Zoom lens and imaging apparatus

Abstract

To provide a zoom lens that has good optical performance over the entire zoom range at a wide angle of view despite its small size.SOLUTION: A zoom lens has a plurality of lens groups including a first lens group L1 having a negative refractive power and a second lens group L2 having a positive refractive power, which are arranged in order from an object side to an image side, and has an aperture diaphragm SP closer to the image side than the second lens group, wherein an interval between the adjacent lens groups changes in zooming. The first lens group includes at least four lens elements. When a focal length of the first lens group is defined as f1, a focal length of a negative lens on the most object side in the first lens group is defined as fG1, a distance on an optical axis from a surface on the most object side of the first lens group to the aperture diaphragm at a telephoto end is defined as St, and the entire lens length of the zoom lens at the telephoto end is defined as TDt, conditions of 0.05≤St / TDt≤0.45 and 0.3≤fG1 / f1≤0.98 are satisfied.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a zoom lens. [Background technology]

[0002] There is a demand for compact, wide-angle zoom lenses as imaging optical systems used in imaging devices such as single-lens reflex cameras, video cameras, broadcast cameras, silver-halide film cameras, etc. As such a zoom lens, Patent Documents 1 and 2 disclose zoom lenses that are arranged in this order from the object side to the image side, and that are composed of a first lens group with negative refractive power, a second lens group with positive refractive power, and a subsequent lens group.

[0003] A so-called negative-lead type zoom lens, in which the first lens group has negative refractive power, has a retrofocus refractive power arrangement at the wide-angle end, making it relatively easy to achieve a wide angle of view. In particular, for ultra-wide-angle zoom lenses with an angle of view exceeding 90 degrees, the negative-lead type, which can adopt a refractive power arrangement advantageous for aberration correction at the wide-angle end, is often selected in order to reduce the difficulty of aberration correction at the wide-angle end.

[0004] Furthermore, Patent Document 3 discloses a zoom lens in which a lens group having a negative refractive power is disposed closest to the object side and closest to the image side, thereby shortening the overall optical length and increasing the aperture. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-135552 A [Patent Document 2] JP 2019-191307 A [Patent Document 3] Patent Publication No. 2022-126058 Summary of the Invention [Problem to be solved by the invention]

[0006] In a negative-lead zoom lens, in order to miniaturize the entire system while also achieving a wide angle of view and high optical performance, it is important that the lens groups that make up the zoom lens are appropriately arranged, and the configuration and power arrangement of the first lens group in particular are important.

[0007] The present invention provides a zoom lens that is compact yet has a wide angle of view and good optical performance over the entire zoom range, and an imaging apparatus using the same. [Means for solving the problem]

[0008] A zoom lens according to one aspect of the present invention has a plurality of lens groups including a first lens group with negative refractive power and a second lens group with positive refractive power arranged in that order from the object side to the image side, an aperture stop is provided on the image side of the second lens group, and the distance between adjacent lens groups changes during zooming. The first lens group includes at least four lens elements. Let f1 be the focal length of the first lens group, fG1 be the focal length of the negative lens in the first lens group closest to the object, St be the distance on the optical axis from the surface of the first lens group closest to the object side to the aperture stop at the telephoto end, and TDt be the total lens length of the zoom lens at the telephoto end. 0.05≦St / TDt≦0.45 0.30≦fG1 / f1≦0.98 The present invention is characterized in that it satisfies the following conditions.

[0009] A zoom lens according to another aspect of the present invention has a plurality of lens groups including a first lens group with negative refractive power and a second lens group with positive refractive power arranged in that order from the object side to the image side, an aperture stop is provided on the image side of the second lens group, and the distance between adjacent lens groups changes during zooming. The first lens group includes at least three lens elements. Let f1 be the focal length of the first lens group, fG1 be the focal length of the negative lens in the first lens group closest to the object, St be the distance on the optical axis from the surface of the first lens group closest to the object side to the aperture stop at the telephoto end, and TDt be the total lens length of the zoom lens at the telephoto end. 0.050≦St / TDt≦0.405 0.30≦fG1 / f1≦0.86 The present invention is characterized in that the following conditions are satisfied: The imaging device includes an imaging element that receives an optical image formed by the zoom lens as described above. Effect of the Invention

[0010] According to the present invention, it is possible to provide a zoom lens that is compact yet has a wide angle of view and good optical performance over the entire zoom range. [Brief description of the drawings]

[0011] [Figure 1] 1A to 1C are cross-sectional views of a zoom lens according to a first embodiment at a wide-angle end, at a middle zoom position, and at a telephoto end. [Diagram 2] 5A to 5C are aberration diagrams of the zoom lens of Example 1 at the wide-angle end, at a middle zoom position, and at the telephoto end. [Diagram 3] 11A to 11C are cross-sectional views of a zoom lens according to a second embodiment at a wide-angle end, at a middle zoom position, and at a telephoto end. [Figure 4] 11A to 11C are aberration diagrams of the zoom lens of Example 2 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. [Diagram 5] 11A to 11C are cross-sectional views of a zoom lens according to a third embodiment at a wide-angle end, at a middle zoom position, and at a telephoto end. [Figure 6] 11A to 11C are aberration diagrams of the zoom lens of Example 3 at the wide-angle end, at a middle zoom position, and at the telephoto end. [Figure 7] 11A to 11C are cross-sectional views of a zoom lens according to a fourth embodiment at a wide-angle end, at a middle zoom position, and at a telephoto end. [Figure 8] 11A to 11C are aberration diagrams of the zoom lens of Example 4 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. [Figure 9] FIG. 1 is a schematic diagram of an imaging device equipped with the zoom lenses according to first to fourth embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013] The zoom lenses of Examples 1 to 4 described below have a plurality of lens groups arranged in order from the object side to the image side, including a first lens group with negative refractive power and a second lens group with positive refractive power. Also, an aperture stop is arranged on the image side of the second lens group. During zooming from the wide-angle end to the telephoto end, at least the first lens group L1 moves, and the distance between the first lens group L1 and the second lens group L2 narrows.

[0014] In a zoom lens, a lens group is a group of one or more lenses that move together during zooming between the wide-angle end and the telephoto end. That is, the spacing between adjacent lens groups changes during zooming. The lens group may include an aperture stop. The wide-angle end and the telephoto end respectively indicate the zoom states of the maximum angle of view (shortest focal length) and the minimum angle of view (maximum focal length) when the lens group that moves during zooming is located at both ends of the range that can be moved mechanically or controlled on the optical axis.

[0015] 1 shows cross sections of a zoom lens of Example 1 at a wide-angle end, a middle zoom position, and a telephoto end. Numerical Example 1 corresponding to Example 1 will be shown later. The zoom lens of Numerical Example 1 is a zoom lens with a zoom ratio of about 1.8 and an aperture ratio of about 2.9.

[0016] 2(A), (B), and (C) respectively show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the zoom lens of Numerical Example 1 at the wide-angle end, the intermediate zoom position, and the telephoto end. In the spherical aberration diagrams, Fno indicates the F-number, the solid line indicates the spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line indicates the spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagrams, the solid line S indicates the sagittal image plane, and the dashed line M indicates the meridional image plane. The distortion aberration is shown for the d-line. The chromatic aberration diagrams show the chromatic aberration of magnification at the g-line. ω is the half angle of view (°).

[0017] 3 shows cross sections of the zoom lens of Example 2 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. Numerical Example 2 corresponding to Example 2 will be shown later. The zoom lens of Numerical Example 2 is a zoom lens with a zoom ratio of about 1.7 and an aperture ratio of about 2.9.

