JP5229954B2 - Zoom lens and imaging device - Google Patents

Description

  The present invention relates to a zoom lens and an imaging apparatus, and more particularly to a zoom lens that can be suitably used for a video camera, an electronic still camera, a surveillance camera, and the like, and an imaging apparatus including the zoom lens.

  Conventionally, as a zoom lens used in a video camera, an electronic still camera, etc., the first lens group and the third lens group are fixed groups, and the second lens group is moved along the optical axis to perform zooming, There is known a rear focus type four-group zoom lens in which a fourth lens group corrects an image plane accompanying zooming.

  As a rear focus type four-group zoom lens, for example, those described in Patent Documents 1 and 2 are known. Patent Document 1 discloses a zoom lens having a two-group three-lens configuration including a negative lens and a cemented lens of a negative lens and a positive lens in order from the object side to the second lens group, and having a zoom ratio of about 10 times. Has been.

  Patent Document 2 discloses a zoom lens in which the second lens group is composed of a negative lens, a negative lens, a biconcave negative lens, and a cemented lens of a positive lens in order from the object side. (The second group described in Patent Document 2 is referred to as a second lens group in this specification).

  On the other hand, in order to realize a zoom lens having a wider angle and a larger zoom ratio, a zoom lens having a five-group configuration is also known. Patent Document 3 discloses a zoom lens in which a fifth lens group having a positive refractive power is added as a fixed group to the four-group zoom lens as described above, and a zoom ratio of about 20 times is ensured. It is disclosed.

  In addition, as a zoom lens having a four-group configuration having a power arrangement and a zoom method different from those of the present application, there is a lens described in Patent Document 4, for example. Patent Document 4 includes first to fourth lens groups having positive, negative, negative, and positive refractive power in order from the object side, and the first lens group and the fourth lens group are fixed groups, An inner zoom type zoom lens is described in which zooming is performed by moving the second lens group along the optical axis, and image plane correction associated with zooming is performed by the third lens group. In the present specification, the first group, the second group, the third group, and the fourth group described in 4 are referred to as a first lens group, a second lens group, a third lens group, and a fourth lens group, respectively. To do).

JP 2000-267006 A JP 2007-148340 A JP-A-9-90221 JP 2008-241884 A

  By the way, in recent years, with the increase in the number of pixels of an image sensor mounted on a camera in the above field, there is a demand for higher performance in an optical system, and further, a high zoom ratio of about 15 to 20 times. The demand for is also increasing. In addition to these needs, there is still a conventional need for a compact configuration.

  The zoom lens described in Patent Document 1 is advantageous for reducing the size of the optical system. However, when the zoom ratio is set to 15 times or more, axial chromatic aberration, spherical aberration, and wide angle at the telephoto end caused by the first lens group. It is difficult to correct coma aberration and curvature of field at the edge, and to achieve high performance over the entire zoom range.

  In the zoom lens described in Patent Document 2, the second lens group has four negative, negative, negative, and positive elements in order from the object side, and the number of lenses in the second lens group is one more than that described in Patent Document 1. Many sheets. However, since the second lens group of the zoom lens described in Patent Document 2 has only one positive lens, the burden of correcting the aberration of the reference wavelength is large, and it is difficult to perform sufficient chromatic aberration correction.

  The zoom lens described in Patent Document 3 has a zoom ratio of about 20 times, but is disadvantageous in reducing the size of the optical system because it has a five-group configuration.

  In the zoom lens described in Patent Document 4, the second lens group and the third lens group are negative lens groups. In order to correct the chromatic aberration in the blue wavelength band at the telephoto end, it is necessary to increase the refractive power of the negative lens group. However, in the zoom lens described in Patent Document 4, if the refractive power of the negative lens group is increased, This increases the size of the fourth lens group and increases spherical aberration, which is not preferable.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a zoom lens that retains high optical performance, has a high magnification, can be configured in a small size, and an imaging device including the zoom lens. It is what.

The zoom lens of the present invention has, in order from the object side, a first lens group having a positive refractive power and fixed at the time of zooming, a negative refractive power, and moving along the optical axis. A second lens group that performs zooming, a stop, a third lens group that has positive refractive power and is fixed at the time of zooming, and has a positive refractive power, and the position of the image plane associated with zooming consists of a fourth lens group for correcting and focusing, the second lens unit, in order from the object side, and one negative lens, a cemented lens consisting of one positive lens and one negative lens, 1 The fourth lens group is composed of two positive lenses and one negative lens in order from the object side. The most positive lens on the most object side in the fourth lens group is non-double-sided. It is a spherical surface, and the negative lens of the fourth lens group has a concave surface facing the image side .

