Optical system, and imaging device provided with optical system

Abstract

Provided is an optical system. The optical system includes, in order from an object side to an image side, a first lens group including at least one lens and having a negative refractive power, a second lens group including at least one lens and having a positive refractive power, and a third lens group including at least one lens and having a negative refractive power. In focusing, the distance of the first lens group and the third lens group from an imaging plane on an optical axis is fixed, and the second lens group moves along the optical axis.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical system having a plurality of lens groups, and an imaging device having the optical system. BACKGROUND

[0002] In the past, optical systems capable of close-up imaging and capable of wide-angle have been known (see Patent Literature 1 and Patent Literature 2). These optical systems each have, in order from the object side toward the image side along the optical axis, a first lens group having a negative refractive power, a second lens group having a positive curvature, and a third lens group having a negative curvature.

[0003] However, in the optical system described in Patent Literature 1 and the optical system described in Patent Literature 2, the magnification and the focal length of each group are not appropriate, and not only is the wide-angle insufficient, but also the size in the optical axis direction is not sufficiently reduced (thinned).

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent No. 5716569

[0007] Patent Literature 2: Japanese Patent No. 6784950 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] Therefore, an object of the present application is to provide an optical system that is sufficiently wide-angled and thinned, and an imaging device having the optical system.

[0010] SOLUTION TO PROBLEM

[0011] The optical system of the present application has:

[0012] a first lens group including at least one lens and having a negative refractive power, a second lens group including at least one lens and having a positive refractive power, and a third lens group including at least one lens and having a negative refractive power, in order from the object side toward the image side;

[0013] In focusing, the first lens group and the third lens group are fixed in distance from the image plane on the optical axis, and the second lens group moves along the optical axis;

[0014] When a lateral magnification of the second lens group at infinity focus is set as b2, a lateral magnification of the third lens group at infinity focus is set as b3, a focal length of the entire optical system at infinity focus is set as f, a focal length of the second lens group is set as f2, a focal length of the third lens group is set as f3, a total value of distances from a lens surface closest to the object side to a lens surface closest to the image side in each lens group is set as OAL123, and a maximum image height is set as Y,

[0015] The optical system satisfies at least one of the following formulas (1) to (4):

[0016] -1.20 ≤ f3 / f ≤ -0.10... (1)

[0017] -0.40 ≤ b2 ≤ -0.06... (2)

[0018] 0.3 ≤ OAL123 / Y ≤ 2.30 and 1.00 ≤ b3 ≤ 1.30... (3)

[0019] 0.60 ≤ f2 / f ≤ 0.90... (4).

[0020] In the optical system,

[0021] The second lens group is configured to be also movable in a direction orthogonal to the optical axis, and can satisfy:

[0022] 1.00 ≤ (1-b2) x b3 ≤ 1.90.

[0023] Further, in the optical system,

[0024] When a focal length of the first lens group is set as f1, it can satisfy:

[0025] -16.00 ≤ f1 / f ≤ -1.80.

[0026] Further, the optical system is provided with an aperture device capable of changing an aperture diameter,

[0027] The aperture device can be disposed between the first lens group and the second lens group.

[0028] Further, in the optical system,

[0029] When a distance from a lens surface closest to the object side in the optical system to an imaging surface is set as OAL, it can satisfy:

[0030] 1.20 ≤ OAL / f ≤ 2.30.

[0031] Further, in the optical system, it can satisfy:

[0032] 1.00 ≤ (1 - b2 2 ) × b3 2 ≤ 1.70.

[0033] Further, in the optical system,

[0034] In the case where a refractive index of at least one lens in the first lens group at the d line is set as nd1 and an Abbe number of at least one lens in the first lens group at the d line reference is set as vd1, the following can be satisfied:

[0035] 1.50 ≤ nd1 ≤ 1.70 and 15.00 ≤ vd1 ≤ 60.00.

[0036] Further, in the optical system,

[0037] In the case where a refractive index of at least one lens in the third lens group at the d line is set as nd3 and an Abbe number of at least one lens in the third lens group at the d line reference is set as vd3, the following can be satisfied:

[0038] 1.50 ≤ nd3 ≤ 1.70 and 15.00 ≤ vd3 ≤ 60.00.

[0039] Further, in the optical system,

[0040] The first lens group, the second lens group, and at least the first lens group of the third lens group are configured to be able to move toward the image side at the time of non-photographing.

[0041] Further, the imaging device of the present application has:

[0042] Any of the above optical systems, and

[0043] An imaging device, which is disposed at an imaging position of the optical system. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 is a schematic view showing the structure of the imaging device of the present embodiment, and is a view showing a photographing state.

[0045] Figure 2 is a schematic view showing the structure of the imaging device, and is a view showing a state in which the optical system is accommodated.

[0046] Figure 3 is a lens structure view of the optical system of Example 1 in an infinite focus state.

[0047] Figure 4 is a lens structure view of the optical system of Example 1 in a closest focus state.

[0048] Figure 5is a longitudinal aberration map for the optical system of Example 1 in an infinite focus state.

[0049] Figure 6 is a longitudinal aberration map for the optical system of Example 1 in a closest focus state.

[0050] Figure 7 is a lens structure map for the optical system of Example 2 in an infinite focus state.

[0051] Figure 8 is a lens structure map for the optical system of Example 2 in a closest focus state.

[0052] Figure 9 is a longitudinal aberration map for the optical system of Example 2 in an infinite focus state.

[0053] Figure 10 is a longitudinal aberration map for the optical system of Example 2 in a closest focus state.

[0054] Figure 11 is a lens structure map for the optical system of Example 3 in an infinite focus state.

[0055] Figure 12 is a lens structure map for the optical system of Example 3 in a closest focus state.

[0056] Figure 13 is a longitudinal aberration map for the optical system of Example 3 in an infinite focus state.

[0057] Figure 14 is a longitudinal aberration map for the optical system of Example 3 in a closest focus state.

[0058] Figure 15 is a lens structure map for the optical system of Example 4 in an infinite focus state.

[0059] Figure 16 is a lens structure map for the optical system of Example 4 in a closest focus state.

