Imaging optical system

Abstract

The purpose of the present invention is to provide an imaging optical system which is suitable for a compact and lightweight telephoto lens by having a compact and lightweight focusing unit itself. The imaging optical system is characterized in that the imaging optical system is composed of a first group (G1) having positive refractive power on the whole, a second group (G2) composed of lenses moving on the optical axis during focusing, and a third group (G3) having refractive power, which are arranged in order from the object side to the image side, and the imaging optical system satisfies a predetermined conditional expression.

Description

Technical Field

[0001] The present invention relates to an imaging optical system, which is suitable for a photographic lens used in a still camera, a video camera, etc. Background Art

[0002] Conventionally, as an imaging optical system suitable for a long focal length photographic lens (hereinafter referred to as a telephoto lens), a telephoto imaging optical system is known in which a lens group with positive focal power and a lens group with negative focal power are sequentially arranged from the object side toward the image side. By adopting a telephoto focal power arrangement, the total optical length of a telephoto lens, which tends to become longer and heavier, can be shortened.

[0003] In addition, telephoto lenses are often used in sports, animal photography, etc., which require high-speed autofocus. If a telephoto lens uses a whole-swing method that moves the entire imaging optical system to focus, the weight of the lens that moves during focusing becomes large, making it difficult to achieve high-speed autofocus, so an internal focusing method is often used.

[0004] In addition, in recent years, telephoto lenses are increasingly being used in animation photography. When used in animation photography, the autofocus often uses a contrast detection method. In the contrast detection method, the focus unit is generally swung to detect contrast, so a telephoto lens equipped with a lighter focus unit than before is expected.

[0005] In addition, in recent years, as the popularity of mirrorless cameras designed to be small has increased, telephoto lenses are also required to be small and light. In the case of making a telephoto lens small and light, it is important to make the movable part small and light in addition to making the imaging optical system small. This is because the size or configuration of the actuator depends on the size or weight of the movable part.

[0006] Patent Document 1: Japanese Patent No. 6627313

[0007] The imaging optical system described in Patent Document 1 achieves high performance while adopting inner focusing, but the focusing unit is not sufficiently compact and lightweight, and the total optical length relative to the focal length cannot be said to be sufficiently small. Summary of the invention

[0008] The present invention has been made in view of such a situation, and an object of the present invention is to provide an imaging optical system which is compact and lightweight and has a compact and lightweight focusing unit, thereby being suitable for a compact and lightweight telephoto lens.

[0009] In order to achieve the above-mentioned purpose, the imaging optical system implementing the present invention is characterized in that it is composed of a first group G1 which has positive optical focal length as a whole and is arranged in sequence from the object side toward the image side, a second group G2 composed of lenses that move on the optical axis when focusing, and a third group G3 with optical focal length, and the imaging optical system satisfies the following conditional formula. (1) -34.00 < Φ_G2G3 / Φ < -6.60 (2) 1.00 < D_EXP / H_Img < 4.60 (3) 0.40 < LT / f < 1.00 in, Φ is the optical power of the imaging optical system when it is focused at infinity, Φ_G2G3 is the combined optical power of the second group G2 and the third group G3 when focusing at infinity. D_EXP is the distance from the exit pupil to the image plane on the optical axis when the imaging optical system is focused at infinity, H_Img is the maximum image height, LT is the distance on the optical axis from the surface closest to the object to the image plane when the imaging optical system is focused at infinity. f is the focal length of the imaging optical system when focused at infinity. Effects of the Invention

[0010] According to the imaging optical system embodying the present invention, it is possible to provide an imaging optical system which is compact and lightweight and has a compact and lightweight focusing unit, thereby being suitable for a compact and lightweight telephoto lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a diagram of the lens structure at infinity according to Example 1 of the present invention. Figure 2 This is a diagram of longitudinal aberration at infinity according to Example 1 of the present invention. Figure 3 This is a diagram of longitudinal aberration at a photographing distance of 3.2 m according to Example 1 of the present invention. Figure 4 This is a diagram of lateral aberration at infinity according to Example 1 of the present invention. Figure 5 This is a diagram of lateral aberration at a photographing distance of 3.2 m according to Example 1 of the present invention. Figure 6 This is a diagram of lateral aberration at 0.3° anti-vibration at infinity according to Example 1 of the present invention. Figure 7 This is a diagram of the lens structure at infinity according to Example 2 of the present invention. Figure 8 This is a diagram of longitudinal aberration at infinity according to Example 2 of the present invention. Fig. 9 This is a diagram of longitudinal aberration at a photographing distance of 3.3 m according to Example 2 of the present invention. Fig.10 This is a lateral aberration diagram at infinity according to Example 2 of the present invention. Fig.11 This is a diagram of lateral aberration at a photographing distance of 3.3 m according to Example 2 of the present invention. Fig.12 This is a lateral aberration diagram of Example 2 of the present invention when the image is anti-vibrated by 0.3° at infinity. Fig.13 This is a diagram of the lens structure at infinity according to Example 3 of the present invention. Fig.14 This is a diagram of longitudinal aberration at infinity according to Example 3 of the present invention. Fig.15 This is a diagram of longitudinal aberration at a photographing distance of 3.1 m in Example 3 of the present invention. Fig.16 This is a diagram of lateral aberration at infinity according to Example 3 of the present invention. Fig.17 This is a diagram of lateral aberration at a photographing distance of 3.1 m according to Example 3 of the present invention. Fig.18 This is a lateral aberration diagram of Example 3 of the present invention when the image is anti-vibrated by 0.3° at infinity. Fig.19 This is a diagram of the lens structure at infinity according to Example 4 of the present invention. Fig. 20 This is a diagram of longitudinal aberration at infinity according to Example 4 of the present invention. Fig.21 This is a diagram of longitudinal aberration at a photographing distance of 3.2 m according to Example 4 of the present invention. Fig. 22 This is a diagram of lateral aberration at infinity according to Example 4 of the present invention. Fig.23 This is a diagram of lateral aberration at a photographing distance of 3.2 m according to Example 4 of the present invention. Fig.24 This is a lateral aberration diagram of Example 4 of the present invention when the image is anti-vibrated by 0.3° at infinity. Fig.25 This is a diagram of the lens structure at infinity according to Example 5 of the present invention. Fig.26 This is a diagram of longitudinal aberration at infinity according to Example 5 of the present invention. Fig. 27 This is a diagram of longitudinal aberration at a photographing distance of 3.3 m according to Example 5 of the present invention. Fig.28 This is a lateral aberration diagram at infinity according to Example 5 of the present invention. Fig.29 This is a diagram of lateral aberration at a photographing distance of 3.3 m according to Example 5 of the present invention. Fig.30 This is a lateral aberration diagram of Example 5 of the present invention when anti-vibration is performed at 0.3° at infinity. DETAILED DESCRIPTION

