JP5197247B2 - Zoom lens and image pickup apparatus having the same - Google Patents

Description

  The present invention relates to a zoom lens. Furthermore, the present invention relates to an imaging apparatus such as a digital camera or a video camera provided with a zoom lens and an imaging element.

  In recent years, in the technical field of imaging devices, digital cameras have become the mainstream instead of silver halide cameras. A digital camera is generally characterized in that it is easy to achieve miniaturization because the imaging surface size is smaller than that of a camera for a film. Recently, since the portability tends to be more important than the conventional one, the digital camera itself is downsized. Furthermore, because there is a customer's need to enjoy taking pictures using a digital camera, both indoors and outdoors, zoom lenses used as optical systems are required to have a wide angle of view and a high zoom ratio. .

  Various zoom lenses have been proposed for the purpose of achieving such a zoom lens having a small size, a wide angle of view, and a high zoom ratio. For example, Patent Documents 1 to 3 disclose a zoom lens of a negative leading type in which a lens group having a negative refractive power is disposed closest to the object side.

  Such a negative leading zoom lens has a retrofocus type refractive power arrangement as a whole. For this reason, it is advantageous for securing the angle of view at the wide-angle end as compared with the front-facing zoom lens, and the size reduction of the lens group closest to the object side is advantageous for miniaturization of the entire zoom lens.

  The zoom lenses disclosed in Patent Documents 1 to 3 exemplified above increase the refractive index of the positive lens of the first lens group to 1.9 or higher, thereby correcting the curvature of field at the wide-angle end and correcting the peripheral portion. The lens thickness is kept small, the entire first lens group is thinned, and the zoom lens is miniaturized.

JP 2007-179015 A JP 2007-272216 A JP 2007-333799 A

However, even higher zoom ratios are required in the field of such negative leading zoom lenses.
The present invention has been made in view of such problems, and is a negative preceding zoom lens that is advantageous for securing the angle of view at the wide-angle end and reducing the size, and is advantageous for securing a zoom ratio and maintaining optical performance. The purpose is to provide a zoom lens. Furthermore, it aims at providing the imaging device provided with such a zoom lens.

In order to solve the above problem, the zoom lens according to the first aspect of the present invention has, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a positive refractive power. The third lens group, and the second lens group and the third lens group move so that the distance between the lens groups changes during zooming from the wide-angle end to the telephoto end. The group includes, in order from the object side, a biconcave negative lens component having an aspherical surface and a positive lens component. The negative lens component has a shape that satisfies the following conditional expression (1). A negative lens that satisfies the conditional expression (2); a positive lens component having a positive lens that satisfies the following conditional expression (3); and a third lens group that satisfies the following conditional expression (4): It is characterized by that.
0.2 <(R ₁ + R ₂ ) / (R ₁ −R ₂ ) <0.99 (1)
1.81 <N ₁ <2.15 (2)
1.9 <N ₂ <2.35 (3)
4.5 <f ₃ / f _w <12.0 (4)
However,
R ₁ is the paraxial radius of curvature of the object side surface of the negative lens component of the first lens group,
R ₂ is the paraxial radius of curvature of the image side surface of the negative lens component of the first lens group,
N ₁ is the refractive index of the d-line of any negative lens in the negative lens component of the first lens group,
N ₂ is the refractive index of the d-line of any positive lens in the positive lens component of the first lens group,
f ₃ is the focal length of the third lens unit, f _w is the focal length of the entire zoom lens system at the wide angle end,
It is.
The lens component means a lens body having only two surfaces that are in contact with air on the optical axis, that is, the object side surface and the image side surface.

By adopting such a configuration, it becomes a lens group arrangement of a power arrangement that can easily ensure a wide angle of view, and the second lens group can have a main zooming function.
Further, since the first lens group has a negative lens component and a positive lens component in order from the object side, the principal point of the first lens group can be from the object side, and the diameter of the first lens group can be reduced. It is also advantageous for correcting off-axis aberrations at the wide-angle end and spherical aberrations at the telephoto end. Furthermore, by making at least one surface of the negative lens component an aspherical surface, it is possible to satisfactorily correct off-axis aberrations at the wide angle end while ensuring the negative refractive power of the negative lens component. Since the negative refractive power of the entire first lens group can be secured, it is advantageous for making the zoom lens compact by shortening the overall length of the zoom lens.

  The first lens group satisfies the conditional expression (1), conditional expression (2), and conditional expression (3), so that the entire zoom range is good even if the angle of view and the zoom ratio at the wide angle end are secured. It is possible to ensure a good performance.

Conditional expression (1) is a conditional expression regarding the shape of the negative lens component of the first lens unit.
By satisfying conditional expression (1), it becomes possible to share negative power well between the object side surface and the image side surface of the first lens component, and the field curvature at the wide-angle end and the spherical aberration at the telephoto end can be reduced. It is advantageous for reduction. By making sure that the lower limit of conditional expression (1) is not exceeded, the negative refractive power on the object side surface of the first lens component can be moderately suppressed, and off-axis aberrations at the wide-angle end can be easily reduced. By ensuring that the upper limit of conditional expression (1) is not exceeded, it is easy to reduce the spherical aberration at the telephoto end by ensuring the negative refracting power of the object side surface of the first lens component.

Conditional expression (2) specifies a preferable refractive index for the d-line of any negative lens in the negative lens component of the first lens group.
By making sure that the lower limit of conditional expression (2) is not exceeded, it is possible to moderately suppress the curvature of the image side surface of the negative lens component, and to easily suppress the occurrence of curvature of field at the wide angle end and spherical aberration at the telephoto end. Become. Further, since the edge thickness of the negative lens component can be reduced, it is advantageous for downsizing the first lens group. By not exceeding the upper limit of conditional expression (2), it becomes easy to suppress the cost of materials and the cost of processing the lens surface.

Conditional expression (3) specifies a preferable refractive index for the d-line of any positive lens in the positive lens component of the first lens group.
By avoiding falling below the lower limit of conditional expression (3), it is possible to satisfactorily correct the curvature of field at the wide-angle end and the spherical aberration at the telephoto end without making the image side surface concave with a small radius of curvature. In addition, since the axial thickness can be reduced while securing the edge thickness of the positive lens component, it is advantageous for reducing the size of the first lens group. By not exceeding the upper limit, it becomes easy to suppress the cost of the material and the cost of processing the lens surface.

Conditional expression (4) specifies a preferable focal length of the third lens group.
Conditional expression (4) is a condition for reducing fluctuations in field curvature that are likely to occur as the zoom ratio increases.

  In the present invention, satisfying conditional expressions (1), (2), and (3) is advantageous in reducing the aberration of the first lens unit alone. On the other hand, it is preferable to correct the variation in field curvature at the time of zooming that occurs in the second lens group by canceling it with the third lens group.

  To increase the zoom ratio, it is necessary to increase the refractive power of the second lens group. Therefore, it is preferable to appropriately perform aberration correction sharing by the third lens group. In the present invention, it is preferable to keep the refractive power of the third lens group weak and to weaken the restriction of movement due to the variable magnification sharing so as to mainly correct the field curvature fluctuation due to the variable magnification.

  By suppressing the refractive power of the third lens group so as not to fall below the lower limit of the conditional expression (4), it becomes easier to suppress aberration fluctuations in the variable power range where the third lens group is relatively close to the object side. By ensuring that the positive refractive power of the third lens group is appropriately secured without exceeding the upper limit, it is easy to suppress an excess of the positive refractive power of the second lens group.

  Note that when the zoom lens includes a focusing mechanism, each of the above structural requirements is a configuration in a state in which an object at the farthest distance is in focus.

  In the present invention, it is more preferable that any one or more of the following configurations are simultaneously satisfied.

  In the present invention, at the time of zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group becomes narrow, and the distance between the second lens group and the third lens group changes. It is preferable to move the third lens unit in the optical axis direction during focusing. The second lens group has a zooming function, and the third lens group has a function of adjusting aberrations. Since the refractive power of the third lens group is moderately suppressed, if this lens group is a focusing lens group, it is easy to reduce aberration fluctuations due to focusing.

Moreover, it is preferable that the negative lens component and the positive lens component in the first lens group have only one glass lens.
This is advantageous for downsizing each lens component. Furthermore, it is more preferable that each lens component is a single glass lens for miniaturization.

In addition, it is desirable that the zoom lens according to the present invention further satisfies the following conditional expression (4 ′) with respect to the above configuration.
5.5 <f ₃ / f _w <15.0 (4 ′)
In order to reduce aberration variation due to a high zoom ratio, it is preferable to set the lower limit of conditional expression (4) to 5.5.