[0060] Figure 17 is a longitudinal aberration map for the optical system of Example 4 in an infinite focus state.

[0061] Figure 18 is a longitudinal aberration map for the optical system of Example 4 in a closest focus state. DETAILED DESCRIPTION

[0062] One embodiment of the present application will be described below with reference to the accompanying drawings.

[0063] As Figure 1 and Figure 2As shown, the camera 1 of the present embodiment includes an optical system 2 that can be housed in a camera body 10 by being extended and contracted, an image pickup element 3 disposed at an image plane position of the optical system 2, and a liquid crystal display 4 that displays image pickup (image) data sent from the image pickup element 3. The image pickup element 3 is an element that converts an optical image formed by the optical system 2 into an electric signal (image pickup data), and the image pickup element 3 of the present embodiment is an image sensor.

[0064] The optical system 2 has at least the first lens group G1, the second lens group G2, and the third lens group G3 in this order from the object side toward the image side along the optical axis C. Each of these lens groups G1, G2, G3 includes at least one lens. The optical system 2 of the present embodiment has the first lens group G1, the second lens group G2, the third lens group G3, and the optical filter 23 in this order from the object side toward the image side along the optical axis C.

[0065] In addition, in the optical system 2 of the present embodiment, the lens groups G1 to G3 are named for convenience, and a lens group composed of only one optical element (lens, etc.) is also included. That is, the first to third lens groups G1, G2, G3 each have at least one optical element such as a lens. In addition, in the optical system 2, the optical elements (lenses, etc.) whose positions on the optical axis C are fixed at the time of focusing and the optical elements that move are divided, the at least one optical element that is fixed in the divided region is taken as one lens group, and the at least one optical element that moves in the divided region is taken as another lens group.

[0066] In addition, the optical system 2 has an aperture stop (aperture device) 21 disposed between the first lens group G1 and the second lens group G2 and a lens barrel 22 that holds the first lens group G1 and the second lens group G2 (see Figure 1 ). The lens barrel 22 extends toward the object side at the time of photographing (see Figure 1 ) and is housed in the camera body (or the like) by being extended and contracted at the time of non-photographing (see Figure 2 ).

[0067] In the optical system 2, at the time of focusing, the distance between the first lens group G1 and the third lens group G3 on the image pickup element 3 (image plane of the optical system 2) along the optical axis C is fixed, and the second lens group G2 moves along the optical axis C. That is, in the optical system 2 of the present embodiment, among the lens groups G1, G2, G3, the second lens group G2 constitutes a focus lens group.

[0068] Further, in the optical system 2, at least the first lens group G1 moves toward the image side at the time of telescopic accommodation. The optical system 2 of the present embodiment is accommodated in the camera body 10 by moving the first lens group G1 and the second lens group G2 toward the image side, respectively, at the time of telescopic accommodation (refer to FIG. 6). Figure 2 The movement of each lens group G1 to G3 and the telescopic movement of the lens barrel 22 are performed by various mechanisms known in the art.

[0069] Hereinafter, each lens group G1 to G3 in the optical system 2 will be described in detail.

[0070] The first lens group G1 includes one lens (optical element) and has a negative refractive power. Further, the second lens group G2 includes a plurality of lenses (optical elements) and has a positive curvature. Further, the third lens group G3 includes a plurality of lenses (optical elements) and has a negative refractive power.

[0071] wherein, when a transverse magnification of the second lens group G2 at infinity focus is set as b2, a transverse magnification of the third lens group G3 at infinity focus is set as b3, a focal length of the optical system 2 as a whole at infinity focus is set as f, a focal length of the second lens group G2 is set as f2, a focal length of the third lens group G3 is set as f3, a total value of distances from a lens surface closest to the object side to a lens surface closest to the image side in each lens group G1, G2, G3 is set as OAL123, and a maximum image height is set as Y, the optical system 2 satisfies at least one of the following equations (1) to (4):

[0072] -1.20 ≤ f3 / f ≤ -0.10... (1)

[0073] -0.40 ≤ b2 ≤ -0.06... (2)

[0074] 0.3 ≤ OAL123 / Y ≤ 2.30 and 1.00 ≤ b3 ≤ 1.30... (3)

[0075] 0.60 ≤ f2 / f ≤ 0.90... (4).

[0076] In the optical system 2, since the first lens group G1 having a negative refractive power is disposed closest to the object side, a reverse focal power configuration is easily obtained, and thus, wide-angle can be achieved by shortening the focal length. Further, since the third lens group G3 having a negative refractive power is disposed closest to the image side, a long focal power configuration is easily obtained, and thus, thinness (miniaturization of the size in the optical axis C direction) can be achieved by shortening the focal length of the second lens group G2.

[0077] Further, at the time of focusing, by enabling the second lens group G2 to move, the balance of aberration variation with the groups before and after (the first lens group G1, the third lens group G3) is adjusted, and compared with the optical system of the overall protruding type, the image surface curvature variation at the time of close-up imaging is suppressed, so the close-up imaging distance can be further shortened.

[0078] Further, at the time of focusing, by fixing the distance of the first lens group G1 and the third lens group G3 on the optical axis C from the imaging element 3 (imaging surface), only the second lens group G2 can be moved in the direction of the optical axis C, the load of the moving mechanism of the lens group G2 by the actuator or the like is reduced, so the thinness and the smallness of the optical system 2 can be achieved.

[0079] In addition, in the optical system 2 of the present embodiment, by satisfying formula (1), a thin and bright optical system 2 can be obtained. Details are as follows.

[0080] Formula (1) specifies the range of the ratio of the focal length of the third lens group G3 to the focal length of the entire optical system 2 at the time of focusing at infinity (f3 / f), and when the ratio (f3 / f) is less than the lower limit value (-1.20), the power of the third lens group G3 becomes weak, so it is difficult to zoom in, and thus the focal length of the second lens group G2 cannot be shortened, so the thinness is insufficient. On the other hand, when the ratio (f3 / f) is greater than the upper limit value (-0.10), the power of the third lens group G3 becomes strong, so the thinness becomes easy, but since the negative power of the group (third lens group) G3 closest to the image side is too strong, it is difficult to constitute a bright (i.e., small F number) optical system 2, and a dark (i.e., large F number) optical system is obtained. Therefore, in the optical system 2 of the present embodiment, by setting the ratio of the focal length of the third lens group G3 to the focal length of the entire optical system 2 at the time of focusing at infinity (f3 / f) to the range of formula (1), a balance between thinness and brightness can be achieved.

