Large-aperture internal focusing optical system

Abstract

The present invention relates to a large-aperture internal-focus optical system comprising a first lens group with positive focal power, a second lens group with negative focal power, and a third lens group with optical power, arranged sequentially from the object side to the image side. The first lens group comprises a first lens group, an aperture stop, and a second lens group, arranged sequentially from the object side to the image side. The second lens group comprises a single lens that can be moved along the optical axis for focusing. By ensuring that the optical system satisfies specified conditional expressions, the present invention enables the optical system to achieve a medium-short focal length equivalent to a 35mm camera, while also achieving a large aperture, lightweight, compact size, and excellent imaging performance.

Description

Technical Field

[0001] The present invention relates to an optical system, and more particularly to a large-aperture inner-focus optical system suitable for use in an imaging device using a solid-state imaging element, such as a digital still camera or a digital video camera. Background Art

[0002] As solid-state imaging elements have become popular in digital still cameras, digital video cameras and other imaging devices, the performance and miniaturization of imaging optical systems have been rapidly promoted, and many internal focusing optical systems with medium and longer focal lengths have been proposed.

[0003] For example, Chinese patent application publication number CN106019541 (hereinafter referred to as Document 1) discloses an internal focusing lens, which is composed of a first lens group with positive optical focal length, a second lens group with negative optical focal length, and a third lens group with negative optical focal length, which are arranged in sequence from the object side, and focusing is performed by moving the second lens group; it satisfies the condition: -7.46≤f2 / f≤-2.11, where f2 is the focal length of the second lens group when the object at infinity is in focus, and f represents the focal length of the entire optical system when the object at infinity is in focus.

[0004] However, the inner focusing lens disclosed in Document 1 has a small aperture, resulting in insufficiently bright images. Furthermore, if the lens disclosed in Document 1 were to achieve a large-aperture optical system with a medium to short focal length equivalent to a 35mm camera, the diameter of the front lens would be large, hindering miniaturization of the optical system and making the product more accessible and affordable.

[0005] Thus, among the existing internal focus lenses, including the technology described in the above-mentioned document 1, there is no lens that has a short focal length in 35mm camera conversion, a large aperture, a bright image quality, and good imaging performance, while being compact.

[0006] In response to the above problems, the designer conducted in-depth thinking and active research and development, which resulted in this project. Summary of the Invention

[0007] An object of the present invention is to provide an inner-focus optical system having a short focal length in terms of a 35mm camera, miniaturization, a large aperture, and excellent imaging performance.

[0008] A large-aperture internal focusing optical system comprises a first lens group with positive optical power, a second lens group with negative optical power, and a third lens group with positive optical power, which are arranged in sequence from the object side to the image side.

[0009] The first lens group includes a first lens group, an aperture stop, and a second lens group arranged in sequence from the object side to the image side; the first lens group includes at least a positive lens and a negative lens arranged in sequence from the object side to the image side;

[0010] The second lens group is a single lens that can move along the optical axis for focusing;

[0011] The optical system meets the following conditions:

[0012] (1) -2.0<f1a / f<-0.3;

[0013] (2) 0.2<D1a / L<0.6;

[0014] Where f1a is the focal length of the first lens group, f is the focal length of the optical system, D1a is the length of the first lens group along the optical axis, and L is the total length of all lens elements along the optical axis from the lens surface closest to the object side to the lens surface closest to the image side.

[0015] The optical system meets the following conditions:

[0016] (3) 3.7<f11 / f<18.0;

[0017] Where f11 is the focal length of the positive lens closest to the object side in the first lens group, and f is the focal length of the optical system.

[0018] The optical system meets the following conditions:

[0019] (4) -2.8<f1b / f1a<-0.6;

[0020] (5) 0.6<D1b / D1a<2.8;

[0021] Wherein, f1b is the focal length of the second lens group, f1a is the focal length of the first lens group; D1b is the length of the second lens group in the optical axis direction, and D1a is the length of the first lens group in the optical axis direction.

