Imaging optical system

Abstract

To provide an imaging optical system suitable for a large-aperture-ratio telephoto lens, achieving reduced weight and good correction of axial chromatic aberration.SOLUTION: An imaging optical system includes; in order from the object side, a first lens group G1 having positive refractive power; a second lens group G2; and a third lens group G3. During focusing from an object at infinity to a nearby object, only the second lens group G2 moves. The first lens group G1 includes, in order from the object side, a group 1a and a group 1b. The group 1b includes: a negative lens L1na having a meniscus shape with its convex surface facing the object side; and another negative lens L1nb different from the negative lens L1na. The negative lens L1na is the negative lens located closest to the object side within the first lens group G1 and satisfies a predetermined conditional expression.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an imaging optical system suitable for a photographic lens used in a digital camera, a video camera, or the like. [Background technology]

[0002] In recent years, digital cameras have become lighter due to the shift to mirrorless cameras, while image sensors have become more highly pixelated. This has created a demand for lighter and more powerful imaging optical systems.

[0003] In particular, in large-aperture telephoto lenses with long focal lengths and large aperture ratios, the weight of the imaging optical system tends to increase due to the large effective aperture and the large diameter of the lens elements located on the object side, so further weight reduction is desired. One method of reducing the weight of large-aperture telephoto lenses is to reduce the number of large-effective-diameter lens elements located on the object side.

[0004] Furthermore, large-aperture telephoto lenses are prone to axial chromatic aberration due to their generally long focal lengths and large aperture ratios. It is known that increasing the number of lenses positioned on the object side is an effective way to correct axial chromatic aberration. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6627313 [Patent Document 2] Patent No. 6847067 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Documents 1 and 2, axial chromatic aberration is well corrected, but the negative lens closest to the object in the first lens group that corrects axial chromatic aberration has a large effective ray diameter relative to the entrance pupil diameter, leaving the challenge of reducing the lens diameter. Furthermore, because the negative lens has a concave surface facing the object side, the effect of diffusing the light beam increases the diameter of the subsequent lenses, resulting in a heavy glass material weight for the entire optical system.

[0007] The present invention has been made in view of the above circumstances, and has as its object to provide an imaging optical system that is lightweight, has good correction for longitudinal chromatic aberration, and is suitable for use as a large aperture ratio telephoto lens. [Means for solving the problem]

[0008] The imaging optical system according to the present invention is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2, and a third lens group G3, wherein only the second lens group G2 moves when focusing from an object at infinity to an object at a close distance, the first lens group G1 is composed of, in order from the object side, a group 1a and a group 1b, the group 1b having a negative meniscus lens L1na with its convex surface facing the object side, and a negative lens L1nb different from the negative lens L1na, the negative lens L1na being the negative lens located closest to the object in the first lens group G1, and wherein the imaging optical system satisfies the following conditional expression: (1)nL1nb>1.73 (2) VdL1nb<35 (3) ΔPgFL1nb<0.013 nL1nb: refractive index of negative lens L1nb VdL1nb: Abbe number of negative lens L1nb ΔPgFL1nb: Anomalous dispersion of negative lens L1nb ΔPgFL1nb=PgFL1nb+0.0018×VdL1nb−0.64833 PgFL1nb is the partial dispersion ratio PgF of the negative lens L1nb for the g-line and F-line. [Effects of the Invention]

[0009] The imaging optical system according to the present invention makes it possible to provide an imaging optical system that is lightweight, has excellent correction for longitudinal chromatic aberration, and is suitable for a large aperture ratio telephoto lens. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a lens configuration diagram of an imaging optical system according to a first embodiment of the present invention. [Figure 2] 4A and 4B are longitudinal aberration diagrams of the imaging optical system of Example 1 at an object distance of infinity. [Figure 3] 1A and 1B are longitudinal aberration diagrams of the imaging optical system of Example 1 at an object distance of 1.7 m. [Figure 4] 4A to 4C are diagrams showing lateral aberration of the imaging optical system of Example 1 at an infinite object distance. [Figure 5] 4A to 4C are diagrams showing lateral aberration of the imaging optical system of Example 1 at an object distance of 1.7 m. [Figure 6] FIG. 10 is a diagram showing lateral aberration at infinity in Example 1 with 0.3° image stabilization. [Figure 7] FIG. 10 is a lens configuration diagram of an imaging optical system according to a second embodiment of the present invention. [Figure 8] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 2 at an infinite object distance. [Figure 9] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 2 at an object distance of 1.7 m. [Figure 10] 10A and 10B are diagrams showing lateral aberration of the imaging optical system of Example 2 at an infinite object distance. [Figure 11] 10A and 10B are diagrams showing lateral aberration of the imaging optical system of Example 2 at an object distance of 1.7 m. [Figure 12] FIG. 10 is a diagram showing lateral aberration at infinity in Example 2 with 0.3° image stabilization. [Figure 13] FIG. 10 is a lens configuration diagram of an imaging optical system according to a third embodiment of the present invention. [Figure 14] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 3 at an infinite object distance. [Figure 15] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 3 at an object distance of 2.0 m. [Figure 16]10A and 10B are diagrams illustrating lateral aberration of the imaging optical system of Example 3 at an infinite object distance. [Figure 17] 10A and 10B are diagrams showing lateral aberration of the imaging optical system of Example 3 at an object distance of 2.0 m. [Figure 18] FIG. 10 is a diagram showing lateral aberration at infinity in Example 3 with 0.3° image stabilization. [Figure 19] FIG. 10 is a lens configuration diagram of an imaging optical system according to a fourth embodiment of the present invention. [Figure 20] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 4 at an infinite object distance. [Figure 21] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 4 at an object distance of 1.9 m. [Figure 22] 10A and 10B are diagrams showing lateral aberration of the imaging optical system of Example 4 at an infinite object distance. [Figure 23] 10A and 10B are diagrams showing lateral aberration of the imaging optical system of Example 4 at an object distance of 1.9 m. [Figure 24] FIG. 10 is a diagram showing lateral aberration at infinity in Example 4 with 0.3° image stabilization. [Figure 25] FIG. 10 is a lens configuration diagram of an imaging optical system according to a fifth embodiment of the present invention. [Figure 26] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 5 at an infinite object distance. [Figure 27] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 5 at an object distance of 1.7 m. [Figure 28] 10A and 10B are diagrams showing lateral aberration of the imaging optical system of Example 5 at an infinite object distance. [Figure 29] 10A to 10C are diagrams showing lateral aberrations of the imaging optical system of Example 5 at an object distance of 1.7 m. [Figure 30] FIG. 13 is a diagram showing lateral aberration at infinity in Example 5 with 0.3° image stabilization. [Figure 31] FIG. 10 is a lens configuration diagram of an imaging optical system according to a sixth embodiment of the present invention. [Figure 32] 13 is a longitudinal aberration diagram of the imaging optical system of Example 6 at an infinite object distance. FIG. [Figure 33] 13A and 13B are longitudinal aberration diagrams of the imaging optical system of Example 6 at an object distance of 1.8 m. [Figure 34]13A to 13C are diagrams showing lateral aberration of the imaging optical system of Example 6 at an infinite object distance. [Figure 35] 13A to 13C are diagrams showing lateral aberrations of the imaging optical system of Example 6 at an object distance of 1.8 m. [Figure 36] FIG. 13 is a diagram showing lateral aberration at infinity in Example 6 with 0.3° image stabilization. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the embodiments of the present invention, a lens simply referred to as a lens refers to a single lens or a single lens portion constituting a cemented lens. A cemented lens refers to a lens in which multiple single lenses are cemented together.