[0012] The imaging optical system of the present invention is described. Figure 1 , Figure 7 , Fig.13 , Fig.19 , Fig.25 As can be seen from the lens structure diagram shown, the imaging optical system of the present invention is characterized in that it is composed of a first group G1 which has positive optical focal length as a whole and is arranged in sequence from the object side toward the image side, a second group G2 composed of lenses that move on the optical axis during focusing, and a third group G3 with optical focal length.

[0013] By adopting such a group structure, the first group G1 having positive refractive power as a whole can reduce the diameter of the second group G2 and the third group G3 as the focusing unit due to the convergence effect of the light beam. By reducing the diameter of the focusing unit as the movable part, it is easy to reduce the weight, so the actuator can also be made small and light. Since the actuator can be made small and light while reducing the diameter of the second group G2 and the third group G3, it is possible to achieve a small and light telephoto lens.

[0014] Furthermore, by arranging the first group G1 having positive power on the object side and the second group G2 and the third group G3 having negative power on the image side, a telephoto power arrangement can be formed, thereby having the effect of shortening the total length of the imaging optical system. Furthermore, since it is easy to provide a dust and drip proof mechanism, it is expected that the first group G1 arranged at the position closest to the object side and the lens arranged at the position closest to the image side of the imaging optical system are always fixed relative to the image plane. Furthermore, it can be considered that when the user attaches and detaches the interchangeable lens to the camera, the lens arranged at the position closest to the image side of the imaging optical system may come into contact with it, so it is expected that a unit that is always fixed relative to the image plane is arranged at the position closest to the image side of the imaging optical system.

[0015] Furthermore, the imaging optical system of the present invention is characterized by satisfying the following conditional expression. (1) -34.00 < Φ_G2G3 / Φ < -6.60 (2) 1.00 < D_EXP / H_Img < 4.60 (3) 0.40 < LT / f < 1.00 in, Φ is the optical power of the imaging optical system when it is focused at infinity, Φ_G2G3 is the combined optical power of the second group G2 and the third group G3 when focusing at infinity. D_EXP is the distance from the exit pupil to the image plane on the optical axis when the imaging optical system is focused at infinity, H_Img is the maximum image height, LT is the distance on the optical axis from the surface closest to the object to the image plane when the imaging optical system is focused at infinity. f is the focal length of the imaging optical system when focused at infinity.

[0016] Conditional expression (1) defines the ratio of the combined power of the second optical group G2 and the third optical group G3 to the power of the entire system when the imaging optical system is focused at infinity.

[0017] If the upper limit of conditional expression (1) is exceeded and the negative combined power of the second group G2 and the third group G3 becomes small, the telephoto effect becomes weak, and it is difficult to achieve miniaturization of the imaging optical system. If the lower limit of conditional expression (1) is exceeded and the negative combined power of the second group G2 and the third group G3 becomes large, the aberration magnification effect becomes large, and it is difficult to obtain good performance.

[0018] By limiting the upper limit value of the conditional expression (1) to -8.30, the above-mentioned effect can be made more reliable, which is preferable. By limiting the lower limit value of the conditional expression (1) to -24.00, the above-mentioned effect can be made more reliable, which is preferable.

[0019] Furthermore, it is expected that the above effect can be made more reliable by limiting the upper limit value of the conditional expression (1) to -9.50, which is preferred. It is also expected that the above effect can be made more reliable by limiting the lower limit value of the conditional expression (1) to -18.00, which is preferred.

[0020] Conditional expression (2) specifies the ratio of the distance from the exit pupil to the image plane to the maximum image height when the imaging optical system is focused at infinity.

[0021] If the upper limit of conditional expression (2) is exceeded and the exit pupil is away from the image plane to the object side, the height of the light near the image plane becomes higher. However, there is a part near the image plane for mounting on the camera, so the light becomes darker and it is difficult to ensure the amount of peripheral light. If the lower limit of conditional expression (2) is exceeded and the exit pupil is close to the image plane, the main light emission angle of the lens arranged at the position closest to the image side becomes larger. In the case of using an imaging element used in a digital camera, the imaging element generally has the characteristic of reduced sensitivity to light with a large incident angle to the imaging element. Therefore, if the incident angle of the light is large, it is difficult to ensure the amount of peripheral light.

[0022] By limiting the upper limit value of the conditional expression (2) to 4.30, the above-mentioned effect can be made more reliable, which is preferable. By limiting the lower limit value of the conditional expression (2) to 2.00, the above-mentioned effect can be made more reliable, which is preferable.

