KR101783986B1 - Zoom lens system - Google Patents

Abstract

A fourth lens group zoom lens system that achieves a high magnification of about 30 times. The zoom lens system includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, Wherein the first lens group and the third lens group are fixed in the optical axis direction at the time of changing from the wide angle end to the telephoto end, The fourth lens group moves in the direction of the optical axis so as to compensate for the fluctuation of the image surface position due to the movement of the second lens group and performs the focusing function, Of the zoom lens system.
0.03 < f2 / ft < 0.08
F2: focal length of the second lens group
ft: Focal length across the lens system at the telephoto end

Description

Zoom lens system

The present invention relates to a zoom lens system and an image pickup apparatus using the same, and more particularly to a zoom lens system suitable for application to a camera receiving light by an image pickup element such as a surveillance camera, a video camera, a digital still camera, will be.

BACKGROUND ART [0002] Conventionally, as a zoom lens system of high image quality and high magnification suitable for a surveillance camera, a video camera, a digital still camera, a broadcast camera, and the like, for example, a four- The fourth-group zoom lens system of the positive correction includes, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power The first lens group and the third lens group are fixed in the optical axis direction at the time of zooming from the wide-angle end to the telephoto end, and the upper surface, which is generated when the second lens group moves from the object side to the image side, The fourth lens unit moves in the optical axis direction so as to compensate for the variation, and at the same time, the focusing function, i.e. focusing, can be performed.

It has recently been required to secure optical performance corresponding to an imaging device of a high pixel and to maintain good performance even when focusing on a nearest distance. In the following Patent Document 1, as a method for securing the optical performance of the telephoto end, a method in which positive refractive power is dispersed by disposing three negative lenses and positive lenses in the first lens group is known. Further, in the following Patent Document 2, the second lens group G2 of the four-lens-group zoom lens system of the corrected version includes at least two negative lenses.

[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2010-139724

[Patent Document 2] Japanese Unexamined Patent Publication No. 2010-102096

However, in the conventional zoom lens system described in Patent Documents 1 and 2, optical performance corresponding to a small-sized, high-magnification, high-sensitivity imaging device can not be obtained. For example, in the configuration described in Patent Document 1, only about 20 times of the magnification can be obtained. Further, in the structure described in Patent Document 1, the negative refractive power is dispersed by the two-group structure consisting of a negative lens, a meniscus negative lens, and a cemented lens of negative lens and positive lens in order from the object side, The coma aberration generated in accordance with the change of the angle of view is corrected to improve the performance. However, since the position of the positive lens is not appropriate, the chromatic aberration correction can not be sufficiently performed and the optical performance can not be satisfied. The zoom lens system having a high magnification of about 30 times can not be constructed even in the configuration described in Patent Document 2.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a four-group zoom lens which is capable of achieving miniaturization and achieving a high- A zoom lens system, and an image pickup apparatus.

According to an aspect of the present invention, there is provided a zoom lens system including a first lens group having a positive refractive power, a second lens group having a negative refractive power, a diaphragm fixed to an image surface, A third lens group having a refractive power and a fourth lens group having a positive refractive power, wherein the first lens group and the third lens group are fixed in the optical axis direction at the time of changing from the wide angle end to the telephoto end, The fourth lens group moves in the optical axis direction so as to compensate for the fluctuation of the image plane position due to the movement of the second lens group and performs the focusing function, Wherein the first lens group includes one negative lens, the second lens group includes one positive lens, the third lens group includes independent positive lenses, and the fourth lens group includes at least one Including a positive lens of The zoom lens system, characterized in that to satisfy the condition, or less, is provided.

0.03 < f2 / ft < 0.08

F2: focal length of the second lens group

ft: Focal length across the lens system at the telephoto end

Wherein the first lens group has the one negative lens and the three positive lenses in order from the object side and the second lens group has at least three negative lenses and one positive lens, And the fourth lens group has the at least one positive lens and at least one negative lens and satisfies the following condition .

5.8 < f1 / f2 < 8.0

F1: focal length of the first lens group

Wherein the most object side positive lens constituting the third lens group has at least one surface including an aspherical shape and the joint surface of the cemented lens constituting the third lens group has a convex shape on the object side, Condition.

0.15 < f3 / ft < 0.35

0.4 < f31 / f3 < 0.8

F3: focal length of the third lens group

f31: focal length of the most object-side positive lens constituting the third lens group

ft: Focal length across the lens system at the telephoto end

At least one of the positive lenses constituting the first lens group uses a superabsorbent having Abbe's number of 80 or more.

