JP2010145696A - Zoom lens and imaging apparatus with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens starting from a negative lens group, which yields an advantage in ensuring a field angle and reducing aberration change. <P>SOLUTION: The zoom lens includes, in order from an object side, the first lens group of negative refractive power, a second lens group of positive refractive power, a third lens group of positive refractive power, and a fourth lens group of negative refractive power. When the zoom lens zooms from a wide-angle end to a tele-photo end, the second lens group moves to the object side so that the interval between the first and second lens groups decreases, the interval between the second and third lens groups increases, and the interval between the third and fourth lens groups changes. The first lens group includes, in order from the object side, one negative lens component at least one face of which is aspherical, and one positive lens component. The third lens group includes a positive meniscus lens component of which the object side face is concave, and which satisfies a following conditional expression (A): 1.01<(R<SB>3a</SB>+R<SB>3b</SB>)/(R<SB>3a</SB>-R<SB>3b</SB>)<30.0. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a zoom lens and an imaging apparatus including the 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, digital cameras that shoot subjects using solid-state image sensors such as CCDs and CMOSs instead of silver salt film cameras have become mainstream, and range from high-functional types for commercial use to compact popular types. It is becoming used in categories.

  Particularly popular digital cameras are favoring small-sized products, especially those that are easy to carry in clothes and bag pockets, and that are thin in the thickness direction. .

  In addition, the magnifying ratio of the photographic lens is generally about 3 times, but in order to satisfy a wide range of user needs, a camera that has a magnifying ratio of 3 times or more and can shoot with a wide angle of view is required. ing.

  A photographic lens that meets such needs needs to be sized so as not to impair the portability of the camera.

  Also, as a means for reducing the thickness of the camera, a so-called collapsible lens barrel is generally used in which a lens barrel is protruded from the camera body in a shooting state and stored in the camera body when being carried.

  In general, as a type of zoom lens that can achieve miniaturization, a negative leading type zoom type in which a lens unit having a negative refractive power is the lens unit closest to the object side is known. Among them, a three-group configuration in which a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power are arranged in order from the object side to the image side. These zoom lenses are generally used.

  Since the negative leading type zoom lens has a retrofocus type refractive power arrangement as a whole, it is suitable for widening the angle of view as compared to the type of zoom lens in which a positive refractive power lens group precedes.

  As a conventional negative leading type zoom lens, in Patent Document 1, Patent Document 2, and Patent Document 3, in order to obtain a zoom ratio of about 4 times or more with the negative leading zoom lens, in order from the object side to the image side A four-group zoom lens in which a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power are arranged. It is disclosed.

JP 2004-318107 A JP 2004-318108 A JP 2007-156385 A

  However, in the case of a three-group zoom lens having negative-positive-positive refractive power arrangement, if the zoom ratio is to be secured, the refractive power tends to increase because the zooming action is secured in the second lens group. At that time, in order to make the exit pupil far from the image plane and to ensure the telecentricity of the incident light beam to the image sensor, the positive refractive power of the third lens group cannot be increased, and the magnification by the third lens group is not increased. Alternatively, it is difficult to increase the image surface sensitivity during focusing.

  Even in a negative-positive-positive-negative four-group zoom lens, the off-axis light beam passing through the third lens group passes through the center of the lens at the wide-angle end and from the periphery of the lens at the telephoto end.

  In particular, when the third lens group is a focusing lens group, the telephoto end has a large amount of focusing movement, and therefore, the height of the light beam through which the off-axis light beam passes through the third lens group is likely to change, and the variation in field curvature is likely to occur. It tends to occur.

  Further, the zoom lenses of Patent Documents 1, 2, and 3 all have a half angle of view of 35 ° or less at the wide angle end.

The present invention has been made in view of the above, and an object of the present invention is to provide a zoom lens that is a negative leading zoom lens and is advantageous in securing a field angle and reducing aberration fluctuations.
Furthermore, it aims at providing the imaging device provided with such a zoom lens.

In order to solve the above problems, a zoom lens of the present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens having a positive refractive power. Group, and a fourth lens group having negative refractive power. During zooming from the wide-angle end to the telephoto end, the second lens group moves to the object side, and the first lens group and the second lens group The distance between the second lens group and the third lens group increases, the distance between the third lens group and the fourth lens group changes, and the first lens group In order from the side, the third lens unit is composed of one negative lens component having an aspheric surface on at least one surface and one positive lens component. The third lens group has a concave object side surface and satisfies the following conditional expression (A): It consists of a meniscus lens component.
1.01 <(R _3a + R _3b ) / (R _3a −R _3b ) <30.0 (A)
However,
R _3a is the paraxial radius of curvature of the object side surface of the positive meniscus lens component in the third lens group,
R _3b is the paraxial radius of curvature of the image side surface of the positive meniscus lens component in the third lens group,
It is.

  The lens component means a lens body having only two surfaces that are in contact with air on the optical axis, ie, the object side surface and the image side surface.

  The zoom lens according to the present invention has a four-group configuration in which negative-positive-positive-negative refractive power is arranged in order from the object side. Then, during zooming from the wide-angle end to the telephoto end, the second lens so that the distance between the first lens group and the second lens group is narrowed and the distance between the second lens group and the third lens group is widened. The group moves and the spacing between each lens group changes.

  By adopting such a configuration, it is possible to provide a lens group arrangement with a refractive power arrangement that facilitates securing a wide angle of view, and the second lens group can have a main zooming function. Even if the positive refractive power of the third lens group is increased to some extent, the back focus can be secured by the action of the negative refractive power of the fourth lens group on the image side, and the exit pupil can be easily separated from the image plane.

