-group zoom lens, and the second lens group having a positive refractive power and the third lens group having a positive refractive power are moved. An optical system for performing magnification is also disclosed.
[0007]
In recent years, for example, Patent Document 6, Patent Document 7, Patent Document 8, Patent Document 9 and the like have been proposed as a three-group zoom lens with a small number of lenses. In these conventional examples, the first lens group is composed of two lenses, a negative lens and a positive lens, the second lens group is composed of two lenses, a positive lens and a negative lens, and the third lens group is 1 An embodiment is disclosed in which the number of lenses constituting each lens group composed of a single positive lens is small.
[0008]
[Patent Document 1]
Japanese Patent Publication No. 7-3507 [Patent Document 2]
Japanese Patent Publication No. 6-40170 [Patent Document 3]
JP 63-135913 A [Patent Document 4]
JP-A-7-261083 [Patent Document 5]
JP-A-3-288113 [Patent Document 6]
JP-A-9-258103 [Patent Document 7]
JP-A-10-213745 [Patent Document 8]
JP-A-11-84243 [Patent Document 9]
Japanese Patent Laid-Open No. 2002-14284
[Problems to be solved by the invention]
Since the three-group zoom lens disclosed in Patent Document 1 and Patent Document 2 is designed mainly for 35 mm film photography, the back focus length required for an optical system using a solid-state imaging device and good telecentric characteristics are provided. It was hard to say that they were compatible.
[0010]
In addition, the zoom lenses disclosed in Patent Documents 3 to 5 have drawbacks such as a relatively large number of lenses in each lens group, a long overall lens length, and a high manufacturing cost.
[0011]
On the other hand, the zoom lenses disclosed in Patent Document 7, Patent Document 8, and Patent Document 9 have a small number of lenses, but the power of the second lens group that performs the main zooming function is relatively weak. The amount of movement of the second lens group is large, which is disadvantageous for shortening the total lens length.
[0012]
Furthermore, the zoom lens of Patent Document 7 has a narrow interval between the second lens group and the third lens group at the wide-angle end, and the zoom lens of Patent Document 6 has a glass block disposed on the object side of the third lens group. For this reason, when focusing is performed with the third lens group that is most advantageous in terms of space efficiency, the imageable range is narrowed.
[0013]
In the present invention, in consideration of the problems of these conventional examples, the number of components of each lens group is reduced, and the amount of movement of the variable magnification lens group is also reduced while ensuring a desired variable magnification ratio, thereby realizing miniaturization. In addition, an object of the present invention is to provide a zoom lens that maintains desired telecentricity.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, a zoom lens according to the present invention includes, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens having a positive refractive power. In a zoom lens having a group and performing zooming by moving each lens group, the first lens group is composed of one negative lens and one positive lens, and the second lens group is formed in a biconvex shape in order. And a negative lens whose image side surface is concave and whose refractive power is larger than that of the object side surface. When the focal length of the system is fw, the focal length of the second lens group is f2, and the distance between the second lens group and the third lens group at the wide angle end is L2w,
1.0 <f2 / fw <1.9
0.4 <L2w / fw <1.3
It is characterized by satisfying the following conditions.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a zoom lens of the present invention and an image pickup apparatus using the same will be described with reference to the drawings.
[0016]
FIG. 1 is a lens cross-sectional view of the zoom lens according to the first embodiment. 2 to 4 are aberration diagrams of the zoom lens according to Embodiment 1 at the wide-angle end, the intermediate zoom position, and the telephoto end. The first embodiment is a zoom lens having a zoom ratio (magnification ratio) of 2.0 times and an F number of 2.9 (wide angle end) to 4.3 (telephoto end).
[0017]
FIG. 5 is a lens cross-sectional view of the zoom lens according to the second embodiment. 6 to 8 are aberration diagrams of the zoom lens according to Embodiment 2 at the wide-angle end, the intermediate zoom position, and the telephoto end. The second embodiment is a zoom lens having a zoom ratio (magnification ratio) of 2.9 times and an F number of 2.9 (wide angle end) to 5.5 (telephoto end).
[0018]
FIG. 9 is a lens cross-sectional view of the zoom lens according to the third embodiment. 10 to 12 are aberration diagrams of the zoom lens according to Embodiment 3 at the wide-angle end, the intermediate zoom position, and the telephoto end. Embodiment 3 is a zoom lens having a zoom ratio (magnification ratio) of 2.9 times and an F number of 2.9 (wide angle end) to 5.6 (telephoto end).