[0018] 4A, 4B, and 4C show longitudinal aberrations of the zoom lens of Numerical Example 2 at the wide-angle end, at the intermediate zoom position, and at the telephoto end, respectively.

[0019] 5 shows cross sections of the zoom lens of Example 3 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. Numerical Example 3 corresponding to Example 3 will be shown later. The zoom lens of Numerical Example 3 is a zoom lens with a zoom ratio of about 1.7 and an aperture ratio of about 2.9.

[0020] 6A, 6B, and 6C show longitudinal aberrations of the zoom lens of Numerical Example 3 at the wide-angle end, at the intermediate zoom position, and at the telephoto end, respectively.

[0021] 7 shows cross sections of the zoom lens of Example 4 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. Numerical Example 4 corresponding to Example 4 will be shown later. The zoom lens of Numerical Example 4 is a zoom lens with a zoom ratio of about 1.8 and an aperture ratio of about 2.9.

[0022] 8A, 8B, and 8C show longitudinal aberrations of the zoom lens of Numerical Example 4 at the wide-angle end, at the intermediate zoom position, and at the telephoto end, respectively.

[0023] The zoom lens of each embodiment is used as an imaging optical system in imaging devices such as video cameras, digital still cameras, silver halide film cameras, and TV cameras. The zoom lens of each embodiment can also be used as a projection optical system for projectors. In each cross-sectional view, the left side is the object side (front) and the right side is the image side (rear). If i is the order of the lens groups counted from the object side, Li indicates the i-th lens group.

[0024] SP is the aperture stop that determines (limits) the light flux at the maximum F-number (Fno). IP is the image plane. The image plane IP is where the imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor, or the film surface (photosensitive surface) of a silver halide film camera is located.

[0025] In each cross-sectional view, an arrow labeled "Focus" below a lens group indicates the direction in which that lens group moves during focusing from infinity to a close distance.

[0026] The zoom lens of Example 1 shown in FIG. 1 has five lens groups: a first lens group L1 having negative refractive power, a second lens group L2 having positive refractive power, a third lens group L3 having negative refractive power, a fourth lens group L4 having positive refractive power, and a fifth lens group L5 having positive refractive power.

[0027] The first lens group L1 has four lens elements. One lens element includes a single lens and a cemented lens in which a negative lens and a positive lens are cemented together. In addition, in the case of a composite optical element such as a replica resin layer (hybrid aspheric surface or replica aspheric surface), the resin layer is included in one lens element. Specifically, for example, in the case where a resin layer having a thickness of 0.5 mm or less on the optical axis is formed on the optical element, an element including the optical element and the resin layer is included in one lens element. Note that the resin layer is not taken into consideration when specifying the material of the optical element.

[0028] In the zoom lens of the first embodiment, when zooming from the wide-angle end to the telephoto end in the infinity focused state, the first to third lens groups L1 to L3 move so that the distance between the first lens group L1 and the second lens group L2 decreases and the distance between the second lens group L2 and the third lens group L3 increases. At this time, the fourth lens group L4 moves monotonically toward the object side. Also, the fifth lens group L5 does not move with respect to the image surface.

[0029] The zoom lens of Example 2 shown in Fig. 3 has seven lens groups, including a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, a third lens group L3 with negative refractive power, a fourth lens group L4 with positive refractive power, a fifth lens group L5 with negative refractive power, a sixth lens group L6 with positive refractive power, and a seventh lens group L7 with positive refractive power. In this example, the first lens group L1 also has four lens elements.

[0030] In the zoom lens of the second embodiment, when zooming from the wide-angle end to the telephoto end in the infinity focused state, the first to third lens groups L1 to L3 move so that the distance between the first lens group L1 and the second lens group L2 decreases and the distance between the second lens group L2 and the third lens group L3 increases. At this time, the fourth lens group L4 and the sixth lens group L6 move monotonically toward the object side. In addition, the seventh lens group L7 does not move with respect to the image surface.

[0031] The zoom lens of Example 3 shown in Fig. 5 has six lens groups, including a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, a third lens group L3 with negative refractive power, a fourth lens group L4 with positive refractive power, a fifth lens group L5 with positive refractive power, and a sixth lens group L6 with positive refractive power. In this example, the first lens group L1 also has four lens elements.

[0032] In the zoom lens of Example 3, when zooming from the wide-angle end to the telephoto end in the infinity focused state, the first to third lens groups L1 to L3 move so that the distance between the first lens group L1 and the second lens group L2 decreases and the distance between the second lens group L2 and the third lens group L3 increases. At this time, the fourth lens group L4 and the fifth lens group L5 move monotonically toward the object side. In addition, the sixth lens group L6 does not move with respect to the image surface.

[0033] The zoom lens of Example 4 shown in Fig. 7 has five lens groups, including a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, a third lens group L3 with negative refractive power, a fourth lens group L4 with positive refractive power, and a fifth lens group L5 with positive refractive power. In this example, the first lens group L1 also has four lens elements.

[0034] In the zoom lens of Example 4, when zooming from the wide-angle end to the telephoto end in the infinity focused state, the first to third lens groups L1 to L3 move so that the distance between the first lens group L1 and the second lens group L2 decreases and the distance between the second lens group L2 and the third lens group L3 increases. At this time, the fourth lens group L4 moves monotonically toward the object side. Also, the fifth lens group L5 is stationary relative to the image surface.

[0035] In the zoom lens of each embodiment, when the first lens group L1 has four lens elements, the focal length of the first lens group L1 is f1, and the focal length of the negative lens closest to the object side of the first lens group L1 (zoom lens) is fG1. The distance on the optical axis from the surface closest to the object side (foreground) of the zoom lens at the telephoto end to the aperture stop SP is St, and the total optical length (total lens length) of the zoom lens at the telephoto end is TDt. In this case, the following conditions of formulas (1) and (2) are satisfied.

[0036] 0.05≦St / TDt≦0.45 (1) 0.30≦fG1 / f1≦0.98 (2) In order to ensure a wide angle of view and a predetermined zoom ratio and to satisfactorily correct aberrations, the zoom lens of each embodiment has, in order from the object side, a first lens group L1 having negative refractive power and a second lens group L2 having positive refractive power, and further has an aperture stop SP on the image side of the second lens group L2. By selecting a negative lead type in this way, the rear principal point position can be positioned toward the image side, and a wide-angle zoom lens that achieves both a wide angle of view and a small diameter of the first lens group can be obtained.

[0037] The first lens group L1 has at least four lens elements including a first lens having a negative refractive power and arranged closest to the object. This makes it possible to reduce the diameter of the first lens group L1 while suppressing chromatic aberration of magnification that is likely to occur when the angle is widened. As mentioned above, the lens element includes a cemented lens as one lens element, and the replica resin layer in the composite optical element is not counted as one lens element.

[0038] In addition, in the zoom lens of each embodiment, when zooming from the wide-angle end to the telephoto end, the first lens group L1 moves toward the image side from the zoom position at the wide-angle end to the intermediate zoom position. By using a retrofocus type power arrangement in the wide-angle range, it is possible to satisfactorily correct the field curvature and lateral chromatic aberration in the wide-angle range. When zooming from the wide-angle end to the telephoto end, the second lens group L2 having positive refractive power moves toward the object side, and the distance between the first lens group L1 and the second lens group L2 decreases. Also, by changing the distances between all of the lens groups during zooming, various aberrations are satisfactorily corrected.

