Large aperture ratio optical system

Abstract

To provide a large-aperture optical system which offers reduced weight of a focusing lens while employing an inner focus system.SOLUTION: An optical system is provided, comprising, in order from the object side, a first lens group G1 having positive refractive power, an aperture stop, a second lens group G2 having negative refractive power, and an image-side lens group GR having positive refractive power, and being configured such that only the second lens group G2 moves along an optical axis when focusing. The first lens group G1 consists of a 1A lens group G1A with negative refractive power located on the object side and a 1B lens group G1B with positive refractive power located on the image side, where the 1A lens group G1A consists of, in order from the object side, a negative meniscus lens having a convex surface on the object side, a negative meniscus lens, and a positive meniscus lens L1p having a convex surface on the object side. The optical system satisfies predetermined conditional expressions.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system suitable for a lens used in an imaging device or a projection device used in a digital camera, a video camera, etc. While effectively correcting chromatic aberration, an appropriate power arrangement of the focus lens group is performed to contribute to weight reduction.

Background Art

[0002] In recent years, with the spread of imaging devices such as digital still cameras and video cameras, the number of pixels of imaging elements has been rapidly increasing, and a higher-quality imaging optical system is required.

[0003] Also, high-speed and accurate focus driving is required. When the weight of the focus lens group increases, the speed of focus driving decreases or the noise during focus driving increases, which is not preferable. In addition, there is a problem that the actuator for moving the lens becomes large-sized and the lens barrel becomes large-sized.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, a large-aperture wide-angle lens having a first lens group having a positive refractive power, an aperture stop, and a second lens group having a positive refractive power is disclosed. However, in the embodiment described in Patent Document 1, the focus lens group is composed of 4 to 5 lenses, and there is a problem that the weight of the focus lens group becomes large.

[0006] Patent Document 2 proposes a system consisting of a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power, and suggests that high-speed focusing is possible by moving the second lens group, which consists of one negative lens, during focusing. However, the optical system described in Patent Document 2 only has examples with an open aperture of F-number of about 1.8 to 2.2, making it difficult to realize a high-performance large-aperture ratio lens with an open aperture of about F-number of 1.4.

[0007] This invention has been made in view of these circumstances, and aims to provide a large-aperture ratio optical system that employs an inner focusing method while reducing the weight of the focusing lens. [Means for solving the problem]

[0008] To solve the above problems, the optical system of the first invention comprises, in order from the object side, a first lens group G1 having positive refractive power, an aperture, a second lens group G2 having negative refractive power, and an image-side lens group GR having positive refractive power, wherein only the second lens group G2 moves in the direction of the optical axis during focusing, the first lens group G1 consists of a first A lens group G1A having negative refractive power located on the object side and a first B lens group G1B having positive refractive power located on the image side, the first A lens group G1A consists of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, a negative meniscus lens, and a positive meniscus lens L1p with a convex surface facing the object side, and is characterized in that it satisfies the following conditional equation. (1) 1.5 <f2R / f<10.0 f: Focal length of the entire lens system when focused at infinity f2R: Combined focal length of the second lens group G2 and the image-side lens group GR when focused at infinity.

[0009] Furthermore, the optical system of the second invention is characterized in that the positive meniscus lens L1p of the first A lens group G1A satisfies the following condition. (2)νd1p<25.00 (3) ΔPgF1p > 0.0150 νd1p: Abbe number of the positive meniscus lens L1p ΔPgF1p: Abnormal dispersibility of the positive meniscus lens L1p Here, when the partial dispersion ratio of the positive meniscus lens L1p with respect to the g-line and F-line is PgF1p, ΔPgF1p is calculated by the following formula. ΔPgF1p = PgF1p + 0.0018 × νd1p - 0.64833

[0010] Further, in the optical system of the third invention, the second lens group G2 consists of only one lens having a negative refractive power, and is characterized by satisfying the following conditional formula. (4) 0.30 < |f / f2| < 0.75 f2: Focal length of the second lens group G2

[0011] Further, the optical system of the fourth invention is characterized by satisfying the following conditional formula. (5) 0.1 < D12 / f < 0.35 D12: Lens group interval on the optical axis between the first lens group G1 and the second lens group G2 when focused at infinity

[0012] Further, the optical system of the fifth invention is characterized in that the air lens formed by the space sandwiched between the first A lens group G1A and the first B lens group G1B has a biconvex shape.

Advantages of the Invention

[0013] According to the present invention, it is possible to provide a large-aperture ratio optical system that adopts an inner focus method while reducing the weight of the focus lens.

