JP2015049285A - Zoom lens, imaging device, and video camera for monitoring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens that has a variable power ratio of more than 25 times and a fewer pieces of components, the zoom lens being small in size and lightweight and being favorably corrected in the color aberration to a near infrared region, and having resolving power responding to an imaging element having 2-million pixels or more.SOLUTION: The zoom lens has a four-group configuration with a sequence of positive, negative, negative and positive powers, in which upon varying magnifications, the lens groups are moved in such a manner that the second lens group G2 is positioned closest to an object at a wide angle end and that the third lens group G3 is positioned closed to an image at a telephoto end. At least either of the second lens group G2 and the third lens group G3 includes a negative lens; and the negative lens satisfies [1]:1.50<nd<1.75 and [2]:60.0<νd<75.0, and [3]:θ-0.0015×νd<0.2550, where nd is a refractive index of the material constituting the negative lens, νd is an Abbe number of the material constituting the negative lens, and θis a partial dispersion ratio of the material constituting the negative lens.

Description

  The present invention relates to a lens having a zooming function for changing a focal angle and changing an angle of view, and mainly a video camera or a TV (television) camera that obtains image data of a subject using a solid-state imaging device, so-called. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens used as an imaging optical system in a digital camera or the like, particularly a zoom lens suitable for a video camera for monitoring purposes, an imaging apparatus using such a zoom lens as an imaging optical system, and a monitoring video camera .

Video cameras and TV cameras have a wide variety of requests from their users. In particular, high image quality and miniaturization / lightening are always desired by users, and occupy a great demand from users. For this reason, zoom lenses used as the imaging optical system of these cameras are also required to achieve both high performance and downsizing / weight reduction.
In particular, in a video camera for surveillance, that is, a surveillance camera, imaging that requires sensitivity up to a near infrared region with a wavelength of about 900 nm or less may be performed. For example, during the daytime when there is enough light, the near-infrared light is cut off and an accurate color image is acquired using only visible light, and the amount of light tends to decrease. An operation is performed in which all the light up to the outside region is transmitted to increase the amount of light, and at night, visible light is cut and infrared rays having a wavelength of about 850 nm are projected and illuminated.
For this reason, a photographing lens, that is, a zoom lens used as an imaging optical system is required to correct chromatic aberration not only in the visible region but also in the near infrared region. If chromatic aberration correction to the near infrared region is not performed in this way, it may be necessary to refocus when switching between visible light and near infrared light, or light from the visible region to the near infrared region may be changed. This is because sufficient resolution cannot be obtained when all the light is transmitted.

Furthermore, it is desired that the zoom ratio is as large as possible. For relatively long-distance surveillance applications, a relatively small zoom lens having a zoom ratio of more than 25 times and close to 30 times is supported by the market as one option.
There are several types of zoom lenses suitable for such video cameras for surveillance applications, but in order to be suitable for high zooming, a positive focal length is sequentially increased from the object side to the image side. That is, a first lens group having a positive refractive power, a second lens group having a negative focal length, that is, a negative refractive power, a third lens group having a negative focal length, that is, a negative refractive power, and a positive And a fourth lens group having a positive refractive power. During zooming, the second lens group and the third lens group are associated with zooming so that the second lens group is positioned closest to the object side at the wide-angle end and the third lens group is positioned closest to the image side at the telephoto end. There is a zoom lens that moves.
In order to satisfactorily correct chromatic aberration in this type of zoom lens, the first lens group in which the axial marginal ray height is increased on the telephoto side and the fourth lens group in which the axial marginal ray height is increased on the wide angle side. In general, special low dispersion glass such as OHARA S-FPL51 and OHARA S-FPL53 (both are glass materials of optical glass manufactured by OHARA INC.) Is generally used. There has also been proposed a technique in which a diffractive optical element is provided in the first lens group and chromatic aberration is corrected using negative dispersion of the diffractive optical element.

The zoom lens of the type described above is disclosed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2008-197534), Patent Document 2 (Japanese Patent Laid-Open No. 2008-241848), Patent Document 3 (Japanese Patent Laid-Open No. 10-54937), and the like. Yes.
Patent Document 1 discloses a zoom lens of the type described above that includes a diffractive optical element in the first lens group.
Patent Document 2 discloses a similar type of zoom lens that does not include a diffractive optical element but corrects chromatic aberration up to the near infrared region.
And what is shown in patent document 3 (Unexamined-Japanese-Patent No. 10-54937) is also a zoom lens of the same type, does not include a diffractive optical element, and does not perform chromatic aberration correction to the near infrared region.

As described above, Patent Document 1, Patent Document 2, and Patent Document 3 sequentially describe a first lens group having a positive refractive power and a second lens having a negative refractive power in order from the object side to the image side. A lens group, a third lens group having negative refracting power, and a fourth lens group having positive refracting power are arranged, and at the time of zooming, the second lens group is positioned closest to the object side at the wide-angle end. A zoom lens is disclosed in which the third lens group is positioned closest to the image side at the telephoto end, and the second lens group and the third lens group are moved with zooming.
However, in the zoom lens of Patent Document 1, chromatic aberration is corrected using a diffractive optical element in the first lens group, but only the visible range is considered, and aberrations up to the near infrared range are considered. Is not considered at all.
Further, in the zoom lens of Patent Document 2, it is shown that aberration correction to the near infrared region is performed using special low dispersion glass for the first lens group and the fourth lens group. In addition, the number of the first lens group having a large lens diameter is particularly large, and the reduction in size and weight is not taken into consideration.
The present invention has been made in view of the circumstances described above, and sequentially from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, In a zoom lens in which a third lens group having a negative refractive power and a fourth lens group having a positive refractive power are arranged, and the second lens group and the third lens group are moved in accordance with zooming, 25 A zoom that has a zoom ratio that is more than double, has a small number of components, is compact and lightweight, has excellent chromatic aberration correction from the visible range to the near-infrared range, and has a resolution corresponding to an image sensor with 2 million pixels or more. It aims to provide a lens.

In order to achieve the above-described object, the zoom lens according to the present invention provides
From the object side to the image side, a first lens group including a diffractive optical element and having a positive refractive power and a second lens group having a negative refractive power are sequentially formed.
With zooming between the wide-angle end and the telephoto end, the second lens group is located closest to the object side at the wide-angle end, and the third lens group is located closest to the image side at the telephoto end. In the zoom lens that moves the second lens group and the third lens group,
At least one of the second lens group and the third lens group includes a negative lens,
The refractive index of the material constituting the negative lens is nd, the Abbe number of the material constituting the negative lens is νd, the partial dispersion ratio of the material constituting the negative lens is θ _{C, A ′} , and the partial dispersion The ratio θ _{C, A ′} is
Refractive indexes for the F-line, C-line, and A′-line of the material constituting the negative lens are n _F , n _C, and n _{A ′} , respectively.
θ _{C, A ′} = (n _C −n _{A ′} ) / (n _F −n _C )
When represented by
The following conditional expressions [1], [2], [3]:
[1] 1.50 <nd <1.75
[2] 60.0 <νd <75.0
[3] θ _C, A′−0.0015 × νd <0.2550
It is characterized by satisfying.

That is, according to the zoom lens according to the present invention,
A first lens group including a diffractive optical element and having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a negative refractive power in order from the object side to the image side And a fourth lens group having a positive refractive power,
With zooming between the wide-angle end and the telephoto end, the second lens group is located closest to the object side at the wide-angle end, and the third lens group is located closest to the image side at the telephoto end. In the zoom lens that moves the second lens group and the third lens group,
At least one of the second lens group and the third lens group includes a negative lens,
The refractive index of the material constituting the negative lens is nd, the Abbe number of the material constituting the negative lens is νd, the partial dispersion ratio of the material constituting the negative lens is θ _{C, A ′} , and the partial dispersion The ratio θ _{C, A ′} is
Refractive indexes for the F-line, C-line, and A′-line of the material constituting the negative lens are n _F , n _C, and n _{A ′} , respectively.
θ _{C, A ′} = (n _C −n _{A ′} ) / (n _F −n _C )
When represented by
The following conditional expressions [1], [2], [3]:
[1] 1.50 <nd <1.75
[2] 60.0 <νd <75.0
[3] θ _C, A′−0.0015 × νd <0.2550
By satisfying
Resolving power with a zoom ratio exceeding 25 times, small number of components, small size and light weight, with good correction of chromatic aberration from visible to near infrared, and at least 2 million pixels It can be set as the structure which has these.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the structure of the optical system of the zoom lens which concerns on Example 1 which is a 1st embodiment of this invention, and the zoom locus | trajectory accompanying zooming, (a) is a wide-angle end (short focus end), (B) is an intermediate focal length, and (c) is a cross-sectional view along the optical axis at each telephoto end (long focal end). FIG. 3 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the wide angle end (short focal end) of the zoom lens according to Example 1 of the present invention shown in FIG. 1. FIG. 3 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the intermediate focal length of the zoom lens according to Example 1 of the present invention shown in FIG. 1. FIG. 3 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the telephoto end (long focal end) of the zoom lens according to Embodiment 1 of the present invention shown in FIG. 1. It is a figure which shows typically the structure of the optical system of the zoom lens in Example 2 which concerns on the 2nd Embodiment of this invention, and the zoom locus | trajectory accompanying zooming, (a) is a wide angle end, (b) is an intermediate focus. The distance and (c) are cross-sectional views along the optical axis at each of the telephoto ends. FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the wide angle end of the zoom lens according to Embodiment 2 of the present invention shown in FIG. 5. FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the intermediate focal length of the zoom lens according to Example 2 of the present invention shown in FIG. 5. FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration and coma aberration at the telephoto end of the zoom lens according to Embodiment 2 of the present invention shown in FIG. 5. It is a figure which shows typically the structure of the optical system of the zoom lens in Example 3 which concerns on the 3rd Embodiment of this invention, and the zoom locus | trajectory accompanying zooming, (a) is a wide angle end, (b) is an intermediate focus. The distance and (c) are cross-sectional views along the optical axis at each of the telephoto ends. FIG. 10 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the wide-angle end of the zoom lens according to Example 3 illustrated in FIG. 9. FIG. 10 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the intermediate focal length of the zoom lens according to Example 3 illustrated in FIG. 9. FIG. 10 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the telephoto end of the zoom lens according to Embodiment 3 of the present invention shown in FIG. 9. FIG. 10 is a diagram schematically showing a configuration of an optical system of a zoom lens and a zoom locus accompanying zooming in Example 4 according to the fourth embodiment of the present invention, where (a) is a short focal end, and (b) is an intermediate. Focal length and (c) are cross-sectional views along the optical axis at each of the long focal ends. FIG. 14 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the wide-angle end of the zoom lens according to Example 4 illustrated in FIG. 13. FIG. 14 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the intermediate focal length of the zoom lens according to Example 4 illustrated in FIG. 13. FIG. 14 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the telephoto end of the zoom lens according to Example 4 shown in FIG. 13. It is a block diagram which shows typically the function structure of the digital camera as an imaging device which concerns on the 5th Embodiment of this invention.

