JP4469642B2 - Zoom lens - Google Patents

Description

  The present invention relates to a zoom lens suitably used for, for example, a digital still camera (hereinafter simply referred to as a digital camera) and a video camera.

  In recent years, digital still cameras (hereinafter simply referred to as digital cameras) and video cameras have been widely used. These cameras convert an optical image into an electrical signal using an image sensor such as a CCD (charge coupled device) and record it as image data.

Conventionally, various zoom lenses have been proposed for use in these cameras. Among them, zoom lenses with a zoom ratio of about 3 times, a zoom lens with a two-group configuration or a three-group configuration is widely used. ing. In particular, considering the weight reduction of the lens and the speeding up of autofocus, the inner focus type and the rear focus type are suitable. Therefore, the number of zoom lens groups should be 3 groups rather than 2 groups. Is desirable. Therefore, the present applicant has proposed zoom lenses as disclosed in, for example, Patent Document 1 and Patent Document 2 as a three-group zoom lens that can cope with such various problems.
JP-A-10-293253 JP 2000-284177 A

  The zoom lens described in Patent Document 1 includes first to third lens groups having negative, positive, and positive refractive power in order from the object side, and performs zooming mainly by the first and second lens groups. Focusing is mainly performed by the third lens group. This zoom lens is configured so as to satisfy two conditional expressions that define the distance from the imaging surface to the exit pupil position, so that the exit pupil position from the imaging surface is sufficiently far away while ensuring an appropriate zoom ratio. Since the position can be set, the light beam can be incident on the imaging surface in a substantially telecentric state, thereby preventing the occurrence of shading or the like.

  When zooming from wide angle to telephoto at the time of focusing on infinity, the zoom lens described in Patent Document 2 moves the second and third lens groups closer to the first lens group while keeping these intervals constant. It is made to move. According to this zoom lens, the rear focus method can be adopted while appropriately setting the exit pupil position from the imaging surface.

Further, as a zoom lens having a three-group configuration, for example, a zoom lens as disclosed in Patent Document 3 has been proposed.
JP 2002-196240 A

  The zoom lens described in Patent Document 3 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 group having a positive refractive power. The second lens group includes a positive lens, a cemented lens of a positive lens and a negative lens, and a single lens in order from the object side. When zooming from the wide-angle side to the telephoto side, the first, second, and third lens groups are arranged such that the distance between the first lens group and the second lens group decreases and the distance between the second lens group and the third lens group increases. The third lens group is moved on the optical axis to perform zooming. The movement of the third lens group is to correct a focus position shift that occurs during zooming.

  By the way, in recent years, in the above-described digital cameras and the like, a bright lens of about F2.8 with high resolution has been desired. In addition, downsizing of digital cameras and the like is also desired, and further downsizing of photographing lenses that influence the size is required. Furthermore, recently, CCDs used in digital cameras and the like have been developed to have a total number of pixels exceeding 5 million, and the number of pixels tends to increase further in the future. Lenses are required to have higher resolution.

  However, in the zoom lenses disclosed in Patent Documents 1 and 2, the F number at the wide-angle end is only F3.2 even at a bright angle, and there is a possibility that further improvement is required in terms of brightness depending on the application. In particular, in the zoom lens disclosed in Patent Document 1, since the first group includes a large number (four) of lenses, it may be assumed that further improvement is required in terms of compactness and lens weight. Further, in the zoom lens of Patent Document 2, since the second group and the third group move together during zooming, the total length tends to be long at the wide-angle end. If there is a request for further shortening, it may not be easy to secure a zoom ratio.

  In the zoom lens of Patent Document 3, although brightness of about F2.8 is secured, not only the first and second lens groups but also the third lens group is moved. When the zooming function is also shared by the third lens group in this way, the refractive power of the third lens group relative to the entire system becomes relatively large. As a result, the eccentric sensitivity (depending on the eccentricity) The degree of optical performance deterioration) becomes high. In particular, recent digital cameras and the like are often constructed so that the entire length is retracted short when not in use for miniaturization. Therefore, like the zoom lens of Patent Document 3, the third lens group has an image plane. In the case of a lens configuration that does not move in a direction far away from the first lens group, the first and second lens groups are mechanically held by one cam cylinder, while the third lens group is Are often held independently, and therefore, performance degradation due to the eccentricity of the third lens group tends to be a problem. On the other hand, if the first to third lens groups are configured to be held by one cam cylinder, it is possible to suppress the eccentricity of the third lens group with respect to the first and second lens groups. However, if it does so, a cam cylinder will become long and it will become difficult to retract shortly.

