JP2001066503A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens whose entire length is shortened, which is suitable for an electronic still camera excellent in portability, which consists of three groups and where chromatic aberration is excellently compensated. SOLUTION: This zoom lens is provided with a 1st group L1 having negative refractive power, a 2nd group L2 having positive refractive power and a 3rd group L3 having positive refractive power in order from an object side. In the case of varying power from a wide-angle end to a telephoto end, a distance between the 1st and the 2nd groups L1 and L2 is shortened and a distance between the 2nd and the 3rd groups L2 and L3 is widened. The 1st group L1 is provided with a meniscus negative lens whose concave surface faces to an image surface side and a meniscus positive lens whose convex surface faces to the object side, and the 2nd group L2 is provided with a combined lens A consisting of a negative lens and a positive lens and having positive refractive power as a whole on a side nearest to the image surface side, and a lens B nearest to the image surface side out of the lenses on the object side from the lens A, and the lens surface on the image surface side of the lens B has shape that its concave surface faces to the image surface side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a zoom lens system in which a lens unit having a negative refractive power precedes the zoom lens system.
By setting the lens configuration of each of these lens groups appropriately, a wide-angle lens suitable for film still cameras, video cameras, digital still cameras, etc., with the overall size of the lens system reduced. The present invention relates to a zoom lens having an angle of view.

[0002]

2. Description of the Related Art Recently, with the advancement of functions of an imaging device (camera) such as a video camera and a digital still camera using a solid-state imaging device, a high-performance and small-sized zoom lens is required for an optical system used therein. I have. In this type of camera, various optical members such as a low-pass filter and a color correction filter are arranged between the rearmost part of the lens and the image pickup device. Required. Further, in the case of a color camera using an image pickup device for a color image, in order to avoid color shading, an optical system used therefor is desired to have good image-side telecentric characteristics.

Conventionally, there are two lens groups, a first lens group having a negative refractive power and a second lens group having a positive refractive power, and the magnification is changed by changing the distance between both lenses. Various types of so-called short zoom type wide-angle two-unit zoom lenses have been proposed. In these short zoom type optical systems, the second system having a positive refractive power
The zooming is performed by moving the group, and the image point position accompanying the zooming is corrected by moving the first group having a negative refractive power.

[0004] In a lens configuration composed of these two lens groups, the zoom magnification is about twice. 2 more
To combine the entire lens into a compact shape while having a high zoom ratio of 2 times or more, for example, Japanese Patent Publication No. 7-3507,
In Japanese Patent Publication No. 6-40170, a third lens unit having a negative or positive refractive power is arranged on the image side of a two-unit zoom lens to correct various aberrations caused by increasing the magnification. Group zoom lenses have been proposed.

However, since these three-group zoom lenses are designed mainly for 35 mm film photography, they have both a back focus length required for an optical system using a solid-state image sensor and good telecentric characteristics. Was hard to say.

[0006]

A wide-angle three-unit zoom lens system satisfying the back focus and telecentric characteristics is disclosed in, for example, JP-A-63-135913 and JP-A-7-26.
It is proposed in, for example, Japanese Patent Publication No. 1083. Also, JP-A-3-288113
In Japanese Patent Laid-Open Publication No. H10-207, there is also provided an optical system in which a first group having a negative refractive power is fixed and a second group having a positive refractive power and a third group having a positive refractive power are moved to perform zooming. It has been disclosed.
However, in these conventional examples, there are disadvantages such as a relatively large number of components in each lens group, a long overall lens length, and a high manufacturing cost.

In the example described in Japanese Patent Application Laid-Open No. Hei 7-261083, a convex lens (positive lens) is arranged closest to the object side of the first lens unit having a negative refractive power. There was a disadvantage that an increase in outer diameter was inevitable.
Further, in this example, since the first group having negative refractive power is moved to perform focusing on a short-distance object, there is a disadvantage that the mechanical structure is complicated together with the movement during zooming.

Further, US Pat. No. 4,999,007 discloses that
There is also disclosed a three-group zoom lens in which the first lens group and the second lens group are each configured by one single lens. However, the overall length of the lens at the wide-angle end is relatively large, and since the stop is far away from the first lens group at the wide-angle end, the incident height of off-axis rays is large and the diameter of the lens constituting the first lens group increases. Therefore, there is a disadvantage that the entire lens system becomes large.

Further, the first and second lens units have only one component, so that the aberration correction in the lens units is insufficient. In particular, the fluctuation of the chromatic aberration of magnification at the time of zooming is likely to occur in the first group where the fluctuation of the height of the optical axis of the off-axis light beam is large. However, since the first group is one concave lens, correction within the group is performed. However, there is a problem that the chromatic aberration of magnification is large even in the entire system.