Hereinafter, based on an embodiment of the present invention, a zoom lens according to the present invention will be described in detail with reference to the drawings. Before describing specific examples, features of the zoom lens according to the present invention will be described first.
The zoom lens according to the present invention includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens having a negative refractive power in order from the object side to the image side. And a fourth lens group having a positive refractive power. In zooming, the second lens group is positioned closest to the object side at the wide-angle end, and the third lens group is positioned closest to the image side at the telephoto end. The zoom lens moves the second lens group and the third lens group in accordance with zooming, and has the following features.
That is, the zoom lens according to the present invention includes a diffractive optical element in the first lens group and a negative lens in at least one of the second lens group and the third lens group, and the negative lens constitutes the negative lens. When the refractive index of the material to be made is nd, the Abbe number of the material constituting the negative lens is νd, and the partial dispersion ratio of the material constituting the negative lens is θ _{C, A ′} , the following conditional expression [1] Conditional expression [3] is satisfied (corresponding to claim 1).

[1] 1.50 <nd <1.75
[2] 60.0 <νd <75.0
[3] θ _C, A′−0.0015 × νd <0.2550
Here, the partial dispersion ratio θ _{C, A ′} is
θ _{C, A ′} = (n _C −n _{A ′} ) / (n _F −n _C )
N _F , n _C and n _{A ′} are the refractive indices of the material constituting the negative lens with respect to the F line, C line and A ′ line, respectively.
The zoom lens according to the present invention further satisfies the following conditional expression [4], where f _{T is} the focal length of the entire system at the telephoto end, and f _DOE is the focal length of the diffractive portion of the diffractive optical element. It is desirable (corresponding to claim 2).
[4] 0.01 <f _T / f _DOE <0.05
Furthermore, in the zoom lens according to the present invention, when the first lens group includes one or more positive lenses and the average value of the Abbe numbers of the materials of the positive lenses included in the first lens group is ν _1GP , It is desirable that the conditional expression [5] is satisfied (corresponding to claim 3).

[5] 75 <ν _1GP <96
The zoom lens according to the present invention further includes a negative lens in both the second lens group and the third lens group, and the negative lens satisfies the conditional expressions [1] to [3] described above. It is desirable (corresponding to claim 4).
In the zoom lens according to the present invention, the distance between the third lens group and the fourth lens group at the wide-angle end is D _34W , the distance between the third lens group and the fourth lens group at the telephoto end is D _34T , and the wide-angle when the focal length of the entire system at the end and f _w, (corresponding to claim 5) is preferable to satisfy the following condition [6].
[6] _{2.5 <(D 34W -D 34T)} / f w <6.0
It is desirable that the zoom lens according to the present invention further includes a state in which the magnification of the third lens group becomes zero during zooming from the wide-angle end to the telephoto end (corresponding to claim 6). To do).
In the zoom lens according to the present invention, the distance along the optical axis from the most object side surface of the fourth lens group to the most image side surface is L ₄ , and the most object side of the fourth lens group is The distance along the optical axis from the surface to the image surface, that is, when an optical element having no refracting power is included on the image side from the fourth lens group, the air equivalent length assumed to be absent is T _{4F When −I} , it is desirable that the following conditional expression [7] is satisfied (corresponding to claim 7).

[7] 0.2 <L ₄ / T _4F-I <0.5
In the zoom lens according to the present invention, it is desirable that the second lens group is composed of three or less lenses and the third lens group is composed of two or less lenses (corresponding to claim 8).
Further, in the zoom lens according to the present invention, the first lens group includes a negative meniscus lens having a concave surface facing the image side sequentially from the object side, a first positive lens cemented to the negative meniscus lens, and an image. Three lenses, the second positive lens with the convex surface having a refractive power stronger than the lens side facing the object side, are arranged, and a diffractive surface is formed at the junction interface between the negative meniscus lens and the first positive lens. Is desirable (corresponding to claim 9).
In the zoom lens according to the present invention, it is desirable that the first lens group and the fourth lens group are fixed without moving with respect to the image plane during zooming (corresponding to claim 10).
The imaging apparatus according to the present invention includes any one of the zoom lenses described above as an imaging optical system (corresponding to claim 11).
A surveillance video camera according to the present invention includes any one of the zoom lenses described above as an imaging optical element (corresponding to claim 12).

Next, the principle of the zoom lens according to the present invention having the above-described features will be described in more detail.
A zoom lens including four lens groups of positive-negative-negative-positive, such as the zoom lens according to the present invention, is generally configured as a so-called variator in which the second lens group bears a main zooming action. In addition, the third lens group can share the zooming action, which is suitable for high zooming. Therefore, in the zoom lens according to the present invention, the second lens group and the second lens group are positioned closest to the object side at the wide-angle end and the third lens group is positioned closest to the image side at the telephoto end. By moving the three lens groups, the third lens group exhibits a sufficient zooming action, thereby achieving high zooming.
When zooming from the wide-angle end to the telephoto end, the distance between the second lens group and the third lens group is temporarily reduced, takes an extreme value in the intermediate range of zooming, and then increases again. The second lens group and the third lens group function integrally as a variator that bears the zooming action, but compensate for the image plane position by changing the mutual distance, and serve as a so-called compensator. Can also be considered.

Further, in the zoom lens according to the present invention, a diffractive optical element is used for the first lens group, and at least one of the second lens group and the third lens group includes the following conditional expressions [1] to [3]. It was set as the structure provided with the negative lens which consists of material which satisfies (corresponding to claim 1).
[1] 1.50 <nd <1.75
[2] 60.0 <νd <75.0
[3] θ _C, A′−0.0015 × νd <0.2550
Here, nd is the refractive index of the material constituting the negative lens, νd is the Abbe number of the material constituting the negative lens, and θ _{C, A} is the partial dispersion ratio of the material constituting the negative lens. Represents.
The partial dispersion ratio θ _{C, A ′} is
θ _{C, A ′} = (n _C −n _{A ′} ) / (n _F −n _C )
N _F , n _C and n _{A ′} are the refractive indices of the material constituting the negative lens with respect to the F line, C line and A ′ line.
In order to increase the zoom ratio, especially when the focal length at the telephoto end is to be increased, it is difficult to correct the secondary spectrum of axial chromatic aberration on the telephoto side.

Furthermore, when it is attempted to correct chromatic aberration not only in the visible region but also in the near infrared region, the degree of difficulty is further increased. In the present invention, the diffractive optical element is provided in the first lens group in which the axial marginal ray height is increased on the telephoto side to correct the chromatic aberration in the telephoto range. Is not sufficient in order to realize over the entire zoom range.
Therefore, in the zoom lens according to the present invention, at least one of the second lens group and the third lens group has a refractive index, Abbe number, and anomalous dispersion within a range satisfying the conditional expressions [1] to [3]. A negative lens made of a material having the above is provided. By doing so, it is possible to satisfactorily correct chromatic aberration from the visible range to the near-infrared range over the entire zooming range exceeding 25 times.
Since the variator that bears the zooming action needs a relatively large refractive power, if the refractive index nd of the material constituting the negative lens is 1.50 or less, the correction of monochromatic aberration is insufficient. If the Abbe number νd of the material constituting the negative lens is 60.0 or less, the basic correction of chromatic aberration becomes insufficient. Furthermore, regarding the partial dispersion ratio θ _{C, A ′} of the material constituting the negative lens, if θ _C, A′−0.0015 × νd is 0.2550 or more, the correction of the secondary spectrum of chromatic aberration is insufficient. Become. In particular, these influences are large in the intermediate focal length range from the wide-angle end where it is difficult to obtain the effect of correcting the chromatic aberration by the diffractive optical element. On the other hand, regarding the conditional expressions [1] and [2] of the refractive index nd and the Abbe number νd, there seems to be no material that exceeds the upper limit, and even if it exists, it is a very special and expensive material. It is not realistic.