[0022] The optical system meets the following conditions:

[0023] (6) 0.06<Df / D<0.2;

[0024] (7)Ndmax-Ndmin<0.3;

[0025] Wherein, Df is the distance on the optical axis from the lens surface closest to the image side in the first lens group to the lens surface closest to the object side in the third lens group; D is the length of the optical system from the lens surface closest to the object side to the imaging plane in the optical axis direction, that is, the total length of the optical system; Ndmax is the maximum refractive index of the lens element between the lens element closest to the image side in the first lens group and the lens element closest to the object side in the third lens group; Ndmin is the minimum refractive index of the lens element between the lens element closest to the image side in the first lens group and the lens element closest to the object side in the third lens group.

[0026] The optical system meets the following conditions:

[0027] (8) 0.2<D21 / D22<0.8;

[0028] D21 is the distance on the optical axis from the lens surface of the second lens group closest to the image side to the lens surface of the third lens group closest to the object side when focused at infinity. D22 is the distance on the optical axis from the lens surface of the second lens group closest to the image side to the lens surface of the third lens group closest to the image side when focused at infinity.

[0029] The optical system meets the following conditions:

[0030] (9) 2.0<L / Y<6.0;

[0031] L is the total length of all lens elements along the optical axis from the lens surface closest to the object side to the lens surface closest to the image side, and Y is the maximum image height at the image plane position.

[0032] The optical system meets the following conditions:

[0033] (10) 0.4<DS / D<1.0;

[0034] Where DS is the distance from the aperture stop of the first lens group to the image side on the optical axis, and D is the length of the optical system from the lens surface closest to the object side to the imaging surface in the optical axis direction, that is, the total length of the optical system.

[0035] With the above arrangement, the optical system of the present invention comprises 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, arranged sequentially from the object side to the image side. By ensuring that the optical system satisfies a specified conditional expression, the present invention achieves a medium-short focal length equivalent to a 35mm camera, while also achieving a large aperture, lightweight, compact size, and excellent imaging performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the optical system structure of Example 1;

[0037] Figure 2Graphs of spherical aberration, astigmatism, and distortion of the optical system of Example 1 at the closest focusing distance with an object at infinity and an imaging magnification of 1 / 40 (where a corresponds to the spherical aberration graph, b corresponds to the astigmatism graph, and c corresponds to the distortion graph);

[0038] Figure 3 Schematic diagram of the optical system structure of Example 2;

[0039] Figure 4 Graphs of spherical aberration, astigmatism, and distortion of the optical system of Example 3 at the closest focusing distance with an object at infinity and an imaging magnification of 1 / 40 (where a corresponds to the spherical aberration graph, b corresponds to the astigmatism graph, and c corresponds to the distortion graph);

[0040] Figure 5 Schematic diagram of the optical system structure of Example 3;

[0041] Figure 6 Graphs of spherical aberration, astigmatism, and distortion of the optical system of Example 3 at the closest focusing distance with an object at infinity and an imaging magnification of 1 / 40 (where a corresponds to the spherical aberration graph, b corresponds to the astigmatism graph, and c corresponds to the distortion graph);

[0042] Figure 7 Schematic diagram of the optical system structure of Example 4;

[0043] Figure 8 Schematic diagrams of spherical aberration, astigmatism, and distortion of the optical system of Example 4 when the object distance is infinite and the imaging magnification is 1 / 40, and the object is in the closest focusing state (where a corresponds to the spherical aberration diagram, b corresponds to the astigmatism diagram, and c corresponds to the distortion diagram). DETAILED DESCRIPTION

[0044] The inner focusing optical system according to the present invention will be described in detail below with reference to the accompanying drawings.

[0045] The present invention discloses a large-aperture internal focusing optical system comprising a first lens group G1 with positive optical power, a second lens group G2 with negative optical power, and a third lens group G3 with optical power, arranged sequentially from the object side to the image side. The first lens group G1 comprises a first lens group G1a, an aperture stop S, and a second lens group G1b, arranged sequentially from the object side to the image side. The second lens group G2 is a single lens that can be moved along the optical axis for focusing. By configuring the second lens group G2, the present invention achieves focusing of the optical system without moving the entire optical system during focusing, thereby achieving miniaturization, lightweighting, and high-speed focusing while maintaining the same length of the optical system.

