JP2000111798A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens consisting of three groups and being suitable for an electronic still camera which is constituted so that a photographing viewing angle is widened and the whole length thereof is shortened and also excellent in portability. SOLUTION: This zoom lens is provided with three lens groups being the 1st lens group L1 whose refractive power is negative, the 2nd lens group L2 whose refractive power is positive and the 3rd lens group L3 whose refractive power is positive. Then, a variable power action is executed by changing a gap between the respective lens groups. The group L1 is composed of three lenses being two negative lenses and one positive lens. The group L2 is composed of three lenses being positive, negative and positive. The group L3 is provided with at least one positive lens.

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 image pickup apparatus (camera) such as a video camera and a digital still camera using a solid-state image pickup device, an optical system used therein has a large aperture ratio zoom including a wide angle of view. Lenses are needed. In this type of camera, between the back of the lens and the image sensor,
In order to dispose various optical members such as a low-pass filter and a color correction filter, a lens system having a relatively long back focus is required for an optical system used therein. further,
In the case of a color camera using a color image pickup device,
In order to avoid color shading, it is desired that the optical system used has good telecentric characteristics on the image side.

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.

In Japanese Patent Application Laid-Open Nos. 55-35323 and 56-158316, a negative first lens unit, a positive second lens unit, and a positive third lens unit are arranged in order from the object side. There is disclosed a three-unit zoom lens that has a second lens unit that moves to perform zooming and corrects an image plane variation caused by zooming with the first lens unit.

In Japanese Patent Application Laid-Open No. 7-52256, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power,
Then, a three-unit zoom lens having three lens units of a third unit having a positive refractive power and performing zooming from the wide-angle end to the telephoto end by increasing the distance between the second and third units has been proposed. ing.

In US Pat. No. 5,443,710, a first group of negative refractive power and a second group of positive refractive power are sequentially arranged from the object side.
A three-group zoom lens that has three lens groups, a first lens group and a third lens group having a positive refractive power, and performs zooming from the wide-angle end to the telephoto end by reducing the distance between the second and third groups. It has been disclosed.

[0009]

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 disposed 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.

Also, 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, 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.

In the present invention, in view of these drawbacks of the conventional example,
In particular, it is an object of the present invention to provide a zoom lens having a small number of constituent lenses, a small size, a high zoom ratio with a small diameter, and excellent optical performance, which is suitable for an imaging system using a solid-state imaging device.

Another object of the present invention is to obtain a zoom lens satisfying at least one of the following items. High performance and compactness while widening the angle of view at the wide-angle end. • Correctly correct astigmatism and distortion, especially on the wide-angle side. Reduce the aberration sharing of the moving lens group while minimizing the lens configuration, reduce the performance degradation due to eccentricity between the lens groups due to manufacturing errors, and facilitate manufacturing. -To achieve a large aperture ratio suitable for a high-pixel image sensor having low sensitivity. To provide good image-side telecentric imaging suitable for an imaging system using a solid-state imaging device while minimizing the number of components. • Correctly correct distortion not only at the wide-angle end but throughout the zoom range. -To reduce the fluctuation of the image side telecentric imaging due to zoom. -To reduce the amount of movement of the variable power lens unit while maintaining telecentric imaging to achieve further miniaturization.・ To simplify the focusing mechanism for near objects. And so on.

[0015]

The zoom lens according to the present invention comprises: (1-1) a first lens unit having a negative refractive power in order from the object side;
A zoom lens having three lens groups, a second lens group having a positive refractive power and a third lens group having a positive refractive power, wherein the distance between the lens groups is changed to perform zooming; The group includes three negative lenses and one positive lens. The second lens group includes three positive lenses, a negative lens, and a positive lens. The third group includes at least one lens. Is characterized by having a positive lens.

(1-2) In order from the object side, there are three lens groups: a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. A first lens group including at least one negative lens having a concave surface on the image side and a positive lens, wherein the second lens group includes a first lens group and a second lens group; Consists of a positive lens, a negative lens, and a positive lens.
The third group has at least one positive lens.

In particular, in the constitution (1-1) or (1-2), (1-2-1) one of the negative lenses constituting the first lens group has a concave surface facing the image side, The positive lens in the first lens group has a convex surface facing the object side.

(1-2-2) The first lens group has at least one aspheric surface.