In the zoom lens according to the present invention, it is desirable that the diffractive optical element provided in the first lens group satisfies the following conditional expression [4] (corresponding to claim 2).
[4] 0.61 <f _T / f _DOE <0.05
Here, f _T represents the focal length of the entire system at the telephoto end, and f _DOE represents the focal length of the diffractive portion of the diffractive optical element.
Here, the focal length f _DOE of the diffractive portion of the diffractive optical element is
f _DOE = -1 / (2 × C2)
It is represented by
If the refractive power of the diffractive optical element is so weak that f _T / f _DOE is 0.01 or less, it becomes difficult to sufficiently perform chromatic aberration correction in the telephoto range. On the other hand, when the refractive power of the diffractive optical element is so strong that f _T / f _DOE is 0.05 or more, the chromatic aberration on the telephoto side is excessively corrected, which is also not preferable.
Furthermore, in the zoom lens according to the present invention, it is desirable that the positive lens included in the first lens group satisfies the following conditional expression [5] (corresponding to claim 3).
[5] 75 <ν _1GP <96
Here, ν _1GP represents the average value of the Abbe number of the material of the positive lens included in the first lens group.

If the average value ν _1GP of the Abbe number of the positive lens material is 75 or less, even if a diffractive optical element is provided in the first lens group, correction of chromatic aberration in the telephoto range tends to be insufficient. On the other hand, a material having ν _1GP of 96 or more does not generally exist, or even if it exists, it is very special and expensive and is not practical.
More preferably, the following conditional expression [5 ′] should be satisfied.
[5 ′] 80 <ν _1GP <96
Further, it is desirable that the negative lens made of a material satisfying the conditional expressions [1] to [3] is provided in both the second lens group and the third lens group (corresponding to claim 4).
In the second lens group, on-axis and off-axis rays pass separately in the wide-angle range, and on-axis and off-axis rays pass through almost the same part in the telephoto range. There is no difference as much as the second lens group in the way of on-axis and off-axis light beams in the telephoto range. By providing a negative lens made of a material that satisfies the above-mentioned conditional expressions [1] to [3] in both of these two lens groups, the correction effects are combined, and chromatic aberration over the entire zoom range. It becomes easy to balance the correction.

In order to make the zoom lens according to the present invention more suitable for high zoom ratio, it is desirable to satisfy the following conditional expression [6] (corresponding to claim 5).
[6] _{2.5 <(D 34W -D 34T)} / f w <6.0
Here, D _34W is the distance between the third lens group and the fourth lens group at the wide angle end, D _34T is the distance between the third lens group and the fourth lens group at the telephoto end, and f _w is at the wide angle end. It represents the focal length of the entire system.
Contribution of the condition in [6] to _{(D 34W -D 34T) / f} w is is the third lens group at 2.5 or less magnification is _reduced, the _{(D 34W -D 34T) / f} w 6 If it is greater than or equal to 0.0, the contribution of the second lens group to the zooming becomes small, and in any case, it becomes easy to cause difficulty in correcting aberrations. In addition, this type of zoom lens can be configured such that the open F value in the telephoto range is regulated not by the aperture stop but by the effective diameter of the first lens group. In this case, (D _34W -D _34T ) / it f _w is greater than 2.5, has the effect of reducing the effective diameter of the third lens group, favoring also the aberration correcting this.
In the zoom lens according to the present invention, it is preferable that the zoom lens includes a state in which the magnification of the third lens unit becomes 0 in the process of zooming from the wide-angle end to the telephoto end (corresponding to claim 6).

The state in which the magnification of the third lens group is 0 is a state in which the combined refractive power of the first lens group and the second lens group is 0. With this state as a boundary, the second lens group and the third lens group Is reversed (when the magnification of the third lens group becomes 0, the magnification of the second lens group becomes infinite). By configuring the zoom lens so as to include this state, it is possible to balance the contribution of the second lens group and the third lens group to the zooming and realize better aberration correction.
Furthermore, in the zoom lens according to the present invention, it is desirable that the following conditional expression [7] is satisfied with respect to the arrangement of the fourth lens group that bears the main image forming action (corresponding to claim 7). .
[7] 0.2 <L ₄ / T _4F-I <0.5
Here, L ₄ is a distance along the optical axis from the most object side surface of the fourth lens group to the most image side surface, and T _4F-I is an image from the most object side surface of the fourth lens group. A distance along the optical axis to the surface, and when an optical element having no refracting power is included on the image side from the fourth lens group, an air conversion length assumed to be absent, respectively. Yes.
If L ₄ / T _4F-I in conditional expression [7] is 0.2 or less, the degree of freedom regarding the configuration of the fourth lens group may be hindered, and various aberration corrections may be difficult.

On the other hand, if L ₄ / T _4F-I is 0.5 or more, a sufficient space cannot be secured between the fourth lens group and the image plane, and an infrared light cut filter or a visible light cut filter It is not preferable that a switching mechanism such as the above is hindered, and a ghost is easily generated due to reflection of each surface or filter in the fourth lens group.
It is more desirable to satisfy the following conditional expression [7 ′].
[7 ′] 0.2 <L ₄ / T _4F-I <0.4
Furthermore, in the zoom lens according to the present invention, it is desirable that the second lens group is composed of three or less lenses, and the third lens group is composed of two or less lenses (corresponding to claim 8). .
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 concave surface facing the image side, a first positive lens cemented to the negative meniscus lens, and an object A second positive lens having a convex surface having a refractive power stronger than that of the image side is disposed on the side, and is composed of three lenses. A diffractive surface is formed at the junction interface between the negative meniscus lens and the first positive lens. Preferably it is formed (corresponding to claim 9).
With the configuration as described above, the effects of the present invention are clearly exhibited, and a zoom lens that is smaller and lighter can be obtained.

In order to achieve the effect of the present invention more effectively, more specifically, the second lens group may be configured by three lenses of a negative lens, a positive lens, and a negative lens sequentially from the object side. Desirably, it is desirable that the third lens group has a negative lens-positive lens structure in order from the object side.
In the zoom lens according to the present invention, it is desirable that the first lens unit and the fourth lens unit are fixedly arranged without being moved with respect to the image plane during zooming. ).
As a zoom lens for a video camera including a so-called TV camera or the like, it is generally desired that the overall length is constant and the weight balance does not change upon zooming, in terms of convenience such as hand-held shooting. The configuration in which the first lens group and the fourth lens group are not moved can be realized. In addition, the small number of moving groups is advantageous in terms of mechanism, leading to reduction in the number of parts, weight reduction, and improvement in reliability.
Further, it is desirable that the fourth lens group has at least three positive lenses and satisfies the following conditional expression [8].
[8] 75 <ν _4GP <96
Here, ν _4GP represents an average value of the Abbe number of the at least three positive lenses.

By configuring the fourth lens group in this way, chromatic aberration from the visible range to the near infrared range can be corrected more satisfactorily, particularly in the wide-angle range of the zoom range.
The refractive power of each lens group preferably satisfies the following conditional expressions [9] to [12].
[9] _{6.0 <f 1 / f W <} 12.0
[10] _{-5.0 <f 2 / f W <} -2.0
[11] _{-4.5 <f 3 / f W <} -1.5
[12] _{1.5 <f 4 / f W <} 4.5
Here, f ₁ is the focal length of the first lens group, f ₂ is the focal length of the second lens group, f ₃ is the focal length of the third lens group, and f ₄ is the focal length of the fourth lens group. , F _W represents the focal length of the entire system at the wide angle end.
By keeping the refractive power of each lens unit in the range of conditional expression [9] to conditional expression [12], it has a zoom ratio exceeding 25 times and the half angle of view at the telephoto end is about 0.5 degrees. It becomes more suitable for such a zoom lens.
In the zoom lens according to the present invention, various methods are conceivable as a method for performing the focusing to a finite distance, but the focusing can be performed most simply by moving the first lens group.

Next, more specific embodiments and examples of the zoom lens, the imaging device, and the surveillance video camera according to the present invention will be described. Here, the first embodiment to the fourth embodiment as specific embodiments of the zoom lens according to the present invention will be described with reference to Examples 1 to 4 as specific examples, respectively. To do.
1 to 4 illustrate a zoom lens according to Example 1 as the first embodiment of the present invention. 5 to 8 are diagrams for explaining a zoom lens according to Example 2 as the second embodiment of the present invention. FIGS. 9-12 is for demonstrating the zoom lens based on Example 3 as the 3rd Embodiment of this invention.
FIGS. 13-16 is for demonstrating the zoom lens based on Example 4 as the 4th Embodiment of this invention.
Each of the zoom lenses according to Examples 1 to 4 has a positive refractive power sequentially from the object side to the image side, a first lens group including a diffractive optical element, and a second lens having a negative refractive power. A lens group, a third lens group having negative refractive power, and a fourth lens group having positive refractive power are arranged to constitute a so-called positive-negative-negative-positive four-group zoom lens.
The maximum image heights in Example 1, Example 2, and Example 4 corresponding to the first embodiment, the second embodiment, and the fourth embodiment, respectively, are 4.0 mm. The maximum image height in Example 3 corresponding to the third embodiment is 4.5 mm.

