Large-aperture telephoto lens, and camera and video camera using large-aperture telephoto lens

Abstract

The invention relates to a large-aperture telephoto lens and a camera and a video camera using the same, and belongs to the technical field of optical devices, the lens sequentially comprises a positive diopter first lens group G1, a positive diopter second lens group G2, a negative diopter third lens group G3 and a positive diopter fourth lens group G4 from an object side to an image surface side; the aperture Stop is arranged between the second lens group G2 and the third lens group G3; when an object reaches a close distance from infinity, the third lens group G3 moves from the object side to the image surface side to realize focusing, and the first lens group G1, the second lens group G2 and the fourth lens group G4 are fixed. According to the lens provided by the invention, the outer diameter of the focusing group is reduced under the action of continuous light contraction of the first group G1 and the second group G2, meanwhile, the weight of the whole optical lens is reduced, and the overall length of the whole optical system is shortened.

Description

Technical Field

[0001] This invention is a large-aperture telephoto lens with an aperture of around F2 and a field of view of less than 20 degrees. It adopts an internal focusing mode and is suitable for use in autofocus optical structures for photographic lenses. It is widely used in digital cameras, camcorders, and especially in the field of interchangeable camera lenses. Background Technology

[0002] In recent years, with the improvement of optical design and the increasing selection of materials, high-performance large-aperture telephoto lenses have been continuously launched, such as the Japanese Special Edition 2020-160100. Although its optical performance is excellent, it corrects aberrations such as on-axis chromatic aberration, off-axis coma, as well as image plane curvature and astigmatism very well. It adopts a positive, negative, positive structure, with the focusing group located in the second group. Because G1A and G1B in the structure of the first group G1 are too close, the outer diameter of the glass is very large, which increases the weight of the entire optical system. At the same time, the focusing group uses 3 lens elements, which is also very heavy. It is difficult to drive with a regular stepper motor. A high-power motor must be used to drive the autofocus system well. Because the third group has an image stabilization system in the middle, the structure is composed of multiple lens elements, which makes the length of the entire optical system relatively long. Therefore, the overall optical system is relatively heavy and bulky.

[0003] There is also an earlier Japanese special license plate number 2008-145584, which also uses a three-group structure of positive, negative, and positive. However, the first group is too complex, and the lens spacing is not wide enough, resulting in many large-diameter glass lenses in the first group, making it very heavy. At the same time, the focusing group is a cemented lens, which is relatively heavy and requires a high-power motor. In addition, the third group has an image stabilization system, which results in more glass lenses in the entire optical system, increasing the weight and length, making it difficult to achieve miniaturization and weight reduction.

[0004] In addition, there is the publicly disclosed Special Application License No. 2014-211497, which also adopts a positive-negative-positive three-group structure. Although the first group uses a separate G1 a and G1 b mode with a relatively large interval, resulting in a small outer diameter of G1 b to reduce weight, the outer diameter of G1 a is very large, consisting of three large-diameter glass elements, making it very heavy. The focusing group G2 consists of two cemented lens elements (four elements in total), which is very heavy and requires a more powerful motor to drive, affecting the focusing speed. From a structural analysis perspective, its back focal length is also too long. Thus, the overall optical system is heavy and long, making it very difficult to make it lightweight and miniaturized. Summary of the Invention

[0005] To overcome the problems of heavy weight and large size of the aforementioned known large-aperture telephoto lenses, this invention provides a four-group structure: positive (G1), positive (G2), negative (G3), and positive (G4). Through the continuous light-contracting effect of the first group G1 and the second group G2, the outer diameter of the focusing group is reduced, thereby decreasing the overall weight of the optical lens and shortening the overall length of the optical system. This results in a lightweight, miniaturized large-aperture telephoto lens. Furthermore, because the focusing group G3 has a small outer diameter and is lightweight, it can be driven by a common small motor, resulting in low cost and ease of mass production.

[0006] To achieve the above objectives, the technical solution of the present invention is: a large aperture telephoto lens, which, from the object side to the image plane side, sequentially includes a first lens group G1 with positive refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with negative refractive power, and a fourth lens group G4 with positive refractive power.

