Telephoto zoom lens

Abstract

This invention discloses a telephoto zoom lens, which, from the object side to the image plane side, sequentially comprises a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with positive refractive power. The first lens group G1 consists of a front group G1a with negative refractive power, a middle group G1b with positive refractive power, and a rear group G1c with positive refractive power. When the object moves from infinity to near, the middle group G1b with positive refractive power moves from the object side to the image plane side to achieve focus. The fifth lens group G5 consists of two parts with positive and negative refractive power; when adjusting the back focal length (BF), the front part of the fifth lens group G5, the positive refractive power lens G5a, is moved. This invention is convenient and quick to use, providing a telephoto zoom lens with a simple structure, small size, low cost, high performance, a zoom ratio exceeding 2x, and a telephoto viewing angle of less than 8°.

Description

Technical Field

[0001] This invention relates to the field of cinema lens technology, and particularly to telephoto zoom lenses. Background Technology

[0002] Currently, most known telephoto zoom cinema lenses use a structure where the first group of lenses with positive refractive power is fixed, combined with several moving groups. For example, Japanese Patent No. 2012-182810 describes a structure consisting of a positive refractive power first group, a negative refractive power second group, a negative refractive power third group, and a positive refractive power fourth group, starting from one side of the object. During zooming, the first and fourth groups are fixed, and the second and third groups are moved to achieve focus. When focusing, the rear part of the first group is moved. Because the first group is positive, consisting of two lens groups with positive refractive power, the entrance pupil distance is relatively far. Simultaneously, the refractive power of the focusing group is relatively weak, resulting in a large focusing movement. This leads to a bulky lens. Furthermore, during zooming, only two groups move, resulting in a large movement amount and making image plane curvature correction relatively difficult.

[0003] There is also the publicly known Japanese Patent No. 4880498, which, starting from one side of the object, consists of a first group of positive refractive power, a second group of negative refractive power, a third group of positive refractive power, and a fourth group of positive refractive power. During zooming, the first and fourth groups are fixed, and zooming is achieved by moving the second and third groups. The first group consists of two parts; when focusing, the rear part of the first group is moved. While the overall structure allows for miniaturization, the first group is composed of two parts, resulting in a significant change in the focal length of the entire optical system when focusing, leading to a large change in the angle of view. In other words, there is a significant focus breathing effect when focusing, making it unsuitable for professional video shooting needs. Summary of the Invention

[0004] The main objective of this invention is to provide a telephoto zoom lens that can effectively solve the problem that although the overall structure can achieve a miniaturized design, the first structure consists of two parts, and when focusing, the focal length of the entire optical system changes greatly, resulting in a large change in the angle of view. In other words, when focusing, there is a large breathing effect, which is not suitable for professional video shooting needs.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The telephoto zoom lens, from the object side to the image plane side, includes a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with positive refractive power.

[0007] The first lens group G1 consists of a negative refractive power front group G1a, a positive refractive power middle group G1b, and a positive refractive power rear group G1c.

[0008] When an object moves from infinity to near, the positive diopter intermediate group G1b of the first lens group G1 moves from the object side to the image plane side to achieve focus; the fifth lens group G5 consists of positive and negative diopter parts. When adjusting the back focal length BF, the front group G5a of the fifth lens group G5 is moved to achieve focus, and the following conditions (1), (2) and (3) are satisfied.

[0009] 0.5 ≤F1b / F1 ≤2.5 (1);

[0010] 0.2 ≤|F1bc / F1a|≤1 (2);

[0011] 1.0≤|F1a / Fw|≤2.5 (3);

[0012] in,

[0013] F1: The focal length of the first lens group G1 at infinity;

[0014] F1a: The focal length of the front group G1a of the first lens group G1;

[0015] F1b: The focal length of the middle group G1b of the first lens group G1;

[0016] F1bc: The combined focal length of the middle group G1b and the rear group G1c of the first lens group G1 at infinity.

[0017] Fw: The focal length of the entire optical system at infinity at the wide-angle end.

[0018] The fifth lens group G5 consists of two parts: the front group G5a and the rear group G5b. The focal length of the front group G5a is F5a. When adjusting the rear focal length BF, the front group G5a is moved to achieve fine adjustment, while the rear group G5b remains fixed and satisfies conditions (4) and (5).

[0019] 0.5 ≤F5a / WL≤2.0 (4;

[0020] 0.2≤ΔBF / G5S≤1.5 (5;

[0021] in,

[0022] F5a: The focal length of the front group G5a in the fifth lens group G5;

[0023] G5S: Adjusts the amount of movement of the front group G5a of the fifth lens group G5 after adjusting the focal length BF.