In each example as each embodiment, the parallel plate-like optical element is disposed on the optical path on the image plane side of the fourth lens group G4. This parallel plate-shaped optical element covers various filters such as an optical low-pass filter and an infrared cut filter, and a light-receiving image sensor such as a CMOS (complementary metal oxide semiconductor) image sensor or a CCD (charge coupled device) image sensor. Glass (seal glass) is assumed. Here, it is shown as an equivalent transparent parallel plate and is generically referred to as a filter or the like FG. Further, the parallel plate-like optical element disposed between the third lens group G3 and the fourth lens group G4 assumes an ND (intermediate density to dimming) filter for light amount adjustment. Here, it is shown as an equivalent transparent parallel plate and is collectively referred to as an adjustment filter ND.
In addition, as for the material of the lens, a resin material is used for the diffractive portion of the first lens group in each of Examples 1 to 4 of the first to fourth embodiments. However, all others use optical glass. The glass material of the optical glass used in each of Examples 1 to 4 is indicated by the optical glass type name of the product of OHARA Co., Ltd.
The aberrations of the first to fourth embodiments are sufficiently corrected, and can be applied to an image sensor with a resolution of 2 million pixels or more. By configuring the zoom lens as in the present invention, it is possible to correct chromatic aberration up to the near-infrared region and achieve a very good image performance while achieving a sufficiently small size. It is clear from each example of Example 4.

The meanings of symbols common to the first to fourth embodiments are as follows.
f: Focal length of the entire system F: F value (F number)
ω: Half angle of view r: Radius of curvature d: Spacing between surfaces nd: Refractive index νd: Abbe number θ _{C, A ′} : Partial dispersion ratio _′ = (n _C −n _{A ′} ) / (n _F −n _C )
C ₂ : Second-order coefficient of phase function C ₄ : Fourth-order coefficient of phase function K: Aspherical conical constant A ₄ : Fourth-order coefficient of aspheric expression A ₆ : Sixth-order coefficient of aspheric expression A ₈ : Aspheric surface However, the diffraction plane used here is defined by the following phase function equation [21], where λ is the reference wavelength and h is the height from the optical axis. Note that the imaging beam, 1 use the order diffracted light, the refractive power of the diffractive portion becomes -2 · C _2.

In Example 4 as the fourth embodiment, an aspherical surface is used. The aspherical shape used here is a cone having a paraxial radius of curvature R and a height from the optical axis H. Using the constant K and the aspheric coefficients A _{4 to} A ₈ of the respective orders, where X is the amount of the aspheric surface in the optical axis direction, it is defined by the following aspheric expression [22], and the paraxial radius of curvature R and the conic constant K As well as the aspheric coefficient A ₄ ~
Specifying the shape giving A _8.

Next, specific embodiments and examples based on the present invention described above will be described in detail.
Examples 1 to 4 of the first embodiment of the present invention to be described below are examples of specific configurations based on numerical examples of the zoom lens according to the present invention.
[First Embodiment]
First, the zoom lens according to the specific example 1 as the first embodiment of the present invention described above will be described in detail.

Example 1 is an example (numerical example) of a specific configuration of the zoom lens according to the first embodiment of the present invention.
1 to 4 illustrate a zoom lens according to Example 1 (Numerical Example 1) as the first embodiment of the present invention.
That is, FIG. 1 shows the lens configuration in the optical system of the zoom lens of Example 1 according to the first embodiment of the present invention and the short focal end, that is, the long focal end, that is, the predetermined focal length from the wide angle end. A zoom locus accompanying zooming to the telephoto end is schematically shown. 1A is a short focal end, that is, a cross-sectional view along the optical axis at the wide-angle end, FIG. 1B is a cross-sectional view along the optical axis at a predetermined intermediate focal length, and FIG. 1C is a long focal end. That is, it is a sectional view along the optical axis at the telephoto end.
The zoom lens shown in FIG. 1 has, in order from the object side to the image side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a negative refractive power. A third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power are disposed. An adjusting filter ND and an aperture stop AD are disposed between the third lens group G3 and the fourth lens group G4.

The first lens group G1 is formed by sequentially arranging a first lens L1, a second lens L2, and a third lens L3 from the object side to the image side. The second lens group G2 is formed by sequentially arranging a fourth lens L4, a fifth lens L5, and a sixth lens L6 from the object side to the image side. The third lens group G3 is formed by sequentially arranging a seventh lens L7 and an eighth lens L8 from the object side to the image side. The fourth lens group G4 sequentially includes a ninth lens L9, a tenth lens L10, an eleventh lens L11, a twelfth lens L12, a thirteenth lens L13, and a fourteenth lens L14 from the object side to the image side. It becomes. Further, an adjustment filter ND and an aperture stop AD are sequentially arranged between the third lens group G3 and the fourth lens group G4 from the object side to the image side, and are inserted between the fourth lens group G4 and the image plane. An FG such as a filter is inserted between the two.
The first lens group G1 to the fourth lens group G4 are supported by a common support frame or the like that is appropriate for each group, and operate integrally for each group during an operation such as zooming. It operates integrally with the fourth lens group G4. FIG. 1 also shows the surface numbers of the optical surfaces.
Note that each reference symbol in FIG. 1 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference symbol. Therefore, a reference symbol common to the drawings according to the other embodiments. Even if attached, they are not necessarily a common configuration with other embodiments.

During zooming from the wide-angle end (short focal end) to the telephoto end (long focal end), the first lens group G1 and the fourth lens group G4 are fixedly positioned without moving, and the second lens The group G2 and the third lens group G3 move to increase the distance dA between the first lens group G1 and the second lens group G2, and the distance dB between the second lens group G2 and the third lens group G3 is intermediate. The focal length is once reduced and then increased, and the distance between the third lens group G3 and the fourth lens group G4 is decreased.
A more detailed lens configuration of the zoom lens according to Example 1 shown in FIG. 1 will be described.
The first lens group G1 includes a first lens L1 made of a negative meniscus lens having a concave surface directed to the image side in order from the object side to the image side, a first resin layer P1 made of a thin resin material, and thin. A diffractive optical element including a second resin layer P2 made of a resin material, a second lens L2 made of a positive meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side A third lens L3 is disposed. The two lenses, the first lens L1 and the second lens L2, are closely bonded to each other with the first resin layer P1 and the second resin layer P2 interposed therebetween to form a cemented lens. Yes. Here, a diffractive surface is formed at the boundary surface between the first resin layer P1 and the second resin layer P2, and the first lens L1, the first resin layer P1, and the second resin that are integrally coupled to each other. The layer P2 and the second lens L2 constitute a cemented lens as a diffractive optical element.

The second lens group G2 includes, from the object side to the image side, a fourth lens L4 composed of a biconcave lens with a concave surface having a larger curvature than the object side surface toward the image side, and the object side from the image surface side. A fifth lens L5 composed of a biconvex lens having a convex surface having a large curvature and a sixth lens L6 composed of a biconcave lens having a concave surface having a larger curvature than the object side surface are disposed on the image side. The two lenses of the fifth lens L5 and the sixth lens L6 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
The third lens group G3 includes, from the object side to the image side, a seventh lens L7 including a biconcave lens having a concave surface with a larger curvature than the object side surface, and a convex surface toward the object side. And an eighth lens L8 made of a positive meniscus lens. The two lenses of the seventh lens L7 and the eighth lens L8 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
An adjustment filter ND composed of a light amount adjustment filter such as a parallel plate-like ND (intermediate density) neutral density filter is interposed between the third lens group G3 and the fourth lens group G4, and further has an aperture. The stop AD is interposed between the adjustment filter ND and the fourth lens group G4.

The fourth lens group G4 includes, in order from the object side to the image side, a ninth lens L9 including a biconvex lens having a convex surface with a larger curvature than the object side surface on the image side, and an image side surface on the object side. A tenth lens L10 made of a biconvex lens having a convex surface with a larger curvature, an eleventh lens L11 made of a biconvex lens having a convex surface with a larger curvature than the image side surface on the object side, and an object side surface on the image side A twelfth lens L12 made of a biconcave lens having a concave surface with a larger curvature, a thirteenth lens L13 made of a biconcave lens having a concave surface having a larger curvature than the object side surface on the image side, and an image side lens on the object side. A fourteenth lens L14 made of a biconvex lens having a convex surface having a larger curvature than the surface is disposed.
The two lenses of the eleventh lens L11 and the twelfth lens L12 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses. The two lenses of the thirteenth lens L13 and the fourteenth lens L14 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
FGs such as various parallel plate optical filters and filters such as a cover glass of the light receiving image sensor are arranged on the image plane side of the fourth lens group G4 on the optical path on the image plane side of the fourth lens group G4. Yes.