[0039] The smaller the zoom lens as a whole is, the more aberrations occur, particularly chromatic aberrations such as axial chromatic aberration and lateral chromatic aberration, and the optical performance tends to deteriorate. In particular, in a retrofocus zoom lens in which the diameter of the first lens unit L1 is made small and the overall lens length is shortened, the more chromatic aberration occurs as the focal length becomes shorter. The first lens group L1 has the role of forming a pupil image of the off-axis chief ray at the center of the aperture stop SP, and since the amount of refraction of the off-axis chief ray is large especially on the wide-angle side, off-axis aberrations, especially astigmatism and distortion, are likely to occur. To achieve compactness, a wide angle is achieved by giving a large refractive power to the negative lens closest to the object, and the distortion and chromatic aberration of magnification that arise as a result are corrected by image processing (electronic distortion correction).

[0040] The reason why the first lens group L1 has at least four lens elements is to ensure a wide angle of view and a predetermined zoom ratio while effectively correcting lateral chromatic aberration and field curvature. By making the power arrangement in the first lens group L1 a retrofocus type, a wide-angle zoom lens with a small first lens group L1 can be obtained.

[0041] Conditional formula (1) defines the distance St from the foreground surface to the aperture stop SP at the telephoto end and the total lens length at the telephoto end as TDt, and indicates the condition for shortening the total lens length and suppressing the occurrence of various aberrations, particularly lateral chromatic aberration. If St becomes large (long) so that St / TDt exceeds the upper limit of conditional formula (1), it is advantageous for aberration correction, but it leads to an increase in the aperture diameter and an increase in the diameter of the subsequent lens group. As a result, it becomes difficult to achieve weight reduction, particularly the weight of the focus lens group. If Tdw becomes large (long) so that St / TDt falls below the lower limit of conditional formula (1), it becomes easy to suppress the aperture diameter, but it leads to an increase in the total optical length, which is not preferable.

[0042] Conditional expression (2) defines the focal length fG1 of the negative lens closest to the object in the first lens group L1 in terms of the focal length of the first lens group L1. This is intended to reduce the diameter of the first lens group L1 and the overall length of the zoom lens, which become problematic when widening the angle. If fG1 / f1 exceeds the upper limit of conditional expression (2), this is advantageous for correcting lateral chromatic aberration, but it results in a larger diameter of the first lens group L1. If fG1 / f1 falls below the lower limit of conditional expression (2), it becomes difficult to correct curvature of field and distortion. This results in an increase in the number of lenses, and therefore in an increase in the overall lens length.

[0043] In addition, by arranging the second lens L2 having positive refractive power closest to the object side on the image side of the first lens group L1, it becomes easier to ensure the accuracy of the decentering position, which becomes an issue when the aperture is increased or the overall length is shortened, and decentering coma aberration can be suppressed.

[0044] As described above, by having an appropriate lens group configuration and simultaneously satisfying conditional expressions (1) and (2), it is possible to obtain an ultra-wide-angle zoom lens that has good optical performance over the entire zoom range and has an angle of view of more than 90 degrees at the wide-angle end.

[0045] On the other hand, when the first lens group L1 has at least three lens elements, the following conditions (1T) and (2T) may be satisfied.

[0046] 0.050≦St / TDt≦0.405 (1T) 0.30≦fG1 / f1≦0.86 (2T) In order to ensure a wide angle of view and a predetermined zoom ratio, and to satisfactorily correct lateral chromatic aberration and curvature of field, the first lens group L1 is composed of at least three lens elements. In this case, it is preferable that at least one of the lens elements is a cemented lens. When the first lens group L1 has three components, a wide-angle zoom lens with a small diameter of the first lens group L1 can be obtained by making the power arrangement in the first lens group L1 a retrofocus type.

[0047] As described above, by having an appropriate lens group configuration and simultaneously satisfying conditional formulas (1T) and (2T), it is possible to obtain an ultra-wide-angle zoom lens that has good optical performance over the entire zoom range and has an angle of view of more than 90 degrees at the wide-angle end.

[0048] It is more preferable that the numerical ranges of the conditional expressions (1) and (2) be as follows:

[0049] 0.10≦St / TDt≦0.43 (1a) 0.52≦fG1 / f1≦0.90 (2a) By satisfying condition (1a), it is possible to suppress an increase in the aperture diameter and to easily suppress the variation of coma with respect to image height, and by satisfying condition (2a), it is possible to reduce the diameter of the first lens unit L1 while satisfactorily correcting various aberrations.

[0050] It is even more preferable that the numerical ranges of the conditional expressions (1a) and (2a) are as follows:

[0051] 0.30≦St / TDt≦0.41 (1b) 0.74≦fG1 / f1≦0.85 (2b) Conditions that the zoom lens of each embodiment should preferably satisfy will be described below.

[0052] The focal lengths of the zoom lens at the wide-angle end and the telephoto end are fw and ft, respectively, and the composite focal length of the rear group LR including at least one lens group on the image side of the aperture stop SP9 (if there is only one lens group, the focal length of that lens group) at the wide-angle end is fLRw. The focal length of the lens group closest to the image side in the zoom lens is fR. The refractive index at the d-line of at least one lens included in the first lens group L1 that is made of a material with the largest refractive index at the d-line is nd1m, the Abbe number based on the d-line is νd1m, and the partial dispersion ratio for the d-line and F-line is θgF1m. The averages of the refractive index and Abbe number of at least one positive lens included in the first lens group L1 are ndpa and νdpa, respectively.

[0053] Furthermore, the first lens group L1 has a negative lens (first negative lens) G1 and a negative lens (second negative lens) G2 arranged in this order from the object side to the image side, and the focal lengths of these negative lenses G1 and G2 are fG1N and fG2N, respectively. The minimum value of the back focus in the entire zoom range is skm. The back focus is the distance on the optical axis from the lens surface (final surface) closest to the image side of the zoom lens to the image surface (paraxial image surface for an infinite object point). If an optical element with extremely weak refractive power is arranged between the final surface and the image surface, but is not a lens group, the air-equivalent value of this optical element is used as the back focus.

[0054] The Abbe number νd and partial dispersion ratio θgF are given by the following, where the refractive indices at the Fraunhofer d-line (587.6 nm), F-line (486.1 nm), C-line (656.3 nm) and g-line (435.8 nm) are Nd, NF, NC and Ng, respectively: νd=(Nd-1) / (NF-NC) θgF=(Ng-NF) / (NF-NC) is defined as:

[0055] Also, let V be the third-order aberration coefficient of distortion at the wide-angle end. Let fX and SFX be the focal length and shape factor of adjacent object-side lens element X on the object side of aperture stop SP, respectively. However, the shape factor when the lens element is a cemented lens is defined by the shapes of the object-side surface and image-side surface of the cemented lens, and the cemented surface is not taken into consideration. If either surface has an aspheric shape, it is expressed by its base R (the radius of the reference quadratic surface). The shape factor SFX is defined by the following equation, where RX1 is the radius of curvature of the object-side surface of object-side lens element X, and RX2 is the radius of curvature of the image-side surface.

[0056] SFX = (RX2 + RX1) / (RX2 - RX1) In the above cases, it is preferable that the zoom lens of each embodiment satisfies at least one of the following conditional expressions (3) to (12).