[0007] The aperture stop is set between the second lens group G2 and the third lens group G3;

[0008] As the object moves from infinity to near, the third lens group G3 moves from the object side to the image plane side to achieve focus, while the first lens group G1, the second lens group G2, and the fourth lens group G4 remain stationary.

[0009] Further technology of the present invention:

[0010] Preferably, the lens satisfies conditions (1), (2), and (3):

[0011] 2.0≤|FL / F3|≤4.0 (1)

[0012] 0.4≤|F3 / F4|≤0.8 (2)

[0013] 1.0≤|F1 / F2|≤3 (3)

[0014] in,

[0015] FL: The focal distance of an optical system at infinity;

[0016] F1: Focal distance of the first lens group G1;

[0017] F2: Focal distance of the second lens group G2;

[0018] F3: Focus distance of the third focus group G3;

[0019] F4: The focal distance of the fourth focus group G4.

[0020] If the upper limit of condition 2.0≤|FL / F3|≤4.0(1) is exceeded, the refractive power of the third lens group G3 is too strong. Although it is easy to achieve close-up function and the whole optical system is conducive to miniaturization, the excessive refractive power makes it difficult to correct spherical aberration, edge coma and image plane curvature, and it is not easy to achieve the high performance design requirements. If the lower limit of condition (1) is exceeded, the refractive power of the third lens group G3 is too weak. The focusing movement from infinity to close distance will be very large, which makes it impossible to control the size of the whole optical system and makes it difficult to achieve close-up function.

[0021] If the upper limit of conditional formula 0.4≤|F3 / F4|≤0.8(2) is exceeded, the positive refractive power of the fourth lens group G4 is too strong, or the negative refractive power of the third lens group G3 is too weak, which can easily lead to a large amount of focus movement, or make it difficult to correct the aberrations caused by the excessive refractive power of the G4 lens group, thus making it difficult to achieve high performance. If the lower limit of conditional formula (2) is exceeded, the refractive power of the fourth lens group G4 is too weak, or the refractive power of the third lens group G3 is too strong. Although this is beneficial for reducing the amount of focus movement and miniaturizing the entire optical system, the aberrations generated by the third lens group G3 during focusing are difficult to be compensated by the fourth focusing group G4.

[0022] If the upper limit of condition 1.0≤|F1 / F2|≤3(3) is exceeded, the refractive power of the first lens group is too weak, the light contraction speed is too slow, which will inevitably lead to the entire light system being too long and miniaturization being difficult to achieve; if the lower limit of condition (3) is exceeded, the refractive power of the first lens group G1 is too strong. Although miniaturization is easy to achieve, various aberrations are not easy to correct because the refractive power is too strong, making it difficult to achieve the design requirements of high performance.

[0023] Preferably, the first lens group G1 is divided into a front portion G1a with positive refractive power and a rear portion G1b with negative refractive power.

[0024] Preferably, the first lens group G1 satisfies condition (4):

[0025] 0.4≤|F1a / F1b|≤1.2 (4)

[0026] in,

[0027] F1 a: The focal length of the front part G1a of the first lens group G1;

[0028] F1 b: The focal length of the rear portion G1b of the first lens group G1.

[0029] If the upper limit of the condition 0.4≤|F1a / F1b|≤1.2(4) is exceeded, the refractive power of the front part G1a of the first lens group G1 will be too weak, which will result in insignificant beam contraction, leading to a large size of the entire optical system, making it difficult to control the overall length and miniaturization impossible; if the lower limit of the condition (4) is exceeded, since the refractive power of the front part G1a of the first lens group G1 is very strong, miniaturization is easy to achieve, but various aberrations such as dispersion and spherical aberration are difficult to correct.

