Optical system, and imaging apparatus having the same

Abstract

To provide an optical system that achieves both a reduction in the weight of a focus lens group and prevention of aberration fluctuation during focusing.SOLUTION: An optical system has a first lens group B1 having a positive refractive power, a second lens group B2 having a positive refractive power, a third lens group B3, a fourth lens group B4 having a positive refractive power, and a fifth lens group B5 having a negative refractive power, which are arranged in order from an object side to an image side. Upon focusing from an infinite distance to a close distance, the second lens group and the fourth lens group move to the object side. At least either one of the second lens group or the fourth lens group is formed of two or more lenses. The first lens group includes two or more negative lenses.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system, and is suitable as an imaging optical system used in imaging devices such as digital still cameras, digital video cameras, broadcast cameras, silver halide film cameras, and surveillance cameras. [Background technology]

[0002] In recent years, there has been a demand for smaller, higher performance large-aperture wide-angle lenses in image pickup devices using solid-state image pickup elements such as CCD and CMOS sensors.

[0003] Patent Document 1 discloses a large-aperture wide-angle lens that is capable of focusing while maintaining good optical performance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-200845 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the wide-angle lens described in Patent Document 1 includes many lenses in the focus lens group. Therefore, although aberration fluctuation during focusing can be effectively suppressed, the focus lens group is heavy and unsuitable for high-speed driving, and there is a problem that quietness is low.

[0006] The present invention provides an optical system that achieves both weight reduction of the focus lens unit and suppression of aberration fluctuations during focusing. [Means for solving the problem]

[0007] An optical system according to one aspect of the present invention has, arranged in order from the object side to the image side, a first lens group with positive refractive power, a second lens group with positive refractive power, a third lens group, a fourth lens group with positive refractive power, and a fifth lens group with negative refractive power, in which the distance between adjacent lens groups changes when focusing from infinity to a close distance, and when focusing from infinity to a close distance, the second lens group and the fourth lens group move toward the object side, at least one of the second lens group or the fourth lens group is composed of two or more lenses, and the first lens group includes two or more negative lenses.

[0008] Other objects and features of the present invention will be described in the following embodiments. Effect of the Invention

[0009] According to the present invention, it is possible to provide an optical system that achieves both a reduction in the weight of the focus lens unit and suppression of aberration fluctuations during focusing. [Brief description of the drawings]

[0010] [Figure 1] 1 is a lens sectional view of the optical system according to Example 1 when focused on an object at infinity. [Diagram 2] 4 is a longitudinal aberration diagram of the optical system according to Example 1 when focused on an object at infinity. FIG. [Diagram 3] 4 is a longitudinal aberration diagram of the optical system according to Example 1 when focusing on a close distance. FIG. [Figure 4] FIG. 11 is a lens sectional view of the optical system according to Example 2 when focused on an object at infinity. [Diagram 5] 11 is a longitudinal aberration diagram of the optical system according to Example 2 when focused on an object at infinity. FIG. [Figure 6] 11 is a longitudinal aberration diagram of the optical system according to Example 2 when focusing on a close distance. FIG. [Figure 7] FIG. 11 is a lens sectional view of the optical system according to Example 3 when focused on an object at infinity. [Figure 8] 11A to 11C are longitudinal aberration diagrams of the optical system according to Example 3 when focused on an object at infinity. [Figure 9]11A to 11C are diagrams illustrating longitudinal aberration of the optical system according to Example 3 when focusing on a close distance. [Figure 10] FIG. 11 is a lens sectional view of the optical system according to Example 4 when focused on an object at infinity. [Figure 11] 13 is a longitudinal aberration diagram of the optical system according to Example 4 when focused on an object at infinity. FIG. [Figure 12] 13 is a longitudinal aberration diagram of the optical system according to Example 4 when focusing on a close distance. FIG. [Figure 13] FIG. 1 is a schematic diagram of an imaging device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an optical system and an image pickup apparatus having the same according to the present invention will be described with reference to the accompanying drawings.

[0012] 1, 4, 7, and 10 are lens cross-sectional views of the optical systems of Examples 1 to 4 when focused on infinity (when focused on an object at infinity), respectively. The optical systems of the respective Examples are imaging optical systems used in imaging devices such as digital still cameras, silver halide film cameras, digital video cameras, surveillance cameras, broadcast cameras, and vehicle-mounted cameras.

[0013] In each lens cross-sectional view, the left side is the object side (magnification conjugate surface side) and the right side is the image side (reduction conjugate surface side). The optical system of each embodiment is configured to have multiple lens groups. In this specification, a lens group is a group of lenses that move or stand still as a unit during focusing. That is, in the optical system of each embodiment, the distance between adjacent lens groups changes during focusing from infinity to a close distance. Note that the lens group may be composed of one lens or multiple lenses. The lens group may also include an aperture stop.