The second lens group is composed of two negative lenses in order from the object side, and a cemented lens of a positive lens and a negative lens whose convex surface faces the object side.

Wherein the fourth lens group is composed of a cemented lens of a positive lens and a negative lens in order from the object side and the positive lens constituting the fourth lens group has at least one surface including an aspherical shape, Satisfaction.

0.08 < f4 / ft < 0.25

F4: focal length of the fourth lens group

ft: Focal length across the lens system at the telephoto end

According to another aspect of the present invention, there is provided an imaging apparatus including the zoom lens system.

According to the present invention, it is possible to attain miniaturization and attain a high magnification of about 30 times in the four-group zoom lens system which is corrected by the correction.

1 is a cross-sectional view of a lens at a wide angle end according to Numerical Embodiment 1 of the present invention.
2 is an aberration diagram of the numerical embodiment 1 of the present invention at the wide angle end.
3 is an aberration diagram at the middle zoom position of the numerical embodiment 1 of the present invention.
4 is an aberration diagram at the telephoto end of Numerical Embodiment 1 of the present invention.
5 is a cross-sectional view of the lens at the wide-angle end of the numerical example 2 of the present invention.
Fig. 6 is an aberration diagram at the wide-angle end of the numerical embodiment 2 of the present invention.
7 is an aberration diagram at the middle zoom position of numerical embodiment 2 of the present invention.
8 is an aberration diagram at the telephoto end of numerical embodiment 2 of the present invention.
9 is a sectional view of the lens at the wide-angle end of the numerical example 3 of the present invention.
10 is an aberration diagram at the wide-angle end of numerical embodiment 3 of the present invention.
11 is an aberration diagram at the middle zoom position of Numerical Embodiment 3 of the present invention.
12 is an aberration diagram at the telephoto end of Numerical Embodiment 3 of the present invention.
13 is a sectional view of the lens at the wide-angle end of the numerical example 4 of the present invention.
14 is an aberration diagram at the wide-angle end of the numerical embodiment 4 of the present invention.
15 is an aberration diagram at the middle zoom position of the numerical example 4 of the present invention.
16 is an aberration diagram at the telephoto end of Numerical Example 4 of the present invention.
17 is a sectional view of the lens at the wide-angle end of the numerical example 5 of the present invention.
18 is an aberration diagram at the wide-angle end of the numerical example 5 of the present invention.
19 is an aberration diagram at the middle zoom position of the numerical example 5 of the present invention.
20 is an aberration diagram at the telephoto end of the numerical example 5 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant description will be omitted.

1 is a schematic diagram showing a zoom lens system according to the present embodiment. The imaging apparatus according to the present embodiment comprises the zoom lens system shown in Fig. 1 and an imaging element having an imaging surface on which a subject image is formed by the zoom lens system. Fig. 1 shows a zoom lens system according to Numerical Example 1 described later. As shown in Fig. 1, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens having a positive refractive power are arranged in order from the object side (left side in Fig. 1) Group G3 and a fourth lens group G4 having a positive refractive power and the diaphragm SP is disposed on the most object side of the third lens group G3.

G shown in Fig. 1 is an optical filter or an optical block corresponding to a face plate or the like. When the zoom lens system according to the embodiment of the present invention is used as a photographing optical system of a surveillance camera, a video camera, and a digital still camera, IP corresponds to an image pickup surface of a solid-state image pickup element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor . When the zoom lens system according to the embodiment of the present invention is a silver salt film camera, the film surface corresponds to IP.

At the time of shifting from the wide angle end to the telephoto end, the second lens group G2 is moved to the upper surface side as shown by an arrow. At this time, the first lens group G1 and the third lens group G3 are fixed in the direction of the optical axis, and the fourth lens group G4 is configured to compensate for the fluctuation of the image plane position due to the movement of the second lens group G2 And moves to the object side at the time of near focusing. The curved line 4a of the solid line and the curved line 4b of the fourth lens group G4 shown in Fig. 1 correspond to the magnification from the wide angle end to the telephoto end when focusing on the near object and the infinite object, respectively And the movement trajectory for correcting the top surface variation according to the above.

The first lens group G1 is composed of a cemented lens of a meniscus-shaped negative lens 11 whose convex surface faces the object side and a positive lens 12 whose convex surface faces the object side, and a cemented lens of a convex surface facing the object side And two positive lenses (13, 14). The second lens group G2 is composed of a cemented lens of two negative lenses 21 and 22 in order from the object side and a positive lens 23 and negative lens 24 with a convex surface facing the object side.