[0081] In addition, in the optical system 2 of the present embodiment, the ratio (f3 / f) is preferably satisfied as follows:

[0082] -1.10 ≤ f3 / f ≤ -0.50;

[0083] More preferably, the following is satisfied:

[0084] -1.00 ≤ f3 / f ≤ -0.70.

[0085] In addition, in the optical system 2 of the present embodiment, by satisfying formula (2), a thin and wide-angle optical system 2 can be obtained. Details are as follows.

[0086] The formula (2) defines a range of the lateral magnification (b2) of the second lens group G2 at infinity focus, and when the lateral magnification (b2) is smaller than the lower limit value (-0.40), it is difficult to shorten the focal length of the second lens group G2, and thus it is difficult to sufficiently perform thinning. On the other hand, when the lateral magnification (b2) is larger than the upper limit value (-0.06), the optical power of the first lens group G1 becomes weak, and thus it is difficult to widen the angle of view. Therefore, in the optical system 2 of the present embodiment, by setting the lateral magnification (b2) of the second lens group G2 at infinity focus to the range of the formula (2), it is possible to achieve a balance between thinning and wide-angle.

[0087] Further, in the optical system 2 of the present embodiment, the lateral magnification (b2) preferably satisfies:

[0088] -0.38 ≤ b2 ≤ -0.10;

[0089] More preferably, it satisfies:

[0090] -0.36 ≤ b2 ≤ -0.15.

[0091] Further, in the optical system 2 of the present embodiment, by satisfying the formula (3), it is possible to obtain a high-performance, thin, and bright optical system 2. Details are as follows.

[0092] The first formula (0.3 ≤ OAL123 / Y ≤ 2.30) of the formula (3) defines a range of a ratio (OAL123 / Y) of the total value of the distances from the lens surface closest to the object side to the lens surface closest to the image side in each lens group G1, G2, G3 to the maximum image height, and when the ratio (OAL123 / Y) is smaller than the lower limit value (0.3), the thicknesses of each lens group G1, G2, G3 are all too thin (i.e., the size in the optical axis C direction is too small), and aberration correction becomes difficult, and thus high performance becomes difficult. On the other hand, when the ratio (OAL123 / Y) is larger than the upper limit value (2.30), the thicknesses of each lens group G1, G2, G3 are all too thick (i.e., the size in the optical axis C direction is too large), and thus it is difficult to thin. Therefore, in the optical system 2 of the present embodiment, by setting the ratio (OAL123 / Y) of the total value of the distances from the lens surface closest to the object side to the lens surface closest to the image side in each lens group G1, G2, G3 to the maximum image height to the first formula (0.3 ≤ OAL123 / Y ≤ 2.30) of the formula (3), it is possible to achieve a balance between high performance and thinning.

[0093] In addition, the total value of the distance from the lens surface closest to the object side to the lens surface closest to the image side in each lens group G1, G2, G3 refers to the sum of the distance from the lens surface closest to the object side to the lens surface closest to the image side of the first lens group G1, the distance from the lens surface closest to the object side to the lens surface closest to the image side of the second lens group G2, and the distance from the lens surface closest to the object side to the lens surface closest to the image side of the third lens group G3.

[0094] In addition, in the optical system 2 of the present embodiment, the ratio (OAL123 / Y) preferably satisfies:

[0095] 0.50 ≤ OAL123 / Y ≤ 2.00;

[0096] More preferably, the ratio (OAL123 / Y) satisfies:

[0097] 0.80 ≤ OAL123 / Y ≤ 1.80.

[0098] In addition, the second formula (1.00 ≤ b3 ≤ 1.30) of the formula (3) defines the range of the lateral magnification (b3) of the third lens group G3 at the time of focusing at infinity, and when the lateral magnification (b3) is less than the lower limit value (1.00), it is difficult to shorten the focal length to the second lens group G2, and thus it is difficult to sufficiently thin the profile. On the other hand, when the lateral magnification (b3) is greater than the upper limit value (1.30), the optical power of the third lens group G3 becomes strong, and thus thinning becomes easy, but the negative optical power of the group closest to the image side (third lens group) G3 is too strong, and thus it is difficult to configure a bright (i.e., small F number) optical system 2, and a dark (i.e., large F number) optical system is formed. Therefore, in the optical system 2 of the present embodiment, by setting the lateral magnification (b3) of the third lens group G3 at the time of focusing at infinity to the second formula (1.00 ≤ b3 ≤ 1.30) of the formula (3), a balance between thinness and brightness can be achieved.

[0099] In addition, in the optical system 2 of the present embodiment, the lateral magnification (b3) preferably satisfies:

[0100] 1.05 ≤ b3 ≤ 1.26;

[0101] More preferably, the lateral magnification (b3) satisfies:

[0102] 1.10 ≤ b3 ≤ 1.24.

[0103] In addition, in the optical system 2 of the present embodiment, by satisfying the formula (4), an optical system 2 that is high in performance and thin in profile can be obtained. Details are as shown below.

[0104] The formula (4) defines a range of the ratio of the focal length of the second lens group G2 to the focal length of the optical system 2 as a whole when focusing at infinity (f2 / f), and when the ratio (f2 / f) is smaller than the lower limit value (0.60), the power of the second lens group G2 becomes stronger, and aberration correction becomes difficult, and thus high performance becomes difficult. On the other hand, when the ratio (f2 / f) is larger than the upper limit value (0.90), the power of the second lens group G2 becomes weaker, and the positive power in the optical system 2 as a whole becomes weaker, and thus thinning of the optical system 2 becomes difficult. Therefore, in the optical system 2 of the present embodiment, by setting the ratio of the focal length of the second lens group G2 to the focal length of the optical system 2 as a whole when focusing at infinity (f2 / f) to the range of the formula (4), a balance between high performance and thinning can be achieved.

