wide-angle zoom lens

Abstract

The present invention discloses a wide-angle zoom lens, which comprises, from the object side to the image side, 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 comprises a front lens group G1a with negative refractive power, a middle lens group G1b with positive refractive power, and a rear lens group G1c with positive refractive power. When an object moves from infinity to a close distance, the middle lens group G1b with positive refractive power of the first lens group G1 moves from the object side to the image side to achieve focusing. The present invention is convenient and quick to use, and can provide a compact, high-performance, low-cost wide-angle zoom lens with a wide-angle end field of view exceeding 70° and a zoom ratio greater than 2x.

Description

Technical Field

[0001] The present invention relates to the technical field of movie lenses, and in particular to a wide-angle zoom lens. Background Art

[0002] At present, most of the known zoom movie lenses are fixed with a first group with positive refractive power, and are combined with several moving groups. For example, the well-known Japanese Patent No. 2015-4917, starting from the object side, when zooming, the first group with positive refractive power is fixed, and the second group with negative refractive power, the third group with negative refractive power, the fourth group with positive refractive power, and the fixed fifth group with positive refractive power are moved respectively. When the object moves from infinity to close distance, the focusing group is the middle part of the first group, which moves toward the image plane to focus. The field of view at the wide-angle end also exceeds 70°, but the focal length distribution of the first group is relatively gentle, resulting in an excessively large volume, making it difficult to achieve a miniaturized effect. In addition, the structure of the fifth group is complex. When the mount accuracy of the matching body is inaccurate, it is necessary to adjust the back focus by means of gaskets, etc., which is very inconvenient.

[0003] There is also the well-known Japanese Patent No. 2020-160264, which consists of a positive refractive power group 1, a negative refractive power group 2, a negative refractive power group 3, a positive refractive power group 4, and a positive refractive power group 5, starting from the object side. When zooming, the first and fifth groups are fixed, and zooming is achieved by moving the second, third, and fourth groups. The field of view at the wide-angle end exceeds 70°. In order to achieve the wide-angle effect, the structure of the first group is complex, resulting in a large volume, which makes it difficult to achieve miniaturization requirements. At the same time, the fifth group has a complex structure and cannot realize the back focus adjustment function. When the camera mount accuracy is inaccurate, the back focus needs to be adjusted through traditional gaskets, which is very inconvenient.

[0004] Although the above structure achieves a field of view of more than 70°, high performance, and wide-angle zoom, it has disadvantages such as being too complex, resulting in a large size, and using aspherical lenses, which are difficult to manufacture and expensive. In addition, due to the complex structure of the last group, the function of optically adjusting the back focal length cannot be realized. When the back focal length is inaccurate, it needs to be adjusted through traditional shims, which is very inconvenient. Summary of the Invention

[0005] The main purpose of the present invention is to provide a wide-angle zoom lens that can effectively solve the problems of the lens structure being too complex, resulting in a large size, and the use of aspherical lenses, which makes manufacturing difficult and costly.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A wide-angle zoom lens comprising, from the object side to the image side, 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;

[0008] The first lens group G1 is composed 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 a close distance, the positive refractive power middle group G1b of the first lens group G1 moves from the object side to the image side to achieve focus, and the following conditions (1), (2), and (3) are satisfied:

[0009] 0.3≤|F1a / F1|≤1 (1);

[0010] 1≤F1 / Fw≤3 (2);

[0011] 8≤WL / (tan(ωw)×WI)≤16 (3);

[0012] in,

[0013] WL: The total optical length of the lens (the distance from the first surface on the object side to the image plane);

[0014] F1: focal length of the first lens group G1 at infinity;

[0015] F1a: focal length of the front lens group G1a of the first lens group G1;

[0016] Fw: focal length of the entire optical system at the wide-angle end at infinity;

[0017] ωw: half field of view at the wide-angle end;

[0018] WI: Maximum paraxial image height at the wide-angle end (WI = tan(ωw) × Fw).

[0019] Preferably, the first lens group G1 has a focal length of F1 at infinity, the negative refractive power front group G1a consists of three negative lenses with a focal length of F1a, and the middle group G1b consists of two positive lenses with a focal length of F1b, and satisfies conditional formula (4);

[0020] 0.3≤|F1a / F1bc| ≤1.2 (4);

[0021] in,

[0022] F1a: focal length of the front lens group G1a in the first lens group G1;

[0023] F1bc: the combined focal length of lens G1b and lens G1c in the first lens group G1 at infinity.

[0024] Preferably, in order to conveniently adjust the back focal length BF, the ratio of the movement amount G5S of the fifth lens group G5 with positive refractive power to the back focal length change amount ΔBF satisfies conditional expressions (5) and (6);

[0025] 0.3 ≤F5 / WL≤1.2 (5);

[0026] 0.2≤ΔBF / G5S≤1.5 (6);

[0027] in,

[0028] F5: focal length of the fifth lens group G5;

[0029] WL: The total length of the optical system from the first surface on the object side to the image plane;

[0030] ΔBF: The change in back focal length BF (i.e., the movement of the image plane) when the fifth lens group G5 is moved;

[0031] G5S: Adjustment movement of the fifth lens group G5.