[0019]
In the lens cross-sectional views of the embodiments, L1 is a first lens unit having a negative refractive power (optical power = reciprocal of focal length), L2 is a second lens unit having a positive refractive power, and L3 is a positive refractive power. The third lens group, SP is an aperture stop, IP is an image plane, and a photosensitive surface of a solid-state imaging device such as a CCD sensor or a CMOS sensor is disposed. G is a glass block provided by design corresponding to a crystal low-pass filter, an infrared cut filter, or the like. In each lens cross-sectional view, the left side is the object side (front), and the right side is the image side (rear).
[0020]
Hereinafter, the configuration and operation of the zoom lens of the present embodiment (the zoom lenses of Embodiments 1 to 3 are collectively referred to as the zoom lens of the present embodiment) will be described.
[0021]
In the zoom lens of this embodiment, during zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves substantially reciprocally along a locus convex to the image side, the second lens unit L2 moves to the object side, and the third lens The group L3 moves to the image side. The main zooming is performed by the movement of the second lens unit L2, and the image point is moved along with the zooming by the substantially reciprocating movement of the first lens unit L1 and the movement of the third lens unit L3 in the image side direction. It is corrected.
[0022]
The third lens unit L3 shares the increase in the refractive power of the entire zoom lens system as the image sensor is downsized. Due to the action of the third lens unit L3, the refractive power of a so-called short zoom system constituted by the first lens unit L1 and the second lens unit L2 can be reduced, and in particular, the lens constituting the first lens unit L1. This suppresses the occurrence of aberrations and achieves good optical performance. Further, the telecentricity on the image side that is particularly necessary for an imaging apparatus using a solid-state imaging device or the like is achieved by providing the third lens unit L3 with the role of a field lens.
[0023]
The aperture stop SP is disposed on the most object side of the second lens unit L2 (between the first lens unit L1 and the second lens unit L2). Thereby, the distance between the entrance pupil on the wide angle side and the first lens unit L1 is shortened, and an increase in the outer diameter of the lenses constituting the first lens unit L1 is suppressed. Further, since it is possible to set the first lens unit L1 and the third lens unit L3 so as to cancel various off-axis aberrations with the aperture stop SP interposed therebetween, it is good without increasing the number of constituent lenses of each lens unit. Has obtained excellent optical performance.
[0024]
Next, the configuration of each lens group will be described.
[0025]
The first lens unit L1 includes two lenses, a negative lens and a positive lens. The second lens unit L2, in order from the object side to the image side, has a biconvex positive lens, and the image side surface has a concave shape, and the absolute value of the refractive power of the concave surface is larger than that of the object side surface. It is composed of two negative lenses.
[0026]
The configuration of each lens group will be described in more detail. The first lens group L1 has a concave surface on the image side in order from the object side to the image side, and the absolute value of the refractive power of the concave surface is the surface on the object side. The negative lens 11 is larger than the negative lens 11 and the meniscus positive lens 12 is convex on the object side. The negative lens 11 is a meniscus lens in the first and third embodiments, and a biconcave lens in the second embodiment.
[0027]
The second lens unit L2, in order from the object side to the image side, has a biconvex positive lens 21 whose refractive power is larger on the object side than the image side, and has a concave surface on the image side. The negative lens 22 has a larger absolute value of refractive power than the object side surface. The negative lens 22 is a biconcave lens in the first embodiment, and is a meniscus lens in the second and third embodiments.
[0028]
The third lens unit L3 includes a positive lens 31. In the first embodiment, the object side has a convex meniscus lens, and in the second and third embodiments, the absolute value of refractive power is on the image side compared to the object side. It is a large biconvex lens. In the first to third embodiments, the third lens unit L3 is configured by only one positive lens, but may be configured by one or more lenses such as a cemented lens.
[0029]
The first lens unit L1 has a role of forming an off-axis chief ray in the center of the aperture stop SP and forms an off-axis aberration, particularly on the wide-angle side, since the refraction amount of the off-axis chief ray is large. Astigmatism and distortion are likely to occur. Therefore, in the present embodiment, the first lens unit L1 is composed of the negative lens 11 and the positive lens 12 that can suppress the increase in the lens diameter closest to the object side, as in the case of a normal wide-angle lens.
