JP5017899B2 - Zoom lens, imaging device, zooming method - Google Patents

Description

  The present invention relates to a zoom lens, an imaging device, and a zooming method.

  Conventionally, so-called minus lead type zoom lenses equipped with a lens unit having negative refractive power on the most object side are many as zoom lenses for wide-angle shooting because of their advantages such as short close-up shooting distance and ease of wide-angle shooting. It is used. This negative lead type zoom lens is a negative and positive retrofocus type from the object side when the refractive power arrangement is at the wide-angle end state, and is a positive and negative telephoto type from the object side at the telephoto end state. Long focus can be achieved even in the end state.

As such a negative lead type zoom lens, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power; And a fourth lens group having positive refracting power, and a configuration in which zooming is performed by changing the interval between the lens groups has been proposed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 5-19170

  However, the conventional zoom lens disclosed in Patent Document 1 has a wide angle of view and a predetermined zoom ratio as a standard zoom lens, and is small, light, and inexpensive, but has good optical performance over the entire zoom range. Since it is difficult to obtain performance, higher image quality is demanded.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a zoom lens, an imaging device, and a zooming method that achieve high image quality.

In order to solve the above problems, the present invention
In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups ,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The first lens group has a negative lens;
The fourth lens group includes at least one positive lens and one negative lens,
The negative lens in the first lens group satisfies the following conditional expression, and provides a zoom lens.
3 0 ≦ νd1 ≦ 71
3 0 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: refractive index νd1: d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group with respect to d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group Abbe number for
The present invention also provides
In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The first lens group has a negative lens;
The third lens group includes one positive lens and one negative lens,
The negative lens in the first lens group satisfies the following conditional expression, and provides a zoom lens.
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: Refractive index for the d-line (wavelength λ = 587.6 nm) of the material of the negative lens in the first lens group
νd1: Abbe number for the d-line (wavelength λ = 587.6 nm) of the material of the negative lens in the first lens group
The present invention also provides
In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The first lens group has a negative lens;
The negative lens in the first lens group satisfies the following conditional expression:
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: Refractive index for the d-line (wavelength λ = 587.6 nm) of the material of the negative lens in the first lens group
νd1: Abbe number for the d-line (wavelength λ = 587.6 nm) of the material of the negative lens in the first lens group
The second lens group includes a positive lens,
The positive lens in the second lens group satisfies the following conditional expression, and provides a zoom lens.
30 ≦ νd2 ≦ 71
When 30 ≦ νd2 <36
-0.013 × νd2 + 2.083 ≦ nd2 ≦ 1.7
When 36 ≦ νd2 <41
-0.013 × νd2 + 2.083 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 41 ≦ νd2 <51
-0.004 × νd2 + 1.714 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 51 ≦ νd2 <61
-0.0015 × νd2 + 1.5865 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 61 ≦ νd2 ≦ 71
-0.0015 × νd2 + 1.5865 ≦ nd2 ≦ −0.009 × νd2 + 2.149
However,
nd2: refractive index with respect to d-line (wavelength λ = 587.6 nm) of the material of the positive lens in the second lens group
νd2: Abbe number for the d-line (wavelength λ = 587.6 nm) of the material of the positive lens in the second lens group
The present invention also provides
In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The first lens group has a negative lens;
The negative lens in the first lens group satisfies the following conditional expression:
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: Refractive index for the d-line (wavelength λ = 587.6 nm) of the material of the negative lens in the first lens group
νd1: Abbe number for the d-line (wavelength λ = 587.6 nm) of the material of the negative lens in the first lens group
The fourth lens group includes the aspheric plastic lens and a positive lens.
The positive lens in the fourth lens group satisfies the following conditional expression, and provides a zoom lens.
30 ≦ νd4 ≦ 71
When 30 ≦ νd4 <36
-0.013 × νd4 + 2.083 ≦ nd4 ≦ 1.7
When 36 ≦ νd4 <41
-0.013 × νd4 + 2.083 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 41 ≦ νd4 <51
-0.004 × νd4 + 1.714 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 51 ≦ νd4 <61
-0.0015 × νd4 + 1.5865 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 61 ≦ νd4 ≦ 71
-0.0015 × νd4 + 1.5865 ≦ nd4 ≦ −0.009 × νd4 + 2.149
However,
nd4: refractive index with respect to d-line (wavelength λ = 587.6 nm) of the positive lens material in the fourth lens group
νd4: Abbe number for the d-line (wavelength λ = 587.6 nm) of the material of the positive lens in the fourth lens group
The present invention also provides
In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The first lens group has a negative lens;
The negative lens in the first lens group satisfies the following conditional expression:
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: Refractive index for the d-line (wavelength λ = 587.6 nm) of the material of the negative lens in the first lens group
νd1: Abbe number for the d-line (wavelength λ = 587.6 nm) of the material of the negative lens in the first lens group
Provided is a zoom lens that satisfies the following conditional expression.
1.0 ≦ f2 / fw ≦ 2.3
However,
fw: focal length of the zoom lens in the wide-angle end state
f2: Focal length of the second lens group
The present invention also provides
In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The aspheric plastic lens in the fourth lens group is disposed closer to the object side than the most image side lens,
The first lens group has a negative lens;
The negative lens in the first lens group satisfies the following conditional expression, and provides a zoom lens.
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: Refractive index for the d-line (wavelength λ = 587.6 nm) of the material of the negative lens in the first lens group
νd1: Abbe number for the d-line (wavelength λ = 587.6 nm) of the material of the negative lens in the first lens group

  Also provided is an imaging apparatus comprising the zoom lens of the present invention.

The present invention also provides
In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power A zoom lens zooming method comprising substantially four lens groups, wherein the fourth lens group comprises an aspheric plastic lens,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The first lens group has a negative lens;
The fourth lens group includes at least one positive lens and one negative lens,
The zoom lens zooming method according to claim 1, wherein the negative lens in the first lens group satisfies the following conditional expression .
3 0 ≦ νd1 ≦ 71
3 0 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: refractive index νd1: d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group with respect to d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group Abbe number for

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a zoom lens, an imaging device, and a zooming method that achieve high image quality.

Hereinafter, the zoom lens, the imaging device, and the zooming method of the present invention will be described.
In general, each lens group constituting the zoom lens corrects aberrations as follows.
Correction of chromatic aberration is performed by combining a positive lens made of low refractive index and low dispersion glass and a negative lens made of high refractive index and high dispersion glass in the positive lens group, and low refractive index and low dispersion in the negative lens group. This is performed by combining a negative lens made of glass and a positive lens made of high refractive index and high dispersion glass. For this reason, it is necessary to set the refractive power of the positive lens large in the positive lens group, and to set the refractive power of the negative lens large in the negative lens group.

Further, various aberrations such as spherical aberration and coma need to be corrected to some extent inside each lens group. In general, various aberrations occur as the declination increases, and become more pronounced as the refractive index decreases.
Therefore, in order to correct various aberrations while correcting chromatic aberration in a zoom lens, it is effective to arrange a plurality of positive lenses in the positive lens group and a plurality of negative lenses in the negative lens group. Become.

  In recent years, in place of conventional glass polishing, a technique for manufacturing a lens by processing plastic by injection molding or the like has been developed. This manufacturing method is effective as a means for correcting various aberrations because the lens surface can be aspherical more easily than glass polishing. However, although plastics have a high degree of freedom in shape, at present, due to environmental resistance such as temperature, humidity, hardness, and coloring by ultraviolet rays, and due to internal distortion, the diameter of the lens is increased and the center and periphery of the lens are increased. It is difficult to increase the wall thickness difference.

  Therefore, compared with a glass lens, the shape and refractive index of a plastic lens are greatly changed by changes in temperature and humidity, and various aberrations are deteriorated. For this reason, a large refractive power cannot be set for the plastic lens. In addition, when the thickness difference between the central portion and the peripheral portion of the lens is large, internal distortion is likely to occur or the refractive index is likely to be nonuniform. For this reason, the plastic lens cannot have a large difference in curvature between the front and back lens surfaces, that is, cannot have a large refractive power.

  Here, a typical plastic that can be used as a material for the photographing lens is a polycarbonate resin having a refractive index and a dispersion value of about 1.6 and 30 for d-line (wavelength λ = 587.6 nm), respectively. There are about 56 polymethyl methacrylate (PMMA) and cyclic olefin polymers. Therefore, it is effective to use the PMMA plastic for the positive lens in the positive lens group, and the polycarbonate resin can be used for both positive and negative lenses.