Brief Description of the Drawings

[0014] [Figure 1] It is a lens configuration diagram of the imaging optical system of Example 1 according to the present invention. [Figure 2] It is a longitudinal aberration diagram of the imaging optical system of Example 1 at an infinite shooting distance. [Figure 3] It is a longitudinal aberration diagram of the imaging optical system of Example 1 at a shooting distance of 0.25 m. [Figure 4]It is a lateral aberration diagram of the imaging optical system of Example 1 at an infinite shooting distance. [Figure 5] It is a lateral aberration diagram of the imaging optical system of Example 1 at a shooting distance of 0.25 m. [Figure 6] It is a lens configuration diagram of the imaging optical system of Example 2 according to the present invention. [Figure 7] It is a longitudinal aberration diagram of the imaging optical system of Example 2 at an infinite shooting distance. [Figure 8] It is a longitudinal aberration diagram of the imaging optical system of Example 2 at a shooting distance of 0.25 m. [Figure 9] It is a lateral aberration diagram of the imaging optical system of Example 2 at an infinite shooting distance. [Figure 10] It is a lateral aberration diagram of the imaging optical system of Example 2 at a shooting distance of 0.25 m. [Figure 11] It is a lens configuration diagram of the imaging optical system of Example 3 according to the present invention. [Figure 12] It is a longitudinal aberration diagram of the imaging optical system of Example 3 at an infinite shooting distance. [Figure 13] It is a longitudinal aberration diagram of the imaging optical system of Example 3 at a shooting distance of 0.25 m. [Figure 14] It is a lateral aberration diagram of the imaging optical system of Example 3 at an infinite shooting distance. [Figure 15] It is a lateral aberration diagram of the imaging optical system of Example 3 at a shooting distance of 0.25 m. [Figure 16] It is a lens configuration diagram of the imaging optical system of Example 4 according to the present invention. [Figure 17] It is a longitudinal aberration diagram of the imaging optical system of Example 4 at an infinite shooting distance. [Figure 18] It is a longitudinal aberration diagram of the imaging optical system of Example 4 at a shooting distance of 0.25 m. [Figure 19] It is a lateral aberration diagram of the imaging optical system of Example 4 at an infinite shooting distance. [Figure 20] It is a lateral aberration diagram of the imaging optical system of Example 4 at a shooting distance of 0.25 m.

Mode for Carrying Out the Invention

[0015] The following describes in detail an embodiment of the imaging optical system according to the present invention. Note that the following description of the embodiment illustrates an example of the optical system of the present invention, and the present invention is not limited to this embodiment without departing from its spirit.

[0016] An embodiment of the imaging optical system according to the present invention comprises, in order from the object side, a first lens group G1 having positive refractive power, an aperture, a second lens group G2 having negative refractive power, and an image-side lens group GR having positive refractive power, wherein only the second lens group G2 moves in the direction of the optical axis during focusing, the first lens group G1 consists of a first A lens group G1A having negative refractive power located on the object side and a first B lens group G1B having positive refractive power located on the image side, the first A lens group G1A consists of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, a negative meniscus lens, and a positive meniscus lens L1p with a convex surface facing the object side, and is characterized by satisfying the following conditional equation. (1) 1.5 <f2R / f<10.0 f: Focal length of the entire lens system when focused at infinity f2R: Combined focal length of the second lens group G2 and the image-side lens group GR when focused at infinity.

[0017] By making the refractive power of the first lens group G1 positive, the height of the on-axial rays incident on the subsequent second lens group G2 can be reduced, thereby making the second lens group G2, which is the focusing lens group, lighter.

[0018] The first lens group G1A reduces the angle of incidence with negative refractive power, causing off-axis rays to enter the first lens group G1B, thereby effectively correcting various aberrations such as astigmatism and distortion. Furthermore, by arranging the first lens group G1A, which has negative refractive power, and the first lens group G1B, which has positive refractive power, spherical aberration and coma aberration generated in each lens group of the first lens group G1 can be canceled out and controlled.

[0019] Because lens group G1A has a negative refractive power, the positive refractive power of lens group G1B must be increased in order to maintain the overall positive refractive power of lens group G1. However, increasing the positive refractive power of lens group G1B makes it difficult to correct aberrations related to aperture.

[0020] Therefore, in order to prevent the refractive power of the first lens group G1B from becoming too large, it is possible to make the refractive power of the first lens group G1 and the first lens group G1B nearly equal by controlling the distance between the principal points of the first lens group G1A and the first lens group G1B. To achieve this, it is necessary to bring the distance between the principal points of the first lens group G1A and the first lens group G1B closer to the focal length of the first lens group G1B, which affects the overall length of the lens.

[0021] To avoid increasing the overall length of the lens, the first lens group G1A is configured with negative and positive polarity in order from the object side, thereby allowing the second principal point of the first lens group G1A to be displaced toward the object side. This makes it possible to maintain a principal point distance equivalent to the focal length of the first lens group G1B even when the air gap between the first lens group G1A and the first lens group G1B is reduced, thereby suppressing the effect of increasing the overall length of the first lens group G1.

