CN1051849C - Zoom lens - Google Patents

Abstract

A pocket zoom lens with a zoom ratio of about 3.5 times, comprising a first lens group with a positive refractive index, a second lens group with a positive refractive index and a first distance from the first lens group, and a lens group with a negative refractive index and A third lens group at a second distance from the second lens group, the first and second distances are changed during zooming, where 3.0<f _T /f _W ; and L _T /f _T <1.0, where f _T is the zoom The focal length of the lens at the telephoto position, f _W is the focal length of the zoom lens at the wide-angle position, and _LT is the distance from the first mirror surface of the zoom lens to the image plane at the telephoto position.

Description

zoom lens

The present invention relates to a pocket zoom lens system with high zoom ratio.

More recently, so-called "pocket" cameras have come to include a zoom function in addition to their automatic function and small size. Zoom lenses have been used in large quantities in single-lens reflex cameras in the past, and there are many types of such zoom lenses. However, zoom lenses designed for SLR cameras are not suitable for compact cameras, because such zoom lenses have a long back focal length and are not small enough.

For compact cameras, there are two types of zoom lenses. One type is a zoom lens composed of two lens groups with a zoom ratio of about 1.5 times. However, for zoom ratios above 2.0, it is practically impossible for such zoom lenses to be small.

Another type is a zoom lens composed of three lens groups with a zoom ratio of about 2.5 times. U.S. Patents US 4978204, US 5002373 and US 5033832 disclose this type of lens. But the zoom ratio of this lens is limited to about 2.6 times, and this zoom ratio is not enough for a compact camera.

For example, the disclosed zoom lens of U.S. Patent No. 4,978,204 and U.S. Pat. No. 5,002,373 has a zoom ratio of about 2.6 times and is composed of 11 mirror lenses. The zoom lens disclosed in U.S. Patent No. 5,033,832 has a zoom ratio of about 2.7 times and is composed of 12 lenses. The disclosed zoom lens of US 5033832 widens the viewing angle of the wide-angle area, but the zoom ratio of 2.7 times is still not large enough. For compact cameras, the zoom ratio should be at least 3.5x.

The present invention overcomes the shortcoming of prior art, and it provides a kind of zoom lens of three lens groups, and this lens volume is small and has enough big magnification, promptly has the zoom ratio of about 3.5 times, has good optical performance simultaneously .

In order to realize the purpose of the present invention, as described in the following embodiments, the zoom lens of the present invention includes: a first lens group with positive refractive power, a second lens group with positive refractive power, and it is the first lens group apart from the first lens group. distance, the third lens group having negative refractive power, which is a second distance from the second lens group, the first and second distances changing during zooming, where:

3.0 < f _T /f _W ; and

L _T /f _T <1.0

Where f _T is the focal length of the zoom lens at the telephoto position, f _W is the focal length of the zoom lens at the wide-angle position, _{and LT} is the distance from the first mirror surface of the zoom lens to the imaging surface at the telephoto position.

Other objectives and advantages of the present invention can be understood better from the following introduction and practice of the present invention. Objects and advantages of the invention will be apparent from the elements and combinations thereof pointed out in particular in the claims.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

Fig. 1 is the cross-sectional view of the zoom lens of the first preferred embodiment of the present invention at (a) wide-angle, (b) mid-focus and (c) telephoto positions;

Fig. 2 is the size of various aberrations when the zoom lens of the first preferred embodiment of the present invention is at (a) wide-angle, (b) medium-focus and (c) telephoto positions;

Fig. 3 is the cross-sectional view of the zoom lens of the second preferred embodiment of the present invention at (a) wide-angle, (b) medium-focus and (c) telephoto positions;

Fig. 4 is the size of various aberrations when the zoom lens of the second preferred embodiment of the present invention is at (a) wide-angle, (b) medium-focus and (c) telephoto positions;

Fig. 5 is a cross-sectional view of the zoom lens of the third preferred embodiment of the present invention at (a) wide-angle, (b) medium-focus and (c) telephoto positions;

FIG. 6 shows the magnitudes of various aberrations of the zoom lens according to the third preferred embodiment of the present invention at (a) wide-angle, (b) medium-focus and (c) telephoto positions.

The first, second and third preferred embodiments of the present invention will be described in detail below with reference to accompanying drawings 1, 3 and 5, respectively. Wherever possible, the same reference numbers will be used in the drawings to refer to the same or similar parts.