  Under the above premise, the zoom lens of the present invention is a lightweight and inexpensive glass as a glass material for the positive lens in the positive lens group and the negative lens in the negative lens group in order to realize a small, light and inexpensive high optical performance. And an aspheric plastic lens in the fourth lens group.

The zoom lens of the present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a positive lens A fourth lens group having a refractive power, and when changing the magnification from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, and the second lens group and the second lens group The lens groups move along the optical axis such that the distance between the third lens group increases and the distance between the third lens group and the fourth lens group decreases.
The fourth lens group includes an aspheric plastic lens,
The first lens group has a negative lens;
The negative lens in the first lens group satisfies the following conditional expressions (1) and (2), and provides a zoom lens.
(1) 30 ≦ νd1 ≦ 71
(2) When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: refractive index νd1: d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group with respect to d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group Abbe number for

  Here, in the minus lead type four-group zoom lens having a wide angle of view, the diameter of the first lens group is large in order to secure the angle of view in the wide-angle end state, and the ratio of the total cost and weight is large. On the other hand, the third lens group, which does not contribute much to zooming and mainly handles adjustment of the principal point position and correction of aberrations, has a small diameter and a small proportion of the total cost and weight. In addition, the second lens group and the fourth lens group having positive refractive power have a large role of zooming, and in particular, the diameter of the fourth lens group is large in order to ensure a field angle in the wide-angle end state.

  Further, in consideration of an appropriate location of the aspheric plastic lens, if it is arranged in the first lens group having a large diameter, the difference in thickness between the central portion and the peripheral portion of the aspheric plastic lens is reduced. In addition, the difference in curvature between the front and back lens surfaces must be reduced. As a result, the aspheric plastic lens becomes a lens having almost no refractive power, and only an effect of correcting aberration can be obtained. Therefore, the zoom lens cannot be reduced in size, but rather the total length increases.

  Further, if an aspheric plastic lens is arranged in the second lens group or the third lens group, the on-axis light beam passes through these lens groups over the entire effective diameter. The effect of can no longer be achieved. Further, the above-described internal distortion or the like has a great influence on the performance deterioration, which is not preferable.

  Therefore, it is most preferable that the aspheric plastic lens is disposed in the fourth lens group. In each example shown below, the aspheric plastic lens is used as a single lens, but it can also be used as a cemented lens with a glass lens. The aspheric plastic lens is preferably arranged on the object side of the final lens, that is, the most image side lens, in order to prevent scratches and the like.

The conditional expression (1) is a conditional expression for appropriately setting the Abbe number of the negative lens in the first lens group having negative refractive power.
If the lower limit of conditional expression (1) is not reached, it will be difficult to correct lateral chromatic aberration in the wide-angle end state.

  On the other hand, if the upper limit value of conditional expression (1) is exceeded, the refractive index generally decreases, and it becomes difficult to correct spherical aberration, distortion, and the like.

The conditional expression (2) is a conditional expression for appropriately setting the refractive index of the negative lens in the first lens group having negative refractive power.
If the lower limit of conditional expression (2) is not reached, it will be difficult to simultaneously correct lateral chromatic aberration and negative distortion in the wide-angle end state.

  On the other hand, if the upper limit value of conditional expression (2) is exceeded, expensive glass such as heavy crown or lanthanum crown will be used as the glass material for the negative lens in the first lens group. Therefore, in order to avoid such an increase in weight and price, the number of lenses in the first lens group must be reduced. As a result, the same problem as that in the case where the value falls below the lower limit value described above is caused. It will occur remarkably.

In the zoom lens according to the present invention, it is preferable that each lens group includes two or more lenses.
With this configuration, it is possible to satisfactorily correct various aberrations including chromatic aberration.

It is desirable that the zoom lens of the present invention satisfies the following conditional expression (3).
(3) 1.5 ≦ f4 / fw ≦ 2.9
However,
f4: focal length of the fourth lens group fw: focal length of the zoom lens in the wide-angle end state

The conditional expression (3) is a conditional expression for defining the focal length of the fourth lens group having a positive refractive power.
If the lower limit of conditional expression (3) is not reached, it will be difficult to correct distortion in the wide-angle end state and coma aberration in the intermediate focal length state.
In addition, if the lower limit of conditional expression (3) is set to 1.80, the effect of the present invention can be exhibited more.
On the other hand, if the upper limit value of conditional expression (3) is exceeded, it will be difficult to correct spherical aberration especially in the telephoto end state.
In addition, if the upper limit of conditional expression (3) is set to 2.7, more preferably 2.4, the effect of the present invention can be exhibited more.

In the zoom lens according to the present invention, it is preferable that the second lens group includes a positive lens, and the positive lens in the second lens group satisfies the following conditional expressions (4) and (5).
(4) 30 ≦ νd2 ≦ 71
(5) When 30 ≦ νd2 <36
-0.013 × νd2 + 2.083 ≦ nd2 ≦ 1.7
When 36 ≦ νd2 <41
-0.013 × νd2 + 2.083 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 41 ≦ νd2 <51
-0.004 × νd2 + 1.714 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 51 ≦ νd2 <61
-0.0015 × νd2 + 1.5865 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 61 ≦ νd2 ≦ 71
-0.0015 × νd2 + 1.5865 ≦ nd2 ≦ −0.009 × νd2 + 2.149
However,
nd2: Refractive index νd2 for the positive lens material d-line (wavelength λ = 587.6 nm) in the second lens group: d-line (wavelength λ = 587.6 nm) for the positive lens material in the second lens group Abbe number for

The conditional expression (4) is a conditional expression for appropriately setting the Abbe number of the positive lens in the second lens group having a positive refractive power.
If the lower limit of conditional expression (4) is not reached, it will be difficult to correct lateral chromatic aberration in the wide-angle end state.

  On the other hand, if the upper limit value of conditional expression (4) is exceeded, the refractive index generally decreases, and it becomes difficult to correct spherical aberration, distortion, and the like.

The conditional expression (5) is a conditional expression for appropriately setting the refractive index of the positive lens in the second lens group having positive refractive power.
If the lower limit of conditional expression (5) is not reached, it will be difficult to simultaneously correct spherical aberration and axial chromatic aberration in the telephoto end state.

  On the other hand, if the upper limit of conditional expression (5) is exceeded, expensive glass such as a heavy crown or a lanthanum crown will be used as the glass material for the positive lens in the second lens group. Therefore, in order to avoid such an increase in weight and price, the number of lenses in the second lens group must be reduced. As a result, the same problem as that in the case where the value falls below the above lower limit value is caused. It will occur remarkably.

In the zoom lens of the present invention, the fourth lens group includes the aspheric plastic lens and a positive lens, and the positive lens in the fourth lens group includes the following conditional expressions (6), ( It is desirable to satisfy 7).
(6) 30 ≦ νd4 ≦ 71
(7) When 30 ≦ νd4 <36
-0.013 × νd4 + 2.083 ≦ nd4 ≦ 1.7
When 36 ≦ νd4 <41
-0.013 × νd4 + 2.083 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 41 ≦ νd4 <51
-0.004 × νd4 + 1.714 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 51 ≦ νd4 <61
-0.0015 × νd4 + 1.5865 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 61 ≦ νd4 ≦ 71
-0.0015 × νd4 + 1.5865 ≦ nd4 ≦ −0.009 × νd4 + 2.149
However,
nd4: refractive index νd4 for the positive lens material d-line (wavelength λ = 587.6 nm) in the fourth lens group: d-line (wavelength λ = 587.6 nm) for the positive lens material in the fourth lens group Abbe number for

The conditional expression (6) is a conditional expression for appropriately setting the Abbe number of the positive lens in the fourth lens group having a positive refractive power.
If the lower limit of conditional expression (6) is not reached, it will be difficult to correct lateral chromatic aberration in the wide-angle end state.

  On the other hand, if the upper limit value of conditional expression (6) is exceeded, the refractive index generally decreases, making it difficult to correct spherical aberration, distortion, and the like.

The conditional expression (7) is a conditional expression for appropriately setting the refractive index of the positive lens in the fourth lens group having a positive refractive power.
If the lower limit of conditional expression (7) is not reached, it will be difficult to simultaneously correct lateral chromatic aberration and field curvature aberration at the wide-angle end state, coma aberration at the intermediate focal length state, and axial chromatic aberration at the telephoto end state. End up.