[0012] As can be seen from the lens construction diagrams shown in FIGS. 1, 7, 13, 19, 25, and 31, the imaging optical system according to the present invention is composed of, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2, and a third lens group G3, wherein only the second lens group G2 moves along the optical axis during focusing from infinity to a close distance, the first lens group G1 is composed of, in order from the object side, a group 1a and a group 1b, and the group 1b has a negative meniscus lens L1na with its convex surface facing the object side, and a negative lens L1nb different from the negative lens L1na, the negative lens L1na being the negative lens located closest to the object in the first lens group G1, and is characterized in that the following conditional expression is satisfied: (1)nL1nb>1.73 (2) VdL1nb<35 (3) ΔPgFL1nb<0.013 nL1nb: refractive index of negative lens L1nb VdL1nb: Abbe number of negative lens L1nb ΔPgFL1nb: Anomalous dispersion of negative lens L1nb ΔPgFL1nb=PgFL1nb+0.0018×VdL1nb−0.64833 PgFL1nb is the partial dispersion ratio PgF of the negative lens for the g-line and F-line.

[0013] By giving the first lens group G1 a positive refractive power, it is possible to converge the light beam, which makes it possible to reduce the diameter of the second lens group G2, which is the focus group. In addition, by reducing the diameter of the focus group, which is the movable group, it is possible to reduce its weight, and it is also possible to reduce the weight of the actuator that moves the focus group.

[0014] Furthermore, of the negative lenses in the first lens group G1, the negative lens L1na, which is positioned closest to the object and has a meniscus shape with its convex surface facing the object side, is located in the 1b group. This reduces the ray height at the first surface of the negative lens L1na, while converging the light beam at the convex surface facing the object side, thereby reducing the diameter of the light beam incident on subsequent lens surfaces and enabling weight reduction. Furthermore, the negative refractive power of the negative lens L1na makes it possible to suppress the occurrence of axial chromatic aberration.

[0015] In the imaging optical system according to the present invention, the first lens group G1 includes a cemented lens having positive refractive power and composed of a positive lens and a negative lens. By reducing the difference in the partial dispersion ratio between the positive and negative lenses in the cemented lens, second-order chromatic aberrations occurring in the cemented lens are corrected. Furthermore, for the multiple positive lenses composed of single lenses in the first lens group G1, first-order chromatic aberrations and other aberrations are corrected by the negative lens L1nb. Therefore, by placing the high-refractive-index, high-dispersion negative lens L1nb in the 1b group as defined by conditional expressions (1) and (2), it is possible to correct first-order axial chromatic aberrations in the first lens group G1 including the 1a group while suppressing the occurrence of other aberrations. Furthermore, by using a glass material with reduced positive anomalous dispersion as defined by conditional expression (3), it becomes easy to effectively correct axial chromatic aberrations, including second-order chromatic aberrations.

[0016] If the refractive power of the negative lens L1nb becomes weaker than the lower limit of conditional expression (1), it becomes difficult to correct spherical aberration and coma.

[0017] It is to be noted that, preferably, the lower limit of conditional expression (1) should be set to 1.80, thereby making it possible to ensure the above-mentioned effect.

[0018] If the dispersion of the negative lens L1nb becomes small beyond the lower limit of conditional expression (2), it becomes difficult to correct axial chromatic aberration.

[0019] It is to be noted that, preferably, the lower limit of conditional expression (2) should be set to 30, thereby making it possible to ensure the above-mentioned effect.

[0020] If the upper limit of conditional expression (3) is exceeded and the positive anomalous dispersion of the negative lens L1nb becomes large, it becomes difficult to correct second-order axial chromatic aberration.

[0021] It is to be noted that, preferably, the upper limit of conditional expression (3) should be set to 0.009, thereby making it possible to ensure the above-mentioned effect.

[0022] Furthermore, in the imaging optical system according to the present invention, it is desirable that group 1a have positive refractive power and be composed of one or two positive lenses. By giving group 1a positive refractive power, the diameter of groups 1b and onward can be made smaller due to the converging effect. Furthermore, by configuring group 1a from one or two positive lenses, it becomes easier to reduce the weight of group 1a, which has a large effective aperture.

[0023] Furthermore, in the image-forming optical system according to the present invention, it is desirable that the first lens group G1 satisfy the following conditional expression. (4) D1 / f>0.08 D1: The largest air gap within the first lens group G1 f: focal length of the entire system when focused at infinity

[0024] Conditional expression (4) defines the ratio of the maximum air gap within first lens group G1 to the focal length of the entire system. As can be seen from the lens construction diagrams shown in Figures 1, 7, 13, 19, 25, and 31, groups 1a and 1b constituting first lens group G1 are separated by the maximum air gap within first lens group G1. By ensuring the maximum air gap within first lens group G1 so as to satisfy conditional expression (4), the diameter of the light beam converged by group 1a, which has positive refractive power, can be made sufficiently small, allowing the diameters of the lenses from group 1b onwards to be reduced, resulting in a reduction in weight.