  In addition, it is preferable to arrange an aperture stop immediately after the image side of the second lens group. In order to achieve a high zoom ratio with a negative leading zoom lens type, it is effective to increase the zooming action of the second lens group. Therefore, it is preferable to arrange an aperture stop behind the second lens group.

  When the aperture stop is disposed on the object side of the second lens group, it is difficult to reduce the axial air space between the first lens group and the second lens group at the telephoto end. By disposing the lens group immediately after the image side of the group, the distance between the first lens group and the second lens group can be reduced without any mechanical restriction. Therefore, it is advantageous for securing the amount of movement of the second lens group at the time of zooming, and it is advantageous for ensuring both the zooming ratio and miniaturization.

  Furthermore, when the aperture stop moves integrally with the second lens group during zooming from the wide-angle end to the telephoto end, the mechanical configuration can be further simplified. In addition, the change in the effective diameter in the second lens group is reduced, which is advantageous for downsizing the second lens group and reducing aberrations.

  Furthermore, it is preferable that the most image side surface of the first lens group has a concave surface facing the image side, and the most object side surface of the second lens group has a shape with a convex surface facing the object side. While the shape is advantageous for aberration correction near the wide-angle end, the principal point of the second lens group can be easily brought closer to the first lens group at the telephoto end, which is further advantageous for both miniaturization and securing a zoom ratio.

  In addition, it is desirable that the zoom lens has a fourth lens group made up of a single lens having an aspheric surface on the image side of the third lens group. In order to further reduce the curvature of field due to the high zoom ratio, the fourth lens group can be provided with a field curvature correction function by arranging the above-described fourth lens group. Thereby, the aberration balance in the entire zoom range can be kept better.

Further, it is more preferable that the fourth lens group satisfies the following conditional expression.
−0.5 <(f ₄ / f _w ) ⁻¹ <0.5 (6)
Here, f ₄ is the focal length of the fourth lens group.

  By reducing the absolute value of the refractive power of the fourth lens unit within the range of the conditional expression (6), it is advantageous for both the reduction of the thickness of the fourth lens unit and the reduction of aberrations, and the off-axis of the entire zoom lens by the aspherical surface is achieved. It becomes easier to obtain the aberration correction function.

  The second lens group includes, in order from the object side, a first positive lens, a second positive lens, a negative lens, and a third positive lens, and one of the first to third positive lenses. Preferably has an aspherical surface.

  In general, the second lens group having a positive refractive power is preferably composed of a triplet of a positive lens, a negative lens, and a positive lens in terms of aberration correction. Here, in order to achieve both a sufficient zoom ratio and a reduction in size, it is preferable to increase the refractive power of the positive lens on the object side so that the principal point is closer to the object side. Therefore, the positive lens on the object side of the triplet lens is replaced with two positive lenses. In order from the object, the first positive lens, the second positive lens, the negative lens, and the third positive lens are configured. This is more advantageous for securing a zoom ratio and correcting aberrations.

  It is desirable that at least one surface of the positive lens included in the second lens group be an aspherical surface. Although the refractive power of the second lens group tends to increase due to the high zoom ratio, using an aspherical surface for the positive lens is advantageous for correcting spherical aberration in the second lens group.

In addition, it is preferable that the first lens group, the second lens group, and the third lens group satisfy the following conditional expressions (7) and (8).
−0.6 <f ₁ / f ₃ <−0.16 (7)
0.15 <f ₂ / f ₃ <0.42 (8)
However,
f ₁ is the focal length of the first lens group,
f ₂ is the focal length of the second lens group,
It is.

  In order to achieve a good balance between miniaturization and performance while ensuring the angle of view and the zoom ratio, the refractive power of the first and second lens groups is appropriately increased, and the refractive power of the third lens group is relatively increased. It is preferable to make the aberration balance easy to adjust.

  Ensuring the negative refracting power of the first lens group without falling below the lower limit of conditional expression (7) is advantageous for a small and wide angle of view. Alternatively, the refractive power of the third lens group can be reduced, which is advantageous for correcting fluctuations in field curvature. By suppressing the refractive power of the first lens unit so as not to exceed the upper limit of conditional expression (7), it becomes more advantageous for reducing aberrations in the first lens unit.

  By suppressing the refractive power of the second lens group so as not to fall below the lower limit of conditional expression (8), it is possible to suppress an increase in the number of lenses for aberration correction. By suppressing the refractive power of the third lens group so as not to exceed the upper limit of conditional expression (8), it becomes easy to suppress fluctuations in off-axis aberrations.

Moreover, it is preferable that the following conditional expression (5) is satisfied.
_{3.85 <f t / f w <} 8 ··· (5)
Where f _t is the focal length of the entire zoom lens system at the telephoto end.

  It is preferable that various shooting scenes can be handled by ensuring the degree of freedom by changing the angle of view so as not to fall below the lower limit of conditional expression (5). By not exceeding the upper limit, it becomes easy to suppress aberrations occurring in the first lens group and the second lens group, which is advantageous for downsizing and ensuring performance in the entire zoom range.

The zoom lens according to the second aspect of the present invention is a reference example. In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, an aperture stop, a positive aperture The second lens group and the third lens group are composed of a third lens group having a refractive power and a fourth lens group, and the second lens group and the third lens group move so that the distance between the lens groups changes upon zooming from the wide-angle end to the telephoto end. The first lens group includes, in order from the object side, a negative lens component and a positive lens component having an aspheric surface, and the second lens group includes, in order from the object side, a first positive lens, a second positive lens, and a negative lens component. The first lens is composed of a lens and a third positive lens, and any one of the first to third positive lenses has an aspheric surface, the third lens group is composed of one positive lens component, and the fourth lens group is non-spherical. It consists of a single lens component with a spherical surface and satisfies the following conditional expression (5 ') is there.
4.1 <f _t / f _w <8 (5 ′)
However,
f _w is the focal length of the entire zoom lens system at the wide angle end,
_ft is the focal length of the entire zoom lens system at the telephoto end,
It is.

  By adopting such a four-group configuration, a lens group arrangement that facilitates securing a wide angle of view is achieved, and a third lens group and an aspherical surface that move off-axis aberration fluctuations at the time of zooming when a zoom ratio is secured. It can be corrected by the fourth lens group, and it is easy to increase the zoom ratio.

  Further, since the first lens group has a negative lens component and a positive lens component in order from the object side, the principal point of the first lens group can be closer to the object side, and the diameter of the first lens group can be reduced. It is also advantageous for correcting off-axis aberrations at the wide-angle end and spherical aberrations at the telephoto end. Furthermore, by making at least one surface of the negative lens component an aspherical surface, it is possible to satisfactorily correct off-axis aberrations at the wide angle end while ensuring the negative refractive power of the negative lens component.

  The location of the aperture stop plays a role of determining the light beam passage position. However, if the aperture stop is arranged near the center of the zoom lens, it becomes easier to balance the size and aberration of each lens group. Compared with the case where the position of the aperture stop is located between the first lens group and the second lens group, the distance between the first lens group and the second lens group can be made closer at the telephoto end, and the high zoom ratio can be achieved. It is advantageous for the conversion. Also, the assembly process is easier than when the aperture stop is positioned between a plurality of lenses in one lens group.

  The second lens group is composed of a positive lens, a positive lens, a negative lens, and a positive lens from the object side, and the function of having an aspherical surface on at least one surface of the positive lens of the second lens group has a variable magnification ratio load. This is a configuration for improving the aberration balance even when the two lens groups are provided. This function is as described above.

  By configuring the second lens group with four lenses, it becomes easy to ensure the zooming function of the second lens group. Therefore, the third lens group having a positive refractive power can be constituted by one lens component that ensures the refractive power for ensuring the correction function. Thereby, it is preferable to reduce the size. Furthermore, when the third lens group is a focusing lens group, the movement burden during focusing can be reduced.

  Further, the fourth lens group is a single lens component having an aspherical surface. This makes it possible to load the fourth lens group to correct field curvature, which is advantageous for maintaining a good aberration balance over the entire zoom range.

  This configuration makes it easy to correct aberrations even if the zoom ratio is ensured. Conditional expression (5) specifically specifies a preferable zoom ratio. It is preferable that various shooting scenes can be handled by ensuring the degree of freedom by changing the angle of view so as not to fall below the lower limit of conditional expression (5). By not exceeding the upper limit, it becomes easy to suppress aberrations occurring in the first lens group and the second lens group, which is advantageous for downsizing and ensuring performance in the entire zoom range.