(1-2-3) The positive lens closest to the object in the second lens group has a convex surface facing the object side, and the negative lens in the second lens group has a concave surface facing the image side. That you are.

(1-2-4) The second lens group has at least one aspherical surface.

(1-2-5) The third lens group is composed of a positive lens having a convex surface facing the object side.

(1-2-6) The positive lens constituting the third lens group has at least one aspheric surface.

(1-2-7) The amount of movement of the third lens unit accompanying zooming from the wide-angle end to the telephoto end is represented by m (however, the third unit has a positive sign when it moves toward the image side). When the focal length at the wide-angle end is fw and the focal length at the telephoto end is ft,

[0024]

(Equation 2) To be satisfied.

(1-2-8) The third lens group moves toward the object side during zooming from the wide-angle end to the telephoto end.

(1-2-9) The third lens group is moved to the object side to perform focusing on a short-distance object. And so on.

(1-3) In order from the object side, there are three lens groups, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power. In the zoom lens in which the first unit has a locus convex toward the image surface side and the second unit is moved toward the object side, the first unit is located on the image surface side. The second group includes a meniscus-shaped negative lens having a concave surface facing the surface, a meniscus-shaped negative lens having a concave surface facing the image side, and a meniscus-shaped positive lens having a convex surface facing the object side. The third lens unit is characterized by comprising a negative lens having a concave surface and a positive lens having both lens surfaces convex, and the third unit comprises a negative lens and a positive lens.

(1-4) From the object side, there are three lens groups, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power. A zoom lens that performs zooming from the zoom lens to the telephoto end by moving the first lens unit toward the image plane side and moving the second lens unit toward the object side and moving the third lens unit toward the image surface. The first group includes a meniscus negative lens having a concave surface facing the image surface side, a meniscus negative lens having a concave surface facing the image surface, and a meniscus positive lens having a convex surface facing the object side. The second group is composed of a positive lens, a negative lens with both lens surfaces concave, and a positive lens with both lens surfaces convex, and the third group is composed of a positive lens with both lens surfaces convex. .

(1-5) From the object side, there are three lens groups, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power. In the zoom lens for performing zooming from the telephoto end to the telephoto end, the first unit has a locus convex toward the image plane side, and the second unit and the third unit are independently moved to the object side. The first group includes a meniscus negative lens having a concave surface facing the image surface side, a meniscus negative lens having a concave surface facing the image surface, and a meniscus positive lens having a convex surface facing the object side. The third unit is characterized by comprising a positive lens, a negative lens having both lens surfaces concave, and a positive lens having both lens surfaces convex, and the third unit is constituted by a positive lens having both lens surfaces convex.

(1-6) From the object side, there are three lens groups, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power. In the zoom lens for performing zooming from the telephoto end to the telephoto end, the first unit has a locus convex toward the image plane side, and the second unit and the third unit are independently moved to the object side. The first group includes a meniscus negative lens having a concave surface facing the image surface side, a meniscus negative lens having a concave surface facing the image surface, and a meniscus positive lens having a convex surface facing the object side. The third lens unit is composed of a positive lens, a negative lens with both lens surfaces concave, and a positive lens with both lens surfaces convex, and the third lens unit is composed of a cemented lens of a negative lens and a positive lens.

(1-7) The third lens group includes, in order from the object side, 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 the zoom lens in which the first unit has a locus convex toward the image surface side and the second unit is moved toward the object side, the first unit is located on the image surface side. The second group includes a meniscus-shaped negative lens having a concave surface facing the surface, a meniscus-shaped negative lens having a concave surface facing the image side, and a meniscus-shaped positive lens having a convex surface facing the object side. The third unit is characterized in that the third lens unit comprises a negative lens having a concave surface and both lens surfaces comprise a positive lens having a convex surface, and the third lens unit comprises a positive lens having both lens surfaces having a convex surface.

(1-8) From the object side, in order from the object side, there are three lens groups, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power. In the zoom lens for performing zooming from the telephoto end to the telephoto end, the first unit has a locus convex toward the image plane side, and the second unit and the third unit are independently moved to the object side. The first group includes a negative lens having a concave surface facing the image surface side and a positive lens. The second group includes a positive lens, a negative lens having both concave lens surfaces, and a positive lens having both convex lens surfaces. The third group is characterized in that both lens surfaces are composed of convex positive lenses.

[0033]

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, which will be described later. 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.