[0023] Furthermore, it is expected that the above effect can be made more reliable by limiting the upper limit value of conditional expression (2) to 4.10, which is preferred. It is also expected that the above effect can be made more reliable by limiting the lower limit value of conditional expression (2) to 2.70, which is preferred.

[0024] Conditional expression (3) specifies the ratio of the total optical length to the focal length when the imaging optical system is focused at infinity.

[0025] If the upper limit of conditional expression (3) is exceeded and the total optical length becomes longer, it is difficult to achieve a compact and lightweight telephoto lens. If the lower limit of conditional expression (3) is exceeded and the total optical length becomes shorter, it is impossible to obtain a large amount of movement of the focusing unit, and the optical power of the focusing unit must be increased to achieve the practical shortest shooting distance. Therefore, the aberration generated in the focusing unit becomes larger, and it is difficult to obtain good performance in a wide shooting distance range.

[0026] By limiting the upper limit value of the conditional expression (3) to 0.64, the above-mentioned effect can be made more reliable, which is preferable. By limiting the lower limit value of the conditional expression (3) to 0.44, the above-mentioned effect can be made more reliable, which is preferable.

[0027] Furthermore, it is expected that the above effect can be made more reliable by limiting the upper limit value of the conditional expression (3) to 0.56, which is preferred. It is also expected that the above effect can be made more reliable by limiting the lower limit value of the conditional expression (3) to 0.48, which is preferred.

[0028] In addition, the imaging optical system of the present invention is characterized in that, when the lens component is set as a single lens or a cemented lens, the lens component Ln arranged at the position closest to the image side in the imaging optical system has negative refractive power, and the imaging optical system satisfies the following conditional expression. (4) -20.00 < Φ_Ln / Φ < -0.01 in, Φ_Ln is the refractive power of the lens component Ln arranged at the position closest to the image side in the image forming optical system.

[0029] Since the lens component Ln arranged at the position closest to the image side in the imaging optical system has negative refractive power, it is possible to simultaneously achieve setting of the exit pupil position and correction of aberrations.

[0030] Conditional expression (4) defines the ratio of the refractive power of the lens component Ln to the refractive power of the entire system when the imaging optical system is focused at infinity.

[0031] If the upper limit of conditional expression (4) is exceeded and the power of lens component Ln becomes smaller, the negative power for controlling the exit pupil is borne by the lens for focusing or image jitter correction, thereby increasing the aberration during focusing or image jitter correction, making it difficult to obtain good performance. If the lower limit of conditional expression (4) is exceeded and the power of lens component Ln becomes larger, the generation of positive distortion aberration becomes larger, making it difficult to obtain good correction.

[0032] By limiting the upper limit value of the conditional expression (4) to -3.00, the above-mentioned effect can be made more reliable, which is preferable. By limiting the lower limit value of the conditional expression (4) to -15.00, the above-mentioned effect can be made more reliable, which is preferable.

[0033] Furthermore, it is expected that the above effect can be made more reliable by limiting the upper limit value of conditional expression (4) to -4.00, which is preferred. It is also expected that the above effect can be made more reliable by limiting the lower limit value of conditional expression (4) to -10.00, which is preferred.

[0034] Furthermore, the imaging optical system of the present invention is characterized by satisfying the following conditional expression. (5) -20.00 < Φ_G3 / Φ < -1.00 Wherein, Φ_G3 is the optical power of the third group G3.

[0035] Conditional expression (5) defines the ratio of the optical power of the third group G3 to that of the entire system.

[0036] If the upper limit of conditional expression (5) is exceeded and the negative power of the third group G3 becomes small, the negative power of the second group G2 needs to be increased in order to maintain the telephoto power configuration while maintaining the focal length of the entire system. If the negative power of the second group G2 as a focusing unit becomes too large, the non-point variation during focusing becomes large, and it is difficult to obtain good performance in a wide shooting distance range. If the lower limit of conditional expression (5) is exceeded and the negative power of the third group G3 becomes large, it is difficult to ensure a sufficient back focus. In addition, since the aberration magnification effect becomes large, it is difficult to obtain good performance.

[0037] By limiting the upper limit value of the conditional expression (5) to -1.50, the above-mentioned effect can be made more reliable, which is preferable. By limiting the lower limit value of the conditional expression (5) to -14.00, the above-mentioned effect can be made more reliable, which is preferable.

[0038] Furthermore, it is expected that the above effect can be made more reliable by limiting the upper limit value of conditional expression (5) to -4.00, which is preferred. It is also expected that the above effect can be made more reliable by limiting the lower limit value of conditional expression (5) to -11.00, which is preferred.

[0039] In addition, the imaging optical system of the present invention is characterized in that the third group G3 has an image jitter correction unit, and has a rear unit on the image side of the image jitter correction unit, the signs of the optical focal lengths of the image jitter correction unit and the rear unit are different, and the imaging optical system satisfies the following conditional formula. (6) 3.00 < |Φ_OS / Φ| < 35.00 Wherein, Φ_OS is the optical power of the image jitter correction unit.

[0040] By configuring a rear unit with a different sign from the optical power of the image shake correction unit, the optical power of the image shake correction unit can be increased while maintaining the optical power of the third group G3, and the image shake correction amount (hereinafter, the anti-vibration coefficient) relative to the movement amount of the image shake correction unit can be increased. If the anti-vibration coefficient is increased, the movement amount of the image shake correction unit can be reduced, so the size of the actuator can be reduced, which is conducive to the compactness and lightness of the telephoto lens.

[0041] Conditional expression (6) specifies the ratio between the refractive power of the image shake correction unit and the refractive power of the imaging optical system.