The third lens group G3 is composed of an independent positive lens 31 having an aspherical shape on the object side in order from the object side and a cemented lens of a positive lens 32 and a negative lens 33. The fourth lens group G4 is composed of a cemented lens of a positive lens 41 and a negative lens 42 having an aspherical shape on the object side in order from the object side.

Hereinafter, the present embodiment will be described in detail. The zoom lens system according to the present embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a diaphragm SP fixed to the upper surface, A third lens group G3 having positive refractive power and a fourth lens group G4 having positive refractive power, wherein the first lens group G1 and the third lens group G3 are arranged at a wide angle end to a telephoto end, And the fourth lens group (g4) is fixed in the direction of the optical axis, and the second lens group (G2) moves from the object side to the image side, In a zoom lens system having a focusing function and moving in the direction of an optical axis,

Wherein the first lens group G1 has one negative lens and three positive lenses in order from the object side and the second lens group G2 has at least three negative lenses and one positive lens, The third lens group G3 has, in order from the object side, an independent positive lens, a cemented lens of a positive lens and a negative lens, the fourth lens group G4 has at least one positive lens and negative lens, Is satisfied.

0.03 < f2 / ft < 0.08 ... (Conditional Expression 1)

5.8 < f1 / f2 | < 8.0 ... (Conditional expression 2)

Here, f1 represents the focal length of the first lens unit, f2 represents the focal length of the second lens unit, and ft represents the focal length of the entire lens system at the telephoto end.

At least three positive lenses constituting the first lens group G1 are disposed to disperse the positive refractive power, and in particular, the spherical aberration at the telephoto end is easily corrected. In addition, the use of a superalloy (glass material, glass material) having Abbe's number of 80 or more in the positive lens facilitates correction of axial chromatic aberration and chromatic aberration of magnification particularly at the telephoto end.

The second lens group G2 disperses the negative refracting power by disposing at least three negative lenses and one positive lens, and corrects the coma aberration caused by the change of the angle of view in the wide angle state, thereby achieving high performance have. In addition, preferably, by arranging the cemented lens of the positive lens and the negative lens, the aberration correction such as chromatic aberration is corrected well, and the influence of attachment error or the like at the time of manufacturing is reduced, and stable optical quality can be obtained.

The third lens group G3 has at least one surface including the aspherical surface, thereby making it possible to satisfactorily correct the off-axis aberration generated at the time of changing the image. Further, the third lens group G3 is composed of two positive lenses and a negative lens, thereby satisfactorily correcting the chromatic aberration generated in the third lens group G3, and further correcting the main point position of the third lens group G3 It is possible to reduce the distance from the third lens group G3 to the imaging plane, thereby contributing to downsizing. Further, by making the negative lens constituting the third lens group G3 a negative meniscus lens having a strong curvature on the image surface side, it is possible to easily correct the spherical aberration, and the third lens group G3 By making the negative lens into a positive lens and a cemented lens, the main point interval with the positive lens on the most object side of the third lens group (G3) is widened, and it is easy to ensure stable optical performance at the time of manufacture.

The fourth lens group G4 is constituted by a cemented lens of a positive lens and a negative lens, so that the axial aberration generated at the time of changing can be satisfactorily corrected. Further, by simplifying the structure by the joining, the weight of the fourth lens group G4 as the movable lens group can be reduced, and the focusing operation can be performed at a high speed. Preferably, by having at least one aspheric surface, it becomes easy to correct spherical aberration generated in the fourth lens group G4 satisfactorily.

Condition (1) defines the focal length of the second lens group G2 and the focal length of the entire lens system at the telephoto end. If the refractive power of the second lens group G2 is weakened beyond the upper limit value of the conditional expression (1), the amount of movement at the time of shifting increases and the overall length becomes longer, making miniaturization difficult. If the refractive power of the second lens group G2 is strengthened beyond the lower limit value of the conditional expression (1), it becomes difficult to correct the aberration variation at the time of changing from the wide angle end state to the telephoto end state, which is not preferable.

Preferably, the numerical range of the conditional expression (1) is set to satisfy the following conditional expression (1a).