FIG. 21 is a sectional view of a lens according to a sixth numerical example of the present invention, which will be described later. FIG. 22 to FIG. 24 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. 25 is a sectional view of a lens according to a seventh numerical example of the present invention, which will be described later. 26 to 28 are aberration diagrams at a wide-angle end, a middle position, and a telephoto end in a numerical example of the present invention.

FIG. 29 is a sectional view of a lens according to a numerical example 8 of the present invention, which will be described later. 30 to 32 are aberration diagrams at the wide-angle end, at the middle, and at the telephoto end 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 zoom lens system according to the present invention, upon zooming from the wide-angle end to the telephoto end, the second unit is moved toward the object side.
The correction of the image plane fluctuation accompanying the zooming is performed by moving the first lens unit non-linearly. The third lens unit is moved to the object side or the image plane side as needed. Focusing is performed in the first group or the third group.

Next, each embodiment (example) will be described in order.

In the first embodiment shown in the figure, in order from the object side,
It has three lens groups, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. When zooming from the wide-angle end to the telephoto end,
The first unit moves substantially toward the image side, and the second unit moves toward the object side. The third unit is fixed during zooming.

In this embodiment, a so-called wide-angle short zoom system is basically constituted by the first negative lens unit and the second positive lens unit.
Magnification is performed by moving the positive second group, and movement of the image point accompanying magnification is corrected by reciprocating the negative first group.

The third positive lens unit is fixed during zooming and does not contribute to zooming, but shares an increase in the refracting power of the photographing lens with the downsizing of the image sensor, and is composed of the first and second lens units. By reducing the refractive power of the short zoom system, it is possible to suppress the occurrence of aberration particularly in the lens that constitutes 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 image pickup device or the like is achieved by making the positive third group function as a field lens.

Further, the aperture SP is placed closest to the object side of the second lens group, and the distance between the entrance pupil and the first lens group on the wide-angle side is reduced to increase the outer diameter of the lens constituting the first lens group. And the first and third groups cancel out off-axis various aberrations with the stop arranged on the object side of the positive second group to obtain good optical performance without increasing the number of components. I have.

Further, in this embodiment, the first negative lens unit is composed of two concave lenses (negative lenses) L11 and L12 having concave surfaces facing the image side in order from the object side, and a convex lens (positive lens) having a convex surface facing the object side. Lens) L13, and the second positive lens unit includes, in order from the object side, a convex lens L21, a concave lens L22, and a convex lens L23. The positive third lens unit includes the concave lens L31 and the object-side surface facing the object side. It is composed of a convex lens L32 having a convex surface.

As described above, by making each unit compatible with a desired refractive power arrangement and aberration correction, a compact lens system is achieved while maintaining good performance. The negative first lens unit has a role of focusing the off-axis chief ray on the center of the stop, and particularly on the wide-angle side, the off-axis chief ray has a large amount of refraction, so various off-axis aberrations, particularly astigmatism Distortion tends to occur.

Therefore, similarly to a normal wide-angle lens system, a concave (negative) -convex (positive) configuration that suppresses an increase in the lens diameter closest to the object side is used, and the negative refractive power is mainly shared. The negative lens is composed of two lenses, L11 and L12, to share the refractive power. Each lens constituting the first group includes:
In order to suppress the occurrence of off-axis aberrations caused by the refraction of off-axis chief rays, the shape is close to a concentric spherical surface centered on the stop center.

The second positive lens unit has a so-called triplet configuration. Because this is a large moving group,
This is because the spherical aberration and the coma are removed to some extent in the group alone in order to prevent the manufacturing deterioration due to the eccentricity between the groups due to the manufacturing error. The most object-side convex lens L21 in the second group has a convex shape on the object side so that off-axis chief rays emitted from the first group are largely refracted and various off-axis aberrations do not occur.

Further, the concave lens L22 is provided with a concave surface on the image side, and a negative air lens is formed together with the convex surface of the convex lens L23 on the image side to correct the spherical aberration generated with the large aperture ratio. I have. The third positive lens unit has a convex lens L32 having a convex surface on the object side, and also has a role as a field lens for making the image side telecentric.