[0042] If the upper limit of conditional expression (6) is exceeded and the power of the image shake correction unit is reduced, the anti-vibration coefficient is reduced, so it is necessary to increase the drive amount of the image shake correction unit, making it difficult to miniaturize the actuator and, in turn, the telephoto lens. If the lower limit of conditional expression (6) is exceeded and the power of the image shake correction unit is increased, the anti-vibration coefficient can be obtained, but the aberration generated in the image shake correction unit is increased, and the variation of coma aberration or astigmatism when driven in a direction perpendicular to the optical axis is increased, so it is difficult to obtain good performance when correcting image shake.

[0043] By limiting the upper limit value of the conditional expression (6) to 26.00, the above-mentioned effect can be made more reliable, which is preferable. By limiting the lower limit value of the conditional expression (6) to 5.00, the above-mentioned effect can be made more reliable, which is preferable.

[0044] Furthermore, it is expected that the above effect can be made more reliable by limiting the upper limit value of conditional expression (6) to 22.00, which is preferred. It is also expected that the above effect can be made more reliable by limiting the lower limit value of conditional expression (6) to 7.00, which is preferred.

[0045] In addition, the imaging optical system of the present invention is characterized in that the third group G3 has an image shake correction unit, a rear unit is provided on the image side of the image shake correction unit, and the image shake correction unit has at least one positive lens and at least one negative lens.

[0046] Since the image shake correction unit has at least one positive lens and at least one negative lens, chromatic aberration can be corrected in the image shake correction unit, and good performance can be obtained during image shake correction.

[0047] Furthermore, the imaging optical system of the present invention is characterized in that the aperture stop is arranged at a position closer to the image side than the first group G1.

[0048] By placing the aperture stop closer to the image side than the first group G1, the second group G2 as the movable group and the image shake correction unit can be placed at a position where the light beam at the peripheral field angle is low, and the movable group can be made smaller. This makes it possible to achieve high-speed focusing, and also to reduce the actuators of the focusing unit and the image shake correction unit, so that the telephoto lens can be made smaller and lighter.

[0049] Furthermore, the imaging optical system of the present invention is characterized in that the aperture stop is arranged between the second group G2 and the third group G3.

[0050] By placing the aperture stop between the second group G2 and the third group G3, the second group G2 and the image jitter correction unit as the movable group can be placed at a position where the light beam at the peripheral field angle is low, and the movable group can be made smaller in diameter. This enables high-speed focusing, and also enables the reduction of the actuators of the focusing unit and the image jitter correction unit, so that the telephoto lens can be made compact and lightweight.

[0051] Furthermore, the imaging optical system of the present invention is characterized by satisfying the following conditional expression. (7) 0.040 < D_pn / LT < 0.40 in, D_pn is the distance on the optical axis from the object-side lens surface of the lens arranged closest to the object side of the imaging optical system to the object-side lens surface of the negative lens arranged closest to the object side among the lenses arranged closer to the image plane than the lens.

[0052] Conditional expression (7) specifies the ratio of the distance on the optical axis from the object side lens surface of the lens arranged at the position closest to the object side to the object side lens surface of the negative lens arranged at the position closest to the object side among the lenses arranged at the position closer to the image plane than the lens, to the distance on the optical axis from the surface closest to the object side to the image plane when focusing at infinity.

[0053] If the upper limit of conditional formula (7) is exceeded and D_Pn becomes longer, the chromatic aberration generated in the object side lens becomes larger. If correction is performed in the subsequent lens group, it is difficult to simultaneously correct the axial chromatic aberration and the lateral chromatic aberration, and it is difficult to obtain good performance. If the lower limit of conditional formula (7) is exceeded and D_Pn becomes shorter, the light height of the negative lens arranged at the position closest to the object side becomes higher, and the weight of the lens also becomes heavier. Therefore, it is difficult to simultaneously achieve miniaturization and lightweight of the entire lens system.

[0054] By limiting the upper limit value of the conditional expression (7) to 0.28, the above effect can be made more reliable, which is preferable. By limiting the lower limit value of the conditional expression (7) to 0.060, the above effect can be made more reliable, which is preferable.

[0055] Furthermore, it is expected that limiting the upper limit of conditional expression (7) to 0.16 will make the above effect more reliable, which is preferred. Limiting the lower limit of conditional expression (7) to 0.070 will make the above effect more reliable, which is preferred.

[0056] Furthermore, the imaging optical system of the present invention is characterized by satisfying the following conditional expression. (8) -12.00 <Φ_G2 / Φ < -0.13 Wherein, Φ_G2 is the optical power of the second group G2.

[0057] Conditional expression (8) defines a preferred range for the ratio of the refractive power of the second group G2 to that of the image-forming optical system.

[0058] If the upper limit of conditional expression (8) is exceeded and the negative power of the second group G2 becomes small, the negative power of the third group G3 becomes large by causing the third group G3 to bear the role of the negative power arranged on the telephoto image side. Since the aberration magnification effect in the third group G3 becomes large, it is difficult to obtain good performance. If the lower limit of conditional expression (8) is exceeded and the negative power of the second group G2 becomes large, aberrations, especially astigmatism, are easily generated in the second group G2 as a focusing unit, so it is difficult to obtain good performance in a wide shooting distance range.

[0059] By limiting the upper limit value of the conditional expression (8) to -0.20, the above effect can be made more reliable, which is preferable. By limiting the lower limit value of the conditional expression (8) to -9.00, the above effect can be made more reliable, which is preferable.

[0060] Furthermore, it is expected that limiting the lower limit value of conditional expression (8) to -6.00 will make the above-mentioned effect more reliable, which is preferred.