[0022] Furthermore, to obtain a wide field of view, it is preferable to place a negative meniscus lens with its convex surface facing the object side in the first lens group G1, which is closest to the object. This reduces the angle between the lens surface and off-axis rays, thereby minimizing astigmatism and field curvature. On the other hand, while placing a lens with positive refractive power closest to the object is good for correcting distortion, obtaining a wide field of view requires increasing the diameter of the lens with positive refractive power, which increases the maximum diameter of the entire lens system, making it undesirable.

[0023] Furthermore, in the first lens group G1, by arranging a negative meniscus lens adjacent to the image side of the negative meniscus lens, the negative refractive force can be shared, the angle between the lens surface and the off-axis rays can be gradually reduced, and the diameter of the first lens group G1 can be reduced while suppressing the occurrence of various aberrations.

[0024] Furthermore, in the first lens group G1, by placing a positive meniscus lens with its convex surface facing the object side after the two negative meniscus lenses, the angle between the lens surface and off-axis rays can be reduced on both sides of the positive meniscus lens, thereby suppressing the occurrence of off-axis aberration. In addition, by placing a positive meniscus lens with its convex surface facing the object side on the image side, negative spherical aberration is generated in response to the positive spherical aberration generated by the two negative meniscus lenses, thereby suppressing spherical aberration.

[0025] Conditional equation (1) specifies the ratio of the combined focal length of the lens system (hereinafter referred to as the "composite lens system"), which is a combination of the second lens group G2, which is the focusing lens group, and the image-side lens group GR, to the focal length of the entire lens system.

[0026] When the lower limit of condition (1) is exceeded, the combined focal length of the second lens group G2 and the image-side lens group GR becomes shorter, and the refractive power of the combined lens system becomes larger. This is undesirable because the refractive power of each lens group constituting the combined lens system becomes larger, making aberration correction difficult. If the negative refractive power of the second lens group G2 becomes large, the aberration fluctuation when the second lens group G2 moves during focusing becomes larger, making it difficult to suppress aberration fluctuations across the entire focus range. On the other hand, if the positive refractive power of the image-side lens group GR becomes large, the amount of spherical aberration and coma aberration increases, degrading the imaging performance.

[0027] When the upper limit of condition (1) is exceeded, the combined focal length of the second lens group G2 and the image-side lens group GR increases, and the refractive power of the combined lens system decreases. This makes it difficult to shorten the overall length of the optical system because the refractive power of each lens group constituting the combined lens system decreases. When the refractive power of the second lens group G2 decreases, the amount of movement of the second lens group G2 during focusing increases, which is undesirable because it increases the overall optical length. Also, when the refractive power of the image-side lens group GR decreases, the back focus increases, which is undesirable because it increases the overall optical length.

[0028] Furthermore, the aforementioned effect can be made more certain by setting the upper limit of condition (1) to 8.50 and the lower limit to 2.5.

[0029] Furthermore, an embodiment of the imaging optical system according to the present invention is characterized in that the positive meniscus lens L1p of the 1A lens group G1A satisfies the following condition. (2)νd1p<25.00 (3) ΔPgF1p > 0.0150 νd1p: Abbe number of the positive meniscus lens L1p ΔPgF1p: Anomalous dispersion of the positive meniscus lens L1p Here, ΔPgF1p is calculated by the following formula, where PgF1p is the partial dispersion ratio of the g-line and F-line of the positive meniscus lens L1p. ΔPgF1p=PgF1p+0.0018×νd1p−0.64833

[0030] Conditional equations (2) and (3) define the Abbe number and anomalous dispersion of the positive meniscus lens L1p of the first A lens group G1A in order to effectively correct chromatic aberration.

[0031] When the upper limit of condition (2) and the lower limit of condition (3) are exceeded, the Abbe number of the positive meniscus lens L1p increases while the anomalous dispersion decreases, resulting in insufficient correction of chromatic aberration.

[0032] Furthermore, the aforementioned effect can be made more certain by setting the upper limit of condition (2) to 21.00 and the lower limit of condition (3) to 0.0250.

[0033] Furthermore, an embodiment of the imaging optical system according to the present invention is characterized in that the second lens group G2 consists of only one lens having negative refractive power and satisfies the following condition. (4) 0.30 < |f / f2| < 0.75 f2: Focal length of the second lens group G2.

[0034] Conditional equation (4) defines the ratio of the focal length of the second lens group G2, which is the focusing lens group, to the focal length of the entire lens system when in focus at infinity.

[0035] When the lower limit of condition (4) is exceeded and the negative refractive power of the second lens group G2 decreases, the amount of movement required for focusing increases, and the overall length of the lens system increases.