[0046] The first lens group G1a comprises at least a positive lens (corresponding to lens L11 in the following embodiments) and a negative lens (corresponding to lens L12 in the following embodiments) arranged in sequence from the object side to the image side. The optical system must also meet the following conditions:

[0047] (1) -2.0<f1a / f<-0.3;

[0048] (2) 0.2<D1a / L<0.6;

[0049] Where, f1a is the focal length of the first lens group G1a, f is the focal length of the optical system; D1a is the length of the first lens group G1a along the optical axis, and L is the total length of all lens elements from the lens surface closest to the object side to the lens surface closest to the image side along the optical axis, that is, L is the total length of the lens group. The above conditional equations (1) and (2) are both limitations on the first lens group G1a of the first lens group G1. Satisfying conditional equations (1) and (2) can reduce the outer diameter of the lens elements in the first lens group G1a while maintaining the wide-angle characteristics of the optical system, thereby achieving a large aperture, compact size, and excellent imaging performance.

[0050] On the basis of the above, the optical system can further define the first lens group G1 to optimize performance.

[0051] (3) 3.7<f11 / f<18.0;

[0052] Where f11 is the focal length of the positive lens closest to the object side in the first lens group G1, and f is the focal length of the optical system. Satisfying condition (3) can effectively control the aberrations of the optical system without increasing the overall size of the optical system.

[0053] On the basis of the above, the optical system can also meet the following conditions:

[0054] (4) -2.8<f1b / f1a<-0.6;

[0055] (5) 0.6<D1b / D1a<2.8;

[0056] Where f1b is the focal length of the second lens group G1b, f1a is the focal length of the first lens group G1a; D1b is the length of the second lens group G1b along the optical axis, and D1a is the length of the first lens group G1a along the optical axis. Conditional equations (4) and (5) define the first lens group G1a and the second lens group G1b of the first lens group G1. When conditional equations (4) and (5) are satisfied, the size of the first lens group G1 and the magnitude of the aberrations can be well balanced, thereby contributing to the miniaturization of the entire optical system.

[0057] When the optical system satisfies conditional expressions (6) and (7), the performance of the optical system will be further improved.

[0058] (6) 0.06<Df / D<0.2;

[0059] (7)Ndmax-Ndmin<0.3;

[0060] Where Df is the distance on the optical axis from the lens surface closest to the image side in the first lens group G1 to the lens surface closest to the object side in the third lens group G3, D is the length of the optical system from the lens surface closest to the object side to the imaging surface in the optical axis direction, that is, the total length of the optical system; Ndmax is the maximum refractive index of the lens element from the lens element closest to the image side in the first lens group to the lens element closest to the object side in the third lens group; Ndmin is the minimum refractive index of the lens element from the lens element closest to the image side in the first lens group to the lens element closest to the object side in the third lens group. When the above-mentioned conditional equations (6) and (7) are met, the miniaturization of the focus group of the internal focus optical system is extremely advantageous, and the imaging magnification change of the optical system during focusing can be reduced, so that the optical system has high-speed focusing and excellent animation shooting characteristics.

[0061] When the optical system satisfies the following conditional expression (8), the size of the optical system can be further miniaturized.

[0062] (8) 0.2<D21 / D22<0.8;

[0063] Where D21 is the distance on the optical axis between the lens surface of the second lens group G2 closest to the image side and the lens surface of the third lens group G3 closest to the object side when focused at infinity, and D22 is the distance on the optical axis between the lens surface of the second lens group G2 closest to the image side and the lens surface of the third lens group G3 closest to the image side when focused at infinity. Meeting conditional equation (8) can shorten the minimum shooting distance and reduce the size of the optical system.

[0064] The optical system can also satisfy the following condition (9):

[0065] (9) 2.0<L / Y<6.0;

[0066] L is the total length of all lens elements along the optical axis, from the lens surface closest to the object side to the lens surface closest to the image side, and Y is the maximum image height at the image plane. When equation (9) is met, the optical system can have a good aspect ratio while still meeting optical performance requirements.