0.05 < f2 / ft < 0.065 ... (Conditional Expression 1a)

Condition (2) defines the focal length of the first lens group G1 and the focal length of the second lens group G2. If the refractive power of the first lens group G1 is weakened beyond the upper limit value of the conditional expression (2), the entire length of the zoom lens system becomes long and further, the lens diameter of the first lens group G1 can not be made large, It becomes difficult to do so. If the refractive power of the first lens group G1 is strengthened beyond the lower limit value of the condition (2), it becomes difficult to correct the spherical aberration at the telephoto end, and high performance can not be achieved.

Preferably, the numerical range of conditional expression (2) is set to satisfy the following conditional expression (2a).

6.0 <| f1 / f2 | <7.0 ... (Conditional expression 2a)

More preferably, the third lens group G3 preferably satisfies the following conditions.

0.15 < f3 / ft < 0.35 ... (Conditional expression 3)

0.4 < f31 / f3 < 0.8 ... (Conditional expression 4)

Here, f3 is the focal length of the third lens group, f31 is the focal length of the most object-side positive lens constituting the third lens group, and ft is the focal length of the entire lens system at the telephoto end.

The conditional expression (3) defines the focal length of the third lens group G3 and the focal length of the entire lens system at the telephoto end. The refractive power of the third lens group G3 becomes too weak when the upper limit value of the conditional expression (3) is exceeded and the refractive power of the entire third lens group G3 and the fourth lens group G4 is maintained. It is difficult to correct the aberrations such as the astigmatism and the coma aberration satisfactorily. If the lower limit value of the conditional expression (3) is exceeded, the refractive power of the third lens group G3 becomes too strong, and aberration such as spherical aberration largely occurs.

Preferably, it is desirable to set the numerical range of conditional expression (3) to satisfy the following conditional expression (3a).

0.2 < f3 / ft < 0.3 ... (Conditional expression 3a)

The conditional expression (4) defines the focal length of the most object-side positive lens and the third lens group G3 constituting the third lens group G32. When the upper limit value of the condition (4) is exceeded, the refractive power of the most object side positive lens constituting the third lens group G3 becomes too weak, and the total length of the zoom lens system becomes long, which is not preferable. When the lower limit value of the condition (4) is exceeded, the refractive power of the most object-side positive lens constituting the third lens group G3 becomes too strong, and aberration such as spherical aberration becomes large.

Preferably, it is preferable to set the numerical range of the conditional expression (4) to satisfy the following conditional expression (4a).

0.55 < f31 / f3 < 0.7 (Conditional expression 4a)

More preferably, the fourth lens group G4 preferably satisfies the following conditions.

0.08 < f4 / ft < 0.25 ... (Conditional expression 5)

Here, f4 represents the focal length of the fourth lens unit, and ft represents the focal length of the entire lens system at the telephoto end.

The conditional expression (5) defines the focal length of the fourth lens group G4 and the focal length of the entire lens system at the telephoto end. When the refractive power of the fourth lens group G4 is weakened beyond the upper limit value of the conditional expression (5), the amount of projection during focusing of the fourth lens group G4 (that is, the moving distance to the object side or the image side of the fourth lens) And the interval between the third lens group G3 and the fourth lens group G4 can not be shortened, making it difficult to downsize. If the refractive power of the fourth lens group G4 is strengthened beyond the lower limit value of the conditional expression (5), it becomes difficult to correct the aberration variation at the time of changing from the wide angle end state to the telephoto end state.

Preferably, the numerical range of the conditional expression (5) is set to satisfy the following conditional expression (5a).

0.1 < f4 / ft < 0.16 ... (Conditional expression 5a)

As described above, in the zoom lens system according to the present embodiment, by appropriately configuring each lens group, miniaturization is realized while maintaining the optical performance corresponding to a high-resolution imaging device with a high aspect ratio and a variable aspect ratio of about 30.

According to this embodiment, in an image pickup apparatus such as a surveillance camera, a video camera, a digital still camera, or the like, it is possible to provide an image pickup device having a high aspect ratio and a small size with a variable aspect ratio of 30 or so and extending from a wide angle end to a telephoto end and an infinite circle, A zoom lens system capable of maintaining a corresponding good optical performance is obtained.

Hereinafter, a specific embodiment of the present embodiment will be described. Numerical Examples 1 to 5 shown below are specific examples suitable for the above conditional expression. In each numerical example, the surface number (i) indicates the order of the optical surface from the object side. ri is the radius of curvature of the i-th optical surface, di is the surface interval between the i-th surface and the (i + 1) th surface, and ndi and vdi are the refractive index and Abbe number of the material of the i- . The back focus BF is a value obtained by converting the distance from the final lens surface to the paraxial upper surface. The total length of the lens is a value obtained by adding the back focus BF to the distance from the lens front surface to the lens final surface.

