JP2850548B2 - Zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small, high-magnification zoom lens suitable for a lens shutter camera, a video camera, and the like. The present invention relates to a zoom lens which is excellent in portability and has a reduced length.

[0002]

2. Description of the Related Art Recently, in a lens shutter camera, a video camera, and the like, a small zoom lens having a short overall lens length has been demanded with the downsizing of the camera. Among them, the applicant of the present invention has proposed a relatively small zoom lens having a standard angle of view (a shooting angle of view of 2ω = 47 degrees and a focal length of about 50 mm in terms of a 35 mm still camera).
No. 214 and Japanese Patent Application Laid-Open No. Sho 64-72114.

In this publication, 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 negative refractive power. A so-called three-unit zoom lens having a zoom ratio of about 2 in which all the units are moved to the object side under certain conditions to perform zooming from the wide-angle end to the telephoto end is disclosed.

Japanese Patent Application Laid-Open No. 64-88512 has four lens groups of negative, positive, positive and negative refractive power in order from the object side, and the four lens groups are independently moved to the object side. A zoom lens having a variable magnification ratio of about 3 has been proposed.

[0005]

In general, if the refractive power of each lens unit is increased in a zoom lens, the amount of movement of each lens unit for obtaining a predetermined zoom ratio is reduced, and the overall length of the lens is reduced. High magnification can be achieved. However, simply increasing the refractive power of each lens group increases aberration fluctuations associated with zooming, and in particular, it is difficult to obtain good optical performance over the entire zooming range, especially when aiming for high zooming. There is a point.

[0006] The present invention relates to Japanese Patent Application Laid-Open No. 63-27 filed by the present applicant.
The zoom lens proposed in Japanese Patent Application Laid-Open No. 1214 and Japanese Patent Application Laid-Open No. 64-72114 is improved, and is composed of four lens groups as a whole. It is an object of the present invention to provide a compact zoom lens which has a high zooming ratio of about 7 and a high optical performance over the entire zooming range while improving the method, and particularly shortening the entire length of the lens.

[0007]

A zoom lens according to the present invention comprises, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, and a negative lens unit. 4th of refractive power
The second and fourth units move toward the object side during zooming from the wide-angle end to the telephoto end, and the distance between the first and second units is minimized at the telephoto end; The third lens unit is moved so that the image plane position at that time is constant, and the first lens unit of the second lens unit is moved.
The distance from the lens surface to the object-side principal point of the second group is O2
(Positive when measuring on the image side, negative when measuring on the object side), -1.25 <O2 / f2 <-0.18 when the focal length of the second group is f2 1) It is characterized by satisfying the following conditions.

In particular, in the present invention, upon zooming from the wide-angle end to the telephoto end, the second and fourth units move linearly independently toward the object side, and the third unit is convex toward the image plane side. And the first lens unit moves nonlinearly toward the object side during zooming from the wide-angle end to the telephoto end.

In zooming from the wide-angle end to the telephoto end,
The second group and the fourth group are always multiplied, and each of the second group and the fourth group is configured such that the amount of change in the imaging magnification of the second group is larger than the amount of change in the imaging magnification of the fourth group. The feature is that the element is set.

[0010]

FIG. 1 is an explanatory view of a paraxial refractive power arrangement of a zoom lens according to the present invention, and FIGS. 2, 3 and 4 are lens sectional views of Numerical Examples 1, 2, and 3 of the present invention, respectively.

In FIGS. 1 to 4, (A) is a wide-angle end,
(B) shows the zoom position at the telephoto end. 5 to 7 are aberration diagrams at the wide-angle end, a middle position, and a telephoto end of Numerical Embodiment 1 of the present invention. FIGS. FIGS. 11 to 13 show various aberration diagrams of the numerical example 3 at the wide-angle end, the middle position, and the telephoto end, respectively.

In the drawing, reference numeral 1 denotes a first group having a negative refractive power (φ1);
2 is a second group of positive refractive power (φ2), 3 is a positive refractive power (φ2)
The third unit 4) and the fourth unit 4 having a negative refractive power (φ4). Arrows indicate the moving direction of each lens group when zooming from the wide-angle side to the telephoto side.