Further, as a specific problem when the angle of view at the zoom wide-angle end is increased, there is a problem of insufficient correction of distortion. Further, a larger aperture ratio is required for use in a high-sensitivity imaging device having relatively low sensitivity.

Further, the present applicant has disclosed in Japanese Patent Application No. 10-301684 a photographic lens having a three-group configuration including three lens groups having negative, positive and positive refractive powers. This photographing lens achieves a compact zoom lens by shortening the overall length as much as possible while ensuring both a lens back necessary for inserting a filter and the like and a telecentric characteristic required for a solid-state imaging device.

On the other hand, in recent years, the number of pixels in a solid-state imaging device has been increased, and the pixel size in a specific image size tends to be smaller. Accordingly, a photographing lens is required to have higher resolution at a higher spatial frequency than a conventional lens having the same image size. Japanese Patent Application No. 10-301684
In the lens configuration disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, the second group, which is responsible for most of the convergence action of the entire system, is composed of a positive / negative / positive so-called triplet in order from the object side, thereby achieving both correction of various aberrations and miniaturization. ing.

In the present invention, the present applicant has further improved the zoom lens disclosed in Japanese Patent Application Laid-Open No. 10-301684, which has been proposed above, and has a number of constituent lenses suitable for a photographing system using a solid-state image sensor. It is an object of the present invention to provide a zoom lens that is small, compact, has a high zoom ratio with a reduced diameter, and has particularly good chromatic aberration correction and excellent optical performance.

[0014]

According to a first aspect of the present invention, there is provided a zoom lens having a first unit having a negative refractive power, a second unit having a positive refractive power, and a third unit having a positive refractive power. Wherein the distance between the first group and the second group is reduced at the time of zooming from the wide-angle end to the telephoto end, and the distance between the second group and the third group is widened. A negative meniscus lens having a concave surface on the side, and a positive meniscus lens having a convex surface on the object side. The second group is composed of a negative lens and a positive lens closest to the image surface side, and has a positive lens as a whole. Refractive power cemented lens A
The lens B closest to the image plane among the lenses closer to the object side than the cemented lens A is characterized in that the lens surface on the image plane side has a concave surface facing the image plane side.

According to a second aspect of the present invention, in the first aspect, the focal length of the cemented lens A in the second group is fc, the focal length of the second group is f2, and the object-side lens of the cemented lens A is When the radius of curvature of the surface is Ra and the radius of curvature of the lens surface on the image surface side of the lens B is Rb, 0.5 <fc / f2 <2.0 0.5 <(Ra + Rb) / (Ra-Rb) <2.5 is satisfied.

According to a third aspect of the present invention, in the second aspect, the second group includes, in order from the object side, a positive lens having a convex surface facing the object side, a negative lens having a concave surface facing the image surface side, and a cemented lens. It is characterized by having.

A zoom lens according to a fourth aspect of the present invention has, in order from the object side, a first unit having a negative refractive power, a second unit having a positive refractive power, and a third unit having a positive refractive power. The distance between the first and second groups is reduced at the time of zooming from the zoom lens to the telephoto end, and the distance between the second and third groups is increased. In the zoom lens, the first group has a concave surface facing the image plane side. The second group includes a meniscus-shaped negative lens, a meniscus-shaped positive lens having a convex surface facing the object side, and the second group is disposed on the object side with respect to the negative lens having both concave lens surfaces and on the object side. It is characterized by having a positive lens with a convex surface, and a negative lens and a positive lens disposed on the image side of the negative lens and having a cemented lens having a positive refractive power as a whole.

According to a fifth aspect of the present invention, in the fourth aspect, the focal length of the negative lens in the second group is fn, the focal length of the second group is f2, and the focal length of the negative lens in the second group is closest to the object side. The radius of curvature of the lens surface on the object side of the positive lens having the convex surface facing the object side is Rc, and the radius of curvature of the lens surface on the image surface side is R.
When d, 0.3 <| fn | / f2 <2.00 <(Rd + Rc) / (Rd-Rc) <2.5 is satisfied.

According to a sixth aspect of the present invention, in the third or fifth aspect, the third unit is constituted by one positive lens or a positive cemented lens as a whole, comprising a positive lens and a negative lens. And

According to a seventh aspect of the present invention, in the third or fifth aspect, at least one lens surface of the negative lenses in the first group is an aspheric surface, and the aspheric surface extends from the optical axis toward the periphery. It is characterized in that the divergence gradually weakens.

According to an eighth aspect of the present invention, in the third or fifth aspect, at least one lens surface of the positive lens in the second group is an aspherical surface, and the aspherical surface increases from the optical axis toward the periphery. It is characterized in that the shape is such that the convergence action is weakened.

According to a ninth aspect of the present invention, in the third or fifth aspect, the third unit has a positive lens, at least one lens surface of the positive lens is an aspherical surface, and the aspherical surface is located away from the optical axis. It is characterized in that the convergence effect gradually weakens toward the periphery.