[0057] 1.90≦nd1m≦2.40 (3) 23≦νd1m≦40 (4) 0.57≦θgF1m≦0.64 (5) 0.35≦|fG1 / fG2|≦0.64 (6) 1.8≦|f1| / skm≦4.2 (7) 0.98≦SFX≦3.00 (8) 1.0≦fX / f1≦2.4 (9) 0.4≦|f1| / fLRw≦0.7 (10) 0.15≦fw / fR≦0.40 (11) 0.2≦V≦1.0 (12) Conditional expressions (3) and (4) stipulate the refractive index nd1m and Abbe number νd1m of the lens made of the material with the largest refractive index among the lenses constituting the first lens group L1. Due to the characteristics of glass, as the refractive index increases, the Abbe number decreases while the partial dispersion ratio θgF tends to increase. When a lens is made of a material with a high refractive index, the curvature becomes small (the radius of curvature becomes large), making it easier to correct various aberrations.

[0058] In a retrofocus zoom lens, if a material with a high refractive index is used for the positive lens of the first lens group L1, which has a negative refractive power as a whole, this is advantageous for the primary achromatic effect of the first lens group L1 and for the miniaturization of the entire zoom lens system. However, this makes it difficult to correct the secondary spectrum of lateral chromatic aberration. In addition, if a material with a high refractive index is used for the negative lens of the first lens group L1, which has a negative refractive power as a whole, the primary achromatic effect of lateral chromatic aberration tends to be insufficient. For this reason, it is important to appropriately set the refractive index and Abbe number of the lens made of the material with the largest refractive index.

[0059] If nd1m exceeds the upper limit of conditional expression (3), it is advantageous for image plane correction, but it becomes difficult to correct lateral chromatic aberration. If nd1m falls below the lower limit of conditional expression (3), it is necessary to weaken the refractive power of the negative lens in order to correct the field curvature, which undesirably results in an increase in the diameter of the first lens unit L1 and an increase in the back focus.

[0060] If νd1m exceeds the upper limit of conditional formula (4), it is advantageous for correcting lateral chromatic aberration, but it becomes difficult to ensure the desired refractive power for the glass material.If νd1m falls below the lower limit of conditional formula (4), it becomes difficult to achieve first-order achromatization of lateral chromatic aberration and axial chromatic aberration, which is not preferable.

[0061] Conditional formula (5) specifies the partial dispersion ratio of the lens made of the material with the largest refractive index among the lenses constituting the first lens group L1, and is a condition for improving the balance of various aberrations such as lateral chromatic aberration and axial chromatic aberration. If θgF1m exceeds the upper limit of conditional formula (5), it is advantageous for correcting axial chromatic aberration, but the partial dispersion ratio becomes too large, which causes a change (curvature) in the lateral chromatic aberration for each image height, which is not preferable. If θgF1m falls below the lower limit of conditional formula (5), the chromatic aberration burden of the lens on the image side of the aperture stop SP increases, and it becomes necessary to place a lens with a large partial dispersion ratio at a position with a high light ray height, which leads to an increase in diameter and mass, which is not preferable.

[0062] Conditional formula (6) defines the refractive power sharing between the negative lens G1N and the negative lens G2N. When the negative lenses G1N and G2N are composite optical elements such as a replica resin layer, the resin layer is included and treated as one lens element as described above. In each embodiment, in order to reduce the size of the entire zoom lens system while widening the angle, two negative lenses are arranged in order from the object side, and the refractive power sharing between them is defined by conditional formula (6).

[0063] If |fG1 / fG2| exceeds the upper limit of conditional expression (6), the refractive power of the negative lens G1N closest to the object becomes weak, leading to an increase in the diameter of the first lens unit L1. If |fG1 / fG2| falls below the lower limit of conditional expression (6), the refractive power of the negative lens G1N closest to the object becomes strong, which is advantageous for making the first lens unit L1 compact, but makes it difficult to correct field curvature and astigmatism.

[0064] Conditional formula (7) defines the focal length f1 of the first lens group L1 as the minimum back focus value skm over the entire zoom range, and indicates the condition for shortening the total optical length at the wide-angle end and ensuring high optical performance. The total optical length is the length on the optical axis from the frontmost surface to the last surface of the zoom lens (total lens length) plus the back focus BF as an air-equivalent value.

[0065] In a negative-lead zoom lens, the refractive power arrangement at the wide-angle end is a retrofocus type as a whole to achieve a wide angle. Therefore, in order to shorten the overall lens length at the wide-angle end, it is necessary to appropriately set the refractive power of the first lens unit L1. By satisfying conditional expression (7), it is possible to achieve both compactness and high performance of the zoom lens.

[0066] If |f1| / skm exceeds the upper limit of conditional expression (7), the refractive power of the first lens group L1 becomes small, and the total lens length increases when securing a desired angle of view at the wide-angle end, which is not preferable.If |f1| / skm falls below the lower limit of conditional expression (7), the refractive power of the first lens group L1 becomes large, making it difficult to correct lateral chromatic aberration and field curvature on the telephoto side, and also inviting insufficient correction of spherical aberration and coma on the telephoto side, which is not preferable.

[0067] Conditional formula (8) prescribes the shape factor of the object-side lens element X adjacent to the aperture stop SP on the object side, and is a condition for appropriately correcting spherical aberration and coma. If SFX exceeds the upper limit of conditional formula (8), the meniscus shape of lens element X becomes stronger, making it difficult to manufacture the lens. If SFX falls below the lower limit of conditional formula (8), the angle of incidence of the lens surface with respect to off-axis rays becomes large, and performance changes due to manufacturing errors during lens assembly become large, which is not preferable.

[0068] Conditional formula (9) defines the refractive power of lens element X and indicates a condition for achieving a wide angle while effectively suppressing spherical aberration and coma aberration. When fX / f1 exceeds the upper limit of conditional formula (9), the refractive power of lens element X becomes weak, which makes it difficult to shorten the distance St described above, which is undesirable. It also becomes difficult to achieve both a wide angle of view and compactness. When fX / f1 falls below the lower limit of conditional formula (9), the refractive power of lens element X becomes strong, which is advantageous for achieving a wide angle of view, but it is undesirable because it makes it difficult to correct spherical aberration and coma aberration in the telephoto range.

[0069] Conditional expression (10) defines the focal length f1 of the first lens group L1, which has a negative refractive power, as the composite focal length fRw of the rear group LR at the wide-angle end, which is closer to the image side than the aperture stop SP. If |f1| / fLRw exceeds the upper limit of conditional expression (10), the negative refractive power of the first lens group L1 becomes strong, the divergence effect of marginal rays becomes large, and it becomes difficult to correct spherical aberration and coma in the rear group LR. Also, if |f1| / fLRw falls below the lower limit of conditional expression (10), the positive refractive power of the rear group LR becomes strong, the convergence effect becomes large, and it becomes difficult to simultaneously suppress the secondary spectrum of lateral chromatic aberration and axial chromatic aberration, which is not preferable.

[0070] Conditional expression (11) specifies the focal length fw at the wide-angle end of the zoom lens as the focal length fR of the lens group closest to the image side among the lens groups whose spacing does not change during zooming. By satisfying this conditional expression (11), the total lens length can be shortened while ensuring the back focus. If the focal length at the wide-angle end is long so that fw / fR exceeds the upper limit of conditional expression (11), the deterioration of off-axis aberrations can be mitigated, but this is not preferable because it becomes difficult to correct spherical aberration on the telephoto side when increasing the aperture. If the refractive power of the lens group closest to the image side is reduced so that fw / fR falls below the lower limit of conditional expression (11), it becomes difficult to ensure the back focus.