In addition, such a configuration is advantageous for increasing the zoom ratio.
In addition, since the configuration of the first lens group is composed of two lens components, a negative lens component and a positive lens component in order from the object side, it is easy to ensure back focus and is advantageous for making the first lens group thin. It becomes.

  Furthermore, it is advantageous for correcting off-axis aberrations at the wide-angle end and spherical aberrations at the telephoto end.

  Furthermore, by making at least one lens surface of the negative lens component in the first lens group an aspherical surface, it is advantageous for correcting off-axis aberrations at the wide-angle end, and suppressing the occurrence of aberrations even if the refractive power of the negative lens is increased. It becomes easy. This is advantageous for securing the negative refractive power of the entire first lens unit, and is advantageous for shortening the overall length of the zoom lens, making it compact, or increasing the field angle.

  The third lens group is composed of one positive meniscus lens component with the concave surface facing the object side. In the negative-positive-positive-negative type four-group zoom lens of the present invention, the imaging position is adjusted by the lens group on the image side of the second lens group. Here, by making the third lens group a meniscus shape with the concave surface facing the object side, even if the light beam height in the third lens group changes, the change in the incident angle and exit angle of the off-axis light beam can be reduced, This is advantageous for reducing fluctuations in field curvature.

  Conditional expression (A) specifies a preferable shape of the positive meniscus lens component.

  By making sure that the lower limit of conditional expression (A) is not exceeded and the upper limit is not exceeded, the object side surface of the positive meniscus lens component becomes a concave surface with an appropriate curvature, which is advantageous for reducing fluctuations in field curvature, and wide angle of view. This is advantageous for achieving a high zoom ratio.

  In the case where the zoom lens includes a focusing mechanism, the above and following constituent elements are configured in a state in which an object at the farthest distance is in focus.

  Further, in each of the above-described inventions, it is more preferable to satisfy one or more items of the configuration shown below.

In the zoom lens of the present invention, it is preferable that the negative lens component and the positive lens component in the first lens group satisfy the following conditional expression (B).
−0.60 <L ₁ / L ₂ <−0.20 (B)
However,
L ₁ is the focal length of the negative lens component in the first lens group,
L ₂ is the focal length of the positive lens component in the first lens group.

  Conditional expression (B) specifies the preferred focal length ratio of the negative lens component and the positive lens component in the first lens group for ensuring miniaturization and optical performance while ensuring the refractive power of the first lens group. To do.

  By ensuring that the lower limit of conditional expression (B) is not exceeded, securing the refractive power of the negative lens component is advantageous for securing the refractive power of the first lens unit.

  By ensuring that the refractive power of the positive lens component is ensured without exceeding the upper limit of conditional expression (B), it becomes easier to correct the aberration and reduce the diameter of the first lens unit.

The second lens group preferably has at least one negative lens and at least two positive lenses.
This is advantageous for correcting the second lens group, and it is easy to secure the refractive power of the second lens group.

  More preferably, the second lens group has at least three positive lenses, and any positive lens is cemented with any of the negative lenses. This is more advantageous for correcting spherical aberration and chromatic aberration.

In the zoom lens of the present invention, it is preferable that the first lens group and the second lens group satisfy the following conditional expression (C).
_{-1.7 <f 1 / f 2 <} -0.7 ··· (C)
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.

  Conditional expression (C) specifies a favorable ratio of the focal lengths of the first lens group and the second lens group.

  Ensuring the negative refractive power of the first lens group so as not to fall below the lower limit of the conditional expression (C) is advantageous for securing a zoom ratio, and it is easy to reduce the occurrence of aberrations in the second lens group. .

  By suppressing the refractive power burden of the first lens unit so as not to exceed the upper limit of conditional expression (C), it is advantageous for reducing the aberration and reducing the thickness of the first lens unit.

In the zoom lens according to the present invention, it is preferable that the fourth lens group includes one negative lens component having a concave object side surface and satisfies the following conditional expression (1).
−15 <(R _4a + R _4b ) / (R _4a −R _4b ) <− 0.5 (1)
However,
R _4a is the paraxial radius of curvature of the object side surface of the negative lens component in the fourth lens group,
R _4b is the paraxial radius of curvature of the image side surface of the negative lens component in the fourth lens group,
It is.

  By making the fourth lens group one negative lens component having a concave object side surface, it becomes easier to correct aberrations for off-axis light flux while suppressing the influence on the thickness of the zoom lens when retracted, and telephoto from the wide-angle end. This is advantageous for reducing various aberrations toward the end.

  And, when the shape of the negative lens component in the fourth lens group satisfies the conditional expression (1), the field angle and zoom ratio at the wide-angle end are ensured, and good optical performance is ensured in the entire zoom range. More advantageous.

  By making it not below the lower limit of conditional expression (1), it becomes easy to suppress the occurrence of spherical aberration at the telephoto end, and by making it not to exceed the upper limit, it becomes easy to suppress the occurrence of curvature of field at the wide angle end. .

In the zoom lens according to the present invention, it is preferable that the following conditional expression (2) is satisfied.
0.5 <D _T / _ft <2 (2)
However,
D _T is the distance on the optical axis from the object side surface of the lens closest to the object side in the zoom lens at the telephoto end to the imaging plane;
_ft is the focal length of the entire zoom lens system at the telephoto end,
It is.

  Conditional expression (2) specifies a preferable overall length of the zoom lens at the telephoto end.

  Satisfying the conditional expression (2) is advantageous in ensuring both the refractive power required for each lens group in the negative-positive-positive-negative-negative four-group zoom lens and miniaturization.

  By ensuring that the entire length of the zoom lens is ensured so as not to fall below the lower limit of conditional expression (2), it is advantageous for ensuring good aberration performance in the entire zooming range while suppressing the refractive power of each lens unit.