  A zoom lens that satisfies both the invention in the first aspect and the invention in the second aspect may be used. In addition, a zoom lens that satisfies any one or more of the more preferable components and conditions described in the invention of the first aspect in the zoom lens of the invention of the second aspect can be satisfied at the same time. Good.

  The first lens group may be composed of two single lenses. The third lens group may be composed of a single lens. Furthermore, the fourth lens group may be composed of one single lens. Each is advantageous for cost reduction.

  When the zoom lens has a focusing function, each of the above configurations is in a state of focusing on an object at the farthest distance.

  For conditional expression (1), it is more preferable to set the lower limit to 0.3, more preferably 0.5. The upper limit value is more preferably 0.95, and further preferably 0.9.

  For conditional expression (2), it is more preferable to set the lower limit value to 1.83, more preferably 1.85. More preferably, the upper limit value is 2.0, more preferably 1.9.

  For conditional expression (3), it is more preferable to set the lower limit value to 1.91, more preferably 1.92. The upper limit value is more preferably 2.2, and even more preferably 2.1.

  For conditional expression (4), it is more preferable to set the lower limit to 5.5, more preferably 6.0. The upper limit value is more preferably 11.7, and further preferably 11.4.

  For conditional expression (5), it is more preferable to set the lower limit to 4.1, and more preferably 4.5. It is more preferable to set the upper limit value to 7, more preferably 6.

  For conditional expression (6), it is more preferable to let the lower limit value to be −0.3, more preferably −0.15. More preferably, the upper limit value is 0.3, more preferably 0.15.

  For conditional expression (7), it is more preferable to let the lower limit value to be −0.5, more preferably −0.4. More preferably, the upper limit value is -0.18, more preferably -0.2.

  For conditional expression (8), it is more preferable to let the lower limit value to be 0.17, further 0.18. More preferably, the upper limit value is 0.38, more preferably 0.35.

  The image pickup apparatus of the present invention includes a zoom lens and an image pickup element that is disposed on an image side of the zoom lens and converts an optical image obtained by the zoom lens into an electric signal, and the zoom lens includes the zoom lens described above. Any one of the zoom lenses described above is used. As a result, it is possible to provide an imaging apparatus having a good balance of wide angle of view, high zoom ratio, and miniaturization.

  Furthermore, it is preferable to have an image conversion unit that converts an electrical signal including distortion by a zoom lens into an image signal in which distortion is corrected by image processing. It is possible to record and display images after electrically correcting the distortion of the zoom lens. Therefore, by allowing distortion aberration of the zoom lens to occur, it becomes advantageous for correction of field curvature and coma, and as a result, it becomes easy to obtain good image quality with a small zoom lens.

  In addition, it is preferable to have an image conversion unit that converts an electrical signal including chromatic aberration of magnification due to the zoom lens into an image signal corrected for chromatic aberration of magnification by image processing. It is preferable to have an image conversion unit that converts an electrical signal of an image captured by the zoom lens into an image signal in which color shift due to magnification chromatic aberration is corrected by image processing. By electrically correcting the chromatic aberration of magnification of the zoom lens, a better image can be obtained. By allowing the chromatic aberration of magnification of the zoom lens, the degree of freedom in selecting the lens material can be secured, which is advantageous for cost reduction, thinning, and high performance.

  In the zoom lens according to the present invention, it is preferable that at least one of the lenses constituting the zoom lens is provided with an antireflection coating in all the above-described configurations.

  The zoom lens according to the present invention is a negative-advance zoom lens that is advantageous for securing the angle of view at the wide-angle end and miniaturization, and can provide a zoom lens that is advantageous for securing a zoom ratio and maintaining optical performance. Furthermore, an imaging apparatus including such a zoom lens can be provided.

  Embodiments of a zoom lens and an imaging apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  Examples 1 to 6 of the zoom lens according to the present invention will be described below. FIGS. 1 to 6 show lens cross-sectional views of the wide-angle end (a), the intermediate focal length state (b), and the telephoto end (c) when focusing on an object point at infinity in Examples 1 to 6, respectively. 1 to 6, the first lens group is G1, the second lens group is G2, the brightness (aperture) stop is S, the third lens group is G3, the fourth lens group is G4, and infrared light is limited. A parallel plate constituting the low-pass filter to which the wavelength band limiting coat is applied is indicated by F, a parallel plate of the cover glass of the electronic image sensor is indicated by C, and an image plane is indicated by I. In addition, you may give the multilayer film for a wavelength range restriction | limiting to the surface of the cover glass C. FIG. Further, the cover glass C may have a low-pass filter action.

  In each embodiment, the aperture stop S moves integrally with the second lens group G2. All of the numerical data is data in a state where an object at infinity is focused. The unit of length of each numerical value is mm, and the unit of angle is ° (degree). In all the embodiments, focusing is performed by moving the third lens group G3. Further, the zoom data are values at the wide-angle end (WE), the intermediate zoom state (ST) defined in the present invention, and the telephoto end (TE).

  As shown in FIG. 1, the zoom lens according to the first exemplary embodiment includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, an aperture stop S, and a positive lens. A third lens group G3 having a refractive power of 4 and a fourth lens group G4 having a positive refractive power are disposed.

  Upon zooming from the wide angle end to the telephoto end, the first lens group G1 moves to the image side and then moves to the object side. The second lens group G2 moves to the object side. The third lens group G3 moves to the image side after moving to the object side. The fourth lens group G4 is fixed.

  In order from the object side, the first lens group G1 includes a biconcave negative lens and a positive meniscus lens having a concave surface directed toward the image side. The second lens group G2 includes a biconvex positive lens, a cemented lens of a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side, and a biconvex positive lens. The third lens group G3 is composed of a positive meniscus lens having a convex surface directed toward the image side. The fourth lens group G4 is composed of a positive meniscus lens having a convex surface directed toward the image side.

  An aspherical surface is an image of both sides of a biconcave negative lens of the first lens group G1, both sides of a biconvex positive lens on the object side of the second lens group G2, and an image of a biconvex positive lens on the image side of the second lens group G2. And the image side surface of the positive meniscus lens of the third lens group G3, and both surfaces of the positive meniscus lens of the fourth lens group G4.

  As shown in FIG. 2, the zoom lens of Example 2 includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, an aperture stop S, and a positive A third lens group G3 having a refractive power of 4 and a fourth lens group G4 having a positive refractive power are disposed.

  Upon zooming from the wide angle end to the telephoto end, the first lens group G1 moves to the image side and then moves to the object side. The second lens group G2 moves to the object side. The third lens group G3 moves to the image side after moving to the object side. The fourth lens group G4 is fixed.

  In order from the object side, the first lens group G1 includes a biconcave negative lens and a positive meniscus lens having a concave surface directed toward the image side. The second lens group G2 includes a biconvex positive lens, a cemented lens of a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side, and a biconvex positive lens. The third lens group G3 is composed of a positive meniscus lens having a convex surface directed toward the image side. The fourth lens group G4 is composed of a positive meniscus lens having a convex surface directed toward the image side.

  An aspherical surface is an image of both sides of a biconcave negative lens of the first lens group G1, both sides of a biconvex positive lens on the object side of the second lens group G2, and an image of a biconvex positive lens on the image side of the second lens group G2. This is used for eight surfaces, that is, the image side surface of the positive meniscus lens of the third lens group G3 and both surfaces of the positive meniscus lens of the fourth lens group G4.

  As shown in FIG. 3, the zoom lens of Example 3 includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, an aperture stop S, and a positive A third lens group G3 having a refractive power of 4 and a fourth lens group G4 having a positive refractive power are disposed.

  Upon zooming from the wide angle end to the telephoto end, the first lens group G1 moves to the image side and then moves to the object side. The second lens group G2 moves to the object side. The third lens group G3 moves to the image side after moving to the object side. The fourth lens group G4 is fixed.

  In order from the object side, the first lens group G1 includes a biconcave negative lens and a positive meniscus lens having a concave surface directed toward the image side. The second lens group G2 includes a biconvex positive lens, a cemented lens of a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side, and a biconvex positive lens. The third lens group G3 is composed of a positive meniscus lens having a convex surface directed toward the image side. The fourth lens group G4 is composed of a positive meniscus lens having a convex surface directed toward the image side.

  The aspheric surfaces include both surfaces of the biconcave negative lens of the first lens group G1, both surfaces of the positive meniscus lens of the first lens group G1, both surfaces of the biconvex positive lens on the object side of the second lens group G2, 10 surfaces of the image side surface of the biconvex positive lens on the image side of the lens group G2, the image side surface of the positive meniscus lens of the third lens group G3, and both surfaces of the positive meniscus lens of the fourth lens group G4. Used.