[0071] Conditional expression (12) specifies the third-order aberration coefficient of distortion, and is intended to appropriately correct curvature of field and astigmatism, and further suppress degradation of resolution due to enlargement when electronic distortion correction is performed. If V exceeds the upper limit of conditional expression (12), distortion will increase, which is advantageous for making the zoom lens more compact, but undesirably increases degradation of resolution due to enlargement. If V falls below the lower limit of conditional expression (12), it will become difficult to satisfactorily correct curvature of field and lateral chromatic aberration, and is therefore undesirable.

[0072] Furthermore, when an optical image formed by a zoom lens is received by an image sensor, it is desirable to satisfy the following conditional expression (13), where ωw is the half angle of view at the wide-angle end determined by ray tracing.

[0073] 45°≦ωw≦60° (13) If ωw exceeds the upper limit of conditional expression (13), the image compression at each angle of view becomes high, making it difficult to obtain sufficient resolution.If ωw falls below the lower limit of conditional expression (13), it is not preferable because it is not possible to obtain the angle of view required for a wide-angle zoom lens.

[0074] Furthermore, in the zoom lenses of each embodiment, it is preferable that the first lens group L1 is composed of five or less lenses. With this configuration, the number of lenses constituting the first lens group L1, which has a large diameter, can be reduced, thereby making the first lens group L1 smaller and lighter. In addition, in order to make the first lens group L1 smaller and to satisfactorily correct off-axis aberrations such as field curvature and astigmatism in the wide-angle range, it is preferable to arrange three negative lenses consecutively in order from the object side in the first lens group L1. This allows the power arrangement in the first lens group L1 to be of a retrofocus type, making it possible to satisfactorily correct field curvature and coma aberration in the wide-angle range.

[0075] Moreover, it is desirable that the first lens group L1 includes one single lens with positive refractive power, and that the refractive index of the single lens is 1.7 or more, which makes it easy to effectively correct lateral chromatic aberration over the entire zoom range and to reduce the diameter of the first lens group L1.

[0076] In the zoom lens of each embodiment, it is preferable to include three spherical lenses in the first lens group L1. By using three spherical lenses in the first lens group L1, surface shape errors (so-called astigmatism and quirk component errors) that tend to occur in aspherical lenses can be suppressed, and astigmatic difference can be effectively corrected.

[0077] In the zoom lens of each embodiment, it is preferable that the second lens group L2 is composed of one positive lens. This can suppress the diameter of the light beam emitted from the first lens group L1, and the zoom lens can be easily miniaturized. In addition, when a focus lens group is arranged adjacent to the second lens group L2 on the image side, the axial light beam can be made almost afocal, and it is easy to suppress the variation of spherical aberration and coma aberration caused by focusing. It is preferable that the Abbe number based on the d-line of one positive lens constituting the second lens group L2 is 40 or more and 60 or less. This can suppress the aberration variation during focusing on a close object and the variation of coma aberration for each wavelength during focusing.

[0078] In the zoom lens of each embodiment, it is preferable that the third lens group L3 is composed of one negative lens. This facilitates rapid focusing when the third lens group L3 is used as a focus lens group. By using the lens group adjacent to the aperture stop SP as a focus lens group, it is possible to suppress an increase in the mass of the focus lens group, which is likely to become a problem when the aperture is increased. When the focal lengths of the second lens group L2 and the third lens group L3 are f2 and f3, respectively, it is preferable to satisfy the condition of the following formula (14).

[0079] 0.2≦|f3 / f2|≦1.0 (14) Conditional expression (14) defines the focal length of the third lens group L3 in terms of the focal length of the fourth lens group L4. If |f3 / f2| exceeds the upper limit of conditional expression (14), the refractive power of the third lens group L3 becomes weak, and it becomes necessary to secure a large space for the third lens group L3 to move in order to perform focusing within the zoom lens. As a result, the total lens length increases, which is undesirable. If |f3 / f2| falls below the lower limit of conditional expression (14), the convergence of the light beam emerging from the second lens group L2 becomes weak, which is undesirable because fluctuations in spherical aberration and axial chromatic aberration occur due to focusing.

[0080] Moreover, it is desirable that the Abbe number based on the d-line of one of the negative lenses constituting the third lens group L3 is equal to or greater than 45 and equal to or less than 60. This makes it possible to suppress axial chromatic aberration during focusing on a close-up object.

[0081] In the zoom lens of each embodiment, it is preferable that the rear group LR, which is closer to the image side than the aperture stop SP, includes multiple positive lenses whose Abbe number based on the d-line is 75 or more. In order to satisfactorily correct lateral chromatic aberration caused by a wider angle and axial chromatic aberration caused by a larger aperture, it is preferable to arrange at least two positive lenses whose Abbe number is 75 or more. It is even more preferable to arrange three positive lenses whose Abbe number is 75 or more.

[0082] In the zoom lens of each embodiment, the lens group closest to the image side is made immovable (fixed) with respect to the image plane during zooming, which reduces the adhesion of dust, which is a problem when the lens is removed from the imaging device, as with interchangeable lenses, and makes it easier to ensure durability.

[0083] In the zoom lens of each embodiment, it is preferable that the lens closest to the image side in the lens group closest to the image side is a lens having a convex shape toward the image side. This configuration makes it relatively easy to ensure the back focus and also makes it possible to suppress the collection of unnecessary light (ghost) caused by the image sensor.

[0084] In the zoom lens of each embodiment, it is desirable that at least one of the lens surfaces on the image side of the aperture stop SP has an aspheric shape, which makes it possible to effectively correct the curvature of field at the wide-angle end while miniaturizing the zoom lens.

[0085] In the zoom lens of each embodiment, a protective glass for protecting the lens may be arranged on the object side of the first lens group L1. A protective glass or a low-pass filter may be arranged between the lens arranged on the most image side and the image plane. Optical members with extremely weak refractive power, such as protective glass or a low-pass filter arranged on the most object side or the most image side, are not treated as lenses constituting the zoom lens. An "optical member with extremely weak refractive power" is, for example, an optical member whose absolute focal length is 5 times or more the focal length of the entire zoom lens system.

[0086] In the zoom lens of each embodiment, it is preferable that the aperture stop SP is adjacent to the third lens unit L3 on its image side, which ensures a predetermined angle of view at the wide-angle end and makes it easier to suppress an increase in the diameter of the first lens unit L1 when increasing the zoom ratio.

[0087] In the zoom lens of each embodiment, it is preferable that the lens adjacent to the aperture stop SP on the image side is composed of a lens element (single lens or cemented lens) having a strong convex shape toward the object side. By arranging a lens surface with a strong convex shape toward the aperture stop SP, it becomes easier to suppress spherical aberration that occurs with a large aperture and to correct off-axis aberrations in the wide-angle range. Furthermore, by configuring the strongly convex element as a cemented lens, it becomes easier to correct spherical aberration, coma aberration, and field curvature at the same time.

[0088] In the zoom lens of each embodiment, any of the lens groups may be moved in whole or in part as a vibration-proof group in a direction perpendicular to the optical axis to perform vibration proofing (image blur correction). Movement in a direction perpendicular to the optical axis includes movement in a direction including a component in a direction perpendicular to the optical axis (for example, rotation around a point on the optical axis). In the zoom lenses of embodiments 1 to 4, vibration proofing is performed by moving a cemented lens consisting of a tenth lens and an eleventh lens. There is no restriction on the number or shape of the lenses in the vibration-proof group. In addition, it is preferable that the vibration-proof group has a negative refractive power.

