JP2004279489A - Zoom lens - Google Patents

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Publication number
JP2004279489A
JP2004279489A JP2003067388A JP2003067388A JP2004279489A JP 2004279489 A JP2004279489 A JP 2004279489A JP 2003067388 A JP2003067388 A JP 2003067388A JP 2003067388 A JP2003067388 A JP 2003067388A JP 2004279489 A JP2004279489 A JP 2004279489A
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JP
Japan
Prior art keywords
lens
negative
zoom
lenses
focal length
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
JP2003067388A
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Japanese (ja)
Inventor
Yasuhisa Kitaoka
Akihiro Muramatsu
泰久 北岡
昭宏 村松
Original Assignee
Matsushita Electric Ind Co Ltd
松下電器産業株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Matsushita Electric Ind Co Ltd, 松下電器産業株式会社 filed Critical Matsushita Electric Ind Co Ltd
Priority to JP2003067388A priority Critical patent/JP2004279489A/en
Publication of JP2004279489A publication Critical patent/JP2004279489A/en
Pending legal-status Critical Current

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Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens keeping a zoom ratio such as 10 to 20 with a small number of lenses, having high image quality suitable for a video camera and a digital still camera and realizing miniaturization and the reduction of the cost. <P>SOLUTION: The zoom lens has a 1st lens group 1 to a 4th lens group 4 sequentially from an object side to an image surface side. When it is assumed that the refractive index of a negative lens whose refractive index is the smallest out of negative lenses constituting the 2nd lens group 2 is n2min, the focal distance of the 3rd lens group 3 is f3, the focal distance of the positive lens of the 3rd lens group is f3p and the focal distance of the negative lens of the 3rd lens group is f3n, the zoom lens satisfies conditions; 1.65<n2min, 0.3<f3p/f3<0.5, 0.3<¾f3n/f3¾<0.6 and 0.75<¾f3p/f3n¾<1.1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a zoom lens, and more particularly, to a zoom lens used for a video camera or the like.
[0002]
[Prior art]
Recent consumer video cameras are strongly demanded to have high image quality, small size and high zoom ratio. To meet such demands, for example, there are those described in Patent Literature 1 and Patent Literature 2. According to Patent Document 1, a high zoom ratio of about 17 times is achieved with a small number of components such as ten. Further, according to Patent Document 2, an optical system that achieves a zoom ratio of 10 times and achieves downsizing with a configuration of nine images, which is one less, is proposed.
[0003]
[Patent Document 1]
JP-A-11-52241 (FIGS. 1 to 5 to 8)
[0004]
[Patent Document 2]
JP 2001-116999 A (Pages 5 to 7 FIG. 1)
[0005]
[Problems to be solved by the invention]
As described above, in the prior art, when the number of lenses is 10 or more, a certain high zoom ratio is achieved, but it is necessary to increase the total optical length corresponding to the number of lenses. In a configuration having nine lenses, the zoom ratio is reduced to about 10 times, although the size is reduced. As described above, there is a problem that a small size and a high zoom ratio cannot be realized while maintaining high image quality with a small number of lens components such as nine.
[0006]
The present invention has been made in view of the above points, has a zoom ratio of 10 to 20 times with a small number of lens components, and has high image quality, small size, and low power suitable for a video camera and a digital still camera. It is an object of the present invention to provide a cost-effective zoom lens.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, a zoom lens according to the present invention includes:
In order from the object side to the image plane side, a first lens group having a positive refractive power and a fixed structure, and a function of changing the magnification by being movable on the optical axis and having a negative A second lens group having a refractive power, a third lens group having a positive refractive power and a fixed structure, and an image plane accompanying zooming or a change in object distance due to being movable on the optical axis. A fourth lens group having a function of correcting fluctuations and having a positive refractive power,
The first lens group includes three lenses, one negative lens and two positive lenses, and the second lens group includes three negative lenses and one positive lens that are biconcave. The third lens group has two lenses, one positive lens and one negative lens, and has at least one aspheric surface, and the fourth lens group has at least one aspheric surface. It has one positive lens including an aspheric surface,
The negative lens having the smallest refractive index among the negative lenses constituting the second lens group has a refractive index of n2min, the focal length of the third lens group is f3, and the focal length of the positive lens of the third lens group is f2. f3p, when the focal length of the negative lens of the third lens group is f3n,
1.65 <n2min (1)
0.3 <f3p / f3 <0.5 (2)
0.3 <| f3n / f3 | <0.6 (3)
0.75 <| f3p / f3n | <1.1 (4)
The following conditions are satisfied.