[0024] ΔBF: The change in back focal length BF when the front group G5a is moved to G5S.

[0025] When zooming from the wide-angle end to the telephoto end, the second lens group G2 moves from the object side to the image side by a distance of S2, which is used to achieve miniaturization while meeting high performance requirements; the third lens group G3 and the fourth lens group G4 need to move in conjunction with the second lens group G2 to achieve high performance requirements, while correcting spherical aberration and image plane curvature aberration, satisfying condition (6).

[0026] 0.3≤(S2+S3+S4) / Fw≤1.2 (6);

[0027] in,

[0028] S2: The amount of movement of the second lens group G2 when zooming from the wide-angle end to the telephoto end;

[0029] S3: The amount of movement of the third lens group G3 when zooming from the wide-angle end to the telephoto end;

[0030] S4: The amount of movement of the fourth lens group G4 when zooming from the wide-angle end to the telephoto end;

[0031] Fw: The focal length of the entire optical system at infinity.

[0032] If the upper limit of the condition 0.5≤F1b / F1≤2.5(1) is exceeded, the refractive power of F1b is too weak. If close-range shooting is achieved, the movement of the focusing lens group G1b will be too large, which will lead to an increase in the volume of the first lens group G1, making it difficult to achieve the miniaturization requirement. If the lower limit of the condition (1) is exceeded, the refractive power of the focusing lens group G1b is very strong. Although it is easier to achieve the miniaturization requirement, the strong refractive power will lead to a sharp increase in a series of aberrations such as spherical aberration, chromatic aberration, and coma, making it difficult to achieve the high performance requirement.

[0033] If the upper limit of condition 0.2≤|F1bc / F1a|≤1(2) is exceeded, the negative refractive power of G1a in the first lens group G1 is too strong. Although it is easy to achieve miniaturization at the wide-angle end, it will make it difficult to achieve the requirement of less than 8° at the telephoto end, which will lead to an increase in the amount of zoom group movement and an increase in the volume of the entire optical system. If the lower limit of condition (2) is exceeded, the combined refractive power of the middle part G1b and the rear part G1c in the first lens group G1 is very strong. Although it is easy to achieve a zoom ratio of more than 2 times, the refractive power of the front part G1a is weak, which will lead to an increase in the outer diameter of the foremost lens of the first lens group G1 at the wide-angle end, resulting in a large outer diameter of the entire optical system.

[0034] If the upper limit of condition 1.0≤|F1a / Fw|≤2.5(3) is exceeded, the refractive power of the front part G1a of the first lens group G1 will be too weak, or the refractive power of the wide-angle end of the entire optical group will be too strong, which will cause the outer diameter of the first lens group G1 to become very thick, making it difficult to achieve the miniaturization requirement. If the lower limit of condition (3) is exceeded, although it is easy to achieve the miniaturization design requirement of the first lens group G1, it becomes more difficult to achieve the design requirement of a telephoto angle of less than 8°. If this is to be achieved, the amount of movement of the second lens group G2, the third lens group G3, and the fourth lens group G4 will increase significantly, resulting in a significant increase in the axial length of the lens, which will also make it difficult to achieve the miniaturization design requirement.

[0035] If the upper limit of condition 0.5≤F5a / WL≤2.0(4) is exceeded, the refractive power of the front part G5a of the 5th lens group is too weak, and the amount of movement required to adjust the focal length BF is too large, which will lead to insensitivity. At the same time, the space at the rear end is limited, making the structural design difficult. If the lower limit of condition (4) is exceeded, the refractive power of the front part G5a of the 5th lens group is too strong, and the amount of movement required to adjust the focal length BF is too small, which will lead to too much change in performance during the adjustment process, making it impossible to achieve the high performance requirements.

[0036] If the upper limit of the condition 0.2≤ΔBF / G5S≤1.5(5) is exceeded, the effect of adjusting the focal length of the fifth lens group G5a is too sensitive, which can easily lead to excessive performance changes and make it difficult to achieve the high performance requirement. If the lower limit of the condition (5) is exceeded, the sensitivity of the focal length BF of the fifth lens group G5a after adjustment is too weak, which can lead to excessive movement and make it difficult to implement in terms of structure.