[0014] In each lens cross-sectional view, Bi represents the i-th lens group (i is a natural number) counted from the object side in the optical system.

[0015] Also, SP is an aperture stop. The aperture stop SP determines (limits) the light flux of the open F-number (Fno). IP is an image plane, and when the zoom lens of each embodiment is used as the photographing optical system of a digital still camera or video camera, the imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor is disposed thereon. When the zoom lens of each embodiment is used as the photographing optical system of a silver halide film camera, a photosensitive surface equivalent to the film surface is disposed on the image plane IP.

[0016] The arrow in the optical axis direction indicates the movement direction of the focus lens group that moves during focusing from an infinity distance to a close distance.

[0017] 2, 5, 8, and 11 are longitudinal aberration diagrams when the optical systems of Examples 1 to 4 are focused on infinity, respectively. Figures 3, 6, 9, and 12 are longitudinal aberration diagrams when the optical systems of Examples 1 to 4 are focused on close objects, respectively.

[0018] In the spherical aberration diagram, Fno is the F-number, and the amount of spherical aberration for the d-line (wavelength 587.56 nm), g-line (wavelength 435.84 nm), C-line (wavelength 656.27 nm), and F-line (wavelength 486.13 nm) is shown. In the astigmatism diagram, S indicates the amount of astigmatism at the sagittal image plane for the d-line, and M indicates the amount of astigmatism at the meridional image plane for the d-line. In the distortion aberration diagram, the amount of distortion aberration for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line, C-line (wavelength 656.27 nm), and F-line (wavelength 486.13 nm) is shown. ω is the imaging half angle of view (°) (angle of view in paraxial calculation), and indicates the angle of view calculated by ray tracing.

[0019] Next, the characteristic configuration of the optical system of each embodiment will be described.

[0020] The optical system of each embodiment includes, in order from the object side to the image side, a first lens group B1 with positive refractive power, a second lens group B2 with positive refractive power, a third lens group B3, a fourth lens group B4 with positive refractive power, and a fifth lens group B5 with negative refractive power. In the optical system of each embodiment, the distance between adjacent lens groups changes when focusing from infinity to a close distance.

[0021] By making the first lens group B1 have a positive refractive power, the emergent light can be made into a convergent light, and the lens diameter of the second lens group B2 can be made small, thereby making it possible to reduce the weight.

[0022] The second lens group B2 and the fourth lens group B4 function as a focus lens group that moves during focusing, and during focusing from an infinity distance to a close distance, the second lens group B2 and the fourth lens group B4 move toward the object side.

[0023] The second lens group B2 and the fourth lens group B4 are moved simultaneously during focusing, thereby suppressing the variation of spherical aberration in the entire system during focusing. The second lens group B2 is made to have a positive refractive power, thereby making the diameter of the succeeding lens group smaller. This allows the weight of the fourth lens group B4 arranged behind the second lens group B2 to be reduced, and the focus lens group can be driven at high speed and quietly. If the second lens group B2 has a negative refractive power and is provided with a focusing function, the movement direction of the second lens group B2 during focusing needs to be in the image direction. In order to move the second lens group B2 in the image direction, it is necessary to move the second lens group B2 as close to the object side as possible, but in that case, the diameter of the second lens group B2 is increased, resulting in a heavy lens. Furthermore, if the power of the first lens group B1 is increased in order to reduce the diameter of the second lens group B2, the amount of spherical aberration generated in the first lens group B1 will be too large, making it impossible to completely correct the spherical aberration of the entire optical system.

[0024] If the fourth lens group B4 is a lens group with negative refractive power, the diameter of the fourth lens group B4 must be made larger than if it were a lens group with positive refractive power, and the fourth lens group B4 becomes heavier. This is because the fourth lens group B4 receives focused light emitted from the third lens group B3, and the air space between the third lens group B3 and the fourth lens group B4 must be narrowed in order to move the fourth lens group B4 toward the image side when focusing from infinity to a close distance. If the fourth lens group B4 is moved toward the object, the lens diameter must be made larger in order to receive unfocused light beams.

[0025] At least one of the second lens group B2 and the fourth lens group B4 is composed of two or more lenses, which suppresses aberrations.

[0026] The first lens group B1 includes two or more negative lenses, which contribute to achieving a wider angle of view for the entire optical system and suppress distortion that occurs when the lens is provided with the power required for achieving a wider angle of view.

[0027] As described above, by satisfying the above-mentioned configuration, the optical system of each embodiment can achieve both weight reduction of the focus lens unit and suppression of aberration fluctuation during focusing.

[0028] Next, conditions that are preferably satisfied in the optical system of each embodiment will be described. It is preferable that the optical system according to each embodiment satisfies one or more of the following conditional expressions (1) to (8).