  By not exceeding the upper limit of conditional expression (2), the overall length of the zoom lens is reduced, which is advantageous for compactness.

  The negative lens component in the first lens group has a biconcave shape, and the negative lens component of the biconcave shape has the absolute value of the paraxial radius of curvature of the image side rather than the absolute value of the paraxial radius of curvature of the object side. The positive lens component in the first lens group is preferably small and has a meniscus shape having a convex object side surface.

  By making the negative lens component and the positive lens component have the above-described shapes, it becomes easy to suppress the influence of spherical aberration while maintaining the negative refractive power of the lens group as well as downsizing the lens unit. Therefore, it is more advantageous for correcting spherical aberration at the telephoto end when high zooming is used.

  The negative lens component in the fourth lens group preferably has an aspheric surface. This is more advantageous for correction of field curvature.

  In addition, the negative lens component in the fourth lens group is preferably a single lens. It is advantageous for thinning when retracted.

The zoom lens according to the present invention preferably satisfies the following conditional expression (3).
0 <(R _1a + R _1b ) / (R _1a −R _1b ) <1 (3)
However,
R _1a is the paraxial radius of curvature of the object side surface of the negative lens component in the first lens group,
R _1b is the paraxial radius of curvature of the image side surface of the negative lens component in the first lens group.

Satisfying the conditional expression (3) is more advantageous for securing the angle of view and the zoom ratio at the wide-angle end, and securing good performance in the entire zoom range.
Conditional expression (3) specifies a preferable shape of the negative lens component in the first lens group.

  In order to satisfy the conditional expression (3), by sharing the negative power between the object side surface and the image side surface of the negative lens component, it is possible to correct the field curvature when the field angle is widened and the spherical aberration at the telephoto end. It will be advantageous.

  By avoiding exceeding the upper limit of conditional expression (3) and not falling below the lower limit, the curvature of the lens surface on either the object side surface or the image side surface becomes too strong, so that the curvature of field at the wide angle end and the telephoto end are reduced. It is easy to suppress the occurrence of spherical aberration.

The zoom lens according to the present invention preferably satisfies the following conditional expressions (4) and (5).
1.81 <N ₁ <2.15 (4)
1.9 <N ₂ <2.35 (5)
However,
N ₁ is the refractive index at the d-line of any negative lens in the negative lens component in the first lens group,
N ₂ is the refractive index at the d-line of any positive lens in the positive lens component in the first lens group,
It is.

  This is more advantageous for securing the angle of view at the wide-angle end, securing the zoom ratio, and ensuring good performance in the entire zoom range.

  By satisfying conditional expression (4), the curvature of the image side surface of the negative lens component can be reduced, and the curvature of field at the wide-angle end can be corrected well. In addition, the edge thickness of the negative lens component can be reduced, which is advantageous for downsizing the first lens group.

  By making sure that the lower limit of conditional expression (4) is not exceeded, it is advantageous for correction of field curvature at the wide angle end and spherical aberration at the telephoto end. In addition, the edge thickness of the negative lens component can be reduced, leading to downsizing of the first lens group.

  By not exceeding the upper limit of the conditional expression (4), it becomes easy to suppress the cost of the material and the cost of processing the lens surface.

  Satisfying conditional expression (5) is advantageous in correcting the curvature of field at the wide-angle end and spherical aberration at the telephoto end while suppressing the axial thickness of the positive lens component. In addition, it becomes easy to secure the edge thickness of the positive lens component.

  By making sure that the lower limit of conditional expression (5) is not exceeded, it becomes easy to suppress curvature of field at the wide-angle end and spherical aberration at the telephoto end. In addition, since the absolute value of curvature on the image side can be reduced, the reduction in the axial thickness of the positive lens leads to the reduction in the size of the first lens group.

  By not exceeding the upper limit of the conditional expression (5), it becomes easy to suppress the cost of the material and the cost of processing the lens surface.

  Further, it is preferable that focusing is performed by moving the third lens group during zooming from the wide-angle end to the telephoto end, and moving the third lens group in the optical axis direction.

  The second lens group can have a zoom function, and the third lens group can have a function of adjusting the image position. In the present invention, it is preferable to move the third lens group at the time of focusing because fluctuations in field curvature can be reduced even if the refractive power of the third lens group is increased.

Further, it is preferable that each of the negative lens component and the positive lens component in the first lens group is a single glass single lens.
This is advantageous in securing the refractive power of each lens component and reducing the size.

  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, it is preferable that 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.
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.

Moreover, it is preferable that the zoom lens according to the present invention satisfies the following conditional expression (6).
3.6 < _ft / _fw <10 (6)
However,
f _w is the focal length of the entire zoom lens system at the wide-angle end,
f _t is the focal length of the entire zoom lens system at the telephoto end,
It is.

  Conditional expression (6) is a conditional expression regarding a preferable zoom ratio of the zoom lens.

  It is preferable that the zoom ratio is ensured so as not to fall below the lower limit of the conditional expression (6) because the function of the present invention can be exhibited.

  By not exceeding the upper limit of conditional expression (6), it becomes easy to reduce the size and cost. Moreover, it becomes easy to make optical performance favorable.

The image pickup apparatus of the present invention includes any one of the zoom lenses described above and an image pickup element that is disposed on the image side of the zoom lens and converts an optical image obtained by the zoom lens into an electric signal.
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, the imaging apparatus of the present invention preferably includes 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 the image pickup apparatus of the present invention, it is preferable that 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 is provided.

  Furthermore, 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 a 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 desirable to apply an antireflection coating to at least one surface of the lenses constituting the zoom lens in all the above-described configurations.