[0008]
According to the configuration of such a zoom lens, the first lens group has three lenses, the second lens group has three lenses, the third lens group has two lenses, and the fourth lens group has one lens, for a total of nine lenses. In addition, as shown in the above equations (2) to (4), by adopting an optimum power arrangement for the third lens group, a high zoom ratio of 10 to 20 times can be obtained with a small lens configuration. In addition, it is possible to realize a small zoom lens in which aberrations are favorably corrected.
[0009]
In the above-described zoom lens configuration, it is preferable that the following conditional expression be satisfied when the focal length at the wide-angle end of the entire system is fw.
3.5 <f3 / fw <6.0 (5)
According to this preferred example, the afocal property of the axial marginal ray exiting from the third lens group is maintained while securing the optimum back focus, and a compact zoom lens is realized.
[0010]
In the configuration of the zoom lens, when the absolute value of the smaller radius of curvature of the negative lens in the third lens group is R3n2, it is preferable that the following conditional expression is satisfied.
[0011]
0.25 <R3n2 / f3 <0.4 (6)
According to this preferred example, it is possible to realize a zoom lens in which coma and curvature of field are well corrected.
[0012]
In the configuration of the zoom lens, it is preferable that the following conditional expression is satisfied when the focal length of the fourth lens group is f4.
2.0 <f4 / fw <4.0 (7)
According to this preferred example, it is possible to realize a wide-angle zoom lens having an angle of view of about 60 ° at the wide-angle end while securing an optimum back focus.
[0013]
In the configuration of the zoom lens, it is preferable that the following conditional expression is satisfied when the focal length of the second lens group is f2.
0.9 <| f2 / fw | <1.5 (8)
According to this preferred example, it is possible to realize a small zoom lens in which the field curvature is corrected to be small.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
(Embodiment 1)
FIG. 1 shows a zoom lens according to a first embodiment of the present invention. Specifically, in the zoom lens of FIG. 1, 1 is a first lens group, 2 is a second lens group, 3 is a third lens group, 4 is a fourth lens group, and S is The stop is an aperture, and EG is an equivalent glass such as a cover glass of the image sensor and a low-pass filter. These are arranged in this order from the object side to the image plane side in the order of the first lens group 1, the second lens group 2, the stop S, the third lens group 3, the fourth lens group 4, and the equivalent glass EG. Of these, the second lens group 2 and the fourth lens group 4 are movable and move on the optical axis.
[0015]
In the present embodiment, as shown in FIG. 1, the first lens group 1 includes three lenses 1a, 1b, and 1c, one negative lens 1a and two positive lenses 1b and 1c. As a result, it has a positive refractive power and has a fixed structure. The second lens group 2 has a negative refracting power by being constituted by three lenses 2a, 2b, 2c including two biconcave negative lenses 2a, 2b and one positive lens 2c. In addition, as described above, the magnification is changed by moving on the optical axis. The third lens group 3 includes two lenses 3a and 3b, one positive lens 3a and one negative lens 3b, and has a positive refractive power and a fixed structure. I have. The third lens group 3 includes at least one aspheric surface. The fourth lens group 4 includes one positive lens 4a including at least one aspherical surface, has a positive refracting power, and changes by moving on the optical axis as described above. It has a function to correct the image plane fluctuation due to the change of the magnification or the object distance.