  As shown in FIG. 4, the zoom lens of Example 4 includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, an aperture stop S, and a positive lens. A third lens group G3 having a refractive power of 4 and a fourth lens group G4 having a positive refractive power are disposed.

  Upon zooming from the wide angle end to the telephoto end, the first lens group G1 moves to the image side and then moves to the object side. The second lens group G2 moves to the object side. The third lens group G3 moves to the image side after moving to the object side. The fourth lens group G4 is fixed.

  In order from the object side, the first lens group G1 includes a biconcave negative lens and a positive meniscus lens having a concave surface directed toward the image side. The second lens group G2 includes a biconvex positive lens, a cemented lens of a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side, and a biconvex positive lens. The third lens group G3 is composed of a positive meniscus lens having a convex surface directed toward the image side. The fourth lens group G4 is composed of a positive meniscus lens having a convex surface directed toward the image side.

  The aspherical surfaces include both surfaces of the biconcave negative lens of the first lens group G1, both surfaces of the positive meniscus lens of the first lens group G1, both surfaces of the biconvex positive lens on the object side of the second lens group G2, and the second lens. Used on 10 surfaces of the image side surface of the biconvex positive lens on the image side of the group G2, the image side surface of the positive meniscus lens of the third lens group G3, and both surfaces of the positive meniscus lens of the fourth lens group G4. ing.

  As shown in FIG. 5, the zoom lens of Example 5 includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, an aperture stop S, and a positive lens in order from the object side. A third lens group G3 having a negative refractive power and a fourth lens group G4 having a negative refractive power are disposed.

  Upon zooming from the wide angle end to the telephoto end, the first lens group G1 moves to the image side and then moves to the object side. The second lens group G2 moves to the object side. The third lens group G3 moves to the image side after moving to the object side. The fourth lens group G4 is fixed.

  In order from the object side, the first lens group G1 includes a biconcave negative lens and a positive meniscus lens having a concave surface directed toward the image side. The second lens group G2 includes a positive meniscus lens having a convex surface facing the object side, a cemented lens of a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side, and a biconvex positive lens And consist of The third lens group G3 is composed of a positive meniscus lens having a convex surface directed toward the image side. The fourth lens group G4 is composed of a negative meniscus lens having a convex surface directed toward the image side.

  The aspherical surfaces include both surfaces of the biconcave negative lens of the first lens group G1, both surfaces of the positive meniscus lens of the first lens group G1, both surfaces of the positive meniscus lens on the object side of the second lens group G2, and the second lens group. It is used for 10 surfaces including the image side surface of the biconvex positive lens of G2, the image side surface of the positive meniscus lens of the third lens group G3, and both surfaces of the negative meniscus lens of the fourth lens group G4.

  As shown in FIG. 6, the zoom lens of Example 6 includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a first lens group having a positive refractive power. Three lens groups G3 are arranged.

  Upon zooming from the wide angle end to the telephoto end, the first lens group G1 moves to the image side and then moves to the object side. The second lens group G2 moves to the object side. The third lens group G3 moves to the image side after moving to the object side.

  In order from the object side, the first lens group G1 includes a biconcave negative lens and a positive meniscus lens having a concave surface directed toward the image side. The second lens group G2 includes a positive meniscus lens having a convex surface facing the object side, a cemented lens of a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side, and a biconvex positive lens And consist of The third lens group G3 is composed of a positive meniscus lens having a convex surface directed toward the image side.

  The aspherical surfaces include both surfaces of the biconcave negative lens of the first lens group G1, both surfaces of the positive meniscus lens of the first lens group G1, both surfaces of the positive meniscus lens on the object side of the second lens group G2, and the second lens. It is used on eight surfaces, that is, the image side surface of the biconvex positive lens of the group G2 and the image side surface of the positive meniscus lens of the third lens group G3.

Below, the numerical data of each said Example are shown. Symbols are the above, f is the focal length of the entire system, BF is the back focus, f1, f2... Are the focal lengths of the lens groups, IH is the image height, _FNO is the F number, ω is the half field angle, and WE is the wide angle. ST, intermediate focal length state, TE telephoto end, r1, r2..., Radius of curvature of each lens surface, d1, d2..., Spacing between lens surfaces, nd1, nd2. The ratio, νd1, νd2,... Is the Abbe number of each lens. The total lens length described later is obtained by adding back focus to the distance from the lens front surface to the lens final surface. BF (back focus) represents the distance from the last lens surface to the paraxial image plane in terms of air.

Each aspheric shape is expressed by the following expression using each aspheric coefficient in each embodiment.
However, the coordinate in the optical axis direction is Z and the coordinate in the direction perpendicular to the optical axis is Y.
Z = (Y ² / r) / [1+ {1− (1 + K) · (Y / r) ² } ^1/2 ]
+ A4 × Y ⁴ + A6 × Y ⁶ + A8 × Y ⁸ + A10 × Y ¹⁰ + A12 × Y ¹²
Here, r is a paraxial radius of curvature, K is a conical coefficient, and A4, A6, A8, A10, and A12 are fourth, sixth, eighth, tenth, and twelfth aspheric coefficients, respectively. In the aspheric coefficient, “e−n” (n is an integer) indicates “10 ⁻ⁿ ”.

Numerical example 1
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * -36.121 0.85 1.85135 40.10
2 * 6.613 2.40
3 12.132 1.76 1.92286 18.90
4 32.163 Variable
5 * 6.094 1.63 1.58313 59.38
6 * -193.979 0.10
7 7.205 1.70 1.88300 40.76
8 35.008 0.68 1.84666 23.78
9 4.067 0.80
10 42.637 0.80 1.52540 56.25
11 * -15.492 0.30
12 (Aperture) ∞ Variable
13 -18.564 1.27 1.52540 56.25
14 * -10.395 variable
15 * -16.887 0.85 1.52540 56.25
16 * -11.717 0.30
17 ∞ 0.50 1.51633 64.14
18 ∞ 0.50
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.37
Image plane ∞

Aspheric data first surface
K = 0.000
A4 = 5.23384e-04, A6 = -8.99800e-06, A8 = 5.58642e-08
Second side
K = 0.000
A4 = 1.53184e-04, A6 = 2.36186e-06, A8 = -4.85067e-07
5th page
K = 0.000
A4 = -6.87558e-04, A6 = 3.61041e-05, A8 = -2.43068e-06
6th page
K = 0.000
A4 = -2.16456e-04, A6 = 5.64134e-05, A8 = -3.68492e-06
11th page
K = 0.000
A4 = 3.42256e-04, A6 = -6.70299e-05, A8 = 1.21276e-05
14th page
K = 0.000
A4 = 1.34406e-04, A6 = 1.61801e-06, A8 = -2.13189e-07
15th page
K = 0.000
A4 = -3.47016e-03, A6 = 1.29634e-04
16th page
K = 0.000
A4 = -3.11938e-03, A6 = 1.39866e-04

Zoom data
Wide angle Medium telephoto focal length 4.48 9.90 21.39
Fno. 2.86 4.45 6.12
Angle of view 2ω 89.98 41.95 19.71
BF 1.83 1.83 1.83
Total length 38.16 31.33 37.38
d4 17.49 5.26 0.20
d12 2.78 7.54 20.25
d14 2.92 3.57 1.96

Each group focal length
f1 = -11.16 f2 = 9.90 f3 = 42.68 f4 = 68.94

Numerical example 2
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * -39.192 0.85 1.85135 40.10
2 * 6.869 2.41
3 11.734 1.58 1.94595 17.98
4 25.053 Variable
5 * 6.133 1.52 1.58313 59.38
6 * -329.489 0.10
7 7.223 1.69 1.88300 40.76
8 25.780 0.60 1.84666 23.78
9 4.136 0.70
10 45.318 0.81 1.58313 59.38
11 * -15.535 0.30
12 (Aperture) ∞ Variable
13 -17.977 1.32 1.52540 56.25
14 * -10.904 variable
15 * -16.661 0.85 1.52540 56.25
16 * -11.659 0.30
17 ∞ 0.50 1.51633 64.14
18 ∞ 0.50
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.37
Image plane ∞