It is more preferable that the zoom lens of the present invention satisfies a plurality of the above requirements at the same time.
For each conditional expression, it is preferable to limit the lower limit value, the upper limit value, or both as follows, because the effect can be more easily obtained.

  For conditional expression (A), it is more preferable to set the lower limit value to 1.5, and further to 2.0. The upper limit is more preferably 20.0, more preferably 10.0.

  For conditional expression (B), it is more preferable to set the lower limit value to −0.50, more preferably to −0.40. The upper limit value is more preferably −0.25, and further preferably −0.3.

  For conditional expression (C), it is more preferable to set the lower limit to −1.3, more preferably −1.0. The upper limit value is more preferably −0.55, and further preferably −0.4.

  For conditional expression (1), the lower limit value is more preferably −4.0, more preferably −3.8, and even more preferably −3.6. The upper limit value is more preferably −1.0, and further preferably −2.0.

  For conditional expression (2), it is more preferable to set the lower limit value to 0.8, and further to 1.2. The upper limit is more preferably 1.9, and even more preferably 1.8.

  For conditional expression (3), the lower limit value is more preferably 0.3, and even more preferably 0.55. The upper limit value is more preferably 0.95, and further preferably 0.92.

  For conditional expression (4), it is more preferable to set the lower limit value to 1.83, more preferably 1.85. The upper limit is more preferably 2.00, more preferably 1.90.

  For conditional expression (5), it is more preferable to set the lower limit value to 1.95, more preferably 2.00. The upper limit is more preferably 2.25, and even more preferably 2.15.

  For conditional expression (6), it is more preferable to set the lower limit value to 4.3, more preferably 4.6. The upper limit is more preferably 8.0, and even more preferably 6.0.

  The zoom lens and the imaging apparatus according to the present invention have an effect that it is possible to provide a zoom lens that is advantageous for securing the angle of view and reducing aberration fluctuations.

  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 third lens group is G3, the fourth lens group is G4, the brightness (aperture) stop is S, 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 wavelength range limitation 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, and a brightness (aperture) stop. S, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power are disposed.

  During zooming from the wide-angle end to the telephoto end, the first lens group G1 moves to the object side after moving to the image side. The second lens group G2 moves to the object side. The third lens group G3 moves to the object side after moving to the image 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 convex surface directed toward the object 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 includes a negative meniscus lens having a concave surface directed toward the object side.

  The aspheric surfaces include both surfaces of a biconcave negative lens of the first lens group G1, both surfaces of a positive meniscus lens on the object side of the second lens group G2, both surfaces of a positive meniscus lens of the third lens group G3, and a fourth lens. 7 surfaces including the object side surface of the negative meniscus lens of the group G4.

  As shown in FIG. 2, the zoom lens according to the second 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, and a brightness (aperture) stop. S, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power are disposed.

  During zooming from the wide-angle end to the telephoto end, the first lens group G1 moves to the object side after moving to the image side. The second lens group G2 moves to the object side. The third lens group G3 moves to the object side after moving to the image 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 convex surface directed toward the object 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 includes a negative meniscus lens having a concave surface directed toward the object side.

  The aspheric surfaces include both surfaces of a biconcave negative lens of the first lens group G1, both surfaces of a positive meniscus lens on the object side of the second lens group G2, both surfaces of a positive meniscus lens of the third lens group G3, and a fourth lens. 7 surfaces including the object side surface of the negative meniscus lens of the group G4.

  As shown in FIG. 3, the zoom lens according to the third 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, and a brightness (aperture) stop. S, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power are disposed.

  During zooming from the wide-angle end to the telephoto end, the first lens group G1 moves to the object side after moving to the image side. The second lens group G2 moves to the object side. The third lens group G3 moves to the object side after moving to the image 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 convex surface directed toward the object 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 includes a negative meniscus lens having a concave surface directed toward the object side.

  The aspheric surfaces are the double-sided negative lens of the first lens group G1, the image side surface of the positive meniscus lens, the double side of the positive meniscus lens on the object side of the second lens group G2, and the positive side of the third lens group G3. It is provided on eight surfaces including both surfaces of the meniscus lens and the object side surface of the negative meniscus lens of the fourth lens group G4.

  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, and a brightness (aperture) stop. S, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power are disposed.

  During zooming from the wide-angle end to the telephoto end, the first lens group G1 moves to the object side after moving to the image side. The second lens group G2 moves to the object side. The third lens group G3 moves to the object side after moving to the image 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 convex surface directed toward the object 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 includes a negative meniscus lens having a concave surface directed toward the object side.

  The aspheric surfaces include both surfaces of a biconcave negative lens of the first lens group G1, both surfaces of a positive meniscus lens on the object side of the second lens group G2, both surfaces of a positive meniscus lens of the third lens group G3, and a fourth lens. 7 surfaces including the object side surface of the negative meniscus lens of the group G4.

  As shown in FIG. 5, the zoom lens of Example 5 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 brightness (aperture) stop. S, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power are disposed.

  During zooming from the wide-angle end to the telephoto end, the first lens group G1 moves to the object side after moving to the image side. The second lens group G2 moves to the object side. The third lens group G3 moves to the object side after moving to the image 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 convex surface directed toward the object 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 includes a negative meniscus lens having a concave surface directed toward the object side. The flare stop FS is provided between the first lens group G1 and the second lens group G2.

  The aspheric surfaces are the double-sided negative lens of the first lens group G1, the image side surface of the positive meniscus lens, the double side of the positive meniscus lens on the object side of the second lens group G2, and the positive side of the third lens group G3. It is provided on eight surfaces including both surfaces of the meniscus lens and the object side surface 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 brightness (aperture) stop. S, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power are disposed.