[0016]
In the present embodiment, as shown in FIG. 1, the first lens group 1 has three lenses, the second lens group 2 has three lenses, the third lens group 3 has two lenses, and the fourth lens group 4 has However, with a configuration having a small number of lenses, that is, a total of nine lenses, a zoom ratio can be increased and miniaturization can be achieved. In particular, in the second lens group 2, by using two biconcave negative lenses 2a and 2b, the front principal point of the second lens group 2 is arranged as close to the object side as possible, and the first lens group 1 The distance between the principal points is made small, thereby contributing to downsizing of the front lens diameter and downsizing of the overall length.
[0017]
Generally, to reduce the size of a zoom lens, the refractive power of the movable lens group is increased to minimize the amount of movement. However, in the four-group configuration used in the present invention, increasing the refractive power of the second lens group leads to an increase in the negative Petzval sum, making it difficult to flatten the image surface characteristics. Therefore, in the zoom lens according to the present embodiment, the following conditional expression (1) is satisfied, where n2min is the refractive index of the negative lens having the smallest refractive index among the negative lenses 2a and 2b constituting the second lens group 2. It is configured to
[0018]
1.65 <n2min (1)
It is desirable that the two negative lenses 2a and 2b in the second lens group 2 have relatively high refractive indices. If the value deviates from the expression (1), when the refractive power of the second lens unit 2 is increased in order to keep the overall length compact, the Petzval sum of the entire system increases in the negative direction, and it is difficult to correct the field curvature. become. Further, the curvature of the lens constituting the second lens group 2 becomes smaller, and the coma becomes larger.
[0019]
In the zoom lens of the present embodiment, the focal length of the third lens group 3 is f3, the focal length of the positive lens 3a in the third lens group 3 is f3p, and the focal length of the negative lens 3b in the third lens group 3 is When f3n is set, it is necessary to satisfy the following conditional expressions (2) to (4).
[0020]
0.3 <f3p / f3 <0.5 (2)
0.3 <| f3n / f3 | <0.6 (3)
0.75 <| f3p / f3n | <1.1 (4)
Here, the conditional expressions (2) and (3) relate to the refractive power of the positive lens 3a and the negative lens 3b of the third lens group 3, respectively, and the conditional expression (4) expresses the positive lens 3a and the negative lens. 3b.
[0021]
In order to reduce the size, it is desired that the front principal point and the rear principal point of the third lens unit 3 be arranged as close to the object as possible. By locating the front principal point of the third lens group 3 in the object side space, the distance between the principal points between the second lens group 2 and the third lens group 3 on the telephoto side can be reduced. Therefore, it is possible to prevent the moving area of the second lens group 2 from becoming longer. Further, since the third lens group 3 can be arranged at a position where the ray height is low in the paraxial region, the power of the fourth lens group 4 can be increased, and the Petzval sum when the size is reduced is improved. Can contribute to. It is important to reduce the air gap between the third lens group 3 and the fourth lens group 4. However, when the stop S is disposed in front of the third lens group 3, the third lens group 3 and the fourth lens group The distance between the principal point and the principal point 4 is for determining the condition of telecentricity. If this distance is shortened and the exit pupil position is too close to the image plane, the angle of the principal ray exiting from the fourth lens group 4 is reduced. As a result, undesired phenomena such as shading or the like, in which color reproducibility deteriorates, occur. In order to solve this problem, the rear principal point of the third lens group 3 is arranged as close to the object side as possible, and the air gap between the third lens group 3 and the fourth lens group 4 is shortened. Need to be large.
[0022]
Conditional expressions (2), (3) and (4) are for satisfying the above-mentioned contents in order to achieve miniaturization. If the lower limit of conditional expressions (2) and (3) is exceeded and the refractive power is too strong, the curvature will be too strong and the amount of coma will increase. Conversely, if the refractive power is weaker than the upper limit, the convergence of the light beam is weakened, and the back focus becomes longer, and the principal point cannot be located on the object side, and so on. Conditional expression (4) is correlated with conditional expressions (2) and (3). However, if the value exceeds the upper limit, the refractive power of the third lens unit 3 becomes weak, the back focus becomes long, and miniaturization cannot be achieved. . When the value is below the lower limit, the principal point position is not located on the object side, the exit pupil position approaches the image plane, or the moving area of the second lens unit 2 for zooming becomes large, and the lens system is downsized. Adverse effects, such as being unable to do so.