[0036] When the negative refractive power of the second lens group G2 exceeds the upper limit of condition (4), it becomes difficult to suppress spherical aberration and astigmatism that occur in the second lens group G2 during focusing.

[0037] Furthermore, an embodiment of the imaging optical system according to the present invention is characterized by satisfying the following conditional expression. (5) 0.1 <D12 / f<0.35 D12: The distance between the first lens group G1 and the second lens group G2 on the optical axis when focused at infinity.

[0038] Conditional equation (5) appropriately defines the ratio between the lens group spacing between the first lens group G1 and the second lens group G2 on the optical axis when the lens is focused at infinity, and the focal length of the entire lens system when the lens is focused at infinity.

[0039] When the lower limit of condition (5) is exceeded, and the distance between the first lens group G1 and the second lens group G2 on the optical axis at infinity focus decreases, the incident height of the on-axial light beam incident on the second lens group G2 increases, and the fluctuation of spherical aberration during focusing becomes larger.

[0040] When the upper limit of condition (5) is exceeded, and the distance between the first lens group G1 and the second lens group G2 on the optical axis at infinity focus becomes large, the incident height of the off-axis light beam increases, and the fluctuations of coma aberration and astigmatism during focusing become larger.

[0041] Furthermore, an embodiment of the imaging optical system according to the present invention is characterized in that the air lens formed by the space between the first A lens group G1A and the first B lens group G1B has a biconvex shape.

[0042] The lens with positive refractive power within the first lens group G1A is preferably a positive meniscus lens in order to suppress off-axis aberrations. Furthermore, as mentioned above, it is desirable that the positive meniscus lens has a convex surface facing the object in order to cancel out the positive spherical aberration generated by the negative meniscus lens within the first lens group G1A. This makes it possible to suppress both off-axis aberrations and the positive spherical aberration of the first lens group G1A.

[0043] Furthermore, it is desirable that the surface of the first B lens group G1B that is closest to the object be concave towards the object in order to reduce the angle of incidence of light rays diverged from the first A lens group G1A.

[0044] Therefore, the space between the first lens group G1A and the first lens group G1B forms a biconvex air lens, formed by the concave surface facing the image side of the image-side lens surface of the positive meniscus lens L1p in the first lens group G1A, which has a convex surface facing the object side, and the concave surface facing the object side of the lens surface closest to the object in the first lens group G1B.

[0045] Furthermore, it is desirable that the third lens group G3 includes an aspherical lens with a negative meniscus shape such that the negative refractive power increases towards the periphery of the image-side surface. By placing an aspherical lens of this shape in the third lens group G3, the effects of coma aberration and field curvature can be effectively corrected.

[0046] The following describes an embodiment of the imaging optical system according to the present invention. In the following description, the lens configuration will be described in order from the object side to the image plane side.

[0047] In the [surface data], the surface number is the number of the lens surface or aperture diaphragm counted from the object side, r is the radius of curvature of each lens surface, d is the spacing between each lens surface, nd is the refractive index for the d line (wavelength λ=587.56nm), νd is the Abbe number for the d line, PgF is the partial dispersion ratio of the g line (wavelength λ=435.84nm) and the F line (wavelength λ=486.13nm), and ΔPgF indicates the anomalous dispersion.

[0048] The asterisk (*) next to the lens surface number indicates that the lens surface shape is aspherical. BF represents the back focus, and the object surface distance represents the distance from the subject to the first lens surface.

[0049] The (diaphragm) next to the face number indicates that an aperture diaphragm is located at that position. The radius of curvature relative to the plane or aperture diaphragm is indicated with ∞ (infinity).

[0050] The [Aspherical Data] section shows the coefficient values ​​that give the aspherical shape of the lens surface marked with an asterisk (*) in the [Surface Data] section. The shape of the aspherical surface is expressed by the following formula, where y is the displacement in the direction perpendicular to the optical axis, z is the displacement (sag) in the direction of the optical axis from the intersection of the aspherical surface and the optical axis, r is the radius of curvature of the reference sphere, K is the conic coefficient, and A4, A6, A8, A10, and A12 are the 4th, 6th, 8th, 10th, and 12th order aspherical coefficients, respectively. z=(y 2 / r) / [1+{1-(1+K)(y / r) 2} 1 / 2 ]+A4y 4 +A6y 6 +A8y 8 +A10y 10 +A12y 12

[0051] The [Various Data] section shows values ​​such as focal length at each shooting distance and in focus state.

[0052] The [Variable Interval Data] section shows the variable interval and BF (back focus) values ​​for each shooting distance and focus state.

[0053] The [Lens Group Data] shows the object-side face number for each lens group and the combined focal length of the entire group.