  During zooming from the wide-angle end to the telephoto end, the first lens group G1 moves to the object side after moving to the image side. The second lens group G2 moves to the object side. The third lens group G3 moves to the object side after moving to the image 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 convex surface directed toward the object 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 includes a negative meniscus lens having a concave surface directed toward the object side.

  The aspherical surface includes both surfaces of a biconcave negative lens and a positive meniscus lens of the first lens group G1, both surfaces of a positive meniscus lens on the object side of the second lens group G2, and an image side surface of the biconvex positive lens. It is provided on 10 surfaces, that is, 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.

  Below, the numerical data of each said Example are shown. In addition to the above, r is the radius of curvature of each lens surface, d is the thickness or spacing of each lens, nd is the refractive index at the d-line of each lens, νd is the Abbe number at the d-line of each lens, and K is the cone Each coefficient is shown.

Each aspheric shape is expressed by the following formula (I) 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 (I)
However,
r is the paraxial radius of curvature,
K is the cone coefficient,
A4, A6, A8, A10 and A12 are the fourth, sixth, eighth, tenth and twelfth aspherical 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 * -47.643 0.85 1.85 135 40.10
2 * 6.135 1.68
3 10.167 1.80 2.00178 19.30
4 22.997 Variable
5 * 4.840 1.80 1.58313 59.38
6 * 11.243 0.10
7 6.567 1.20 1.88300 40.76
8 16.755 0.60 1.92286 20.88
9 4.166 0.50
10 10.589 1.00 1.67270 32.10
11 -23.507 0.50
12 Aperture variable
13 * -16.664 1.70 1.55332 71.68
14 * -7.149 variable
15 * -9.621 0.85 1.52540 56.25
16 -17.144 0.30
17 ∞ 0.30 1.51633 64.14
18 ∞ 0.50
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.37
Image plane (imaging plane) ∞

Aspheric data first surface
k = 0.000
A4 = 3.57128e-04, A6 = -6.63505e-06, A8 = 2.50508e-08, A10 = 3.08729e-10
Second side
k = 0.000
A4 = -5.36474e-07, A6 = -8.93302e-06, A8 = -1.17768e-07, A10 = -9.55808e-09
5th page
k = 0.000
A4 = -8.47352e-05, A6 = 3.01885e-06, A8 = 2.88087e-06
6th page
k = 0.000
A4 = 8.80509e-04, A6 = 5.47311e-05, A8 = 2.98587e-07, A10 = 4.79526e-07
13th page
k = 0.000
A4 = -1.00016e-03, A6 = -8.62351e-05, A8 = 8.90710e-06, A10 = -8.22775e-08
14th page
k = 0.000
A4 = -2.69125e-04, A6 = -7.45922e-05, A8 = 4.54677e-06, A10 = 6.88885e-08
15th page
k = 0.000
A4 = 5.28228e-04, A6 = -1.24484e-04, A8 = 5.07560e-06

Zoom data
Wide angle Medium telephoto focal length 4.63 11.55 22.16
FNO. 2.86 4.91 6.00
Angle of view 2ω 92.15 36.08 18.82

D4 16.21 4.56 0.20
D12 2.90 10.89 20.93
D14 3.03 1.95 2.85

fb (in air) 1.70 1.70 1.70
Total length (in air) 36.42 31.69 38.26
Image height 3.83 3.83 3.83

Group focal length
f1 = -11.23 f2 = 9.81 f3 = 21.27 f4 = -43.42

Numerical example 2
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * -29.322 0.85 1.85135 40.10
2 * 7.203 1.71
3 11.177 1.68 2.00178 19.30
4 25.650 Variable
5 * 5.019 1.85 1.58313 59.38
6 * 26.956 0.10
7 8.399 1.52 1.88300 40.76
8 32.055 0.60 1.84666 23.78
9 4.170 0.60
10 9.972 1.13 1.65412 39.68
11 -63.359 0.30
12 Aperture variable
13 * -15.933 1.89 1.55332 71.68
14 * -6.470 variable
15 * -7.637 0.85 1.52540 56.25
16 -15.470 0.30
17 ∞ 0.30 1.51633 64.14
18 ∞ 0.50
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.37
Image plane (imaging plane) ∞

Aspheric data first surface
k = 0.000
A4 = 4.99109e-04, A6 = -8.94706e-06, A8 = 1.00727e-07, A10 = -7.91343e-10
Second side
k = 0.000
A4 = 2.61070e-04, A6 = -5.93572e-06, A8 = 7.91557e-08, A10 = -6.87609e-09
5th page
k = 0.000
A4 = -2.51325e-05, A6 = -7.06371e-06, A8 = 7.37768e-06
6th page
k = 0.000
A4 = 9.96217e-04, A6 = 2.63226e-06, A8 = 1.36408e-05, A10 = -4.27886e-10
13th page
k = 0.000
A4 = -5.04802e-04, A6 = -1.76423e-04, A8 = 1.60553e-05, A10 = -2.50741e-07
14th page
k = 0.000
A4 = 5.55538e-04, A6 = -1.72511e-04, A8 = 1.01417e-05, A10 = 4.95291e-09
15th page
k = 0.000
A4 = 1.83506e-03, A6 = -2.90323e-04, A8 = 1.26326e-05

Zoom data
Wide angle Medium Telephoto focal length 4.95 11.19 23.33
FNO. 2.87 4.71 6.02
Angle of view 2ω 84.29 37.40 17.99

D4 15.65 5.19 0.20
D12 2.84 9.80 21.06
D14 2.80 1.85 2.32

fb (in air) 1.70 1.70 1.70
Total length (in air) 36.06 31.61 38.35
Image height 3.83 3.83 3.83