[0025] If the lower limit of conditional expression (4) is exceeded and the air gap within the first lens group G1 becomes narrow, the diameter of the light beam entering the 1b group cannot be made sufficiently small, and the lens diameter becomes large, making it difficult to reduce the weight.

[0026] It should be noted that, with regard to conditional expression (4), it is desirable to limit the upper limit to 0.26 and the lower limit to 0.10, thereby making it possible to ensure the above-mentioned effect.

[0027] Furthermore, it is desirable that the imaging optical system according to the present invention satisfy the following conditional expression: (5) 0.4 <f1a / f<1.7 (6) 0.3 <R1na / EPD<1.2 f1a: focal length of 1a group f: focal length of the entire system when focused at infinity R1na: Radius of curvature of the negative lens L1na on the object side EPD:Entrance pupil diameter

[0028] Condition (5) defines the ratio of the focal length of group 1a to the focal length of the entire system when focused at infinity. Satisfying condition (5) is advantageous for reducing the weight of the imaging optical system and correcting various aberrations.

[0029] If the upper limit of conditional expression (5) is exceeded and the focal length of group 1a becomes too long, the converging action of group 1a will not work sufficiently, and the diameter of the lenses from group 1b onwards cannot be made small, making it difficult to reduce the weight.

[0030] If the focal length of group 1a becomes short beyond the lower limit of conditional expression (5), the refractive power of group 1a becomes too strong, causing large spherical aberrations and coma aberrations that are difficult to correct.

[0031] It should be noted that, with regard to conditional expression (5), it is desirable to set the lower limit to 0.6 and the upper limit to 1.3, thereby making it possible to more reliably achieve the above-mentioned effect.

[0032] Conditional expression (6) defines the ratio of the radius of curvature of the object-side surface of the negative lens L1na to the diameter of the entrance pupil, and relates to the refractive power and aberration correction ability of the object-side surface of the negative lens L1na. Satisfying conditional expression (6) is advantageous for reducing the weight of the imaging optical system and correcting various aberrations.

[0033] If the radius of curvature of the negative lens L1na on the object side becomes large beyond the upper limit of conditional expression (6), the converging action of the object side surface of the negative lens L1na becomes weak, and the diameters of the subsequent lenses cannot be made small, making it difficult to reduce the weight.

[0034] If the radius of curvature of the object side of the negative lens L1na becomes small beyond the lower limit of conditional expression (6), the refractive power of the object side surface of the negative lens L1na becomes strong, causing large spherical aberration and coma aberration, which become difficult to correct.

[0035] It is to be noted that, preferably, the lower limit of conditional expression (6) should be set to 0.5 and the upper limit to 1.0, thereby making it possible to ensure the above-mentioned effect.

[0036] Furthermore, in the image-forming optical system according to the present invention, it is desirable that the negative lens L1na satisfy the following conditional expression. (7) 1.65 <nL1na<1.80 (8) VdL1na>40 nL1na: refractive index of negative lens L1na VdL1na: Abbe number of negative lens L1na

[0037] Condition (7) defines a preferable range for the refractive index of the negative lens L1na. Satisfying condition (7) is advantageous for correcting various aberrations and reducing the weight of the imaging optical system.

[0038] If the refractive index of the negative lens L1na becomes high beyond the upper limit of conditional expression (7), it becomes difficult to correct coma and astigmatism.

[0039] If the refractive index of the negative lens L1na falls below the lower limit of conditional expression (7), it becomes difficult to correct axial chromatic aberration. Also, the convex surface of the negative lens L1na facing the object side becomes weaker, making it difficult to reduce the lens weight.

[0040] It should be noted that, with regard to conditional expression (7), it is desirable to set the lower limit to 1.68 and the upper limit to 1.76, thereby making it possible to ensure the above-mentioned effect.

[0041] Conditional expression (8) defines a preferable range for the Abbe number of the negative lens L1na. By satisfying conditional expression (8), it becomes possible to effectively correct axial chromatic aberration.

[0042] If the dispersion of the negative lens L1na increases beyond the lower limit of conditional expression (8), it becomes difficult to correct axial chromatic aberration.

[0043] It is to be noted that, preferably, the lower limit of conditional expression (8) should be set to 45, thereby making it possible to ensure the above-mentioned effect.

[0044] Furthermore, in the imaging optical system according to the present invention, it is desirable that the third lens group G3 include, in order from the object side, a vibration reduction group Gos with negative refractive power that moves in a direction including a component perpendicular to the optical axis during image blur correction, and a rear group Gr with positive refractive power. By arranging the vibration reduction group Gos in the third lens group, the diameter of the light beam passing through the vibration reduction group becomes smaller, making it possible to downsize the vibration reduction mechanism. Furthermore, by arranging the rear group Gr with positive refractive power on the image side of the vibration reduction group Gos, the negative refractive power of the vibration reduction group Gos can be strengthened, thereby reducing the amount of movement during vibration reduction.

[0045] It is also desirable to satisfy the following conditional expression: (9)-1.5 <fGos / fGr<-0.7 fGos: focal length of vibration isolation group Gos fGr: focal length of rear group Gr

[0046] Conditional expression (9) defines the ratio of the focal lengths of the image stabilization group Gos and the rear group Gr. Satisfying conditional expression (9) is advantageous for reducing aberration fluctuations during image stabilization and for making the product more compact.

[0047] If the focal length of the image stabilization group Gos becomes short, exceeding the upper limit of conditional expression (9), the refractive power of the image stabilization group Gos becomes too strong, resulting in large fluctuations in coma and astigmatism when the image stabilization group Gos moves vertically during image stabilization.

[0048] If the focal length of the image stabilization group Gos increases beyond the lower limit of conditional expression (9), the amount of movement required to correct camera shake during image stabilization increases, making it difficult to reduce the size of the entire product.