In order to better understand the structure and working principle of the zoom lens of the present invention, the zoom lenses of the three embodiments of the present invention will be introduced together in paragraphs I to IX below.

I. With reference to Fig. 1, 3 and 5, the zoom lens of the present invention comprises: a first lens group I, a second lens group II, and a third lens group III, which are separated from each other and arranged sequentially from the object. The second lens group II includes a first lens group IIa and a second lens group IIb, which are separated from each other by a certain interval and arranged sequentially from the object side. The first and second lens groups I and II preferably have positive refractive power, while the third lens group III has negative refractive power.

In this zoom lens, the distance between the first lens group I and the second lens group II, and the distance between the second lens group II and the third lens III can be changed during zooming. In order to obtain a high zoom ratio, the zoom lens preferably satisfies the following relationship:

3.0＜f _T /f _W (1)

Where f _T is the focal length of the zoom lens at the telephoto position, and f _w is the focal length of the zoom lens at the wide-angle position.

II. In order to obtain a compact structure, the zoom lens preferably satisfies the following relationship:

L _T /f _T <1.0 (2)

3.5＜ _mIIIT ＜5.5 (3)

Where L _T is the distance from the first lens surface to the image plane of the zoom lens at the telephoto position, and mIII _T is the lateral magnification of the third lens group III at the telephoto position. The first lens plane represents the surface of the zoom lens that faces the object, while the image plane represents the camera's film or focal plane on the side opposite the object.

III. zoom lens of the present invention preferably satisfies the following relationship:

0.18<fI, _IIT / _fT <0.28 (4)

-0.20<fIII/ _fT <-0.10 (5)

Where fI, II _T are the composite focal lengths of the first and second lens groups I and II at the telephoto position, and fIII is the focal length of the third lens group III in the zoom lens.

IV. the first lens group I of zoom lens of the present invention preferably comprises the eyeglass of at least one negative lens sheet and positive lens, and satisfies:

-1.0＜ _fIN / _fT ＜-0.5 (6)

40<υI _p -υI _N (7)

Wherein _fIN is the focal length of the negative lens in the first lens group, υI _p is the average value of the Abbe number of the positive lens in the first lens group I, and _υIN is the average value of the Abbe number of the negative lens in the first lens group I. Here, a negative lens means a lens with negative refractive power, and a positive lens means a lens with positive refractive power.

V. In the second lens group II of the zoom lens, the first lens group IIa preferably includes at least one negative lens and a positive lens sheet. The second lens group IIb preferably includes at least one negative lens and a positive lens sheet. The second lens group II preferably satisfies the following formula:

40<υIIb _P -υIIb _N (8)

Wherein υIIb _P is the average Abbe number of the positive lens in the second group IIb in the second lens group II, and υIIb _N is the average Abbe number of the negative lens in the second group IIb in the second lens group II.

VI. The third lens group III of zoom lens of the present invention preferably comprises two negative lens elements and a positive lens element, and meets:

0.15< _fIIIp / _fT <0.28 (9)

Where fIII _P is the focal length of the positive lens in the third lens group III.

VII. zoom lens of the present invention preferably satisfies the following formula:

ΔD _I,II /f _T =-ΔD _II,III /f _T (10)

Δ|ΔD _{I, II} /f _T |<0.10 (11)

Among them, D _{I, II} is the change of the distance between the first and second lens groups I and II when the zoom lens is changed from the telephoto position to the wide-angle position, and D _{II, III} is the change of the distance between the zoom lens from the telephoto position to the wide-angle position The distance between the second and third lens groups II and III varies.

VIII. zoom lens of the present invention can satisfy following formula:

f _I /f _T <0.55 (12)

|f _{II, IIIW} / f _{II, IIIT} | >5; f _{II, IIIT} < 0 (13)

Where f _I is the focal length of the first lens group I, f _{II, IIIW} is the composite focal length of the second and third lens groups II and III at wide-angle position, f _{II, IIIT} is the second and third lens group II and III Compound focal length at the telephoto position.

IX. The surface of each lens in the zoom lens of the present invention is preferably spherical.

The above paragraphs I to IX generally introduce the working principles of the first, second and third embodiments of the present invention.

The first paragraph provides the basic conditions of the zoom lens structure, especially the configuration of the refractive power between the lens groups in the zoom lens, so as to obtain the basic feature of the present invention, that is, a large zoom ratio.