Aspheric data first surface
K = 0.000
A4 = 5.35330e-04, A6 = -8.67116e-06, A8 = 4.51209e-08
Second side
K = 0.000
A4 = 2.38314e-04, A6 = 5.35853e-06, A8 = -4.99255e-07
5th page
K = 0.000
A4 = -7.70741e-04, A6 = 2.83015e-05, A8 = -4.35533e-06
6th page
K = 0.000
A4 = -3.14549e-04, A6 = 3.60394e-05, A8 = -4.98647e-06
11th page
K = 0.000
A4 = 2.43798e-04, A6 = -4.53369e-05, A8 = 8.62818e-06
14th page
K = 0.000
A4 = 2.38072e-04, A6 = -1.20387e-05, A8 = 4.38193e-08
15th page
K = 0.000
A4 = -1.63985e-03, A6 = 2.23619e-05
16th page
K = 0.000
A4 = -1.06692e-03, A6 = 3.12519e-05

Zoom data
Wide angle Medium telephoto focal length 4.62 10.06 21.95
Fno. 2.86 4.37 6.12
Angle of view 2ω 88.13 41.33 19.21
BF 1.83 1.83 1.83
Total length 37.70 31.20 37.35
d4 17.07 5.27 0.20
d12 2.86 7.42 20.66
d14 3.22 3.96 1.94

Each group focal length
f1 = -11.17 f2 = 9.85 f3 = 49.57 f4 = 69.82

Numerical Example 3
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * -55.310 0.85 1.85135 40.10
2 * 6.568 2.22
3 * 9.905 1.80 2.00178 19.30
4 * 17.477 Variable
5 * 5.848 1.70 1.58313 59.38
6 * -595.150 0.10
7 7.072 1.55 1.88300 40.76
8 15.131 0.60 1.84666 23.78
9 4.052 0.70
10 17.929 0.75 1.58313 59.38
11 * -34.293 0.30
12 (Aperture) ∞ Variable
13 -8.791 1.30 1.52540 56.25
14 * -6.930 variable
15 * -12.362 0.85 1.52540 56.25
16 * -12.086 0.30
17 ∞ 0.50 1.51633 64.14
18 ∞ 0.50
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.37
Image plane ∞

Aspheric data first surface
K = 0.000
A4 = 6.29147e-04, A6 = -1.09060e-05, A8 = 5.99850e-08
Second side
K = 0.000
A4 = -3.60728e-04, A6 = 4.71665e-05, A8 = -1.23411e-06
Third side
K = 0.000
A4 = -1.10232e-03, A6 = 3.73924e-05, A8 = -4.29166e-07
4th page
K = 0.000
A4 = -8.55694e-04, A6 = 2.65450e-05, A8 = -3.14820e-07
5th page
K = 0.000
A4 = -5.10380e-04, A6 = 7.65810e-06, A8 = -2.83620e-07
6th page
K = 0.000
A4 = -3.00819e-05, A6 = 1.81730e-05, A8 = -3.80335e-07
11th page
K = 0.000
A4 = 4.60385e-04, A6 = -3.37836e-05, A8 = 6.28934e-06
14th page
K = 0.000
A4 = 2.07326e-04, A6 = 4.98692e-06, A8 = 2.33245e-07
15th page
K = 0.000
A4 = -3.49411e-03, A6 = 9.13012e-05
16th page
K = 0.000
A4 = -2.45682e-03, A6 = 5.95790e-05

Zoom data
Wide angle Medium telephoto focal length 4.51 9.90 25.07
Fno. 2.87 4.28 6.16
Angle of view 2ω 90.09 41.75 16.81
BF 1.83 1.83 1.83
Total length 39.69 31.18 38.14
d4 19.34 6.02 0.20
d12 2.93 5.39 21.93
d14 2.87 5.22 1.46

Each group focal length
f1 = -11.34 f2 = 9.66 f3 = 50.22 f4 = 500.26

Numerical Example 4
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * -58.197 0.85 1.85135 40.10
2 * 6.557 2.19
3 * 9.191 1.76 2.00178 19.30
4 * 15.054 variable
5 * 5.701 1.83 1.58313 59.38
6 * -5147.531 0.10
7 7.163 1.49 1.88300 40.76
8 15.469 0.60 1.84666 23.78
9 4.145 0.70
10 17.199 0.66 1.58313 59.38
11 * -42.828 0.30
12 (Aperture) ∞ Variable
13 -8.752 1.38 1.52540 56.25
14 * -6.937 variable
15 * -12.070 0.85 1.52540 56.25
16 * -12.311 0.30
17 ∞ 0.50 1.51633 64.14
18 ∞ 0.50
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.37
Image plane ∞

Aspheric data first surface
K = 0.000
A4 = 6.75398e-04, A6 = -1.18456e-05, A8 = 6.58162e-08
Second side
K = 0.000
A4 = -4.06863e-04, A6 = 5.13645e-05, A8 = -1.29930e-06
Third side
K = 0.000
A4 = -1.30204e-03, A6 = 3.92755e-05, A8 = -4.08741e-07
4th page
K = 0.000
A4 = -1.01988e-03, A6 = 2.83769e-05, A8 = -2.90079e-07
5th page
K = 0.000
A4 = -4.59761e-04, A6 = 3.75214e-06, A8 = 4.21709e-07
6th page
K = 0.000
A4 = 2.45003e-05, A6 = 1.89720e-05, A8 = 1.50558e-07
11th page
K = 0.000
A4 = 7.04505e-04, A6 = -4.01432e-05, A8 = 1.07392e-05
14th page
K = 0.000
A4 = 1.91230e-04, A6 = 3.08490e-06, A8 = 4.59629e-07
15th page
K = 0.000
A4 = -3.40694e-03, A6 = 1.10543e-04
16th page
K = 0.000
A4 = -2.05594e-03, A6 = 5.90357e-05

Zoom data
Wide angle Medium Telephoto focal length 4.45 9.90 25.70
Fno. 2.86 4.29 6.12
Angle of view 2ω 90.93 41.60 16.38
BF 1.83 1.83 1.83
Total length 39.72 31.04 38.35
d4 19.55 6.06 0.20
d12 3.02 5.34 22.13
d14 2.62 5.11 1.48

Each group focal length
f1 = -11.22 f2 = 9.53 f3 = 50.49 f4 = 5471.43

Numerical Example 5
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * -75.513 0.85 1.85135 40.10
2 * 6.575 1.87
3 * 8.310 1.83 2.00178 19.30
4 * 13.070 Variable
5 * 5.923 1.72 1.58313 59.38
6 * 77.755 0.10
7 7.546 1.41 1.88300 40.76
8 17.737 0.60 1.84666 23.78
9 4.669 0.70
10 11.982 0.60 1.58313 59.38
11 * -263.242 0.30
12 (Aperture) ∞ Variable
13 -8.490 1.69 1.58313 59.38
14 * -6.138 variable
15 * -8.555 0.85 1.52540 56.25
16 * -15.738 0.30
17 ∞ 0.50 1.51633 64.14
18 ∞ 0.50
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.37
Image plane ∞

Aspheric data first surface
K = 0.000
A4 = 6.33994e-04, A6 = -1.09314e-05, A8 = 5.62486e-08
Second side
K = 0.000
A4 = -6.33514e-04, A6 = 6.19211e-05, A8 = -1.45182e-06
Third side
K = 0.000
A4 = -1.56534e-03, A6 = 4.77192e-05, A8 = -5.32958e-07
4th page
K = 0.000
A4 = -1.18060e-03, A6 = 3.31937e-05, A8 = -3.42019e-07
5th page
K = 0.000
A4 = -3.80197e-04, A6 = 2.27438e-06, A8 = -4.02765e-07
6th page
K = 0.000
A4 = -1.05596e-04, A6 = 5.81845e-06, A8 = -5.19839e-07
11th page
K = 0.000
A4 = 9.91845e-04, A6 = 3.99228e-06, A8 = 7.49200e-06
14th page
K = 0.000
A4 = 3.97998e-04, A6 = 8.60846e-06, A8 = 4.07634e-07
15th page
K = 0.000
A4 = -6.69660e-03, A6 = 2.45830e-04
16th page
K = 0.000
A4 = -6.14930e-03, A6 = 1.93177e-04

Zoom data
Wide angle Medium Telephoto focal length 4.79 9.85 26.72
Fno. 2.86 4.08 6.12
Angle of view 2ω 85.78 42.15 15.75
BF 1.83 1.83 1.83
Total length 39.81 31.71 38.65
d4 19.36 6.97 0.20
d12 3.29 6.80 21.94
d14 2.82 3.61 2.18