[0049] It should be noted that, with regard to conditional expression (9), it is desirable to set the lower limit to -1.3 and the upper limit to -0.8, thereby making it possible to ensure the above-mentioned effect.

[0050] Furthermore, in the imaging optical system according to the present invention, it is desirable that the second lens group G2 be composed of a single lens or one cemented lens. Because the second lens group G2 is a focus group, by using a single lens or one cemented lens, the weight of the lens can be reduced, and the weight of the actuator that moves the focus group can also be reduced.

[0051] Furthermore, it is desirable that the imaging optical system according to the present invention be configured without including a diffractive optical element. While the use of a diffractive optical element is expected to effectively correct chromatic aberration, it also generates flare due to unnecessary diffracted light other than first-order diffracted light. By not including a diffractive optical element, it is possible to prevent the generation of flare that is specific to surfaces with diffraction gratings.

[0052] The imaging optical system according to the present invention is more effective when it has the following configuration.

[0053] It is preferable to position the aperture stop S closer to the image side than the second lens group G2, which allows the aperture stop diameter to be made smaller, thereby enabling the entire product to be made smaller in diameter.

[0054] Next, the lens configuration of an embodiment of the imaging optical system of the present invention will be described. In the following description, the lens configuration will be described in order from the object side to the image side.

[0055] [Example 1] FIG. 1 is a lens configuration diagram of an imaging optical system according to a first embodiment of the present invention.

[0056] The first lens group G1 is composed of groups 1a and 1b, and has positive refractive power overall. Group 1a consists of a biconvex positive lens and a meniscus positive lens with its convex surface facing the object side. Group 1b consists of a cemented lens consisting of a meniscus negative lens L1na with its convex surface facing the object side and a meniscus positive lens with its convex surface facing the object side, a biconcave negative lens L1nb, and a cemented lens consisting of a meniscus negative lens with its convex surface facing the object side and a biconvex positive lens.

[0057] The second lens group G2 is composed of a negative meniscus lens element with its convex surface facing the object side, and has negative refractive power as a whole. Furthermore, the second lens group G2 moves from the object side to the image side along the optical axis when focusing from an object at infinity to a close object.

[0058] The third lens group G3 is composed of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, an aperture stop S, an image stabilization group Gos, and a rear group Gr, and has positive refractive power overall. The image stabilization group Gos consists of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a biconcave negative lens. The rear group Gr consists of a cemented lens consisting of a biconvex positive lens and a meniscus negative lens with its concave surface facing the object side, a biconvex positive lens, a meniscus positive lens with its concave surface facing the object side, a biconcave negative lens, and a meniscus negative lens with its concave surface facing the object side. The image stabilization group Gos moves in a direction that includes a component perpendicular to the optical axis to reduce image blur caused by vibrations in the imaging optical system.

[0059] [Example 2] FIG. 7 is a lens configuration diagram of an imaging optical system according to a second embodiment of the present invention.

[0060] The first lens group G1 is composed of groups 1a and 1b, and has positive refractive power overall. Group 1a consists of a meniscus positive lens with its convex surface facing the object side. Group 1b consists of a meniscus positive lens with its convex surface facing the object side, a cemented lens consisting of a meniscus negative lens L1na with its convex surface facing the object side and a meniscus positive lens with its convex surface facing the object side, and a biconcave negative lens L1nb, and a cemented lens consisting of a meniscus negative lens with its convex surface facing the object side and a biconvex positive lens.

[0061] The second lens group G2 is composed of a negative meniscus lens element with its convex surface facing the object side, and has negative refractive power as a whole. Furthermore, the second lens group G2 moves from the object side to the image side along the optical axis when focusing from an object at infinity to a close object.

[0062] The third lens group G3 is composed of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, an aperture stop S, an image stabilization group Gos, and a rear group Gr, and has an overall negative refractive power. The image stabilization group Gos consists of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a biconcave negative lens. The rear group Gr consists of a cemented lens consisting of a biconvex positive lens and a meniscus negative lens with its concave surface facing the object side, a cemented lens consisting of a biconvex positive lens, a meniscus positive lens with its concave surface facing the object side, and a biconcave negative lens, and a meniscus negative lens with its concave surface facing the object side. The image stabilization group Gos moves in a direction that includes a component perpendicular to the optical axis to reduce image blur caused by vibrations in the imaging optical system.

[0063] [Example 3] FIG. 13 is a lens configuration diagram of an imaging optical system according to a third embodiment of the present invention.

[0064] The first lens group G1 is composed of groups 1a and 1b, and has positive refractive power overall. Group 1a consists of a meniscus positive lens with its convex surface facing the object side, and a meniscus positive lens with its convex surface facing the object side. Group 1b consists of a cemented lens consisting of a meniscus negative lens L1na with its convex surface facing the object side and a biconvex positive lens, and a biconcave negative lens L1nb, and a cemented lens consisting of a meniscus negative lens with its convex surface facing the object side and a biconvex positive lens.

[0065] The second lens group G2 is composed of a negative meniscus lens element with its convex surface facing the object side, and has negative refractive power as a whole. Furthermore, the second lens group G2 moves from the object side to the image side along the optical axis when focusing from an object at infinity to a close object.

[0066] The third lens group G3 is composed of a cemented lens consisting of a meniscus positive lens with its convex surface facing the object side and a meniscus negative lens with its convex surface facing the object side, an aperture stop S, an image stabilization group Gos, and a rear group Gr, and has negative refractive power overall. The image stabilization group Gos consists of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a biconcave negative lens. The rear group Gr consists of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, a biconvex positive lens, a meniscus positive lens with its convex surface facing the object side, and a meniscus negative lens with its concave surface facing the object side. The image stabilization group Gos moves in a direction that includes a component perpendicular to the optical axis to reduce image blur caused by vibrations in the imaging optical system.

[0067] [Example 4] FIG. 19 is a lens configuration diagram of an imaging optical system according to a fourth embodiment of the present invention.