[0029] Here, f is the focal length of the optical system when focusing at infinity. f2 is the focal length of the second lens group B2. f4 is the focal length of the fourth lens group B4. f5 is the focal length of the fifth lens group B5. DT is the optical axial distance from the object side lens surface of the first lens group B1 to the image side lens surface of the lens group arranged closest to the image side when focusing at infinity. D12 is the optical axial distance from the image side lens surface of the first lens group B1 to the object side lens surface of the second lens group B2 when focusing at infinity. D34 is the optical axial distance from the image side lens surface of the third lens group B3 to the object side lens surface of the fourth lens group B4 when focusing at infinity. TTL is the optical total length of the optical system when focusing at infinity. T2 is the optical axial thickness of the second lens group B2. T4 is the optical axial thickness of the fourth lens group B4.

[0030] 0.30 <f4 / f<4.80 ···(1) 0.70 <f2 / f<26.80 ···(2) 0.05 <f4 / f2<1.50 ···(3) -25.80 <f5 / f<-0.90 ···(4) 0.008 <D12 / DT<0.210 ···(5) 0.020 <D34 / DT<0.530 ···(6) 0.004 <T2 / TTL<0.120 ···(7) 0.040 <T4 / TTL<0.590 ···(8) Conditional formula (1) specifies the ratio between the focal length of the optical system when focusing at infinity and the focal length of the fourth lens group B4. If the upper limit of conditional formula (1) is exceeded, the refractive power of the fourth lens group B4 becomes too weak. If the refractive power of the fourth lens group B4 becomes too weak, the light-gathering power is weakened and the entire optical system must be lengthened, which is not preferable. If the lower limit of conditional formula (1) is exceeded, the refractive power of the fourth lens group B4 becomes too strong. If the refractive power of the fourth lens group becomes too strong, the light-gathering power is strong, but the amount of aberration generated is too large, making it impossible to obtain a good sense of resolution in the entire optical system, which is not preferable. In addition, if the number of lenses is increased to suppress the generated aberration, the fourth lens group B4 becomes heavy. This is not preferable because it slows down the driving speed and impairs quietness.

[0031] Conditional formula (2) specifies the ratio between the focal length of the optical system when focused at infinity and the focal length of the second lens group B2. If the upper limit of conditional formula (2) is exceeded, the refractive power of the second lens group B2 becomes too weak. If the refractive power of the second lens group B2 becomes too weak, it becomes necessary to increase the amount of movement of the second lens group B2 or the fourth lens group B4, which is undesirable as it requires a longer optical system. If the lower limit of conditional formula (2) is exceeded, the refractive power of the second lens group B2 becomes too strong. If the refractive power of the second lens group B2 becomes too strong, it becomes necessary to increase the number of lenses in the second lens group B2 to suppress the generated aberration, which is undesirable.

[0032] Conditional expression (3) defines the ratio between the focal length of the second lens group B2 and the focal length of the fourth lens group B4. If the upper limit of conditional expression (3) is exceeded or the lower limit is exceeded, the balance between the second lens group B2 and the fourth lens group B4, which are focus lens groups, is lost, making it impossible to suppress aberration fluctuations, which is undesirable.

[0033] Conditional expression (4) defines the ratio between the focal length of the optical system when focused at infinity and the focal length of the fifth lens group B5. If the upper limit of conditional expression (4) is exceeded, the refractive power of the fifth lens group B5 becomes too weak. If the refractive power of the fifth lens group B5 becomes too weak, the function of canceling out the distortion generated in the first lens group B1 becomes weak, and it becomes impossible to provide the fourth lens group B4 with refractive power, which is undesirable. If the lower limit of conditional expression (4) is exceeded, the refractive power of the fifth lens group B5 becomes too strong. If the refractive power of the fifth lens unit B5 becomes too strong, the refractive power of the fourth lens unit B4 must be made strong, which is undesirable because it becomes difficult to suppress aberrations occurring within the fourth lens unit B4.

[0034] Conditional formula (5) defines the ratio of the distance between the first lens group B1 and the lens group arranged closest to the image to the distance between the first lens group B1 and the second lens group B2. Exceeding the upper limit of conditional formula (5) means that the distance between the first lens group B1 and the second lens group B2 is significantly secured relative to the amount of movement during focusing. If the distance between the first lens group B1 and the second lens group B2 is made too wide, it becomes necessary to thin the group thickness of the other lens groups, which is not preferable because it becomes impossible to arrange a sufficient number of lenses. Falling below the lower limit of conditional expression (5) means that the distance between the first lens group B1 and the second lens group B2 is not sufficiently secured for the amount of movement during focusing, which is undesirable because it makes it difficult to correct aberrations occurring within the fourth lens group B4 during focusing.