Paragraph II relates to another feature of the present invention, ie small size. The zoom lens of the present invention includes three lens groups I, II and III, and the total length of the zoom lens is maximum when it is in the telephoto position. However, in order to obtain a large zoom ratio while maintaining a small size, the zoom lens of the present invention satisfies the condition of formula (2) so that its total length is smaller than the focal length of the zoom lens at the telephoto position.

The following formula is established: f=f _I m _II m _III , where f is the focal length of the zoom lens, f _I is the focal length of the first lens group I, m _II is the lateral magnification of the second lens II, m _III is the second The lateral magnification of the three-lens group.

Correspondingly, in order to increase the focal length f of the zoom lens at the telephoto position, all or part of the above three items f _I , m _II and m _III should be increased.

However, increasing f _I is inappropriate because it reduces the refractive power of the first lens group I, making it difficult to make the zoom lens compact. Further, although increasing m _II can make the zoom lens compact, it makes it difficult to compensate the aberrations associated with the third lens group III because the first and second lens groups I and II have strong positive refractive power.

In this way, the present invention can make the volume of the zoom lens small and increase the focal length f by setting m _III (that is, the lateral magnification of the third lens group) at the telephoto position to a value within the range of formula (3). If the value of m _III is less than the lower limit of the range of formula (3), it is impossible to obtain a large zoom ratio. On the other hand, if it exceeds the upper limit, the refractive power of the third lens group III becomes too strong, making it difficult to compensate positive aberration and causing problems because the lens is too sensitive during assembly.

Section III details how to obtain a large zoom ratio and a small size. Formula (4) represents the composite refractive power of the first and second lens groups I and II in the zoom lens at the telephoto position, if the composite refractive power falls below the lower limit set by Formula (4), then the first and second The refractive power of the lens groups I and II is too strong, making it difficult to compensate for the aberration of the negative refractive power of the third lens group III. On the other hand, if it exceeds the upper limit, although it helps to compensate the aberration of the third lens group III. However, it is difficult to make the system small in size.

Equation (5) gives the range of the refractive power of the third lens group III. The distance between the second and third lens groups II and III is determined by equations (4) and (5). Under the condition given by formula (5), if the focal length of the third lens group III is lower than the lower limit, the distance between the second and third lens groups will be increased, making it difficult for the zoom lens to be small in size. If the focal length exceeds the upper limit, performance will be reduced due to increased aberration.

Paragraph IV gives the conditions for compensating the general aberrations and chromatic aberrations of the first lens group I of the zoom lens. Specifically, in order to obtain high performance by minimizing the change in chromatic aberration that occurs when zooming, the chromatic aberration associated with each lens group of the zoom lens is eliminated by satisfying the above conditions.

Although the aberration of the first lens group I is compensated by at least one negative lens and one positive lens, if the corresponding value in (6) exceeds the upper limit given by (6) or is lower than the lower limit, it is difficult to compensate the spherical Aberration and coma. The formula (7) gives the conditions for eliminating the chromatic aberration of the first lens group I. According to an embodiment of the present invention, in order to compensate for aberration and eliminate chromatic aberration, the refractive power of the positive lens and the negative lens in the first lens group should be a small value, and as determined by (7), the material of the positive lens in the first lens group I should have a large Abbe number.

In addition, if there is at least one positive refractive lens element made of a material with an Abbe number greater than 75 in the first lens group I, the negative lens can be made of a material with a higher refractive power, while satisfying formula (7), And it can compensate chromatic aberration and other aberrations with a small lens structure.

Paragraph V relates to the lens structure of the second lens group II. As described above, the second lens group II in the zoom lens of the present invention includes the first lens group IIa with negative refractive power and the second lens group IIb with positive refractive power. Although one positive lens and one negative lens in each lens group can eliminate chromatic aberration and compensate aberration, but the elimination of chromatic aberration is mainly performed by the second group TIb with strong positive refractive power that satisfies the relationship of (8). Achieved.

In addition, in the second lens group II, if at least one positive lens element in the second group IIb is made of a material with an Abbe number greater than 75, a negative lens can be made of a material with high refractive power, while satisfying (8) formula, and can compensate for chromatic aberration and other aberrations in the lenslet structure.