[0068] The first lens group G1 is composed of groups 1a and 1b, and has positive refractive power overall. Group 1a consists of a meniscus positive lens with its convex surface facing the object side, and a meniscus positive lens with its convex surface facing the object side. Group 1b consists of a cemented lens consisting of a meniscus negative lens L1na with its convex surface facing the object side and a biconvex positive lens, and a meniscus negative lens L1nb with its convex surface facing the object side, and a cemented lens consisting of a meniscus positive lens with its convex surface facing the object side and a meniscus negative lens with its convex surface facing the object side.

[0069] The second lens group G2 is composed of a meniscus-shaped positive lens element with its convex surface facing the object side, and has positive refractive power as a whole. Furthermore, the second lens group G2 moves along the optical axis from the image side to the object side when focusing from an object at infinity to a close object.

[0070] The third lens group G3 is composed of a meniscus negative lens with its convex surface facing the object side, an image stabilization group Gos, and a rear group Gr, and has negative refractive power overall. The image stabilization group Gos consists of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a biconcave negative lens. The rear group Gr consists of a cemented lens consisting of a biconvex positive lens and a meniscus negative lens with its concave surface facing the object side, a biconvex positive lens, a biconcave negative lens, and a meniscus negative lens with its concave surface facing the object side. The image stabilization group Gos moves in a direction that includes a component perpendicular to the optical axis to reduce image blur caused by shaking of the imaging optical system.

[0071] An aperture stop S is disposed between the second lens group G2 and the third lens group G3.

[0072] [Example 5] FIG. 25 is a lens configuration diagram of an imaging optical system according to a fifth embodiment of the present invention.

[0073] The first lens group G1 is composed of groups 1a and 1b, and has positive refractive power overall. Group 1a consists of a meniscus positive lens with a convex surface facing the object side and a meniscus positive lens with a convex surface facing the object side. Group 1b consists of a cemented lens consisting of a meniscus negative lens L1na with a convex surface facing the object side and a meniscus positive lens with a convex surface facing the object side, a biconcave negative lens L1nb, and a cemented lens consisting of a meniscus negative lens with a convex surface facing the object side and a biconvex positive lens.

[0074] The second lens group G2 is composed of a cemented lens consisting of a meniscus positive lens element with its convex surface facing the object side and a meniscus negative lens element with its convex surface facing the object side, and has negative refractive power as a whole. Furthermore, the second lens group G2 moves from the object side to the image side along the optical axis when focusing from an object at infinity to a close object.

[0075] The third lens group G3 is composed of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, an aperture stop S, an image stabilization group Gos, and a rear group Gr, and has positive refractive power overall. The image stabilization group Gos consists of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a biconcave negative lens. The rear group Gr consists of a cemented lens consisting of a biconvex positive lens and a meniscus negative lens with its concave surface facing the object side, a biconvex positive lens, a biconvex positive lens, a biconcave negative lens, and a meniscus negative lens with its concave surface facing the object side. The image stabilization group Gos moves in a direction that includes a component perpendicular to the optical axis to reduce image blur caused by vibrations in the imaging optical system.

[0076] [Example 6] FIG. 31 is a diagram showing the lens arrangement of an imaging optical system according to a sixth embodiment of the present invention.

[0077] The first lens group G1 is composed of groups 1a and 1b, and has positive refractive power overall. Group 1a consists of a meniscus positive lens with a convex surface facing the object side and a meniscus positive lens with a convex surface facing the object side. Group 1b consists of a cemented lens consisting of a meniscus negative lens L1na with a convex surface facing the object side and a meniscus positive lens with a convex surface facing the object side, a biconcave negative lens L1nb, and a cemented lens consisting of a meniscus negative lens with a convex surface facing the object side and a biconvex positive lens.

[0078] The second lens group G2 is composed of a negative meniscus lens element with its convex surface facing the object side, and has negative refractive power as a whole. Furthermore, the second lens group G2 moves from the object side to the image side along the optical axis when focusing from an object at infinity to a close object.

[0079] The third lens group G3 is composed of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, an aperture stop S, an image stabilization group Gos, and a rear group Gr, and has positive refractive power overall. The image stabilization group Gos is composed of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens with an aspherical surface on the image side. The rear group Gr is composed of a cemented lens consisting of a biconvex positive lens and a meniscus negative lens with its concave surface facing the object side, a biconvex positive lens, a biconvex positive lens, a biconcave negative lens, and a meniscus negative lens with its concave surface facing the object side. The image stabilization group Gos moves in a direction that includes a component perpendicular to the optical axis to reduce image blur caused by shaking of the imaging optical system.

[0080] Specific numerical data for each of the embodiments of the imaging optical system of the present invention described above will be shown below.

[0081] In the [Surface Data] section, the surface number is the lens surface or aperture stop number counted from the object side, r is the radius of curvature of each surface, d is the spacing between surfaces, nd is the refractive index for the d-line (wavelength 587.56 nm), vd is the Abbe number for the d-line, and PgF is the partial dispersion ratio for the g-line and F-line.

[0082] An asterisk (*) next to a surface number indicates that the lens surface is aspherical, and BF represents the back focal length.

[0083] The (diaphragm) next to the surface number indicates that an aperture diaphragm is located at that position. The radius of curvature for the plane or aperture diaphragm is marked as ∞ (infinity).

[0084] [Aspherical Data] shows the values ​​of each coefficient that determines the aspherical shape of lens surfaces marked with an * in [Surface Data]. The shape of an aspherical surface is determined by the following equation, where y is the displacement from the optical axis in a direction perpendicular to the optical axis, z is the displacement (sag) from the intersection of the aspherical surface and the optical axis in the direction of the optical axis, r is the radius of curvature of the reference sphere, K is the Conic coefficient, and A4, A6, and A8 are the fourth-order, sixth-order, and eighth-order aspherical coefficients, respectively. TIFF2025162727000002.tif23124

[0085] [Various Data] shows values ​​such as focal length for each focal length state.

[0086] [Variable Distance Data] shows the variable distance and BF values ​​for each focal length state.

[0087] [Lens Group Data] shows the surface number of each lens group closest to the object and the composite focal length of the entire group.