[0061] Furthermore, the imaging optical system of the present invention is characterized by having a negative lens satisfying the following conditional expression at a position closer to the image side than the aperture stop. (9) 10.00 < ν_d < 30.00 (10) 0.020 < P_gF+0.0018*ν_d-0.6483 < 0.080 in, ν_d is the Abbe number of the negative lens for the d-line, P_gF is the partial dispersion ratio of the negative lens for the g-line and the F-line. Define P_gF=(ng-nF) / (nF-nC) and the partial dispersion ratio. ng: refractive index for g-line (wavelength λ=435.84 nm). nF: refractive index for F line (wavelength λ=486.13 nm). nC: refractive index for C line (wavelength λ=656.27 nm).

[0062] By providing a negative lens satisfying conditional expressions (9) and (10) at a position closer to the image side than the aperture stop, good chromatic aberration correction can be achieved.

[0063] Conditional expression (9) defines a preferred range of the Abbe number of the negative lens for the d-line.

[0064] If the upper limit of conditional expression (9) is exceeded and the Abbe number for the d-line increases, the effect of eliminating chromatic aberration becomes weaker, and it is difficult to correct chromatic aberration in the entire lens system. In addition, it is difficult to select a material that satisfies conditional expression (10). If the lower limit of conditional expression (9) is exceeded and the Abbe number for the d-line decreases, the effect of magnifying chromatic aberration becomes greater, and it is difficult to correct chromatic aberration in the entire lens system.

[0065] By limiting the upper limit value of the conditional expression (9) to 24.00, the above-mentioned effect can be made more reliable, which is preferable. By limiting the lower limit value of the conditional expression (9) to 15.00, the above-mentioned effect can be made more reliable, which is preferable.

[0066] Furthermore, it is expected that the above effect can be made more reliable by limiting the upper limit value of the conditional expression (9) to 21.00, which is preferred. It is also expected that the above effect can be made more reliable by limiting the lower limit value of the conditional expression (9) to 16.00, which is preferred.

[0067] Conditional expression (10) defines a preferred range of the partial dispersion ratio of the negative lens for the g-line and the F-line.

[0068] If the upper limit value of the conditional expression (10) is exceeded and the partial dispersion ratio for the g-line and the F-line increases, the chromatic aberration of the g-line increases in the positive direction, making it difficult to correct the chromatic aberration in the entire lens system. If the lower limit value of the conditional expression (10) is exceeded and the partial dispersion ratio for the g-line and the F-line decreases, the chromatic aberration of the g-line increases in the negative direction, making it difficult to correct the chromatic aberration in the entire lens system.

[0069] By limiting the upper limit value of the conditional expression (10) to 0.048, the above-mentioned effect can be made more reliable, which is preferable. By limiting the lower limit value of the conditional expression (10) to 0.024, the above-mentioned effect can be made more reliable, which is preferable.

[0070] Furthermore, it is expected that limiting the upper limit of conditional expression (10) to 0.041 will make the above effect more reliable, which is preferred. Limiting the lower limit of conditional expression (10) to 0.027 will make the above effect more reliable, which is preferred.

[0071] In addition, the imaging optical system of the present invention is characterized in that the object side surface and the image side surface of all lenses are composed of curved surfaces or flat surfaces. Specifically, it is characterized by not using a diffractive optical element. It is assumed that the diffractive surface can have a chromatic aberration correction effect or an aspherical effect by using a diffractive optical element, but it leads to the generation of unnecessary diffracted light caused by the shape or halo caused by light outside the field of view. Since the imaging optical system of the present invention does not use a diffractive optical element, it is possible to prevent the generation of halo or ghosting caused by the diffractive optical element.

[0072] In addition, the imaging optical system of the present invention is characterized in that the object side and image side of all lenses are composed of spherical surfaces or planes. Even if a spherical lens is rotated with the center of the sphere as the rotation center during processing, it can be processed equivalently, so it is easier to manufacture than an aspherical lens. Since the lenses constituting the imaging optical system of the telephoto lens are easy to have large diameters, it is expected that lenses with good processing accuracy can be obtained at low processing costs.

[0073] In addition, the imaging optical system of the present invention is characterized in that the third group G3 has an image shake correction unit, a rear unit is provided on the image side of the image shake correction unit, the signs of the optical focal lengths of the image shake correction unit and the rear unit are different, the image shake correction unit has at least one positive lens and at least one negative lens, the aperture stop is arranged between the second group G2 and the third group G3, and the imaging optical system satisfies the following conditional formula. (6) 3.00 < |Φ_OS / Φ| < 35.00 Wherein, Φ_OS is the focal length of the image jitter correction unit.

[0074] In particular, by adopting this structure, the main light passes through the vicinity of the optical axis of the image jitter correction unit, and through the achromatic effect of the positive lens and the negative lens and the use of an appropriate optical power configuration, good chromatic aberration correction can be performed during image jitter correction.

[0075] Next, the lens configuration of the 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. [Example 1]

[0076] Figure 1: This is a lens structure diagram of the imaging optical system of Example 1 of the present invention. The first group G1 is composed of a positive lens L1 with a convex surface facing the object side, a positive lens L2 with a convex surface facing the object side, a negative lens L3 with a convex surface facing the object side, a positive lens L4 with a convex surface facing the object side, a biconcave negative lens L5, a biconvex positive lens L6, and a cemented lens composed of a negative lens L7 with a convex surface facing the object side and a meniscus lens L8 with a convex surface facing the object side, and has positive refractive power as a whole. In addition, the first group G1 is always fixed relative to the image plane.