[0030] Preferably, the front part G1a consists of two consecutive positive lenses, and the rear part G1b consists of a positive lens A and a negative lens B, satisfying conditions (5) and (6):

[0031] 4≤FL / D1-2≤8 (5)

[0032] 40≤Vda-Vdb≤80 (6)

[0033] in,

[0034] D1-2: The interval between the first lens group G1 and the second lens group G2;

[0035] Vda: The Abbe number of the positive lens A in the rear part G1b of the first lens group G1;

[0036] Vdb: The Abbe number of the negative lens B in the rear part G1b of the first lens group G1.

[0037] If the upper limit of the condition 4≤FL / D1-2≤8(5) is exceeded, the interval between the first lens group G1 and the second lens group G2 will be too small, which will result in the outer diameter of the second lens group being too large, making it difficult to control the weight of the entire optical system; if the lower limit of the condition (5) is exceeded, although the second lens group G2 and the subsequent third lens group G3 and fourth lens group G4 can be miniaturized and the weight reduced, the length of the optical system will increase, and miniaturization will be difficult to achieve.

[0038] If the upper limit of the condition 40≤Vda-Vdb≤80(6) is exceeded, the Abbe number of the positive lens A in the rear part G1b of the first lens group G1 is too large. Although it is very beneficial for correcting dispersion, it is difficult to find such materials in reality, and it is difficult to commercialize them. If the lower limit of the condition (6) is exceeded, the difference between the Abbe numbers of the positive lens A and the negative lens B in the rear part G1b of the first lens group G1 is too small. Although the materials are easy to select, the ability to correct dispersion is weakened, which is not conducive to correcting dispersion.

[0039] Preferably, the third lens group G3 is a meniscus negative lens with the object side being convex and the image side being concave, or a cemented lens with the object side being convex and the image side being concave. When the object moves from infinity to near distance, the third lens group G3 moves from the object side to the image side to achieve focus, and satisfies conditions (7) and (8):

[0040] 3.5≤FL / D3-4≤12 (7)

[0041] 30≤FocVd≤97 (8)

[0042] in,

[0043] D3-4: The distance between the third lens group G3 and the fourth lens group G4 of the optical system at infinity;

[0044] FocVd: The Abbe value of the negative lens in the third lens G3.

[0045] If the upper limit of condition 3.5≤FL / D3-4≤12(7) is exceeded, the interval between the third lens group G3 and the fourth lens group G4 will be too small, resulting in insufficient spacing when the third lens group G3 is in focus, thus making the close-up distance relatively far; if the lower limit of condition (7) is exceeded, the interval between the third lens group G3 and the fourth lens group G4 will be too large. Although the focusing interval is sufficient and beneficial to the close-up function, the size of the entire optical system will increase, making miniaturization difficult.

[0046] If the upper limit of the condition 30≤FocVd≤97(8) is exceeded, although the Abbe number of the negative lens in the third lens group G3 is large enough and the dispersion is small enough, which is conducive to the control of dispersion, the material in reality is difficult to select. At the same time, the material with a large Abbe number has a low refractive index. For the same diopter, the surface is stronger and the weight is greater. Thus, the weight of the focusing group is also difficult to control. If the lower limit of the condition (8) is exceeded, the Abbe number of the negative lens in the third lens group is too small, which will lead to easy dispersion. During the focusing process, the chromatic aberration changes too much, which is not conducive to the optimization of close-up performance.

[0047] Preferably, the second lens group G2 includes a positive diopter lens G2a on the object side, a negative diopter lens G2b in the middle position, and a positive diopter lens G2c on the image side.

[0048] The front part G2a, the middle part G2b, and the rear part G2c are all convex surfaces; the middle part G2b and the rear part G2c are both concave surfaces.

[0049] Preferably, the second lens group G2 satisfies conditions (9), (10) and (11):

[0050] 0.8≤|F2a / F2b|≤1.5 (9)

[0051] 0.9≤|F2 / F2c|≤1.8 (10)

[0052] 0.4≤(Vd1+Vd2) / Vd3≤1.2 (11)

[0053] in,

[0054] F2: Focal distance of the second lens group G2;

[0055] F2a: The focal distance of the front part G2a on the object side of the second lens group G2;

[0056] F2b: The focal distance of the middle part G2b of the second lens group G2;

[0057] F2c: The focal distance of the rear portion of the second lens group G2 on the image side;

[0058] Vd1: Abbe number of the second lens group G2a;

[0059] Vd2: Abbe number of the second lens group G2b;

[0060] Vd3: Abbe number of the second lens group G2c.