Next, the characteristics of the paraxial refractive power arrangement of the zoom lens according to the present embodiment will be described.

When the first lens unit having the refractive power φ1 and the second lens unit having the refractive power φ2 are arranged at the principal point interval e, the combined refractive power φ of the entire lens system is φ = φ1 + φ2-eφ1 · φ2 (a) Becomes In order to change the combined refractive power φ at this time, that is, to change the magnification, the principal point interval e may be changed as follows. (A) When both the refractive powers φ1 and φ2 are positive values, the synthetic refractive power φ can be reduced, that is, the principal point interval e can be increased to change to the telephoto end. (B) When the sign of the refractive power φ1 is different from the sign of the refractive power φ2, in order to reduce the combined refractive power φ, that is, to change to the telephoto end, the principal point interval e may be reduced.

The zoom lens of this embodiment moves the second and fourth units toward the object side when zooming from the wide-angle end to the telephoto end, as well as the air gap between the second and third units (principal point). The distance is gradually increased so as to become the widest at the middle zoom position. Then, the air interval is slightly narrowed from the intermediate zoom position to the telephoto end.

That is, the third lens unit is moved so as to have a locus convex toward the image plane. As a result, as shown in FIG. 1, the paraxial refractive power arrangement of the combined system of the second and third lens groups from the wide-angle end to the intermediate zoom position corresponds to the above-mentioned case (a), and from the wide-angle end. Effective zooming to an intermediate zoom position facilitates high zooming.

By satisfying conditional expression (1), the size of the zoom lens is reduced, and a high zoom ratio is achieved.

If the lower limit of conditional expression (1) is exceeded, the total length of the lens becomes longer and the diameter of the front lens increases, which is not good. If the upper limit is exceeded, the range of movement of the second lens unit due to zooming becomes narrow, and it becomes difficult to obtain a high zooming ratio of about 7 times.

Further, it is possible to effectively prevent the curvature of field at the intermediate zoom position when the refractive power arrangement as in the present invention is taken from increasing in the negative direction. At the time of zooming from the intermediate zoom position to the telephoto end, the air gap between the second lens unit and the third lens unit is narrowed, and aberration fluctuations mainly due to zooming are corrected well. Further, the image plane fluctuation due to zooming is also corrected.

The zoom lens according to this embodiment has a first lens unit having a negative refractive power (φ1 <0) and a positive refractive power (φ2> 0), as is apparent from the refractive power arrangement of each lens unit shown in FIG. ) Second
The refractive power relationship of the group and the refractive power relationship of the third lens unit having a positive refractive power (φ3> 0) and the refractive power relationship of the fourth lens unit having a negative refractive power (φ4 <0) are both larger at the telephoto end than at the wide-angle end. (B) It corresponds to the case.

As described above, at the time of zooming from the wide-angle end to the telephoto end, the distance between the principal points (air distance) between the first and second units is shortened so that the system of combining the first and second units, in particular, Each element is set such that the imaging magnification of the second group is always multiplied, and the amount of change in the imaging magnification at this time is larger than that of the other lens groups.

Similarly, the distance between the principal points of the third lens unit and the fourth lens unit is set shorter at the telephoto end than at the wide-angle end, so that the image forming magnification of the third lens unit and the fourth lens unit, particularly, the imaging magnification of the fourth lens unit, Is always multiplied.

As described above, both the second lens unit and the fourth lens unit are multiplied at the time of zooming from the wide-angle end to the telephoto end, thereby facilitating high zooming of the entire lens system. In particular, as described above, the change in the imaging magnification of the second group is made larger than the change of the imaging magnification of the fourth group, so that the high magnification is effectively performed.

Contrary to the present invention, when the amount of change in the imaging magnification of the fourth lens unit is larger than the amount of change in the imaging magnification of the second lens unit, the amount of movement of the fourth lens unit increases. This is not good because the effective diameter of the four lens units increases and the brightness (F number) of the lens system on the telephoto side becomes dark.

Also, the refractive power of the fourth lens unit becomes too strong, positive distortion increases at the wide-angle end, negative Petzval sum increases, and the field curvature tends to be overcorrected, which is not good.