  In the zoom lens of the present invention, of the four lens groups, only the second lens group is a negative lens group, and the refractive power of the second lens group is inevitably increased, so that the blue wavelength band at the telephoto end is reduced. This is advantageous for correcting chromatic aberration. In the zoom lens according to the present invention, the configuration of the second lens group includes at least two positive lenses including a cemented lens including positive and negative lenses and second and fourth positive lenses arranged from the object side. A four-sheet configuration is possible. This facilitates correction of axial chromatic aberration at the telephoto end, and facilitates realizing high magnification and miniaturization while maintaining high optical performance.

  In the zoom lens of the present invention, the second lens group includes, in order from the object side, one negative lens having a surface with a smaller absolute value of the radius of curvature facing the image side, and a cemented surface with the convex surface facing the image side. A three-group four-lens configuration including a cemented lens including one positive lens having a surface and one negative lens and one positive lens having a concave surface facing the image side is preferable.

Further, in the zoom lens according to the present invention, when the Abbe numbers in the d-line of the positive lens and the negative lens constituting the cemented lens of the second lens group are respectively ν22 and ν23, the following conditional expression (1) is satisfied. preferable.
ν23−ν22> 15.0 (1)

In the zoom lens of the present invention, when the focal length of the second lens group is f2 and the radius of curvature of the cemented surface of the cemented lens of the second lens group is R23f, the following conditional expression (2) is satisfied. preferable.
0.90 <R23f / f2 <1.50 (2)

Here, the sign of the curvature radius R23f of the joint surface is positive when convex on the object side and negative when convex on the image side.
In the zoom lens according to the present invention, it is preferable that the following conditional expression (3) is satisfied, where N24 is a refractive index at the d-line of the most positive lens on the image side in the second lens group.
1.75 <N24 (3)

  In the zoom lens according to the present invention, the first lens group includes, in order from the object side, a cemented lens including one negative lens and one positive lens, and two positive single lenses. It may be configured.

At this time, the Abbe number in the d-line of the negative lens constituting the cemented lens of the first lens group is ν1n, and the positive lens constituting the cemented lens of the first lens group and the two positive single lenses of the first lens group. When the average Abbe number at the d-line of the lens is ν1p and the refractive index at the d-line of the negative lens constituting the cemented lens of the first lens group is N1n, the following conditional expressions (4), (5), (6 It is preferable to satisfy at least one of
18.0 <ν1n <30.0 (4)
50.0 <ν1p−ν1n (5)
1.75 <N1n (6)

  In the zoom lens of the present invention, the third lens group includes one positive lens and one negative lens, and at least one positive lens in the third lens group has at least one aspheric surface. You may comprise so that it may have.

  The sign of the refractive power of the lenses having the aspheric surfaces of the third lens group and the fourth lens group is in the paraxial region.

In the zoom lens of the present invention, when the distance on the optical axis from the most object side surface to the image plane in the entire system is Td and the focal length at the telephoto end is ft, the following conditional expression (7) is satisfied. It is preferable to satisfy.
1.00 <Td / ft <1.50 (7)

  Here, in calculating the above-described Td, an air equivalent length is used for the back focus.

  An image pickup apparatus according to the present invention includes the zoom lens according to the present invention described above.

  According to the present invention, the first lens group and the third lens group are fixed groups, and the second lens group is moved along the optical axis to perform zooming, and correction of the image plane position accompanying zooming and In a zoom lens that performs focusing by moving the fourth lens group, only the second lens group of the first to fourth lens groups is set as a negative lens group, and the configuration of the second lens group is suitably set. Therefore, it is possible to provide a zoom lens that has high optical performance, has a high magnification, and can be configured in a small size, and an imaging device including the zoom lens.

Sectional drawing which shows the lens structure of the zoom lens of Example 1 of this invention. Sectional drawing which shows the lens structure of the zoom lens of Example 2 of this invention. Sectional drawing which shows the lens structure of the zoom lens of Example 3 of this invention. Sectional drawing which shows the lens structure of the zoom lens of Example 4 of this invention. Sectional drawing which shows the lens structure of the zoom lens of Example 5 of this invention. Sectional drawing which shows the lens structure of the zoom lens of Example 6 of this invention. 7A to 7L are aberration diagrams of the zoom lens according to Example 1 of the present invention. 8A to 8L are aberration diagrams of the zoom lens according to Example 2 of the present invention. FIGS. 9A to 9L are graphs showing aberrations of the zoom lens according to Example 3 of the present invention. FIGS. 10A to 10L are aberration diagrams of the zoom lens according to Example 4 of the present invention. 11A to 11L are aberration diagrams of the zoom lens according to Example 5 of the present invention. 12A to 12L are graphs showing aberrations of the zoom lens according to Example 6 of the present invention. 1 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating a configuration of a zoom lens according to an embodiment of the present invention, and corresponds to a zoom lens of Example 1 described later.