  On the other hand, if the upper limit of conditional expression (7) is exceeded, expensive glass such as a heavy crown or a lanthanum crown will be used as the glass material for the positive lens in the fourth lens group. Therefore, in order to avoid such an increase in weight and price, the number of lenses in the fourth lens group must be reduced. As a result, the same problem as that in the case where the value falls below the lower limit value described above is caused. It will occur remarkably.

In the zoom lens according to the present invention, it is preferable that the aspheric plastic lens in the fourth lens group satisfies the following conditional expression (8).
(8) | f4 / fP | ≦ 0.9
However,
f4: focal length of the fourth lens group fP: focal length of the aspheric plastic lens in the fourth lens group

The conditional expression (8) is a conditional expression for maintaining the excellent optical performance even if the aspheric plastic lens in the fourth lens group is easy to manufacture and changes in the environment such as temperature and humidity.
Exceeding the upper limit of conditional expression (8) is not preferable because off-axis aberrations such as coma and curvature of field aberrations deteriorate.
In addition, if the upper limit of conditional expression (8) is set to 0.7, the effect of the present invention can be exhibited more.

In the zoom lens according to the present invention, it is preferable that the fourth lens group includes at least one positive lens and one negative lens.
In this way, a positive lens is arranged on the object side in the fourth lens group, and a negative lens is arranged on the image side, so that it is a telephoto type, and a bright F number is secured in the telephoto end state.

In the zoom lens according to the present invention, the first lens group includes, in order from the object side, a negative meniscus lens having a convex object side lens surface, a negative lens having a concave image side lens surface, and a convex lens having an object side lens surface. It is desirable to have a positive lens and satisfy the following conditional expression (9).
(9) 0.7 ≦ (−f1) /fw≦1.7
However,
f1: Focal length fw of the first lens group fw: Focal length of the zoom lens in the wide-angle end state

  In general, as a method for suppressing the enlargement of the front lens diameter, that is, the diameter of the lens closest to the object side, while securing a sufficient angle of view in the zoom lens, a negative lens is disposed on the object side in the first lens group. It is well known. In addition, by arranging a plurality of negative lenses in the first lens group, it becomes possible to satisfactorily correct various aberrations related to the angle of view such as field curvature aberration and distortion. The occurrence of aberration can be prevented by making the surface aplanatic toward the aperture stop. Furthermore, by arranging a positive lens in the first lens group, it becomes possible to achieve both correction of chromatic aberration and correction of spherical aberration.

  As described above, in this zoom lens, when focusing on the correction of the field angle aberration in the wide-angle end state and the image side lens surface of the second negative lens from the object side in the first lens group is concave, the telephoto end state In this case, a large amount of spherical aberration occurs. Therefore, in order to correct this spherical aberration, a lens having a convex lens surface on the object side is required immediately after the second negative lens from the object side (image side), and this lens has a need for correcting chromatic aberration. It becomes a positive lens in consideration.

The conditional expression (9) is a conditional expression for defining the focal length of the first lens group.
If the lower limit of conditional expression (9) is not reached, it will be difficult to correct various aberrations relating to the angle of view such as distortion, curvature of field, and astigmatism in the wide-angle end state.
In addition, if the lower limit value of the conditional expression (9) is set to 1.0, more preferably 1.4, the effect of the present invention can be exhibited more.

  On the other hand, if the upper limit value of conditional expression (9) is exceeded, it is possible to correct the above-mentioned various aberrations, but it becomes difficult to ensure the back focus. Therefore, in order to ensure the back focus, the focal length of the third lens group must be reduced. As a result, it becomes difficult to correct spherical aberration in the telephoto end state and coma aberration over the entire zoom range. End up.

It is desirable that the zoom lens of the present invention satisfies the following conditional expression (10).
(10) 1.0 ≦ f2 / fw ≦ 2.3
However,
fw: focal length of the zoom lens in the wide-angle end state f2: focal length of the second lens group

The conditional expression (10) is a conditional expression for defining the focal length of the second lens group having a positive refractive power.
If the lower limit of conditional expression (10) is not reached, it will be difficult to correct spherical aberration in the telephoto end state.
In addition, if the lower limit value of conditional expression (10) is set to 1.2, more preferably 1.4, the effect of the present invention can be exhibited more.

On the other hand, if the upper limit of conditional expression (10) is exceeded, it will be difficult to ensure the zoom ratio. For this reason, the focal length of the fourth lens group must be reduced in order to ensure the zoom ratio, and as a result, it becomes difficult to correct distortion aberration in the wide-angle end state and coma aberration in the intermediate focal length state. turn into.
In addition, if the upper limit of conditional expression (10) is set to 1.6, the effect of this invention can be exhibited more.

It is desirable that the zoom lens of the present invention satisfies the following conditional expression (11).
(11) 0.8 ≦ (−f3) /fw≦3.0
However,
fw: focal length of the zoom lens in the wide-angle end state f3: focal length of the third lens group

The conditional expression (11) is a conditional expression for defining the focal length of the third lens group having negative refractive power.
If the lower limit of conditional expression (11) is not reached, it will be difficult to correct coma and spherical aberration over the entire zoom range.
If the lower limit value of conditional expression (11) is set to 1.2, more preferably 1.6, the effect of the present invention can be further exerted.

On the other hand, if the upper limit of conditional expression (11) is exceeded, it will be difficult to ensure the back focus. For this reason, in order to ensure the back focus, the focal length of the first lens group must be reduced. As a result, various aberrations relating to the angle of view such as distortion and field curvature aberration in the wide-angle end state are corrected. It becomes difficult.
In addition, if the upper limit of conditional expression (11) is set to 2.6, more preferably 2.2, the effect of the present invention can be exhibited more.

In the zoom lens of the present invention, it is preferable that at least one aspheric surface is provided in the first lens group.
With this configuration, it is possible to satisfactorily correct field curvature aberration and astigmatism.

In the zoom lens according to the present invention, the negative meniscus lens in the first lens group , that is , the image side lens surface of the negative meniscus lens having a convex object side lens surface described in the description of the conditional expression (9) is the aspheric surface. It is desirable that the following conditional expression (12) is satisfied.
(12) 0.32 ≦ Rasp / (− f1) ≦ 1.0
However,
Rasp: Paraxial radius of curvature of the aspheric surface f1: Focal length of the first lens group

Conditional expression (12) is a conditional expression that defines the shape of the aberration correction performed by the aspherical surface in the first lens group.
If the upper limit value of conditional expression (12) is exceeded, the paraxial radius of curvature of the aspheric surface in the first lens group will become smaller. For this reason, it becomes difficult to correct aberration related to the angle of view such as distortion in the wide-angle end state by the aspheric surface.
In addition, if the upper limit of conditional expression (12) is set to 0.8, the effect of this invention can be exhibited more.

On the other hand, if the lower limit value of conditional expression (12) is not reached, the paraxial radius of curvature of the aspheric surface in the first lens group becomes large. For this reason, correction of spherical aberration generated on the paraxial spherical surface itself in the telephoto end state must be performed by the aspheric surface, which is difficult.
In addition, if the lower limit of conditional expression (12) is set to 0.37, the effect of the present invention can be exhibited more.

In the zoom lens according to the aspect of the invention, it is preferable that the second lens group includes two positive lenses and one negative lens.
As described above, by arranging a plurality of positive lenses in the second lens group having a positive refractive power, various aberrations including chromatic aberration can be favorably corrected. Further, a positive lens is disposed on the object side, and a negative lens is disposed on the image side, thereby providing a telephoto type, and a bright F number is ensured in the telephoto end state.

In the zoom lens of the present invention, it is desirable that one of the two positive lenses and the one negative lens are cemented in the second lens group.
With this configuration, various aberrations including chromatic aberration can be corrected more favorably.

In the zoom lens of the present invention, it is preferable that the third lens group is composed of one positive lens and one negative lens.
With this configuration, it is possible to satisfactorily correct various aberrations including chromatic aberration. Further, by arranging a positive lens on the object side and a negative lens on the image side, the principal point position is adjusted in accordance with the telephoto conversion of the second lens group and the fourth lens group. An air space between the three lens groups can be secured.

The zoom lens according to the present invention preferably has an aperture stop in the vicinity of the third lens group, and the aperture stop moves integrally with the third lens group.
As described above, in this zoom lens optical system, the aperture stop is disposed in the vicinity of the third lens group in which the land light beam (the light beam that reaches the image height of 0 and which is farthest from the optical axis) is narrowed. This is preferable because the configuration of the lens barrel can be simplified.