Paragraph VI relates to the lens structure of the third lens group III in the zoom lens. Although the entire third lens group III has a strong negative refractive power, the negative lens alone cannot eliminate chromatic aberration or compensate the Petzval sum of the imaging plane.

Correspondingly, the third lens group III includes a positive lens in addition to two negative lenses. In addition, in order to eliminate chromatic aberration and compensate for the Petzval sum, the refractive power of the positive lens in the third lens group III should be in the numerical range given by formula (9). If the corresponding value in formula (9) exceeds the upper limit or is lower than the lower limit set by formula (9), the refractive power of the negative lens will become too large or too small, making it difficult to compensate for aberrations.

Paragraph VII deals with the movement of each lens group during zooming. In the zoom lens of the present invention, although each of the first, second and third lens groups should move independently during the zooming process, a smaller and more compact lens can be obtained by satisfying formulas (10) and (11). Economical zoom lens.

For example, formula (10) involves moving the first and third lens groups together during zooming, which can make the lens barrel structure of the lens simple and economical. If the expression (10) is not satisfied, the barrel structure or the zoom lens has to move the first to third lens groups independently, which increases the number of components and increases the assembly cost, thereby increasing the cost.

Equation (11) involves making the lens smaller by limiting the variation of the distance between lens groups during zooming. When the zoom ratio is greater than 3, although the distance between the lens groups usually changes by about 0.15 during the zooming process from wide-angle to telephoto, according to the embodiment of the present invention, this range of change is preferably limited to the given formula (11) range to make the zoom lens smaller.

Referring to paragraph VIII, in the zoom lens of the present invention, the focal length of the first lens group I having positive refractive power is preferably limited to the range given by equation (12) to make the lens small. In addition, the compound focal length of the second lens group II with positive refractive power and the third lens group III with negative refractive power should be limited within the range given by (13) to reduce the total length of the lens at the telephoto position .

Formula (13) sets the composite refractive power of the second and third lens groups II and III to a smaller value at the wide-angle position. In other words, at the telephoto position, the second and third lens groups II and III with composite strong negative refractive power are placed in the first lens group I with strong positive refractive power satisfying the formula (12) from the perspective of the object after. This configuration contributes to volume reduction. In other words, if the relevant values in formulas (12) and (13) exceed the range of the two formulas, it will be difficult to obtain small volume and large zoom ratio at the same time.

Paragraph IX deals with the use of inexpensive spherical lenses to make the aforementioned high zoom ratio zoom lenses. Although the technology for making aspheric lenses has improved, such aspheric lenses are still expensive. Thus, for low-cost lenses, it is best to use spherical lenses. By adopting the above-mentioned principle and concept of the present invention, a compact zoom lens with high zoom ratio and high performance can be obtained, and a cheap spherical lens can still be used.

More specifically, the zoom lenses of the first, second and third embodiments of the present invention will be discussed separately below. FIG. 1 shows the zoom lens of the first embodiment of the present invention, and FIG. 2 shows various aberrations of the zoom lens of the first embodiment at different zoom positions, which is self-explanatory. Referring to FIG. 1, the zoom lens of the present invention preferably has an aperture stop "A" between the second and third lens groups II and III near the second group IIb of the second lens group II.

The aperture stop "A" is generally always located in the middle of the zoom lens, ie in the middle of the second lens group II. However, the configuration of the aperture diaphragm A divides the second lens group II into two parts, which makes the assembly more complicated and prone to errors, making it difficult to obtain a high-performance lens. Like this, in order to overcome these problems of function and assembly, and make cost reduction, zoom lens of the present invention is preferably provided with an aperture stop A between second and third lens group II and III, thereby avoids separating second lens group II. Table 1 gives an example of a set of parameters of the zoom lens of the present invention.

Table 1

Wide Angle Medium Focus Telephoto

f 39.5 80.0 136.9

F _no 1:3.8 1:6.7 1:10.5

ω ω 28.9° 14.8° 8.9°

(ω=half viewing angle)