In this case, as shown in FIG. 1, the first lens group G1 and the fourth lens group G4 do not move with the zooming from the wide-angle end (short focal end) to the telephoto end (long focal end). It is fixedly located. The second lens group G2 moves greatly from the object side to the image side from the wide-angle end to the intermediate focal length, and moves small from the object side to the image side from the intermediate focal length to the telephoto end. The third lens group G3 moves small from the object side to the image side from the wide angle end to the intermediate focal length, and largely moves from the object side to the image side from the intermediate focal length to the telephoto end.
First, in Example 1, the focal length f, F number F, and half angle of view ω of the entire optical system are f = 17.1 to 487, F = 4.01 to 6.96, and ω = 14 by zooming, respectively. .Varies in the range of 1 to 0.470. The optical characteristics of each optical element are as shown in Table 1 below.

In Table 1, the optical surface indicated by adding “# (hash mark; number sign)” to the surface number is a diffractive surface. Table 1 also shows the material of each lens. The same applies to the other embodiments.
That is, in Table 1, the third surface to which “#” is attached is the diffractive surface, and the parameters of the diffractive surface in Equation [21] are as follows.
Here, C ₂ is a coefficient of the second order term of the phase function of the diffraction surface, and C ₄ is a coefficient of the fourth order term of the phase function.
Diffraction surface: Third surface λ = 587.56 (nm)
C ₂ = -1.80594 × 10 ⁻⁵
C ₄ = 1.02994 × 10 ⁻⁹
In the state of Example 1, the focal length f of the entire optical system at the wide-angle end (short focal end), the intermediate focal length and the telephoto end (long focal end), and the first lens group G1 and the second lens group G2 The variable distance dA between them, the variable distance dB between the second lens group G2 and the third lens group G3, and the variable distance dC between the third lens group G3 and the adjustment filter ND are as follows. It changes like 2.

  In the state of Example 1, the focal length f of the entire optical system at the wide-angle end (short focal end), the intermediate focal length and the telephoto end (long focal end), the magnification of the second lens group G2, the third lens The magnification of the group G3 and the magnification of the fourth lens group G4 change as shown in Table 3 along with zooming.

In this case, conditional expression [1] to conditional expression [3], conditional expression [5], conditional expression [6], conditional expression [7], conditional expression [8] and conditional expression [9] to conditional expression [12] The values corresponding to are as follows: Conditional Expression [1] to Conditional Expression [3], Conditional Expression [5], Conditional Expression [6], Conditional Expression [7], Conditional Expression [8] and Conditional Expression, respectively The conditional expressions [9] to [12] are satisfied.
<< Numerical value of conditional expression >>
[1]: nd = 1.61800 (L4)
nd = 1.60300 (L7)
[2]: νd = 63.33 (L4)
νd = 65.44 (L7)
[3]: θ _{C, A ′} −0.0015 × νd − 0.255 = −0.0046 ... OHARA S-PHM52 (L4)
θ _{C, A ′} −0.0015 × νd − 0.255 = −0.0034… OHARA S-PHM53 (L7)
[4]: f _T / f _DOE = 0.0176
[5]: ν _1GP = 82.6
_{[6]: (D 34W -D 34T) /} f W = 4.32
[7]: L ₄ / T _4F-I = 0.284
[8]: ν _4GP = 81.5
[9]: _f 1 _{/ f} W = 8.68
[10]: f ₂ / f _W = −3.30
[11]: f ₃ / f _W = −2.60
[12]: f ₄ / f _W = 2.75

2, 3, and 4 show spherical aberration, astigmatism, distortion, and lateral aberration at the wide-angle end (short focal end), the intermediate focal length, and the telephoto end (long focal end), respectively, in Example 1. Each aberration diagram of the aberration is shown. In these aberration diagrams, the broken line in the spherical aberration diagram represents the sine condition, the solid line in the astigmatism diagram represents sagittal, and the broken line represents meridional. The same applies to the aberration diagrams of the other examples.
[Second Embodiment]
Next, the zoom lens according to Example 2 as the second embodiment of the present invention described above will be described in detail.

Example 2 is an example (numerical example) of a specific configuration of the zoom lens according to the second embodiment of the present invention.
5 to 8 are diagrams for explaining a zoom lens according to Example 2 as the second embodiment of the present invention.
That is, FIG. 5 shows the lens configuration in the optical system of the zoom lens of Example 2 according to the second embodiment of the present invention and the short focal point, that is, the long focal point, that is, the predetermined focal length from the wide angle end. A zoom locus accompanying zooming to the telephoto end is schematically shown. 5A is a cross-sectional view along the optical axis at the short focal end, that is, the wide-angle end, FIG. 5B is a cross-sectional view along the optical axis at a predetermined intermediate focal length, and FIG. It is sectional drawing along the optical axis in an edge.
In FIG. 5 showing the lens group arrangement of Example 2, the left side in the figure is the object (subject) side, and the right side in the figure is the image side (image sensor side).
The zoom lens shown in FIG. 5 has, in order from the object side to the image side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a negative refractive power. A third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power are disposed. Furthermore, an adjustment filter ND and an aperture stop AD are disposed between the third lens group G3 and the fourth lens group G4.

The first lens group G1 is formed by sequentially arranging a first lens L1, a second lens L2, and a third lens L3 from the object side to the image side. The second lens group G2 is formed by sequentially arranging a fourth lens L4, a fifth lens L5, and a sixth lens L6 from the object side to the image side. The third lens group G3 is formed by sequentially arranging a seventh lens L7 and an eighth lens L8 from the object side to the image side. The fourth lens group G4 sequentially includes a ninth lens L9, a tenth lens L10, an eleventh lens L11, a twelfth lens L12, a thirteenth lens L13, and a fourteenth lens L14 from the object side to the image side. It becomes. An FG such as a filter is interposed between the fourth lens group G4 and the image plane.
The first lens group G1 to the fourth lens group G4 are supported by a common support frame or the like that is appropriate for each group, and operate integrally for each group during an operation such as zooming. It operates integrally with the fourth lens group G4. FIG. 5 also shows the surface numbers of the optical surfaces.
During zooming from the wide-angle end (short focal end) to the telephoto end (long focal end), the first lens group G1 and the fourth lens group G4 are fixedly positioned without moving, and the second lens The group G2 and the third lens group G3 move to increase the distance dA between the first lens group G1 and the second lens group G2, and the distance dB between the second lens group G2 and the third lens group G3 is intermediate. The focal length is once reduced and then increased, and the distance between the third lens group G3 and the fourth lens group G4 is decreased.

A more detailed lens configuration of the zoom lens according to Example 2 shown in FIG. 5 will be described.
The first lens group G1 includes a first lens L1 made of a negative meniscus lens having a concave surface directed to the image side in order from the object side to the image side, a first resin layer P1 made of a thin resin material, and thin. A diffractive optical element including a second resin layer P2 made of a resin material, a second lens L2 made of a positive meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side A third lens L3 is disposed. The two lenses, the first lens L1 and the second lens L2, are closely bonded to each other with the first resin layer P1 and the second resin layer P2 interposed therebetween to form a cemented lens. Yes. Here, a diffractive surface is formed at the boundary surface between the first resin layer P1 and the second resin layer P2, and the first lens L1, the first resin layer P1, and the second resin that are integrally coupled to each other. The layer P2 and the second lens L2 constitute a cemented lens as a diffractive optical element.
The second lens group G2 includes, from the object side to the image side, a fourth lens L4 composed of a biconcave lens with a concave surface having a larger curvature than the object side surface toward the image side, and the object side from the image surface side. A fifth lens L5 composed of a biconvex lens having a convex surface having a large curvature and a sixth lens L6 composed of a biconcave lens having a concave surface having a larger curvature than the object side surface are disposed on the image side. The two lenses of the fifth lens L5 and the sixth lens L6 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.

The third lens group G3 includes, from the object side to the image side, a seventh lens L7 including a biconcave lens having a concave surface with a larger curvature than the object side surface, and a convex surface toward the object side. And an eighth lens L8 made of a positive meniscus lens. The two lenses of the seventh lens L7 and the eighth lens L8 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
An adjustment filter ND made up of a light quantity adjustment filter such as a parallel plate-like ND (intermediate density) neutral density filter is interposed between the third lens group G3 and the fourth lens group G4. Further, the aperture stop AD is disposed between the adjustment filter ND and the fourth lens group G4.
The fourth lens group G4 includes, in order from the object side to the image side, a ninth lens L9 including a biconvex lens having a convex surface with a larger curvature than the object side surface on the image side, and an image side surface on the object side. A tenth lens L10 made of a biconvex lens having a convex surface with a larger curvature, an eleventh lens L11 made of a biconvex lens having a convex surface with a larger curvature than the image side surface on the object side, and an object side surface on the image side A twelfth lens L12 made of a biconcave lens having a concave surface with a larger curvature, a thirteenth lens L13 made of a biconcave lens having a concave surface having a larger curvature than the object side surface on the image side, and an image side lens on the object side. A fourteenth lens L14 made of a biconvex lens having a convex surface having a larger curvature than the surface is disposed.