[0067] The optical system can also satisfy the following condition (10):

[0068] (10) 0.4<DS / D<1.0;

[0069] Where DS is the distance from the aperture stop S of the first lens group G1 to the image side on the optical axis, and D is the length of the optical system from the lens surface closest to the object side to the imaging surface along the optical axis, i.e., the total length of the optical system. When equation (10) is met, the aperture sizes of the lenses within the first lens group G1 and the third lens group G3 can be balanced, achieving overall miniaturization of the optical system.

[0070] To further elaborate on the technical content of the invention, the following embodiments are given to describe in detail the large-aperture inner-focusing optical system.

[0071] In the following embodiments, a protective glass CG is disposed between the optical system and the imaging surface IMG. The protective glass CG can be disposed as needed and can be omitted if not needed.

[0072] Example 1

[0073] Reference Figure 1 As shown, the inner focusing optical system in this embodiment includes a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power, which are arranged in sequence from the object side to the image side.

[0074] The first lens group G1 includes a first lens group G1a, an aperture stop S, and a second lens group G1b.

[0075] The first lens group G1a includes, arranged in sequence from the object side to the image side, a meniscus lens L11 with positive optical power and convex toward the object side, a convex-concave lens L12 with negative optical power and convex toward the object side, a convex-concave lens L13 with negative optical power and convex toward the object side, a meniscus lens L14 with positive optical power and convex toward the image side, and a lens L15 with negative optical power and a concave surface facing the object side.

[0076] Second lens group G1b consists of, arranged in order from the object side to the image side, biconvex lens L16, biconvex lens L17, a meniscus lens L18 convex toward the image side, and a meniscus lens L19 with positive refractive power and convex toward the image side. The concave surface of meniscus lens L18 is cemented to the image-side surface of biconvex lens L17.

[0077] The second lens group G2 is composed of a single lens that can move along the optical axis for focusing. The single lens is a lens L21 with a negative refractive power and a concave surface facing the image side.

[0078] The third lens group G3 includes a biconvex lens L31 and a convex-concave lens L32, which are arranged from the object side to the image side. The convex-concave lens L32 has a convex surface on the image side.

[0079] In this embodiment, the lens data of the optical system are set as follows:

[0080] Optical parameters

[0081]

[0082] Aspheric surface data

[0083] Page 17

[0084] K=0.00000E+00, A4=-3.39535E-05, A6=-8.92578E-08, A8=-7.47006E-11

[0085] Page 18

[0086] K=0.00000E+00, A4=-7.20328E-06, A6=-5.22251E-08, A8=-4.50264E-11

[0087] Page 19

[0088] K=0.00000E+00, A4=1.35811E-04, A6=-4.70456E-07, A8=1.26859E-09, A10=-1.74958E-12

[0089] Page 20

[0090] K=0.00000E+00, A4=1.26338E-04, A6=-3.42899E-07, A8=9.19836E-10, A10=-1.58404E-12

[0091] Page 21

[0092] K=0.00000E+00, A4=-2.22701E-06, A6=1.22415E-07, A8=-1.55651E-10

[0093] Page 22

[0094] K=0.00000E+00, A4=-9.49890E-06, A6=7.12292E-08, A8=-7.15592E-11

[0095]

[0096]

[0097] According to the above lens parameters, the optical system of this embodiment satisfies the conditional expressions (1) to (10), and the total length of the optical system is 100.700 mm, and the shortest photographic distance is 240.0 mm.

[0098] Figure 2 The spherical aberration, astigmatism and distortion diagram of the optical system of this embodiment when the object distance is infinite and the imaging magnification is 1 / 40 times, and the closest focusing state is shown. Figure 2 It can be seen that the imaging performance of this embodiment is excellent.

[0099] Example 2

[0100] Reference Figure 3 As shown, the inner focusing optical system in this embodiment includes a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power, which are arranged in sequence from the object side to the image side.

[0101] The first lens group G1 includes a first lens group G1a, an aperture stop S, and a second lens group G1b.