[0089] In the zoom lens of each embodiment, focusing can be performed by moving all or a part of any of the lens groups in the optical axis direction as a focusing group.

[0090] It is preferable that the zoom lens of each embodiment does not include a diffractive optical element. Although providing a diffractive optical element is advantageous from the viewpoint of correcting chromatic aberration, it is not preferable because the diffractive optical element generates diffraction flare.

[0091] It is more preferable that the numerical ranges of the conditions (3) to (12) be as follows:

[0092] 1.905≦nd1m≦2.200 (3a) 25≦νd1m≦38 (4a) 0.575≦θgF1m≦0.625 (5a) 0.39≦|fG1 / fG2|≦0.60 (6a) 2.2≦|f1| / skm≦3.5 (7a) 1.00≦SFX≦2.00 (8a) 1.1≦fX / f1≦2.0 (9a) 0.45≦|f1| / fLRw≦0.65 (10a) 0.18≦fw / fR≦0.30 (11a) 0.22≦V≦0.50 (12a) It is even more preferable that the numerical ranges of the conditional expressions (3) to (12) be as follows:

[0093] 1.91≦nd1m≦2.10 (3b) 28≦νd1m≦36 (4b) 0.58≦θgF1m≦0.61 (5b) 0.42≦|fG1 / fG2|≦0.56 (6b) 2.5≦|f1| / skm≦3.1 (7b) 1.1≦SFX≦1.4 (8b) 1.2≦fX / f1≦1.6 (9b) 0.5≦|f1| / fLRw≦0.6 (10b) 0.20≦fw / fR≦0.26 (11b) 0.25≦V≦0.32 (12b) In the zoom lenses of Examples 1 to 4, the lens groups are moved during zooming to reduce the size of the entire system. According to each example, a zoom lens with high imaging performance can be obtained by appropriately setting the magnification load due to the configuration of each lens group and the power arrangement.

[0094] Numerical examples 1 to 4 are shown below. In each numerical example, surface number i indicates the order of the surface when counted from the object side. r is the radius of curvature (mm) of the i-th surface from the object side, d is the lens thickness or air space (mm) between the i-th and (i+1)-th surfaces, and nd is the refractive index at the d-line of the optical material between the i-th and (i+1)-th surfaces. νd and θgF are the Abbe number and partial dispersion ratio of the optical material between the i-th and (i+1)-th surfaces, as described above. BF represents the back focus (mm). The back focus and the overall lens length are as described above. The half angle of view is determined by ray tracing.

[0095] An asterisk (*) next to a surface number indicates that the surface has an aspheric shape. The aspheric shape is expressed by the following formula, where X is the displacement from the apex of the surface in the optical axis direction, H is the height from the optical axis in a direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, A10, and A12 are aspheric coefficients.

[0096]