[0105] Further, in the optical system 2 of the present embodiment, the ratio (f2 / f) is preferably satisfied by:

[0106] 0.70 ≤ f2 / f ≤ 0.85;

[0107] More preferably, the following is satisfied:

[0108] 0.75 ≤ f2 / f ≤ 0.80.

[0109] Further, in the optical system 2, the second lens group G2 is configured to be able to move in the direction orthogonal to the optical axis C also at the time of optical hand-shake correction, and the following can be satisfied:

[0110] 1.00 ≤ (1 - b2) x b3 ≤ 1.90.

[0111] According to this configuration, a small-sized optical system 2 in which the accuracy of the stop position of the lens group G2 when moved in the direction orthogonal to the optical axis C at the time of optical hand-shake correction is easily ensured can be obtained. Details are as follows.

[0112] In optical hand-shake correction by optical image stabilization (OIS) of a conventional optical system, it is necessary to move (displace) the optical system or the imaging element with respect to the optical axis in the orthogonal direction. Therefore, by being configured such that only a part of the plurality of lens groups (the second lens group G2) constituting the optical system 2 is moved with respect to the optical axis C in the orthogonal direction as in the optical system 2 of the present embodiment, it is possible to suppress the weight of the unit moved in the direction orthogonal to the optical axis C at the time of OIS (i.e., to be lightweight). As a result, the load on the drive system that drives the unit is suppressed, and as a result, it is possible to achieve thinning of the optical system 2 and the imaging device 1 having the optical system 2. Further, when the optical system 2 is applied to an imaging device 1 having a large imaging element 3, this effect can be obtained significantly.

[0113] In addition, the above formula defines a range of a ratio of the movement amount of the second lens group G2 when the second lens group G2 is moved in the orthogonal direction with respect to the optical axis C to the movement amount of the image due to the movement of the second lens group G2, the ratio being obtained by using a calculation formula ((1 - b2) x b3) of the lateral magnification of the second lens group G2 at the time of focusing at infinity and the lateral magnification of the third lens group G3 at the time of focusing at infinity. When the ratio (the value of the calculation formula) is smaller than the lower limit value (1.00), the movement amount of the image due to the movement of the second lens group G2 in the orthogonal direction with respect to the optical axis C is small, and thus it is necessary to increase the movement amount (the movement in the orthogonal direction) of the second lens group G2 at the time of OIS, and thus the load of the driving system becomes large, and the miniaturization of the optical system 2 and the entire camera device 1 provided with the optical system 2 becomes difficult. On the other hand, when the ratio (the value of the calculation formula) is larger than the upper limit value (1.90), the movement amount of the image due to the movement of the second lens group G2 in the orthogonal direction with respect to the optical axis C becomes large (that is, becomes sensitive), and thus it is difficult to secure the accuracy of the stop position of the lens group G2 when the lens group G2 is moved in the direction orthogonal to the optical axis C in the optical hand-shake correction. Thus, in the optical system 2 of the present embodiment, by setting the ratio (the value of the calculation formula) of the movement amount of the second lens group G2 when the second lens group G2 is moved in the orthogonal direction with respect to the optical axis C to the movement amount of the image due to the movement of the second lens group G2 in the orthogonal direction with respect to the optical axis C to the range of the above formula, it is possible to achieve a balance between the miniaturization and the difficulty of securing the accuracy of the stop position of the lens group G2 when the lens group G2 is moved in the direction orthogonal to the optical axis C in the optical hand-shake correction.

[0114] In addition, in the optical system 2 of the present embodiment, the ratio (the value of the calculation formula) is preferably satisfied as follows:

[0115] 1.15 ≤ (1 - b2) x b3 ≤ 1.80;

[0116] More preferably, the ratio (the value of the calculation formula) is satisfied as follows:

[0117] 1.30 ≤ (1 - b2) x b3 ≤ 1.70.

[0118] In addition, in the optical system 2, when the focal length of the first lens group G1 is set to f1, the following can be satisfied:

[0119] -16.00 ≤ f1 / f ≤ -1.80.

[0120] According to this configuration, it is possible to obtain an optical system 2 which is wide-angled and thin. Details are as follows.

[0121] The above formula defines a range of the ratio of the focal length of the first lens group G1 to the focal length of the entire optical system 2 when focusing at infinity (f1 / f), and when the ratio (f1 / f) is smaller than the lower limit value (-16.00), the power of the first lens group G1 becomes weaker, and the negative power on the object side becomes weaker, so it becomes difficult to widen the angle of view. On the other hand, when the ratio (f1 / f) is larger than the upper limit value (-1.80), the power of the first lens group G1 becomes stronger, so the number of lens pieces increases in order to have positive power at the second lens group G2, and thus it becomes difficult to thin the optical system 2. Therefore, in the optical system 2 of the present embodiment, by setting the ratio of the focal length of the first lens group to the focal length of the entire optical system 2 when focusing at infinity (f1 / f) to the range of the above formula, it is possible to achieve a balance between widening the angle of view and thinning.

[0122] In addition, in the optical system 2 of the present embodiment, the ratio (f1 / f) is preferably satisfied as follows:

[0123] -10.00 ≤ f1 / f ≤ -2.00;

[0124] More preferably, the ratio (f1 / f) is satisfied as follows:

[0125] -6.00 ≤ f1 / f ≤ -2.20.

[0126] In addition, the optical system 2 is provided with an aperture stop (iris) 21 that can change the aperture diameter, and the aperture stop 21 is disposed between the first lens group G1 and the second lens group G2.

[0127] When the aperture stop (iris) 21 is disposed on the object side of the first lens group G1, the size of the optical system 2 in the optical axis direction increases due to the thickness of the mechanism part, but as shown in the above configuration, by disposing the aperture stop 21 between the first lens group G1 and the second lens group G2, the aperture diameter of the optical system 2 can be changed, so it is possible to thin the optical system 2.