When zooming from the wide-angle end to the telephoto end, the zoom lens according to the present embodiment moves the first lens unit in a non-linear manner and independently of the other lens units in the object side direction as shown in FIG. Are moved so as to satisfy the conditions.

As described above, in this embodiment, at the time of zooming from the wide-angle end to the telephoto end, each lens group is moved to the object side while satisfying the above-mentioned conditions, thereby achieving a zoom ratio of 7 and a high zoom ratio. While effectively reducing the overall length of the lens at the wide-angle end. That is, a refractive power arrangement is adopted in which the entire length of the lens is short on the wide-angle side and long on the telephoto side.

In addition, in the present invention, in order to effectively obtain a high zoom ratio, at the time of zooming from the wide-angle end to the telephoto end, the i.
When the amount of movement of the group is Mi (positive on the image plane side) and the amount of change in the focal length of the entire system is Δf, 0.3 <| M2 / Δf | <0.9 (2) 0.3 <| M4 / Δf | <0.9 (3) The following condition is satisfied.

When the amount of movement of the second and fourth units exceeds the upper limit of conditional expressions (2) and (3) and the amount of movement of the second and fourth units increases, the entire lens system increases. If the amount of movement of the group becomes too small, the amount of change in the value of the principal point interval e in the above-described equation (a) of the second and fourth groups, which most contributes to zooming, becomes small, and a desired zoom ratio is secured. It is not good because it becomes difficult.

In this embodiment, in order to obtain high optical performance over the entire screen, it is preferable that each lens group is constituted as follows.

It is preferable that the first group has at least one negative lens and at least one positive lens, and that an air lens having a convex shape on the object side is formed in the first group. It is particularly preferable that the second lens unit has at least two positive lenses and at least one negative lens closest to the object side in order to satisfactorily correct spherical aberration over the entire zoom range. When the Abbe number of the material of one of the two positive lenses is ν _2P , the following condition is preferably satisfied: ν _2P > 50 (4)

If conditional expression (4) is not satisfied, the fluctuation of the axial chromatic aberration mainly increases during zooming, which is not good.

It is preferable from the viewpoint of aberration correction to dispose a stop at an arbitrary position in the second lens unit and move it together with the second lens unit in accordance with zooming.

At this time, the negative lens in the second lens unit is disposed so as to face the stop, and when the refractive index of the material of the negative lens is N _2n , 1.75 <N _2n. b) It is better to satisfy the following condition.

If the condition (b) is not satisfied, the Petzval sum increases in the negative direction, and the field curvature becomes excessively corrected. Particularly in this embodiment, the Abbe number ν _2P of the material of the positive lens in the second group and the refractive index N of the negative lens in the second group are preferable.
_2n is preferably set as follows: 60 <ν _2P (c) 1.8 <N _2n (d)

In this embodiment, the diaphragm is arranged between the second and third groups instead of being arranged in the lens system of the second group.
The zoom lens may be moved independently of the second lens unit with zooming, and this is preferable because fluctuation of the F-number due to zooming can be reduced.

It is preferable that the fourth unit has at least one positive lens having a convex surface facing the image surface side and at least one negative lens having a concave surface facing the object side.

In the present invention, the second lens unit and the fourth lens unit may be moved integrally during zooming, which is preferable because the lens barrel is simplified.

In addition, in the present invention, when the focal length of the i-th lens unit is fi and the focal length of the entire system at the wide-angle end is fw, 1.5 <| f1 / fw | <3.0 (3) .. (5) 0.9 <f2 / fw <2.5... (6) 2 <| f4 / fw | <4.0. It is preferable to satisfy the conditions in order to reduce the size of the entire lens system while effectively securing a desired zoom ratio.

If the refractive power of each lens unit becomes too weak beyond the upper limit of conditional expressions (5), (6) and (7), the amount of movement of each lens unit for obtaining a desired zoom ratio increases. However, it is not good because the entire lens system becomes large.

If the refractive power of the first lens unit becomes too strong beyond the lower limit value of the conditional expression (5), the aberration fluctuation when focusing on the first lens unit becomes large.