The unit of length is mm. Assuming that the displacement of the optical axis direction at the position of the aspherical surface coefficient and the height H from the optical axis is denoted by x with the conic constant, A4, A6, A8, A10 as the reference, .

Where R is the radius of curvature. Further, for example, the indication of "E-Z" means "10-Z". f denotes a focal length, Fno denotes an F number, and? denotes a half angle of view.

[Example 1]

[Table 1]

[Table 2]

[Example 2]

[Table 3]

[Table 4]

[Example 3]

[Table 5]

[Table 6]

[Example 4]

[Table 7]

[Table 8]

[Example 5]

[Table 9]

[Table 10]

The following table shows the conditional equation correspondence table of each numerical example. Each value represents the value specified in each conditional expression. Thus, all the numerical embodiments satisfy the respective conditional expressions.

[Table 11]

While the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. It will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. .

G1 first lens group
G2 second lens group
G3 third lens group
G4 fourth lens group
SP Aperture
IP image plane
MERIDIONAL top surface
ΔS Sagittal top surface
ω half angle of view
Fno F number

Claims (10)

In order from the object side,
A first lens group having a positive refractive power;
A second lens group having negative refractive power;
A diaphragm fixed relative to the image plane;
A third lens group having positive refractive power;
And a fourth lens group having positive refractive power,
The first lens group and the third lens group are fixed in the optical axis direction at the time of changing from the wide angle end to the telephoto end and the second lens group moves upward from the object side to effect magnification, Moves in the optical axis direction and performs a focusing function to compensate for the variation of the image plane position due to the movement of the second lens group,
Wherein the first lens group includes one negative lens and three positive lenses, the second lens group includes one positive lens, the third lens group includes, from the object side, And a cemented lens of a positive lens and a negative lens having a convex shape on the object side, and the fourth lens group includes at least one positive lens,
Wherein the Abbe number of two consecutive positive lenses among the three positive lenses included in the first lens group is 80 or more, and the following condition is satisfied.
0.03 < f2 / ft < 0.08
F2: focal length of the second lens group
ft: Focal length across the lens system at the telephoto end The method according to claim 1,
Wherein the second lens group has at least three negative lenses and one positive lens, the fourth lens group has at least one positive lens and at least one negative lens, and satisfies the following conditions Features a zoom lens system.
5.8 < f1 / f2 < 8.0
F1: focal length of the first lens group
f2: focal length of the second lens group [Claim 3 is abandoned upon payment of the registration fee.] 3. The method of claim 2,
Wherein the most object-side positive lens constituting the third lens group has at least one surface including an aspherical surface, and the following condition is satisfied.
0.15 < f3 / ft < 0.35
0.4 < f31 / f3 < 0.8
F3: focal length of the third lens group
f31: focal length of the most object-side positive lens constituting the third lens group
ft: Focal length across the lens system at the telephoto end delete delete 3. The method according to claim 1 or 2,
The one positive lens of the second lens group is a positive lens whose convex surface faces the object side,
Wherein the second lens group is composed of a cemented lens of two negative lenses in order from the object side and a positive lens and a negative lens with a convex surface facing the object side. [7] has been abandoned due to the registration fee. The method of claim 3,
The one positive lens of the second lens group is a positive lens whose convex surface faces the object side,
Wherein the second lens group is composed of a cemented lens of two negative lenses in order from the object side and a positive lens and a negative lens with a convex surface facing the object side. 3. The method according to claim 1 or 2,
Wherein the fourth lens group is composed of a cemented lens of a positive lens and a negative lens in order from the object side and the positive lens constituting the fourth lens group has at least one surface including an aspherical shape, Of the zoom lens system.
0.08 < f4 / ft < 0.25
F4: focal length of the fourth lens group
ft: Focal length across the lens system at the telephoto end [Claim 9 is abandoned upon payment of registration fee.] The method of claim 3,
Wherein the fourth lens group is composed of a cemented lens of a positive lens and a negative lens in order from the object side and the positive lens constituting the fourth lens group has at least one surface including an aspherical shape, Of the zoom lens system.
0.08 < f4 / ft < 0.25
F4: focal length of the fourth lens group
ft: Focal length across the lens system at the telephoto end delete

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