[0035] Conditional formula (6) defines the ratio of the distance between the first lens group B1 and the lens group arranged closest to the image to the distance between the third lens group B3 and the fourth lens group B4. Exceeding the upper limit of conditional formula (6) means that the distance between the third lens group B3 and the fourth lens group B4 is significantly secured relative to the amount of movement during focusing. If the distance between the third lens group B3 and the fourth lens group B4 is made too wide, it becomes necessary to thin the group thickness of the other lens groups, which is undesirable because it becomes impossible to arrange the number of lenses necessary for aberration correction. Falling below the lower limit of conditional formula (6) means that the distance between the third lens group B3 and the fourth lens group B4 is not sufficiently secured relative to the amount of movement during focusing. This is undesirable because it becomes impossible to secure the minimum shooting distance sufficiently.

[0036] Conditional formula (7) specifies the ratio between the total optical length of the optical system when focusing at infinity and the thickness of the second lens group B2. If the upper limit of conditional formula (7) is exceeded, the second lens group B2 becomes too thick. If the second lens group B2 becomes too thick, it becomes necessary to thin the thickness of the other lens groups, which is undesirable because it becomes impossible to arrange the number of lenses necessary for aberration correction. Furthermore, if the second lens group B2 becomes too thick, it becomes heavy, which is undesirable because it becomes difficult to drive the second lens group B2 at high speed. If the lower limit of conditional formula (7) is exceeded, the second lens group B2 becomes too thin. This undesirably weakens the focusing function of the second lens group B2.

[0037] Conditional formula (8) specifies the ratio between the total optical length of the optical system when focusing at infinity and the thickness of the fourth lens group B4. If the upper limit of conditional formula (8) is exceeded, the fourth lens group B4 becomes too thick. If the fourth lens group B4 becomes too thick, it becomes necessary to thin the group thickness of the other lens groups, which is not preferable because it becomes impossible to arrange the number of lenses necessary for aberration correction. Also, if the fourth lens group B4 becomes too thick, it becomes heavy, which is not preferable because it becomes difficult to drive the fourth lens group B4 at high speed. If the lower limit of conditional formula (8) is exceeded, the fourth lens group B4 becomes too thin. This weakens the focusing function of the fourth lens group B4, or makes it difficult to suppress aberrations occurring in the fourth lens group B4, which is not preferable.

[0038] Furthermore, it is more preferable that the numerical ranges of the conditional expressions (1) to (8) be within the ranges of the following conditional expressions (1a) to (8a).

[0039] 0.50 <f4 / f<3.20 ···(1a) 1.20 <f2 / f<17.90 ···(2a) 0.08 <f4 / f2<1.00 ···(3a) -17.20 <f5 / f<-1.50 ···(4a) 0.010 <D12 / DT<0.140 ···(5a) 0.040 <D34 / DT<0.360 ···(6a) 0.007 <T2 / TTL<0.079 ···(7a) 0.070 <T4 / TTL<0.390 ···(8a) It is further preferable that the numerical ranges of the conditional expressions (1) to (8) are within the range of (1b) to (1b).

[0040] 0.90 <f4 / f<1.80 ···(1b) 2.20 <f2 / f<9.90 ···(2b) 0.10 <f4 / f2<0.60 ···(3b) -9.50 <f5 / f<-2.70 ···(4b) 0.020 <D12 / DT<0.080 ···(5b) 0.070 <D34 / DT<0.200 ···(6b) 0.014 <T2 / TTL<0.044 ···(7b) 0.120 <T4 / TTL<0.220 ···(8b) Next, the optical system of each embodiment will be described in detail.

[0041] Example 1 The optical system of the first embodiment is composed of, arranged in order from the object side to the image side, a first lens group B1 with positive refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with negative refractive power, a fourth lens group B4 with positive refractive power, and a fifth lens group B5 with negative refractive power. The second lens group B2 and the fourth lens group B4 function as focus lens groups, and both the second lens group B2 and the fourth lens group B4 move toward the object side during focusing from an infinity distance to a close distance.

[0042] The first lens unit B1 is fixed with respect to the image plane IP during focusing from infinity to a close distance.

[0043] In the optical system of Example 1, the number of lenses arranged in the first lens group B1 is five, and the first lens group B1 is made up of first to fifth lenses G1 to G5 arranged in order from the object side to the image side.

[0044] The first lens G1 has a negative refractive power, which contributes to a wider angle of the entire optical system. The first lens G1 also has an aspheric surface, which makes it possible to suppress the amount of distortion.

[0045] The second lens G2 has negative refractive power. This contributes to the wide-angle of the entire optical system. If either the first lens G1 or the second lens G2 were to be eliminated, distortion would become too large when the lens is given the power required for a wide angle.

[0046] The third lens G3 has a positive refractive power, and the fourth lens G4 has a negative refractive power. The third lens G3 and the fourth lens G4 are cemented together to form a cemented lens with a positive refractive power as a whole. As the angle of view becomes wider, the on-axis light beam emitted from the second lens G2 becomes a diverging light. For this reason, the light beam needs to be converged with a strong power, but if the light is converged by a single lens, large on-axis chromatic aberration and chromatic aberration of magnification occur.