[0128] In addition, in the optical system 2, when the distance from the lens surface closest to the object side in the optical system 2 to the imaging element (i.e., the imaging surface) 3 is set as OAL, it is possible to satisfy:

[0129] 1.20 ≤ OAL / f ≤ 2.30.

[0130] According to this configuration, it is possible to obtain an optical system 2 that is high in performance and thin. Details are as follows.

[0131] The above formula defines a range of the ratio (OAL / f) of the distance from the lens surface on the object side closest to the optical system 2 to the imaging element 3 to the focal length of the entire optical system 2 when focused at infinity, and when the ratio (OAL / f) is smaller than the lower limit value (1.20), the optical total length of the optical system 2 becomes short, and aberration correction becomes difficult, and thus high performance becomes difficult. On the other hand, when the ratio (OAL / f) is larger than the upper limit value (2.30), the optical total length of the optical system 2 becomes long, and thus it is difficult to thin. Therefore, in the optical system 2 of the present embodiment, by setting the ratio (OAL / f) of the distance from the lens surface on the object side closest to the optical system 2 to the imaging element (imaging surface) 3 to the focal length of the entire optical system 2 when focused at infinity to the range of the above formula, it is possible to achieve a balance between high performance and thinness.

[0132] In addition, in the optical system 2 of the present embodiment, the ratio (OAL / f) is preferably satisfied as follows:

[0133] 1.35 ≤ OAL / f ≤ 2.10;

[0134] More preferably, the ratio (OAL / f) is satisfied as follows:

[0135] 1.50 ≤ OAL / f ≤ 1.90.

[0136] In addition, in the optical system 2, the following can be satisfied:

[0137] 1.00 ≤ (1-b2 2 ) × b3 2 ≤ 1.70.

[0138] According to this configuration, it is possible to obtain an optical system 2 that is thinned and in which it is easy to ensure the accuracy of the stop position of the second lens group G2 at the time of focusing. Details are as follows.

[0139] The above formula defines a range of the ratio of the movement amount of the second lens group G2 when the second lens group G2 is moved in the direction of the optical axis C to the movement amount of the imaging position in the direction of the optical axis C due to the movement of the second lens group G2, which is calculated using the lateral magnification of the second lens group G2 when focused at infinity and the lateral magnification of the third lens group G3 when focused at infinity ((1-b2 2 ) × b3 2) is smaller than the lower limit value (1.00), the movement amount of the imaging position when the second lens group G2 is moved in the optical axis C direction becomes small (i.e., becomes sluggish), and thus it is necessary to increase the movement amount of the second lens group G2 at the time of focusing, whereby thinning of the optical system 2 becomes difficult. On the other hand, when the ratio (value of the calculation formula) is larger than the upper limit value (1.70), the movement amount of the imaging position when the second lens group G2 is movable in the optical axis C direction becomes large (i.e., becomes sensitive), and thus it is difficult to ensure the precision of the stop position of the second lens group G2 at the time of focusing. Therefore, in the optical system 2 of the present embodiment, by setting the ratio of the movement amount of the second lens group G2 when the second lens group G2 is moved in the optical axis C direction to the movement amount of the imaging position in the optical axis C direction due to movement of the second lens group G2 to the range of the above formula, it is possible to achieve a balance of the easiness and difficulty of thinning and ensuring the precision of the stop position of the second lens group G2 at the time of focusing.

[0140] Further, in the optical system 2 of the present embodiment, the ratio (value of the calculation formula) is preferably satisfied by:

[0141] 1.10 ≤ (1 - b2 2 ) x b3 2 ≤ 1.60;

[0142] More preferably, it is satisfied by:

[0143] 1.20 ≤ (1 - b2 2 ) x b3 2 ≤ 1.50.

[0144] Further, in the optical system 2, when the refractive index on the d line of at least one lens in the first lens group G1 is set to nd1, and the Abbe number of the d line reference of at least one lens in the first lens group G1 is set to vd1, it is possible to satisfy:

[0145] 1.50 ≤ nd1 ≤ 1.70 and 15.00 ≤ vd1 ≤ 60.00.

[0146] According to this configuration, it is possible to obtain an optical system 2 that is wide-angled, high-performing, and thin. Details are shown below.

[0147] The above first formula (1.50 ≤ nd1 ≤ 1.70) defines a range of the refractive index (nd1) on the d line of at least one lens in the first lens group G1, and when the refractive index (nd1) is less than the lower limit value (1.50), the power of the first lens group G1 becomes weak, and thus it is difficult to widen the angle of view. On the other hand, when the refractive index (nd1) is greater than the upper limit value (1.70), the error at the time of manufacture causes the performance to significantly deteriorate, and thus it is difficult to achieve high performance. Therefore, in the optical system 2 of the present embodiment, by setting the refractive index (nd1) on the d line of at least one lens in the first lens group G1 to the above first formula (1.50 ≤ nd1 ≤ 1.70), it is possible to achieve a balance between widening the angle of view and high performance.

[0148] In addition, in the optical system 2 of the present embodiment, the refractive index (nd1) preferably satisfies:

[0149] 1.54 ≤ nd1 ≤ 1.69;

[0150] More preferably, it satisfies:

[0151] 1.57 ≤ nd1 ≤ 1.68.

[0152] In addition, the above second formula (15.00 ≤ vd1 ≤ 60.00) defines a range of the Abbe number (vd1) on the d line reference of at least one lens in the first lens group G1, and when the Abbe number (vd1) is less than the lower limit value (15.00), the number of lens pieces is increased in order to correct the axial chromatic aberration and the magnification chromatic aberration of the first lens group G1, and thus it is difficult to thin the optical system 2. On the other hand, when the Abbe number (vd1) is greater than the upper limit value (60.00), it is difficult to adjust the balance of the chromatic aberration correction with other groups, and thus it is difficult to achieve high performance. Therefore, in the optical system 2 of the present embodiment, by setting the Abbe number on the d line reference of at least one lens in the first lens group G1 to the above second formula (15.00 ≤ vd1 ≤ 60.00), it is possible to achieve a balance between thinness and high performance.