In this embodiment, an aspherical surface is effectively introduced in order to achieve a further improvement in optical performance while configuring each group with a small number. In the first embodiment shown in FIG. 1, the concave surface of the concave lens L11 constituting the first lens unit has an aspheric surface whose positive refracting power becomes strong around the object side. In particular, correction of astigmatism and distortion on the wide-angle side is performed. Is going. The image side surface of the convex lens L32 constituting the third lens unit has an aspheric surface having a weak positive refractive power at the periphery, and contributes to correction of various off-axis aberrations throughout the zoom range.

Usually, barrel distortion at the wide-angle end poses a problem for distortion. In this embodiment, correction is performed not only at the wide-angle end but also over the entire zoom range together with the aspherical surface introduced into the first lens unit.

When photographing (focusing) 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. It is better to move the three lens groups integrally to the object side. This is because the movement by zooming and the movement by focusing can be separated, so that the first and second groups can be moved simply in cooperation with a cam etc., and the mechanical structure can be simplified. is there.

Numerical Example 1 has a magnification ratio of 2.5 and an aperture ratio of 2.8.
It is a zoom lens of about 4.0.

Next, a second embodiment shown in FIG. 5 will be described. In the present embodiment, a lens configuration having negative-positive-positive refractive power is used, which is the same as that of the first embodiment. However, when zooming from the wide-angle end to the telephoto end, as shown in FIG. The second group moves toward the object side, and the third group moves toward the image side. The positive third lens group is fixed during zooming in the first embodiment, but may be moved during zooming. Now, assuming that the back focus is sk ', the focal length of the third lens group is f3, and the imaging magnification of the third lens group is β3, the relationship of sk' = f3 (1-β3) holds. However, 0 <β3 <1.0. Here, when zooming from the wide-angle end to the telephoto end,
When the third lens group is moved to the image side, the back focus sk 'decreases, and the imaging magnification β3 of the third lens group increases on the telephoto side.

As a result, zooming can be shared by the third lens group, and the amount of movement of the second lens group is reduced. This saves space and contributes to downsizing of the lens system. In the case of focusing on a short-distance object, when the positive third unit is moved, it is impossible to separate the movement of zoom and focus.However, a so-called electronic cam or the like which stores the third unit in a camera with a zoom locus for each distance object is provided. If means for correcting a change in the image point position during zooming by autofocusing is used, a simple mechanical structure similar to the case of fixing the third lens unit is obtained.

The concave lens L closest to the object side in the negative first group
Numeral 11 has an aspherical surface near the image side surface where the negative refractive power becomes weak at the periphery, and effectively corrects astigmatism and distortion on the wide-angle side similarly to the first embodiment. Also, the image side surface of the convex lens L23 constituting the second group has an aspheric surface in which the positive refractive power is weak at the periphery, and effectively corrects the spherical aberration which becomes conspicuous with a large aperture. .

The third positive lens unit includes one convex lens L31 having a convex surface facing the object side, and further shortens the total lens length while maintaining telecentric imaging. As in the first embodiment, the object side surface has an aspheric surface whose positive refractive power becomes weak at the periphery, and effectively corrects off-axis various aberrations over the entire zoom range.

In the second numerical embodiment, the zoom ratio 2. 5 times, aperture ratio
The zoom lens is about 2.5 to 3.8.

Next, a third embodiment shown in FIG. 9 will be described. In this embodiment, the lens arrangement having negative-positive-positive refractive power is the same as that of the first embodiment. However, as shown in the figure, upon zooming from the wide-angle end to the telephoto end, the first unit is convex toward the image side. In the reciprocating movement, the second group moves to the object side, and the third group moves to the object side.

In a zoom lens suitable for a camera using a solid-state image pickup device, it is desirable that telecentric imaging on the image side be achieved in the entire zoom range. In the zoom lens of the present invention, the position of the exit pupil fluctuates because the second lens group including the stop moves during zooming. Therefore, by moving the third positive lens unit toward the object side, the zoom fluctuation of the exit pupil position is canceled.

In Numerical Example 3, the zoom ratio was 2.5 times and the aperture ratio was 2.
It is a zoom lens of about 8 to 4.0.

The basic configuration of the zoom type of the fourth embodiment shown in FIG. 13 is the same as that of the third embodiment.

In Numerical Example 4, the zoom ratio is 2.5 times and the aperture ratio is 2.
It is a zoom lens of about 8 to 4.0.

The basic structure of the zoom type of the fifth embodiment shown in FIG. 17 is the same as that of the third embodiment. In the present embodiment, the third unit includes a cemented lens of a negative lens and a positive lens.