  The zoom lens includes, in order from the object side along the optical axis Z, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, an aperture stop St, and a positive lens. A third lens group G3 having a refractive power and a fourth lens group G4 having a positive refractive power are provided.

  This zoom lens is a rear focus type zoom lens. When zooming from the wide-angle end to the telephoto end, the first lens group G1 and the third lens group G3 are fixed on the optical axis Z, and The second lens group G2 is moved to the image side along the optical axis Z, and zooming is performed. At the same time, the fourth lens group G4 is moved along the optical axis Z to correct and focus the image plane position accompanying the zooming. It is comprised so that it may be performed by moving.

  In FIG. 1, the left side is the object side, the right side is the image side, the upper stage shows the lens arrangement at the wide-angle end, the lower stage shows the lens arrangement at the telephoto end, and each lens group when zooming from the wide-angle end to the telephoto end The general movement trajectory is indicated by arrows. Note that the aperture stop St shown in FIG. 1 does not necessarily indicate the size or shape, but indicates the position on the optical axis Z.

  In FIG. 1, the image plane is shown as Sim. For example, when this zoom lens is applied to an image pickup apparatus equipped with an image pickup device, the zoom lens is arranged so that the image pickup surface of the image pickup device is positioned on the image plane Sim.

  When applying a zoom lens to an imaging device, depending on the configuration on the camera side where the lens is mounted, a cover glass, prism, infrared cut filter, low-pass filter, etc. Various filters and the like are preferably arranged, and FIG. 1 shows an example in which a parallel plate-shaped optical member PP assuming these is arranged between the lens group closest to the image side and the image plane Sim.

  The zoom lens according to the present embodiment mainly has a characteristic configuration in the second lens group G2. As in the example illustrated in FIG. 1, the second lens group G2 includes, in order from the object side, a cemented lens including one negative lens L21, one positive lens L22, and one negative lens L23, and one lens. And a positive lens L24.

  In the second lens group of the conventional example described in Patent Documents 1 to 3, there is only one positive lens on the most image side, which makes it difficult to perform sufficient chromatic aberration correction. On the other hand, in the zoom lens according to the present embodiment shown in FIG. 1, the second and fourth positive lenses from the object side of the second lens group G2 are arranged, and a total of two positive lenses are provided. Therefore, it is possible to correct chromatic aberration satisfactorily.

  In particular, in the present embodiment, the point that the positive lens L22 is arranged second from the object side of the second lens group G2 is significantly different from the conventional examples of Patent Documents 1 to 3. By constructing a cemented lens with the positive lens L22 and the negative lens L23, the radius of curvature of the cemented surface of the cemented lens can be reduced, thereby favorably correcting chromatic aberration, particularly axial chromatic aberration at the telephoto end. It becomes possible to do.

  In this type of zoom lens, in order to correct chromatic aberration at the telephoto end, it is conceivable to use an anomalous dispersion material as the lens material of the first lens group. There is a high possibility that chromatic aberration in the blue wavelength band that cannot be ignored in the lens group will occur. In order to satisfactorily suppress the chromatic aberration of the entire system, it is necessary to cancel the chromatic aberration in the blue wavelength band that occurs in the first lens group in the other lens groups. For this purpose, it is conceivable to use the second lens group which has a high light beam and is a divergent group.

  However, in the configuration of the second lens group having only one positive lens as in the conventional examples of Patent Documents 1 to 3, chromatic aberration in the blue wavelength band that occurs when an anomalous dispersion material is used for the first lens group. It was difficult to cancel. On the other hand, according to the configuration of the second lens group G2 of the present embodiment, even if an anomalous dispersion material is used for the first lens group, the chromatic aberration in the blue wavelength band that occurs at that time is canceled, and the entire system Thus, satisfactory chromatic aberration correction can be performed. In addition, since the chromatic aberration at the telephoto end tends to be greatly developed as the magnification is increased, the configuration of the second lens group G2 of the present embodiment is particularly effective for increasing the magnification.

  In order to correct chromatic aberration in the blue wavelength band at the telephoto end, it is necessary to increase the refractive power of the negative lens group. However, in this embodiment, the second lens group is the only negative lens group. Inevitably, the refractive power of the second lens group is strong, which is advantageous for correcting chromatic aberration in the blue wavelength band at the telephoto end. Further, in the present embodiment, since the third lens group disposed subsequent to the image side of the second lens group is a positive lens group, the light diverged by the second lens group can be converged by the third lens group. Even if the refractive power of the second lens group is increased, there is no need to worry about an increase in the size of the fourth lens group.

  On the other hand, in the conventional example of Patent Document 4, the second lens group and the third lens group are both negative lens groups, and the negative refractive power is distributed between these two negative lens groups. It is difficult to increase the refractive power of the lens group. Further, in the conventional example of Patent Document 4, since light beams diverged from the second lens group and the third lens group are incident on the fourth lens group, the negative lens group (second lens group and / or third lens group) Increasing the refractive power is not preferable because it increases the size of the fourth lens group and increases spherical aberration.