[0102] The first lens group G1a includes a meniscus lens L11 with positive optical power and a convex surface facing the object side, a convex-concave lens L12 with negative optical power and a convex surface facing the object side, a convex-concave lens L13 with negative optical power and a convex surface facing the object side, and a convex-concave lens L14 with negative optical power and a convex surface facing the image side, which are arranged in sequence from the object side to the image side.

[0103] The second lens group G1b includes, arranged in order from the object side to the image side, a biconvex lens L15, a biconcave lens L16, a biconvex lens L17, a meniscus lens L18 with its convex surface facing the image side, and a biconvex lens L19. The biconvex lens L15, biconcave lens L16, and biconvex lens L17 are cemented together in this order.

[0104] The second lens group G2 is composed of a single lens that can move along the optical axis for focusing. The single lens is a lens L21 with a negative refractive power and a concave surface facing the image side.

[0105] The third lens group G3 is composed of a convex-concave lens L31 , and the lens surface of the convex-concave lens L31 on the object side is convex.

[0106] In this embodiment, the lens data of the optical system are set as follows:

[0107] Optical parameters

[0108]

[0109] Aspheric surface data

[0110] Page 14

[0111] K=0.00000E+00

[0112] A4=1.42697E-04, A6=2.71272E-07, A8=-4.86978E-09, A10=2.25375E-11, A12=-2.89916E-14

[0113] Page 15

[0114] K=0.00000E+00

[0115] A4=1.25455E-04, A6=2.73504E-07, A8=-3.20541E-09, A10=9.56276E-12, A12=-9.28913E-15

[0116] Page 18

[0117] K=0.00000E+00, A4=5.57137E-05, A6=-2.52882E-07, A8=8.55583E-10, A10=-1.46895E-12

[0118] Page 19

[0119] K=0.00000E+00, A4=5.54966E-05, A6=-2.18495E-07, A8=7.56056E-10, A10=-1.29868E-12

[0120]

[0121]

[0122] According to the above lens parameters, the optical system of this embodiment satisfies the conditional expressions (1) to (10), and the total length of the optical system is 100.700 mm, and the shortest photographic distance is 240.8 mm.

[0123] Figure 4 The spherical aberration, astigmatism and distortion diagram of the optical system of this embodiment when the object distance is infinite and the imaging magnification is 1 / 40 times, and the closest focusing state is shown. Figure 4 It can be seen that the imaging performance of this embodiment is excellent.

[0124] Example 3

[0125] Reference Figure 5 As shown, the inner focusing optical system in this embodiment includes a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with negative refractive power, which are arranged in sequence from the object side to the image side.

[0126] The first lens group G1 includes a first lens group G1a, an aperture stop S, and a second lens group G1b.

[0127] The first lens group G1a includes, arranged in sequence from the object side to the image side, a meniscus lens L11 with positive refractive power and the convex surface facing the object side, a convexo-convex lens L12 with negative optical power and the convex surface facing the object side, a convexo-convex lens L13 with negative optical power and the convex surface facing the object side, and a convexo-convex lens L14 with negative optical power and the convex surface facing the image side.

[0128] Second lens group G1b consists of, arranged in order from the object side to the image side, a meniscus lens L15 (convex surface facing the object side), a biconvex lens L16, a biconvex lens L17, a meniscus lens L18 (convex surface facing the image side), a meniscus lens L19 (convex surface facing the image side), and a biconvex lens L110. The object-side surface of meniscus lens L18 is cemented to biconvex lens L17.

[0129] The second lens group G2 is composed of a single lens that can move along the optical axis for focusing. The single lens is a lens L21 with a negative refractive power and a concave surface facing the image side.

[0130] The third lens group G3 includes a biconvex lens L31 and a convex-concave lens L32, which are arranged from the object side to the image side. The convex-concave lens L32 has a convex surface on the image side.