曲率半径厚度或距离折射率色散系数r1 -36.452r2 -65.659 d1 1.500 n1 1.84666 υ1 23.83r3 94.014 d2 0.150r4 37078.444 d3 2.400 n2 1.49700 υ2 81.61r5 47.876 d4 0.150r6 -51.426 d5 3.900 n3 1.49700 υ3 81.61r7 -25.378 d6 * ¹ r8 15.454 d7 1.000 n4 1.77250 υ4 49.62r9 -61.544 d8 3.860 n5 1.72825 υ5 28.32r10 85.933 d9 7.890r11 -11.816 d10 4.250 n6 1.48749 υ6 70.44r12 -21.172 d11 1.200 n7 1.84666 υ7 23.83r13 74.806 d12 0.150r14 -26.927 d13 2.650 n8 1.49700 υ8 81.61r15 -174.349 d14 * ² r16 -20.267 d15 3.290 n9 1.80518 υ9 25.46r17 -28.027 d16 0.150r18 74.906 d17 1.200 n10 1.77250 υ10 49.62r19 -13.028 d18 4.310r20 -84.078 d19 1.500 n11 1.77250 υ11 49.62

d20 * ³ Wide Angle Medium Telephoto* ¹ d6 3.020 10.069 13.470* ² d14 13.824 6.775 3.374* ³ d20 8.492 32.25 64.928

d20 represents the back focal length fb, that is, the distance from the imaging surface to the lens surface facing the imaging surface in the third lens group.

The numerical values of the conditions given in formulas (1)-(13) are as follows:

(1) f _T /f _W : 3.466

(2) L _T /f _T : 0.886

(3) mIII _T : 4.474

(4) fI,II _T /f _T : 0.224

(5) fIII/f _T : -0.139

(6) fI _N /f _T : -0.724

(7) υI _P -υI _N : 57.78

(8) υIIb _P -υIIb _N : 52.2

(9) fIII _P /f _T : 0.206

(10) ΔD _{I, II} /f _T = -ΔD _{II, III} /f _T : 0.076

(11) |ΔD _{I, II} /f _T |: 0.076

(12) f _I /f _T : 0.464

(13) | fII, III _W / fII, III _T |: 39.7

Fig. 3 is a zoom lens according to a second embodiment of the present invention. Fig. 4 shows various aberrations at different zoom positions of the zoom lens according to the second embodiment of the present invention, which is self-explanatory. Referring to FIG. 3, the zoom lens of the present invention preferably has an aperture stop A between the first lens group IIa and the second lens group IIb of the second lens group II.

Table 2

                                                             

f 39.5 80.0 130.0

F _no 1:3.9 1:6.7 1:10.0

ω 28.2° 14.6° 9.2°

  Radius of Curvature                                                                                

r1 -45.472

r2 -105.785 d1 1.500 n1 1.84666 υ1 23.83

r3 85.583 d2 0.150

r4 -133.005 d3 2.600 n2 1.49700 υ2 81.61

r5 41.913 d4 0.150

r6 -64.302 d5 3.700 n3 1.49700 υ3 81.61

r7 -25.216 d6 * ¹

r8 14.911 d7 1.000 n4 1.77250 υ4 49.62

r9 -74.331 d8 3.000 n5 1.69895 υ5 30.05

r10 40.637 d9 9.710

r11 -29.525 d10 2.650 n6 1.48749 υ6 70.44

r12 83.270 d11 0.150 n7 1.48749 υ7 70.44

r13 -11.927 d12 4.250

r14 -19.730 d13 1.200 n8 1.84666 υ8 23.83

r15 -47.721 d14 * ²

r16 -18.417 d15 3.110 n9 1.80518 υ9 25.46

r17 -25.781 d16 0.150

r18 69.200 d17 1.200 n10 1.64000 υ10 60.15

r19 -12.485 d18 4.950

r20 -71.822 d19 1.500 n11 1.77250 υ11 49.62

d20 * ³

Wide Angle Medium Focus Telephoto

* ¹ d6 3.067 9.090 11.836

* ² d14 9.769 3.746 1.000

* ³ d20 8.5 30.54 56.995

The values of the given conditions in (1)-(13) are as follows:

(1) f _T /f _W : 3.291

(2) L _T /f _T : 0.852

(3) mIII _T : 4.550

(4) fI,II _T /f _T : 0.220

(5) fIII/f _T : -0.128

(6) fI _N /f _T : -0.733

(7) υI _P -υI _N : 57.78

(8) υIIb _P -υIIb _N :41.61

(9) fIII _P /f _T : 0.274

(10) ΔD _{I, II} /f _T = -ΔD _{II, III} /f _T : 0.067

(11) |ΔD _{I, II} /f _T |: 0.067

(12) f _I /f _T : 0.403

(13) | fII, III _W / fII, III _T |: 4.96

FIG. 5 is a zoom lens according to a third embodiment of the present invention. Fig. 6 shows various aberrations at different zoom positions of the zoom lens according to the third embodiment of the present invention, which is self-explanatory. The zoom lens of the present invention preferably has an aperture stop A between the first lens group IIa and the second lens group IIb of the second lens group II.