[0061] If the upper limit of the condition 0.8≤|F2a / F2b|≤1.5(9) is exceeded, the refractive power of the front part G2a of the second lens group is too weak, or the refractive power of the middle part G2b is too strong. This will result in an insignificant beam contraction effect and an increased effective aperture of the entire group, which is not conducive to miniaturization. If the lower limit of the condition (9) is exceeded, the refractive power of the front part G2a of the second lens group G2 will be too strong. Although this is beneficial to miniaturization, it will generate too many aberrations that are difficult to correct well, and it will be difficult to achieve high performance.

[0062] If the upper limit of the condition 0.9≤|F2 / F2c|≤1.8(10) is exceeded, the refractive power of the rear part G2c of the second lens group G2 will be too strong. Although this is beneficial for miniaturization, too many aberrations will be generated and they will not be easy to correct, making it difficult to achieve high performance. If the lower limit of the condition is exceeded, the refractive power of the rear part G2c of the second lens group G2 will be too weak. Although the aberrations will be easy to correct and high performance will be achieved, the beam contraction will be relatively weak, resulting in a relatively large outer diameter of the third lens group behind the second lens group. At the same time, it will be difficult to miniaturize the entire optical system.

[0063] If the Abbe number of the lens in the rear part of the second lens group G2 is too small, it is easy to produce dispersion, which is not conducive to the high-performance design effect. If the Abbe number of the lens in the rear part of the second lens group G2 is too large, it is difficult to find in real glass materials, and it is not easy to commercialize and mass-produce.

[0064] The present invention also provides a camera having the aforementioned large aperture telephoto lens.

[0065] The present invention also provides a camera having the aforementioned large aperture telephoto lens.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] The beneficial effects of this invention are that existing technologies struggle to reduce the overall size of the optical system in a large-aperture telephoto lens, resulting in a heavy system, especially since the focusing group consists of multiple lenses, making it large and heavy. This requires a powerful motor to achieve high-speed focusing. This invention, by continuously shrinking the beam diameter of the first lens group G1 and the second lens group G2, reduces the diameter of the third lens group G3 in the focusing group. Simultaneously, the lens structure is simple and lightweight, allowing for high-speed focusing with a moderately powerful motor. Furthermore, the sufficient spacing D3-4 between the third and fourth lens groups provides ample space for the focusing group to move at close range, effectively enabling close-up photography. Ultimately, this achieves a small, lightweight, and easily mass-producible large-aperture telephoto lens, making it highly feasible for mass production and widespread adoption. Attached Figure Description

[0068] Figure 1 This is an optical structure diagram of Embodiment 1 of the present invention;

[0069] Figure 2 These are the spherical aberrations, field curvature aberrations, distortion aberrations, and magnification chromatic aberrations at infinity and near distance in Example 1;

[0070] Figure 3 This is an optical structure diagram of Embodiment 2 of the present invention;

[0071] Figure 4 These are the spherical aberrations, field curvature aberrations, distortion aberrations, and magnification chromatic aberrations at infinity and near distance in Example 2;

[0072] Figure 5 This is an optical structure diagram of Embodiment 3 of the present invention;

[0073] Figure 6 These are the spherical aberrations, field curvature aberrations, distortion aberrations, and magnification chromatic aberrations at infinity and near distance in Example 3. Detailed Implementation

[0074] The present invention will be further described below with reference to the accompanying drawings and embodiments. The present invention includes, but is not limited to, the following embodiments.

[0075] Example 1: As Figure 1 As shown, from the object side to the image plane side, it consists of four lens groups in total: a positive refractive power first lens group G1, a positive refractive power second lens group G2, a negative refractive power third lens group G3, and a positive refractive power G4. The first lens group G1 consists of a front part G1a and a rear part G1b. The second lens group consists of a front part G2a, a middle part G2b, and a rear part G2c. When the object moves from infinity to near, the third lens group G3 moves to achieve focus, while the first lens group G1, the second lens group G2, and the fourth lens group G4 remain stationary.