  As a more detailed configuration of the second lens group G2 of the present embodiment, it is preferable that the negative lens L21 closest to the object side has the surface with the smaller absolute value of the curvature radius facing the image side, and the positive lens L22 and The cemented surface of the cemented lens including the negative lens L23 preferably has a convex surface facing the image side, and the positive lens L24 preferably has a concave surface facing the image side.

  If the negative lens L21 is configured so that the surface with the larger radius of curvature is directed to the image side, the curvature of field at the wide angle end falls to the minus side, and the spherical aberration at the telephoto end falls to the minus side. End up.

  If the cemented surface of the cemented lens composed of the positive lens L22 and the negative lens L23 is configured so that the concave surface faces the image side, the lateral chromatic aberration at the wide angle end increases and the blue wavelength band on the telephoto end is on the axis. Chromatic aberration is undercorrected.

  If the positive lens L24 is configured so that its convex surface faces the image side, coma from the middle to the telephoto end becomes large.

  For example, the second lens group G2 in the example shown in FIG. 1 includes, in order from the object side, a meniscus negative lens L21 having a concave surface facing the image side, a meniscus positive lens L22 having a convex surface facing the image side, and both A three-group four-lens configuration is adopted in which a cemented lens obtained by bonding a concave negative lens L23 and a meniscus positive lens L24 having a concave surface facing the image side are arranged.

  The second lens group G2 may be configured to have five or more lenses. However, when importance is attached to compactness, the negative lens L21, the positive lens L22, and the negative lens L23 are used as described above. It is preferable to have a three-group four-lens configuration including a cemented lens and a positive lens L24.

  As a configuration of the first lens group G1, for example, as in the example shown in FIG. 1, a cemented lens including one negative lens L11 and one positive lens L12 and two single lenses are sequentially arranged from the object side. It is preferable to include certain positive lenses L13 and L14.

  By configuring the first lens group G1 in this way, positive refractive power is dispersed, and axial chromatic aberration and spherical aberration at the telephoto end due to the first lens group G1, coma aberration at the wide angle end, and field curvature Can be corrected satisfactorily.

  As a more detailed configuration of the first lens group G1, the negative lens L11 has a meniscus shape with a concave surface facing the image side, and the positive lenses L12, L13, and 14 all have a meniscus shape with a convex surface facing the object side. Is preferred. With such a configuration, it is possible to suppress an increase in the incident angle at each surface of the peripheral light beam at the telephoto end and the off-axis light beam at the wide-angle end, so that spherical aberration at the telephoto end, coma aberration at the wide-angle end, image surface The curvature correction effect can be enhanced.

  The first lens group G1 may have a configuration having five or more lenses. However, when importance is attached to compactness, the negative lens L11 and the positive lens L12 are used in order from the object side as described above. It is preferable to have a three-group four-lens configuration in which a cemented lens and two positive lenses L13 and 14 that are single lenses are arranged.

  Here, focusing on the number of lenses in the first lens group G1, the zoom lens of the present embodiment shown in FIG. 1 and the zoom lens described in Patent Document 4 are compared. The first lens group of the zoom lens described in Patent Document 4 (that is, the first group G1 in the description of Patent Document 4) has a five-lens configuration, which is one more than that of the present embodiment shown in FIG. In the zoom lens described in Patent Document 4, since the axial chromatic aberration close to the telephoto end is corrected by the first lens group by appropriately setting the configuration of the first lens group, the second lens group (that is, patent) The effect of correcting the chromatic aberration in the blue wavelength band of the second group G2) in the description in Literature 4 is small.

  Therefore, when the number of the first lens group of the zoom lens described in Patent Document 4 is simply reduced for the purpose of downsizing or the like, the number of lenses of the first lens group and the second lens group is apparently the same as in the present embodiment. However, the chromatic aberration correction capability cannot be expected to be equivalent to that of the present embodiment. If the number of the first lens group of the zoom lens described in Patent Document 4 is reduced, it is necessary to use an anomalous dispersion material for correcting axial chromatic aberration, and in that case, the above-described consideration is required.

  The configuration of the third lens group G3 according to the embodiment of the present invention includes one positive lens and one negative lens, and at least one positive lens included in the third lens group G3 is at least one. The surface is preferably an aspherical surface. Since the third lens group G3 includes both the positive lens and the negative lens, it becomes easy to balance in correcting the chromatic aberration. Also, by having an aspheric lens, it acts on both the on-axis light beam and off-axis light beam in the entire zoom range, and it becomes easy to obtain high optical performance by satisfactorily correcting aberrations.