  Furthermore, in Patent Documents 1 to 3, although some aberration performance is ensured, there are cases where further improvements in various aberrations are required in response to recent demands for higher resolution.

  SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an object thereof is to provide an imaging device having a large F-number at the wide-angle end, a high-speed focusing, a small and simple structure, and a large number of pixels. Another object of the present invention is to provide a zoom lens in which various aberrations are satisfactorily corrected to such an extent that a high resolving power can be exhibited.

The zoom lens according to the present invention includes, in order from the object side, a first lens group having a negative refractive power as a whole, a second lens group having a positive refractive power as a whole, and a third lens group having a positive refractive power. And are arranged. The first lens group includes a negative first lens and a positive second lens arranged in order from the object side , and includes at least two aspheric surfaces. The second lens group includes a stop for adjusting the amount of light arranged in order from the object side , a cemented lens composed of a positive third lens, a positive fourth lens, and a negative fifth lens, and a negative sixth lens. It includes at least two aspheric surfaces. The third lens group includes a positive seventh lens. This zoom lens further satisfies the following conditional expressions (1) and (2).
0.4 <fw / | f1 | <0.6 (1)
0.25 <f2 / f3 <0.45 (2)
Here, fi is the focal length of the i-th lens group (i = 1, 2, 3), and fw is the focal length of the entire system at the wide angle end.

  In the zoom lens according to the present invention, when zooming from wide angle to telephoto, the first and second lens groups move to reduce the mutual distance between the first and second lens groups, while the second And the mutual distance of the third lens group increases. When zooming while maintaining an infinitely focused state, the distance from the third lens group to the image plane is kept substantially constant. That is, the third lens group does not move during zooming. When shifting from the infinite focus state to the short distance focus state, the third lens unit moves to the object side. In this zoom lens, since the third lens group is fixed and only the first and second lens groups move during zooming, the third lens group does not have a zooming function. For this reason, it is possible to relatively reduce the refractive power of the third lens group with respect to the entire system, and as a result, the decentration sensitivity of the third lens group can be kept low. In particular, in order to make the structure retractable when not in use, the first and second lens groups are held by one cam cylinder, and the third lens group is held separately. Since the decentering sensitivity of the three lens groups is low, the aberration performance is hardly deteriorated. In addition, since only the first and second lens groups are moved, the lens moving mechanism is simplified as compared with the case where the entire group moves.

  In this zoom lens, the image forming magnification at the wide-angle end in the composite lens group composed of the second lens group and the third lens group, that is, the refractive power (1 / f1) of the first lens group and the wide-angle end. Since the quantity (fw / | f1 |) representing the ratio to the refractive power (1 / fw) of the entire system is optimized, miniaturization and correction of various aberrations are realized in a well-balanced manner. Furthermore, since the ratio (f2 / f3) between the refractive power (1 / f3) of the third lens group and the refractive power (1 / f2) of the second lens group is optimized, the moving distance during focusing is shortened. In addition, it is easy to configure the third lens group with a positive single lens.

In the zoom lens according to the present invention, the negative lens of the first lens group is a positive meniscus lens having a concave surface facing the image side and at least one surface being an aspherical surface, and the positive lens of the first lens group having a convex surface facing the object side. It is preferable to configure so as to satisfy the conditional expressions (3) and (4). In this case, it is more preferable that both surfaces of the negative lens of the first lens group are aspherical.
Nd1> 1.72 (3)
νd1−νd2> 14 (4)
Where Nd1 is the refractive index of the negative lens of the first lens group, νd1 is the Abbe number of the negative lens of the first lens group, and νd2 is the Abbe number of the positive lens of the first lens group.