[0037] If the upper limit of condition 0.3≤(S2+S3+S4) / Fw≤1.2(6) is exceeded, the movement of the second lens group G2, the third lens group G3, and the fourth lens group G4 will be too large, or the focal length at the wide-angle end will be too short, and the angle of view will be too wide, which will result in the entire optical system being too large and unable to meet the requirements of miniaturization design. If the lower limit of condition (5) is exceeded, the movement of the second lens group G2, the third lens group G3, and the fourth lens group G4 will be too small. Although the requirements of miniaturization design can be met, it will be difficult to meet the requirements of zoom ratio design of more than 2 times.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] This telephoto zoom lens offers a simple, compact, low-cost, high-performance zoom ratio exceeding 2x and a telephoto end angle of view of less than 8°. Attached Figure Description

[0040] Figure 1This is a schematic diagram of a telephoto zoom lens provided in Embodiment 1 of the present invention.

[0041] Figure 2 For example, at infinity and the closest photographic distance, spherical aberration, field curvature aberration, distortion aberration, and magnification chromatic aberration are considered.

[0042] Figure 3 This is a schematic diagram of a telephoto zoom lens provided in Embodiment 2 of the present invention.

[0043] Figure 4 For example 2, the spherical aberration, field curvature aberration, distortion aberration, and magnification chromatic aberration are at infinity and the closest photographic distance. Detailed Implementation

[0044] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0045] Example 1

[0046] like Figure 1 As shown, the telephoto zoom lens, from the object side to the image plane side, includes a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with positive refractive power. When zooming from the wide-angle end to the telephoto end, the first lens group G1 is fixed, the second lens group G2 moves from the object side to the image plane side by a movement amount of S2, the third lens group G3 first moves from the object side to the image plane direction, then reverses midway and moves from the image side to the object side by a total movement amount of S3, and the fourth lens group G4 moves from the image plane side to the object side.

[0047] The first lens group G1 consists of a negative refractive power front group G1a, a positive refractive power middle group G1b, and a positive refractive power rear group G1c.

[0048] When an object moves from infinity to near, the positive diopter intermediate group G1b of the first lens group G1 moves from the object side to the image plane side to achieve focus; the fifth lens group G5 consists of positive and negative diopter parts. When adjusting the back focal length BF, the front part of the fifth lens group G5, the positive diopter lens G5a, is moved to adjust the amount of change in the back focal length BF.

[0049] Example 1: Spherical aberration, field curvature aberration, distortion aberration, and magnification chromatic aberration at infinity and closest photographic distance, as shown below. Figure 2 As shown.

[0050] Focal distance: 51.84~75.014~124.93;

[0051] Fno: 2.85~2.85~2.85;

[0052] Half-angle ω: 17.19~11.61~6.834;

[0053] NS R D Nd ABV 1 -429.6428 1.0000 1.48749 70.44 2 159.0735 3.5212 3 -121.3602 1.0000 1.72916 57.00 4 476.1346 D（4） 5 181.3634 4.7000 1.69680 58.00 6 -135.2407 0.1500 7 213.6949 3.5000 1.67845 57.72 8 -318.0269 D（8） 9 -4929.3261 1.0000 1.87779 30.70 10 57.4900 7.3000 1.49700 81.61 11 -174.0858 0.1500 12 52.0902 5.0000 1.83481 44.00 13 183.0073 D（13） 14 -439.9782 0.8000 1.85817 38.82 15 22.3067 3.7000 1.92286 20.88 16 55.7440 3.2327 17 -41.1893 0.7000 1.49700 81.61 18 70.3952 D（18） 19 39.6859 0.8000 1.89336 30.34 20 24.4131 6.0450 1.49700 81.61 21 -106.9780 2.6500 22 STOP INF D（22） 23 22.8566 6.5000 1.49700 81.61 24 186.1401 14.6642 25 56.6854 3.2000 1.69680 59.00 26 226.1973 D（26） 27 263.0000 2.3000 1.84666 23.78 28 -263.0000 D（28） 29 -18.1385 0.8000 1.90366 31.31 30 -40.0525 1.0000 31 INF 2.0000 1.51680 64.20 32 INF BF

[0054] F 51.8398 75.0143 124.9258 0.02 times 0.02 times 0.02 times D（4） 0.8916 0.8916 0.8916 3.7010 2.9018 2.0827 D（8） 11.9477 11.9477 11.9477 9.1383 9.9375 10.7566 D（13） 7.7474 21.3385 35.0783 7.7474 21.3385 35.0783 D（18） 23.1464 16.0611 0.7000 23.1464 16.0611 0.7000 D（22） 8.5000 1.5388 2.8845 8.5000 1.5388 2.8845 D（26） 1.2562 1.7116 1.9872 1.2562 1.7116 1.9872 D（28） 4.0390 4.0390 4.0390 4.0390 4.0390 4.0390 BF 32.4614 32.4614 32.4614 32.4614 32.4614 32.4614

[0055] D（26）+0.2 1.4562 1.9116 2.1872 1.4562 1.9116 2.1872 D（28）-0.2 3.8390 3.8390 3.8390 3.8390 3.8390 3.8390 BF 32.6661 32.6661 32.6661 32.6661 32.6661 32.6661

[0056] Where R (mm): the radius of curvature of each surface;

[0057] D (mm): Spacing between lenses and lens thickness;

[0058] Nd: The refractive index of each glass along the d-line;

[0059] Vd: Abbe number of glass.