[0023]
The zoom lens according to the present embodiment may satisfy the following conditional expression (5) when the focal length of the third lens unit 3 is f3 and the focal length at the wide-angle end of the entire system is fw. desirable.
[0024]
3.5 <f3 / fw <6.0 (5)
This expression (5) is a conditional expression relating to the refractive power of the third lens group 3. If the refractive power is lower than the lower limit and the refractive power is increased, the size is reduced, but it becomes difficult to secure a back focus for inserting a crystal filter or the like. Conversely, if the refractive power is weaker than the upper limit, the back focus is extended, thereby causing the fourth lens group 4 to be enlarged, and the overall size tends to be increased.
[0025]
Further, when the focal length of the third lens group 3 is f3 and the absolute value of the smaller radius of curvature of the negative lens 3b in the third lens group 3 is R3n2, the zoom lens of the present embodiment has the following (6) It is desirable to satisfy the conditional expression (1).
[0026]
0.25 <R3n2 / f3 <0.4 (6)
Equation (6) defines the range in which coma and curvature of field are favorably corrected. If the curvature falls below the lower limit and the curvature becomes small, outward coma aberration occurs near the middle position of the zoom, and the curvature of field may fall to the over side and cannot be corrected completely. Conversely, if the curvature exceeds the upper limit and the curvature becomes large, inward coma aberration that cannot be completely corrected in the vicinity of the middle position of the zoom is likely to occur, and in that case, the curvature of field tends to fall under.
[0027]
The zoom lens according to the present embodiment may satisfy the following conditional expression (7) when the focal length of the fourth lens unit 4 is f4 and the focal length at the wide-angle end of the entire system is fw. desirable.
[0028]
2.0 <f4 / fw <4.0 (7)
Expression (7) is a conditional expression relating to the refractive power of the fourth lens group 4. When the refractive power is lower than the lower limit, the size tends to be small, but it tends to be difficult to secure a back focus for inserting a quartz filter or the like. Conversely, if the refractive power is weaker than the upper limit, the back focus is extended, the movement area of the fourth lens unit 4 is enlarged, and the overall size tends to be large.
[0029]
It is preferable that the zoom lens according to the present embodiment satisfies the following conditional expression (8) when the focal length of the second lens group is f2 and the focal length at the wide-angle end of the entire system is fw. .
[0030]
0.9 <| f2 / fw | <1.5 (8)
Equation (8) relates to the refractive power of the second lens group during zooming. It is desirable to achieve a small amount of movement and a high zoom ratio with strong refracting power, but if the value falls below the lower limit, the Petzval sum tends to be large, although in the direction of miniaturization, and it tends to be difficult to correct the field curvature. Occurs. Conversely, if the value exceeds the upper limit, the amount of movement of the second lens group 2 increases, and it tends to be difficult to reduce the size of the entire system.
[0031]
Table 1 shows numerical examples of the first embodiment. In the table, r1, r2,... Are the radius of curvature of each lens surface counted in order from the object side, d1, d2,... Are the thickness and air spacing of each lens, and n1, n2,. Are the Abbe numbers based on the d-line. FIGS. 2 to 4 are aberration diagrams of this numerical example, showing the aberrations at the wide-angle end (FIG. 2), the middle position (FIG. 3), and the telephoto end (FIG. 4). The focal length of the entire system is represented by f, the F number is represented by F /, and the angle of view is represented by ω. In the examples of Table 1, the surface marked with * is an aspheric surface, and the aspheric surface shape is represented by the following equation.