[0077] The second group G2 is composed of a cemented lens consisting of a positive lens L9 with a convex surface facing the object side and a negative lens L10 with a convex surface facing the object side, and has a negative optical power as a whole. In addition, when focusing from an infinitely distant object to a close object, the second group G2 moves from the object side to the image side on the optical axis.

[0078] The third group G3 is composed of the image shake correction unit IU and the rear unit RU, and has negative refractive power as a whole. In addition, the third group G3 is fixed relative to the image plane during focusing.

[0079] The image jitter correction unit IU is composed of a cemented lens of a biconvex positive lens L11 and a biconcave negative lens L12 and a biconcave negative lens L13, and has negative optical power as a whole. In addition, the image jitter correction unit IU moves in a direction perpendicular to the optical axis to reduce image jitter caused by the jitter of the imaging optical system.

[0080] The rear unit RU is composed of a biconvex positive lens L14, a cemented lens composed of a biconcave negative lens L15 and a positive lens L16 with a convex surface facing the object side, a three-piece cemented lens composed of a biconvex positive lens L17, a biconcave negative lens L18 and a biconvex positive lens L19, and a negative lens L20 with a concave surface facing the object side, and has negative optical power as a whole. In addition, the rear unit RU is always fixed relative to the image plane.

[0081] The aperture stop S is arranged between the second group G2 and the third group G3. In the imaging optical system, the lens component Ln arranged at the position closest to the image side is the negative lens L20. [Example 2]

[0082] Figure 7: This is a lens structure diagram of the imaging optical system of Example 2 of the present invention. The first group G1 is composed of a biconvex positive lens L1, a meniscus positive lens L2 with a convex surface facing the object side, a meniscus negative lens L3 with a convex surface facing the object side, a meniscus positive lens L4 with a convex surface facing the object side, a biconcave negative lens L5, a biconvex positive lens L6, and a cemented lens composed of a meniscus negative lens L7 with a convex surface facing the object side and a meniscus lens L8 with a convex surface facing the object side, and has positive refractive power as a whole. In addition, the first group G1 is always fixed relative to the image plane.

[0083] The second group G2 is composed of a cemented lens consisting of a positive lens L9 with a convex surface facing the object side and a negative lens L10 with a convex surface facing the object side, and has a negative optical power as a whole. In addition, when focusing from an infinitely distant object to a close object, the second group G2 moves from the object side to the image side on the optical axis.

[0084] The third group G3 is composed of the image shake correction unit IU and the rear unit RU, and has negative refractive power as a whole. In addition, the third group G3 is fixed relative to the image plane during focusing.

[0085] The image jitter correction unit IU is composed of a cemented lens of a biconvex positive lens L11 and a biconcave negative lens L12 and a biconcave negative lens L13, and has negative optical power as a whole. In addition, the image jitter correction unit IU moves in a direction perpendicular to the optical axis to reduce image jitter caused by the jitter of the imaging optical system.

[0086] The rear unit RU is composed of a biconvex positive lens L14, a cemented lens composed of a biconcave negative lens L15 and a positive lens L16 with a convex surface facing the object side, a three-piece cemented lens composed of a biconvex positive lens L17, a biconcave negative lens L18 and a biconvex positive lens L19, and a negative lens L20 with a concave surface facing the object side, and has negative optical power as a whole. In addition, the rear unit RU is always fixed relative to the image plane.

[0087] The aperture stop S is arranged between the second group G2 and the third group G3. In the imaging optical system, the lens component Ln arranged at the position closest to the image side is the negative lens L20. [Example 3]

[0088] Fig.13: This is a lens structure diagram of the imaging optical system of Example 3 of the present invention. The first group G1 is composed of a positive lens L1 with a convex surface facing the object side, a positive lens L2 with a convex surface facing the object side, a negative lens L3 with a convex surface facing the object side, a positive lens L4 with a convex surface facing the object side, a biconcave negative lens L5, a biconvex positive lens L6, and a cemented lens composed of a negative lens L7 with a convex surface facing the object side and a meniscus lens L8 with a convex surface facing the object side, and has positive refractive power as a whole. In addition, the first group G1 is always fixed relative to the image plane.

[0089] The second group G2 is composed of a cemented lens consisting of a positive lens L9 with a convex surface facing the object side and a negative lens L10 with a convex surface facing the object side, and has a negative optical power as a whole. In addition, when focusing from an infinitely distant object to a close object, the second group G2 moves from the object side to the image side on the optical axis.

[0090] The third group G3 is composed of the image shake correction unit IU and the rear unit RU, and has negative refractive power as a whole. In addition, the third group G3 is fixed relative to the image plane during focusing.

[0091] The image jitter correction unit IU is composed of a cemented lens of a biconvex positive lens L11 and a biconcave negative lens L12, and a meniscus-shaped negative lens L13 with the convex surface facing the object side, and has negative optical power as a whole. In addition, the image jitter correction unit IU moves in a direction perpendicular to the optical axis to reduce image jitter caused by the jitter of the imaging optical system.

[0092] The rear unit RU is composed of a biconvex positive lens L14, a cemented lens composed of a biconcave negative lens L15 and a positive lens L16 with a convex surface facing the object side, a three-piece cemented lens composed of a biconvex positive lens L17, a biconcave negative lens L18 and a biconvex positive lens L19, and a negative lens L20 with a concave surface facing the object side, and has negative optical power as a whole. In addition, the rear unit RU is always fixed relative to the image plane.