[0060] The adjustment amount of the front part G5a in the fifth lens group G5 is: G5S = +0.2;

[0061] The change in back focal length is: ΔBF = 32.6661 - 32.4614 = +0.2047;

[0062] D（26）-0.2 1.0562 1.15116 1.7872 1.0562 1.5116 1.7872 D（28）+0.2 4.2390 4.2390 4.2390 4.2390 4.2390 4.2390 BF 32.2567 32.2567 32.2567 32.2567 32.2567 32.2567

[0063] The adjustment amount of the front part G5a in the fifth lens group G5 is: G5S = -0.2;

[0064] The change in back focal length is: ΔBF = 32.2567 - 32.4614 = -0.2049.

[0065] Example 2

[0066] like Figure 3 As shown, the telephoto zoom lens, from the object side to the image plane side, includes a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with positive refractive power. When zooming from the wide-angle end to the telephoto end, the first lens group G1 is fixed, the second lens group G2 moves from the object side to the image plane side by a movement amount of S2, the third lens group G3 first moves from the object side to the image plane direction, then reverses midway and moves from the image side to the object side by a total movement amount of S3, and the fourth lens group G4 moves from the image plane side to the object side.

[0067] The first lens group G1 consists of a negative refractive power front group G1a, a positive refractive power middle group G1b, and a positive refractive power rear group G1c.

[0068] When an object moves from infinity to near, the positive diopter intermediate group G1b of the first lens group G1 moves from the object side to the image plane side to achieve focus; the fifth lens group G5 consists of positive and negative diopter parts. When adjusting the back focal length BF, the front part of the fifth lens group G5, the positive diopter lens G5a, is moved to adjust the amount of change in the back focal length BF.

[0069] Example 2: Spherical aberration, field curvature aberration, distortion aberration, and magnification chromatic aberration at infinity and closest photographic distance, as shown below. Figure 4 As shown.

[0070] Focal distance: 77.057~115.025~173.27;

[0071] Fno: 2.85~2.85~2.85;

[0072] Half-angle ω: 16.194~10.615~6.947;

[0073] NS R D Nd ABV 1 -772.3650 1.3000 1.53842 81.25 2 209.7398 5.0244 3 -160.2225 1.3000 1.61275 66.00 4 973.1959 D（4） 5 236.9120 6.0000 1.68989 60.00 6 -218.3348 0.1500 7 506.7265 4.3000 1.49700 81.61 8 -327.1846 D（8） 9 643.0304 1.3000 1.90366 31.31 10 77.4928 8.7000 1.49700 81.61 11 -372.2497 0.2000 12 77.1755 5.7500 1.88300 40.80 13 224.4428 D（13） 14 -413.7540 0.9000 1.88012 37.00 15 42.0564 4.7000 1.92286 20.88 16 133.5895 3.5639 17 -79.4245 0.7999 1.49700 81.61 18 106.3677 D（18） 19 76.5575 0.9000 1.90366 31.31 20 37.8373 6.5000 1.49700 81.61 21 -2832.1773 0.1500 22 83.5038 2.5000 1.65678 59.29 23 180.2637 3.0000 24 STOP 0.0000 D（24） 25 41.1984 8.0000 1.49700 81.61 26 -254.9109 31.5797 27 140.4972 3.0000 1.91403 23.32 28 -1143.1847 D（28） 29 500.0000 2.5000 1.71774 55.29 30 -500.0000 D（30） 31 -30.5671 1.0000 1.69895 30.05 32 -213.3980 0.5000 33 INF 2.0000 1.51680 64.20 34 INF BF

[0074] F 77.0570 115.0252 173.2715 0.02 times 0.02 times 0.02 times D（4） 0.8000 0.8000 0.8000 4.9505 3.6722 2.6975 D（8） 21.8573 21.8573 21.8573 17.7067 18.9850 19.9598 D（13） 12.1586 36.0522 56.6321 12.1586 36.0522 56.6321 D（18） 40.5078 23.2526 0.8000 40.5078 23.2526 0.8000 D（24） 10.0040 1.8748 3.4434 10.0040 1.8748 3.4434 D（28） 1.4500 2.9408 3.2449 1.4500 2.9408 3.2449 D（30） 4.8036 4.8036 4.8036 4.8036 4.8036 4.8036 BF 44.6318 44.6318 44.6318 44.6318 44.6318 44.6318

[0075] D（28）+0.2 1.6500 3.1408 3.4449 1.6500 3.1408 3.4449 D（30）-0.2 4.6036 4.6036 4.6036 4.6036 4.6036 4.6036 BF 44.7531 44.7531 44.7531 44.7531 44.7531 44.7531

[0076] Where R (mm): the radius of curvature of each surface;

[0077] D (mm): Spacing between lenses and lens thickness;

[0078] Nd: The refractive index of each glass along the d-line;

[0079] Vd: Abbe number of glass.