table 3

Wide Angle Medium Focus Telephoto

f 39.5 80.0 136.0

F _no 1:4.0 1:6.9 1:10.8

ω ω 28.9° 14.8° 8.9°

曲率半径厚度或距离折射率色散系数r1 -25.509r2 -49.004 d1 1.500 n1 1.84666 υ1 23.83r3 -64.874 d2 0.150r4 -24.980 d3 3.600 n2 1.49700 υ2 81.61r5 29.518 d4 0.150r6 -116.064 d5 3.700 n3 1.49700 υ3 81.61r7 - 29.790 d6 * ¹ r8 12.022 d7 1.000 n4 1.77250 υ4 49.62r9 -176.144 d8 3.000 n5 1.74077 υ5 27.76r10 47.826 d9 9.750r11 -80.926 d10 2.650 n6 1.49700 υ6 81.61r12 44.171 d11 0.150 n7 1.51728 υ7 69.68r13 -10.227 d12 4.250r14 -16.557 d13 1.200 n8 1.84666 υ8 23.83r15 -44.973 d14 * ² r16 -16.780 d15 3.210 n9 1.80518 υ9 25.46r17 -23.230 d16 0.150r18 93.346 d17 1.200 n10 1.77250 υ10 49.62r19 -11.412 d18 4.900r20 -43.980 d19 1.500 n11 1.77250 υ11 49.62

d20 * ³

Wide Angle Medium Focus Telephoto

* ¹ d6 3.808 9.423 12.203

* ² d14 9.395 3.780 1.000

* ³ d20 8.502 30.074 59.006

(1)-(13) The numerical values of the given conditions are as follows:

(1)f _T /f _W : 3.433

(2) L _T /f _T : 0.840

(3) mIII _T : 4.940

(4) fI, II _T /f _T : 0.201

(5) fIII/f _T : -0.115

(6) fI _N /f _T : -0.476

(7)υI _P -υI _N : 57.78

(8)υIIb _P -υIIb _N : 51.82

(9) fIII _P /f _T : 0.233

(10) ΔD _{I, II} /f _T = -ΔD _{II, III} /f _T : 0.062

(11)|ΔD _{I, II} / f _T |: 0.062

(12) f _I /f _T : 0.350

(13) | fII, III _W / fII, III _T |: 3.3

According to the present invention, a compact zoom lens with a high magnification (f _T /f _w ) of about 3.5 times and a telephoto ratio (L _T /f _T ) below 0.9 at the telephoto position can be obtained. In addition, the zoom lens of the present invention uses an inexpensive spherical lens to replace an expensive aspheric lens, while still maintaining the optical performance of the lens.

Other embodiments of the present invention will be readily apparent to those skilled in the art from this specification and practice of the present invention. The description and the examples are for illustration only, and the protection scope of the present invention is defined by the claims.

Claims (14)

1. zoom lens comprises:

First lens combination with positive refractive power;

Have positive refractive power and separate second lens combination of first distance with first lens combination;

Have negative refractive power and the 3rd lens combination of separating second distance with second lens combination, described first distance and second distance change when zoom,

It is characterized in that this zoom lens satisfies following condition:

3.0＜f _T/f _W；

L _T/f _T＜1.0；

0.18＜fI, II _T/ f _T＜0.25; And

-0.20＜f _III/ f _TIn＜-0.11 formula, f _TBe the focal length of zoom lens when growing burnt position,

f _WBe the focal length of zoom lens when the wide-angle position,

L _TBe first minute surface of zoom lens when the long burnt position distance apart from imaging surface,

FI, II _TBe the compound focal length of first and second lens combination when growing burnt position,

f _IIIIt is the focal length of the 3rd lens combination.

2. zoom lens as claimed in claim 1, also satisfy following condition:

The lateral magnification of the 3rd lens combination when 4.0 mIIIT is for long burnt position in＜mIIIT＜5.5 formulas.