A tenth aspect of the present invention is characterized in that, in the third or fifth aspect, the third lens unit moves upon zooming.

In the zoom lens according to the eleventh aspect of the present invention, the first group having a negative refractive power, the second group having a positive refractive power,
A zoom lens having a third lens unit having a positive refractive power, wherein the distance between the first lens unit and the second lens unit is reduced and the distance between the second lens unit and the third lens unit is widened during zooming from the wide-angle end to the telephoto end. In the first group, a meniscus-shaped negative lens having a concave surface facing the image surface side, a meniscus-shaped positive lens having a convex surface facing the object side, and the second group has one or two lenses in order from the object side. It has a positive lens, a negative lens B with both lens surfaces concave, and a cemented lens A of a negative lens and a positive lens, the focal length of the cemented lens A in the second group being fc, The focal length is f2, the radius of curvature of the lens surface on the object side of the cemented lens A is Ra,
The radius of curvature of the image side surface of the lens B is Rb, the focal length of the lens B in the second group is fn, and the object side surface of the positive lens of the second group which is disposed closest to the object side and has a convex surface facing the object side. Is the radius of curvature of Rc, and the radius of curvature of the lens surface on the image side is Rd.
0.5 <fc / f2 <2.0 0.5 <(Ra + Rb) / (Ra-Rb) <2.5 0.3 <| fn | / f2 <2.00 <(Rd + Rc) /(Rd-Rc)<2.5.

[0025]

FIG. 1 is a lens sectional view of a numerical example 1 of the present invention described later. 2 to 4 are aberration diagrams at the wide-angle end, at the middle, and at the telephoto end in a numerical example of the present invention.

FIG. 5 is a sectional view of a lens according to a second numerical example of the present invention. 6 to 8 are aberration diagrams at a wide-angle end, a middle position, and a telephoto end in a numerical example of the present invention.

FIG. 9 is a sectional view of a lens according to a third numerical example of the present invention, which will be described later. FIGS. 10 to 12 are aberration diagrams at the wide-angle end, at the middle, and at the telephoto end in the numerical examples of the present invention.

FIG. 13 is a sectional view of a lens according to a fourth numerical example of the present invention, which will be described later. FIGS. 14 to 16 are aberration diagrams at the wide-angle end, at the middle, and at the telephoto end in the numerical examples of the present invention.

FIG. 17 is a sectional view of a lens according to a fifth numerical example of the present invention, which will be described later. FIGS. 18 to 20 are aberration diagrams at the wide-angle end, at the middle, and at the telephoto end, respectively, in the numerical examples of the present invention.

In the sectional view of the lens, L1 is a first group (first lens group) having a negative refractive power, L2 is a second group (second lens group) having a positive refractive power, and L3 is a third group having a positive refractive power. A group (third lens group), SP denotes an aperture stop, and IP denotes an image plane. G is a glass block such as a filter or a color separation prism.

In the basic configuration of the zoom lens of the present invention, a first group having a negative refractive power and a second group having a positive refractive power constitute a so-called wide-angle short zoom system. The magnification is changed by moving the group, and the movement of the image point accompanying the magnification is corrected by reciprocating the first group having a negative refractive power. The third unit having a positive refractive power does not contribute to zooming when fixed during zooming, but shares an increase in the refractive power of the photographing lens with the downsizing of the image sensor, and is composed of the first and second units. By reducing the refractive power of the short zoom system, it is possible to suppress the occurrence of aberration particularly in each lens constituting the first group, thereby achieving good optical performance. In particular, telecentric imaging on the image side required for a photographing apparatus using a solid-state imaging device or the like is achieved by providing the third lens unit having a positive refractive power as a field lens. If the third group moves during zooming,
Since the height of the optical axis of the off-axis ray entering the third lens group can be controlled, the ability to correct various off-axis aberrations is increased, and better performance is achieved over the entire zoom range.

Further, the stop SP is placed on the object side in the second lens unit, and the distance between the entrance pupil and the first lens unit on the wide-angle side is reduced, so that the outer diameter of the lens constituting the first lens unit can be prevented from increasing. In addition, good optical performance can be achieved without increasing the number of constituent lenses by canceling various off-axis aberrations in the first and third units with a stop disposed on the object side of the second unit having a positive refractive power interposed therebetween. It has gained.

The present invention is based on the basic structure described above. (1-1) In the first invention, the first group is a meniscus negative lens having a concave surface facing the image surface side, and having a convex surface facing the object side. The second group includes a negative lens and a positive lens closest to the image surface side, and has a cemented lens A having a positive refractive power as a whole, and the most lens among the lenses closer to the object side than the cemented lens A. The lens B on the image plane side is characterized in that the lens surface on the image plane side has a concave surface facing the image plane side.

In the first invention, it is more preferable to satisfy at least one of the following conditions.