  For example, the third lens group G3 in the example shown in FIG. 1 has a two-group two-lens configuration in which a positive lens L31 and a negative lens L32 are arranged in order from the object side. The third lens group G3 is described later. As shown in the embodiment, the lens may be composed of two positive lenses and one negative lens, or may be composed of one positive lens and two negative lenses. Further, the third lens group G3 may employ a configuration in which adjacent positive lenses and negative lenses are cemented.

  As a configuration of the fourth lens group G4, for example, as in the example illustrated in FIG. 1, the fourth lens group G4 includes two positive lenses L41 and L42 and one negative lens L43 in order from the object side. It is preferable that the most object side positive lens L41 in FIG. 4 has two aspheric surfaces, and the negative lens L43 in the fourth lens group G4 has a concave surface facing the image side.

  If the negative lens L43 is configured so that the convex surface faces the image side, the spherical aberration falls to the plus side from the wide-angle end to the middle.

  Since the fourth lens group G4 has both the positive lens and the negative lens, it becomes easy to achieve a balance in correcting chromatic aberration, and the fourth lens group G4 has two positive lenses, which is necessary for the fourth lens group G4. It is easy to secure a positive refractive power. Also, by having an aspheric lens, it mainly acts on the on-axis light beam and off-axis light beam at the wide-angle end, and off-axis light beam at the telephoto end, and it becomes easy to obtain high optical performance with good aberration correction.

  The zoom lens according to the embodiment of the present invention preferably further satisfies the following conditional expressions. In addition, as a preferable aspect, any one of the following conditional expressions may be satisfied, or any combination may be satisfied. The conditional expressions and their effects are described below.

When the Abbe numbers in the d-line of the positive lens L22 and the negative lens L23 constituting the cemented lens of the second lens group G2 are ν22 and ν23, respectively, it is preferable that the following conditional expression (1) is satisfied.
ν23−ν22> 15.0 (1)

  Conditional expression (1) defines the range of the difference between the Abbe numbers of the positive lens L22 and the negative lens L23 constituting the cemented lens of the second lens group G2. In general, when the zoom ratio is high, it is difficult to correct axial chromatic aberration at the telephoto end. Conditional expression (1) is an expression for satisfactorily correcting axial chromatic aberration. If the lower limit of conditional expression (1) is not reached, a difference in Abbe number necessary for correcting axial chromatic aberration cannot be obtained, and it becomes difficult to correct axial chromatic aberration well.

When the focal length of the second lens group G2 is f2, and the curvature radius of the cemented surface of the cemented lens of the second lens group G2 is R23f, it is preferable that the following conditional expression (2) is satisfied.
0.90 <R23f / f2 <1.50 (2)

  Conditional expression (2) defines the relationship between the focal length of the second lens group G2 and the curvature radius of the cemented surface. If the lower limit of conditional expression (2) is not reached, the axial chromatic aberration in the red wavelength band at the telephoto end becomes large, which is not preferable. If the upper limit of conditional expression (2) is exceeded, axial chromatic aberration in the blue wavelength band at the telephoto end increases, which is not preferable.

When the refractive index at the d-line of the most image-side positive lens (positive lens L24 in the example shown in FIG. 1) in the second lens group G2 is N24, it is preferable to satisfy the following conditional expression (3).
1.75 <N24 (3)

  Conditional expression (3) defines the range of the refractive index of the positive lens closest to the image side in the second lens group G2. If the lower limit of conditional expression (3) is not reached, the radius of curvature becomes small in order to obtain the necessary refractive power, and the length in the optical axis direction of the entire second lens group G2 when considering the lens periphery is considered. It becomes long and is not preferable.

When the first lens group G1 includes a cemented lens including one negative lens L11 and one positive lens L12 and two positive single lenses L13 and L14 in order from the object side. When the Abbe number in the d-line of the negative lens L11 is ν1n, and the average Abbe number in the d-line of the positive lens L12 and the two positive single lenses L13 and L14 constituting the cemented lens is ν1p, the following conditional expression It is preferable to satisfy (4) and (5).
18.0 <ν1n <30.0 (4)
50.0 <ν1p−ν1n (5)

  Conditional expressions (4) and (5) are for satisfactorily correcting chromatic aberration at the telephoto end. By selecting a combination of lens materials satisfying conditional expressions (4) and (5), axial chromatic aberration generated in the first lens group G1 can be reduced, and performance deterioration due to color blurring at the telephoto end can be suppressed. it can.