Group focal length
f1 = -11.64 f2 = 9.84 f3 = 18.38 f4 = -29.83

Numerical Example 3
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * -29.659 0.85 1.85135 40.10
2 * 7.252 1.94
3 10.470 1.75 2.00178 19.30
4 * 21.675 variable
5 * 4.836 1.88 1.58313 59.38
6 * 27.362 0.10
7 8.675 1.44 1.88300 40.76
8 27.723 0.60 1.84666 23.78
9 4.076 0.60
10 9.821 1.09 1.65412 39.68
11 -75.537 0.30
12 Aperture variable
13 * -16.273 1.83 1.55332 71.68
14 * -6.109 variable
15 * -7.355 0.85 1.52540 56.25
16 -15.794 0.30
17 ∞ 0.30 1.51633 64.14
18 ∞ 0.50
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.37
Image plane (imaging plane) ∞

Aspheric data first surface
k = 0.000
A4 = 3.40995e-04, A6 = -5.13343e-06, A8 = 3.35710e-08
Second side
k = 0.000
A4 = -3.33261e-05, A6 = -5.81602e-06, A8 = -6.03232e-08,
4th page
k = 0.000
A4 = 9.48874e-05, A6 = 1.76986e-06, A8 = -4.31922e-08
5th page
k = 0.000
A4 = -1.44419e-04, A6 = -5.59810e-07, A8 = 7.06727e-06
6th page
k = 0.000
A4 = 9.35523e-04, A6 = 2.05726e-05, A8 = 1.32121e-05
13th page
k = 0.000
A4 = 7.29618e-05, A6 = -1.48545e-04, A8 = 7.20359e-06, A10 = 1.15579e-10
14th page
k = 0.000
A4 = 1.45067e-03, A6 = -1.84082e-04, A8 = 6.92278e-06, A10 = 4.71448e-08
15th page
k = 0.000
A4 = 2.66399e-03, A6 = -3.80171e-04, A8 = 1.55021e-05

Zoom data
Wide angle Medium Telephoto focal length 4.86 11.73 22.48
FNO. 2.86 4.86 6.02
Angle of view 2ω 84.50 35.56 18.66

D4 16.14 4.68 0.20
D12 3.04 10.58 20.84
D14 2.66 1.87 2.35

fb (in air) 1.70 1.70 1.70
Total length (in air) 36.77 32.06 38.32
Image height 3.83 3.83 3.83

Group focal length
f1 = -11.86 f2 = 10.04 f3 = 16.61 f4 = -27.14

Numerical Example 4
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * -29.770 0.85 1.85135 40.10
2 * 7.223 1.69
3 11.193 1.67 2.00178 19.30
4 25.783 Variable
5 * 5.028 1.88 1.58313 59.38
6 * 26.919 0.10
7 8.396 1.48 1.88300 40.76
8 32.017 0.60 1.84666 23.78
9 4.168 0.60
10 9.935 1.09 1.65412 39.68
11 -61.878 0.30
12 Aperture variable
13 * -15.998 1.90 1.55332 71.68
14 * -6.455 variable
15 * -7.654 0.85 1.52540 56.25
16 -15.418 0.30
17 ∞ 0.30 1.51633 64.14
18 ∞ 0.50
19 ∞ 0.50 1.51633 64.14
20 ∞ 0.37
Image plane (imaging plane) ∞

Aspheric data first surface
k = 0.000
A4 = 5.79963e-04, A6 = -1.48583e-05, A8 = 2.04528e-07, A10 = -1.26564e-09
Second side
k = 0.000
A4 = 3.39406e-04, A6 = -1.07046e-05, A8 = -1.11476e-07, A10 = 1.68906e-10
5th page
k = 0.000
A4 = -1.26615e-04, A6 = -1.07869e-05, A8 = 6.13180e-06
6th page
k = 0.000
A4 = 8.19692e-04, A6 = 4.53322e-06, A8 = 1.05330e-05, A10 = 3.19520e-08
13th page
k = 0.000
A4 = -2.57078e-04, A6 = -1.48954e-04, A8 = 1.07509e-05, A10 = -8.21444e-08
14th page
k = 0.000
A4 = 9.62948e-04, A6 = -1.55832e-04, A8 = 6.49494e-06, A10 = 8.75571e-08
15th page
k = 0.000
A4 = 2.48017e-03, A6 = -3.09823e-04, A8 = 1.14834e-05

Zoom data
Wide angle Medium Telephoto focal length 4.97 11.14 23.29
FNO. 2.86 4.66 6.02
Angle of view 2ω 83.79 37.54 18.00

D4 15.64 5.20 0.20
D12 2.87 9.70 21.04
D14 2.84 1.97 2.33

fb (in air) 1.70 1.70 1.70
Total length (in air) 36.05 31.58 38.28
Image height 3.83 3.83 3.83

Group focal length
f1 = -11.74 f2 = 9.89 f3 = 18.26 f4 = -30.06

Numerical Example 5
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * -125.379 0.85 1.85135 40.10
2 * 6.533 1.53
3 10.567 1.76 2.00178 19.30
4 * 21.169 variable
5 ∞ 0.00
6 * 4.591 1.60 1.58313 59.38
7 * 32.489 0.10
8 10.167 1.01 1.88300 40.76
9 14.013 0.60 1.84666 23.78
10 3.990 0.60
11 8.610 1.00 1.65475 38.56
12 -35.265 0.30
13 Aperture variable
14 * -14.600 1.81 1.55332 71.68
15 * -6.184 variable
16 * -6.509 0.85 1.52540 56.25
17 -16.639 0.30
18 ∞ 0.30 1.51633 64.14
19 ∞ 0.50
20 ∞ 0.50 1.51633 64.14
21 ∞ 0.37
Image plane (imaging plane) ∞