In Numerical Example 5, the variable power ratio is 2.5 and the aperture ratio is 2.
It is a zoom lens of about 8 to 4.0.

The basic structure of the zoom type of the sixth embodiment shown in FIG. 21 is the same as that of the third embodiment. In the present embodiment, the third unit includes a cemented lens of a negative lens and a positive lens.

In the present embodiment, the concave lens L12 in the negative first unit
The object has an aspheric surface on the lens side surface where the positive refracting power becomes strong around, and astigmatism on the wide-angle side as in Example 1,
The distortion is effectively corrected.

In Numerical Embodiment 6, the zoom ratio is 2.5 times and the aperture ratio is 2.
It is a zoom lens of about 8 to 4.0. In Numerical Example 6, k, B, and C are aspherical coefficients. The aspherical surface shape is defined as x = R ｛1− (1− (1 + k) h ² / R ^2, where x is the displacement in the optical axis direction at the position of height h from the optical axis with reference to the surface vertex. ) ^1/2 ｝ + Bh ⁴
+ Ch ⁶ . Here, R is a radius of curvature.

Next, the basic configuration of the zoom type according to the seventh embodiment of FIG. 25 is the same as that of the first embodiment. In the present embodiment, the image side surface of the concave lens L12 in the negative first lens unit has an aspheric surface in which the negative refractive power becomes weak at the periphery, and correction of astigmatism and distortion on the wide-angle side as in the first embodiment. Have gone effectively. The third group is composed of a positive lens having both lens surfaces convex.

In this numerical example, the zoom ratio is 2.5 and the aperture ratio is 2.8.
It is a zoom lens of about 4.0. The basic configuration of the zoom type according to the eighth embodiment of FIG. 29 is the same as that of the third embodiment. In the present embodiment, in order to further reduce the number of lenses in order to reduce the size at the time of storage, the negative first group is composed of a concave lens having a concave surface facing the image side and a convex lens having a convex surface facing the object side. . The image side surface of the concave lens has an aspheric surface in which negative refractive power is weakened in the periphery, and effectively corrects astigmatism and distortion on the wide angle side similarly to the first embodiment. Positive third
The group is composed of one convex lens whose convex surface faces the object side, and further shortens the overall length of the lens. As in the first embodiment, the object side surface has an aspheric surface whose positive refractive power becomes weak at the periphery, and effectively corrects off-axis various aberrations over the entire zoom range.

In this numerical example, the zoom ratio is twice and the aperture ratio is 2.8 to 2.8.
It is a zoom lens of about 3.8.

In the zoom lens of the present invention,
It is desirable that the following conditional expression be satisfied for the amount of movement of the three lens units.

[0077]

(Equation 3) m: the amount of movement of the third lens unit from the wide-angle end to the telephoto end fw: the focal length of the wide-angle end ft: the focal length of the telephoto end When the third lens group moves to the object side beyond the lower limit, the fluctuation of the exit pupil position is canceled, but the magnification of the third lens group drops significantly on the telephoto side. To get the zoom ratio
The amount of movement of the group must be increased, which is not good because the overall length of the lens increases.

Conversely, if the third lens unit moves to the image side beyond the upper limit of conditional expression (1), the magnification of the third lens unit increases on the telephoto side, and the amount of movement of the second lens unit can be reduced. Since the position of the exit pupil is in the same direction as the effect of the movement of the two groups including the stop, the image side telecentric state cannot be maintained, and thus it is not suitable for an imaging system using a solid-state imaging device.

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,
Ri is the radius of curvature of the lens surface, Di is the lens thickness and air gap between the i-th surface and the (i + 1) -th surface, and Ni and vi are the refractive index and Abbe number for the d-line, respectively. The two surfaces closest to the image are glass materials such as a face plate.
B, C, D, E, and F are aspherical coefficients. Aspheric shape is x = R when it the optical axis direction of the displacement at the height h from the optical axis with respect to the surface vertex and ^{x {1- (1-h 2} / R 2) 1/2} + Bh ⁴ + Ch
⁶ + Dh ⁸ + Eh ¹⁰ + Fh ¹² Here, R is a radius of curvature.

[0080]

[Outside 1]

[0081]

[Outside 2]

[0082]

[Outside 3]

[0083]

[Outside 4]

[0084]

[Outside 5]

[0085]

[Outside 6]

[0086]

[Outside 7]

[0087]

[Outside 8] Below, the correspondence with the conditional expression (1) of each embodiment described above is shown.