In the zoom lens according to the present invention, it is desirable that the second lens group and the fourth lens group move integrally when zooming from the telephoto end state to the wide-angle end state.
This configuration is preferable because the configuration of the lens barrel can be simplified.

In the zoom lens of the present invention, it is preferable that the aspheric plastic lens in the fourth lens group is disposed closer to the object side than the most image side lens.
With this configuration, it is possible to prevent the aspheric plastic lens from being damaged.

The imaging apparatus of the present invention includes the zoom lens having the above-described configuration.
As a result, it is possible to realize an imaging device that achieves high image quality.

In the zoom lens zooming method according to the present invention, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens having a negative refractive power. And a fourth lens group having a positive refracting power, wherein the fourth lens group includes a non-spherical plastic lens. Upon zooming, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, and the third lens group and the fourth lens The lens groups move along the optical axis so that the distance from the group decreases, the first lens group includes a negative lens, and the negative lens in the first lens group satisfies the following conditions: Expressions (1) and (2) are satisfied.
(1) 30 ≦ νd1 ≦ 71
(2) When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: refractive index νd1: d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group with respect to d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group Abbe's number with respect to () With this configuration, it is possible to improve the image quality of the zoom lens.

Hereinafter, zoom lenses according to numerical examples of the present invention will be described with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a diagram illustrating the configuration of a zoom lens according to the first embodiment of the present invention and the movement locus of each lens group.
The zoom lens according to the present embodiment has, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, an aperture stop S, and a negative refractive power. The third lens group G3 includes a fourth lens group G4 having a positive refractive power, and a flare cut stop FS. Then, upon zooming from the wide-angle end state (W) to the telephoto end state (T), the distance between the first lens group G1 and the second lens group G2 decreases, and the second lens group G2 and the third lens group G3. The lens groups G1, G2, G3, and G4 move along the optical axis so that the distance between the third lens group G3 and the fourth lens group G4 decreases.

The first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconcave negative lens L2, and a positive meniscus lens L3 having a convex surface facing the object side.
The second lens group G2 includes, in order from the object side, a biconvex positive lens L4, and a cemented lens of a biconvex positive lens L5 and a biconcave negative lens L6.

The third lens group G3 includes, in order from the object side, a cemented lens of a positive meniscus lens L7 having a convex surface directed toward the image side and a biconcave negative lens L8.
The fourth lens group G4 includes, in order from the object side, a negative meniscus lens L9 having a convex surface facing the image side, which is an aspheric plastic lens, and a biconvex positive lens L10.

The aperture stop S is disposed in the vicinity of the third lens group G3 on the object side, and moves integrally with the third lens group G3 upon zooming from the wide-angle end state to the telephoto end state.
In addition, the flare cut stop FS is disposed on the image side of the fourth lens group G4, so that coma flare with an intermediate image height can be effectively removed.

Table 1 below lists values of specifications of the zoom lens according to the first example of the present invention.
In [Overall specifications], f represents a focal length, FNO represents an F number, and 2ω represents an angle of view.
In [Lens data], the surface represents the order of the lens surfaces from the object side, r represents the radius of curvature of the lens surfaces, and d represents the distance between the lens surfaces. Further, nd represents the refractive index with respect to the d line (λ = 587.6 nm), and νd represents the Abbe number with respect to the d line (λ = 587.6 nm). Furthermore, an aspherical surface in the lens data is marked with an asterisk (*) and the paraxial radius of curvature is indicated in the column of curvature radius r, and κ and each aspherical coefficient are described in the column of [Aspherical data]. To do. Further, the radius of curvature r = 0.000 indicates a plane, and the refractive index nd = 1.00000 of air is omitted from the description.

In [Aspherical data], “En” indicates “× 10 ⁻ⁿ ”. The rotationally symmetric aspherical surface shown in the specification table has a distance (sag amount) along the optical axis direction from the tangential plane of the apex of each aspherical surface at a height y in the vertical direction from the optical axis, X (y), Where the radius of curvature is r, the cone coefficient is κ, and the n-th order aspheric coefficient is C n, the following aspheric expression is used. Note that the description of the aspherical coefficient that is 0 (zero) is omitted.
X (y) = (y ² / r) / [1+ (1−κ · y ² / r ² ) ^1/2 ]
+ C4 · y ⁴ + C6 · y ⁶ + C8 · y ⁸ + C10 · y ¹⁰ + C12 · y ¹²

In [lens data] and “variable interval data”, BF indicates back focus.
In [Conditional Expression Corresponding Value], when there are a plurality of corresponding lenses, a plurality of conditional expression corresponding values are also shown. The lens L2 is formed with a thin resin layer on the surface of the base lens. In this case, the base lens is the corresponding lens.
Here, the unit of the focal length f, the radius of curvature r, and other lengths listed in all the following specification values is generally “mm”. However, the optical system is not limited to this because an equivalent optical performance can be obtained even when proportional expansion or proportional reduction is performed.
In addition, also in the specification values of all the following examples, the same symbols as in this example are used.

(Table 1)
[Overall specifications]
f = 18.54 to 53.4
FNO = 3.6 to 5.85
2ω = 29.86 to 78.18 °

[Lens data]
Surface r d nd νd
1 79.2009 1.0000 1.589130 61.18
2 19.8444 0.1000 1.553890 38.09
* 3 17.5584 8.1794
4 -121.7843 1.0000 1.589130 61.18
5 30.2816 3.7035
6 41.1845 4.0000 1.846660 23.78
7 146.6886 D7

8 29.6454 3.0000 1.517420 52.42
9 -47.3732 4.2849
10 25.3774 3.5000 1.516330 64.14
11 -32.5214 1.0000 1.846660 23.78
12 204.7269 D12

13 0.0000 1.8782 Aperture stop S
14 -34.8637 2.0000 1.761820 26.52
15 -12.8952 1.0000 1.723420 37.95
16 63.9205 D16

17 -50.0000 0.5000 1.585180 30.24 Aspheric plastic lens
* 18 -144.3076 0.1000
19 67.6843 4.0000 1.516330 64.14
20 -19.2326 D20

21 0.0000 BF Flare cut aperture FS

[Aspherical data]
<Third lens surface>
κ = -1.00000
C4 = 1.02890E-05
C6 = 9.30490E-09
C8 = -1.26540E-11
C10 = 4.87520E-14
C12 = 0.0000

<18th lens surface>
κ = 0.00000
C4 = 2.97790E-05
C6 = 1.34120E-07
C8 = -1.63730E-09
C10 = 7.50900E-12
C12 = 0.00000

[Variable interval data]
Wide-angle end state Intermediate focal length state Telephoto end state f 18.50 35.00 53.40
D7 35.355 1.000 1.787
D12 1.084 5.335 9.325
D16 10.294 6.035 2.054
D20 0.000 14.721 30.000
BF 38.500 38.500 38.500

[Conditional expression values]
Conditional expression (1) νd1 = 61.18 (L1), 61.18 (L2)
Conditional expression (2) nd1 = 1.589130 (L1), 1.589130 (L2)
Conditional expression (3) f4 / fw = 2.00
Conditional expression (4) νd2 = 52.42 (L4), 64.14 (L5)
Conditional expression (5) nd2 = 1.517420 (L4), 1.516330 (L5)
Conditional expression (6) νd4 = 64.14 (L10)
Conditional expression (7) nd4 = 1.516330 (L10)
Conditional expression (8) | f4 / fP | = 0.28
Conditional expression (9) (−f1) /fw=1.56
Conditional expression (10) f2 / fw = 1.55
Conditional expression (11) (−f3) /fw=1.77
Conditional expression (12) Rasp / (− f1) = 0.60

  FIGS. 2A, 2B, and 2C are graphs showing various aberrations in the zoom lens according to the first example of the present invention in the wide-angle end state, the intermediate focal length state, and the telephoto end state, respectively.

In each aberration diagram, FNO represents an F number, Y represents an image height, and A represents a half angle of view (unit: “°”). In the astigmatism diagram and the distortion diagram, the maximum value of the image height Y is shown. D and g indicate aberration curves of the d-line (λ = 587.6 nm) and the g-line (λ = 435.8 nm), respectively. In the spherical aberration diagram, FNO represents the F-number value corresponding to the maximum aperture. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the dotted line indicates the meridional image plane. The coma aberration diagram represents the coma aberration at each half angle of view.
In addition, in the various aberration diagrams of each example shown below, the same reference numerals as those in this example are used.