number

[0097] The conic constant and the aspheric coefficient "ex" are expressed as x10 -x means. Table 1 shows the values ​​relating to the above-mentioned conditional expressions (1) to (12) in each numerical example. [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd θgF 1 144.3036 1.600 1.88202 37.22 0.5770 2* 22.1371 6.609 3 83.0958 1.200 1.80420 46.50 0.5572 4 28.6986 9.218 5 -44.7549 1.200 1.49700 81.61 0.5386 6 125.9165 0.600 7 59.3716 7.271 1.91082 35.25 0.5824 8 -70.2249 (variable) 9 50.1715 2.830 1.65160 58.54 0.5390 10 -660.8048 (variable) 11 -34.0489 1.200 1.77250 49.63 0.5508 12 -526.4616 (variable) 13(Aperture) ∞ 3.000 14 74.6203 5.539 1.55032 75.50 0.5405 15 -30.9554 0.300 16 33.7448 8.252 1.49700 81.61 0.5386 17 -20.0789 1.200 1.80440 39.59 0.5729 18 -130.5977 2.863 19 -66.6857 3.246 1.84666 23.79 0.6191 20 -26.7237 1.000 1.60562 43.70 0.5721 21 72.9080 3.410 22 33.2273 5.671 1.43700 95.10 0.5326 23 -27.5238 0.200 24 22.7871 6.500 1.43700 95.10 0.5326 25 -31.6567 1.000 1.83481 42.72 0.5650 26 25.0720 3.826 27* -64.2569 1.700 1.58313 59.46 0.5418 28* -800.0000 (variable) 29 -1991.3434 7.318 1.48749 70.44 0.5303 30 -33.1143 13.270 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4=-7.11444e-06 A 6= 2.28099e-09 A 8=-8.75851e-11 A10=2.46405e-13 A12=-4.26701e-16 Page 27 K = 0.00000e+00 A 4=-7.98050e-05 A 6= 4.31831e-07 A 8=-1.02601e-08 A10=9.74514e-11 A12=-3.31880e-13 Page 28 K = 0.00000e+00 A 4=-3.06766e-05 A 6= 2.19257e-07 A 8=-3.28288e-09 A10=3.23801e-11 A12=-9.88714e-14 Various data Zoom ratio 1.754 Wide Angle Mid-Telephoto Focal length 15.488 24.114 27.160 F-number 2.900 2.900 2.900 Half angle of view (°) 54.532 42.075 38.744 Image height 17.550 20.100 20.460 Lens length 140.161 129.781 129.964 BF 13.270 13.270 13.270 d 8 26.926 5.641 1.872 d10 6.971 8.548 9.157 d12 4.664 3.088 2.479 d28 1.575 12.481 16.432 Lens Group Data Group starting plane focal length 1 1 -36.383 2 9 71.676 3 11 -47.174 4 13 27.146 5 29 68.992 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd θgF 1 91.0024 1.600 1.95375 32.32 0.5898 2 22.9141 0.250 1.51640 52.16 0.5566 3* 20.6753 6.317 4 74.3507 1.200 1.71300 53.94 0.5439 5 28.0389 8.910 6 -40.8896 1.200 1.49700 81.61 0.5386 7 79.2087 0.600 8 54.0309 7.068 1.91082 35.25 0.5824 9 -70.3602 (variable) 10 47.2746 2.602 1.65160 58.40 0.5399 11 471.6859 (variable) 12 -35.2786 1.200 1.69350 53.34 0.5462 13 -403.9895 (variable) 14(Aperture) ∞ 3.000 15 289.8874 4.608 1.55032 75.50 0.5405 16 -30.3005 0.300 17 41.4830 7.511 1.49700 81.61 0.5386 18 -22.5302 1.300 1.80610 40.73 0.5670 19 -130.7862 (variable) 20 -292.1911 1.000 1.70154 41.15 0.5765 21 35.6517 2.663 1.84666 23.79 0.6191 22 86.6772 (variable) 23 46.5997 3.838 1.43700 95.10 0.5326 24 -460.5014 0.200 25 33.9936 5.541 1.49700 81.61 0.5386 26 -42.0956 0.200 27 35.8410 6.500 1.55032 75.50 0.5405 28 -25.2113 1.000 1.83481 42.72 0.5650 29 21.4777 4.257 30* -78.3877 1.200 1.58313 59.46 0.5418 31* -1000.0000 (variable) 32 -794.2155 7.195 1.48749 70.44 0.5303 33 -33.1520 14.138 Image plane ∞ Aspheric Data 3rd page K = 0.00000e+00 A 4=-1.01362e-05 A 6= 1.09536e-08 A 8=-2.12261e-10 A10= 6.98940e-13 A12=-1.19477e-15 Page 30 K = 0.00000e+00 A 4=-5.32124e-05 A 6= 4.76879e-07 A 8=-1.02863e-08 A10=8.98188e-11 A12=-2.75136e-13 Page 31 K = 0.00000e+00 A 4=-1.85160e-05 A 6= 2.91270e-07 A 8=-5.21828e-09 A10= 4.45444e-11 A12=-1.26266e-13 Various data Zoom ratio 1.656 Wide Angle Mid-Telephoto Focal length 16.482 24.144 27.299 F-number 2.900 2.900 2.900 Half angle of view (°) 52.826 41.811 38.443 Image height 18.100 20.150 20.460 Lens length 141.472 133.916 132.922 BF 14.138 14.138 14.138 d 9 24.526 7.062 1.845 d11 7.469 9.000 8.929 d13 3.970 2.439 2.510 d19 3.524 3.838 3.524 d22 4.309 3.995 4.309 d31 2.276 12.185 16.407 Lens Group Data Group starting plane focal length 1 1 -35.685 2 10 80.438 3 12 -55.812 4 14 39.298 5 20 -123.718 6 23 86.827 7 32 70.749 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd θgF 1 76.5467 1.300 2.00100 29.13 0.5997 2 22.4418 6.615 3* 88.7043 0.100 1.51640 52.20 0.5565 4 64.8907 1.000 1.91082 35.25 0.5824 5 31.0140 8.823 6 -37.6193 1.000 1.49700 81.61 0.5386 7 63.5472 0.600 8 53.2335 7.706 1.95375 32.32 0.5898 9 -62.3908 (variable) 10 55.1718 2.205 1.71700 47.92 0.5605 11 408.0859 (variable) 12 -33.7809 1.100 1.65844 50.88 0.5560 13 -223.7955 (variable) 14(Aperture) ∞ 3.000 15 103.2989 4.869 1.55032 75.50 0.5405 16 -30.8935 0.300 17 32.8265 7.880 1.48071 85.29 0.5362 18 -20.0628 1.200 1.80100 34.97 0.5864 19 -83.1668 2.752 20 -51.2246 3.193 1.84666 23.87 0.6205 21 -23.3554 1.000 1.61340 44.27 0.5633 22 77.7350 (variable) 23 32.2685 5.817 1.43700 95.10 0.5326 24 -27.6423 0.200 25 26.6231 6.500 1.55032 75.50 0.5405 26 -27.1134 1.000 1.83481 42.74 0.5648 27 22.2325 4.370 28* -63.9148 1.300 1.58313 59.46 0.5418 29* -800.0000 (variable) 30 575.7567 7.464 1.48749 70.44 0.5303 31 -33.6058 13.451 Image plane ∞ Aspheric Data 3rd page K = 0.00000e+00 A 4= 6.17177e-06 A 6=-1.29518e-08 A 8= 7.88098e-11 A10=-2.12643e-13 A12= 2.51829e-16 Page 28 K = 0.00000e+00 A 4=-1.03256e-04 A 6= 6.08804e-07 A 8=-1.15508e-08 A10= 1.01885e-10 A12=-3.26591e-13 Page 29 K = 0.00000e+00 A 4=-5.85318e-05 A 6= 4.06348e-07 A 8=-4.66597e-09 A10=4.05409e-11 A12=-1.14325e-13 Various data Zoom ratio 1.651 Wide Angle Mid-Telephoto Focal length 16.475 24.092 27.202 F-number 2.900 2.900 2.900 Half angle of view (°) 52.731 41.964 38.429 Image height 18.100 20.150 20.420 Lens total length 136.256 129.250 129.690 BF 13.451 13.451 13.451 d 9 21.615 5.293 1.793 d11 7.910 10.917 12.042 d13 6.437 3.429 2.304 d22 3.924 3.614 3.511 d29 1.627 11.254 15.297 Lens Group Data Group starting plane focal length 1 1 -38.998 2 10 88.746 3 12 -60.564 4 14 44.682 5 23 129.769 6 30 65.397 [Numerical example 4] Unit: mm Surface Data Surface number rd nd νd θgF 1 127.4188 1.400 1.95375 32.32 0.5898 2 24.9178 0.100 1.51640 52.16 0.5566 3* 22.4657 6.955 4 98.9687 1.000 1.71300 53.94 0.5439 5 33.6571 9.494 6 -41.0481 1.000 1.49700 81.61 0.5386 7 144.1644 0.600 8 67.9850 7.804 1.91082 35.25 0.5824 9 -64.9779 (variable) 10 54.3568 2.484 1.65160 58.54 0.5390 11 609.5662 (variable) 12 -35.7502 1.000 1.64850 53.02 0.5547 13 -287.7205 (variable) 14(Aperture) ∞ 2.500 15 1537.8893 4.844 1.55032 75.50 0.5405 16 -32.4433 0.300 17 38.6332 8.251 1.52841 76.46 0.5396 18 -25.4116 1.000 1.79360 37.09 0.5828 19 -200.3780 7.553 20 -132.9533 3.460 1.85896 22.73 0.6284 21 -40.8207 1.000 1.74400 44.78 0.5655 22 116.4327 2.961 23 39.6295 3.294 1.43700 95.10 0.5326 24 -1056.6036 0.200 25 45.5758 5.408 1.49700 81.61 0.5386 26 -42.9428 0.200 27 32.0183 6.500 1.55397 71.76 0.5389 28 -30.3223 1.000 1.88100 40.14 0.5706 29 23.3060 4.890 30* -58.6534 1.200 1.58313 59.46 0.5418 31* -700.0000 (variable) 32 -583.9845 7.559 1.48749 70.44 0.5303 33 -33.2011 13.330 Image plane ∞ Aspheric Data 3rd page K = 0.00000e+00 A 4=-7.45027e-06 A 6= 4.25581e-09 A 8=-9.63349e-11 A10=2.71199e-13 A12=-4.22553e-16 Page 30 K = 0.00000e+00 A 4=-1.05495e-04 A 6= 8.55788e-07 A 8=-1.06693e-08 A10=7.47737e-11 A12=-2.06882e-13 Page 31 K = 0.00000e+00 A 4=-6.84221e-05 A 6= 6.50483e-07 A 8=-5.61205e-09 A10=3.36657e-11 A12=-7.90314e-14 Various data Zoom ratio 1.789 Wide Angle Mid-Telephoto Focal length 17.423 24.044 31.170 F-number 2.900 2.900 2.900 Half angle of view (°) 51.201 42.348 34.556 Image height 18.100 20.150 20.430 Lens length 153.392 143.135 141.859 BF 13.330 13.330 13.330 d 9 30.057 11.866 1.842 d11 9.116 10.473 11.922 d13 5.232 3.875 2.427 d31 1.701 9.635 18.383 Lens Group Data Group starting plane focal length 1 1 -40.840 2 10 91.426 3 12 -63.048 4 14 30.594 5 32 71.888

[0098] [Table 1]

[0099] [Imaging device] 9 shows a digital still camera (imaging device) using the zoom lens of Examples 1 to 4 as an imaging optical system. Reference numeral 10 denotes a camera body, and 11 denotes an imaging optical system. Reference numeral 12 denotes a solid-state imaging element such as a CCD sensor or a CMOS sensor that is built into the camera body 10 and receives an optical image formed by the imaging optical system 11 and photoelectrically converts (imaging) it. The camera body 10 may be a single-lens reflex camera having a quick-turn mirror, or may be a mirrorless camera without a quick-turn mirror.