Each group focal length
f1 = -11.78 f2 = 9.71 f3 = 30.06 f4 = -37.19

Numerical Example 6
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * -94.381 0.85 1.85 135 40.10
2 * 6.612 2.31
3 * 8.592 1.73 2.00178 19.30
4 * 13.008 Variable
5 * 5.763 1.77 1.58313 59.38
6 * 142.941 0.10
7 6.939 1.73 1.88300 40.76
8 16.536 0.60 1.84666 23.78
9 4.057 0.70
10 13.551 0.60 1.58313 59.38
11 * -437.950 0.30
12 (Aperture) ∞ Variable
13 -9.634 1.36 1.52540 56.25
14 * -7.140 variable
15 ∞ 0.50 1.51633 64.14
16 ∞ 0.50
17 ∞ 0.50 1.51633 64.14
18 ∞ 0.37
Image plane ∞

Aspheric data first surface
K = 0.000
A4 = 7.26361e-04, A6 = -1.29478e-05, A8 = 6.89655e-08
Second side
K = 0.000
A4 = -3.58096e-04, A6 = 4.77895e-05, A8 = -1.22371e-06
Third side
K = 0.000
A4 = -1.40387e-03, A6 = 3.14286e-05, A8 = -3.00061e-07
4th page
K = 0.000
A4 = -1.12627e-03, A6 = 2.31533e-05, A8 = -2.10399e-07
5th page
K = 0.000
A4 = -4.56577e-04, A6 = 7.52433e-06, A8 = -4.36188e-07
6th page
K = 0.000
A4 = -6.09644e-05, A6 = 1.56792e-05, A8 = -5.60172e-07
11th page
K = 0.000
A4 = 9.34937e-04, A6 = 6.99884e-06, A8 = 1.07582e-05
14th page
K = 0.000
A4 = 5.64174e-04, A6 = -1.18595e-05, A8 = 6.85347e-07

Zoom data
Wide angle Medium telephoto focal length 4.57 9.83 25.46
Fno. 2.86 4.33 6.12
Angle of view 2ω 90.63 42.27 16.73
BF 5.28 5.57 4.62
Total length 38.89 31.11 38.13
d4 19.07 6.65 0.20
d12 2.49 6.84 21.26
d14 3.75 4.04 3.09

Each group focal length
f1 = -11.79 f2 = 9.63 f3 = 44.19

  Aberration diagrams at the time of focusing on an object point at infinity in Examples 1 to 6 are shown in FIGS. In these aberration diagrams, (a) is the wide angle end, (b) is the intermediate focal length state, (c) is the spherical aberration (SA), astigmatism (AS), distortion (DT), and magnification at the telephoto end. Chromatic aberration (CC) is shown. In each figure, “ω” indicates a half angle of view.

Next, the values of conditional expressions (1) to (8) in each example will be listed. The image height at the intermediate and telephoto ends is 3.83 mm. Regarding the distortion correction, there is no change to the above-described values in the intermediate focal length state and the telephoto end state. For this reason, the description of overlapping values is omitted.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6
Distortion correction image height (wide-angle end) 3.49 3.49 3.49 3.49 3.51 3.48
Full field angle after distortion correction (wide-angle end) 82.85 81.05 82.40 83.12 79.01 81.64


<Conditional expression>
Example 1 Example 2 Example 3 Example 4 Example 5 Example 6
(1) (R ₁ + R ₂ ) / (R ₁ −R ₂ )
0.69 0.7 0.79 0.8 0.84 0.87
(2) N ₁ 1.85135 1.85135 1.85135 1.85135 1.85135 1.85135
(3) N ₂ 1.92286 1.94595 2.00178 2.00178 2.00178 2.00178
(4) f ₃ / f _w 9.54 10.73 11.14 11.34 6.28 9.67
(5) f _t / f _w 4.78 4.75 5.56 5.77 5.58 5.57
(6) f ₄ / f _w 0.06491 0.06616 0.00901 0.00081 -0.12877-
(7) f ₁ / f ₃ -0.261 -0.225 -0.226 -0.222 -0.392 -0.267
(8) f ₂ / f ₃ 0.232 0.199 0.192 0.189 0.323 0.218

(Anti-reflective coating)
In order to prevent the occurrence of ghost and flare, it is common practice to apply an antireflection coating to the air contact surface of the lens. On the other hand, the refractive index of the adhesive is sufficiently higher than the refractive index of air on the cemented surface of the cemented lens. For this reason, the reflectance is often the same as or lower than that of a single-layer coating, and it is rare to apply a coating.

  However, if an anti-reflection coating is also applied to the joint surface, ghosts and flares can be further reduced, and still better images can be obtained. In recent years, high refractive index glass materials have become widespread and have been used extensively in camera optical systems due to their high aberration correction effects. However, when high refractive index glass materials are used as cemented lenses, reflection on the cemented surface is ignored. It becomes impossible. In such a case, it is particularly effective to provide an antireflection coating on the joint surface.

The effective usage of the bonding surface coat is disclosed in JP-A-2-27301, JP-A-2001-324676, JP-A-2005-92115, USP 7116482, and the like. As a coating material to be used, Ta ₂ O ₅ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , HfO ₂ , and CeO having a relatively high refractive index are selected according to the refractive index of the base lens and the refractive index of the adhesive. ₂ , SnO ₂ , In ₂ O ₃ , ZnO, Y ₂ O 3 and other coating materials, relatively low refractive index MgF ₂ , SiO ₂ , Al ₂ O ₃ coating materials, etc. What is necessary is just to set to the film thickness which satisfy | fills.

  As a matter of course, the coating on the bonding surface may be a multi-coat as in the case of the coating on the air contact surface of the lens. By appropriately combining two or more layers of coating materials and film thicknesses, it becomes possible to further reduce the reflectance and control the spectral characteristics and angular characteristics of the reflectance. Needless to say, it is effective to coat the cemented surfaces other than the first lens group based on the same concept.

(Distortion signal processing)
In the zoom lens of this embodiment, barrel distortion occurs at the wide-angle end on the rectangular photoelectric conversion surface. On the other hand, the occurrence of distortion is suppressed near the intermediate focal length state and at the telephoto end. In order to electrically correct the distortion, the effective imaging area has a barrel shape at the wide angle end and a rectangular shape at the intermediate focal length state or the telephoto end. Then, the effective imaging area set in advance is image-converted by image processing and converted into rectangular image information with reduced distortion. The image height IHw at the wide angle end is set to be smaller than the image height IHs at the intermediate focal length state and the image height IHt at the telephoto end.

(Signal processing of chromatic aberration of magnification)
In general, in an electronic still camera, an image of a subject is separated into three primary color images of a first primary color, a second primary color, and a third primary color, and a color image is reproduced by superimposing respective output signals by calculation. I have to. When the zoom lens has chromatic aberration of magnification, the image of the first primary color is formed at the position where the image of the second primary color and the third primary light is formed, considering the image of the first primary color as a reference. Will deviate from the position.

  In order to electronically correct the magnification chromatic aberration of the image, the amount of deviation of the imaging position of the light of the second primary color and the third primary color with respect to the first primary color is determined for each pixel of the image sensor based on the aberration information of the zoom lens. Find in advance. Then, coordinate conversion may be performed for each pixel of the captured image so as to correct the amount of deviation from the first primary color. For example, if an image composed of output signals of three primary colors of red (R), green (G), and blue (B) is described, an R and B imaging position shift with respect to G is obtained for each pixel. It is only necessary to perform coordinate conversion of the captured image so as to eliminate the deviation, and then output R and B signals.

  The chromatic aberration of magnification varies depending on the zoom, focus, and aperture value, but for each lens position (zoom, focus, and aperture value), the deviation amounts of the second primary color and the third primary color from the first primary color are stored and retained as correction data. It may be stored in the device. By referring to the correction data according to the zoom position, it is possible to output the second and third primary color signals in which the deviation of the second and third primary colors from the first primary color signal is corrected.

(Correction of distortion)
By the way, when the zoom lens of the present invention is used, image distortion is digitally corrected electrically. The basic concept for digitally correcting image distortion will be described below.

  For example, as shown in FIG. 13, the magnification on the circumference (image height) of the radius R inscribed in the long side of the effective imaging surface around the intersection of the optical axis and the imaging surface is fixed, and this circumference is The standard for correction. Then, correction is performed by moving each point on the circumference (image height) of any other radius r (ω) in a substantially radial direction and concentrically so as to have the radius r ′ (ω). To do.

For example, in FIG. 13, a point P ₁ on the circumference of an arbitrary radius r ₁ (ω) located inside the circle of radius R is a radius r ₁ ′ (ω) circle to be corrected toward the center of the circle. point on the circumference moves to P _2. A point Q ₁ on the circumference of an arbitrary radius r ₂ (ω) located outside the circle of radius R is a radius r ₂ ′ (ω) circumference to be corrected in a direction away from the center of the circle. It is moved to the point Q ₂ of the above.