[0131] In this embodiment, the lens data of the optical system are set as follows:

[0132] Optical parameters

[0133]

[0134] Aspheric surface data

[0135] Page 7

[0136] K=0.00000E+00, A4=2.65677E-04, A6=-9.14954E-07, A8=3.19490E-09

[0137] Page 8

[0138] K=0.00000E+00, A4=2.37162E-04, A6=-8.16467E-07, A8=2.06029E-09

[0139] Page 19

[0140] K=0.00000E+00, A4=3.89832E-06, A6=-9.81729E-09, A8=-6.12098E-11

[0141] Page 20

[0142] K=0.00000E+00, A4=3.17387E-05, A6=-3.21481E-08, A8=1.76309E-11

[0143] Page 22

[0144] K=0.00000E+00, A4=-5.90244E-06, A6=1.94725E-07, A8=-9.81309E-10, A10=1.83601E-12

[0145] Page 23

[0146] K=0.00000E+00, A4=-1.28885E-05, A6=2.61931E-07, A8=-1.07587E-09, A10=1.75315E-12

[0147]

[0148]

[0149] According to the above lens parameters, the optical system of this embodiment satisfies the conditions (1) to (10), and the total length of the optical system is 100.700 mm, and the shortest photographic distance is 234.64 mm.

[0150] Figure 6 The spherical aberration, astigmatism and distortion diagram of the optical system of this embodiment when the object distance is infinite and the imaging magnification is 1 / 40 times, and the closest focusing state is shown. Figure 6 It can be seen that the imaging performance of this embodiment is excellent.

[0151] Example 4

[0152] Reference Figure 7 As shown, the inner focusing optical system in this embodiment includes a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with negative refractive power, which are arranged in sequence from the object side to the image side.

[0153] The first lens group G1 includes a first lens group G1a, an aperture stop S, and a second lens group G1b.

[0154] The first lens group G1a includes a meniscus lens L11 with positive optical power and the convex surface facing the object side, a convex-concave lens L12 with negative optical power and the convex surface facing the object side, a convex-concave lens L13 with negative optical power and the convex surface facing the object side, and a convex-concave lens L14 with negative optical power and the convex surface facing the image side, which are arranged in sequence from the object side to the image side.

[0155] Second lens group G1b consists of, arranged in order from the object side to the image side, a meniscus lens L15 (convex surface facing the object side), a biconvex lens L16, a biconvex lens L17, a meniscus lens L18 (convex surface facing the image side), a meniscus lens L19 (convex surface facing the image side), and a biconvex lens L110. The object-side surface of meniscus lens L18 is cemented to that of biconvex lens L17.

[0156] The second lens group G2 is composed of a single lens that can move along the optical axis for focusing. The single lens is a lens L21 with a negative refractive power and a concave surface facing the image side.

[0157] The third lens group G3 includes a meniscus lens L31 and a convexo-concave lens L32, arranged from the object side to the image side. The image-side lens surface of the meniscus lens L31 is convex, while the image-side lens surface of the convexo-concave lens L32 is convex.

[0158] In this embodiment, the lens data of the optical system are set as follows:

[0159] Optical parameters

[0160]

[0161]

[0162] Aspheric surface data

[0163] Page 7

[0164] K=0.00000E+00, A4=2.06740E-04, A6=-6.94336E-07, A8=2.66403E-09

[0165] Page 8

[0166] K=0.00000E+00, A4=1.72515E-04, A6=-6.42045E-07, A8=1.51776E-09

[0167] Page 18

[0168] K=0.00000E+00, A4=5.14046E-06, A6=-1.69513E-08, A8=-2.07809E-10

[0169] Page 19

[0170] K=0.00000E+00, A4=3.32202E-05, A6=-4.70945E-08, A8=-9.29096E-11

[0171] Page 21

[0172] K=0.00000E+00, A4=-2.00798E-05, A6=3.59527E-07, A8=-1.50526E-09, A10=2.61798E-12

[0173] Page 22

[0174] K=0.00000E+00, A4=-2.88584E-05, A6=4.21608E-07, A8=-1.32213E-09, A10=2.13433E-12

[0175] Page 23

[0176] K=0.00000E+00, A4=-1.63182E-05, A6=-1.42012E-07, A8=6.60115E-10

[0177] Page 24

[0178] K=0.00000E+00, A4=-1.39009E-05, A6=-1.09383E-07, A8=4.16271E-10

[0179]

[0180]

[0181]

[0182] According to the above lens parameters, the optical system of this embodiment satisfies the conditions (1) to (10), and the total length of the optical system is 99.8241 mm, and the shortest photographic distance is 234.97 mm.