In the zoom lens according to the present invention, at least one surface of the positive lens closest to the object side in the second lens group forms an aspherical surface, and the negative lens closest to the image side in the second lens group faces a concave surface toward the image side and at least It is preferable that one surface is an aspherical surface, the stop is disposed on the most object side in the second lens group, and further satisfies the conditional expressions (5) and (6). In this case, it is more preferable that both surfaces of the negative lens closest to the image side in the second lens group are aspherical.
(Nd3 + Nd4) / 2> 1.65 (5)
νd4−νd5> 20 (6)
However, Nd3 is the refractive index of the positive lens closest to the object in the second lens group, Nd4 is the refractive index of the positive lens in the cemented lens in the second lens group, and νd4 is in the second lens group. This is the Abbe number of the positive lens in the cemented lens, and νd5 is the Abbe number of the negative lens in the cemented lens in the second lens group.

  In this specification, the refractive index Ndj (j = 1 to 7) is for the d-line, and the Abbe number νdj is expressed using the refractive index Ndj.

  According to the zoom lens of the present invention, in order from the object side, the first lens group having a negative refractive power as a whole, the second lens group having a positive refractive power as a whole, and the third lens having a positive refractive power. And a lens group, and when zooming from wide angle to telephoto, the first and second lens groups move to reduce the mutual distance between the first and second lens groups. On the other hand, the distance between the second lens unit and the third lens unit is configured to increase, and when zooming while maintaining the infinite focus state, the distance from the third lens unit to the image plane is substantially constant. The third lens group is configured not to move at the time of zooming so that the third lens group does not carry a zooming function. Therefore, the refractive power of the third lens group with respect to the entire system is relative to each other. The third lens group can be made smaller. Sensitivity can be kept low, aberration performance degradation is less likely to occur. In addition, since only the first and second lens groups are moved, the lens moving mechanism is simplified as compared with the case where the entire group moves.

  The first lens group includes a negative lens and a positive lens in order from the object side, and includes at least two aspheric surfaces. The second lens group includes a diaphragm for adjusting the amount of light, and the positive lens and the positive lens sequentially from the object side. Since it has a cemented lens consisting of a lens and a negative lens, and a negative lens, it includes at least two aspheric surfaces, and the third lens group is made of a positive lens. At the same time, it is possible to satisfactorily correct various aberrations. Furthermore, since the conditional expressions (1) and (2) are satisfied, it is easy to achieve downsizing while at the same time ensuring the brightness at the wide-angle end and to increase the focusing speed.

  In the zoom lens of the present invention, when the first lens group satisfies the conditional expressions (3) and (4) and the second lens group satisfies the conditional expressions (5) and (6), the pixel Various aberrations can be satisfactorily corrected to such an extent that high resolution that can be applied to a large number of image sensors can be exhibited.

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

  FIG. 1 shows a configuration of a zoom lens according to an embodiment of the present invention. The zoom lens 1 is preferably used for a particularly compact digital camera or video camera. FIGS. 1A and 1B show lens arrangements at the wide-angle end and the telephoto end, respectively. The side indicated by the symbol Zobj is the object side (subject side), and the side indicated by the symbol Zimg is the image plane side (imaging side). The reference symbol Ri indicates the radius of curvature of the surface Si of the i-th component that increases sequentially toward the image plane side, with the surface S1 of the component closest to the object side including the stop St as the first. Reference symbol Di indicates a surface interval on the optical axis Z1 between the i-th surface and the i + 1-th surface.

  The zoom lens 1 includes a first lens group G1, a second lens group G2, and a third lens group G3 in order from the object side along the optical axis Z1. An aperture stop St is provided at the forefront of the second lens group G2. An imaging element (not shown) such as a CCD is disposed on the imaging plane (imaging plane) Ip of the zoom lens 1, and a cover glass low-pass for protecting the imaging plane is provided in the vicinity of the imaging plane of the imaging element. A filter L8 is arranged.

  In the zoom lens 1, the third lens group G3 is a fixed group at the time of zooming, and the second lens group G2 and the third lens group G3 are a moving group at the time of zooming. More specifically, when zooming while maintaining an infinitely focused state, the distance from the third lens group G3 to the imaging plane Ip (image plane) is kept substantially constant. When zooming from wide angle to telephoto, the mutual distance between the first lens group G1 and the second lens group G2 decreases, while the mutual distance between the second lens group G2 and the third lens group G3 increases. In addition, the first and second lens groups G1 and G2 move. Note that the third lens group G3 moves to the object side when shifting from the infinite focus state to the short distance focus state.