Aspheric data first surface
k = 0.000
A4 = 1.62111e-04, A6 = -6.07086e-06, A8 = 5.96970e-08
Second side
k = 0.000
A4 = 1.22310e-04, A6 = -1.34058e-05, A8 = -1.94237e-07
4th page
k = 0.000
A4 = -1.65315e-04, A6 = 3.77200e-06, A8 = -3.58859e-08
6th page
k = 0.000
A4 = -5.94521e-04, A6 = -1.58611e-05, A8 = 3.19594e-07
7th page
k = 0.000
A4 = 2.30559e-04, A6 = -3.27821e-06, A8 = 2.12462e-06
14th page
k = 0.000
A4 = 6.53464e-05, A6 = -1.31379e-04, A8 = 7.46808e-06, A10 = -3.35062e-09
15th page
k = 0.000
A4 = 1.36585e-03, A6 = -1.67655e-04, A8 = 7.06557e-06, A10 = 3.48165e-08
16th page
k = 0.000
A4 = 2.41340e-03, A6 = -2.91695e-04, A8 = 1.12706e-05

Zoom data
Wide angle Medium Telephoto focal length 5.02 11.41 23.86
FNO. 2.86 4.53 6.00
Angle of view 2ω 83.62 36.65 17.50

D4 17.29 5.69 0.20
D13 3.64 10.39 21.35
D15 2.88 1.99 2.53

fb (in air) 1.70 1.70 1.70
Total length (in air) 37.51 31.78 37.78
Image height 3.83 3.83 3.83

Group focal length
f1 = -12.37 f2 = 10.13 f3 = 18.01 f4 = -20.95

Numerical Example 6
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 (imaging 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

D4 19.36 6.97 0.20
D12 3.29 6.80 21.94
D14 2.82 3.61 2.18

fb (in air) 1.83 1.83 1.83
Total length (in air) 39.81 31.71 38.65
Image height 3.83 3.83 3.83

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

  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 (6) in each example will be listed. 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
(1) (R _4a + R _4b ) / (R _4a -R _4b )
-3.56 -2.95 -2.74 -2.97 -2.28 -3.38
(2) D _T / f _t 1.74 1.66 1.72 1.66 1.60 1.46
(3) (R _1a + R _1b ) / (R _1a -R _1b )
0.77 0.61 0.61 0.61 0.90 0.84
(4) N ₁ 1.85135 1.85135 1.85135 1.85135 1.85135 1.85135
(5) N ₂ 2.00178 2.00178 2.00178 2.00178 2.00178 2.00178
(6) ft / fw 4.79 4.72 4.62 4.68 4.76 5.58
Image height during distortion correction (wide-angle end)
3.39 3.42 3.41 3.42 3.41 3.43
Full angle of view after widening distortion (wide angle end)
79.26 75.49 76.46 75.23 74.73 77.31

(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 , a coating material such as SnO ₂ , In ₂ O ₃ , ZnO, Y ₂ O ₃ , a coating material such as MgF ₂ , SiO ₂ , Al ₂ O ₃ having a relatively low refractive index, etc. The film thickness may be set so as to satisfy the above.

  As a matter of course, the coating on the bonding surface may be a multi-coat as in 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.

  Then, at the wide-angle end, the length in the short side direction of the photoelectric conversion surface is the same as the length in the short side direction of the effective image pickup region, and the effective image pickup region so that distortion after image processing remains about -3%. Is stipulated. Of course, an image obtained by converting a smaller barrel-shaped area into a rectangular shape as an effective imaging area may be recorded and reproduced.

(Signal processing of lateral chromatic aberration)
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 shift 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 in accordance with the zoom position, it is possible to output the second and third primary color signals in which the shift between the second and third primary colors with respect to the first primary color signal is corrected.

  In each embodiment, the zoom lens has a wide angle of view at the wide-angle end, a small size, a high zoom ratio, and a good optical performance.

(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. Move to point P ₂ on the circumference. 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
However,
ω is the half angle of view of the subject,
f is the focal length of the imaging optical system (in the present invention, the zoom lens),
α is 0 or more and 1 or less.

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 possessed by 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 reducing the size is ensured even if the angle of view is widened. it can.

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 in 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. A small size and wide angle of view 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 of view 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 the zoom ratio and the brightness while ensuring the angle of view at the wide-angle end and reducing the size.

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. FIG. 5 is a lens cross-sectional view at a wide angle end (a), an intermediate state (b), and a telephoto end (c) when focusing on an object point at infinity according to a second embodiment of the zoom lens of the present invention. FIG. 6 is a lens cross-sectional view at a wide angle end (a), an intermediate state (b), and a telephoto end (c) when focusing on an object point at infinity according to a third embodiment of the zoom lens of the present invention. FIG. 6 is a lens cross-sectional view at a wide-angle end (a), an intermediate state (b), and a telephoto end (c) when focusing on an object point at infinity according to Embodiment 4 of the zoom lens of the present invention. FIG. 6 is a lens cross-sectional view at a wide-angle end (a), an intermediate state (b), and a telephoto end (c) when focusing on an object point at infinity according to Example 5 of the zoom lens of the present invention. FIG. 10 is a lens cross-sectional view at a wide-angle end (a), an intermediate state (b), and a telephoto end (c) when focusing on an object point at infinity according to Example 6 of the zoom lens of the present 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 F ... Low pass filter C ... Cover glass I ... Image surface 112 ... Operation part 113 ... Control part 114 ... Bus 115 ... Bus 116 ... Imaging drive circuit 117 ... Temporary storage memory 118 ... Image processing part 119 ... Storage medium part 120 ... Display part 121 ... Setting information storage memory part 122 ... Bus 124 ... CDS / ADC part 140 ... Digital camera 141 ... Optical optical system 142 ... Optical optical path 143 ... Finder optical system 144 ... Optical path for finder 145 ... Shutter button 146 ... Flash 147 ... LCD 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 (20)