[0032]
Here, the optical axis direction is x axis, the distance from the optical axis is h, the radius of curvature of the reference spherical surface is r, and the aspherical coefficients K, A, B, C, D, and E are as shown in Table 1.
[0033]
[Table 1]
In the spherical aberration diagrams of FIGS. 2 to 4, F represents the F line, and C represents the C line. In the astigmatism diagram, S represents a sagittal image plane, and M represents a meridional image plane. As can be seen from these aberration diagrams, good optical performance with small aberration can be realized.
[0034]
The zoom ratio is 10 times, the value of n2min is 1.68, the value of f3p / f3 is 0.40, | f3n / f3 | is 0.44, | f3p / f3n | is 0.90, and f3 / fw is 3.0. 8, R3n2 / f3 is 0.30, f4 / fw is 2.18, and | f2 / fw | is 1.0, which satisfies the conditional expressions (1) to (8), respectively.
(Embodiment 2)
FIG. 5 shows a zoom lens according to Embodiment 2 of the present invention. In FIG. 5, all of the first lens group 1, the second lens group 2, the third lens group 3, and the fourth lens group 4 have the configuration shown in FIG. Is similar to Here, numerical examples are different from those of the first embodiment as shown in Table 2. In Table 2, the meanings of the respective symbols are the same as those in Table 1.
[0035]
Here, the zoom ratio is 16 times, the value of n2min is 1.68, the value of f3p / f3 is 0.45, the value of | f3n / f3 | is 0.57, and the value of | f3p / f3n | is 0. .80, the value of f3 / fw was 4.5, the value of R3n2 / f3 was 0.35, the value of f4 / fw was 3.09, and the value of | f2 / fw | was 1.3. Equations (1) to (8) are satisfied.
[0036]
[Table 2]
The aberration performance of this lens is shown in the aberration diagrams at the wide-angle end (FIG. 6), the middle position (FIG. 7), and the telephoto end (FIG. 8) in FIGS. As in the first embodiment, good optical performance with small aberration can be realized.
(Embodiment 3)
FIG. 9 shows a zoom lens according to Embodiment 3 of the present invention. In FIG. 9, all of the first lens group 1, the second lens group 2, the third lens group 3, and the fourth lens group 4 have the configuration shown in FIG. Is similar to Here, numerical examples are different from those of the first embodiment as shown in Table 3. In Table 3, the meanings of the respective symbols are the same as those in Table 1.
[0037]
Here, the zoom ratio is 20 times, the value of n2min is 1.68, the value of f3p / f3 is 0.44, the value of | f3n / f3 | is 0.55, and the value of | f3p / f3n | is 0. .80, the value of f3 / fw was 5.0, the value of R3n2 / f3 was 0.35, the value of f4 / fw was 3.35, and the value of | f2 / fw | was 1.4. Equations (1) to (8) are satisfied.
[0038]
[Table 3]
The aberration performance of this lens is shown in FIGS. 10 to 12 at the wide-angle end (FIG. 10), the middle (FIG. 11), and the telephoto end (FIG. 12). As in the first embodiment, good optical performance with small aberration can be realized.
[0039]
The first to third embodiments described above are all intended to clarify the technical contents of the present invention, and the present invention is interpreted by limiting to only such specific embodiments. Instead, the present invention should be embodied with various modifications within the spirit and scope of the invention and the present invention should be interpreted in a broad sense.