When the first lens group G1 includes a cemented lens including one negative lens L11 and one positive lens L12 and two positive single lenses L13 and L14 in order from the object side. When the refractive index at the d-line of the negative lens L11 is N1n, it is preferable that the following conditional expression (6) is satisfied.
1.75 <N1n (6)

Conditional expression (1) defines the refractive index of the negative lens closest to the object side in the first lens group G1. If the lower limit of conditional expression (1) is not reached, various aberrations, particularly coma, increase at the telephoto end when the telephoto ratio is reduced, and high performance cannot be maintained.
When the distance on the optical axis from the most object-side surface to the image plane in the entire system is Td and the focal length at the telephoto end is ft, it is preferable that the following conditional expression (7) is satisfied.
1.00 <Td / ft <1.50 (7)

  Conditional expression (7) defines the total length of the optical system with respect to the focal length at the telephoto end. If the lower limit of conditional expression (7) is not reached, it is advantageous for shortening the overall length of the optical system, but it becomes difficult to correct various aberrations, particularly axial chromatic aberration at the telephoto end, and high performance is maintained throughout the entire zoom range. I can't. If the upper limit of conditional expression (7) is exceeded, it is advantageous for correcting aberrations, but it is not preferable because the total length of the optical system becomes long and this is contrary to miniaturization.

When the refractive indexes of the positive lens L22 and the negative lens L23 constituting the cemented lens of the second lens group G2 at the d-line are N22 and N23, respectively, it is preferable that the following conditional expression (8) is satisfied.
| N22-N23 | <0.035 (8)

  Conditional expression (8) defines the range of the difference in refractive index between the positive lens L22 and the negative lens L23 constituting the cemented lens of the second lens group G2. If the upper limit of conditional expression (8) is exceeded, it will be difficult to satisfactorily correct various aberrations other than axial chromatic aberration.

The zoom lens according to the embodiment of the present invention further includes the following conditional expressions (1-1), (2-1), (3-1), (4-1), (5-1), and (6-1). ) And (7-1) are more preferably satisfied. Conditional expressions (1-1), (2-1), (3-1), (4-1), (5-1), (6-1), (7-1) The effect obtained by satisfying the expressions (1), (2), (3), (4), (5), (6), and (7) can be further enhanced.
ν23-ν22> 18.0 (1-1)
1.00 <R23f / f2 <1.40 (2-1)
1.84 <N24 (3-1)
18.0 <ν1n <26.0 (4-1)
56.0 <ν1p−ν1n (5-1)
1.80 <N1n (6-1)
1.10 <Td / ft <1.40 (7-1)

  In addition, when this zoom lens is used in harsh environments such as outdoors, the lens placed closest to the object is resistant to surface deterioration due to wind and rain, temperature changes due to direct sunlight, and oils and detergents. It is preferable to use a material resistant to chemicals, that is, a material having high water resistance, weather resistance, acid resistance, chemical resistance, and the like, and further, a material that is hard and difficult to break. From the above, as the material disposed closest to the object side, specifically, glass is preferably used, or transparent ceramics may be used.

  When the zoom lens is used in a harsh environment, a protective multilayer coating is preferably applied. In addition to the protective coat, an antireflection coating film for reducing ghost light during use may be applied.

  In the example shown in FIG. 1, an example in which the optical member PP is arranged between the lens system and the image plane Sim is shown, but instead of arranging a low-pass filter, various filters that cut a specific wavelength range, or the like, These various filters may be disposed between the lenses, or a coating having the same action as the various filters may be applied to the lens surface of any lens.

  As described above, according to the zoom lens of the present embodiment, the number of lenses in the rear focus type zoom lens having four groups is appropriately adopted by appropriately adopting the above-described preferable configuration in accordance with required specifications. Without significantly increasing the size, it is possible to achieve a compact configuration, high magnification, and high optical performance.

  Next, numerical examples of the zoom lens according to the present invention will be described. A lens cross-sectional view of the zoom lens of Example 1 is shown in FIG. Cross-sectional views of the zoom lenses of Examples 2 to 6 are shown in FIGS. The method shown in FIGS. 2 to 6 is the same as that shown in FIG.

  Table 1 shows basic lens data of the zoom lens according to Example 1, Table 2 shows aspheric data, Table 3 shows various data, and Table 4 shows focal lengths of the respective groups. Similarly, basic lens data, aspheric surface data, various data, and focal lengths of the respective groups of the zoom lenses according to Examples 2 to 6 are shown in Tables 5 to 24. In the following, the meaning of the symbols in the table will be described using Example 1 as an example, but the same applies to Examples 2 to 6.

  In the basic lens data in Table 1, the position of the object plane is set to infinity, and Si is the i-th (i = 1, 2, 3, ...), Ri represents the radius of curvature of the i-th surface, and Di represents the surface spacing on the optical axis Z between the i-th surface and the i + 1-th surface. In the basic lens data, Ndj is the d-line (wavelength: 587.6 nm) of the j-th (j = 1, 2, 3,...) Optical element that sequentially increases toward the image side with the most object-side lens as the first lens. ), And νdj represents the Abbe number of the j-th optical element with respect to the d-line. The basic lens data includes the aperture stop St and the optical member PP. In the column of the surface number of the surface corresponding to the aperture stop St, (aperture stop) is described. The sign of the radius of curvature of the basic lens data is positive when convex on the object side and negative when convex on the image side.