[0080] The adjustment amount of the front part G5a in the fifth lens group G5 is: G5S = +0.2;

[0081] The change in back focal length is: ΔBF = 44.7531 - 44.6318 = +0.1213;

[0082] D（28）-0.2 1.2500 2.7408 3.0449 1.2500 2.7408 3.0449 D（30）+0.2 5.0036 5.0036 5.0036 5.0036 5.0036 5.0036 BF 44.5102 44.5102 44.5102 44.5102 44.5102 44.5102

[0083] The adjustment amount of the front part G5a in the fifth lens group G5 is: G5S = -0.2;

[0084] The change in back focal length is: ΔBF = 44.5102 - 44.6318 = -0.1216.

[0085] Conditional summary table:

[0086] Example 1 Example 2 Conditional expression (1): 0.5≤F1b / F1≤2.5 0.940 2.080 Condition (2): 0.2≤|F1bc / F1a|≤1 0.603 0.395 Condition (3): 1.0 ≤ |F1a / Fw| ≤ 2.5 1.625 1.586 Condition (4): 0.5 ≤ F5a / WL ≤ 2.0 0.940 1.442 Conditional expression (5): 0.2≤ΔBF / G5S≤1.5 1.024 0.502 Condition (6): 0.3 ≤ (S2 + S3 + S4) / Fw ≤ 1.2 0.637 0.663

[0087] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A telephoto zoom lens, characterized in that, From the object side to the image plane side, the lens group consists of a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with positive refractive power. The first lens group G1 consists of a negative refractive power front group G1a, a positive refractive power middle group G1b, and a positive refractive power rear group G1c. When an object moves from infinity to near, the positive diopter intermediate group G1b of the first lens group G1 moves from the object side to the image plane side to achieve focus; the fifth lens group G5 consists of positive and negative diopter parts. When adjusting the back focal length BF, the front group G5a of the fifth lens group G5 is moved to achieve focus, and the following conditions (1), (2) and (3) are satisfied. 0.5≤F1b / F1≤2.5 (1); 0.2≤|F1bc / F1a|≤1 (2); 1.0≤|F1a / Fw|≤2.5 (3); in, F1: The focal length of the first lens group G1 at infinity; F1a: The focal length of the front group G1a of the first lens group G1; F1b: The focal length of the middle group G1b of the first lens group G1; F1bc: The combined focal length of the middle group G1b and the rear group G1c of the first lens group G1 at infinity. Fw: The focal length of the entire optical system at infinity at the wide-angle end; The fifth lens group G5 consists of two parts: the front group G5a and the rear group G5b. The focal length of the front group G5a is F5a. When adjusting the rear focal length BF, the front group G5a is moved to achieve fine adjustment, while the rear group G5b remains fixed and satisfies conditions (4) and (5). 0.5≤F5a / WL≤2.0 (4); 0.2≤ΔBF / G5S≤1.5 (5); in, F5a: The focal length of the front group G5a in the fifth lens group G5; G5S: Adjusts the amount of movement of the front group G5a of the fifth lens group G5 after adjusting the focal length BF. ΔBF: The change in back focal length BF when the front group G5a is moved to G5S.

2. The telephoto zoom lens according to claim 1, characterized in that: When zooming from the wide-angle end to the telephoto end, the second lens group G2 moves from the object side to the image side by a distance of S2, which is used to achieve miniaturization while meeting high performance requirements; the third lens group G3 and the fourth lens group G4 need to move in conjunction with the second lens group G2 to achieve high performance requirements, while correcting spherical aberration and image plane curvature aberration, satisfying condition (6). 0.3≤(S2+S3+S4) / Fw≤1.2 (6); in, S2: The amount of movement of the second lens group G2 when zooming from the wide-angle end to the telephoto end; S3: The amount of movement of the third lens group G3 when zooming from the wide-angle end to the telephoto end; S4: The amount of movement of the fourth lens group G4 when zooming from the wide-angle end to the telephoto end; Fw: The focal length of the entire optical system at infinity.

Images