If the refracting power of the second lens unit that performs a zooming operation exceeds the lower limit of conditional expression (6), the Petzval sum increases in the positive direction, and the image plane is corrected over the entire zooming range. It is not good because it becomes insufficient (under).

If the refractive power of the fourth lens unit becomes too strong beyond the lower limit value of the conditional expression (7), the Petzval sum increases in the negative direction, contrary to the conditional expression (6), and the image becomes over the entire zoom range. This is not good because the surface is overcorrected.

In the present invention, in order to reduce the size of the entire lens system, if the shortest distance of the back focus in the entire zoom range is bf · min, 0.13 <bf · min / fw <0.7 ...
(8) It is preferable to set the refractive power and the lens configuration of each lens group so as to satisfy the following conditions.

If the upper limit of conditional expression (8) is exceeded, the entire lens system will be large. If the lower limit is exceeded, the fourth lens unit will be too close to the image-forming surface, and dust and the like in the fourth lens unit will adhere to the photosensitive surface. It is not good because it comes out.

In the present invention, in order to satisfactorily correct inward coma flare and barrel distortion mainly due to downward light rays on the wide-angle side, at least one lens surface of the first group has positive refraction toward the lens periphery. It is preferable to apply an aspheric surface having a shape in which the power becomes strong or the negative refractive power becomes weak.

Further, in order to correct the introverted coma due to the upper ray on the telephoto side, at least one lens surface of the third or fourth lens unit has a weaker positive refractive power or a negative refractive power toward the lens peripheral portion. It is preferable to provide an aspherical surface having a shape having a high refractive power.

Focusing is preferably performed in the first lens unit,
It may be performed in a group or a third group. Alternatively, only a specific area, for example, a close distance, may be focused by the fourth group or the third group.
This is preferable because closer focus becomes possible and an increase in the diameter of the front lens can be prevented.

In this embodiment, it is desirable to further satisfy the following conditional expression in relation to conditional expression (1).

−1.25 <O2 / fw <−0.25 (1) -a If the lower limit of the expression (1) -a is exceeded, not only the overall length becomes longer but also the front lens diameter becomes larger. Is not preferred. If the upper limit is exceeded, the movable range of the second lens unit due to zooming becomes narrow, and it becomes difficult to obtain a zoom ratio of about 7 times.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass.

Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples. Numerical Example 1 F = 28.8 to 194.0 FNO = 1: 4.1 to 9.2 2ω = 73.8 ° to 12.7 ° R 1 = 1102.99 D 1 = 1.80 N 1 = 1.77250 ν 1 = 49.6 R 2 = 29.12 D 2 = 3.98 R 3 = 30.24 D 3 = 5.50 N 2 = 1.68893 ν 2 = 31.1 R 4 = 50.89 D 4 = Variable R 5 = 54.35 D 5 = 2.96 N 3 = 1.49700 ν 3 = 81.6 R 6 = -267.62 D 6 = 0.09 R 7 = 26.69 D 7 = 4.00 N 4 = 1.48749 ν 4 = 70.2 R 8 = 63.40 D 8 = 0.09 R 9 = 18.39 D 9 = 4.72 N 5 = 1.48749 ν 5 = 70.2 R10 = 48.06 D10 = 3.30 R11 = (aperture) D11 = 2.52 R12 = -703.30 D12 = 1.26 N 6 = 1.83400 ν 6 = 37.2 R13 = 16.78 D13 = 1.18 R14 = 24.12 D14 = 2.83 N 7 = 1.48749 ν 7 = 70.2 R15 = -123.77 D15 = Variable R16 = 49.06 D16 = 2.50 N 8 = 1.53172 ν 8 = 48.9 R17 = -61.27 D17 = 0.07 R18 = -107.95 D18 = 2.03 N 9 = 1.78590 ν 9 = 44.2 R19 = 59.74 D19 = 0.32 R20 = 111.87 D20 = 1.97 N10 = 1.56732 ν10 = 42.8 R21 = -621.42 D21 = Variable R22 = 45.30 D22 = 3.86 N11 = 1.68893 ν11 = 31.1 R23 = -105.41 D23 = 1.31 R24 = -40.69 D24 = 1.34 N12 = 1.71299 ν12 = 53.8 R25 = -127.98 D25 = 3.70 R26 = -21.73 D26 = 1.67 N13 = 1.69680 ν13 = 55.5 R27 = -135.01 Numerical Example 2 F = 28.8 to 194.0 FNO = 1: 4.1 to 9.2 2ω = 73.8 ° to 12.7 ° R 1 = -1588.68 D 1 = 1.80 N 1 = 1.77250 ν 1 = 49.6 R 2 = 29.62 D 2 = 4.76 R 3 = 31.37 D 3 = 5.49 N 2 = 1.68893 ν 2 = 31.1 R 4 = 55.84 D 4 = Variable R 5 = 41.15 D 5 = 3.46 N 3 = 1.48749 ν 3 = 70.2 R 6 = -422.32 D 6 = 0.09 R 7 = 22.09 D 7 = 5.07 N 4 = 1.51633 ν 4 = 64.1 R 8 = 81.17 D 8 = 0.09 R 9 = 22.71 D 9 = 3.57 N 5 = 1.51633 ν 5 = 64.1 R10 = 53.49 D10 = 3.39 R11 = (Aperture) D11 = 1.94 R12 = -171.87 D12 = 1.39 N 6 = 2.02244 ν 6 = 29.1 R13 = 17.97 D13 = 0.91 R14 = 24.83 D14 = 2.98 N 7 = 1.56732 ν 7 = 42.8 R15 = -123.12 D15 = Variable R16 = 153.86 D16 = 2.24 N 8 = 1.51742 ν 8 = 52.4 R17 = -42.13 D17 = 0.11 R18 = -60.28 D18 = 0.78 N 9 = 1.78590 ν 9 = 44.2 R19 = 86.88 D19 = 0.44 R20 = 97.24 D20 = 1.77 N10 = 1.56732 ν10 = 42.8 R21 =- 221.80 D21 = Variable R22 = 40.51 D22 = 5.66 N11 = 1.68893 ν11 = 31.1 R23 = -35.72 D23 = 0.99 R24 = -26.42 D24 = 1.34 N12 = 1.71299 ν12 = 53.8 R25 = -193.52 D25 = 3.77 R26 = -23.84 D26 = 1.67 N13 = 1.69680 ν13 = 55.5 R27 = -400.66 Numerical example 3 F = 28.8 to 194.0 FNO = 1: 4.1 to 9.2 2ω = 73.8 ° to 12.7 ° R 1 = -555.76 D 1 = 1.47 N 1 = 1.80400 ν 1 = 46.6 R 2 = 26.88 D 2 = 3.20 R 3 = 29.16 D 3 = 4.20 N 2 = 1.80518 ν 2 = 25.4 R 4 = 50.39 D 4 = Variable R 5 = 34.65 D 5 = 4.04 N 3 = 1.48749 ν 3 = 70.2 R 6 = -180.30 D 6 = 0.07 R 7 = 18.38 D 7 = 5.26 N 4 = 1.48749 ν 4 = 70.2 R 8 = 89.22 D 8 = 0.07 R 9 = 19.87 D 9 = 3.68 N 5 = 1.51633 ν 5 = 64.1 R10 = 52.82 D10 = 2.38 R11 = (aperture) D11 = 0.92 R12 = -145.45 D12 = 1.11 N 6 = 2.02244 ν 6 = 29.1 R13 = 15.36 D13 = 1.10 R14 = 23.41 D14 = 2.30 N 7 = 1.51454 ν 7 = 54.7 R15 = 121.66 D15 = Variable R16 = 117.94 D16 = 2.58 N 8 = 1.58144 ν 8 = 40.8 R17 = -30.58 D17 = 1.17 R18 = -39.14 D18 = 0.67 N 9 = 1.77250 ν 9 = 49.6 R19 = 74.29 D19 = 0.13 R20 = 51.54 D20 = 2.35 N10 = 1.58144 ν10 = 40.8 R21 = -74.41 D21 = Variable R22 = 41.01 D22 = 4.13 N11 = 1.72825 ν11 = 28.5 R23 = -87.39 D23 = 2.94 R24 = -22.38 D24 = 1.07 N12 = 1.71299 ν12 = 53.8 R25 = -257.20 D25 = 1.92 R26 = -44.10 D26 = 1.34 N13 = 1.69680 ν13 = 55.5 R27 = -739.08 (Table-1)