[0047] The fifth lens G5 has positive refractive power. If the light beam were to be focused using only the cemented lens consisting of the third lens G3 and the fourth lens G4, a problem would arise in that significant spherical aberration would occur. By placing the fifth lens G5, which has positive refractive power, the on-axis light beam is focused while suppressing spherical aberration.

[0048] The second lens group B2 moves simultaneously with the fourth lens group B4 during focusing from infinity to a close distance.

[0049] In the optical system of the first embodiment, the second lens group B2 is composed of one sixth lens G6 with positive refractive power. The lens surface on the object side of the sixth lens G6 is convex, and the lens surface on the image side of the sixth lens G6 is concave. This suppresses the amount of spherical aberration generated when focusing at infinity.

[0050] The third lens unit B3 is fixed with respect to the image plane IP during focusing from infinity to a close distance.

[0051] In the optical system of the first embodiment, the third lens group G3 is composed of one seventh lens G7 with negative refractive power. The lens surface on the object side of the seventh lens G7 is convex, and the lens surface on the image side of the seventh lens G7 is concave. This suppresses spherical aberration.

[0052] The aperture stop SP is disposed between the second lens unit B2 and the third lens unit B3, and is fixed with respect to the image plane IP during focusing from infinity to a close distance, which contributes to reducing the weight of the lens units that move during focusing.

[0053] The fourth lens group B4 moves simultaneously with the second lens group B2 during focusing from infinity to a close distance.

[0054] In the optical system of Example 1, the number of lenses arranged in the fourth lens group B4 is four, and the fourth lens group B4 is made up of eighth to eleventh lenses G8 to G11 arranged in this order from the object side to the image side.

[0055] The eighth lens G8 has a positive refractive power, and the ninth lens G9 has a negative refractive power. The eighth lens G8 and the ninth lens G9 are cemented together to form a cemented lens having a negative refractive power as a whole. The lens surface of the eighth lens G8 facing the object side is concave. This corrects aberration occurring in the positive lens disposed in the fourth lens group B4, and suppresses aberration in the fourth lens group B4 as a whole. The cemented lens consisting of the eighth lens G8 and the ninth lens G9 makes it possible to provide a strong negative refractive power in total for the eighth lens G8 and the ninth lens G9 while suppressing the occurrence of chromatic aberration.

[0056] The tenth lens G10 has a positive refractive power. By using a low dispersion, high anomalous dispersion material for the tenth lens G10, chromatic aberration in the entire optical system is suppressed.

[0057] The eleventh lens G11 has a positive refractive power. The eleventh lens G11 has an aspheric surface. This makes it possible to suppress spherical aberration while strengthening the refractive power of the eleventh lens G11. In addition, the aspheric surface is disposed at a position where the off-axis chief rays are sufficiently separated, and the shape of the aspheric surface is shaped so that the power weakens toward the periphery, thereby correcting the image plane.

[0058] The fifth lens group B5 is fixed with respect to the image plane IP during focusing from infinity to a close distance, and has a negative refractive power as a whole. This makes it possible to strengthen the refractive power of the fourth lens group B4. In addition, by arranging the fifth lens group B5, which has a negative refractive power, at a position where the off-axis chief ray is high, the lateral chromatic aberration and distortion aberration generated in the first lens group B1 are corrected. This eliminates the need to completely suppress distortion within the first lens group B1, so the number of lenses arranged on the object side can be reduced, making it possible to miniaturize the entire optical system.

[0059] In the optical system of Example 1, the number of lenses arranged in the fifth lens group B5 is four, and the fifth lens group B5 is made up of twelfth to fifteenth lenses G12 to G15 arranged in this order from the object side to the image side.

[0060] The twelfth lens G12 has positive refractive power, and the thirteenth lens G13 has negative refractive power. The twelfth lens G12 and the thirteenth lens G13 are cemented together to form a cemented lens having negative refractive power as a whole. The cemented lens consisting of the twelfth lens G12 and the thirteenth lens G13 mainly suppresses chromatic aberration of magnification. This makes it possible to impart strong refractive power to the fifth lens group B5, and the strong negative refractive power of the fifth lens group B5 makes it possible to strengthen the positive refractive power of the fourth lens group B4.

[0061] The 14th lens G14 has negative refractive power, and the 15th lens G15 has positive refractive power. The 14th lens G14 and the 15th lens G15 are cemented together to form a cemented lens having negative refractive power as a whole. The cemented lens consisting of the 14th lens G14 and the 15th lens G15 mainly suppresses chromatic aberration of magnification. The cemented lens consisting of the 14th lens G14 and the 15th lens G15 shares refractive power with the cemented lens consisting of the 12th lens G12 and the 13th lens G13.