Here, r ′ (ω) can be expressed as follows.
r ′ (ω) = α · f · tan ω (0 ≦ α ≦ 1)
However,
ω is the subject half angle of view, and f is the focal length of the imaging optical system (in the present invention, the zoom lens).

Here, if the ideal image height corresponding to the circle (image height) of the radius R is Y,
α = R / Y = R / (f · tan ω)
It becomes.

  The optical system is ideally rotationally symmetric with respect to the optical axis, that is, distortion is also generated rotationally symmetric with respect to the optical axis. Therefore, as described above, when the optically generated distortion aberration is electrically corrected, the radius inscribed in the long side of the effective imaging surface around the intersection of the optical axis and the imaging surface on the reproduced image. The magnification on the circumference of the circle of R (image height) is fixed, and the other points on the circumference of the circle (image height) of radius r (ω) are moved in a substantially radial direction to obtain a radius r ′ ( If correction can be performed by moving the concentric circles so that ω), it is considered advantageous in terms of data amount and calculation amount.

  However, the optical image is no longer a continuous amount (due to sampling) when captured by the electronic image sensor. Therefore, strictly speaking, the circle with the radius R drawn on the optical image is not an accurate circle unless the pixels on the electronic image sensor are arranged radially.

  That is, in the shape correction of the image data represented for each discrete coordinate point, there is no circle that can fix the magnification. Therefore, it is preferable to use a method of determining the coordinates (Xi ′, Yj ′) of the movement destination for each pixel (Xi, Yj). When two or more points (Xi, Yj) have moved to the coordinates (Xi ′, Yj ′), the average value of the values of each pixel is taken. If there is no moving point, interpolation may be performed using the values of the coordinates (Xi ′, Yj ′) of some surrounding pixels.

  Such a method is particularly distorted with respect to the optical axis due to manufacturing errors of an optical system and an electronic imaging device in an electronic imaging apparatus having a zoom lens, and the circle with the radius R drawn on the optical image is It is effective for correction when it becomes asymmetric. Further, it is effective for correction when a geometric distortion or the like occurs when a signal is reproduced as an image in an image sensor or various output devices.

  In the electronic imaging apparatus of the present invention, in order to calculate the correction amount r ′ (ω) −r (ω), r (ω), that is, the relationship between the half field angle and the image height, or the real image height r and the ideal image height. The relationship between r ′ / α may be recorded on a recording medium built in the electronic imaging apparatus.

  Note that the radius R preferably satisfies the following conditional expression so that the image after distortion correction does not have an extremely short amount of light at both ends in the short side direction.

0 ≦ R ≦ 0.6Ls
However, Ls is the length of the short side of the effective imaging surface.

Preferably, the radius R satisfies the following conditional expression.
0.3Ls ≦ R ≦ 0.6Ls
Furthermore, it is most advantageous to make the radius R coincide with the radius of the inscribed circle in the short side direction of the substantially effective imaging surface. In the case of correction in which the magnification is fixed in the vicinity of the radius R = 0, that is, in the vicinity of the axis, there is a slight disadvantage in terms of image quality, but the effect of downsizing can be ensured even if the angle is widened.

The focal length section that needs to be corrected is divided into several focal zones. And approximately near the telephoto end in the divided focal zone,
r ′ (ω) = α · f · tan ω
You may correct | amend with the same correction amount as the case where the correction result which satisfies is obtained.

  However, in that case, some barrel distortion remains at the wide-angle end in the divided focal zone. Further, if the number of divided zones is increased, it becomes unnecessary to store extraneous data necessary for correction on the recording medium, which is not preferable. Therefore, one or several coefficients related to each focal length in the divided focal zone are calculated in advance. This coefficient may be determined on the basis of simulation or actual measurement.

And approximately near the telephoto end in the divided zone,
r ′ (ω) = α · f · tan ω
It is also possible to calculate a correction amount when a correction result satisfying the above is obtained, and uniformly multiply the correction amount for each focal distance to obtain a final correction amount.

By the way, if there is no distortion in the image obtained by imaging an object at infinity,
f = y / tan ω
Is established.
Where y is the height of the image point from the optical axis (image height), f is the focal length of the imaging system (in the present invention, the zoom lens), and ω is the image point connected from the center on the imaging surface to the y position. It is an angle (subject half field angle) with respect to the optical axis in the corresponding object direction.

If the imaging system has barrel distortion,
f> y / tan ω
It becomes. That is, if the focal length f of the imaging system and the image height y are constant, the value of ω increases.

(Digital camera)
14 to 16 are conceptual diagrams of the configuration of the digital camera according to the present invention in which the zoom lens as described above is incorporated in the photographing optical system 141. FIG. 14 is a front perspective view showing the appearance of the digital camera 140, FIG. 15 is a rear front view thereof, and FIG. 16 is a schematic cross-sectional view showing the configuration of the digital camera 140. However, in FIGS. 14 and 16, the photographing optical system 141 is not retracted. In this example, the digital camera 140 includes a photographing optical system 141 having a photographing optical path 142, a finder optical system 143 having a finder optical path 144, a shutter button 145, a flash 146, a liquid crystal display monitor 147, a focal length change button 161, When the photographic optical system 141 is retracted, including the setting change switch 162, the photographic optical system 141, the finder optical system 143, and the flash 146 are covered with the cover 160 by sliding the cover 160. When the cover 160 is opened and the camera 140 is set to the photographing state, the photographing optical system 141 is brought into the non-collapsed state of FIG. 16, and when the shutter button 145 arranged on the upper part of the camera 140 is pressed, photographing is performed in conjunction therewith. Photographing is performed through the optical system 141, for example, the zoom lens of the first embodiment. An object image formed by the photographic optical system 141 is formed on the imaging surface of the CCD 149 through a low-pass filter F and a cover glass C that are provided with a wavelength band limiting coat. The object image received by the CCD 149 is displayed as an electronic image on a liquid crystal display monitor 147 provided on the back of the camera via the processing means 151. Further, the processing means 151 is connected to a recording means 152 so that a photographed electronic image can be recorded. The recording unit 152 may be provided separately from the processing unit 151, or may be configured to perform recording / writing electronically using a flexible disk, a memory card, an MO, or the like. Further, instead of the CCD 149, a silver salt camera in which a silver salt film is arranged may be configured.

  Further, a finder objective optical system 153 is disposed on the finder optical path 144. The finder objective optical system 153 includes a plurality of lens groups (three groups in the figure) and two prisms, and includes a zoom optical system whose focal length changes in conjunction with the zoom lens of the photographing optical system 141. The object image formed by the finder objective optical system 153 is formed on the field frame 157 of the erecting prism 155 that is an image erecting member. Behind the erecting prism 155, an eyepiece optical system 159 that guides the erect image to the observer eyeball E is disposed. A cover member 150 is disposed on the exit side of the eyepiece optical system 159.

  The digital camera 140 configured in this way has the imaging optical system 141 according to the present invention, which is extremely thin when retracted, and has high zooming performance and extremely stable imaging performance in the entire zooming range. Miniaturization and wide angle can be realized.

(Internal circuit configuration)
FIG. 17 is a block diagram showing the internal circuitry of the main part of the digital camera 140. In the following description, the processing means includes, for example, the CDS / ADC unit 124, the temporary storage memory 117, the image processing unit 118, and the like, and the storage means includes, for example, the storage medium unit 119.

  As shown in FIG. 17, the digital camera 140 is connected to the operation unit 112, the control unit 113 connected to the operation unit 112, and the control signal output port of the control unit 113 via buses 114 and 115. An imaging drive circuit 116, a temporary storage memory 117, an image processing unit 118, a storage medium unit 119, a display unit 120, and a setting information storage memory unit 121 are provided.

  The temporary storage memory 117, the image processing unit 118, the storage medium unit 119, the display unit 120, and the setting information storage memory unit 121 are configured so that data can be input or output with each other via the bus 122. In addition, a CCD 149 and a CDS / ADC unit 124 are connected to the imaging drive circuit 116.

  The operation unit 112 includes various input buttons and switches, and is a circuit that notifies the control unit of event information input from the outside (camera user) via these input buttons and switches.

  The control unit 113 is a central processing unit composed of, for example, a CPU and the like. The control unit 113 includes a program memory (not shown) and is input from the camera user via the operation unit 112 according to a program stored in the program memory. This is a circuit that controls the entire digital camera 140 in response to an instruction command.

  The CCD 149 receives an object image formed through the photographing optical system 141 according to the present invention. The CCD 149 is an image pickup element that is driven and controlled by the image pickup drive circuit 116, converts the light amount of each pixel of the object image into an electrical signal, and outputs the electric signal to the CDS / ADC unit 124.