[0088]

[Table 1]

[0089]

According to the present invention, by setting each element as described above, a high zoom ratio which has a small number of constituent lenses, is compact and has a small diameter, is suitable for a photographing system using a solid-state image sensor. Thus, a zoom lens having excellent optical performance can be achieved.

In particular, (a-1) the first lens unit having a negative refractive power in order from the object side,
Three lens groups, a second lens group having a positive refractive power and a third lens group having a positive refractive power, are arranged, and the magnification of the first lens group is changed from the object side by changing the distance between the groups. Two concave lenses and three convex lenses in this order, or one concave lens and two convex lenses, and the second lens group is composed of at least one convex lens, concave lens, and three convex lenses, and at least one third lens group from the object side.
By using a single convex lens, it is suitable for an imaging system using a solid-state imaging device, and particularly suitable for an imaging system using a solid-state imaging device. As a result, a zoom lens having excellent optical performance can be obtained.

(A-2) By effectively introducing an aspherical surface into each lens unit, it is possible to effectively correct off-axis aberrations, particularly astigmatism and distortion, and spherical aberration when a large aperture ratio is obtained. Can be done. And the like.

[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.

FIG. 21 is a sectional view of a lens according to a numerical example 6 of the present invention.

FIG. 22 is an aberration diagram at a wide angle end according to Numerical Example 6 of the present invention.

FIG. 23 is an intermediate aberration diagram of the numerical example 6 of the present invention.

FIG. 24 is an aberration diagram at a telephoto end in Numerical Example 6 of the present invention.

FIG. 25 is a sectional view of a lens according to a numerical example 7 of the present invention.

FIG. 26 is an aberration diagram at a wide angle end according to Numerical Example 7 of the present invention.

FIG. 27 is an intermediate aberration diagram of the numerical example 7 of the present invention.

FIG. 28 is an aberration diagram at a telephoto end in Numerical Example 7 of the present invention.

FIG. 29 is a sectional view of a lens according to a numerical example 8 of the present invention;

FIG. 30 is an aberration diagram at a wide angle end according to Numerical Example 8 of the present invention.

FIG. 31 is an intermediate aberration diagram of the numerical example 8 of the present invention.

FIG. 32 is an aberration diagram at a telephoto end in Numerical Example 8 of the present invention;

[Explanation of symbols]

 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

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H087 KA02 KA03 MA12 MA14 NA01 PA06 PA07 PA08 PA17 PA18 PB06 PB07 PB08 QA02 QA03 QA07 QA17 QA19 QA21 QA22 QA25 QA34 QA41 QA42 QA45 QA46 RA05 RA12 RA13 SA36 RA41 SA64 SB03 SB04 SB14 SB22 SB23 9A001 HH23

Claims (17)