[0054] Furthermore, in the aberration diagrams corresponding to each embodiment, d, g, and C represent the d line, g line, and C line, respectively, and △S and △M represent the sagittal image plane and meridional image plane, respectively.

[0055] In addition, for all the specifications listed below, the units of focal length f, radius of curvature r, lens plane spacing d, and other lengths are millimeters (mm) unless otherwise specified. However, since equivalent optical performance can be obtained in both proportional magnification and proportional reduction in the optical system, this is not the only unit of measurement. [Examples]

[0056] Figure 1 is a lens configuration diagram of the imaging optical system of Embodiment 1 of the present invention.

[0057] The imaging optical system of Example 1 consists of, in order from the object side, a first lens group G1, an aperture diaphragm S, a second lens group G2, and a third lens group G3. When focusing from an object at infinity to a nearby object, the first lens group G1, the aperture diaphragm S, and the third lens group G3 are fixed relative to the image plane, while the second lens group G2 moves toward the image side along the optical axis.

[0058] The first lens group G1 consists of the first A lens group G1A, which is composed of a negative meniscus lens L11 with its convex surface facing the object, a negative meniscus lens L12 with its convex surface facing the object, and a positive meniscus lens L13 with its convex surface facing the object, in that order from the object side; and the first B lens group G1B, which is composed of a cemented lens consisting of a biconcave lens L14 and a biconvex lens L15, and a cemented lens consisting of a biconvex lens L16, a biconvex lens L17, a biconvex lens L18, and a biconcave lens L19.

[0059] The second lens group G2 is composed of a negative meniscus lens L21, which has an aspherical convex surface facing the object.

[0060] The third lens group G3 consists of a cemented lens comprising a negative meniscus lens L31 with a convex surface facing the object side and a biconvex lens L32, and a negative meniscus lens L33 with aspherical surfaces on both sides and a concave surface facing the image side.

[0061] The specifications of the imaging optical system according to Example 1 are shown below.

[0062] Numerical Example 1 Unit: mm [Surface data] Face number rd nd vd PgF1p Object surface ∞ (d0) 1 95.7011 1.200 1.55032 75.50 2 16.8636 7.443 3 76.8530 0.950 1.51680 64.20 4 33.7030 2.538 5 56.2568 3.600 1.94595 17.98 0.6546 6 174.2087 8.717 7 -25.7938 0.900 1.77047 29.74 8 91.6288 4.612 1.87071 40.73 9 -60.5055 0.150 10 269.5616 4.541 1.91082 35.25 11 -45.5516 0.350 12 129.9318 5.152 1.59282 68.62 13 -46.8478 0.150 14 38.6911 7.909 1.59282 68.62 15 -29.0872 0.900 1.85451 25.15 16 246.9248 1.979 17 (aperture) ∞ (d17) 18* 238.1843 1.100 1.69350 53.20 19 23.7911 (d19) 20 48.8216 0.900 1.56732 42.84 21 19.5605 8.205 1.76385 48.49 22 -37.7493 2.100 23* 179.6006 1.500 1.80610 40.73 24* 53.2850 (BF) Image plane ∞ [Aspherical data] Pages 18, 23, and 24 K 0.00000 0.00000 0.00000 A4 -5.27480E-06 1.06941E-05 3.33861E-05 A6 -5.56773E-09 4.17930E-08 6.67769E-08 A8 6.44743E-12 -7.73151E-10 -6.06177E-10 A10 -5.11734E-13 -6.18608E-13 5.03576E-13 A12 2.64452E-15 9.42967E-15 2.49819E-15 [Various Data] INF 0.25m Focal length 22.31 22.51 F-number 1.46 1.59 Full angle of view 2ω 67.85 60.77 Image height Y 14.20 14.20 Lens length 94.32 94.32 [Variable interval data] INF 0.25m d0 ∞ 155.00 d17 3.2524 7.3364 d19 7.3908 3.3069 BF 18.7827 18.7827 [Lens group data] Group starting plane focal length G1 1 24.85 G2 18 -38.19 G3 20 31.65 G23 18 82.48 G1A 1 -44.35 G1B 7 27.00 [Examples]

[0063] Figure 6 is a lens configuration diagram of the imaging optical system according to Embodiment 2 of the present invention.

[0064] The imaging optical system of Example 2 consists of, in order from the object side, a first lens group G1, an aperture diaphragm S, a second lens group G2, and a third lens group G3. When focusing from an object at infinity to a nearby object, the first lens group G1, the aperture diaphragm S, and the third lens group G3 are fixed relative to the image plane, while the second lens group G2 moves toward the image side along the optical axis.