[0053]

According to the present invention, in a zoom lens composed of four lens units having a predetermined refractive power, the zooming ratio is set to 7 by setting the moving conditions of each lens unit, the lens configuration, and the like upon zooming as described above. A zoom lens having high optical performance over the entire zoom range with a high zoom ratio and a short overall lens length can be achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a paraxial refractive power arrangement of a zoom lens according to the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 4 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 5 is a diagram illustrating various aberrations at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 6 is a diagram showing various aberrations in the middle of Numerical Example 1 of the present invention.

FIG. 7 is a diagram showing various types of aberration at the telephoto end according to Numerical Example 1 of the present invention.

FIG. 8 is a diagram illustrating various aberrations at the wide-angle end according to Numerical Example 2 of the present invention.

FIG. 9 is a diagram showing various aberrations in the middle of Numerical Example 2 of the present invention;

FIG. 10 is a diagram showing various aberrations at the telephoto end according to Numerical Example 2 of the present invention.

FIG. 11 is a diagram illustrating various aberrations at the wide-angle end according to Numerical Example 3 of the present invention.

FIG. 12 is a diagram showing various aberrations in the intermediate state of Numerical Example 3 of the present invention.

FIG. 13 is a diagram showing various types of aberration at the telephoto end according to Numerical Example 3 of the present invention.

[Explanation of symbols]

 1 First group 2 Second group 3 Third group 4 Fourth group SP aperture d d line gg line S. C Sine condition S Sagittal image plane M Meridional image plane

Claims (8)

(57) [Claims] 1. A wide-angle lens having a first group of negative refractive power, a second group of positive refractive power, a third group of positive refractive power, and a fourth group of negative refractive power in order from the object side. In zooming from the end to the telephoto end, the second and fourth units move toward the object side, and the distance between the first and second units becomes the smallest at the telephoto end.
The group is moved so as to keep the image plane position at that time constant, and the distance from the first lens surface of the second group to the object-side principal point of the second group is set to O2 (positive when measuring to the image plane side). A zoom lens characterized by satisfying the following condition: -1.25 <O2 / f2 <-0.18, where f2 is the focal length of the second lens unit. 2. In zooming from the wide-angle end to the telephoto end, the second and fourth units move linearly independently toward the object side, and the third unit moves along a locus convex toward the image plane. 2. The zoom lens according to claim 1, wherein the zoom lens is moving. 3. The zoom lens according to claim 2, wherein at the time of zooming from the wide-angle end to the telephoto end, the first unit moves nonlinearly toward the object side. 4. In zooming from the wide-angle end to the telephoto end, the second unit and the fourth unit are always multiplied, and the change in the imaging magnification of the second unit at this time is larger than the fourth unit. 2. The zoom lens according to claim 1, wherein each element is set so as to be larger than a change amount of the imaging magnification of the group. 5. When zooming from the wide-angle end to the telephoto end, the amount of movement of the i-th lens unit is Mi, and the amount of change of the focal length of the entire system is Δf.
The zoom lens according to claim 1, wherein the following condition is satisfied: 0.3 <| M2 / Δf | <0.9 0.3 <| M4 / Δf | <0.9. 6. When the focal length of the i-th lens unit is fi and the focal length of the entire system at the wide-angle end is fw, 1.5 <| f1 / fw | <3.0 0.9 <f2 / fw <2. 6. The zoom lens according to claim 5, wherein a condition of 0.52 <| f4 / fw | <4.0 is satisfied. 7. The second lens group includes at least two objects closest to the object side.
7. The zoom lens according to claim 6, wherein the zoom lens has two positive lenses, and satisfies the condition of 50 <ν _2P when the Abbe number of the material of one of the positive lenses is ν _2P . 8. The zoom lens according to claim 6, wherein a condition of -1.25 <O2 / fw <-0.25 is satisfied.