[0088] In the following specification values, the focal length f, radius of curvature r, lens surface spacing d, and other length units are given in millimeters (mm) unless otherwise specified; however, this is not a limitation, as optical systems can achieve equivalent optical performance with proportional magnification and proportional reduction.

[0089] In the aberration diagrams corresponding to the respective examples, d, g, and C represent the d-line, g-line, and C-line, respectively, and ΔS and ΔM represent the sagittal image surface and meridional image surface, respectively.

[0090] Numerical Example 1 Unit: mm [Face Data] Surface number rd nd vd PgF Object surface ∞ (d0) 1 212.8145 7.4926 1.48749 70.44 0.5306 2 -3741.0747 1.9000 3 88.7689 11.1469 1.43700 95.10 0.5336 4 311.8544 32.0000 5 62.7550 2.0000 1.72916 54.67 0.5453 6 41.2488 15.2817 1.43700 95.10 0.5336 7 326.4366 3.0213 8 -352.0999 1.8000 1.85451 25.15 0.6103 9 192.6785 6.5400 10 100.1622 1.5000 1.75500 52.32 0.5473 11 47.0478 11.2712 1.59410 60.47 0.5552 12 -256.8810 (d12) 13 424.4891 1.2000 1.51823 58.96 0.5442 14 49.7913 (d14) 15 119.8435 8.0834 1.85883 30.00 0.5979 16 -42.6903 1.0000 1.80440 39.58 0.5762 17 155.7968 2.9331 18 (Aperture) ∞ 1.9984 19 126.1592 3.1081 1.98612 16.48 0.6656 20 -164.7066 0.9000 1.71300 53.94 0.5442 21 48.6121 2.8437 22 -750.1799 0.9000 1.85451 25.15 0.6103 23 66.7431 1.8897 24 45.2550 9.5268 1.77250 49.63 0.5504 25 -32.6534 0.9000 2.00069 25.46 0.6136 26 -360.8672 6.8814 27 80.6631 10.0000 1.77047 29.74 0.5951 28 -71.9091 0.1500 29 -192.5873 9.7103 1.56732 42.84 0.5744 30 -48.2101 0.1500 31 -60.9006 0.9000 1.57144 71.61 0.5419 32 78.9803 7.3037 33 -26.3842 0.9000 1.98612 16.48 0.6656 34 -42.1224 (BF) Image plane ∞ [Various data] INF 1700mm Focal length 194.30 153.36 F-number 2.07 2.25 Full angle of view 2ω 12.45 9.64 Image height Y 21.63 21.63 Lens total length 212.00 212.00 [Variable Interval Data] INF 1700mm d0 ∞ 1488.0000 d12 3.4000 17.9678 d14 20.9224 6.3545 BF 22.4456 22.4457 [Lens group data] Group Starting plane Focal length G1 1 124.55 G2 13 -108.97 G3 15 1807.38 1a 1 167.70 1b 5 323.74 Gos 19 -52.92 Gr 24 51.80

[0091] Numerical Example 2 Unit: mm [Face Data] Surface number rd nd vd PgF Object surface ∞ (d0) 1 157.5957 8.0000 1.59349 67.00 0.5366 2 921.0193 34.0000 3 85.7774 10.0683 1.43700 95.10 0.5336 4 388.5532 7.1670 5 66.0429 2.0000 1.69680 55.46 0.5426 6 43.7541 15.1337 1.43700 95.10 0.5336 7 266.2950 3.3888 8 -415.1074 1.8000 1.90110 27.06 0.6072 9 226.1287 7.5465 10 102.8754 1.5000 1.71300 53.94 0.5442 11 43.2319 12.6650 1.55032 75.50 0.5401 12 -230.5175 (d12) 13 393.4221 1.2000 1.51823 58.96 0.5442 14 47.9295 (d14) 15 178.5940 7.7339 1.85883 30.00 0.5979 16 -39.3760 1.0000 1.80440 39.58 0.5762 17 306.2211 2.4681 18 (Aperture) ∞ 2.4757 19 232.1757 2.7082 1.98612 16.48 0.6656 20 -136.1022 0.9000 1.69680 55.46 0.5426 21 46.6978 2.5660 22 -6382.2488 0.9000 1.80610 33.27 0.5884 23 68.4057 1.8152 24 40.5851 9.7684 1.71300 53.94 0.5442 25 -33.8193 0.9000 2.00069 25.46 0.6136 26 -199.3648 7.6595 27 66.2565 8.2767 1.73037 32.23 0.5899 28 -60.2793 0.1500 29 -116.6478 6.9058 1.62280 57.05 0.5464 30 -26.0788 0.9000 1.59282 68.62 0.5440 31 77.3746 8.8529 32 -24.9346 0.9000 1.98612 16.48 0.6656 33 -38.0814 (BF) Image plane ∞ [Various data] INF 1700mm Focal length 194.30 152.59 F-number 2.06 2.16 Full angle of view 2ω 12.45 9.77 Image height Y 21.63 21.63 Lens total length 217.00 217.00 [Variable Interval Data] INF 1700mm d0∞1483.0000 d12 3.4000 16.5023 d14 19.8883 6.7859 BF 22.3621 22.3622 [Lens group data] Group Starting plane Focal length G1 1 117.22 G2 13 -105.44 G3 15 -1742.11 1a 1 319.11 1b 3 156.30 Gos 19 -48.70 Gr 24 50.89