[0183] Figure 8 The spherical aberration, astigmatism and distortion diagram of the optical system of this embodiment when the object distance is infinite and the imaging magnification is 1 / 40 times, and the closest focusing state is shown. Figure 8 It can be seen that the imaging performance of this embodiment is excellent.

[0184] It can be seen that the above embodiments can meet the requirements of a large-aperture internal focusing optical system having a medium-short focal length when converted to a 35mm camera, and can achieve a large aperture, small size, light weight and excellent imaging performance.

[0185] The above description is merely an embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A large-aperture internal-focus optical system, characterized by: The lens comprises a first lens group with positive optical power, a second lens group with negative optical power, and a third lens group with positive optical power, which are arranged in sequence from the object side to the image side. The first lens group includes a first lens group, an aperture stop, and a second lens group arranged in sequence from the object side to the image side; the first lens group includes at least a positive lens and a negative lens arranged in sequence from the object side to the image side; The second lens group is a single lens that can move along the optical axis for focusing; The optical system meets the following conditions: (1) -2.0<f1a / f<-0.3; (2) 0.2<D1a / L<0.6; Where f1a is the focal length of the first lens group, f is the focal length of the optical system, D1a is the length of the first lens group along the optical axis, and L is the total length of all lens elements along the optical axis from the lens surface closest to the object side to the lens surface closest to the image side.

2. The large-aperture internal-focus optical system according to claim 1, wherein: The optical system meets the following conditions: (3) 3.7<f11 / f<18.0; Where f11 is the focal length of the positive lens closest to the object side in the first lens group, and f is the focal length of the optical system.

3. The large-aperture inner-focus optical system according to claim 1, wherein: The optical system meets the following conditions: (4)-2.8<f1b / f1a<-0.6; (5) 0.6<D1b / D1a<2.8; Wherein, f1b is the focal length of the second lens group, f1a is the focal length of the first lens group; D1b is the length of the second lens group in the optical axis direction, and D1a is the length of the first lens group in the optical axis direction.

4. The large-aperture internal-focus optical system according to claim 1, wherein: The optical system meets the following conditions: (6) 0.06<Df / D<0.2; (7) Ndmax - Ndmin < 0.3; Wherein, Df is the distance on the optical axis from the lens surface closest to the image side in the first lens group to the lens surface closest to the object side in the third lens group; D is the length of the optical system from the lens surface closest to the object side to the imaging plane in the optical axis direction, that is, the total length of the optical system; Ndmax is the maximum refractive index of the lens element between the lens element closest to the image side in the first lens group and the lens element closest to the object side in the third lens group; Ndmin is the minimum refractive index of the lens element between the lens element closest to the image side in the first lens group and the lens element closest to the object side in the third lens group.

5. The large-aperture inner-focus optical system according to claim 1, wherein: The optical system meets the following conditions: (8) 0.2<D21 / D22<0.8; D21 is the distance on the optical axis from the lens surface of the second lens group closest to the image side to the lens surface of the third lens group closest to the object side when focusing at infinity. D22 is the distance on the optical axis from the lens surface of the second lens group closest to the image side to the lens surface of the third lens group closest to the image side when focusing at infinity.

6. The large-aperture internal-focusing optical system according to claim 1, wherein: The optical system meets the following conditions: (9) 2.0<L / Y<6.0; L is the total length of all lens elements along the optical axis from the lens surface closest to the object side to the lens surface closest to the image side, and Y is the maximum image height at the image plane position.

7. The large-aperture inner-focusing optical system according to claim 1, wherein: The optical system meets the following conditions: (10) 0.4<DS / D<1.0; Where DS is the distance from the aperture stop of the first lens group to the image side on the optical axis, and D is the length of the optical system from the lens surface closest to the object side to the imaging surface in the direction of the optical axis, that is, the total length of the optical system.

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