  From the various aberration diagrams, the zoom lens according to the present embodiment corrects various aberrations well in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state, and has excellent imaging performance. I understand that.

(Second embodiment)
FIG. 3 is a diagram showing the configuration of the zoom lens according to the second embodiment of the present invention and the movement locus of each lens group.
The zoom lens according to the present embodiment has, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, an aperture stop S, and a negative refractive power. The third lens group G3 includes a fourth lens group G4 having a positive refractive power, and a flare cut stop FS. Then, upon zooming from the wide-angle end state (W) to the telephoto end state (T), the distance between the first lens group G1 and the second lens group G2 decreases, and the second lens group G2 and the third lens group G3. The lens groups G1, G2, G3, and G4 move along the optical axis so that the distance between the third lens group G3 and the fourth lens group G4 decreases.

The first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconcave negative lens L2, and a positive meniscus lens L3 having a convex surface facing the object side.
The second lens group G2 includes, in order from the object side, a biconvex positive lens L4, a cemented lens of a biconvex positive lens L5, and a negative meniscus lens L6 having a convex surface facing the image side.

The third lens group G3 includes, in order from the object side, a cemented lens of a positive meniscus lens L7 having a convex surface directed toward the image side and a biconcave negative lens L8.
The fourth lens group G4 includes, in order from the object side, a positive meniscus lens L9 having a convex surface facing the image side, which is an aspheric plastic lens, a biconvex positive lens L10, and a plano-concave lens L11.

The aperture stop S is disposed in the vicinity of the third lens group G3 on the object side, and moves integrally with the third lens group G3 upon zooming from the wide-angle end state to the telephoto end state.
In addition, the flare cut stop FS is disposed on the image side of the fourth lens group G4, so that coma flare with an intermediate image height can be effectively removed.
Table 2 below provides values of specifications of the zoom lens according to the second example of the present invention.

(Table 2)
[Overall specifications]
f = 18.54 to 53.4
FNO = 3.6 to 5.45
2ω = 29.86 to 78.18 °

[Lens data]
Surface r d nd νd
1 64.1663 1.0000 1.589130 61.18
2 19.8759 0.1000 1.553890 38.09
* 3 17.6687 8.7577
4 -74.6681 1.0000 1.516330 64.14
5 29.9024 4.3884
6 41.8165 2.5740 1.805180 25.43
7 123.6822 D7

8 45.8168 2.7826 1.487490 70.24
9 -38.5977 4.1127
10 24.3027 3.5000 1.516330 64.14
11 -38.5376 1.0000 1.846660 23.78
12 -537.5618 D12

13 0.0000 1.9099 Aperture stop S
14 -38.1662 2.0000 1.846660 23.78
15 -19.0782 1.0000 1.772500 49.61
16 60.1310 D16

17 -40.0000 1.2188 1.585180 30.24 Aspheric plastic lens
* 18 -27.7873 0.1000
19 99.0502 4.1140 1.589130 61.18
20 -17.9625 0.1000
21 -42.4892 1.0000 1.846660 23.78
22 0.0000 D22

23 0.0000 BF Flare cut aperture FS

[Aspherical data]
<Third lens surface>
κ = -1.00000
C4 = 1.00191E-05
C6 = 1.95672E-08
C8 = -4.00558E-11
C10 = 1.18346E-13
C12 = 0.0000

<18th lens surface>
κ = 0.00000
C4 = 3.95862E-05
C6 = 1.65623E-07
C8 = -1.92869E-10
C10 = 1.72254E-13
C12 = 0.0000

[Variable interval data]
Wide angle end state Intermediate focal length state Telephoto end state f 18.500 35.000 53.400
D7 34.961 9.516 1.100
D12 0.974 6.197 11.116
D16 12.362 7.139 2.219
D22 0.000 12.225 24.709
BF 38.500 38.500 38.500

[Conditional expression values]
Conditional expression (1) νd1 = 61.18 (L1), 64.14 (L2)
Conditional expression (2) nd1 = 1.589130 (L1), 1.516330 (L2)
Conditional expression (3) f4 / fw = 2.13
Conditional expression (4) νd2 = 70.24 (L4), 64.14 (L5)
Conditional expression (5) nd2 = 1.487490 (L4), 1.516330 (L5)
Conditional expression (6) νd4 = 61.18 (L10)
Conditional expression (7) nd4 = 1.589130 (L10)
Conditional expression (8) | f4 / fP | = 0.26
Conditional expression (9) (−f1) /fw=1.55
Conditional expression (10) f2 / fw = 1.49
Conditional expression (11) (−f3) /fw=1.71
Conditional expression (12) Rasp / (− f1) = 0.59

4A, 4B, and 4C are graphs showing various aberrations of the zoom lens according to Example 2 of the present invention in the wide-angle end state, the intermediate focal length state, and the telephoto end state, respectively.
From the various aberration diagrams, the zoom lens according to the present embodiment corrects various aberrations well in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state, and has excellent imaging performance. I understand that.

(Third embodiment)
FIG. 5 is a diagram showing the configuration of a zoom lens according to the third embodiment of the present invention and the movement locus of each lens group.
The zoom lens according to the present embodiment has, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, an aperture stop S, and a negative refractive power. The third lens group G3 includes a fourth lens group G4 having a positive refractive power, and a flare cut stop FS. Then, upon zooming from the wide-angle end state (W) to the telephoto end state (T), the distance between the first lens group G1 and the second lens group G2 decreases, and the second lens group G2 and the third lens group G3. The lens groups G1, G2, G3, and G4 move along the optical axis so that the distance between the third lens group G3 and the fourth lens group G4 decreases.

The first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconcave negative lens L2, and a positive meniscus lens L3 having a convex surface facing the object side.
The second lens group G2 includes, in order from the object side, a biconvex positive lens L4, and a cemented lens of a biconvex positive lens L5 and a biconcave negative lens L6.

The third lens group G3 includes, in order from the object side, a cemented lens of a positive meniscus lens L7 having a convex surface directed toward the image side and a biconcave negative lens L8.
The fourth lens group G4 includes, in order from the object side, a cemented lens of a biconcave negative lens L9, which is an aspheric plastic lens, and a biconvex positive lens L10, and a biconvex positive lens L11.

The aperture stop S is disposed in the vicinity of the third lens group G3 on the object side, and moves integrally with the third lens group G3 upon zooming from the wide-angle end state to the telephoto end state.
In addition, the flare cut stop FS is disposed on the image side of the fourth lens group G4, so that coma flare with an intermediate image height can be effectively removed.
Table 3 below lists values of specifications of the zoom lens according to the third example of the present invention.

(Table 3)
[Overall specifications]
f = 18.54 to 53.4
FNO = 3.6 to 5.76
2ω = 29.86 to 78.18 °

[Lens data]
Surface r d nd νd
1 45.3636 1.0000 1.589130 61.18
2 18.0047 0.1000 1.553890 38.09
* 3 16.2706 9.6651
4 -111.9321 1.0000 1.589130 61.18
5 30.9798 4.0188
6 37.2483 3.1980 1.846660 23.78
7 82.4283 D7

8 29.2959 2.8333 1.581439 40.75
9 -45.4968 1.2436
10 26.9363 3.5000 1.516330 64.14
11 -30.2204 1.0000 1.846660 23.78
12 170.5988 D12

13 0.0000 1.8561 Aperture stop S
14 -35.3429 2.0000 1.784718 25.71
15 -13.6521 1.0000 1.723420 37.95
16 54.7652 D16

17 -63.7885 0.5000 1.585180 30.24 Aspheric plastic lens
* 18 74.9879 0.1000
19 80.0562 3.2643 1.516330 64.15
20 -23.3244 0.1000
21 225.0632 2.3577 1.516330 64.15
22 -43.0774 D22

23 0.0000 BF Flare cut aperture FS

[Aspherical data]
<Third lens surface>
κ = -1.00000
C4 = 1.79370E-05
C6 = 1.99850E-08
C8 = 7.76380E-12
C10 = 1.32429E-13
C12 = 0.0000

<18th lens surface>
κ = 0.00000
C4 = 1.32435E-05
C6 = 1.03858E-07
C8 = -1.69082E-09
C10 = 8.76925E-12
C12 = 0.0000

[Variable interval data]
Wide angle end state Intermediate focal length state Telephoto end state f 18.500 35.000 53.400
D7 33.501 9.235 1.100
D12 1.104 4.583 7.955
D16 8.880 5.407 2.020
D22 0.000 14.637 30.000
BF 38.499 38.498 38.502