The two lenses of the eleventh lens L11 and the twelfth lens L12 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses. The two lenses of the thirteenth lens L13 and the fourteenth lens L14 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
FG such as various parallel plate-like optical filters and filters such as a cover glass of the light receiving image pickup element are arranged on the optical path on the image plane side of the fourth lens group G4.
In this case, as shown in FIG. 5, the first lens group G1 and the fourth lens group G4 do not move with the zooming from the wide-angle end (short focal end) to the telephoto end (long focal end). The second lens group G2 moves fixedly from the object side to the image side from the wide-angle end to the intermediate focal length, and moves slightly from the object side to the image side from the intermediate focal length to the telephoto end. The third lens group G3 moves small from the object side to the image side from the wide angle end to the intermediate focal length, and largely moves from the object side to the image side from the intermediate focal length to the telephoto end.
First, in the state shown in FIG. 5 in the second embodiment, the focal length f, F number F, and half angle of view ω of the entire optical system are f = 17.1 to 486 and F = 4.00, respectively, by zooming. It varies in the range of 6.95 and ω = 14.2 to 0.471. The optical characteristics of each optical element are as shown in Table 4 below.

In Table 4, the optical surface indicated by attaching “#” to the surface number is a diffractive surface. Table 4 also shows the material of each lens. The same applies to the other embodiments.
That is, in Table 4, the third surface to which “#” is attached is the diffractive surface, and the parameters of the diffractive surface in Equation [13] are as follows.
Diffraction surface: Third surface λ = 587.56 (nm)
C ₂ = -2.05523 × 10 ⁻⁵
C ₄ = 8.88676 × 10 ⁻¹⁰
In Example 2, the focal length f of the entire optical system at the wide-angle end (short focal end), the intermediate focal length, and the telephoto end (long focal end), between the first lens group G1 and the second lens group G2. The variable distance dA, the variable distance dB between the second lens group G2 and the third lens group G3, and the variable distance dC between the third lens group G3 and the adjustment filter ND are as shown in the following Table 5 along with zooming. To change.

  In Example 2, the focal length f of the entire optical system at the wide-angle end (short focal end), the intermediate focal length and the telephoto end (long focal end), the magnification of the second lens group G2, and the third lens group G3. And the magnification of the fourth lens group G4 change as shown in Table 6 along with zooming.

In this case, values corresponding to the conditional expressions [1] to [12] are as follows, and satisfy the conditional expressions [1] to [12], respectively.
<< Numerical value of conditional expression >>
[1]: nd = 1.59522 (L4; L7)
[2]: νd = 67.73 (L4; L7)
[3]: θ _{C, A ′} −0.0015 × νd −0.255 = −0.0135
... OHARA S-FPM2 (L4; L7)
[4]: f _T / f _DOE = 0.0200
[5]: ν _1GP = 82.6
_{[6]: (D 34W -D 34T) /} f W = 3.54
[7]: L ₄ / T _4F-I = 0.322
[8]: ν _4GP = 86.0
[9]: _f 1 _{/ f} W = 8.45
[10]: f ₂ / f _W = −3.04
[11]: f ₃ / f _W = −2.25
[12]: _f 4 _{/ f} W = 2.48

6, FIG. 7, and FIG. 8 show spherical aberration, astigmatism, distortion, and lateral aberration at the wide angle end (short focal end), intermediate focal length, and telephoto end (long focal end), respectively, in Example 2. Each aberration diagram of the aberration is shown. In these aberration diagrams, the broken line in the spherical aberration diagram represents the sine condition, the solid line in the astigmatism diagram represents sagittal, and the broken line represents meridional. The same applies to the aberration diagrams of the other examples.
[Third Embodiment]
Next, the zoom lens according to Example 3 as the third embodiment of the present invention described above will be described in detail.

Example 3 is an example (numerical example) of a specific configuration of the zoom lens according to the third embodiment of the present invention.
FIGS. 9-12 is for demonstrating the zoom lens based on Example 3 as the 3rd Embodiment of this invention.
That is, FIG. 9 shows the lens configuration and the short focal end, that is, the long focal end from the wide-angle end to the long focal end, that is, the wide focal end, in the optical system of the zoom lens of Example 3 according to the third embodiment of the present invention. A zoom locus accompanying zooming to the telephoto end is schematically shown. 9A is a cross-sectional view along the optical axis at the short focal end, that is, the wide-angle end, FIG. 9B is a cross-sectional view along the optical axis at a predetermined intermediate focal length, and FIG. It is sectional drawing along the optical axis in a telephoto end.
The zoom lens shown in FIG. 9 has, in order from the object side to the image side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a negative refractive power. A third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power are disposed. Furthermore, an adjustment filter ND and an aperture stop AD are disposed between the third lens group G3 and the fourth lens group G4.

The first lens group G1 is formed by sequentially arranging a first lens L1, a second lens L2, and a third lens L3 from the object side to the image side. The second lens group G2 is formed by sequentially arranging a fourth lens L4, a fifth lens L5, and a sixth lens L6 from the object side to the image side. The third lens group G3 is formed by sequentially arranging a seventh lens L7 and an eighth lens L8 from the object side to the image side. The fourth lens group G4 sequentially includes a ninth lens L9, a tenth lens L10, an eleventh lens L11, a twelfth lens L12, a thirteenth lens L13, and a fourteenth lens L14 from the object side to the image side. It becomes.
The first lens group G1 to the fourth lens group G4 are supported by a common support frame or the like that is appropriate for each group, and operate integrally for each group during an operation such as zooming. It operates integrally with the fourth lens group G4. FIG. 9 also shows the surface numbers of the optical surfaces.
During zooming from the wide-angle end (short focal end) to the telephoto end (long focal end), the first lens group G1 and the fourth lens group G4 are fixedly positioned without moving. The second lens group G2 and the third lens group G3 move to increase the distance dA between the first lens group G1 and the second lens group G2, and the distance dB between the second lens group G2 and the third lens group G3. Is once reduced at the intermediate focal length, then increased, and moved so that the distance between the third lens group G3 and the fourth lens group G4 decreases.

A more detailed lens configuration of the zoom lens according to Example 3 shown in FIG. 9 will be described.
The first lens group G1 includes a first lens L1 made of a negative meniscus lens having a concave surface directed to the image side in order from the object side to the image side, a first resin layer P1 made of a thin resin material, and thin. A diffractive optical element including a second resin layer P2 made of a resin material, a second lens L2 made of a positive meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side A third lens L3 is disposed. The two lenses, the first lens L1 and the second lens L2, are closely bonded to each other with the first resin layer P1 and the second resin layer P2 interposed therebetween to form a cemented lens. Yes. Here, a diffractive surface is formed at the boundary surface between the first resin layer P1 and the second resin layer P2, and the first lens L1, the first resin layer P1, and the second resin that are integrally coupled to each other. The layer P2 and the second lens L2 constitute a cemented lens as a diffractive optical element.
The second lens group G2 includes, from the object side to the image side, a fourth lens L4 composed of a biconcave lens with a concave surface having a larger curvature than the object side surface toward the image side, and the object side from the image surface side. A fifth lens L5 composed of a biconvex lens having a convex surface having a large curvature and a sixth lens L6 composed of a biconcave lens having a concave surface having a larger curvature than the object side surface are disposed on the image side. The two lenses of the fifth lens L5 and the sixth lens L6 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.

The third lens group G3 includes, from the object side to the image side, a seventh lens L7 including a biconcave lens having a concave surface with a larger curvature than the object side surface, and a convex surface toward the object side. And an eighth lens L8 made of a positive meniscus lens. The two lenses of the seventh lens L7 and the eighth lens L8 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
An adjustment filter ND made up of a light quantity adjustment filter such as a parallel plate-like ND (intermediate density) neutral density filter is interposed between the third lens group G3 and the fourth lens group G4. Further, the aperture stop AD is disposed between the adjustment filter ND and the fourth lens group G4.
The fourth lens group G4 includes, in order from the object side to the image side, a ninth lens L9 including a biconvex lens having a convex surface with a larger curvature than the object side surface on the image side, and an image side surface on the object side. A tenth lens L10 made of a biconvex lens having a convex surface with a larger curvature, an eleventh lens L11 made of a biconvex lens having a convex surface with a larger curvature than the image side surface on the object side, and an object side surface on the image side A twelfth lens L12 made of a biconcave lens having a concave surface with a larger curvature, a thirteenth lens L13 made of a biconcave lens having a concave surface having a larger curvature than the object side surface on the image side, and an image side lens on the object side. A fourteenth lens L14 made of a biconvex lens having a convex surface having a larger curvature than the surface is disposed. The two lenses of the eleventh lens L11 and the twelfth lens L12 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
The two lenses of the thirteenth lens L13 and the fourteenth lens L14 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
FG such as various parallel plate-like optical filters and filters such as a cover glass of the light receiving image pickup element are arranged on the optical path on the image plane side of the fourth lens group G4.

First, in Example 3, in the state shown in FIG. 9, the focal length f, F number F, and half angle of view ω of the entire optical system are f = 17.1 to 487, F = 4.01 to 6.96 and ω = 16.0-0.529
It varies in the range. The optical characteristics of each optical element are as shown in Table 7 below.

In Table 7, the optical surface indicated by attaching “#” to the surface number is a diffractive surface. Table 7 also shows the material of each lens. The same applies to the other embodiments.
That is, in Table 7, the third surface to which “#” is attached is the diffractive surface, and the parameters of the diffractive surface in Equation [21] are as follows.
Diffraction surface: Third surface λ = 587.56 (nm)
C ₂ = -2.06961 × 10 ⁻⁵
C ₄ = 1.17380 × 10 ⁻⁹
In Example 3, the focal length f of the entire optical system at the wide-angle end (short focal end), the intermediate focal length and the telephoto end (long focal end), and between the first lens group G1 and the second lens group G2. The variable distance dA, the variable distance dB between the second lens group G2 and the third lens group G3, and the variable distance dC between the third lens group G3 and the adjustment filter ND are as shown in the following Table 8 along with zooming. To change.