(A-1) The focal length of the cemented lens A in the second group is fc, the focal length of the second group is f2, the radius of curvature of the object-side lens surface of the cemented lens A is Ra, When the radius of curvature of the lens surface on the image surface side of the lens B is Rb, 0.5 <fc / f2 <2.0 (1) 0.5 <(Ra + Rb) / (Ra−Rb) <2.5 .. (2) must be satisfied.

(A-2) The second group includes, in order from the object side, a positive lens having a convex surface facing the object side, a negative lens having a concave surface facing the image surface side, and a cemented lens.

(1-2) In the second invention, the first group has a meniscus-shaped negative lens having a concave surface facing the image surface side and a meniscus-shaped positive lens having a convex surface facing the object side. The second group includes a negative lens having both concave lens surfaces, a positive lens disposed on the object side of the negative lens, and having a convex surface facing the object side, and a negative lens and a positive lens disposed on the image surface side of the negative lens. It is characterized by having a cemented lens having a positive refractive power as a whole.

In the second aspect, it is more preferable that at least one of the following conditions be satisfied.

(A-1) The focal length of the negative lens in the second lens unit is fn, the focal length of the second lens unit is f2, and the convex surface of the second lens unit which is disposed closest to the object side and faces the object side. When the radius of curvature of the lens surface on the object side of the positive lens is Rc, and the radius of curvature of the lens surface on the image side is Rd, 0.3 <| fn | / f2 <2.0 (3) 0 <( Rd + Rc) / (Rd-Rc) <2.5 (4)

(A-2) The third unit is composed of one positive lens or a positive lens and a negative lens, and is composed of a positive cemented lens as a whole.

(1-3) The first group has a meniscus negative lens with a concave surface facing the image surface side, and a meniscus positive lens with a convex surface facing the object side. One or two positive lenses in order and a negative lens B with both lens surfaces concave,
And a cemented lens A of a negative lens and a positive lens,
The focal length of the cemented lens A in the second group is fc, the focal length of the second lens group is f2, the radius of curvature of the object-side lens surface of the cemented lens A is Ra, and the radius of curvature of the image side surface of the lens B is Is Rb, and the focal length of the lens B in the second group is f
n, where Rc is the radius of curvature of the object side surface of the positive lens with the convex surface facing the object side in the second group and closest to the object side, and Rd is the radius of curvature of the lens surface on the image side. <Fc / f2 <2.0 (1) 0.5 <(Ra + Rb) / (Ra-Rb) <2.5 (2) 0.3 <| fn | / f2 <2.0 (3) 0 <(Rd + Rc) / (Rd−Rc) <2.5 (4)

Next, the features of each invention will be described. still,
The first, second, and third inventions are also collectively referred to as “the present invention”.

The zoom lens according to the present invention includes a first lens unit having a negative refractive power, a meniscus negative lens having a convex surface facing the object side in order from the object side, and a meniscus positive lens having a convex surface facing the object side. The first group is composed of three lenses: a concave lens (negative lens) 11 having a concave surface facing the image side, a concave lens 12, and a convex lens (positive lens) 13 having a convex surface facing the object side. are doing. The second lens group having a positive refractive power has a convex lens 21 having a convex surface facing the object side in order from the object side, a concave lens 22 having both lens surfaces concave, and a cemented lens 23 including a negative lens and a positive lens. Or the second group is composed of two positive lenses in order from the object side,
It comprises four groups and five negative lenses 22, both of which have concave surfaces, and a cemented lens 23 composed of a negative lens and a positive lens.

The third group having a positive refractive power comprises one convex lens or a cemented lens of a positive lens and a negative lens. As described above, by making each unit a desired refractive power arrangement compatible with aberration correction, a compact lens system is achieved while maintaining good performance.

The first group having a negative refractive power has a role of forming a pupil image of the off-axis principal ray at the center of the stop. Particularly on the wide-angle side, the amount of refraction of the off-axis principal ray is large. aberration,
In particular, astigmatism and distortion tend to occur. Therefore, similarly to a normal wide-angle lens, a concave-convex configuration in which an increase in the lens diameter closest to the object side is suppressed, and the two negative lenses 11 and 12, which mainly share negative refractive power, perform refraction. They are trying to share power. Each lens constituting the first group has a shape close to a concentric spherical surface centered on the stop center in order to suppress the occurrence of off-axis aberration caused by the refraction of the off-axis principal ray.
That is, the negative lenses 11 and 12 have a meniscus shape with the concave surface facing the image plane, and the positive lens 13 has a meniscus shape with the convex surface facing the object side.

The second group having a positive refractive power has a positive lens disposed before and after the concave lens 22 having both concave lens surfaces, and has a symmetric configuration in terms of the refractive power arrangement. This is because the group moves greatly during zooming, and in order to prevent manufacturing deterioration due to eccentricity of the groups due to manufacturing errors, etc., it is necessary to remove spherical aberration, coma, etc. to some extent by the group alone. is there.