[0065] The first lens group G1 consists of the first A lens group G1A, which is composed of a negative meniscus lens L11 with its convex surface facing the object, a negative meniscus lens L12 with its convex surface facing the object, and a positive meniscus lens L13 with its convex surface facing the object, in that order from the object side; and the first B lens group G1B, which is composed of a cemented lens consisting of a biconcave lens L14 and a biconvex lens L15, and a cemented lens consisting of a biconvex lens L16, a biconvex lens L17, a biconvex lens L18, and a biconcave lens L19.

[0066] The second lens group G2 is composed of a negative meniscus lens L21, which has an aspherical convex surface facing the object.

[0067] The third lens group G3 consists of a cemented lens comprising a negative meniscus lens L31 with a convex surface facing the object side and a biconvex lens L32, and a negative meniscus lens L33 with aspherical surfaces on both sides and a concave surface facing the image side.

[0068] The specifications of the imaging optical system according to Example 2 are shown below.

[0069] Numerical Example 2 Unit: mm [Surface data] Face number rd nd vd PgF1p Object surface ∞ (d0) 1 36.6189 1.200 1.49700 81.61 2 16.4870 8.627 3* 78.2086 0.950 1.51633 64.07 4* 23.1797 2.482 5 32.3159 3.600 1.94595 17.98 0.6546 6 49.6296 9.266 7 -22.6502 0.900 1.77047 29.74 8 83.4568 5.500 1.88300 40.81 9 -57.1505 0.150 10 2456.2344 5.000 1.88100 40.14 11 -38.0531 1.648 12 53.7686 5.369 1.59282 68.62 13 -71.6206 0.150 14 38.5693 7.272 1.59282 68.62 15 -31.6849 0.900 1.90110 27.06 16 797.1977 1.132 17 (aperture) ∞ (d17) 18* 143.9273 1.000 1.69350 53.20 19 22.0878 (d19) 20 37.3595 0.900 1.54814 45.82 21 19.1909 7.298 1.76385 48.49 22 -34.7649 0.250 23* 44.9072 1.485 1.80610 40.73 24* 21.0808 (BF) Image plane ∞ [Aspherical data] 3 sides 4 sides 18 sides 23 sides K 0.00000 0.00000 0.00000 0.00000 A4 1.07888E-05 9.91812E-06 -6.99005E-06 -3.51617E-06 A6 -1.13818E-07 -1.35583E-07 -1.47026E-09 -5.13470E-07 A8 4.23669E-10 4.26930E-10 -9.96358E-12 5.11315E-09 A10 -7.67049E-13 -8.38959E-13 -3.26808E-13 -3.79586E-11 A12 0.00000E+00 0.00000E+00 5.75759E-16 1.19869E-13 24 sides K 0.00000 A4 2.68883E-05 A6 -5.58487E-07 A8 6.66317E-09 A10 -5.23107E-11 A12 1.79690E-13 [Various Data] INF 0.25m Focal length 22.31 22.13 F-number 1.45 1.56 Full angle of view 2ω 65.64 59.70 Image height Y 14.20 14.20 Lens length 94.32 94.32 [Variable interval data] INF 0.25m d0 ∞ 155.00 d17 2.7750 6.2888 d19 7.1436 3.6299 BF 19.3262 19.3262 [Lens group data] Group starting plane focal length G1 1 23.03 G2 18 -37.75 G3 20 33.96 G23 18 124.30 G1A 1 -46.39 G1B 7 24.93 [Examples]

[0070] Figure 11 is a lens configuration diagram of the imaging optical system according to Embodiment 3 of the present invention.

[0071] The imaging optical system of Example 3 consists of, in order from the object side, a first lens group G1, an aperture diaphragm S, a second lens group G2, and a third lens group G3. When focusing from an object at infinity to a nearby object, the first lens group G1, the aperture diaphragm S, and the third lens group G3 are fixed relative to the image plane, while the second lens group G2 moves toward the image side along the optical axis.

[0072] The first lens group G1 consists of the first A lens group G1A, which is composed of a negative meniscus lens L11 with its convex surface facing the object, a negative meniscus lens L12 with its convex surface facing the object, and a positive meniscus lens L13 with its convex surface facing the object, in that order from the object side; and the first B lens group G1B, which is composed of a cemented lens consisting of a biconcave lens L14 and a biconvex lens L15, a positive meniscus lens L16 with its convex surface facing the image side, a biconvex lens L17, and a cemented lens consisting of a biconvex lens L18 and a biconcave lens L19.

[0073] The second lens group G2 is composed of a negative meniscus lens L21, which has an aspherical convex surface facing the object.

[0074] The third lens group G3 consists of a cemented lens comprising a negative meniscus lens L31 with a convex surface facing the object side and a biconvex lens L32, and a negative meniscus lens L33 with aspherical surfaces on both sides and a concave surface facing the image side.

[0075] The specifications of the imaging optical system according to Example 3 are shown below.