[0092] Numerical Example 3 Unit: mm [Face Data] Surface number rd nd vd PgF Object surface ∞ (d0) 1 190.4521 6.3143 1.48749 70.44 0.5306 2 537.0147 11.5030 3 139.2066 10.1815 1.43700 95.10 0.5336 4 1392.0544 60.2047 5 80.3098 2.0000 1.69680 55.46 0.5426 6 48.0217 15.8120 1.43700 95.10 0.5336 7 -292.7233 3.5870 8 -178.3030 1.8000 1.90110 27.06 0.6072 9 433.9555 14.8253 10 90.1247 1.5000 1.69680 55.46 0.5426 11 53.5632 9.7241 1.55397 71.76 0.5392 12 -212.7083 (d12) 13 521.3103 1.2000 1.65844 50.86 0.5576 14 65.4784 (d14) 15 42.7563 3.0534 1.94594 17.98 0.6546 16 78.4619 1.0000 1.69895 30.05 0.6028 17 34.0994 5.5828 18 (Aperture) ∞ 1.8102 19 -10393.9834 4.3000 1.84666 23.78 0.6192 20 -53.4040 0.9000 1.77250 49.63 0.5504 21 89.8258 1.5000 22 -560.1647 0.9000 1.71300 53.94 0.5442 23 109.3462 14.4675 24 38.7656 10.0000 1.73037 32.23 0.5899 25 -57.1805 0.9000 2.00069 25.46 0.6136 26 54.8428 2.8345 27 50.7506 10.0000 1.60342 38.01 0.5828 28 -89.2755 2.9530 29 78.9065 10.0000 1.71736 29.50 0.6040 30 202.5054 19.0022 31 -26.3135 0.9000 1.98612 16.48 0.6656 32 -44.4795 (BF) Image plane ∞ [Various data] INF 2000mm Focal length 290.30 204.27 F-number 2.90 3.12 Full angle of view 2ω 8.35 6.26 Image height Y 21.63 21.63 Lens length 286.83 286.83 [Variable Interval Data] INF 2000mm d0 ∞ 1713.1749 d12 3.4000 18.5066 d14 25.1140 10.0074 BF 29.5555 29.5557 [Lens group data] Group Starting plane Focal length G1 1 136.72 G2 13 -113.85 G3 15 -303.93 1a 1 226.61 1b 5 184.48 Gos 19 -65.82 Gr 24 66.80

[0093] Numerical Example 4 Unit: mm [Face Data] Surface number rd nd vd PgF Object surface ∞ (d0) 1 212.5532 8.0000 1.59349 67.00 0.5366 2 904.8287 0.3836 3 83.8527 12.6164 1.43700 95.10 0.5336 4 347.1350 24.0000 5 61.7203 2.0000 1.69680 55.46 0.5426 6 44.0332 14.8240 1.43700 95.10 0.5336 7 252.5695 1.4113 8 682.0781 1.8000 1.90110 27.06 0.6072 9 119.8764 12.5270 10 58.9734 3.5827 1.94594 17.98 0.6546 11 88.7654 1.3000 2.00100 29.13 0.5995 12 41.4854 (d12) 13 47.2689 7.2980 1.59282 68.62 0.5440 14 418.7619 (d14) 15 (Aperture) ∞ 2.0000 16 149.2274 1.0000 1.68430 26.81 0.6232 17 57.9269 6.0051 18 337.6848 5.2879 1.98612 16.48 0.6656 19 -90.0821 0.9000 1.61340 44.27 0.5633 20 36.3468 3.5896 21 -165.9201 0.9000 1.85883 30.00 0.5979 22 172.3448 1.3225 23 56.8223 11.9177 1.72825 28.32 0.6075 24 -32.6031 1.0000 1.94594 17.98 0.6546 25 -88.2138 3.7000 26 53.2003 10.0000 1.56732 42.84 0.5744 27 -48.2475 0.1500 28 -66.3037 5.6446 1.49700 81.61 0.5389 29 62.3923 6.7818 30 -28.4746 0.9000 1.98612 16.48 0.6656 31 -37.5769 (BF) Image plane ∞ [Various data] INF 1900mm Focal length 193.00 164.58 F-number 2.06 2.33 Full angle of view 2ω 12.57 10.17 Image height Y 21.63 21.63 Lens total length 202.47 202.47 [Variable Interval Data] INF 1900mm d0 ∞ 1697.5314 d12 14.6449 3.6654 d14 11.7595 22.7392 BF 25.2219 25.2219 [Lens group data] Group Starting plane Focal length G1 1 481.54 G2 13 89.23 G3 15 -111.22 1a 1 163.40 1b 5 -123.67 Gos 18 -49.80 Gr 23 49.15

[0094] Numerical Example 5 Unit: mm [Face Data] Surface number rd nd vd PgF Object surface ∞ (d0) 1 209.1635 6.5775 1.48749 70.44 0.5306 2 1797.8328 1.9000 3 93.3731 11.0915 1.43700 95.10 0.5336 4 365.5515 32.0000 5 69.0349 2.0000 1.69680 55.46 0.5426 6 43.7016 15.2020 1.43700 95.10 0.5336 7 319.9534 2.7434 8 -626.0523 1.8000 1.90110 27.06 0.6072 9 257.8342 6.8065 10 97.4850 1.5000 1.71300 53.94 0.5442 11 44.4323 12.5390 1.59282 68.62 0.5440 12 -886.8146 (d12) 13 383.4827 2.2198 1.69680 55.46 0.5426 14 142.9200 1.1000 1.48749 70.44 0.5306 15 50.2867 (d15) 16 110.4575 11.3200 1.85883 30.00 0.5979 17 -43.2879 1.0000 1.80000 29.84 0.6017 18 181.9370 2.8078 19 (Aperture) ∞ 1.9464 20 118.9931 3.3417 1.98612 16.48 0.6656 21 -137.1580 0.9000 1.77250 49.63 0.5504 22 44.8454 3.0414 23 -288.8846 0.9000 1.80518 25.46 0.6157 24 70.3717 1.8000 25 38.2028 9.6908 1.69680 55.46 0.5426 26 -38.7924 0.9000 2.00100 29.13 0.5995 27 -572.5354 5.9477 28 133.8498 10.0000 1.80610 33.27 0.5884 29 -166.6990 0.1500 30 49.7691 10.0000 1.60342 38.01 0.5828 31 -56.2892 0.1500 32 -76.9729 0.9223 1.59282 68.62 0.5440 33 46.6786 9.1784 34 -24.0246 0.9000 1.98612 16.48 0.6656 35 -37.4041 (BF) Image plane ∞ [Various data] INF 1700mm Focal length 194.30 152.04 F-number 2.07 2.24 Full angle of view 2ω 12.45 9.57 Image height Y 21.63 21.63 Lens length 217.87 217.87 [Variable Interval Data] INF 1700mm d0 ∞ 1482.1330 d12 3.4000 18.0315 d15 20.8947 6.2632 BF 21.1963 21.1962 [Lens group data] Group Starting plane Focal length G1 1 126.42 G2 13 -107.38 G3 16 1258.39 1a 1 179.89 1b 5 302.58 Gos 20 -46.73 Gr 25 48.00