The most object-side convex lens 21 in the second group
Has a shape that is convex toward the object side so that off-axis chief rays emitted from the first lens unit do not refract greatly and do not generate off-axis aberrations. The convex lens 21 has a convex shape on the object side in order to suppress the amount of spherical aberration generated with respect to the on-axis light flux emitted from the first lens unit in a divergent state.

Further, the concave lens 22 has a concave surface on both the object side and the image surface, and the front and rear convex lenses 21 and the positive cemented lens 23
In addition, a negative air lens is formed, so that spherical aberration and coma aberration generated with a large aperture ratio are corrected well.

Further, a cemented lens 23 is disposed on the image plane side of the concave lens 22 to correct chromatic aberration well. In the configuration of the zoom lens of the present invention, the off-axis luminous flux in the first group has a high bending angle at the wide-angle end and a low height at the telephoto end, so that variation in chromatic aberration of magnification due to zooming occurs particularly in the first group. I do. Therefore, the refractive power arrangement and the selection of the glass material in the first group are configured so that the fluctuation of the chromatic aberration of magnification is minimized. In the case where the number of constituent members is about two to three as the concave-convex structure as described above in order to make the first group compact, a fluctuation component of axial chromatic aberration tends to remain in the first group. Therefore, axial chromatic aberration is favorably corrected by using a cemented lens in the second group.

Further, it is effective to arrange the cemented lens at a position farther from the stop in order to at least partially correct the chromatic aberration of magnification in the second lens unit. Have been placed.

The third unit having a positive refractive power is constituted by a convex lens having a convex surface on the object side, or a cemented lens of a positive lens and a negative lens so that the image side is telecentric. I have. Further, it also has a role as a field lens.

In this embodiment, an aspherical surface is effectively introduced in order to further improve the optical performance while configuring each lens unit with a small number of lenses.

In Numerical Embodiment 1 shown in FIG.
The image side surface of the concave lens 11 constituting the group is formed as an aspherical surface having a shape in which the diverging effect is weak at the periphery, and particularly, the image surface curvature on the wide angle side,
Astigmatism and distortion are corrected to reduce aberration fluctuation due to zooming.

The lens surface on the object side of the convex lens 21 constituting the second lens unit is formed as an aspheric surface having a weak convergence function in the periphery, and effectively corrects spherical aberration which becomes conspicuous with a large aperture. .

Further, the lens surface on the object side of the convex lens 31 constituting the third lens unit is formed as an aspheric surface having a weak convergence function at the periphery, and corrects curvature of field, astigmatism, and distortion over the entire zoom range. We are doing it effectively.

When photographing an object at a short distance using the zoom lens of this embodiment, good performance can be obtained by moving the first lens unit to the object side, but moving the third lens unit to the object side. A rear focus type may be used. According to this, it is possible to prevent the diameter of the front lens from increasing due to focusing, to shorten the minimum imaging distance, and to reduce the weight of the focus group.

Next, the technical meaning of each of the above conditional expressions will be described.

Conditional expression (1) defines the refractive power of the cemented lens of the second group. As described above, the second group of the present invention has a symmetrical refractive power arrangement of positive, negative, and positive refractive powers. The refractive power of the cemented lens has a positive refractive power on the image side of the second group, and is preferably within a certain range as compared with the refractive power of the second group.

When the refractive power of the cemented lens is weakened beyond the upper limit of the conditional expression (1), the refractive power of the positive lens on the object side in the second group must be increased in order to provide the necessary convergence action for the second group. However, excessive spherical aberration occurs, and even if an aspherical surface is used, correction will be insufficient, which is not good. If the refractive power of the positive lens on the object side is not increased, the refractive power of the second lens unit itself is weakened, so that the amount of movement for zooming is increased, and the overall length of the lens and the diameter of the front lens are increased, resulting in a compact zoom. This is not good because the lens cannot be configured.

If the refractive power of the cemented lens exceeds the lower limit of the conditional expression (1), the Petzval sum in the second lens unit becomes large in the positive direction, which is not good because an under field curvature occurs. In addition, the curvature of the cemented lens surface must be tight in order to correct longitudinal chromatic aberration, and the center thickness is large in order to secure the edge thickness of the positive lens that constitutes the cemented lens, which is good in terms of compactness. Absent.

The conditional expression (2) defines the shape factor of the air lens having a negative refractive power and composed of the cemented lens disposed on the image side of the second lens unit and the concave lens immediately before the cemented lens.