[0076] Numerical Example 3 Unit: mm [Surface data] Face number rd nd vd PgF1p Object surface ∞ (d0) 1 51.7977 1.200 1.49700 81.61 2 16.5212 9.782 3 190.4902 0.950 1.51680 64.20 4 26.2284 2.543 5 64.8974 2.990 1.92286 20.88 0.6390 6 574.4171 11.687 7 -23.8214 1.000 1.77047 29.74 8 104.1091 4.176 1.90043 37.37 9 -55.8544 0.150 10 -1889.0621 4.338 1.88100 40.14 11 -39.7413 0.350 12 84.6552 5.500 1.59282 68.62 13 -48.7271 0.150 14 31.5728 8.100 1.59282 68.62 15 -32.0933 0.900 1.90110 27.06 16 494.3356 1.184 17 (aperture) ∞ (d17) 18* 182.2154 1.000 1.69350 53.20 19 19.3351 (d19) 20 30.8654 0.900 1.68893 31.16 21 18.9072 8.076 1.74400 44.90 22 -29.9272 0.150 23* 98.2183 1.000 1.80610 40.73 24* 30.0000 (BF) Image plane ∞ [Aspherical data] Pages 18, 23, and 24 K 0.00000 0.00000 0.00000 A4 -4.22916E-06 -2.92214E-05 -2.96356E-06 A6 -8.83461E-09 5.85304E-08 9.06643E-08 A8 -8.68436E-11 1.07088E-09 1.09372E-09 A10 6.38880E-13 -1.42562E-11 -1.18808E-11 A12 -4.20039E-15 4.19998E-14 3.41266E-14 [Various Data] INF 0.25m Focal length 20.37 20.22 F-number 1.43 1.52 Full angle of view 2ω 72.96 67.39 Image height Y 14.20 14.20 Lens length 94.32 94.32 [Variable interval data] INF 0.25m d0 ∞ 155.00 d17 2.8347 5.1984 d19 6.0044 3.6409 BF 19.3592 19.3592 [Lens group data] Group starting plane focal length G1 1 19.26 G2 18 -31.27 G3 20 31.71 G23 18 162.95 G1A 1 -41.17 G1B 7 23.74 [Examples]

[0077] Figure 16 is a lens configuration diagram of the imaging optical system according to Embodiment 4 of the present invention.

[0078] The imaging optical system of Example 4 consists of, in order from the object side, a first lens group G1, an aperture diaphragm S, a second lens group G2, and a third lens group G3. When focusing from an object at infinity to a nearby object, the first lens group G1, the aperture diaphragm S, and the third lens group G3 are fixed relative to the image plane, while the second lens group G2 moves toward the image side along the optical axis.

[0079] The first lens group G1 consists of the first A lens group G1A, which is composed of a negative meniscus lens L11 with its convex surface facing the object, a negative meniscus lens L12 with its convex surface facing the object, and a positive meniscus lens L13 with its convex surface facing the object, in that order from the object side; and the first B lens group G1B, which is composed of a cemented lens consisting of a biconcave lens L14 and a biconvex lens L15, and a cemented lens consisting of a biconvex lens L16, a biconvex lens L17, a biconvex lens L18, and a biconcave lens L19.

[0080] The second lens group G2 is composed of a negative meniscus lens L21, which has an aspherical convex surface facing the object.

[0081] The third lens group G3 consists of a biconvex lens L31 and a negative meniscus lens L32, which has aspherical surfaces on both sides and a concave surface facing the image side.

[0082] The specifications of the imaging optical system according to Example 4 are shown below.

[0083] Numerical Example 4 Unit: mm [Surface data] Face number rd nd vd PgF1p Object surface ∞ (d0) 1 76.2198 1.000 1.63854 55.45 2 16.8582 8.414 3 1000.0023 0.950 1.59282 68.62 4 32.3998 1.001 5 47.3179 3.600 1.98613 16.48 0.6656 6 185.0610 9.900 7 -25.8961 1.727 1.77047 29.74 8 67.7033 5.500 1.90043 37.37 9 -43.2786 0.150 10 320.5118 3.874 1.88100 40.14 11 -53.0659 0.350 12 72.8518 5.500 1.59282 68.62 13 -53.4660 0.150 14 32.6107 8.056 1.59282 68.62 15 -31.4175 0.850 1.85451 25.15 16 51.3642 2.415 17 (aperture) ∞ (d17) 18* 140.2516 1.000 1.69350 53.20 19 26.9730 (d19) 20 32.9953 8.550 1.74400 44.90 21 -31.4490 0.150 22* 67.7605 1.000 1.80610 40.73 23* 33.2401 (BF) Image plane ∞ [Aspherical data] Pages 18, 22, and 23 K 0.00000 0.00000 0.00000 A4 -6.46458E-06 3.10748E-05 6.19667E-05 A6 -6.44476E-09 -8.13823E-07 -8.26449E-07 A8 -1.09507E-10 1.04202E-08 1.16939E-08 A10 -2.34594E-13 -8.02734E-11 -8.89371E-11 A12 -3.34241E-16 2.34889E-13 2.61722E-13 [Various Data] INF 0.25m Focal length 19.40 19.85 F-number 1.42 1.54 Full angle of view 2ω 75.17 67.97 Image height Y 14.20 14.20 Lens length 94.31 94.31 [Variable interval data] INF 0.25m d0 ∞ 155.00 d17 2.7845 7.6263 d19 7.9300 3.0885 BF 19.4592 19.4592 [Lens group data] Group starting plane focal length G1 1 26.41 G2 18 -48.33 G3 20 29.93 G23 18 52.67 G1A 1 -31.74 G1B 7 26.55