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;
A fourth lens group having negative refractive power;
Consists of
During zooming from the wide-angle end to the telephoto end, the second lens group moves toward the object side,
The interval between the first lens group and the second lens group is reduced, the interval between the second lens group and the third lens group is increased, and the third lens group and the fourth lens are increased. The distance between the groups changes,
The first lens group includes, in order from the object side, one negative lens component having an aspheric surface on at least one surface and one positive lens component.
The zoom lens according to claim 3, wherein the third lens group includes a positive meniscus lens component that has a concave object side surface and satisfies the following conditional expression (A).
1.01 <(R _3a + R _3b ) / (R _3a −R _3b ) <30.0 (A)
However,
R _3a is a paraxial radius of curvature of the object side surface of the positive meniscus lens component in the third lens group,
R _3b is a paraxial radius of curvature of the image side surface of the positive meniscus lens component in the third lens group,
It is. 2. The zoom lens according to claim 1, wherein the negative lens component and the positive lens component in the first lens group satisfy the following conditional expression (B).
−0.60 <L ₁ / L ₂ <−0.20 (B)
However,
L ₁ is the focal length of the negative lens component in the first lens group,
L ₂ is the focal length of the positive lens component in the first lens group,
It is.   The zoom lens according to claim 1, wherein the second lens group includes at least one negative lens and at least two positive lenses.   4. The zoom lens according to claim 3, wherein the second lens group includes at least three positive lenses, and one of the positive lenses is joined to one of the negative lenses. The zoom lens according to claim 3 or 4, wherein the first lens group and the second lens group satisfy the following conditional expression (C).
_{-1.7 <f 1 / f 2 <} -0.7 ··· (C)
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 said 4th lens group consists of one negative lens component whose object side surface is a concave surface, and satisfies the following conditional expressions (1), The any one of Claims 1-5 characterized by the above-mentioned. Zoom lens.
−15 <(R _4a + R _4b ) / (R _4a −R _4b ) <− 0.5 (1)
However,
R _4a is the paraxial radius of curvature of the object side surface of the negative lens component in the fourth lens group,
R _4b is a paraxial radius of curvature of the image side surface of the negative lens component in the fourth lens group,
It is. The zoom lens according to any one of claims 1 to 6, wherein the following conditional expression (2) is satisfied.
0.5 <D _T / _ft <2 (2)
However,
D _T is the distance on the optical axis from the object side surface of the lens closest to the object side in the zoom lens at the telephoto end to the imaging plane;
_ft is the focal length of the entire zoom lens system at the telephoto end,
It is.   The negative lens component in the first lens group has a biconcave shape, and the negative lens component of the biconcave shape has an absolute value of the paraxial radius of curvature of the image side rather than an absolute value of the paraxial radius of curvature of the object side surface. The zoom lens according to claim 1, wherein the positive lens component in the first lens group has a meniscus shape having a convex object side surface.   9. The zoom lens according to claim 1, wherein the negative lens component in the fourth lens group has an aspherical surface.   The zoom lens according to any one of claims 1 to 9, wherein the negative lens component in the fourth lens group is a single lens. The zoom lens according to any one of claims 1 to 10, wherein the following conditional expression (3) is satisfied.
0 <(R _1a + R _1b ) / (R _1a −R _1b ) <1 (3)
However,
R _1a is a paraxial radius of curvature of the object side surface of the negative lens component in the first lens group,
R _1b is the paraxial radius of curvature of the image side surface of the negative lens component in the first lens group. The zoom lens according to any one of claims 1 to 11, wherein the following conditional expressions (4) and (5) are satisfied.
1.81 <N ₁ <2.15 (4)
1.9 <N ₂ <2.35 (5)
However,
N ₁ is the refractive index at the d-line of any negative lens in the negative lens component in the first lens group,
N ₂ is the refractive index at the d-line of any positive lens in the positive lens component in the first lens group,
It is.   13. The focusing according to claim 1, wherein the third lens group moves during zooming from the wide-angle end to the telephoto end, and focusing is performed by moving the third lens group in the optical axis direction. The zoom lens according to any one of the above items.   14. The zoom lens according to claim 1, wherein each of the negative lens component and the positive lens component in the first lens group is a single glass single lens.   The zoom lens according to any one of claims 1 to 14, further comprising an aperture stop disposed immediately after the image side of the second lens group.   The most image-side refractive surface in the first lens group has a shape with a concave surface facing the image side, and the most object-side refractive surface in the second lens group has a shape with a convex surface facing the object side. The zoom lens according to claim 15. The zoom lens according to any one of claims 1 to 16, wherein the zoom lens satisfies the following conditional expression (6).
3.6 < _ft / _fw <10 (6)
However,
f _w is the focal length of the entire zoom lens system at the wide-angle end,
f _t is the focal length of the entire zoom lens system at the telephoto end,
It is. The zoom lens according to any one of claims 1 to 17,
An image sensor that is disposed on the image side of the zoom lens and converts an optical image by the zoom lens into an electrical signal;
An imaging device comprising:   The image pickup apparatus according to claim 18, 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.   The imaging apparatus according to claim 18 or 19, further comprising an image conversion unit that converts an electrical signal including chromatic aberration of magnification by the zoom lens into an image signal in which the chromatic aberration of magnification is corrected by image processing.

Images