[0076] Spherical aberration, field curvature aberration, distortion aberration, and magnification chromatic aberration at infinity and near distance in Example 1 are as follows: Figure 2 As shown.

[0077] The data for Example 1 are as follows:

[0078] R (mm): Radius of curvature of each surface

[0079] D (mm): Spacing between lenses and lens thickness

[0080] Nd: The refractive index of various glasses along the d-line.

[0081] Vd: Abbe number of glass

[0082] Focal length: 194.5224

[0083] FNO: 2.06

[0084] Half-stroke angle ω: 6.296°.

[0085]

[0086]

[0087]

[0088] Example 2: Figure 3As shown, from the object side to the image plane side, it consists of four lens groups in total: a positive refractive power first lens group G1, a positive refractive power second lens group G2, a negative refractive power third lens group G3, and a positive refractive power G4. The first lens group G1 consists of a front part G1a and a rear part G1b. The second lens group consists of a front part G2a, a middle part G2b, and a rear part G2c. When the object moves from infinity to near, the third lens group G3 moves to achieve focus, while the first lens group G1, the second lens group G2, and the fourth lens group G4 remain stationary.

[0089] Example 2: Spherical aberration, field curvature aberration, distortion aberration, and magnification chromatic aberration at infinity and near distances, such as... Figure 4 As shown.

[0090] The data for Example 2 are as follows:

[0091] R (mm): Radius of curvature of each surface

[0092] D (mm): Spacing between lenses and lens thickness

[0093] Nd: The refractive index of various glasses along the d-line.

[0094] Vd: Abbe number of glass

[0095] Half-stroke angle ω: 6.303°.

[0096] NS R D Nd ABV 1 168.8618 7.7500 1.92286 20.88 2 1328.2996 1.9605 3 102.2270 9.7000 1.45860 90.19 4 501.0536 6.1762 5 69.5912 17.0000 1.49700 81.61 6 -252.7420 1.8000 1.89663 22.56 7 64.7220 35.2569 8 79.8776 6.9842 1.87022 21.86 9 -346.0254 0.1500 10 151.5812 1.2500 1.78225 24.07 11 37.2175 8.4354 12 42.4578 4.8000 1.72916 54.67 13 98.5474 5.5519 14STOP inf D(14) 15 178.4986 1.0000 1.61467 62.96 16 35.9698 D(16) 17 644.0417 1.0000 1.49700 81.61 18 103.3711 2.0000 19 81.4531 5.8000 1.77236 33.40 20 -36.0146 1.0000 1.64378 30.70 21 566.4761 3.0000 22 inf 2.0000 1.51680 64.20 23 inf BF

[0097]

[0098]

[0099] Example 3: As Figure 5 As shown, from the object side to the image plane side, it consists of four lens groups in total: a positive refractive power first lens group G1, a positive refractive power second lens group G2, a negative refractive power third lens group G3, and a positive refractive power G4. The first lens group G1 consists of a front part G1a and a rear part G1b. The second lens group consists of a front part G2a, a middle part G2b, and a rear part G2c. When the object moves from infinity to near, the third lens group G3 moves to achieve focus, while the first lens group G1, the second lens group G2, and the fourth lens group G4 remain stationary.

[0100] Example 3 shows spherical aberration, field curvature aberration, distortion aberration, and magnification chromatic aberration at infinity and near distances, such as... Figure 6 As shown.

[0101] The data for Example 3 are as follows:

[0102] R (mm): Radius of curvature of each surface

[0103] D (mm): Spacing between lenses and lens thickness

[0104] Nd: The refractive index of various glasses along the d-line.

[0105] Vd: Abbe number of glass

[0106] Focal length: 194.4765

[0107] FNO: 2.06

[0108] Half-stroke angle ω: 6.278°.