[0030]
Further, by making the lens surface on the image side of the negative lens 11 having a meniscus shape an aspherical surface in which the negative refractive power is weak at the periphery, astigmatism and distortion are corrected in a well-balanced manner, and the number of the two is small. The first lens unit L1 is configured by the number of lenses, which contributes to downsizing.
[0031]
Each of the lenses constituting the first lens unit L1 has a concentric spherical surface centered at a point (pupil center) where the aperture stop SP intersects the optical axis in order to suppress the occurrence of off-axis aberration caused by refraction of the off-axis principal ray. A shape close to is adopted.
[0032]
Next, in the second lens unit L2, the biconvex positive lens 21 having a large refractive power on the object side is disposed on the object side, thereby reducing the refraction angle of the off-axis chief ray emitted from the first lens unit L1. The occurrence of various off-axis aberrations is suppressed.
[0033]
Further, the positive lens 21 is a lens that has the highest height for passing on-axis rays, and is a lens that is mainly involved in correction of spherical aberration and coma aberration. Therefore, in the present embodiment, spherical aberration and coma aberration are favorably corrected by making the object side surface of the positive lens 21 an aspherical surface in which the positive refractive power becomes weak at the periphery. Further, in the first and second embodiments, spherical aberration and coma are corrected more satisfactorily by making the lens surfaces on both sides of the positive lens 21 aspherical.
[0034]
On the other hand, the shape of the negative lens 22 arranged on the image side of the positive lens 21 is a shape that follows the surface on the image side, and the refractive power of the concave surface is made larger than that on the object side. Aberrations that occur on the surface are canceled. Further, by making the image side surface of the negative lens 22 an aspherical surface in which the negative refracting power becomes stronger in the periphery, the curvature of field in particular is corrected more favorably.
[0035]
The third lens unit L3 is configured by the meniscus or biconvex positive lens 31 as described above, and has a role as a field lens for image side telecentricity.
[0036]
Here, when the back focus is sk ′, the focal length of the third lens unit L3 is f3, and the imaging magnification of the third lens unit L3 is β3,
sk ′ = f3 (1-β3)
The relationship is established.
However,
0 <β3 <1.0
It is.
[0037]
Here, during zooming from the wide-angle end to the telephoto end, when the third lens unit L3 moves to the image side, the back focus sk ′ decreases, and the imaging magnification β3 of the third lens unit L3 increases on the telephoto side. To do. That is, when the third lens unit L3 is moved to the image side during zooming, the third lens unit L3 eventually shares the zooming action. As a result, the amount of movement of the second lens unit L2, which is the main variable power group, can be reduced, so that a space for movement of the second lens unit L2 can be saved, contributing to downsizing of the entire system.
[0038]
In the case of shooting by changing the subject distance from an infinitely distant object to a close object using the zoom lens of this embodiment, good performance can be obtained by moving the first lens unit L1 to the object side and performing focusing. However, it is more desirable to move the third lens unit L3 to the object side.
[0039]
This is to prevent an increase in the front lens diameter that occurs when the first lens unit L1 disposed closest to the object side is focused, and an increase in the load on the actuator that moves the first lens unit L1 having the heaviest lens weight. is there. Further, when the first lens unit L1 is released from the focus function, the first lens unit L1 and the second lens unit L2 can be simply linked by a cam or the like and moved during zooming, thereby simplifying the mechanical structure. This is because an improvement in accuracy can be achieved.
[0040]
Further, when performing focusing with the third lens unit L3, during zooming from the wide-angle end to the telephoto end, as described above, the third lens unit L3 is moved to the image side, so that at the telephoto end where the amount of focusing movement is large. The third lens unit L3 is located closer to the image side. Therefore, it is possible to minimize the total amount of movement of the third lens unit L3 required for zooming and focusing, and as a result contributes to downsizing of the entire system.
[0041]
As described above, by making each lens group have a lens configuration that achieves both desired refractive power arrangement and aberration correction, the entire system can be made compact while maintaining good performance.
[0042]
Further, the zoom lens according to the present embodiment satisfies the following conditions in order to obtain good optical performance and to reduce the size of the entire lens system.
[0043]
(1-1) The following conditions are preferable for shortening the overall lens length of the optical system.
1.0 <f2 / fw <1.9 (1)
Here, f2 is the focal length of the second lens unit L2, and fw is the focal length at the wide-angle end of the entire system.