[0153] In addition, in the optical system 2 of the present embodiment, the Abbe number (vd1) preferably satisfies:

[0154] 18.00 ≤ vd1 ≤ 57.00;

[0155] More preferably, it satisfies:

[0156] 19.00 ≤ vd1 ≤ 38.00.

[0157] In addition, in the optical system 2, when the refractive index on the d line of at least one lens in the third lens group G3 is set to nd3, and the Abbe number on the d line reference of at least one lens in the third lens group G3 is set to vd3, it can satisfy:

[0158] 1.50≤nd3≤1.70 and 15.00≤vd3≤60.00.

[0159] According to this configuration, the optical system 2 can be wide-angled, high- performance, and thin. Details are as follows.

[0160] The above first formula (1.50≤nd3≤1.70) defines a range of the refractive index (nd3) on the d line of at least one lens in the third lens group G3. When the refractive index (nd3) is less than the lower limit value (1.50), the power of the third lens group G3 becomes weak, and thus wide-angling becomes difficult. On the other hand, when the refractive index (nd3) is greater than the upper limit value (1.70), the error at the time of manufacture causes a significant decline in performance, and thus high performance becomes difficult. Therefore, in the optical system 2 of the present embodiment, by setting the refractive index (nd3) on the d line of at least one lens in the third lens group G3 to the above first formula (1.50≤nd3≤1.70), a balance between wide-angling and high performance can be achieved.

[0161] In addition, in the optical system 2 of the present embodiment, the refractive index (nd3) preferably satisfies:

[0162] 1.54≤nd3≤1.69;

[0163] More preferably, it satisfies:

[0164] 1.57≤nd3≤1.68.

[0165] In addition, the above second formula (15.00≤vd3≤60.00) defines a range of the Abbe number (vd3) on the d line reference of at least one lens in the third lens group G3. When the Abbe number (vd3) is less than the lower limit value (15.00), the number of lens pieces is increased in order to correct the axial chromatic aberration and the magnification chromatic aberration of the third lens group G3, and thus thinning of the optical system 2 becomes difficult. On the other hand, when the Abbe number (vd3) is greater than the upper limit value (60.00), the balance adjustment of the chromatic aberration correction with other groups becomes difficult, and thus high performance becomes difficult. Therefore, in the optical system 2 of the present embodiment, by setting the range of the Abbe number (vd3) on the d line reference of at least one lens in the third lens group G3 to the above second formula (15.00≤vd3≤60.00), a balance between thinning and high performance can be achieved.

[0166] In addition, in the optical system 2 of the present embodiment, the Abbe number (vd3) preferably satisfies:

[0167] 18.00≤vd3≤57.00;

[0168] More preferably, the following are satisfied:

[0169] 19.00 ≤ vd3 ≤ 38.00.

[0170] Further, in the optical system 2, at least the first lens group G1 among the first lens group G1, the second lens group G2, and the third lens group G3 is configured to be movable toward the image side in the non-photographing time.

[0171] Therefore, in the non-photographing time, by moving at least the first lens group G1 (in the optical system 2 of the present embodiment, the first lens group G1 and the second lens group G2) toward the image pickup element (image plane) 3 side, further thinness can be achieved. Further, the optical system 2 is provided to the image pickup device 1, and at least the first lens group G1 is moved toward the image pickup element (image plane) 3 side in the non-photographing time to house the entire optical system 2 in the image pickup device main body 10 (i.e., to make it retractable), thereby achieving thinness of the image pickup device 1 as well.

[0172] According to the image pickup device 1 configured as above, sufficient wide-angle and thinness can be achieved.

[0173] Next, the embodiments 1 to 4 of the optical system of the present application will be described. In each of the following embodiments, the same reference numerals are used for the structures corresponding to the structures of the optical system of the above-described embodiment. Further, in the tables in each of the following embodiments, r is the radius of curvature, d is the lens thickness or the lens interval, nd is the refractive index of the d line, and vd indicates the Abbe number of the d line reference. Further, the aspheric surface is defined by the formula 1 shown below.

[0174] Formula 1

[0175] z = ch 2 / [1 + {1 - (1 + k)c 2 h 2} 1 / 2 ]+ A4h 4 + A6h 6 + A8h 8 + A10h 10 ...

[0176] (where c is the curvature (1 / r), h is the height from the optical axis (distance), k is the conic coefficient, and A4, A6, A8, A10,... are the aspheric coefficients of each order.)

[0177] In addition, each longitudinal aberration diagram sequentially shows, from the left, spherical aberration (SA (mm)), astigmatism (AST (mm)), and distortion aberration (DIS (%)). In the spherical aberration diagram, the vertical axis indicates F number (indicated by FNO in the drawing), the solid line is the characteristic of d-line, the short-dashed line is the characteristic of F-line, and the long-dashed line is the characteristic of C-line. In the astigmatism diagram, the vertical axis indicates maximum image height (indicated by Y in the drawing), the solid line is the characteristic of sagittal plane (indicated by S in the drawing), and the dashed line is the characteristic of meridional plane (indicated by M in the drawing). In the distortion aberration diagram, the vertical axis indicates maximum image height (indicated by Y in the drawing).

[0178] Example 1

[0179] Figure 3 and Figure 4 is a lens configuration diagram of the optical system of Example 1, Figure 3 indicates an infinite focus state, Figure 4 indicates a closest focus state. In addition, the reference numerals indicating each configuration of the optical system are the same as those of the corresponding configuration of the optical system 2 of the above-described embodiment. In addition, in this optical system, the positions of the first lens group and the third lens group on the optical axis with respect to the imaging element (image plane) are fixed at the time of focusing.

[0180] In addition, Figure 5 is a longitudinal aberration diagram in the infinite focus state, Figure 6 is a longitudinal aberration diagram in the closest focus state, Table 1 below shows surface data of each lens, Table 2 shows aspherical surface data, Table 3 shows various data, and Table 4 shows lens group data.