When the stop in the second group is arranged on the object side, the second
The same coma aberration occurs between the object-side lens surface of the positive lens on the object side of the group and the object-side lens surface of the concave lens. On the other hand, the object side lens surface of the air lens has a coma of the opposite sign, and the image side lens surface has the same sign of the same coma. If the curvature is made to some extent in a state where the concave surface is directed toward the lens, and the lens surface on the image side of the air lens has a relatively gentle curvature, on the contrary, there is an effect of correcting coma. When the shape factor is larger than 1, the lens has a meniscus shape, and when the shape factor is smaller than 1, it is a biconvex lens. As the radius of curvature of the lens surface on the image side becomes larger than 1, it becomes smaller while having a center of curvature on the image side. As the size becomes smaller, the curvature becomes smaller while having the center of curvature on the object side.

If the upper limit of the conditional expression (2) is exceeded and the degree of meniscus of the air lens increases, the curvature of the lens surface on the image side of the air lens becomes too strong, and the ability of the air lens to correct coma aberration decreases. As a result, the second group is not good because coma is undercorrected.

If the shape factor of the air lens is smaller than 1, the image surface of the air lens has a center of curvature on the object side, so that the air lens has a biconvex shape. Accordingly, the cemented lens on the image side has a meniscus shape. In order for the cemented lens to have a refractive power satisfying the conditional expression (1), the curvature of the lens surface on the image side of the cemented lens becomes tight. If the lower limit value of the conditional expression (2) is exceeded, the curvature of the lens surface on the image side of the cemented lens will become too tight as a result, causing under-spherical aberration and insufficient correction even if an aspherical surface is used. .

Conditional expression (3) is an expression that defines the refractive power of a negative lens having both concave surfaces in the second group.

If the refractive power is weakened beyond the upper limit of the conditional expression (3), the Petzval sum in the second lens unit becomes large in the positive direction, which causes an under-surface curvature, which is not good. Also, a sufficient back focus for arranging the filter group cannot be obtained. Further, there arises a problem that the exit pupil cannot be sufficiently moved away from the image plane.

If the refractive power exceeds the lower limit of conditional expression (3), the spherical aberration will be overcorrected, the field curvature will be excessive, and the back focus will be too long, and it will be difficult to make it compact, which is not good. .

Conditional expression (4) defines the shape factor of the positive lens on the object side in the second lens unit.

When the value exceeds the upper limit of the conditional expression (4) and the curvature of the lens surface on the image side becomes tight with the center of curvature on the image side, coma aberration particularly becomes remarkable, and an aspherical surface is used. Is also not good because the correction becomes difficult.

If the lower limit of conditional expression (4) is exceeded and the curvature of the lens surface on the image side becomes tight while having the center of curvature on the object side, the incident angle of the axial land ray on the image side surface becomes too tight and the under-spherical surface It is not good because aberration occurs.

Hereinafter, numerical examples of the present invention will be described. In each numerical example, i indicates the order of the surface from the object side, and R
i is the radius of curvature of the i-th surface, Di is the lens thickness or air gap between the i-th surface and the (i + 1) -th surface, and Ni and νi are d, respectively.
The refractive index and Abbe number for the line are shown. The two surfaces closest to the image side are filter members such as a quartz low-pass filter and an infrared cut filter. B, C, D,
E and F are aspheric coefficients. The aspherical shape is obtained by calculating the displacement in the optical axis direction at a position of height h from the optical axis with respect to the surface vertex as x
When a, x = R {1- (1 -h 2 / R 2) 1/2} + Bh 4 + Ch 6 +
It is represented by Dh ⁸ + Eh ¹⁰ + Fh ¹² . Here, R is a radius of curvature. “E-0X” means “10 ^−X ”. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

[Numerical Embodiment 1] FIG. 1 is a sectional view of this numerical embodiment, and FIG. 2 is an aberration diagram at the wide-angle end, an intermediate position, and a telephoto end.
3 and 4.

This embodiment comprises, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power. The zooming from the wide-angle end to the telephoto end is performed. The first group moves reciprocally to the image side, the second group moves to the object side, and the third group moves to the object side.
The group moves to the image side. The lens data is shown below.

[0074]

[Outside 1]

[Numerical Embodiment 2] FIG. 5 is a sectional view of this embodiment.
The aberration diagrams at the wide-angle end, the intermediate position, and the telephoto end are shown in FIGS.
FIG.

This embodiment comprises, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power. The zooming from the wide-angle end to the telephoto end is performed. The first group moves reciprocally to the image side, the second group moves to the object side, and the third group moves to the object side.
The group moves to the image side. The lens data is shown below.

[0077]

[Outside 2]

[Numerical Embodiment 3] A sectional view of this embodiment is shown in FIG.
FIGS. 10 and 1 show aberration diagrams at the wide-angle end, the intermediate position, and the telephoto end.
1 and 12.

This embodiment is composed of, in order from the object side, a first unit having a positive refractive power, a second unit having a negative refractive power, and a third unit having a positive refractive power. When zooming from the wide-angle end to the telephoto end, zooming is performed. The first group moves reciprocally to the image side, the second group moves to the object side, and the third group moves to the object side.
The group moves to the image side.