[0093] The aperture stop S is arranged between the second group G2 and the third group G3. In the imaging optical system, the lens component Ln arranged at the position closest to the image side is the negative lens L20. [Example 4]

[0094] Fig.19: This is a lens structure diagram of the imaging optical system of Example 4 of the present invention. The first group G1 is composed of a positive lens L1 with a convex surface facing the object side, a positive lens L2 with a convex surface facing the object side, a negative lens L3 with a convex surface facing the object side, a cemented lens composed of a biconvex positive lens L4 and a biconcave negative lens L5, a positive lens L6 with a convex surface facing the object side, and a cemented lens composed of a negative lens L7 with a convex surface facing the object side and a biconvex positive lens L8, and has positive refractive power as a whole. In addition, the first group G1 is always fixed relative to the image plane.

[0095] The second group G2 is composed of a meniscus-shaped negative lens L9 with a convex surface facing the object side, and has negative refractive power as a whole. When focusing from an infinitely distant object to a close object, the second group G2 moves from the object side to the image side on the optical axis.

[0096] The third group G3 is composed of the image shake correction unit IU and the rear unit RU, and has negative refractive power as a whole. In addition, the third group G3 is fixed relative to the image plane during focusing.

[0097] The image jitter correction unit IU is composed of a cemented lens of a biconvex positive lens L10 and a biconcave negative lens L11 and a biconcave negative lens L12, and has negative optical power as a whole. In addition, the image jitter correction unit IU moves in a direction perpendicular to the optical axis to reduce image jitter caused by the jitter of the imaging optical system.

[0098] The rear unit RU is composed of a biconvex positive lens L13, a cemented lens composed of a biconcave negative lens L14 and a biconvex positive lens L15 facing the object, a three-piece cemented lens composed of a biconvex positive lens L16, a biconcave negative lens L17 and a meniscus positive lens L18 with the convex surface facing the object, and a meniscus negative lens L19 with the concave surface facing the object, and has negative optical power as a whole. The rear unit RU is always fixed relative to the image plane.

[0099] The aperture stop S is arranged between the second group G2 and the third group G3. In the imaging optical system, the lens component Ln arranged at the position closest to the image side is the negative lens L19. [Example 5]

[0100] Fig.25: This is a lens structure diagram of the imaging optical system of Example 5 of the present invention. The first group G1 is composed of a positive lens L1 with a convex surface facing the object side, a positive lens L2 with a convex surface facing the object side, a negative lens L3 with a convex surface facing the object side, a cemented lens composed of a biconvex positive lens L4 and a biconcave negative lens L5, a positive lens L6 with a convex surface facing the object side, and a cemented lens composed of a negative lens L7 with a convex surface facing the object side and a positive lens L8 with a convex surface facing the object side, and has positive refractive power as a whole. In addition, the first group G1 is always fixed relative to the image plane.

[0101] The second group G2 is composed of a negative meniscus lens L9 with a convex surface facing the object side and a positive meniscus lens L10 with a convex surface facing the object side, and has negative refractive power as a whole. In addition, L9 in the second group G2 moves from the object side to the image side on the optical axis when focusing from an infinitely distant object to a close object, and L10 moves from the image side to the object side on the optical axis when focusing from an infinitely distant object to a close object.

[0102] The third group G3 is composed of lens components, an image stabilization unit IU, and a rear unit RU, and has negative refractive power as a whole. In addition, the third group G3 is fixed relative to the image plane during focusing.

[0103] The lens component is composed of a positive meniscus lens L11 having a concave surface facing the object side.

[0104] The image jitter correction unit IU is composed of a biconvex positive lens L12 and a biconcave negative lens L13, and a biconcave negative lens L14, and has negative optical power as a whole. In addition, the image jitter correction unit IU moves in a direction perpendicular to the optical axis to reduce image jitter caused by the jitter of the imaging optical system.

[0105] The rear unit RU is composed of a biconvex positive lens L15, a cemented lens composed of a biconcave negative lens L16 and a biconvex positive lens L17 facing the object, a three-piece cemented lens composed of a biconvex positive lens L18, a biconcave negative lens L19 and a biconvex positive lens L20, and a meniscus negative lens L21 with the concave surface facing the object, and has negative optical power as a whole. In addition, the rear unit RU is always fixed relative to the image plane.

[0106] The aperture stop S is arranged between the second group G2 and the third group G3. The lens component Ln arranged at the most image side in the image forming optical system is a negative lens L21.

[0107] Specific numerical data of each embodiment of the imaging optical system of the present invention described above are shown below.

[0108] In [Surface Data], the surface number is the number of the lens surface or aperture stop counted from the object side, r represents the radius of curvature of each surface, d represents the interval between each surface, nd represents the refractive index for the d-line (wavelength 587.56nm), vd represents the Abbe number for the d-line, and P_gF represents the partial dispersion ratio for the g-line and F-line.

[0109] BF stands for back focal length.

[0110] The "(Stop)" attached to the surface number indicates that the aperture stop is located at that position. ∞ (infinity) is written as the radius of curvature relative to the plane or the aperture stop.

[0111] [Various Data] shows values ​​such as focal length when the shooting distance is INF, 20m, and 3.2m.

[0112] [Variable Interval Data] shows the variable interval and BF value when the shooting distance is INF, 20m, and 3.2m.

[0113] [Lens Group Data] shows the number of the surface closest to the object side constituting each lens group and the composite focal length of the entire group.

[0114] In addition, in all the following specification values, unless otherwise specified, the focal length f, curvature radius r, lens surface interval d, and other lengths are recorded in millimeters (mm). However, in an optical system, even if the scale is enlarged or reduced, the same optical performance can be obtained, so it is not limited to this.

[0115] Furthermore, a list of corresponding values ​​of the conditional expressions in these respective embodiments is shown.

[0116] Furthermore, in the aberration diagrams corresponding to the respective embodiments, d, g, and C represent the d-line, g-line, and C-line, respectively, and ΔS and ΔM represent the sagittal image plane and the meridional image plane, respectively.