  In the basic lens data in Table 1, the symbols D7, D14, D19, and D25 are described in the column of the surface interval in which the interval changes at the time of zooming, and (variable) is described after each symbol. Similarly, in the embodiments to be described later, corresponding reference numerals are described in the column of the surface interval in which the interval changes at the time of zooming.

In the basic lens data in Table 1, the surface number of the aspheric surface is marked with *, and the numerical value of the curvature radius near the optical axis is shown as the curvature radius of the aspheric surface. The aspheric data in Table 2 shows the surface number of the aspheric surface and the aspheric coefficient of each aspheric surface. The aspheric coefficient is a value of each coefficient KA, RB _m (m = 3, 4, 5,... 20) in the aspheric expression expressed by the following expression (A).
Zd = C · h ² / {1+ (1−KA · C ² · h ² ) ^1/2 } + ΣRB _m · h ^m (A)
However,
Zd: Depth of aspheric surface (length of perpendicular drawn from a point on the aspherical surface of height h to a plane perpendicular to the optical axis where the aspherical vertex contacts)
h: Height (distance from the optical axis to the lens surface)
C: Reciprocal of radius of curvature near optical axis KA, RA _m : aspheric coefficient (m = 3, 4, 5,... 20)

In the numerical values of the aspherical coefficients in Table 2, the symbol E indicates that the next numerical value is an exponent that should have a base of 10, and the numerical value indicated by the exponential function with the base of 10 is E. Indicates that the previous number is multiplied. For example, “1.0E-2” indicates “1.0 × 10 ⁻² ”.

  The various data in Table 3 include the zoom ratio, the focal length f, the F number, the half field angle ω, the maximum image height Y, the total length of the lens system, the back focus, the variable at the wide angle end, the middle, and the telephoto end. The values of the surface spacings D7, D14, D19, and D25 that change at the time of doubling are shown.

  The focal length of each group in Table 4 indicates the start surface (the most object-side surface) and the focal length of each of the first to fourth lens groups.

  Here, as an example, “mm” is used as the unit of length in Tables 1 to 4, “degree” is used as the unit of angle, and “mm” is used as the unit of Zd and h in formula (A). ing. However, since the same optical performance can be obtained even if the optical system is proportionally enlarged or reduced, the unit is not limited to “mm”, and other appropriate units can also be used.

  In the zoom lens according to the first embodiment, the third lens group G3 includes the positive lens L31 and the negative lens L32. However, the zoom lens according to the second embodiment includes the third lens group G3 as the positive lens L31. , The positive lens L32 and the negative lens L33. The third lens group G3 in Examples 3 to 6 also has a three-lens configuration.

  Table 25 shows values corresponding to the conditional expressions (1) to (8) in Examples 1 to 6. As can be seen from Table 25, all of Examples 1 to 6 satisfy the conditional expressions (1) to (8).

  FIGS. 7A to 7L show aberration diagrams of spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration at the wide-angle end, the middle, and the telephoto end of the zoom lens according to the first exemplary embodiment. Each aberration diagram shows the aberration with the d-line (wavelength 587.6 nm) as the reference wavelength, but the spherical aberration diagram and the lateral chromatic aberration diagram show the aberration at the wavelength 587.6 nm as a solid line and the wavelength at 460.0 nm. Aberrations are indicated by broken lines, and aberrations at a wavelength of 615.0 nm are indicated by alternate long and short dash lines. Fno. Of spherical aberration diagram. Means F number, and ω in other aberration diagrams means half angle of view.

  Similarly, FIG. 8 (A) to FIG. 8 (L), FIG. 9 (A) to FIG. 9 (L), FIG. 10 (A) to FIG. 10 (L), FIG. 11 (A) to FIG. FIGS. 12A to 12H show spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration at the wide-angle end, intermediate point, and telephoto end of the zoom lenses of Examples 2 to 6, respectively. The figure is shown.

  From the above data, the zoom lenses of Examples 1 to 6 have a high magnification of about 15 to 20 times, and the F-number at the wide-angle end is as small as about 1.6 while achieving downsizing. It can be seen that each aberration is well corrected over the telephoto end and has high optical performance in the visible range. These zoom lenses can be suitably used for imaging devices such as surveillance cameras, video cameras, and electronic still cameras.

  FIG. 13 shows a configuration diagram of a video camera 10 configured using the zoom lens 1 according to the embodiment of the present invention as an example of the imaging apparatus of the embodiment of the present invention. In FIG. 13, the positive first lens group G1, the negative second lens group G2, the aperture stop St, the positive third lens group G3, and the positive fourth lens group G4 included in the zoom lens 1 are schematically illustrated. Show.