[0095] Numerical Example 6 Unit: mm [Face Data] Surface number rd nd vd PgF Object surface ∞ (d0) 1 159.1112 7.5000 1.48749 70.44 0.5306 2 583.1761 2.0000 3 90.4243 11.6561 1.43700 95.10 0.5336 4 378.2022 32.7767 5 66.8508 2.0000 1.71300 53.94 0.5442 6 39.7714 16.0715 1.43700 95.10 0.5336 7 464.4841 2.8100 8 -251.3297 1.8000 1.77047 29.74 0.5951 9 175.5525 8.8857 10 103.7283 1.5000 1.71300 53.94 0.5442 11 54.2772 9.8652 1.59282 68.62 0.5440 12 -234.1227 (d12) 13 268.6773 1.0000 1.59349 67.00 0.5366 14 52.1505 (d14) 15 55.4558 8.5417 1.92119 23.96 0.6202 16 -70.0040 1.0000 1.85451 25.15 0.6103 17 61.7226 6.8202 18 (Aperture) ∞ 3.5116 19 -244.0228 2.4718 1.94594 17.98 0.6546 20 -65.8073 0.9000 1.76450 49.09 0.5528 21* 41.0665 2.9308 22 47.4921 8.8793 1.77250 49.63 0.5504 23 -31.7013 1.0000 2.00069 25.46 0.6136 24 -402.5213 2.1321 25 100.8842 12.2400 1.65412 39.68 0.5737 26 -422.8292 2.0866 27 115.1365 6.0864 1.77047 29.74 0.5951 28 -59.1836 2.1581 29 -82.3617 2.0000 1.59282 68.62 0.5440 30 67.6562 7.6515 31 -27.7967 0.9000 1.98612 16.48 0.6656 32 -40.0978 (BF) Image plane ∞ [Aspherical data] 21 pages K 0.00000 A4 -1.48938E-06 A6 -1.16771E-09 A8 8.46462E-13 [Various data] INF 1800mm Focal length 194.00 159.31 F-number 2.06 2.24 Full angle of view 2ω 12.54 9.83 Image height Y 21.63 21.63 Lens total length 215.00 215.00 [Variable Interval Data] INF 1800mm d0 ∞ 1585.0000 d12 2.0000 16.1577 d14 18.2512 4.0935 BF 25.5735 25.5735 [Lens group data] Group Starting plane Focal length G1 1 130.82 G2 13 -109.22 G3 15 419.58 1a 1 169.20 1b 5 341.50 Gos 19 -50.44 Gr 22 52.05

[0096] Also shown is a list of values ​​corresponding to the conditional expressions in each of these embodiments.

[0097] [Table 1]

[0098] The above description of the embodiment has been given of one example of the imaging optical system of the present invention, and the present invention is not limited to this embodiment as long as it does not deviate from the gist of the present invention. Various design changes, modifications, combinations, and sub-combinations are possible, and all of these are included in the equivalent scope of the present invention. [Explanation of symbols]

[0099] G1 First lens group G2 Second lens group G3 Third lens group 1a 1a group 1b 1b group L1na negative lens L1na L1nb negative lens L1nb Gos anti-vibration group Gr rear group S aperture stop I image plane

Claims

1. the first lens group G1 is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2, and a third lens group G3, wherein only the second lens group G2 moves when focusing from an object at infinity to an object at a close distance, the first lens group G1 is composed of, in order from the object side, a group 1a and a group 1b, the group 1b has a negative meniscus lens L1na with a convex surface facing the object side, and a negative lens L1nb different from the negative lens L1na, the negative lens L1na being the negative lens located closest to the object side in the first lens group G1, An imaging optical system that satisfies the following conditional expression: (1) nL1nb>1.73 (2) VdL1nb<35 (3) ΔPgFL1nb<0.013 nL1nb: refractive index of negative lens L1nb VdL1nb: Abbe number of negative lens L1nb ΔPgFL1nb: Anomalous dispersion of negative lens L1nb ΔPgFL1nb=PgFL1nb+0.0018×VdL1nb−0.64833 PgFL1nb is the partial dispersion ratio PgF of the negative lens L1nb for the g-line and F-line.

2. 2. The imaging optical system according to claim 1, wherein the group 1a has positive refractive power and is made up of one or two positive lenses.

3. 3. The imaging optical system according to claim 2, wherein the first lens group G1 satisfies the following condition: (4) D1 / f>0.08 D1: maximum air gap within the first lens group G1 f: focal length of the entire system when focused at infinity

4. 3. The imaging optical system according to claim 2, which satisfies the following condition: (5) 0.4<f1a / f<1.7 (6) 0.3<R1na / EPD<1.2 f1a: focal length of 1a group f: focal length of the entire system when focused at infinity R1na: radius of curvature of the negative lens L1na on the object side EPD: Entrance pupil diameter

5. 5. The imaging optical system according to claim 1, wherein the negative lens L1na satisfies the following condition: 1<n< ... (7) 1.65<nL1na<1.80 (8) VdL1na>40 nL1na: refractive index of negative lens L1na VdL1na: Abbe number of negative lens L1na

6. 5. The imaging optical system according to claim 1, wherein the third lens group G3 includes, in order from the object side, a vibration reduction group Gos having negative refractive power that moves in a direction including a component perpendicular to the optical axis during image blur correction, and a rear group Gr having positive refractive power, and wherein the following conditional expression is satisfied: (9) -1.5<fGos / fGr<-0.7 fGos: focal length of the vibration isolation group fGr: focal length of rear group

7. 5. The imaging optical system according to claim 1, wherein the second lens group G2 is composed of a single lens or one cemented lens.

8. 5. The imaging optical system according to claim 1, wherein the imaging optical system does not include a diffractive optical element.

Images