  The first to third lens groups G1, G2, and G3 are configured to satisfy the following conditional expressions (1) and (2). Here, f1, f2, and f3 are the focal lengths of the first to third lens groups G1, G2, and G3, respectively, and fw is the focal length of the entire system at the wide angle end.

0.4 <fw / | f1 | <0.6 (1)
0.25 <f2 / f3 <0.45 (2)

  The first lens group G1 has a negative refractive power as a whole, and has a configuration in which a negative first lens L1 and a positive second lens L2 are arranged in order from the object side. Of the surfaces S1 to S4 of the first lens group G1, at least two surfaces are aspherical. It is preferable that the first lens L1 has a concave surface with a strong curvature toward the image surface side and at least one surface is aspherical. More preferably, both surfaces of the first lens L1 are aspherical. The second lens L2 is a positive meniscus lens having a convex surface facing the object side.

The first lens group G1 preferably satisfies the following conditional expressions (3) and (4). Here, Nd1 is the refractive index of the first lens L1, νd1 is the Abbe number of the first lens L1, and νd2 is the Abbe number of the second lens L2. The refractive index Ndj (j = 1 to 7) is for the d-line, and the Abbe number νdj is expressed using the refractive index Ndj. The same applies to conditional expressions (5) and (6) described later.
Nd1> 1.72 (3)
νd1−νd2> 14 (4)

  The second lens group G2 has a positive refractive power as a whole. The second lens group G2 has a stop St for adjusting the amount of light, and in order from the object side, a positive third lens L3, and a cemented lens L45 including a positive fourth lens L4 and a negative fifth lens L5. The negative sixth lens L6 is disposed. The aperture stop St is disposed on the object side of the third lens L3, and moves integrally as a part of the second lens group G2. Of the surfaces S6 to S12 in the second lens group G2, at least two surfaces are aspheric. Among these, it is preferable that at least one of the surfaces S6 and S7 of the third lens L3 is aspheric. The sixth lens L6 preferably has a concave surface having a strong curvature toward the image side, and at least one of the surfaces S11 and S12 is preferably aspheric. More preferably, both surfaces of the sixth lens L6 are aspherical. For example, the four surfaces S6, S7, S11, and S12 can be aspherical.

The second lens group G2 preferably satisfies the following conditional expressions (5) and (6). Here, Nd3 is the refractive index of the third lens L3, Nd4 is the refractive index of the fourth lens L4 of the cemented lens L45, νd4 is the Abbe number of the fourth lens L4, and νd5 is the fifth of the cemented lens L45. It is the Abbe number of the lens.
(Nd3 + Nd4) / 2> 1.65 (5)
νd4−νd5> 20 (6)

  The third lens group G3 includes a single positive seventh lens L7, and has a positive refractive power as a whole. The seventh lens L7 is constituted by, for example, a biconvex lens.

  Next, the operation and effect of the zoom lens 1 configured as described above will be described.

  In the zoom lens 1, zooming is performed by fixing the third lens group G3 and moving the first lens group G1 and the second lens group G2 in the direction of the optical axis Z1. Specifically, the first lens group G1 draws a concave locus on the object side during zooming from the wide-angle end to the telephoto end (that is, once toward the image plane side Zimg and then toward the object side Zobj). Move as you head. The second lens group G2 moves monotonously toward the object side Zobj during zooming from the wide-angle end to the telephoto end. The third lens group G3 does not move and maintains a fixed position when zooming from the wide-angle end to the telephoto end while maintaining an infinitely focused state. However, at the time of zooming, the mutual distance between the first lens group G1 and the second lens group G2 is decreased, and the mutual distance between the second lens group G2 and the third lens group G3 is increased. Collaborate. The third lens group G3 moves toward the object side Zobj when shifting from the infinite focus state to the short distance focus state.

  With this configuration, the zoom lens 1 can be configured with a minimum number of lenses to achieve miniaturization, and at the same time, various aberrations can be corrected well. In particular, the use of at least two aspheric surfaces for the first lens group G1 and the second lens group G2, respectively, makes it easy to reduce the size and improve various aberrations. In the zoom lens 1, the first lens group G1 and the second lens group G2 can be moved by the zoom mechanism, while the third lens group can be moved by the focusing mechanism. It is relatively easy to retract the lens group while making the distance between the lens groups as narrow as possible. Therefore, it is easy to shorten the total lens length when the camera is not used.