[Conditional expression values]
Conditional expression (1) νd1 = 61.18 (L1), 61.18 (L2)
Conditional expression (2) nd1 = 1.589130 (L1), 1.589130 (L2)
Conditional expression (3) f4 / fw = 2.03
Conditional expression (4) νd2 = 40.75 (L4), 64.14 (L5)
Conditional expression (5) nd2 = 1.581439 (L4), 1.516330 (L5)
Conditional expression (6) νd4 = 64.15 (L10), 64.15 (L11)
Conditional expression (7) nd4 = 1.516330 (L10), 1.516330 (L11)
Conditional expression (8) | f4 / fP | = 0.64
Conditional expression (9) (−f1) /fw=1.55
Conditional expression (10) f2 / fw = 1.45
Conditional expression (11) (−f3) /fw=1.72
Conditional expression (12) Rasp / (− f1) = 0.63

FIGS. 6A, 6B, and 6C are graphs showing various aberrations of the zoom lens according to the third example of the present invention in the wide-angle end state, the intermediate focal length state, and the telephoto end state, respectively.
From the various aberration diagrams, the zoom lens according to the present embodiment corrects various aberrations well in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state, and has excellent imaging performance. I understand that.

(Fourth embodiment)
FIG. 7 is a diagram showing the configuration of a zoom lens according to the fourth embodiment of the present invention and the movement locus of each lens group.
The zoom lens according to the present embodiment has, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, an aperture stop S, and a negative refractive power. The third lens group G3 includes a fourth lens group G4 having a positive refractive power, and a flare cut stop FS. Then, upon zooming from the wide-angle end state (W) to the telephoto end state (T), the distance between the first lens group G1 and the second lens group G2 decreases, and the second lens group G2 and the third lens group G3. The lens groups G1, G2, G3, and G4 move along the optical axis so that the distance between the third lens group G3 and the fourth lens group G4 decreases.

The first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconcave negative lens L2, and a positive meniscus lens L3 having a convex surface facing the object side.
The second lens group G2 includes, in order from the object side, a biconvex positive lens L4, and a cemented lens of a biconvex positive lens L5 and a biconcave negative lens L6.

The third lens group G3 includes, in order from the object side, a cemented lens of a positive meniscus lens L7 having a convex surface directed toward the image side and a biconcave negative lens L8.
The fourth lens group G4 includes, in order from the object side, a positive meniscus lens L9 having a convex surface facing the image side, which is an aspheric plastic lens, a biconvex positive lens L10, and a plano-concave lens L11.

The aperture stop S is disposed in the vicinity of the third lens group G3 on the object side, and moves integrally with the third lens group G3 upon zooming from the wide-angle end state to the telephoto end state.
In addition, the flare cut stop FS is disposed on the image side of the fourth lens group G4, so that coma flare with an intermediate image height can be effectively removed.
Table 4 below provides values of specifications of the zoom lens according to Example 4 of the present invention.

(Table 4)
[Overall specifications]
f = 18.54 to 53.4
FNO = 3.6 to 5.68
2ω = 29.86 to 78.18 °

[Lens data]
Surface r d nd νd
1 65.3290 1.0000 1.589130 61.18
2 19.6848 0.1000 1.553890 38.09
* 3 17.4453 8.8628
4 -74.5250 1.0000 1.516330 64.14
5 29.1392 4.0560
6 41.8460 2.7483 1.805180 25.43
7 140.0310 D7

8 42.0101 2.7332 1.487490 70.24
9 -42.2685 4.7621
10 24.2832 3.5000 1.516330 64.14
11 -46.8420 1.0000 1.846660 23.78
12 462.4247 D12

13 0.0000 1.8772 Aperture stop S
14 -40.1900 2.0000 1.846660 23.78
15 -21.1336 1.0000 1.772500 49.61
16 70.4504 D16

17 -40.0000 0.9463 1.585180 30.24 Aspheric plastic lens
* 18 -35.1163 0.1000
19 76.8171 4.0986 1.589130 61.18
20 -18.7592 0.1000
21 -54.0847 1.0000 1.846660 23.78
22 0.0000 D22

23 0.0000 BF Flare cut aperture FS

[Aspherical data]
<Third lens surface>
κ = -1.00000
C4 = 1.05417E-05
C6 = 1.23041E-08
C8 = -9.58113E-12
C10 = 3.55941E-14
C12 = 0.0000

<18th lens surface>
κ = 0.00000
C4 = 3.75962E-05
C6 = 1.51983E-07
C8 = -4.00722E-10
C10 = 3.69316E-13
C12 = 0.0000

[Variable interval data]
Wide angle end state Intermediate focal length state Telephoto end state f 18.500 35.000 53.400
D7 34.105 9.173 1.100
D12 1.040 6.236 11.080
D16 12.211 7.009 2.173
D22 0.000 13.775 28.000
BF 38.500 38.500 38.500

[Conditional expression values]
Conditional expression (1) νd1 = 61.18 (L1), 64.14 (L2)
Conditional expression (2) nd1 = 1.589130 (L1), 1.516330 (L2)
Conditional expression (3) f4 / fw = 2.12
Conditional expression (4) νd2 = 70.24 (L4), 64.14 (L5)
Conditional expression (5) nd2 = 1.487490 (L4), 1.516330 (L5)
Conditional expression (6) νd4 = 61.18 (L10)
Conditional expression (7) nd4 = 1.589130 (L10)
Conditional expression (8) | f4 / fP | = 0.09
Conditional expression (9) (−f1) /fw=1.53
Conditional expression (10) f2 / fw = 1.56
Conditional expression (11) (−f3) /fw=1.87
Conditional expression (12) Rasp / (− f1) = 0.62

FIGS. 8A, 8B, and 8C are graphs showing various aberrations in the wide-angle end state, the intermediate focal length state, and the telephoto end state, respectively, of the zoom lens according to Example 4 of the present invention.
From the various aberration diagrams, the zoom lens according to the present embodiment corrects various aberrations well in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state, and has excellent imaging performance. I understand that.

(5th Example)
FIG. 9 is a diagram showing a configuration of a zoom lens according to Example 5 of the present invention and a movement locus of each lens group.
The zoom lens according to the present embodiment has, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, an aperture stop S, and a negative refractive power. The third lens group G3 includes a fourth lens group G4 having a positive refractive power, and a flare cut stop FS. Then, upon zooming from the wide-angle end state (W) to the telephoto end state (T), the distance between the first lens group G1 and the second lens group G2 decreases, and the second lens group G2 and the third lens group G3. The lens groups G1, G2, G3, and G4 move along the optical axis so that the distance between the third lens group G3 and the fourth lens group G4 decreases.

The first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconcave negative lens L2, and a positive meniscus lens L3 having a convex surface facing the object side.
The second lens group G2 includes, in order from the object side, a biconvex positive lens L4, and a cemented lens of a biconvex positive lens L5 and a biconcave negative lens L6.

The third lens group G3 includes, in order from the object side, a cemented lens of a positive meniscus lens L7 having a convex surface directed toward the image side and a biconcave negative lens L8.
The fourth lens group G4 includes, in order from the object side, a positive meniscus lens L9 having a convex surface facing the image side, which is an aspheric plastic lens, a biconvex positive lens L10, and a plano-concave lens L11.

The aperture stop S is disposed in the vicinity of the third lens group G3 on the object side, and moves integrally with the third lens group G3 upon zooming from the wide-angle end state to the telephoto end state.
In addition, the flare cut stop FS is disposed on the image side of the fourth lens group G4, so that coma flare with an intermediate image height can be effectively removed.
Table 5 below provides values of specifications of the zoom lens according to the fifth example of the present invention.