[Claims] 1. A lens system comprising: a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power in order from the object side. In a zoom lens that changes magnification by changing the distance between groups,
The lens group includes three negative lenses and one positive lens. The second lens group includes three positive lenses, a negative lens, and a positive lens. The third lens group includes at least one lens. A zoom lens having a number of positive lenses. 2. A lens system comprising: a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power in order from the object side. In a zoom lens that changes magnification by changing the distance between groups,
The lens group includes at least one negative lens having a concave surface on the image side and a positive lens. The second lens group includes three lenses: a positive lens, a negative lens, and a positive lens. And a zoom lens comprising at least one positive lens. 3. One of the negative lenses constituting the first lens group has a concave surface facing the image side, and the positive lens in the first lens group has a convex surface facing the object side. The zoom lens according to claim 1 or 2, wherein 4. The zoom lens according to claim 3, wherein said first lens group has at least one aspheric surface. 5. The positive lens closest to the object side in the second lens group has a convex surface facing the object side, and the negative lens in the second lens group has a concave surface facing the image side. The zoom lens according to claim 1, wherein: 6. The zoom lens according to claim 5, wherein said second lens group has at least one aspheric surface. 7. The zoom lens according to claim 1, wherein said third lens group comprises a positive lens having a convex surface facing the object side. 8. The zoom lens according to claim 7, wherein the positive lens forming the third lens group has at least one aspheric surface. 9. The focal length at the wide-angle end, where m is the amount of movement associated with zooming from the wide-angle end to the telephoto end of the third lens group (where the third group moves to the image side with a positive sign). Distance fw,
When the focal length at the telephoto end is ft, The zoom lens according to claim 1, wherein the following is satisfied. . 10. The zoom lens according to claim 1, wherein said third lens group moves toward the object side when zooming from a wide-angle end to a telephoto end. 11. The zoom lens according to claim 1, wherein the third lens group is moved to the object side to perform focusing on a short-distance object. 12. A first group having a negative refractive power in order from the object side,
The zoom lens has three lens groups, a second group having a positive refractive power and a third group having a positive refractive power, and performs zooming from the wide-angle end to the telephoto end.
In a zoom lens having a group having a convex locus on the image plane side and moving the second group to the object side, the first group includes a meniscus negative lens having a concave surface facing the image plane, The second group includes a meniscus-shaped negative lens having a concave surface facing the surface side and a meniscus-shaped positive lens having a convex surface facing the object side. The second group includes a positive lens, a negative lens having both lens surfaces concave, and both lens surfaces. Is a positive lens having a convex surface, and the third group is composed of a negative lens and a positive lens. 13. A first group having a negative refractive power in order from the object side,
The zoom lens has three lens groups, a second group having a positive refractive power and a third group having a positive refractive power, and performs zooming from the wide-angle end to the telephoto end.
In a zoom lens having a group having a convex locus on the image plane side and moving the second group to the object side and the third group to the image plane side, the first group has a concave surface on the image plane side. The second group includes a positive meniscus lens having both a negative lens and 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. A zoom lens comprising: a negative lens having a concave surface; a positive lens having both convex surfaces formed on both lens surfaces; and the third group includes a positive lens having both convex surfaces formed on both lens surfaces. 14. A first group having a negative refractive power in order from the object side,
The zoom lens has three lens groups, a second group having a positive refractive power and a third group having a positive refractive power, and performs zooming from the wide-angle end to the telephoto end.
A zoom lens having a group having a convex locus on the image plane side and performing the second group and the third group by independently moving to the object side;
The first group includes a meniscus negative lens having a concave surface facing the image surface side, a meniscus negative lens having a concave surface facing the image surface side, and a meniscus positive lens having a convex surface facing the object side. The second unit is composed of a positive lens, a negative lens having both concave surfaces and a positive lens having both convex surfaces, and the third unit is composed of a positive lens having both convex surfaces. Zoom lens. 15. A first group having a negative refractive power in order from the object side,
The zoom lens has three lens groups, a second group having a positive refractive power and a third group having a positive refractive power, and performs zooming from the wide-angle end to the telephoto end.
A zoom lens having a group having a convex locus on the image plane side and performing the second group and the third group by independently moving to the object side;
The first group includes a meniscus negative lens having a concave surface facing the image surface side, a meniscus negative lens having a concave surface facing the image surface side, and a meniscus positive lens having a convex surface facing the object side. The second group comprises a positive lens, a negative lens having both lens surfaces concave, and the positive lens having both lens surfaces convex, and the third group comprises a cemented lens of a negative lens and a positive lens. Zoom lens. 16. A first group having a negative refractive power in order from the object side,
The zoom lens has three lens groups, a second group having a positive refractive power and a third group having a positive refractive power, and performs zooming from the wide-angle end to the telephoto end.
In a zoom lens having a group having a convex locus on the image plane side and moving the second group to the object side, the first group includes a meniscus negative lens having a concave surface facing the image plane, The second group includes a meniscus-shaped negative lens having a concave surface facing the surface side and a meniscus-shaped positive lens having a convex surface facing the object side. The second group includes a positive lens, a negative lens having both lens surfaces concave, and both lens surfaces. Is a zoom lens, wherein the third lens unit comprises a positive lens having both convex surfaces. 17. A first group having a negative refractive power in order from the object side,
The zoom lens has three lens groups, a second group having a positive refractive power and a third group having a positive refractive power, and performs zooming from the wide-angle end to the telephoto end.
A zoom lens having a group having a convex locus on the image plane side and performing the second group and the third group by independently moving to the object side;
The first group includes a negative lens having a concave surface facing the image surface side and a positive lens, and the second group includes a positive lens, a negative lens having both lens surfaces concave, and a positive lens having both lens surfaces convex, The third group is a zoom lens, wherein both lens surfaces are composed of convex positive lenses.