  Here, the significance of the above-described conditional expressions (1) to (6) will be described. Conditional expression (1) indicates that the imaging magnification at the wide-angle end (in other words, the first refractive power (power) at the wide-angle end with respect to the entire system at the wide-angle end in the combined lens group including the second lens group G2 and the third lens group G3 This is a formula representing a desirable range of the refractive power ratio of the lens group G1. By appropriately defining the refractive power distribution of the first lens group G1, it is possible to achieve a reduction in size and correction of various aberrations in a balanced manner. If the lower limit of conditional expression (1) is not reached, the total length of the optical system at the wide-angle end becomes long, and miniaturization cannot be realized. On the other hand, if the upper limit of conditional expression (1) is exceeded, the refractive power of the first lens group will be excessive, and it will not be possible to satisfactorily correct distortion, chromatic aberration of magnification at the wide-angle end, and spherical aberration at the telephoto end. As a result, it is difficult to configure the first lens group with two lenses.

  Conditional expression (2) defines a desirable range of refractive power distribution in the second lens group G2 and the third lens group G3. If the lower limit of conditional expression (2) is not reached, the refractive power of the third lens group G3 becomes too small, so that the moving distance during focusing becomes long, and as a result, it is difficult to increase the focus speed. On the other hand, if the upper limit of conditional expression (2) is exceeded, the refractive power of the third lens group G3 becomes excessive, making it difficult to form a single lens. Further, the decentration sensitivity of the third lens group G3 is increased, and when the retracting mechanism is attached, deterioration of performance becomes a problem.

  Conditional expression (3) defines a desirable refractive index range in the negative lens L1 of the first lens group G1. If the lower limit of conditional expression (3) is not reached, the curvature of the negative lens L1 becomes stronger in the negative direction, so that it is difficult to correct astigmatism and distortion at the wide angle end even if an aspherical surface is used. In practice, the upper limit of conditional expression (3) is about 1.90.

  Conditional expression (4) defines a desirable range of Abbe number differences between the negative lens L1 and the positive lens L2 in the first lens group G1. If the lower limit of conditional expression (4) is not reached, it will be difficult to sufficiently suppress the lateral chromatic aberration at the wide-angle end and the variation in axial chromatic aberration during zooming. In practice, the upper limit of conditional expression (4) is about 35.

  Conditional expression (5) defines a desirable average refractive index range in the positive lenses L3 and L4 in the second lens group G2. If the lower limit of conditional expression (5) is not reached, the balance of the Petzval sum will deteriorate, and it will be difficult to correct astigmatism and curvature of field even if an aspherical surface is used. In reality, the upper limit of conditional expression (5) is about 1.90.

  Conditional expression (6) defines a desirable range of the difference in Abbe number between the two lenses L4 and L5 constituting the cemented lens L45 in the second lens group G2. If the lower limit of conditional expression (6) is not reached, it will be difficult to sufficiently suppress axial chromatic aberration and lateral chromatic aberration in the entire area during zooming. In practice, the upper limit of conditional expression (6) is about 40.

  As described above, according to the zoom lens according to the present embodiment, the third lens group G3 is fixed and only the first and second lens groups G1 and G2 are moved during zooming. The lens group G3 does not have a zoom function. For this reason, the refractive power of the third lens group G3 with respect to the entire system can be relatively reduced, and as a result, the decentration sensitivity of the third lens group G3 can be reduced. In particular, the first lens group G1 and the second lens group G2 are held by one cam barrel and the third lens group G3 is held separately from the first lens group G1 and the second lens group G2 so as to be retractable when not in use. However, since the decentration sensitivity of the third lens group G3 is low, the aberration performance is hardly deteriorated. In addition, since only the first lens group G1 and the second lens group G2 are moved, the lens moving mechanism is simplified as compared with the case where the entire group moves.

  Further, by setting the imaging magnification at the wide-angle end of the combined lens group composed of the second lens group G2 and the third lens group G3 within the range of the expression (1), the combined refractive power (power) of all the lens groups is set. Since the ratio of refractive power of the first lens group G1 is optimized, the total length of the optical system at the wide angle end is shortened. In addition, since various aberrations at the wide-angle end can be corrected satisfactorily, it is easy to configure the first lens group G1 with only two lenses. Therefore, it is possible to achieve downsizing while ensuring the brightness at the wide-angle end.