[0109]

[0110]

[0111]

[0112] (Conditional Summary Table)

[0113]

[0114] The large-aperture telephoto lens provided in any of the above embodiments can be used in cameras and video cameras.

[0115] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A large-aperture telephoto lens, characterized in that, From the object side to the image plane side, the lenses consist of a positive refractive power first lens group G1, a positive refractive power second lens group G2, a negative refractive power third lens group G3, and a positive refractive power fourth lens group G4. The aperture stop is set between the second lens group G2 and the third lens group G3; As the object moves from infinity to near, the third lens group G3 moves from the object side to the image plane side to achieve focus, while the first lens group G1, the second lens group G2, and the fourth lens group G4 remain stationary.

2. The large aperture telephoto lens according to claim 1, characterized in that, The lens satisfies conditions (1), (2), and (3): 2.0≤|FL / F3|≤4.0 (1) 0.4≤|F3 / F4|≤0.8 (2) 1.0≤|F1 / F2|≤3 (3) in, FL: The focal distance of an optical system at infinity; F1: Focal distance of the first lens group G1; F2: Focal distance of the second lens group G2; F3: Focus distance of the third focus group G3; F4: The focal distance of the fourth focus group G4.

3. A large aperture telephoto lens according to claim 2, characterized in that, The first lens group G1 is divided into a positive refractive power front part G1a and a negative refractive power rear part G1b.

4. A large aperture telephoto lens according to claim 3, characterized in that, The first lens group G1 satisfies condition (4): 0.4≤|F1 a / F1 b|≤1.2 (4) in, F1 a: The focal length of the front part G1 a of the first lens group G1; F1 b: The focal length of the rear portion G1 b of the first lens group G1.

5. A large aperture telephoto lens according to claim 3, characterized in that, The front part G1a consists of two consecutive positive lenses, and the rear part G1b consists of a positive lens A and a negative lens B, satisfying conditions (5) and (6): 4≤FL / D1-2≤8 (5) 40≤Vda-Vdb≤80 (6) in, D1-2: The interval between the first lens group G1 and the second lens group G2; Vda: The Abbe number of the positive lens A in the rear part G1b of the first lens group G1; Vdb: The Abbe number of the negative lens B in the rear part G1b of the first lens group G1.

6. A large aperture telephoto lens according to claim 2, characterized in that, The third lens group G3 is a meniscus negative lens with the object side being convex and the image side being concave, or a cemented lens with the object side being convex and the image side being concave. When the object moves from infinity to near distance, the third lens group G3 moves from the object side to the image side to achieve focus, and satisfies conditions (7) and (8): 3.5≤FL / D3-4≤12 (7) 30≤FocVd≤97 (8) in, D3-4: The distance between the third lens group G3 and the fourth lens group G4 of the optical system at infinity; FocVd: The Abbe value of the negative lens in the third lens G3.

7. A large aperture telephoto lens according to claim 1, characterized in that, The second lens group G2 includes a positive diopter lens G2a on the object side, a negative diopter lens G2b in the middle position, and a positive diopter lens G2c on the image side. The front part G2a, the middle part G2b, and the rear part G2c are all convex surfaces; the middle part G2b and the rear part G2c are both concave surfaces.

8. A large aperture telephoto lens according to claim 7, characterized in that, The second lens group G2 satisfies conditions (9), (10) and (11): 0.8≤|F2a / F2b|≤1.5 (9) 0.9≤|F2 / F2c|≤1.8 (10) 0.4≤(Vd1+Vd2) / Vd3≤1.2 (11) in, F2: Focal distance of the second lens group G2; F2a: The focal distance of the front part G2a on the object side of the second lens group G2; F2b: The focal distance of the middle part G2b of the second lens group G2; F2c: The focal distance of the rear portion of the second lens group G2 on the image side; Vd1: Abbe number of the second lens group G2a; Vd2: Abbe number of the second lens group G2b; Vd3: Abbe number of the second lens group G2c.

9. A camera having a large aperture telephoto lens as described in any one of claims 1-9.

10. A camera having a large aperture telephoto lens as described in any one of claims 1-9.

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