[0084] The corresponding values ​​for each example are shown below.

[0085] [Conditional expression corresponding value] Conditional expression Example 1 Example 2 Example 3 Example 4 (1) f2R / f 3.70 5.57 8.00 2.71 (2)νd1p 17.98 17.98 20.88 16.48 (3)ΔPgF1p 0.0386 0.0386 0.0283 0.0469 (4)|f / f2| 0.58 0.59 0.65 0.40 (5) D12 / f 0.23 0.18 0.20 0.27 [Explanation of symbols]

[0086] G1 First Lens Group G2 2nd lens group G3 3rd lens group G1A 1A lens group G1B 1B lens group

Claims

1. Starting from the object side, it consists of a first lens group G1 with positive refractive power, an aperture, a second lens group G2 with negative refractive power, and an image-side lens group GR with positive refractive power. During focusing, only the second lens group G2 moves in the direction of the optical axis. The second lens group G2 consists of only one lens having negative refractive power. The first lens group G1 consists of a first A lens group G1A having a negative refractive power and positioned on the object side, and a first B lens group G1B having a positive refractive power and positioned on the image side. The first lens group G1A consists of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, another negative meniscus lens, and a positive meniscus lens L1p with a convex surface facing the object side. An optical system characterized by satisfying the following conditional equation. (1) 1.5<f2R / f<10.0 (2) νd1p<25.00 (3) ΔPgF1p>0.0150 f: Focal length of the entire lens system when focused at infinity f2R: The combined focal length of the second lens group G2 and the image-side lens group GR when focused at infinity. νd1p: Abbe number of the positive meniscus lens L1p ΔPgF1p: Abnormal dispersion of the positive meniscus lens L1p Here, ΔPgF1p is calculated by the following formula, where PgF1p is the partial dispersion ratio of the g-line and F-line of the positive meniscus lens L1p. ΔPgF1p=PgF1p+0.0018×νd1p−0.64833

2. The lens consists of, in order from the object side, a first lens group G1 having positive refractive power, an aperture, a second lens group G2 having negative refractive power, and an image-side lens group GR having positive refractive power. During focusing, only the second lens group G2 moves in the direction of the optical axis. The first lens group G1 consists of a first A lens group G1A having a negative refractive power and positioned on the object side, and a first B lens group G1B having a positive refractive power and positioned on the image side. The first lens group G1A consists of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, another negative meniscus lens, and a positive meniscus lens L1p with a convex surface facing the object side. An optical system characterized by satisfying the following conditional equation. (1) 1.5<f2R / f<10.0 (2) νd1p<25.00 (3) ΔPgF1p>0.0250 f: Focal length of the entire lens system when focused at infinity f2R: The combined focal length of the second lens group G2 and the image-side lens group GR when focused at infinity. νd1p: Abbe number of the positive meniscus lens L1p ΔPgF1p: Abnormal dispersion of the positive meniscus lens L1p Here, ΔPgF1p is calculated by the following formula, where PgF1p is the partial dispersion ratio of the g-line and F-line of the positive meniscus lens L1p. ΔPgF1p=PgF1p+0.0018×νd1p−0.64833

3. The optical system according to claim 1 or 2, characterized in that it satisfies the following conditional expression. (4) 0.30<|f / f2|<0.75 f2: Focal length of the second lens group G2

4. The optical system according to claim 2, wherein the second lens group G2 consists of only one lens having negative refractive power.

5. The optical system according to claim 1 or 2, characterized in that it satisfies the following conditional expression. (5) 0.1<D12 / f<0.35 D12: The distance between the first lens group G1 and the second lens group G2 on the optical axis when focused at infinity.

6. The optical system according to claim 1 or 2, characterized in that the air lens formed by the space between the first A lens group G1A and the first B lens group G1B has a biconvex shape.

Images