(Table 5)
[Overall specifications]
f = 18.54 to 53.4
FNO = 3.6 to 5.42
2ω = 29.86 to 78.18 °

[Lens data]
Surface r d nd νd
1 61.2844 1.0000 1.672700 32.10
2 20.5207 0.1000 1.553890 38.09
* 3 17.9384 9.0668
4 -53.4082 1.0000 1.516330 64.15
5 29.2891 3.2796
6 40.2136 3.2760 1.846660 23.78
7 260.6866 D7

8 36.9155 3.1184 1.581439 40.75
9 -41.8216 0.1027
10 30.8834 4.0000 1.516330 64.14
11 -27.5191 1.0000 1.805180 25.43
12 293.1614 D12

13 0.0000 1.8112 Aperture stop S
14 -49.1649 2.0000 1.805180 25.43
15 -22.3120 1.0000 1.772500 49.61
16 69.0171 D16

17 -162.8962 2.1812 1.525380 56.31 Aspheric plastic lens
* 18 -26.8044 0.1000
19 323.0430 3.8457 1.516330 64.14
20 -18.2256 0.1000
21 -33.3681 1.0000 1.805180 25.43
22 -555.4187 D22

23 0.0000 BF Flare cut aperture FS

[Aspherical data]
<Third lens surface>
κ = -1.00000
C4 = 6.92835E-06
C6 = 1.00707E-08
C8 = -3.25392E-11
C10 = 1.47666E-14
C12 = 0.0000

<18th lens surface>
κ = 0.00000
C4 = 3.71384E-05
C6 = 1.05201E-07
C8 = 4.31819E-11
C10 = 0.0000
C12 = 0.0000

[Variable interval data]
Wide angle end state Intermediate focal length state Telephoto end state f 18.500 35.000 53.400
D7 37.703 11.760 2.971
D12 1.071 7.105 12.123
D16 12.934 6.912 1.874
D22 0.000 11.741 25.093
BF 38.500 38.500 38.500

[Conditional expression values]
Conditional expression (1) νd1 = 32.10 (L1), 64.15 (L2)
Conditional expression (2) nd1 = 1.672700 (L1), 1.516330 (L2)
Conditional expression (3) f4 / fw = 2.29
Conditional expression (4) νd2 = 40.75 (L4), 64.14 (L5)
Conditional expression (5) nd2 = 1.581439 (L4), 1.516330 (L5)
Conditional expression (6) νd4 = 64.14 (L10)
Conditional expression (7) nd4 = 1.516330 (L10)
Conditional expression (8) | f4 / fP | = 0.70
Conditional expression (9) (−f1) /fw=1.60
Conditional expression (10) f2 / fw = 1.58
Conditional expression (11) (−f3) /fw=2.04
Conditional expression (12) Rasp / (− f1) = 0.61

FIGS. 10A, 10B, and 10C show various aberration diagrams of the zoom lens according to Example 5 of the present invention in the wide-angle end state, the intermediate focal length state, and the telephoto end state, respectively.
From the various aberration diagrams, the zoom lens according to the present embodiment corrects various aberrations well in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state, and has excellent imaging performance. I understand that.

According to each of the embodiments described above, it is possible to realize a zoom lens with high image quality that is particularly suitable for a single-lens reflex digital camera.
The numerical example of the zoom lens according to the present invention is a four-group configuration. However, the group configuration of the zoom lens according to the present invention is not limited to this, and the zoom lens according to another group configuration such as the third group, the fifth group, etc. Can also be configured.

  In the zoom lens of the present invention, in order to focus from an object at infinity to an object at a short distance, a part of the lens group, one lens group, or a plurality of lens groups is used as the focusing lens group in the optical axis direction. It is good also as a structure moved to. This focusing lens group can be applied to autofocus, and is also suitable for driving an autofocus motor, such as an ultrasonic motor. In the zoom lens according to the present invention, it is particularly preferable that the first lens group is a focusing lens group.

In the zoom lens of the present invention, in order to correct image blur caused by camera shake, a part of the lens group or one lens group is moved as a vibration-proof lens group in a direction perpendicular to the optical axis. Also good. In the zoom lens according to the present invention, it is particularly preferable that the third lens group is an anti-vibration lens group.
The lens surface of the lens constituting the zoom lens of the present invention may be an aspherical surface. This aspherical surface may be any of an aspherical surface by grinding, a glass mold aspherical surface obtained by molding glass into an aspherical shape, or a composite aspherical surface in which a resin provided on the glass surface is formed into an aspherical shape.

Further, an antireflection film having a high transmittance in a wide wavelength range may be applied to the lens surface of the lens constituting the zoom lens of the present invention. Thereby, flare and ghost can be reduced, and high optical performance can be achieved with high contrast.
In addition, each said Example has shown one specific example of this invention, and this invention is not limited to these.

Next, a camera equipped with the zoom lens of the present invention will be described with reference to FIG.
FIG. 11 is a diagram illustrating a configuration of a camera including the zoom lens according to the present invention.
The camera 1 is a digital single-lens reflex camera provided with the zoom lens according to the first embodiment as a photographing lens 2 as shown in FIG.

  In the camera 1, light from an object (subject) (not shown) is collected by the taking lens 2 and imaged on the focusing screen 4 through the quick return mirror 3. The light imaged on the focusing screen 4 is reflected in the pentaprism 5 a plurality of times and guided to the eyepiece lens 6. Thus, the photographer can observe the subject image as an erect image through the eyepiece 6.

  When the release button (not shown) is pressed by the photographer, the quick return mirror 3 is retracted out of the optical path, and light from the subject (not shown) reaches the image sensor 7. Thereby, the light from the subject is picked up by the image pickup device 7 and recorded as a subject image in a memory (not shown). In this way, the photographer can shoot the subject with the camera 1.

Here, as described in the first embodiment, the zoom lens according to the first embodiment mounted on the camera 1 as the photographing lens 2 achieves high image quality by its characteristic lens configuration and zooming method. Has been. As a result, the camera 1 can achieve high image quality.
Note that the present invention is not limited to the above, and the above camera may be configured even if a camera equipped with the zoom lens according to the second embodiment, the third embodiment, the fourth embodiment, or the fifth embodiment as the photographing lens 2 is configured. Of course, the same effect as 1 can be achieved.

  As described above, it is possible to realize a zoom lens, an imaging device, and a zooming method that achieve high image quality particularly suitable for a single-lens reflex digital camera.

It is a figure which shows the structure of the zoom lens which concerns on 1st Example of this invention, and the movement locus | trajectory of each lens group. (A), (b), and (c) show various aberration diagrams in the wide-angle end state, intermediate focal length state, and telephoto end state of the zoom lens according to Example 1 of the present invention, respectively. It is a figure which shows the structure of the zoom lens which concerns on 2nd Example of this invention, and the movement locus | trajectory of each lens group. (A), (b), and (c) show various aberration diagrams of the zoom lens according to Example 2 of the present invention in the wide-angle end state, the intermediate focal length state, and the telephoto end state, respectively. It is a figure which shows the structure of the zoom lens which concerns on 3rd Example of this invention, and the movement locus | trajectory of each lens group. (A), (b), and (c) show various aberration diagrams in the wide-angle end state, intermediate focal length state, and telephoto end state of the zoom lens according to Example 3 of the present invention, respectively. It is a figure which shows the structure of the zoom lens which concerns on 4th Example of this invention, and the movement locus | trajectory of each lens group. (A), (b), and (c) show various aberration diagrams in the wide-angle end state, intermediate focal length state, and telephoto end state of the zoom lens according to Example 4 of the present invention, respectively. It is a figure which shows the structure of the zoom lens which concerns on 5th Example of this invention, and the movement locus | trajectory of each lens group. (A), (b), and (c) show various aberration diagrams in the wide-angle end state, intermediate focal length state, and telephoto end state of the zoom lens according to Example 5 of the present invention, respectively. It is a figure which shows the structure of the camera provided with the zoom lens of this invention.