  In addition, since the refractive power distribution in the second lens group G2 and the third lens group G3 is set and optimized within the range of the conditional expression (2), the amount of focusing movement can be reduced, and the focusing speed can be increased. It becomes easy. Further, since the refractive power of the third lens group G3 is set to be relatively small according to the conditional expression (2), it is easy to configure the third lens group G3 with one lens, which is advantageous for downsizing, and The decentering sensitivity of the three lens group G3 can be suppressed.

Further, since the first lens group G1 satisfies the conditional expressions (3) and (4), it is possible to reduce various aberrations at the wide-angle end that may be caused by the first lens group G1. Furthermore, since the second lens group G2 satisfies the conditional expressions (5) and (6), various aberrations in the entire area at the time of zooming can be reduced. Therefore,
Various aberrations can be satisfactorily corrected to such an extent that high resolution that can be applied to an image sensor having a large number of pixels can be exhibited.

  Next, two specific examples 1 and 2 (first example and second example) related to the zoom lens according to the present embodiment will be described. Here, these two Examples 1 and 2 will be described together.

2 to 4 show the lens data of Example 1 in the zoom lens 1 shown in FIG. 1, and FIGS. 5 to 7 show the lens data of Example 2 in the zoom lens 2 shown in FIG. . 2 and 5 show basic lens data, FIGS. 3 and 6 show data related to the aspheric shape, and FIGS. 4 and 7 show data related to the variable surface distance.

  The column of surface number Si in the lens data of FIG. 2 and FIG. 5 shows the number of the surface of the component that sequentially increases toward the image surface side with the aperture stop St as the first for the zoom lens of each embodiment. Yes. In the column of the radius of curvature Ri, the value of the radius of curvature of the surface of the i-th component from the object side including the stop St is shown in correspondence with the symbol Ri shown in FIG. The portion where the value of the curvature radius Ri is ∞ indicates that it is a plane. Also in the column of the surface interval Di, the interval on the optical axis between the i-th surface Si and the i + 1-th surface Si + 1 from the object side is shown in correspondence with the symbol Di shown in FIG. The unit of the value of the curvature radius Ri and the surface interval Di is millimeter (mm). The Ndj and νdj columns indicate the refractive index and Abbe number values for the d-line (wavelength 587.6 nm) of the j-th lens element from the object side, respectively. f represents the focal length (mm) of the entire system, and ω represents a half angle of view. As shown in FIGS. 2 and 5, the ranges of the focal lengths of the zoom lenses of Examples 1 and 2 are each 8.00 (wide-angle end) to 22.01 (telephoto end). The ratio is about 2.75 times.

  The aspheric data shown in FIGS. 4 and 7 are constants and coefficients in the aspheric polynomial expressed by the following equation (7). The aspherical polynomial in equation (7) represents the shape of the aspherical surface taking the h axis in the direction orthogonal to the optical axis Z1. An aspherical surface is a curved surface obtained by rotating the curve represented by the equation (1) around the optical axis Z1. The value of h represents the distance (height) from the optical axis Z1 to the lens surface, and the value of Z represents the tangent plane (on the optical axis) from the point on the aspheric surface at the position of the height h. It represents the length of the perpendicular line drawn to the (vertical plane), that is, the depth of the aspherical surface. Reference sign R is the radius of curvature of the lens surface in the vicinity of the optical axis (paraxial curvature radius), and reference sign K is a conic constant. Symbols A4, A6, A8, and A10 represent fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients, respectively.

Z = (h ² / R) / [1+ {1− (1 + K) × h ² / R ² } ^1/2 ]
+ A4 h ⁴ + A6 h ⁶ + A8 h ⁸ + A10 h ¹⁰ (7)

  As shown in FIGS. 3 and 6, in the zoom lenses of Examples 1 and 2, both surfaces of the first lens L1 constituting the first lens group G1 (the first surface S1 and the second surface S2). ), Both surfaces (sixth surface S6 and seventh surface S7) of the third lens L3 disposed on the most object side in the second lens group G2, and the most image side in the second lens group G2. Both surfaces (the eleventh surface S11 and the twelfth surface S12) of the sixth lens L6 are aspherical.