3. zoom lens as claimed in claim 1 is characterized in that, first lens combination comprises a negative lens with negative refractive power, and satisfies following condition:

-1.0＜fI _N/ f _TIn＜-0.5 formula, fI _NIt is the focal length of negative lens in first lens combination.

4. zoom lens as claimed in claim 1 is characterized in that, first lens combination comprises a positive lens and the negative lens with negative refractive power with positive refractive power, and this zoom lens also satisfies following condition:

40＜υ I _P-υ I _Nυ I in the formula _PBe the Abbe number mean value of the positive lens in first lens combination,

υ I _NBe the Abbe number mean value of the negative lens in first lens combination.

5. zoom lens as claimed in claim 1, it is characterized in that, described second lens combination comprises the grouping of first and second lens, and each lens grouping includes a negative lens and the positive lens with positive refractive power with negative refractive power, and this zoom lens also satisfies following condition:

40＜υ IIb _P-υ IIb _Nυ IIb in the formula _PBe the Abbe number mean value of the positive lens in the grouping of second lens,

υ IIb _NBe the Abbe number mean value of the negative lens in the grouping of second lens.

6. zoom lens as claimed in claim 1 is characterized in that, the 3rd lens combination comprises a positive lens with positive refractive power, and this zoom lens also satisfies following condition:

0.15＜f _IIIP/ f _TIn＜0.28 formula, f _IIIPIt is the focal length of the positive lens of the 3rd lens combination.

7. zoom lens as claimed in claim 1, also satisfy following condition:

Δ D _{I, II}/ f _T=-Δ D _{II, III}/ f _TIn the formula, Δ D _{I, II}The variation of first distance during for zoom,

Δ D _{II, III}The variation of second distance during for zoom.

8. zoom lens as claimed in claim 1, also satisfy following condition:

| Δ D _{I, II}/ f _T| Δ D in＜0.10 formula _{I, II}The variation of first distance during for zoom.

9. zoom lens as claimed in claim 1, also satisfy following condition:

f _I/f _T＜0.55

F in the formula _IIt is the focal length of first lens combination.

10. zoom lens comprises:

First lens combination with positive refractive power, it comprises a positive lens and the negative lens with negative refractive power with positive refractive power;

Have positive refractive power and and first lens combination, second lens combination of first distance separately, second lens combination comprises: the grouping of first lens comprises negative lens with negative refractive power and the positive lens with positive refractive power; The grouping of second lens comprises negative lens with negative refractive power and the positive lens with positive refractive power;

The 3rd lens combination that has negative refractive power and separate second distance with second lens combination, first distance and second distance change when zoom,

It is characterized in that this zoom lens satisfies following condition:

3.0＜f _T/f _W；

L _T/f _T＜1.0；

4.0＜mIII _T＜5.5

40＜υ I _P-υ I _NAnd

40＜υ IIb _P-υ IIb _NIn the formula, f _TBe the focal length of zoom lens when growing burnt position,

f _WBe the focal length of zoom lens when the wide-angle position,

L _TBe first minute surface of zoom lens when the long burnt position distance apart from imaging surface,

MIII _TBe the lateral magnification of the 3rd lens combination when growing burnt position,

υ I _PBe the Abbe number mean value of positive lens in first lens combination,

υ I _NBe the Abbe number mean value of negative lens in first lens combination,

υ IIb _PBe the Abbe number mean value of positive lens in the grouping of second lens,

υ IIb _NBe the Abbe number mean value of negative lens in the grouping of second lens,

And the Abbe number of the positive lens in described second lens grouping is more than or equal to 75.

11. zoom lens as claimed in claim 10 is characterized in that, the 3rd lens combination comprises a positive lens with positive refractive power, and this zoom lens also satisfies following condition:

0.15＜fIII _P/ f _TIn＜0.28 formula, fIII _PIt is the focal length of the positive lens of the 3rd lens combination.

12. zoom lens as claimed in claim 10, it also satisfies following condition:

Δ DI, II/f _T=-Δ DII, _III/ f _TΔ DI in the formula, the variation of first distance when II is zoom,

Δ D _{II, III}The variation of second distance during for zoom.

13. zoom lens as claimed in claim 10, it also satisfies following condition:

|ΔD _I，II/f _T|＜0.10

Δ D in the formula _{I, II}The variation of first distance during for zoom.

14. zoom lens as claimed in claim 10, it also satisfies following condition:

f _I/ f _TF in＜0.55 formula _IIt is the focal length of first lens combination.

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