[0117] Numerical Example 1 Unit: mm [Surface data] [Various data] [Variable interval data] [Lens group data]

[0118] Numerical Example 2 Unit: mm [surface data] [Various data] [Variable interval data] [Lens group data]

[0119] Numerical Example 3 Unit: mm [surface data] [Various data] [Variable interval data] [Lens group data]

[0120] Numerical Example 4 Unit: mm [surface data] [Various data] [Variable interval data] [Lens group data]

[0121] Numerical Example 5 Unit: mm [surface data] [Various data] [Variable interval data] [Lens group data]

[0122] Conditional corresponding value Explanation of symbols

[0123] G1-1st group, G2-2nd group, G3-3rd group, IU-image shake correction unit, RU-rear unit, Ln-lens component arranged at the position closest to the image side, S-aperture stop, I-image plane.

Claims

1. An imaging optical system, characterized in that: The lens system is composed of a first group (G1) having positive refractive power as a whole, a second group (G2) consisting of lenses that move on the optical axis when focusing, and a third group (G3) having refractive power, which are arranged in order from the object side to the image side. The imaging optical system satisfies the following conditional formula: (1) -34.00 < Φ_G2G3 / Φ < -6.60 (2) 1.00 < D_EXP / H_Img < 4.60 (3) 0.40 < LT / f < 1.00 in, Φ is the optical power of the imaging optical system when it is focused at infinity, Φ_G2G3 is the combined power of the second group (G2) and the third group (G3) when focusing at infinity. D_EXP is the distance from the exit pupil to the image plane on the optical axis when the imaging optical system is focused at infinity, H_Img is the maximum image height, LT is the distance on the optical axis from the surface closest to the object to the image plane when the imaging optical system is focused at infinity. f is the focal length of the imaging optical system when focused at infinity.

2. The imaging optical system according to claim 1, characterized in that: When the lens component is a single lens or a cemented lens, the lens component (Ln) arranged at the position closest to the image side has negative refractive power, and the imaging optical system satisfies the following conditional expression, (4) -20.00 < Φ_Ln / Φ < -0.01 in, Φ_Ln is the refractive power of the lens component (Ln) arranged at the position closest to the image side in the image forming optical system.

3. The imaging optical system according to claim 1, characterized in that: Satisfy the following conditions: (5) -20.00 < Φ_G3 / Φ < -1.00 Among them, Φ_G3 is the optical focal length of the third group (G3).

4. The imaging optical system according to claim 1, characterized in that: The third group (G3) has an image shake correction unit, and a rear unit is provided on the image side of the image shake correction unit. The signs of the optical powers of the image shake correction unit and the rear unit are different. The imaging optical system satisfies the following conditional expression: (6) 3.00 < |Φ_OS / Φ| < 35.00 Wherein, Φ_OS is the optical power of the image jitter correction unit.

5. The imaging optical system according to claim 1, characterized in that: The third group (G3) includes an image shake correction unit and a rear unit on the image side of the image shake correction unit. The image shake correction unit includes at least one positive lens and at least one negative lens.

6. The imaging optical system according to claim 1, characterized in that: The imaging optical system includes an aperture stop, and the aperture stop is arranged at a position closer to the image side than the first group (G1).

7. The imaging optical system according to claim 1, characterized in that: The imaging optical system includes an aperture stop, and the aperture stop is arranged between the second group (G2) and the third group (G3).

8. The imaging optical system according to claim 1, characterized in that: Satisfy the following conditions: (7) 0.040 < D_pn / LT < 0.40 in, D_pn is the distance on the optical axis from the object-side lens surface of the lens arranged closest to the object side of the imaging optical system to the object-side lens surface of the negative lens arranged closest to the object side among the lenses arranged closer to the image plane than the lens.

9. The imaging optical system according to claim 1, characterized in that: Satisfy the following conditions: (8) -12.00 <Φ_G2 / Φ < -0.13 Among them, Φ_G2 is the optical focal length of the second group (G2).

10. The imaging optical system according to claim 1, characterized in that: The imaging optical system has an aperture stop, and has a negative lens satisfying the following conditional expression at a position closer to the image side than the aperture stop. (9) 10.00 < ν_d < 30.00 (10) 0.020 < P_gF+0.0018*ν_d-0.6483 < 0.080 in, ν_d is the Abbe number of the negative lens arranged closer to the image side than the aperture stop for the d-line, P_gF is the partial dispersion ratio of the negative lens arranged closer to the image side than the aperture stop for the g-line and the F-line, P_gF=(ng-nF) / (nF-nC), ng is the refractive index for the g-line, the wavelength of the g-line is λ = 435.84nm, nF is the refractive index for F-line, the wavelength of F-line is λ=486.13nm, nC is the refractive index for the C line, and the wavelength of the C line is λ=656.27 nm.

11. The imaging optical system according to claim 1, characterized in that: The object and image sides of all lenses consist of either curved or flat surfaces.

12. The imaging optical system according to claim 1, characterized in that: The object and image sides of all lenses consist of either spherical or flat surfaces.

13. The imaging optical system according to claim 1, characterized in that: The third group (G3) has an image shake correction unit, and a rear unit is provided on the image side of the image shake correction unit, the signs of the optical power of the image shake correction unit and the rear unit are different, the image shake correction unit has at least one positive lens and at least one negative lens, and an aperture stop is arranged between the second group (G2) and the third group (G3), and the imaging optical system satisfies the following conditional expression, (6) 3.00 < |Φ_OS / Φ| < 35.00 Wherein, Φ_OS is the focal length of the image jitter correction unit.

Images