[0181] Table 1

[0182] (Table 1) Surface data

[0183] Face number r d nd vd 1* 19.169 0.500 1.5731 37.65 2* 8.520 0.398 3 ∞ d3 (aperture stop) 4* 7.134 1.051 1.5445 55.96 5* -30.682 0.100 6* 45.330 1.512 1.5445 55.96 7* -9.064 0.100 8* 4.372 0.500 1.6714 19.27 9* 2.742 1.037 10* 41.560 1.455 1.5445 55.96 11* -6.627 d11 12* -4.298 0.847 1.5731 37.65 13* -59.840 0.400 14 ∞ 0.300 1.5168 64.20 15 ∞ 0.100

[0184] * is an aspherical surface

[0185] Table 2

[0186]

[0187] Table 3

[0188] (Table 3) Various data

[0189] Object distance ∞ 100.000 F number 1.440 1.545 Half view angle 41.111 37.996 Lens total length 14.163 14.163 d3 1.660 1.064 d11 4.203 4.799

[0190] The focal length is 8.480, and the maximum image height is 6.293.

[0191] Table 4

[0192] Lens group data

[0193] Group Starting face Focal length Lens constituent length Lens movement amount Magnification 1 1 -27.226 0.898 0.000 0.000 2 4 6.571 5.755 0.596 -0.269 3 12 -8.125 0.847 0.000 1.156

[0194] Example 2

[0195] Figure 7 and Figure 8 is a lens configuration diagram of the optical system of this Example 2, Figure 7 represents an infinite focus state, Figure 8 represents a closest focus state. In addition, the reference numerals of each structure of the optical system are the same as those of the corresponding structure of the optical system 2 of the above-described embodiment. In addition, in this optical system, the positions of the first lens group and the third lens group on the optical axis with respect to the imaging element (image plane) are also fixed at the time of focusing.

[0196] In addition, Figure 9 is a longitudinal aberration diagram in the infinite focus state, Figure 10 is a longitudinal aberration diagram in the closest focus state, Table 5 below shows the surface data of each lens, Table 6 shows the aspherical surface data, Table 7 shows various data, and Table 8 shows the lens group data.

[0197] Table 5

[0198] Surface data (Table 5)

[0199] Face number r d nd vd 1* 100.000 0.500 1.5731 37.65 2* 14.838 0.416 3* 10.417 0.532 1.5445 55.96 4* 7.669 0.315 5 ∞ d5 (aperture stop) 6* 8.588 1.335 1.5445 55.96 7* -10.522 0.211 8* 30.812 1.538 1.5445 55.96 9* -8.191 0.100 10* 5.114 0.516 1.6714 19.27 11* 3.092 1.799 12* -61.079 1.791 1.5445 55.96 13* -5.480 d13 14* -5.139 1.011 1.5880 28.42 15* 16.915 0.536 16 ∞ 0.300 1.5168 64.20 17 ∞ 0.100

[0200] * is an aspherical surface

[0201] Table 6

[0202]

[0203] Table 7

[0204] Various data (Table 7)

[0205] Object distance ∞ 100.000 F number 1.440 1.539 Half view angle 41.993 38.595 Lens total length 15.000 15.000 d5 1.154 0.583 d13 2.846 3.417

[0206] The focal length is 8.264, and the maximum image height is 6.324.

[0207] Table 8

[0208] Lens group data (Table 8)

[0209] Group Starting face Focal length Lens constituent length Lens movement amount Magnification 1 1 -19.499 1.763 0.000 0.000 2 6 6.278 7.290 0.571 -0.354 3 14 6.591 1.011 0.000 1.198

[0210] Example 3

[0211] Figure 11 and Figure 12 is a lens configuration diagram of the optical system of this Example 3, Figure 11 represents an infinite focus state,Figure 12 indicates a closest focus state. In addition, the reference numerals of the respective structures of the optical system are the same as those of the corresponding structures of the optical system 2 of the above-described embodiment. In addition, in this optical system, the positions of the first lens group and the third lens group on the optical axis with respect to the imaging element (image plane) are also fixed at the time of focusing.

[0212] In addition, Figure 13 is a longitudinal aberration diagram in an infinite focus state, Figure 14 is a longitudinal aberration diagram in a closest focus state, Table 9 below shows surface data of each lens, Table 10 shows aspherical surface data, Table 11 shows various data, and Table 12 shows lens group data.

[0213] Table 9

[0214] (Table 9) Surface Data

[0215] Face number r d nd vd 1* 11.315 0.400 1.6714 19.27 (aperture stop) 2* 7.991 d2 3* 8.664 0.633 1.5445 55.96 4* -108.143 0.108 5* -83.676 1.365 1.5445 55.96 6* -5.866 0.100 7* 3.991 0.598 1.6714 19.27 8* 2.805 1.671 9* -34.161 1.435 1.5445 55.96 10* -5.123 d10 11* -6.400 1.040 1.6362 23.91 12* 13.389 0.550 13 ∞ 0.300 1.5168 64.20 14 ∞ 0.100

[0216] Table 10

[0217]

[0218] Table 11

[0219] (Table 11) Various Data

[0220] Object distance ∞ 120.000 F number 1.950 2.036 Half view angle 40.999 39.061 Lens total length 12.742 12.742 d2 1.219 0.783 d10 3.222 3.658

[0221] The focal length is 8.417, and the maximum image height is 7.150.

[0222] Table 12

[0223] (Table 12) Lens Group Data

[0224] Group Starting face Focal length Lens constituent length Lens movement amount Magnification 1 1 -42.573 0.400 0.000 0.000 2 3 6.522 5.911 0.436 -0.166 3 11 -6.671 1.040 0.000 1.188

[0225] Example 4

[0226] Figure 15 and Figure 16 is a lens structure diagram of the optical system of this embodiment 3, Figure 15 indicates an infinite focus state, Figure 16 indicates a closest focus state. In addition, the reference numerals of the respective structures of the optical system are the same as those of the corresponding structures of the optical system 2 of the above-described embodiment. In addition, in this optical system, the positions of the first lens group and the third lens group on the optical axis with respect to the imaging element (image plane) are also fixed at the time of focusing.