  The video camera 10 includes a zoom lens 1, a filter 2 having functions such as a low-pass filter and an infrared cut filter disposed on the image side of the zoom lens 1, an image pickup device 4 disposed on the image side of the filter 2, and a signal. And a processing circuit 5. The image sensor 4 converts an optical image formed by the zoom lens 1 into an electric signal. For example, the image sensor 4 may be a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor), or the like. it can. The image sensor 4 is arranged such that its image plane coincides with the image plane of the zoom lens 1.

  An image picked up by the zoom lens 1 is formed on the image pickup surface of the image pickup device 4, an output signal from the image pickup device 4 relating to the image is subjected to arithmetic processing by the signal processing circuit 5, and the image is displayed on the display device 6. The

  Note that FIG. 13 illustrates a so-called single-plate type imaging apparatus using one imaging element 4, but the imaging apparatus according to the present invention has an R (between the zoom lens 1 and the imaging element 4. A so-called three-plate system may be used in which color separation prisms for each color such as red), G (green), and B (blue) are inserted and three image pickup devices corresponding to the respective colors are used.

  Since the zoom lens 1 according to the embodiment of the present invention has the above-described advantages, the imaging apparatus of the present embodiment has a zoom ratio of about 15 to 20 times, can be configured in a small size, and has a high level. An image with high image quality can be obtained.

  The present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, the values of the radius of curvature, the surface spacing, the refractive index, the Abbe number, etc. of each lens component are not limited to the values shown in the above numerical examples, but can take other values.

DESCRIPTION OF SYMBOLS 1 Zoom lens 2 Filter 4 Image pick-up element 5 Signal processing circuit 6 Display apparatus 10 Video camera G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group PP Optical member St Aperture stop Z Optical axis

Claims (11)

In order from the object side, a first lens group having positive refractive power and fixed at the time of zooming, and a second lens having negative refractive power and zooming by moving along the optical axis A third lens group having a positive refracting power and fixed at the time of zooming, a first lens having a positive refracting power, and correcting and focusing the image plane position accompanying the zooming. It consists of a fourth lens group,
The second lens group includes, in order from the object side, one negative lens, one cemented lens including one positive lens and one negative lens, and one positive lens .
The fourth lens group is composed of two positive lenses and one negative lens in order from the object side, and the positive lens closest to the object side in the fourth lens group is aspheric on both sides, The zoom lens according to claim 4, wherein the negative lens of the fourth lens group has a concave surface facing the image side .   The second lens group includes, in order from the object side, one negative lens having a surface with a smaller radius of curvature on the image side and a positive surface having a cemented surface with a convex surface on the image side. 2. The zoom lens according to claim 1, wherein the zoom lens has a three-group four-lens configuration including a cemented lens including a lens and one negative lens, and one positive lens having a concave surface facing the image side. 2. The following conditional expression (1) is satisfied, where the Abbe numbers in the d-line of the positive lens and the negative lens constituting the cemented lens of the second lens group are ν22 and ν23, respectively. Or the zoom lens according to 2;
ν23−ν22> 15.0 (1) The following conditional expression (2) is satisfied, where f2 is the focal length of the second lens group and R23f is the radius of curvature of the cemented surface of the cemented lens of the second lens group. 4. The zoom lens according to any one of items 3.
0.90 <R23f / f2 <1.50 (2) The conditional expression (3) below is satisfied, where N24 is a refractive index of the positive lens closest to the image side in the second lens group at the d-line. Zoom lens.
1.75 <N24 (3)   6. The first lens group includes a cemented lens including one negative lens and one positive lens and two positive single lenses in order from the object side. The zoom lens according to any one of the above. The Abbe number at the d-line of the negative lens constituting the cemented lens of the first lens group is ν1n, and the two lenses of the positive lens and the first lens group constituting the cemented lens of the first lens group 7. The zoom lens according to claim 6, wherein the following conditional expressions (4) and (5) are satisfied, where an average of Abbe number in the d-line of the positive single lens is ν1p.
18.0 <ν1n <30.0 (4)
50.0 <ν1p−ν1n (5) The zoom lens according to claim 6 or 7, wherein the following conditional expression (6) is satisfied, where N1n is a refractive index at the d-line of the negative lens constituting the cemented lens of the first lens group. .
1.75 <N1n (6)   The third lens group includes one positive lens and one negative lens, and at least one positive lens of the third lens group has at least one aspheric surface. Item 9. The zoom lens according to any one of Items 1 to 8. The following conditional expression (7) is satisfied, where Td is the distance on the optical axis from the most object side surface to the image plane in the entire system, and ft is the focal length at the telephoto end. 10. The zoom lens according to any one of 9 above.
1.00 <Td / ft <1.50 (7) Imaging apparatus characterized by comprising a zoom lens according to any one of claims 1 10.

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