The present embodiment is different from Numerical Embodiment 1 in that the number of components of the first lens unit is two. In this embodiment, a negative meniscus lens having a concave surface facing the image side and a positive meniscus lens having a convex surface facing the object side are used. are doing. As a result, there are advantages that the number of lenses is reduced, leading to cost reduction, and that the front lens is reduced in weight. The lens data is shown below.

[0081]

[Outside 3]

[Numerical Embodiment 4] FIG. 1 is a sectional view of this embodiment.
FIG. 3 shows aberration diagrams at the wide-angle end, the intermediate position, and the telephoto end in FIG.
15 and 16.

This embodiment comprises, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power. When zooming from the wide-angle end to the telephoto end, zooming is performed. The first group moves reciprocally to the image side, the second group moves to the object side, and the third group moves to the object side.
The group moves to the image side.

The present embodiment differs from Numerical Embodiment 1 in that the second group has four members and four groups. The second lens unit of the present embodiment includes, in order from the object side, a meniscus positive lens having a convex surface facing the object side, a convex lens having both lens surfaces convex, a concave lens having both lens surfaces concave, and a concave lens and a convex lens as a whole. It is composed of a positive cemented lens, and one positive lens on the object side in Numerical Example 1 is composed of two lenses. Thereby, the function of converging the on-axis luminous flux emitted from the first group in the divergent state can be shared by the two lenses,
There is an advantage that generation of spherical aberration can be reduced and a larger-diameter photographing lens can be configured. The lens data is shown below.

[0085]

[Outside 4]

[Numerical Embodiment 5] FIG. 1 is a sectional view of the present embodiment.
FIG. 7 shows aberration diagrams at the wide-angle end, at the intermediate position, and at the telephoto end.
19 and 20.

This embodiment comprises, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power. When zooming from the wide-angle end to the telephoto end, zooming is performed. The first group moves reciprocally to the image side, the second group moves to the object side, and the third group moves to the object side.
Groups are fixed.

The present embodiment is different from Numerical Embodiment 1 in that the number of components of the third lens unit is two per group. The third group of the present embodiment is composed of a concave lens and a convex lens, and is composed of a positive cemented lens as a whole, and one single lens of Numerical Embodiment 1 is composed of a cemented lens. Thereby, the chromatic aberration of magnification can be particularly corrected in the third lens unit. Although the chromatic aberration of magnification has a large zoom variation in the first lens unit as described above, in the case of the present embodiment, the return variation component can be corrected by the first lens unit, and the absolute amount can be shared by the third lens unit. This has the advantage that chromatic aberration of magnification can be favorably corrected over the entire zoom range even when the zoom ratio is increased.

Also, it differs from Numerical Embodiment 1 in that the third lens unit is fixed during zooming. By fixing the third group, there is an advantage that a moving mechanism is not required and the lens barrel configuration is simplified. The lens data is shown below.

[0090]

[Outside 5]

The values of the conditional expressions in the embodiment of the present invention are shown below.

[0092]

[Table 1]

[0093]

According to the present invention, a compact zoom lens having a small number of constituent lenses, a high zoom ratio achieving a small diameter, and particularly excellent chromatic aberration, which is suitable for a photographing system using a solid-state image sensor, can be obtained. Thus, a zoom lens having excellent optical performance can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 3 is an intermediate aberration diagram of the numerical example 1 of the present invention.

FIG. 4 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 5 is a sectional view of a lens according to a second numerical embodiment of the present invention;

FIG. 6 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

FIG. 7 is an intermediate aberration diagram of the numerical example 2 of the present invention.

FIG. 8 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

FIG. 9 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 10 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 11 is an intermediate aberration diagram of the numerical example 3 of the present invention.

FIG. 12 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 13 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 14 is an aberration diagram at a wide angle end according to Numerical Example 4 of the present invention.

FIG. 15 is an intermediate aberration diagram of the numerical example 4 of the present invention.

FIG. 16 is an aberration diagram at a telephoto end in Numerical Example 4 of the present invention.

FIG. 17 is a sectional view of a lens according to a numerical example 5 of the present invention.

FIG. 18 is an aberration diagram at a wide angle end according to Numerical Example 5 of the present invention.

FIG. 19 is an intermediate aberration diagram of the numerical example 5 of the present invention.