  FIG. 4 shows data of the surface distances D4, D12, and D14 in Example 1 for each of the wide-angle end (focal length f = 8.00 mm) and the telephoto end (focal length f = 22.01 mm). The data of the surface distances D4, D12, and D14 in Example 2 are shown for the wide-angle end (focal length f = 8.00 mm) and the telephoto end (focal length f = 22.01 mm), respectively. As shown in these drawings, in the zoom lenses of Examples 1 and 2, the first lens group G1 and the second lens group G2 move during zooming, and the first lens group G1 and the second lens group are moved. The surface distance D4 between G2 and the surface distance D12 between the second lens group G2 and the third lens group G3 change with zooming. On the other hand, the distance between the third lens group G3 and the imaging plane Ip is unchanged at the time of zooming, and is 5.61 in Example 1 and 5.60 in Example 2.

  As is clear from the data shown in FIGS. 2 and 5, the zoom lenses of Examples 1 and 2 satisfy the conditional expressions (1) to (6) described above. In particular, when considering conditional expression (2) “0.25 <f2 / f3 <0.45” indicating the relative magnitude of the refractive power of the third lens group G3, in Examples 1 and 2, the conditional expression The values are 0.32 and 0.33, respectively, which satisfy the range of conditional expression (2), whereas in Patent Document 3, the minimum example is 0.58, which is the upper limit of conditional expression (2). Is over. That is, it is understood that the eccentric sensitivity is smaller in this embodiment than in Patent Document 3. The relative magnitude of the refractive power of the third lens group G3 is expressed by the expression “fw / f3” as the ratio of the refractive power 1 / f3 of the third lens group G3 to the refractive power 1 / fw of the entire system. However, the value of this equation is at least 0.32 in Patent Document 3 described above, whereas it is 0.19 in both Embodiments 1 and 2 of the present invention. From this, it can be seen that the eccentricity sensitivity of the present embodiment is smaller than that of Patent Document 3.

  8 to 11 show various aberrations regarding the zoom lens of each embodiment. More specifically, FIGS. 8 and 9 show aberrations at the wide-angle end and the telephoto end for the zoom lens of Example 1, respectively. 10 and 11 show aberrations at the wide-angle end and the telephoto end for the zoom lens of Example 2, respectively. Here, FIGS. 8 (A), 9 (A), 10 (A), and 11 (A) show spherical aberration, and FIGS. 8 (B), 9 (B), 10 (B), 11B shows astigmatism, FIG. 8C, FIG. 9C, FIG. 10C, and FIG. 11C show distortion (distortion aberration), and FIG. FIG. 9D, FIG. 10D, and FIG. 11D show lateral chromatic aberration. In the diagram showing the spherical aberration, the values for d-line (wavelength 587.6 nm), F-line (wavelength 486.1 nm), and C-line (wavelength 656.3 nm) are shown. In the diagram showing astigmatism, the solid line shows the aberration with respect to the sagittal image plane, and the broken line shows the aberration with respect to the tangential (meridional) image plane. In the figure showing the lateral chromatic aberration, the values for the F-line and the C-line when the d-line is used as a reference are shown. In each aberration diagram of FIGS. 8 to 11, those for which the wavelength is not specified indicate aberration with respect to the d-line. FNo represents an F number, and ω represents a half angle of view.

  FIG. 12 shows values corresponding to the conditional expressions (1) to (6) described above for the respective examples. As shown in this figure, the conditional expressions (1) to (6) are satisfied in any of the embodiments.

  As can be seen from the above lens data and aberration diagrams, in each example, the overall length of the lens is shortened while the zoom ratio and the brightness at the wide-angle end are secured, and the aberration is corrected well.

  In addition, this invention is not limited to the said embodiment and each Example, A various deformation | transformation implementation is possible. For example, the values of the radius of curvature Ri, the surface interval Di, the refractive index Ndj, the Abbe number νdj and the like of each lens component are not limited to the values shown in the above numerical examples, and may take other values.

  In each of the above embodiments, both surfaces of the first lens L1 in the first lens group G1 are aspherical. Instead, one surface of the first lens L1 and one surface of the second lens L2 are used. May be aspherical, or both surfaces of the second lens L2 may be aspherical, and the first lens group G1 only needs to include at least two aspherical surfaces.