[0040]
【The invention's effect】
As described above, according to the present invention, a unique power arrangement is adopted for the third lens unit, and the refractive power of each lens unit is set optimally, so that 10 to 20 can be achieved with a small lens configuration of 9 lenses. This makes it possible to provide a small, low-cost zoom lens having a high magnification and a well corrected aberration. For this reason, it is possible to provide a compact, high-performance, low-cost zoom lens having high magnification, which is suitable for a video camera or a digital still camera.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a zoom lens according to a first embodiment of the present invention; FIG. 2 is a diagram illustrating aberration performance at a wide-angle end in the zoom lens of FIG. 1; FIG. FIG. 4 is a diagram showing aberration performance. FIG. 4 is a diagram showing aberration performance at the telephoto end in the zoom lens of FIG. 1. FIG. 5 is a configuration diagram of a zoom lens according to a second embodiment of the present invention. FIG. 7 is a diagram showing aberration performance at a wide-angle end in FIG. 7 FIG. 7 is a diagram showing aberration performance at an intermediate position in the zoom lens of FIG. 5 FIG. 8 is a diagram showing aberration performance at a telephoto end in the zoom lens of FIG. 9 is a configuration diagram of a zoom lens according to Embodiment 3 of the present invention. FIG. 10 is a diagram showing aberration performance at the wide-angle end in the zoom lens of FIG. 9. FIG. 11 is aberration performance at an intermediate position in the zoom lens of FIG. FIG. 12 shows the zoom lens of FIG. Figure [EXPLANATION OF SYMBOLS] showing the aberration performance at the telephoto end in the
DESCRIPTION OF SYMBOLS 1 1st lens group 2 2nd lens group 3 3rd lens group 4 4th lens group S Stop EG Equivalent glass, such as a cover glass of an image sensor, a low-pass filter, etc.

Claims (5)

  1. In order from the object side to the image plane side, a first lens group having a positive refractive power and a fixed structure, and a function of changing the magnification by being movable on the optical axis and having a negative A second lens group having a refractive power, a third lens group having a positive refractive power and a fixed structure, and an image plane accompanying zooming or a change in object distance due to being movable on the optical axis. A fourth lens group having a function of correcting fluctuations and having a positive refractive power,
    The first lens group includes three lenses, one negative lens and two positive lenses, and the second lens group includes three negative lenses and one positive lens that are biconcave. The third lens group has two lenses, one positive lens and one negative lens, and has at least one aspheric surface, and the fourth lens group has at least one aspheric surface. It has one positive lens including an aspheric surface,
    The negative lens having the smallest refractive index among the negative lenses constituting the second lens group has a refractive index of n2min, the focal length of the third lens group is f3, and the focal length of the positive lens of the third lens group is f2. f3p, when the focal length of the negative lens of the third lens group is f3n,
    1.65 <n2min
    0.3 <f3p / f3 <0.5
    0.3 <| f3n / f3 | <0.6
    0.75 <| f3p / f3n | <1.1
    A zoom lens that satisfies certain conditions.
  2. When the focal length at the wide-angle end of the entire system is fw,
    3.5 <f3 / fw <6.0
    The zoom lens according to claim 1, wherein the following condition is satisfied.
  3. When the absolute value of the smaller radius of curvature of the negative lens in the third lens group is R3n2,
    0.25 <R3n2 / f3 <0.4
    3. The zoom lens according to claim 1, wherein the following condition is satisfied.
  4. When the focal length of the fourth lens group is f4 and the focal length at the wide-angle end of the entire system is fw,
    2.0 <f4 / fw <4.0
    The zoom lens according to any one of claims 1 to 3, wherein the following condition is satisfied.
  5. When the focal length of the second lens group is f2 and the focal length at the wide-angle end of the entire system is fw,
    0.9 <| f2 / fw | <1.5
    The zoom lens according to any one of claims 1 to 4, wherein the following condition is satisfied.
JP2003067388A 2003-03-13 2003-03-13 Zoom lens Pending JP2004279489A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008216440A (en) * 2007-03-01 2008-09-18 Canon Inc Zoom lens with image stabilization function
WO2012046450A1 (en) * 2010-10-08 2012-04-12 富士フイルム株式会社 Zoom lens and imaging device

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008216440A (en) * 2007-03-01 2008-09-18 Canon Inc Zoom lens with image stabilization function
WO2012046450A1 (en) * 2010-10-08 2012-04-12 富士フイルム株式会社 Zoom lens and imaging device
US8670186B2 (en) 2010-10-08 2014-03-11 Fujifilm Corporation Zoom lens and image pickup apparatus

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