[0062] Example 2 The optical system of the second embodiment is composed of, arranged in order from the object side to the image side, a first lens group B1 with positive refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with negative refractive power, a fourth lens group B4 with positive refractive power, and a fifth lens group B5 with negative refractive power. The second lens group B2 and the fourth lens group B4 function as focus lens groups, and both the second lens group B2 and the fourth lens group B4 move toward the object side during focusing from infinity to a close distance.

[0063] In the optical system of the second embodiment, the cemented lens arranged closest to the image side is a single lens compared to the optical system of the first embodiment.

[0064] Example 3 The optical system of the third embodiment is composed of, arranged in order from the object side to the image side, a first lens group B1 with positive refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with negative refractive power, a fourth lens group B4 with positive refractive power, and a fifth lens group B5 with negative refractive power. The second lens group B2 and the fourth lens group B4 function as focus lens groups, and both the second lens group B2 and the fourth lens group B4 move toward the object side during focusing from an infinity distance to a close distance.

[0065] In the optical system of the third embodiment, compared to the optical systems of the first and second embodiments, the number of negative lenses in the first lens unit B1 is increased to achieve a wider angle.

[0066] Example 4 The optical system of Example 4 is composed of, arranged in order from the object side to the image side, a first lens group B1 with positive refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with positive refractive power, a fourth lens group B4 with positive refractive power, and a fifth lens group B5 with negative refractive power. The second lens group B2 and the fourth lens group B4 function as focus lens groups, and both the second lens group B2 and the fourth lens group B4 move toward the object side during focusing from an infinity distance to a close distance.

[0067] In the optical system of Example 4, compared to the optical system of Example 3, the negative lens disposed in the first lens unit B1 is made aspheric, thereby achieving a wider angle while suppressing distortion.

[0068] Numerical examples 1 to 4 corresponding to the first to fourth embodiments, respectively, are shown below.

[0069] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial distance (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. In addition, nd represents the refractive index of each optical member with respect to the d-line, and νd represents the Abbe number based on the d-line of the optical member. The Abbe number νd based on the d-line of a certain material is expressed as νd=(Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the Fraunhofer d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm). Φ is the effective diameter (mm).

[0070] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when the optical system of each example is focused on an object at infinity. The back focus is the distance on the optical axis from the final lens surface (the lens surface closest to the image) of the optical system to the paraxial image surface, expressed as an air-equivalent length. The total lens length of the optical system is the distance on the optical axis from the first lens surface (the lens surface closest to the object) to the final lens surface plus the back focus. The lens group is not limited to being composed of multiple lenses, but may also be composed of a single lens.

[0071] If the optical surface is aspheric, a * symbol is added to the right of the surface number. The aspheric shape is expressed as follows, 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, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, and A12 are the aspheric coefficients of each order: x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ]+A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 In addition, "e±XX" in each aspheric coefficient is "×10± XX " It means.

[0072] In addition, the 18th surface in Table 1 is a flare cut surface (not shown). The 10th and 19th surfaces in Table 3 are flare cut surfaces (not shown). The 10th and 21st surfaces in Table 5 are flare cut surfaces.

[0073] (Numerical Example 1)

[0074] [Table 1]

[0075] [Table 2]

[0076] (Numerical Example 2)

[0077] [Table 3]

[0078] [Table 4]

[0079] (Numerical Example 3)

[0080] [Table 5]

[0081] [Table 6]

[0082] (Numerical Example 4)

[0083] [Table 7]

[0084] [Table 8]

[0085] The various values ​​in each numerical example are summarized in Table 9 below.

[0086] [Table 9]

[0087] [Imaging device] Next, an embodiment of a digital still camera (imaging device) 10 using the optical system of each embodiment as an imaging optical system will be described with reference to FIG. 13. FIG. 13 is a diagram showing the configuration of the imaging device 10. The imaging device 10 includes a camera body 13, a lens device 11 including the optical system of any one of the above-mentioned embodiments 1 to 4, and an imaging element (light receiving element) 12 that photoelectrically converts an image formed by the optical system. An imaging element such as a CCD sensor or a CMOS sensor can be used as the imaging element 12. The lens device 11 and the camera body 13 may be integrally configured, or may be detachably configured. The camera body 13 may be a so-called single-lens reflex camera having a quick-turn mirror, or may be a so-called mirrorless camera not having a quick-turn mirror.

[0088] In this way, by applying the optical system in each of the above embodiments to an imaging device 10 such as a digital still camera, it is possible to obtain an imaging device 10 equipped with an optical system that achieves both weight reduction of the focus lens group and suppression of aberration fluctuation during focusing.

[0089] The imaging device 10 of this embodiment is not limited to the digital still camera shown in FIG. 13, but can be applied to various imaging devices such as broadcast cameras, cameras for silver halide film, and surveillance cameras.

[0090] The disclosure of each of the above embodiments includes the following configurations.