[0044]
Exceeding the upper limit of conditional expression (1) is not preferable because the amount of movement of the second lens unit L2 during zooming increases and the overall length of the optical system becomes longer. On the other hand, when the lower limit value of conditional expression (1) is exceeded, the total length of the optical system becomes short, but the focal length of the second lens unit L2 becomes too short, and aberration correction over the entire zoom range becomes difficult, which is not preferable.
[0045]
(1-2) The following conditions are preferable for securing the overall length of the optical system and the focusing range.
0.4 <L2w / fw <1.3 (2)
Here, L2w is an interval between the second lens unit L2 and the third lens unit L3 at the wide angle end.
[0046]
Exceeding the upper limit value of conditional expression (2) is not preferable because the distance between the second lens unit L2 and the third lens unit L3 increases more than necessary, and the total lens length increases. On the other hand, when the lower limit value of conditional expression (2) is exceeded, the movable range by focusing becomes narrow, so that the closest distance that can be photographed becomes long, and the effect of the field lens by the third lens unit L3 decreases, and the image side This is not desirable because it is no longer telecentric.
[0047]
(1-3) The following are preferable conditions for suppressing performance deterioration due to manufacturing errors while reducing the size.
−1.5 <(R22b + R22a) / (R22b−R22a) <− 0.2
... (3)
Here, R22a is the radius of curvature of the object side surface of the negative lens 22 in the second lens unit L2, and R22b is the radius of curvature of the image side surface of the negative lens 22.
[0048]
If the upper limit value of conditional expression (3) is exceeded, the effect of positioning the rear principal point of the second lens unit L2 on the object side by the negative lens 22 is reduced, and the total lens length increases, which is not preferable. On the other hand, if the lower limit value of conditional expression (3) is exceeded, the change in performance when the negative lens 22 is decentered due to manufacturing errors increases, which is not preferable.
[0049]
The numerical data of Numerical Examples 1 to 3 corresponding to Embodiments 1 to 3 are shown below. In each numerical example, f represents a focal length, fno represents an F number, and ω represents a half angle of view. i indicates the order of the surfaces from the object side, ri is the radius of curvature of the i-th surface, di is the distance between the i-th surface and the (i + 1) -th surface, ni and νi are the refractive index and Abbe number for the d-line, respectively. Show. The two surfaces closest to the image side correspond to a crystal low-pass filter, an infrared cut filter, and the like, and are glass blocks G provided by design. An aspherical shape is when the displacement in the direction of the optical axis at the position of the height H from the optical axis is x with respect to the vertex of the surface.

It is represented by However, R is a paraxial radius of curvature, B and C are aspherical coefficients, and k is a conic constant.
[0050]
“D−X” means “× 10 ^−X ”. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.
[0051]
[Outside 2]

[0052]
[Outside 3]

[0053]
[Outside 4]

[0054]
[Table 1]

[0055]
According to the zoom lens of the present embodiment described above, the zoom ratio is about 2 to 3 times, which is suitable for an imaging system using a solid-state imaging device, is compact with a small number of constituent lenses, and particularly suitable for a retractable zoom lens. A zoom lens having excellent optical performance can be realized.
[0056]
Further, by effectively introducing an aspheric surface into a predetermined lens group, in particular, by introducing two or more aspheric surfaces into the second lens group L2, various off-axis aberrations, particularly astigmatism / distortion aberration and large aberrations. It is possible to effectively correct spherical aberration when the aperture ratio is made.
[0057]
Furthermore, according to the zoom lens of the present embodiment,
(A) High performance and compactness can be achieved while increasing the angle of view at the wide-angle end.
(B) Astigmatism and distortion on the wide angle side can be corrected satisfactorily.
(C) As a zoom lens suitable for a low-sensitivity high-pixel solid-state imaging device, a large aperture ratio can be achieved.
(D) Good image-side telecentric imaging suitable for an imaging system using a solid-state imaging device can be provided while minimizing the number of components.
(E) Distortion can be favorably corrected not only at the wide-angle end but also in the entire zoom range. (F) It is possible to reduce fluctuations associated with zooming of image side telecentric imaging.
(G) It is possible to reduce the amount of movement of the variable power lens group while maintaining telecentric imaging and achieve miniaturization.
(F) The focusing mechanism can be simplified.