[0100] By using the zoom lens of each embodiment as an imaging optical system, it is possible to obtain an imaging device that is small overall and capable of acquiring high-quality images.

[0101] The above embodiment includes the following configurations. (Configuration 1) A zoom lens having a plurality of lens groups including a first lens group having a negative refractive power and a second lens group having a positive refractive power, which are arranged in order from an object side to an image side, an aperture stop is provided on the image side of the second lens group, and a distance between adjacent lens groups changes during zooming, the first lens group includes at least four lens elements; Let f1 be the focal length of the first lens group, fG1 be the focal length of the first negative lens in the first lens group closest to the object, St be the distance on the optical axis from the surface of the first lens group closest to the object to the aperture stop at the telephoto end, and TDt be the total lens length of the zoom lens at the telephoto end. 0.05≦St / TDt≦0.45 0.30≦fG1 / f1≦0.98 A zoom lens characterized by satisfying the following conditions. (Configuration 2) A zoom lens having a plurality of lens groups including a first lens group having a negative refractive power and a second lens group having a positive refractive power, which are arranged in order from an object side to an image side, an aperture stop is provided on the image side of the second lens group, and a distance between adjacent lens groups changes during zooming, the first lens group includes at least three lens elements; Let f1 be the focal length of the first lens group, fG1 be the focal length of the first negative lens in the first lens group closest to the object, St be the distance on the optical axis from the surface of the first lens group closest to the object to the aperture stop at the telephoto end, and TDt be the total lens length of the zoom lens at the telephoto end. 0.050≦St / TDt≦0.405 0.30≦fG1 / f1≦0.86 A zoom lens characterized by satisfying the following conditions. (Configuration 3) Let nd1m be the refractive index at the d-line of at least one lens included in the first lens group, which is made of a material having the largest refractive index at the d-line, and νd1m be the Abbe number based on the d-line. 1.90≦nd1m≦2.40 23≦νd1m≦40 3. The zoom lens according to configuration 1 or 2, which satisfies the following conditions: (Configuration 4) When the partial dispersion ratio of the lens made of a material having the maximum refractive index at the d-line among at least one lens included in the first lens group is θgF1m for the d-line and the F-line, 0.57≦θgF1m≦0.64 4. The zoom lens according to any one of configurations 1 to 3, which satisfies the following condition: (Configuration 5) the first lens group includes the first negative lens and a second negative lens arranged in succession from the object side to the image side, When the focal lengths of the first negative lens and the second negative lens are fG1N and fG2N, respectively, 0.35≦|fG1 / fG2|≦0.64 5. The zoom lens according to any one of configurations 1 to 4, which satisfies the following condition: (Configuration 6) When the minimum back focus value in the entire zoom range of the zoom lens is s km, 1.8≦|f1| / skm≦4.2 6. The zoom lens according to any one of configurations 1 to 5, which satisfies the following condition: (Configuration 7) When the shape factor of adjacent lens elements on the object side with respect to the aperture stop is SFX, 0.98≦SFX≦3.00 7. The zoom lens according to any one of configurations 1 to 6, which satisfies the following condition: (Configuration 8) When the focal length of adjacent lens elements on the object side of the aperture stop is fX, 1.0≦fX / f1≦2.4 3. The zoom lens according to configuration 1 or 2, which satisfies the following conditions: (Configuration 9) When the composite focal length at the wide-angle end of at least one lens group arranged on the image side of the aperture stop is fLRw, 0.4≦|f1| / fLRw≦0.7 4. The zoom lens according to any one of configurations 1 to 3, which satisfies the following condition: (Configuration 10) When the focal length of the zoom lens at the wide-angle end is fw and the focal length of the lens group closest to the image side in the zoom lens is fR, 0.15≦fw / fR≦0.40 4. The zoom lens according to any one of configurations 1 to 3, which satisfies the following condition: (Configuration 11) When V is the third-order aberration coefficient of distortion at the wide-angle end of the zoom lens, 0.2≦V≦1.0 4. The zoom lens according to any one of configurations 1 to 3, which satisfies the following condition: (Configuration 12) A zoom lens according to any one of configurations 1 to 11; and an image sensor that receives an optical image formed by the zoom lens.

[0102] The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment when implementing the present invention. [Explanation of symbols]

[0103] L1 First lens group L2 Second lens group SP aperture stop LR rear group

Claims

1. A zoom lens having a plurality of lens groups including a first lens group having negative refractive power and a second lens group having positive refractive power, which are arranged in this order from the object side to the image side, an aperture stop being located closer to the image side than the second lens group, and in which the spacing between adjacent lens groups changes during zooming, the first lens group includes at least four lens elements; Let f1 be the focal length of the first lens group, fG1 be the focal length of the first negative lens closest to the object side in the first lens group, St be the distance on the optical axis from the surface closest to the object side of the first lens group to the aperture stop at the telephoto end, and TDt be the distance on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the zoom lens at the telephoto end. 0.05≦St / TDt≦0.45 0.30≦fG1 / f1≦0.98 A zoom lens characterized by satisfying the following conditions:

2. A zoom lens having a plurality of lens groups including a first lens group having negative refractive power and a second lens group having positive refractive power, which are arranged in this order from the object side to the image side, an aperture stop being located closer to the image side than the second lens group, and in which the spacing between adjacent lens groups changes during zooming, the first lens group includes at least three lens elements; Let f1 be the focal length of the first lens group, fG1 be the focal length of the first negative lens closest to the object side in the first lens group, St be the distance on the optical axis from the surface closest to the object side of the first lens group to the aperture stop at the telephoto end, and TDt be the distance on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the zoom lens at the telephoto end. 0.050≦St / TDt≦0.405 0.30≦fG1 / f1≦0.86 A zoom lens characterized by satisfying the following conditions:

3. When the refractive index at the d-line of the lens made of a material having the largest refractive index at the d-line among at least one lens included in the first lens group is nd1m and the Abbe number based on the d-line is νd1m, 1.90≦nd1m≦2.40 23≦νd1m≦40 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

4. When the partial dispersion ratio for the d-line and the F-line of the lens made of a material having the largest refractive index at the d-line among at least one lens included in the first lens group is θgF1m, 0.57≦θgF1m≦0.64 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

5. the first lens group includes the first negative lens and the second negative lens arranged in succession in this order from the object side to the image side, When the focal lengths of the first negative lens and the second negative lens are fG1N and fG2N, respectively, 0.35≦|fG1 / fG2|≦0.64 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

6. When the minimum back focus value in the entire zoom range of the zoom lens is s km, 1.8≦|f1| / skm≦4.2 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

7. When the shape factor of adjacent lens elements on the object side of the aperture stop is SFX, 0.98≦SFX≦3.00 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

8. When the focal length of adjacent lens elements on the object side of the aperture stop is fX, 1.0≦fX / f1≦2.4 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

9. When the composite focal length at the wide-angle end of at least one lens group arranged on the image side of the aperture stop is fLRw, 0.4≦|f1| / fLRw≦0.7 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

10. When the focal length of the zoom lens at the wide-angle end is fw and the focal length of the lens unit closest to the image side in the zoom lens is fR, 0.15≦fw / fR≦0.40 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

11. When the third-order aberration coefficient of distortion at the wide-angle end of the zoom lens is V, 0.2≦V≦1.0 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

12. The zoom lens according to claim 1 or 2; and an image sensor that receives an optical image formed by the zoom lens.

Images