[0091] (Configuration 1) An optical system having a first lens group having positive refractive power, a second lens group having positive refractive power, a third lens group, a fourth lens group having positive refractive power, and a fifth lens group having negative refractive power, which are arranged in this order from an object side to an image side, and in which the distance between adjacent lens groups changes during focusing from an infinity distance to a close distance, During focusing from infinity to a close distance, the second lens group and the fourth lens group move toward the object side, at least one of the second lens group and the fourth lens group is composed of two or more lenses, The optical system according to claim 1, wherein the first lens group includes two or more negative lenses. (Configuration 2) 2. The optical system according to configuration 1, wherein the first lens group, the third lens group, and the fifth lens group are fixed with respect to an image plane during focusing from an infinity distance to a close distance. (Configuration 3) 3. The optical system according to configuration 1 or 2, wherein an aperture stop is disposed between the second lens group and the fourth lens group. (Configuration 4) When the focal length of the optical system at the infinity focal point is f, the focal length of the second lens group is f2, and the focal length of the fourth lens group is f4, 0.30 <f4 / f<4.80 0.70 <f2 / f<26.80 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the focal length of the second lens group is f2 and the focal length of the fourth lens group is f4, 0.05 <f4 / f2<1.50 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) When focusing at infinity, the distance on the optical axis from the object side lens surface of the first lens group to the image side lens surface of the lens group arranged closest to the image side is DT, and when focusing at infinity, the distance on the optical axis from the image side lens surface of the first lens group to the object side lens surface of the second lens group is D12. 0.008 <D12 / DT<0.210 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) When focusing at infinity, the distance on the optical axis from the object side lens surface of the first lens group to the image side lens surface of the lens group arranged closest to the image side is DT, and when focusing at infinity, the distance on the optical axis from the image side lens surface of the third lens group to the object side lens surface of the fourth lens group is D34. 0.020 <D34 / DT<0.530 7. The optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) When the total optical length of the optical system when focused at infinity is TTL and the thickness on the optical axis of the second lens group is T2, 0.004 <T2 / TTL<0.120 8. The optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied: (Configuration 9) When the total optical length of the optical system when focused at infinity is TTL and the thickness on the optical axis of the fourth lens group is T4, 0.040 <T4 / TTL<0.590 9. The optical system according to any one of configurations 1 to 8, wherein the following condition is satisfied: (Configuration 10) 10. The optical system according to any one of configurations 1 to 9, wherein the lens surface of the second lens group closest to the object side has a convex shape. (Configuration 11) 11. The optical system according to any one of configurations 1 to 10, wherein the lens surface of the third lens group closest to the image side has a concave shape. (Configuration 12) 12. The optical system according to any one of configurations 1 to 11, wherein the lens surface of the fourth lens group closest to the object side has a concave shape. (Configuration 13) When the focal length of the optical system at the infinity focal point is f and the focal length of the fifth lens group is f5, -25.80 <f5 / f<-0.90 13. The optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied: (Configuration 14) When the focal length of the second lens group is f2 and the focal length of the fourth lens group is f4, 0.05 <f4 / f2<1.50 5. The optical system according to configuration 4, wherein the following condition is satisfied: (Configuration 15) When the focal length of the optical system at the infinity focal point is f and the focal length of the fifth lens group is f5, -25.80 <f5 / f<-0.90 15. The optical system according to claim 14, wherein the following condition is satisfied: (Configuration 16) When focusing at infinity, the distance on the optical axis from the object side lens surface of the first lens group to the image side lens surface of the lens group arranged closest to the image side is DT, and when focusing at infinity, the distance on the optical axis from the image side lens surface of the third lens group to the object side lens surface of the fourth lens group is D34. 0.020 <D34 / DT<0.530 7. The optical system according to configuration 6, wherein the following condition is satisfied: (Configuration 17) When the total optical length of the optical system when focused at infinity is TTL and the thickness on the optical axis of the second lens group is T2, 0.004 <T2 / TTL<0.120 17. The optical system according to claim 16, wherein the following condition is satisfied: (Configuration 18) When the total optical length of the optical system when focused at infinity is TTL and the thickness on the optical axis of the fourth lens group is T4, 0.040 <T4 / TTL<0.590 18. The optical system according to claim 17, wherein the following condition is satisfied: (Configuration 19) 19. The optical system according to any one of configurations 1 to 18, characterized in that the optical system comprises the first lens group, the second lens group, the third lens group, the fourth lens group, and the fifth lens group, arranged in this order from the object side to the image side. (Configuration 20) 20. An imaging device comprising: the optical system according to any one of configurations 1 to 19; and an imaging element that receives an image formed by the optical system.