FIG. 20 is an aberration diagram at a telephoto end in Numerical Example 5 of the present invention;

[Description of Signs] L1 First lens unit L2 Second lens unit L3 Third lens unit SP Aperture IP Image plane d d-line g g-line S Sagittal image plane M Meridional image plane

Continued on the front page F-term (reference) 2H087 KA02 KA03 MA12 MA14 NA02 PA06 PA07 PA08 PA18 PA19 PB07 PB08 PB09 QA02 QA07 QA17 QA21 QA22 QA25 QA34 QA37 QA41 QA45 QA46 RA05 RA12 RA36 RA41 RA43 SA14 SB16 SA32 SB03 SB SB23

Claims (11)

[Claims] A first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power.
In a zoom lens in which the distance between the first group and the second group is reduced at the time of zooming from the wide-angle end to the telephoto end and the distance between the second group and the third group is widened, the first group has a concave surface on the image surface side. A negative meniscus lens directed toward the lens, and a positive meniscus lens directed convex toward the object side. The second group is composed of a negative lens and a positive lens closest to the image plane, and has a positive refractive power as a whole. A zoom lens, characterized in that a lens A and a lens B closest to the image plane among lenses closer to the object side than the cemented lens A have a shape in which a lens surface on the image plane side is concave toward the image plane. 2. The focal length of the cemented lens A in the second group is fc, the focal length of the second group is f2, the radius of curvature of the object-side lens surface of the cemented lens A is Ra, and the lens B is
When the radius of curvature of the lens surface on the image surface side of Rb is Rb, the following conditional expression is satisfied: 0.5 <fc / f2 <2.0 0.5 <(Ra + Rb) / (Ra−Rb) <2.5 The zoom lens according to claim 1, wherein: 3. The second group is a positive lens having a convex surface facing the object side in order from the object side, a negative lens having a concave surface facing the image surface side,
The zoom lens according to claim 2, further comprising a cemented lens. 4. It has a first group of negative refractive power, a second group of positive refractive power, and a third group of positive refractive power in order from the object side,
At the time of zooming from the wide-angle end to the telephoto end, the distance between the first and second groups is reduced and the distance between the second and third groups is increased. In the zoom lens, the first group has a concave surface on the image surface side. A negative meniscus lens directed toward the object, a meniscus positive lens having a convex surface facing the object side, and the second group is disposed on the object side with respect to the negative lens having both concave lens surfaces and the negative lens. A zoom lens, comprising: a positive lens having a convex surface facing the other side; and a cemented lens having a positive refractive power as a whole, comprising a negative lens and a positive lens disposed on the image side of the negative lens. 5. The focal length of the negative lens in the second group is f
n, the focal length of the second group f2, the radius of curvature of the object-side lens surface of the positive lens of the second group closest to the object side with the convex surface facing the object side Rc, and the lens on the image plane side When the radius of curvature of the surface is Rd, the following conditional expression is satisfied: 0.3 <| fn | / f2 <2.00 <(Rd + Rc) / (Rd−Rc) <2.5. Item 8. The zoom lens according to Item 4. 6. The zoom lens according to claim 3, wherein the third group includes one positive lens or a positive lens and a negative lens, and includes a positive cemented lens as a whole. 7. The at least one lens surface of the negative lenses in the first group is an aspheric surface, and the aspheric surface has a shape whose divergence gradually decreases from the optical axis toward the periphery. The zoom lens according to claim 3 or 5, wherein 8. The at least one lens surface of the positive lens in the second group is an aspherical surface, and the aspherical surface has a shape whose convergence gradually decreases from the optical axis toward the periphery. The zoom lens according to claim 3. 9. The third group has a positive lens, and at least one lens surface of the positive lens is an aspheric surface, and the aspheric surface has a shape in which a convergence effect gradually decreases from the optical axis toward the periphery. 6. The zoom lens according to claim 3, wherein: 10. The zoom lens according to claim 3, wherein the third unit moves during zooming. 11. A first group of negative refractive power in order from the object side,
The zoom lens has a second lens unit having a positive refractive power and a third lens unit having a positive refractive power. During zooming from the wide-angle end to the telephoto end, the distance between the first unit and the second unit is reduced, and the second unit and the second unit are changed. In a zoom lens in which the distance between the third lens unit and the third lens unit increases, the first lens unit includes a negative meniscus lens having a concave surface facing the image surface, and a positive meniscus lens having a convex surface facing the object side. In order from the object side, one or two positive lenses, a negative lens B having both concave lens surfaces, and a cemented lens A of the negative lens and the positive lens, and a focal point of the cemented lens A in the second group Distance fc, the second
The focal length of the group is f2, the radius of curvature of the object-side lens surface of the cemented lens A is Ra, the radius of curvature of the image side surface of the lens B is Rb, and the focal length of the lens B in the second group is fn.
When the radius of curvature of the object side surface of the positive lens having the convex surface facing the object side and located closest to the object side in the second group is Rc, and the radius of curvature of the lens surface on the image side is Rd, 0.5 <fc /F2<2.0 0.5 <(Ra + Rb) / (Ra-Rb) <2.5 0.3 <| fn | / f2 <2.00 <(Rd + Rc) / (Rd-Rc) <2. A zoom lens configured to satisfy the conditional expression (5).