  In each of the above embodiments, a total of four surfaces of the second lens group G2, that is, both surfaces of the third lens L3 disposed closest to the object side and both surfaces of the sixth lens L6 disposed closest to the image side are aspheric. Although it is shaped, other configurations are possible as long as the second lens group G2 includes at least two aspheric surfaces. For example, a total of two surfaces, one surface of the third lens L3 and one surface of the sixth lens L6, are aspherical, or a total of three surfaces, one surface of the third lens L3 and both surfaces of the sixth lens L6, are aspheric. Alternatively, a total of three surfaces including both surfaces of the third lens L3 and one surface of the sixth lens L6 can be aspherical. Furthermore, the surfaces of other lenses in the second lens group G2 may be aspherical.

It is sectional drawing which shows the structure of the zoom lens which concerns on one embodiment of this invention. It is a figure which shows the basic data of the 1st Example in the zoom lens which concerns on one embodiment of this invention. It is a figure which shows the aspherical surface data of the zoom lens which concerns on a 1st Example. It is a figure which shows the variable surface distance data of the zoom lens which concerns on a 1st Example. It is a figure which shows the basic data of the 2nd Example in the zoom lens which concerns on one embodiment of this invention. It is a figure which shows the aspherical surface data of the zoom lens which concerns on a 2nd Example. It is a figure which shows the variable surface distance data of the zoom lens which concerns on a 2nd Example. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end of the zoom lens according to Example 1; FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telephoto end of the zoom lens according to Example 1; FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end of the zoom lens according to Example 2; FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telephoto end of a zoom lens according to Example 2; It is a figure which shows the numerical value of the conditional expression of the zoom lens which concerns on the 1st and 2nd Example. It is sectional drawing which shows the structure of the zoom lens of the 2nd Example in this invention. .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 , 2 ... Zoom lens, G1-G3 ... 1st-3rd lens group, L1-L7 ... 1st-7th lens, L8 ... Cover glass low pass filter, St ... Diaphragm, Z1 ... Optical axis.

Claims (5)

A first lens group including a negative first lens and a positive second lens arranged in order from the object side , including at least two aspheric surfaces and having negative refractive power as a whole;
An aspherical surface including at least two aspherical surfaces, which includes a stop for adjusting the amount of light arranged in order from the object side, a cemented lens composed of a positive third lens, a positive fourth lens, and a negative fifth lens, and a negative sixth lens. And a second lens group having a positive refractive power as a whole,
A third lens group including a positive seventh lens and having a positive refractive power;
Are arranged in order from the object side,
When zooming from wide angle to telephoto, the first and second lens groups are decreased in mutual distance, while the second and third lens groups are increased in mutual distance. The second lens group moves,
When zooming while maintaining an infinitely focused state, the distance from the third lens group to the image plane is kept substantially constant,
When shifting from the infinite focus state to the short distance focus state, the third lens group moves to the object side,
A zoom lens satisfying conditional expressions (1) and (2).
0.4 <fw / | f1 | <0.6 (1)
0.25 <f2 / f3 <0.45 (2)
However,
fi: focal length of the i-th lens group (i = 1, 2, 3)
fw: focal length of the entire system at the wide angle end The first lens has a concave surface facing the image side, and at least one surface is aspheric.
The second lens is a positive meniscus lens having a convex surface facing the object side, and
2. The zoom lens according to claim 1, wherein conditional expressions (3) and (4) are satisfied.
Nd1> 1.72 (3)
νd1−νd2> 14 (4)
However,
Nd1: refractive index of the first lens vd1: Abbe number of the first lens vd2: Abbe number of the second lens The zoom lens according to claim 2, wherein the first lens has two aspheric surfaces. The third lens has at least one aspherical surface,
The sixth lens has a concave surface facing the image side, and at least one surface is aspheric.
_ Conditional expression (5) and (6) a zoom lens according to claim 1, characterized by satisfying the.
(Nd3 + Nd4) / 2> 1.65 (5)
νd4−νd5> 20 (6)
However,
Nd3: Abbe number of the fifth lens: third lens refractive index of Nd4: refractive index of the fourth lens vd4: Abbe number of the fourth lens νd5 The zoom lens according to claim 4, wherein the sixth lens has two aspheric surfaces.

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