[0092] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0093] B1 First lens group B2 2nd lens group B3 3rd lens group B4 4th lens group B5 5th lens group

Claims

1. An optical system having a first lens group having positive refractive power, a second lens group having positive refractive power, a third lens group, a fourth lens group having positive refractive power, and a fifth lens group having negative refractive power, arranged in this order from the object side to the image side, wherein the spacing between adjacent lens groups changes during focusing from an infinity distance to a close distance, During focusing from infinity to a close distance, the second lens group and the fourth lens group move toward the object side, at least one of the second lens group and the fourth lens group is composed of two or more lenses, the first lens group includes two or more negative lenses, When the total optical length of the optical system when focused at infinity is TTL and the thickness of the fourth lens group on the optical axis is T4, 0.040<T4 / TTL<0.590 An optical system characterized by satisfying the following conditional expression:

2. 2. The optical system according to claim 1, wherein the first lens group, the third lens group, and the fifth lens group are fixed relative to an image plane during focusing from an infinity distance to a close distance.

3. 2. The optical system according to claim 1, wherein an aperture stop is disposed between the second lens group and the fourth lens group.

4. When the focal length of the optical system at the infinity focal point is f, the focal length of the second lens group is f2, and the focal length of the fourth lens group is f4, 0.30<f4 / f<4.80 0.70<f2 / f<26.80 2. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the focal length of the second lens group is f2 and the focal length of the fourth lens group is f4, 0.05<f4 / f2<1.50 2. The optical system according to claim 1, wherein the following condition is satisfied:

6. When focusing at infinity, the distance on the optical axis from the object-side lens surface of the first lens group to the image-side lens surface of the lens group arranged closest to the image side is defined as DT, and when focusing at infinity, the distance on the optical axis from the image-side lens surface of the first lens group to the object-side lens surface of the second lens group is defined as D12. 0.008<D12 / DT<0.210 2. The optical system according to claim 1, wherein the following condition is satisfied:

7. When focusing at infinity, the distance on the optical axis from the object-side lens surface of the first lens group to the image-side lens surface of the lens group arranged closest to the image side is defined as DT, and when focusing at infinity, the distance on the optical axis from the image-side lens surface of the third lens group to the object-side lens surface of the fourth lens group is defined as D34. 0.020<D34 / DT<0.530 2. The optical system according to claim 1, wherein the following condition is satisfied:

8. When the total optical length of the optical system when focused at infinity is TTL and the thickness of the second lens group on the optical axis is T2, 0.004<T2 / TTL<0.120 2. The optical system according to claim 1, wherein the following condition is satisfied:

9. When the focal length of the optical system at the infinity focal point is f and the focal length of the fifth lens group is f5, -25.80<f5 / f<-0.90 2. The optical system according to claim 1, wherein the following condition is satisfied:

10. When the focal length of the second lens group is f2 and the focal length of the fourth lens group is f4, 0.05<f4 / f2<1.50 5. The optical system according to claim 4, wherein the following condition is satisfied:

11. When the focal length of the optical system at the infinity focal point is f and the focal length of the fifth lens group is f5, -25.80<f5 / f<-0.90 11. The optical system according to claim 10, wherein the following condition is satisfied:

12. When focusing at infinity, the distance on the optical axis from the object-side lens surface of the first lens group to the image-side lens surface of the lens group arranged closest to the image side is defined as DT, and when focusing at infinity, the distance on the optical axis from the image-side lens surface of the third lens group to the object-side lens surface of the fourth lens group is defined as D34. 0.020<D34 / DT<0.530 7. The optical system according to claim 6, wherein the following condition is satisfied:

13. When the total optical length of the optical system when focused at infinity is TTL and the thickness of the second lens group on the optical axis is T2, 0.004<T2 / TTL<0.120 13. The optical system according to claim 12, wherein the following condition is satisfied:

14. When the total optical length of the optical system when focused at infinity is TTL and the thickness of the fourth lens group on the optical axis is T4, 0.040<T4 / TTL<0.590 14. The optical system according to claim 13, wherein the following condition is satisfied:

15. 2. The optical system according to claim 1, wherein the optical system comprises, in order from the object side to the image side, the first lens group, the second lens group, the third lens group, the fourth lens group, and the fifth lens group.

16. 4. The optical system according to claim 2, wherein the lens surface of the second lens group closest to the object side has a convex shape.

17. 4. The optical system according to claim 2, wherein the lens surface of the third lens group closest to the image side has a concave shape.

18. 4. The optical system according to claim 2, wherein the lens surface of the fourth lens group closest to the object side has a concave shape.

19. 16. The optical system according to claim 4, wherein the first lens group, the third lens group, and the fifth lens group are fixed with respect to an image plane during focusing from an infinity distance to a close distance.

20. 16. The optical system according to claim 4, wherein an aperture stop is disposed between the second lens group and the fourth lens group.

21. 10. An imaging device comprising: the optical system according to claim 1; and an imaging element that receives an image formed by the optical system.

Images