  In Example 3, the focal length f of the entire optical system at the wide-angle end (short focal end), the intermediate focal length and the telephoto end (long focal end), the magnification of the second lens group G2, and the third lens group G3. And the magnification of the fourth lens group G4 change as shown in Table 9 along with zooming.

In this case, values corresponding to the conditional expressions [1] to [12] are as follows, and satisfy the conditional expressions [1] to [12], respectively.
<< Numerical value of conditional expression >>
[1]: nd = 1.59522 (L4)
nd = 1.60300 (L7)
[2]: νd = 67.73 (L4)
νd = 65.44 (L7)
[3]: θ _{C, A ′} −0.0015 × νd −0.255 = −0.0135… OHARA S-FPM2 (L4)
θ _{C, A ′} −0.0015 × νd − 0.255 = -0.0034… OHARA S-PHM53 (L7)
[4]: f _T / f _DOE = 0.0202

[5]: ν _1GP = 82.6
_{[6]: (D 34W -D 34T) /} f W = 3.67
[7]: L ₄ / T _4F-I = 0.261
[8]: ν _4GP = 81.5
[9]: _f 1 _{/ f} W = 8.68
[10]: f ₂ / f _W = −3.08
[11]: f ₃ / f _W = −2.50
[12]: f ₄ / f _W = 2.74
10, FIG. 11 and FIG. 12 respectively show spherical aberration, astigmatism, distortion, and lateral aberration at the wide angle end (short focal end), intermediate focal length and telephoto end (long focal end) of Example 3. Each aberration diagram of the aberration is shown. In these aberration diagrams, the broken line in the spherical aberration diagram represents the sine condition, the solid line in the astigmatism diagram represents sagittal, and the broken line represents meridional. The same applies to the aberration diagrams of the other examples.
[Fourth Embodiment]
Next, the zoom lens according to Example 4 as the fourth embodiment of the present invention described above will be described in detail.

Example 4 is an example of a specific configuration of the zoom lens according to the fourth embodiment of the present invention.
FIGS. 13-16 is for demonstrating the zoom lens based on Example 4 as the 4th Embodiment of this invention. In each of these drawings, (a) shows the arrangement of the optical system at each of the wide-angle end (short focal end), (b) the intermediate focal length, and (c) the telephoto end (long focal end). Yes.
That is, FIG. 13 shows the lens configuration and the short focal end of the zoom lens optical system of Example 4 according to the fourth embodiment of the present invention, that is, the long focal end, that is, the predetermined focal length from the wide angle end. A zoom locus accompanying zooming to the telephoto end is schematically shown. 13A is a short focal end, that is, a cross-sectional view along the optical axis at the wide-angle end, FIG. 13B is a cross-sectional view along the optical axis at a predetermined intermediate focal length, and FIG. 13C is a long focal end. That is, it is a sectional view along the optical axis at the telephoto end.
The zoom lens shown in FIG. 13 has, in order from the object side to the image side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a negative refractive power. A third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power are arranged. An adjustment filter ND and an aperture stop AD are disposed between the third lens group G3 and the fourth lens group G4.

The first lens group G1 is formed by sequentially arranging a first lens L1, a second lens L2, and a third lens L3 from the object side to the image side. The second lens group G2 is formed by sequentially arranging a fourth lens L4, a fifth lens L5, and a sixth lens L6 from the object side to the image side. The third lens group G3 is formed by sequentially arranging a seventh lens L7 and an eighth lens L8 from the object side to the image side. The fourth lens group G4 sequentially includes a ninth lens L9, a tenth lens L10, an eleventh lens L11, a twelfth lens L12, a thirteenth lens L13, and a fourteenth lens L14 from the object side to the image side. It becomes.
The first lens group G1 to the fourth lens group G4 are supported by a common support frame or the like that is appropriate for each group, and operate integrally for each group during an operation such as zooming. It operates integrally with the fourth lens group G4. FIG. 13 also shows the surface numbers of the optical surfaces.

During zooming from the wide-angle end (short focal end) to the telephoto end (long focal end), the first lens group G1 and the fourth lens group G4 are fixedly positioned without moving, and the second lens The group G2 and the third lens group G3 move to increase the distance dA between the first lens group G1 and the second lens group G2, and the distance dB between the second lens group G2 and the third lens group G3 is intermediate. The focal length is once reduced and then increased, and the distance between the third lens group G3 and the fourth lens group G4 is decreased.
A more detailed lens configuration of the zoom lens according to Example 4 shown in FIG. 13 will be described.
The first lens group G1 includes a first lens L1 made of a negative meniscus lens having a concave surface facing the image side in order from the object side to the image side, a first resin layer P1 made of a thin resin material, and thin. A diffractive optical element having a second resin layer P2 made of a resin material, a second lens L2 made of a biconvex lens having a convex surface having a larger curvature than the image side surface on the object side, and a convex surface on the object side. And a third lens L3 made of a positive meniscus lens. The two lenses, the first lens L1 and the second lens L2, are closely bonded to each other with the first resin layer P1 and the second resin layer P2 interposed therebetween to form a cemented lens. Yes. Here, a diffractive surface is formed at the boundary surface between the first resin layer P1 and the second resin layer P2, and the first lens L1, the first resin layer P1, and the second resin that are integrally coupled to each other. The layer P2 and the second lens L2 constitute a cemented lens as a diffractive optical element.

The second lens group G2 includes, from the object side to the image side, a fourth lens L4 composed of a biconcave lens with a concave surface having a larger curvature than the object side surface toward the image side, and a curvature from the object side to the image side. A fifth lens L5 made of a biconvex lens having a large convex surface and a sixth lens L6 made of a biconcave lens having a concave surface having a larger curvature than the object side surface on the image side. The two lenses of the fifth lens L5 and the sixth lens L6 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
The third lens group G3 includes, from the object side to the image side, a seventh lens L7 including a biconcave lens having a concave surface with a larger curvature than the object side surface, and a convex surface toward the object side. And an eighth lens L8 made of a positive meniscus lens. The two lenses of the seventh lens L7 and the eighth lens L8 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
An adjustment filter ND composed of a light amount adjustment filter such as a parallel plate-like ND (intermediate density) neutral density filter is interposed between the third lens group G3 and the fourth lens group G4, and further has an aperture. The stop AD is interposed between the adjustment filter ND and the fourth lens group G4.

The fourth lens group G4 includes, from the object side to the image side, a ninth lens L9 including a biconvex lens with a convex surface having a larger curvature than the image side surface facing the object side, and an image side surface facing the object side A tenth lens L10 made of a biconvex lens having a convex surface with a larger curvature, an eleventh lens L11 made of a biconvex lens having a convex surface with a larger curvature than the image side surface on the object side, and an object side surface on the image side A twelfth lens L12 made of a biconcave lens having a concave surface with a larger curvature, a thirteenth lens L13 made of a negative meniscus lens having a concave surface directed to the image side, and a convex surface having a larger curvature than the image side surface on the object side; And a fourteenth lens L14 made of a directed biconvex lens. The two lenses of the eleventh lens L11 and the twelfth lens L12 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses. The two lenses of the thirteenth lens L13 and the fourteenth lens L14 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
FG such as various parallel plate-like optical filters and filters such as a cover glass of the light receiving image sensor are arranged on the image plane side of the fourth lens group G4 on the optical path on the image plane side of the fourth lens group G4. The
In this case, as shown in FIG. 13, the first lens group G1 and the fourth lens group G4 do not move in accordance with zooming from the wide-angle end (short focal end) to the telephoto end (long focal end). The second lens group G2 moves fixedly from the object side to the image side from the wide-angle end to the intermediate focal length, and moves slightly from the object side to the image side from the intermediate focal length to the telephoto end. The third lens group G3 moves small from the object side to the image side from the wide angle end to the intermediate focal length, and largely moves from the object side to the image side from the intermediate focal length to the telephoto end.

  First, in Example 4, in the state shown in FIG. 13, the focal length f, F number F, and half angle of view ω of the entire optical system are f = 17.1 to 487 and F = 3.95 to ZOOM respectively. It varies in the range of 6.96 and ω = 14.0 to 0.470. The optical characteristics of each optical element are as shown in Table 10 below.

In Table 10, the optical surface indicated by attaching “#” to the surface number is a diffractive surface. Table 10 also shows the material of each lens. The same applies to the other embodiments.
That is, in Table 10, the third surface to which “#” is attached is the diffractive surface, and the parameters of the diffractive surface in Equation [21] are as follows.
Diffraction surface: Third surface λ = 587.56 (nm)
C ₂ = -2.07977 × 10 ⁻⁵
C ₄ = 9.76351 × 10 ⁻¹⁰
In Table 10, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface.
That is, in Table 10, the nineteenth surface, which is an optical surface marked with “*”, is an aspheric surface, and the parameters of each aspheric surface in Equation [14] are as follows.