Explanation of symbols

G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group S Aperture stop FS Flare cut stop I Image plane W Wide-angle end state M Intermediate focal length state T Telephoto end state

Claims (25)

In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The first lens group has a negative lens;
The fourth lens group includes at least one positive lens and one negative lens,
The zoom lens according to claim 1, wherein the negative lens in the first lens group satisfies the following conditional expression.
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: refractive index νd1: d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group with respect to d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group Abbe number for In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The first lens group has a negative lens;
The third lens group includes one positive lens and one negative lens,
The zoom lens according to claim 1, wherein the negative lens in the first lens group satisfies the following conditional expression.
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: refractive index νd1: d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group with respect to d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group Abbe number for In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The first lens group has a negative lens;
The negative lens in the first lens group satisfies the following conditional expression:
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: refractive index νd1: d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group with respect to d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group The second lens group has a positive lens,
The zoom lens according to claim 2, wherein the positive lens in the second lens group satisfies the following conditional expression.
30 ≦ νd2 ≦ 71
When 30 ≦ νd2 <36
-0.013 × νd2 + 2.083 ≦ nd2 ≦ 1.7
When 36 ≦ νd2 <41
-0.013 × νd2 + 2.083 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 41 ≦ νd2 <51
-0.004 × νd2 + 1.714 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 51 ≦ νd2 <61
-0.0015 × νd2 + 1.5865 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 61 ≦ νd2 ≦ 71
-0.0015 × νd2 + 1.5865 ≦ nd2 ≦ −0.009 × νd2 + 2.149
However,
nd2: Refractive index νd2 for the positive lens material d-line (wavelength λ = 587.6 nm) in the second lens group: d-line (wavelength λ = 587.6 nm) for the positive lens material in the second lens group Abbe number for In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The first lens group has a negative lens;
The negative lens in the first lens group satisfies the following conditional expression:
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: refractive index νd1: d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group with respect to d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group The Abbe number for the fourth lens group includes the aspheric plastic lens and a positive lens.
The zoom lens according to claim 4, wherein the positive lens in the fourth lens group satisfies the following conditional expression.
30 ≦ νd4 ≦ 71
When 30 ≦ νd4 <36
-0.013 × νd4 + 2.083 ≦ nd4 ≦ 1.7
When 36 ≦ νd4 <41
-0.013 × νd4 + 2.083 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 41 ≦ νd4 <51
-0.004 × νd4 + 1.714 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 51 ≦ νd4 <61
-0.0015 × νd4 + 1.5865 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 61 ≦ νd4 ≦ 71
-0.0015 × νd4 + 1.5865 ≦ nd4 ≦ −0.009 × νd4 + 2.149
However,
nd4: refractive index νd4 for the positive lens material d-line (wavelength λ = 587.6 nm) in the fourth lens group: d-line (wavelength λ = 587.6 nm) for the positive lens material in the fourth lens group Abbe number for In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The first lens group has a negative lens;
The negative lens in the first lens group satisfies the following conditional expression:
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: refractive index νd1: d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group with respect to d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group A zoom lens characterized by satisfying the following conditional expression:
1.0 ≦ f2 / fw ≦ 2.3
However,
fw: focal length of the zoom lens in the wide-angle end state f2: focal length of the second lens group In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power Depending on the group, it consists essentially of four lens groups,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The fourth lens group includes an aspheric plastic lens,
The aspheric plastic lens in the fourth lens group is disposed closer to the object side than the most image side lens,
The first lens group has a negative lens;
The zoom lens according to claim 1, wherein the negative lens in the first lens group satisfies the following conditional expression.
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: refractive index νd1: d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group with respect to d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group Abbe number for   2. The zoom lens according to claim 1, wherein the third lens group includes one positive lens and one negative lens. The second lens group includes a positive lens,
The zoom lens according to claim 1, wherein the positive lens in the second lens group satisfies the following conditional expression.
30 ≦ νd2 ≦ 71
When 30 ≦ νd2 <36
-0.013 × νd2 + 2.083 ≦ nd2 ≦ 1.7
When 36 ≦ νd2 <41
-0.013 × νd2 + 2.083 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 41 ≦ νd2 <51
-0.004 × νd2 + 1.714 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 51 ≦ νd2 <61
-0.0015 × νd2 + 1.5865 ≦ nd2 ≦ −0.004 × νd2 + 1.844
When 61 ≦ νd2 ≦ 71
-0.0015 × νd2 + 1.5865 ≦ nd2 ≦ −0.009 × νd2 + 2.149
However,
nd2: Refractive index νd2 for the positive lens material d-line (wavelength λ = 587.6 nm) in the second lens group: d-line (wavelength λ = 587.6 nm) for the positive lens material in the second lens group Abbe number for The fourth lens group includes the aspheric plastic lens and a positive lens.
4. The zoom lens according to claim 1, wherein the positive lens in the fourth lens group satisfies the following conditional expression. 5.
30 ≦ νd4 ≦ 71
When 30 ≦ νd4 <36
-0.013 × νd4 + 2.083 ≦ nd4 ≦ 1.7
When 36 ≦ νd4 <41
-0.013 × νd4 + 2.083 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 41 ≦ νd4 <51
-0.004 × νd4 + 1.714 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 51 ≦ νd4 <61
-0.0015 × νd4 + 1.5865 ≦ nd4 ≦ −0.004 × νd4 + 1.844
When 61 ≦ νd4 ≦ 71
-0.0015 × νd4 + 1.5865 ≦ nd4 ≦ −0.009 × νd4 + 2.149
However,
nd4: refractive index νd4 for the positive lens material d-line (wavelength λ = 587.6 nm) in the fourth lens group: d-line (wavelength λ = 587.6 nm) for the positive lens material in the fourth lens group Abbe number for The zoom lens according to any one of claims 1 to 4, wherein the following conditional expression is satisfied.
1.0 ≦ f2 / fw ≦ 2.3
However,
fw: focal length of the zoom lens in the wide-angle end state f2: focal length of the second lens group   6. The zoom lens according to claim 1, wherein the aspheric plastic lens in the fourth lens group is disposed closer to the object side than the lens closest to the image side. The first lens group includes, in order from the object side, a negative meniscus lens having a convex object side lens surface, a negative lens having a concave image side lens surface, and a positive lens having a convex object side lens surface.
The zoom lens according to any one of claims 1 to 11, wherein the following conditional expression is satisfied.
0.7 ≦ (−f1) /fw≦1.7
However,
f1: Focal length fw of the first lens group fw: Focal length of the zoom lens in the wide-angle end state   The zoom lens according to any one of claims 1 to 12, wherein the first lens group includes at least one aspherical surface. Image-side lens surface of said negative meniscus lens in the first lens group is an aspherical surface,
The zoom lens according to claim 12, wherein the following conditional expression is satisfied.
0.32 ≦ Rasp / (− f1) ≦ 1.0
However,
Rasp: Paraxial radius of curvature of the aspheric surface f1: Focal length of the first lens group   The zoom lens according to any one of claims 1 to 14, wherein each lens group includes two or more lenses. The zoom lens according to any one of claims 1 to 15, wherein the following conditional expression is satisfied.
1.5 ≦ f4 / fw ≦ 2.9
However,
f4: focal length of the fourth lens group fw: focal length of the zoom lens in the wide-angle end state The zoom lens according to any one of claims 1 to 15, wherein the following conditional expression is satisfied.
1.5 ≦ f4 / fw ≦ 2.4
However,
f4: focal length of the fourth lens group fw: focal length of the zoom lens in the wide-angle end state The zoom lens according to any one of claims 1 to 17, wherein the aspheric plastic lens in the fourth lens group satisfies the following conditional expression.
| f4 / fP | ≦ 0.9
However,
f4: focal length of the fourth lens group fP: focal length of the aspheric plastic lens in the fourth lens group The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
0.8 ≦ (−f3) /fw≦3.0
However,
fw: focal length of the zoom lens in the wide-angle end state f3: focal length of the third lens group   The zoom lens according to any one of claims 1 to 19, wherein the second lens group includes two positive lenses and one negative lens.   21. The zoom lens according to claim 20, wherein in the second lens group, one of the two positive lenses and the one negative lens are cemented. An aperture stop in the vicinity of the third lens group;
The zoom lens according to any one of claims 1 to 21, wherein the aperture stop moves integrally with the third lens group.   23. The method according to claim 1, wherein the second lens group and the fourth lens group move integrally when zooming from the telephoto end state to the wide-angle end state. The described zoom lens.   An imaging apparatus comprising the zoom lens according to any one of claims 1 to 23. In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power A zoom lens zooming method comprising substantially four lens groups, wherein the fourth lens group comprises an aspheric plastic lens,
Upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The lens groups move along the optical axis so that the distance between the third lens group and the fourth lens group decreases,
The first lens group has a negative lens;
The fourth lens group includes at least one positive lens and one negative lens,
The zoom lens zooming method, wherein the negative lens in the first lens group satisfies the following conditional expression:
30 ≦ νd1 ≦ 71
When 30 ≦ νd1 <36
-0.013 × νd1 + 2.083 ≦ nd1 ≦ 1.7
When 36 ≦ νd1 <41
-0.013 × νd1 + 2.083 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 41 ≦ νd1 <51
-0.004 × νd1 + 1.714 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 51 ≦ νd1 <61
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.004 × νd1 + 1.844
When 61 ≦ νd1 ≦ 71
-0.0015 × νd1 + 1.5865 ≦ nd1 ≦ −0.009 × νd1 + 2.149
However,
nd1: refractive index νd1: d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group with respect to d-line (wavelength λ = 587.6 nm) of the negative lens material in the first lens group Abbe number for

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