[0227] In addition, Figure 17 is a longitudinal aberration diagram in an infinite focus state, Figure 18is a longitudinal aberration diagram in the recent focus state, Table 13 below shows surface data of each lens, Table 14 shows aspherical surface data, Table 15 shows various data, and Table 16 shows lens group data.

[0228] Table 13

[0229] (Table 13) Surface data

[0230] Face number r d nd vd 1* 12.754 0.402 1.6714 19.27 (aperture stop) 2* 8.581 d2 3* 8.521 0.654 1.5445 55.96 4* -146.190 0.137 5* -82.877 1.395 1.5445 55.96 6* -5.850 0.100 7* 4.008 0.616 1.6714 19.27 8* 2.857 1.722 9* -36.337 1.518 1.5445 55.96 10* -5.055 d10 11* -6.578 0.600 1.6362 23.91 12* -40.621 0.174 13* -13.896 0.600 1.6714 19.27 14* 42.060 0.505 15 ∞ 0.300 1.5168 64.20 16 ∞ 0.100

[0231] * is an aspherical surface

[0232] Table 14

[0233]

[0234] Table 15

[0235] (Table 15) Various data

[0236] Object distance ∞ 120.000 F number 1.950 2.027 Half view angle 40.996 39.132 Lens total length 13.040 13.040 d2 1.359 0.945 d10 2.858 3.272

[0237] The focal length is 8.419, and the maximum image height is 7.150.

[0238] Table 16

[0239] (Table 16) Lens group data

[0240] Group Starting face Focal length Lens constituent length Lens movement amount Magnification 1 1 -40.268 0.402 0.000 0.000 2 3 6.430 6.142 0.414 -0.172 3 11 -6.669 1.374 0.000 1.215

[0241] In the above Examples 1 to 4, the values corresponding to each condition of the above-described embodiments are shown in Table 17 below.

[0242] In Table 17, condition formula (1) is f3 / f, condition formula (2) is b2, condition formula (3) is OAL123 / Y, condition formula (4) is b3, condition formula (5) is f2 / f, condition formula (6) is (1-b2) x b3, condition formula (7) is f1 / f, condition formula (8) is OAL / f, condition formula (9) is (1-b2) x b3, condition formula (10) is nd1, condition formula (11) is vd1, condition formula (12) is nd3, and condition formula (13) is vd3. 2 2

[0243] Table 17

[0244] (Table 17) Corresponding values of condition formulas

[0245]

[0246] ​​While the present application has been described with reference to the examples described above by way of implementation, as appropriate and sufficient for the purpose of embodying the present application, it should be recognized by those skilled in the art that changes and / or modifications to the above-described examples are readily achievable. Therefore, as long as the changes or modifications made by those skilled in the art are not beyond the level of the claims recited in the claims, it can be interpreted that the changes or modifications are included in the scope of the claims.

[0247] Reference Signs List

[0248] 1: Imaging device

[0249] 2: Optical system

[0250] 21: Aperture stop (aperture device)

[0251] 22: Lens barrel

[0252] 23: Optical filter

[0253] 3: Imaging element

[0254] 4: Liquid crystal display

[0255] 10: Imaging device main body

[0256] C: Optical axis

[0257] F: Focus lens group

[0258] G1: First lens group

[0259] G2: Second lens group

[0260] G3: Third lens group

Claims

1. An optical system, characterized in that, The optical system comprises, in sequence from the object side to the image side, a first lens group including at least one lens and having negative refractive power, a second lens group including at least one lens and having positive refractive power, and a third lens group including at least one lens and having negative refractive power. During focusing, the distances between the first lens group and the third lens group on the optical axis and the imaging plane are fixed, while the second lens group moves along the optical axis. When the lateral magnification of the second lens group at infinity is set to b2, the lateral magnification of the third lens group at infinity is set to b3, the focal length of the entire optical system at infinity is set to f, the focal length of the second lens group is set to f2, the focal length of the third lens group is set to f3, the total distance from the lens surface closest to the object side to the lens surface closest to the image side in each lens group is set to OAL123, and the maximum image height is set to Y, Satisfy at least one of the following formulas (1) to (4): -1.20≤f3 / f≤-0.10 …(1) -0.40≤b2≤-0.06 …（2） 0.3≤OAL123 / Y≤2.30 and 1.00≤b3≤1.30 …(3) 0.60≤f2 / f≤0.90 …(4) The second lens group is configured to also be movable in a direction orthogonal to the optical axis, and satisfies: 1.00≤(1-b2)×b3≤1.

90.

2. The optical system according to claim 1, characterized in that, When the focal length of the first lens group is set to f1, the following conditions are met: -16.00≤f1 / f≤-1.

80.

3. The optical system according to claim 1, characterized in that, It has an aperture mechanism that can change the aperture diameter. The aperture device is positioned between the first lens group and the second lens group.

4. The optical system according to claim 1, characterized in that, When the distance from the lens surface closest to the object side to the imaging plane in this optical system is defined as OAL, the following conditions are met: 1.20≤OAL / f≤2.

30.

5. The optical system according to claim 1, characterized in that, satisfy: 1.00 ≤ (1-b2) 2 )×b3 2 ≤1.70。 6. The optical system according to claim 1, characterized in that, When the refractive index of at least one lens in the first lens group on the d-line is set to nd1, and the Abbe number of the reference on the d-line of at least one lens in the first lens group is set to vd1, the following conditions are met: 1.50≤nd1≤1.70 and 15.00≤vd1≤60.

00.

7. The optical system according to claim 1, characterized in that, When the refractive index of at least one lens in the third lens group on the d-line is set to nd3, and the Abbe number of the d-line reference of at least one lens in the third lens group is set to vd3, the following conditions are met: 1.50≤nd3≤1.70 and 15.00≤vd3≤60.

00.

8. The optical system according to claim 1, characterized in that, The first lens group, the second lens group, and the third lens group are configured such that the first lens group can move toward the image side when not taking pictures.

9. A camera device, characterized in that, have: The optical system according to any one of claims 1 to 8, and A camera element, which is positioned at the imaging surface of the optical system.

Images