Aspherical surface: 19th surface K = 0.0
A ₄ = -7.21843 × 10 ⁻⁶
A ₆ = -6.52396 × 10 ⁻⁹
A ₈ = 4.67279 × 10 ⁻¹²
In Example 4, the focal length f of the entire optical system at the wide-angle end (short focal end), the intermediate focal length and the telephoto end (long focal end), and between the first lens group G1 and the second lens group G2. The variable distance dA, the variable distance dB between the second lens group G2 and the third lens group G3, and the variable distance dC between the third lens group G3 and the adjustment filter ND are as shown in the following Table 11 along with zooming. To change.

  In Example 4, the focal length f of the entire optical system at the wide-angle end (short focal end), the intermediate focal length and the telephoto end (long focal end), the magnification of the second lens group G2, and the third lens group G3. And the magnification of the fourth lens group G4 change as shown in Table 12 along with zooming.

In this case, values corresponding to the conditional expressions [1] to [12] are as follows, and satisfy the conditional expressions [1] to [12], respectively.
<< Numerical value of conditional expression >>
[1]: nd = 1.59522 (L4; L7)
[2]: νd = 67.73 (L4; L7)
[3]: θ _{C, A ′} −0.0015 × νd −0.255 = −0.0135
... OHARA S-FPM2 (L4; L7)
[4]: f _T / f _DOE = 0.0203
[5]: ν _1GP = 82.6
_{[6]: (D 34W -D 34T) /} f W = 3.64
[7]: L ₄ / T _4F-I = 0.334
[8]: ν _4GP = 86.0
[9]: _f 1 _{/ f} W = 8.39
[10]: _f 2 _{/ f} W = -3.19
[11]: f ₃ / f _W = −2.27
[12]: f ₄ / f _W = 2.47

14, FIG. 15 and FIG. 16 are respectively the wide-angle end (short focal end), the intermediate focal length and the telephoto end (long focal end) spherical aberration, astigmatism, distortion, and coma aberration in Example 4. Each aberration diagram is shown. In these aberration diagrams, the broken line in the spherical aberration diagram represents the sine condition, the solid line in the astigmatism diagram represents sagittal, and the broken line represents meridional. The same applies to the aberration diagrams of the other examples.
[Fifth Embodiment]
Next, the zoom lens according to the first embodiment to the fourth embodiment of the present invention described above, which employs a zoom lens such as the first to fourth embodiments as an imaging optical system, is configured. An imaging apparatus according to the fifth embodiment will be described.

An imaging apparatus according to the fifth embodiment of the present invention will be described with reference to FIG.
The imaging apparatus shown in FIG. 17 includes the zoom lens according to Examples 1 to 4 of the first to fourth embodiments of the present invention described above as an imaging optical system.
The imaging apparatus includes a photographing lens 101, an imaging element 102, a signal processing unit 103, a zoom control unit 104, a focus control unit 106, an aperture control unit 107, and a filter control unit 108.
In this case, the photographing lens 101 is configured by using any of the zoom lenses according to the first to fourth embodiments of the first to fourth embodiments of the present invention described above. As the image sensor 102, an area sensor is generally used, and in many cases, it is constituted by a CMOS (complementary metal oxide semiconductor) image sensor, a CCD (charge coupled device) image sensor, or the like. The image sensor 102 converts the subject image formed by the photographing lens 101 into an electrical image signal. The signal processing unit 103 processes the image signal obtained by the image sensor 102 and converts it into digital image information. The zoom control unit 104 performs a zooming operation of the photographing lens 101 that is a zoom lens.

The focus control unit 106 performs focusing operation control for driving a lens group contributing to focusing in the photographing lens 101 to focus on the subject. The aperture control unit 107 variably operates the aperture diameter of the aperture stop AD in the photographing lens 101. The filter control unit 108 performs switching control of FG such as a filter such as an infrared light cut filter and a visible light cut filter in the photographing lens 101.
That is, the imaging apparatus includes an imaging element 101 such as an imaging sensor 101 and an area sensor. The imaging object formed on the imaging element 102 by the imaging lens 101, that is, an optical image of the subject is photoelectrically converted into an image signal. It is configured to read. An imaging device or a monitoring video camera can be realized by using the photographing lens 101 as an imaging optical system in the zoom lens according to the present invention described above (corresponding to claim 11 or claim 12).
An image signal output from the image sensor 102 is processed by the signal processing unit 103 and converted into digital information. The image information digitized by the signal processing unit 103 is subjected to predetermined image processing in an image processing unit (not shown), recorded in a semiconductor memory (not shown), or via communication means (not shown). Or transmit to the outside. Further, an image being shot can be displayed by a display device such as a monitor (not shown), and an image recorded in a semiconductor memory or the like can be displayed.

The photographic lens 101 that is a zoom lens is zoomed by the zoom controller 104 and focused by the focus controller 106. Further, the aperture value of the aperture stop AD can be changed by the aperture control unit 107 to control the F value (F number). In addition, the filter control unit 108 can switch between an infrared light cut filter and a visible light cut filter.
In the imaging apparatus as described above, the zoom lens according to the first to fourth embodiments can be used as the photographing lens 101. Therefore, seamless imaging from the visible range to the near-infrared range is supported, and a small and high-quality imaging device and a monitoring video camera can be realized using an imaging device having 2 million pixels or more.

G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group ND Adjustment filter AD Aperture stop L1 to L14 Lens P1, P2 Resin layer FG filter etc. 101 Shooting lens 102 Imaging element 103 Signal processing part 104 Zoom Control unit 106 Focus control unit 107 Aperture control unit 108 Filter control unit

JP 2008-197534 A JP 2008-241884 A Japanese Patent Laid-Open No. 10-054937

Claims (12)

A first lens group including a diffractive optical element and having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a negative refractive power in order from the object side to the image side And a fourth lens group having a positive refractive power,
With zooming between the wide-angle end and the telephoto end, the second lens group is located closest to the object side at the wide-angle end, and the third lens group is located closest to the image side at the telephoto end. In the zoom lens that moves the second lens group and the third lens group,
At least one of the second lens group and the third lens group includes a negative lens,
The refractive index of the material constituting the negative lens is nd, the Abbe number of the material constituting the negative lens is νd, the partial dispersion ratio of the material constituting the negative lens is θ _{C, A ′} , and the partial dispersion The ratio θ _{C, A ′} is
Refractive indexes for the F-line, C-line, and A′-line of the material constituting the negative lens are n _F , n _C, and n _{A ′} , respectively.
θ _{C, A ′} = (n _C −n _{A ′} ) / (n _F −n _C )
When expressed
Conditional expression:
[1] 1.50 <nd <1.75
[2] 60.0 <νd <75.0
[3] θ _C, A′−0.0015 × νd <0.2550
A zoom lens characterized by satisfying The focal length of the entire system at the telephoto end is f _T , and the focal length of the diffractive portion of the diffractive optical element is f _DOE .
Conditional expression:
[4] 0.02 <f _T / f _DOE <0.10
The zoom lens according to claim 1, wherein: The first lens group includes one or more positive lenses, and an average value of Abbe numbers of materials of the positive lenses included in the first lens group is ν _1GP .
Conditional expression:
[5] 75 <ν _1GP <96
The zoom lens according to claim 1, wherein the zoom lens satisfies the following.   The negative lens is included in both the second lens group and the third lens group, and the negative lens satisfies the conditional expressions [1] to [3] according to claim 1. The zoom lens according to any one of claims 1 to 3. The distance between the third lens group and the fourth lens group at the wide angle end is D _34W , the distance between the third lens group and the fourth lens group at the telephoto end is D _34T , and the focal point of the entire system at the wide angle end distance as _{f w,}
Conditional expression:
[6] _{2.5 <(D 34W -D 34T)} / f w <6.0
The zoom lens according to claim 1, wherein the zoom lens satisfies the following.   The zoom lens according to any one of claims 1 to 5, wherein a state in which the magnification of the third lens group is 0 is included during zooming from the wide-angle end to the telephoto end. . The distance along the optical axis from the most object side surface of the fourth lens group to the most image side surface is L ₄ , and along the optical axis from the most object side surface of the fourth lens group to the image plane. When an optical element having a refractive power and having no refractive power on the image side from the fourth lens group is included, T _4F-I is an air conversion length that is assumed to be absent.
Conditional expression:
[7] 0.2 <L ₄ / T _4F-I <0.5
The zoom lens according to claim 1, wherein the zoom lens satisfies the following.   8. The device according to claim 1, wherein the second lens group includes three or less lenses, and the third lens group includes two or less lenses. Zoom lens.   The first lens group includes a negative meniscus lens having a concave surface facing the image side sequentially from the object side, a first positive lens bonded to the negative meniscus lens, and a convex surface having a refractive power stronger than that of the image side. Three lenses, the second positive lens facing the object side, are arranged, and a diffractive surface of the diffractive optical system is formed at the junction interface between the negative meniscus lens and the first positive lens. The zoom lens according to claim 1, wherein the zoom lens is a zoom lens.   10. The zoom according to claim 1, wherein at the time of zooming, the first lens group and the fourth lens group are fixed without moving with respect to the image plane. lens.   An image pickup apparatus comprising the zoom lens according to any one of claims 1 to 10 as an image pickup optical system.   A surveillance video camera comprising the zoom lens according to any one of claims 1 to 10 as an imaging optical system.

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