  The CDS / ADC unit 124 amplifies the electric signal input from the CCD 149 and performs analog / digital conversion, and temporarily stores the raw video data (Bayer data, hereinafter referred to as RAW data) that has just been subjected to the amplification and digital conversion. This is a circuit for outputting to the storage memory 117.

  The temporary storage memory 117 is a buffer made of, for example, SDRAM or the like, and is a memory device that temporarily stores the RAW data output from the CDS / ADC unit 124. The image processing unit 118 reads out the RAW data stored in the temporary storage memory 117 or the RAW data stored in the storage medium unit 119, and performs various corrections including distortion correction based on the image quality parameter designated from the control unit 113. It is a circuit that performs image processing electrically.

  The recording medium unit 119 detachably mounts a card-type or stick-type recording medium made of, for example, a flash memory, and RAW data transferred from the temporary storage memory 117 to the card-type or stick-type flash memory. This is a control circuit of an apparatus for recording and holding image data processed by the image processing unit 118.

  The display unit 120 includes a liquid crystal display monitor, and is a circuit that displays an image, an operation menu, and the like on the liquid crystal display monitor. The setting information storage memory unit 121 stores a ROM unit in which various image quality parameters are stored in advance, and an image quality parameter selected by an input operation of the operation unit 112 among the image quality parameters read from the ROM unit. RAM section is provided. The setting information storage memory unit 121 is a circuit that controls input and output to these memories.

  In the digital camera 140 configured in this way, the imaging optical system 141 has a sufficiently wide angle range and a compact configuration according to the present invention, and the imaging performance is extremely stable at a high zoom ratio and in a full zoom ratio range. Therefore, high performance, downsizing, and wide angle can be realized. In addition, fast focusing operation on the wide-angle side and the telephoto side is possible.

  As described above, the zoom lens according to the present invention is useful for securing optical performance and reducing the size while having a high zoom ratio.

FIG. 2 is a lens cross-sectional view at the wide-angle end (a), the intermediate state (b), and the telephoto end (c) when focusing on an object point at infinity according to the first exemplary embodiment of the zoom lens of the present invention. It is the same figure as FIG. 1 of Example 2 of the zoom lens of this invention. It is the same figure as FIG. 1 of Example 3 of the zoom lens of this invention. It is the same figure as FIG. 1 of Example 4 of the zoom lens of this invention. It is the same figure as FIG. 1 of Example 5 of the zoom lens of this invention. It is the same figure as FIG. 1 of Example 6 of the zoom lens of this invention. FIG. 6 is an aberration diagram for Example 1 upon focusing on an object point at infinity. FIG. 6 is an aberration diagram for Example 2 upon focusing on an object point at infinity. FIG. 10 is an aberration diagram for Example 3 upon focusing on an object point at infinity. FIG. 10 is an aberration diagram for Example 4 upon focusing on an object point at infinity. FIG. 10 is an aberration diagram for Example 5 upon focusing on an object point at infinity. FIG. 10 is an aberration diagram for Example 6 upon focusing on an object point at infinity. It is a figure explaining correction | amendment of a distortion aberration. It is a front perspective view which shows the external appearance of the digital camera incorporating the retractable zoom lens by this invention. It is a rear perspective view of the digital camera. It is sectional drawing of the said digital camera. It is a block diagram of the internal circuit of the main part of the digital camera.

Explanation of symbols

G1 ... 1st lens group G2 ... 2nd lens group G3 ... 3rd lens group G4 ... 4th lens group S ... Brightness stop LPF ... Low pass filter CG ... Cover Glass I ... Image surface 112 ... Operation unit 113 ... Control unit 114 ... Bus 115 ... Bus 116 ... Imaging drive circuit 117 ... Temporary storage memory 118 ... Image processing unit 119: Storage medium unit 120: Display unit 121: Setting information storage memory unit 122 ... Bus 124 ... CDS / ADC unit 140 ... Digital camera 141 ... Imaging optical system 142 ..Optical path for photographing 143 ... finder optical system 144 ... optical path for viewfinder 145 ... shutter button 146 ... flash 147 ... liquid crystal display monitor 149 ... CCD
150 ... cover member 151 ... processing means 152 ... recording means 153 ... finder objective optical system 155 ... erecting prism 157 ... field frame 159 ... eyepiece optical system 160 ... -Cover 161 ... Focal length change button 162 ... Setting change switch

Claims (14)

From the object side,
A first lens group having negative refractive power;
A second lens group having a positive refractive power;
A third lens group having positive refractive power;
Have
The second lens group and the third lens group move so that the distance between the lens groups changes during zooming from the wide-angle end to the telephoto end,
The first lens group includes, in order from the object side, a biconcave negative lens component having an aspheric surface, and a positive lens component.
The negative lens component has a shape that satisfies the following conditional expression (1):
The negative lens component has a negative lens that satisfies the following conditional expression (2):
The positive lens component has a positive lens that satisfies the following conditional expression (3):
The zoom lens according to claim 3, wherein the third lens group satisfies the following conditional expression (4).
0.2 <(R ₁ + R ₂ ) / (R ₁ −R ₂ ) <0.99 (1)
1.81 <N ₁ <2.35 (2)
1.9 <N ₂ <2.35 (3)
4.5 <f ₃ / f _w <12.0 (4)
However,
R ₁ is the paraxial radius of curvature of the object side surface of the negative lens component of the first lens group,
R ₂ is the paraxial radius of curvature of the image side surface of the negative lens component of the first lens group,
N ₁ is the refractive index with respect to the d-line of any negative lens in the negative lens component of the first lens group,
N ₂ is a refractive index with respect to d-line of any positive lens in the positive lens component of the first lens group,
f ₃ is the focal length of the third lens group,
f _w is the focal length of the entire zoom lens system at the wide-angle end,
Der is,
The lens component means a lens body having only two surfaces that are in contact with air on the optical axis, that is, the object side surface and the image side surface.   At the time of zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group becomes narrow, and the distance between the second lens group and the third lens group changes. 2. The zoom lens according to claim 1, wherein the zoom lens moves while moving the third lens group in the optical axis direction during focusing.   The zoom lens according to claim 1, wherein each of the negative lens component and the positive lens component in the first lens group has only one glass lens. The zoom lens according to any one of claims 1 to 3, wherein the third lens group satisfies the following conditional expression (4 ').
5.5 <f ₃ / f _w <12.0 (4 ′)   5. The zoom lens according to claim 1, further comprising an aperture stop disposed immediately after the image side of the second lens group.   The most image side surface of the first lens group has a shape with a concave surface facing the image side, and the most object side surface of the second lens group has a shape with a convex surface facing the object side. The zoom lens according to claim 5.   The zoom lens according to any one of claims 1 to 6, further comprising a fourth lens group that is disposed on the image side of the third lens group and includes a single lens having an aspherical surface. The zoom lens according to claim 7, wherein the fourth lens group satisfies the following conditional expression.
−0.5 <(f ₄ / f _w ) ⁻¹ <0.5 (6)
Here, f ₄ is the focal length of the fourth lens group.   The second lens group includes, in order from the object side, a first positive lens, a second positive lens, a negative lens, and a third positive lens, and any one of the first to third positive lenses. The zoom lens according to claim 1, wherein the zoom lens has an aspherical surface. 10. The device according to claim 1, wherein the first lens group, the second lens group, and the third lens group satisfy the following conditional expressions (7) and (8): The described zoom lens.
−0.6 <f ₁ / f ₃ <−0.16 (7)
0.15 <f ₂ / f ₃ <0.42 (8)
However,
f ₁ is the focal length of the first lens group,
f ₂ is the focal length of the second lens group,
It is. The zoom lens according to any one of claims 1 to 10, wherein the following conditional expression (5) is satisfied.
4.1 <f _t / f _w <8 (5)
Where f _t is the focal length of the entire zoom lens system at the telephoto end. 12. The zoom lens according to claim 1, further comprising: a zoom lens; and an image sensor that is disposed on an image side of the zoom lens and converts an optical image obtained by the zoom lens into an electric signal. An image pickup apparatus comprising the zoom lens described above. The imaging apparatus according to claim 12, further comprising an image conversion unit that converts an electrical signal including distortion by the zoom lens into an image signal in which distortion is corrected by image processing. 14. The imaging apparatus according to claim 12, further comprising an image conversion unit that converts an electrical signal including lateral chromatic aberration caused by the zoom lens into an image signal corrected for lateral chromatic aberration by image processing.

Images