Various effects such as are obtained.
[0058]
Next, an embodiment of a digital still camera using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG.
[0059]
In FIG. 13, reference numeral 40 denotes a camera body, 41 denotes a photographing optical system constituted by the zoom lens of the present invention, and 42 denotes a CCD sensor or CMOS sensor built in the camera body and receiving a subject image formed by the photographing optical system 41. A solid-state imaging device (photoelectric conversion device) such as 43, a memory 43 for recording information corresponding to a subject image photoelectrically converted by the solid-state imaging device 42, and a liquid crystal display panel 44 are formed on the solid-state imaging device 42. It is a finder for observing the subject image.
[0060]
In this way, by applying the zoom lens of the present invention to an optical apparatus such as a digital still camera, a small-sized optical apparatus having high optical performance can be realized.
[0061]
【The invention's effect】
As described above, the zoom lens according to the present invention can achieve downsizing by reducing the number of constituent elements of each lens group and reducing the amount of movement of the zoom lens group while ensuring a desired zoom ratio. it can. Moreover, the desired telecentricity can be maintained.
[Brief description of the drawings]
FIG. 1 is a lens cross-sectional view of a zoom lens according to a first embodiment.
FIG. 2 is an aberration diagram at the wide-angle end of the zoom lens according to Embodiment 1;
FIG. 3 is an aberration diagram at an intermediate zoom position of the zoom lens according to the first embodiment;
FIG. 4 is an aberration diagram at a telephoto end of the zoom lens according to Embodiment 1;
FIG. 5 is a lens cross-sectional view of a zoom lens according to a second embodiment.
6 is an aberration diagram at a wide-angle end of the zoom lens according to Embodiment 2; FIG.
FIG. 7 is an aberration diagram at an intermediate zoom position of the zoom lens according to the second embodiment.
FIG. 8 is an aberration diagram at a telephoto end of the zoom lens according to the second embodiment.
9 is a lens cross-sectional view of a zoom lens according to Embodiment 3. FIG.
FIG. 10 is an aberration diagram at a wide-angle end of the zoom lens according to Embodiment 3;
FIG. 11 is an aberration diagram for the zoom lens of Embodiment 3 at an intermediate zoom position.
FIG. 12 is an aberration diagram at a telephoto end of a zoom lens according to Embodiment 3;
FIG. 13 is a schematic diagram of a main part of a digital still camera.
[Explanation of symbols]
L1 First lens unit L2 Second lens unit L3 Third lens unit SP Aperture stop IP Image plane G Glass block d d line g g line ΔS Sagittal image plane ΔM Meridional image plane

Claims (8)

In order from the object side to the image side, there are a first lens unit having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, and each lens group is moved for zooming. In the zoom lens to be performed, the first lens group includes one negative lens and one positive lens, and the second lens group includes one positive lens having a biconvex shape in order from the object side to the image side. And a single negative lens having a concave surface on the image side and an absolute value of the refractive power of the image side surface larger than that of the object side surface, and the focal point of the entire system at the wide angle end. When the distance is fw, the focal length of the second lens group is f2, and the distance between the second lens group and the third lens group at the wide angle end is L2w,
1.0 <f2 / fw <1.9
0.4 <L2w / fw <1.3
A zoom lens characterized by satisfying the following conditions: When the radius of curvature of the object side surface of the negative lens in the second lens group is R22a and the radius of curvature of the image side surface is R22b,
−1.5 <(R22b + R22a) / (R22b−R22a) <− 0.2
The zoom lens according to claim 1, wherein the following condition is satisfied. During zooming from the wide-angle end to the telephoto end, the first lens group moves along a convex locus toward the image side, the second lens group moves monotonously toward the object side, and the third lens group moves toward the image side. The zoom lens according to claim 1, wherein the zoom lens moves. The zoom lens according to claim 1, wherein the positive lens in the second lens group has two aspheric surfaces. The zoom lens according to claim 1, wherein at least one surface of the negative lens in the second lens group is an aspherical surface. 6. The zoom lens according to claim 1, wherein the third lens unit moves toward the object side during focusing from an infinitely distant object to a close object. The zoom lens according to claim 1, wherein an image is formed on a photosensitive surface of the photoelectric conversion element. An image pickup apparatus comprising: the zoom lens according to claim 1; and a photoelectric conversion element that receives an image formed by the zoom lens.

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