[0032] Preferably, in order to achieve a wide-angle field angle greater than 70° and a zoom ratio greater than 2 times, while achieving the purpose of miniaturization of the first lens group G1, the entrance pupil distance ENPW at the wide-angle end satisfies the conditional formula (7); 1.5≤ENPW / (WI×tan(ωw))≤3.0 (7);

[0033] in,

[0034] ENPW: entrance pupil distance of the entire optical system at infinity at the wide-angle end;

[0035] ωw: half field of view at the wide-angle end;

[0036] WI: Maximum paraxial image height at the wide-angle end (WI = tan(ωw) × Fw).

[0037] If the upper limit of the conditional expression 0.3≤|F1a / F1|≤1(1) is exceeded, the refractive power of F1a is too weak. If the field of view angle is to be greater than 70°, the outer diameter of the first lens group G1 will become very thick, and the volume will be difficult to control. If the lower limit of the conditional expression (1) is exceeded, although ultra-wide angle and miniaturization can be achieved, the refractive power of F1a is too strong, which will cause various aberrations to increase sharply and become difficult to correct. It is necessary to add aspherical surfaces or more lenses, resulting in increased costs, volume, and weight.

[0038] If the upper limit of the conditional expression 1 ≤ F1 / Fw ≤ 3 (2) is exceeded, the refractive power F1 of the first group G1 will be relatively weak, and the movement required to achieve the zoom ratio in conjunction with G2, G3, and G4 in the entire optical system will become very large, making the entire optical system very large and difficult to miniaturize. If the lower limit of the conditional expression (2) is exceeded, the refractive power F1 of the first group G1 will be very strong, making it easy to achieve a zoom ratio of more than 2x. However, the refractive power of F1 will be too strong, making it difficult to correct various aberrations.

[0039] If the upper limit of the conditional expression 8 ≤ WL / (tan (ωw) × WI) ≤ 16 (3) is exceeded, the total optical length WL will be very long, or the wide-angle field of view will be very small, thus failing to achieve the requirements for a miniaturized wide-angle zoom lens. If the lower limit of the conditional expression (3) is exceeded, the total optical length will be very small, or the ultra-wide-angle requirement can be achieved, but the excessively small size will lead to a sharp increase in various aberrations, making it difficult to achieve high performance requirements and making manufacturing extremely difficult.

[0040] If the upper limit of the conditional expression 0.3 ≤ |F1a / F1bc| ≤ 1.2 (4) is exceeded, the negative refractive power F1a of the front group G1a in the first group will be very weak. Therefore, if a wide-angle field of view exceeding 70° is to be achieved, the volume of the first group G1 will be very large, making it difficult to achieve miniaturization. If the lower limit of the conditional expression (4) is exceeded, although the requirements for miniaturization and ultra-wide angle can be achieved, the refractive power of G1a will be too strong, making it difficult to correct various aberrations, making it very difficult to achieve high performance.

[0041] If the upper limit of the conditional expression 0.3 ≤ F5 / WL ≤ 1.2 (5) is exceeded, the refractive power of the fifth group G5 is too weak, and the sensitivity of moving the fifth group G5 to adjust the back focus is too weak. The amount of movement will be too large, the space required will be too large, and the mechanism design will be very difficult. If the lower limit of the conditional expression (5) is exceeded, the refractive power F5 of the fifth group G5 will be very strong. Although the amount of movement required to adjust the back focus is small and the mechanism design is simple, the refractive power of F5 is too strong, and the aberration caused by the movement is too large, which can easily lead to performance degradation due to adjusting the back focus.

[0042] If the upper limit of the conditional expression 0.2≤ΔBF / G5S≤1.5(6) is exceeded, the back focus adjustment is too sensitive and the adjustment accuracy is difficult to ensure. At the same time, because the fifth group is too sensitive to the entire optical system, the adjustment of the back focus will lead to performance degradation. If the lower limit of the conditional expression (5) is exceeded, the back focus change is too small when adjusting the fifth group. In this way, the adjustment amount of the fifth group will be large, the mechanism design will be more difficult, and miniaturization will be difficult to achieve.

[0043] If the upper limit of the conditional expression 1.5 ≤ ENPW / (WI × tan (ωw)) ≤ 3.0 ≤ 3.0 (7) is exceeded, the entrance pupil distance at the wide-angle end will be relatively large. Thus, if a 70° field of view is to be achieved, the diameter of the first lens group will become very large, making it difficult to achieve miniaturization. If the lower limit of the conditional expression (7) is exceeded, although the ultra-wide-angle miniaturization requirement can be achieved, the refractive power F1a of G1a in the first lens group G1 will become very strong, causing a sharp increase in various aberrations and making them difficult to correct. This will require the addition of aspherical lenses and complicate the lens structure.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The wide-angle zoom lens comprises a first lens group G1 consisting 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 a close distance, the positive refractive power middle group G1b of the first lens group G1 moves from the object side to the image side to achieve focusing, thereby providing a compact, high-performance, low-cost wide-angle zoom lens with a wide-angle field of view exceeding 70° and a zoom ratio greater than 2x. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of a wide-angle zoom lens provided in Example 1 of the present invention.

[0047] Figure 2 These are the spherical aberration, field curvature, distortion, and lateral chromatic aberration at infinity and minimum photographic distance in Example 1.

[0048] Figure 3 Schematic diagram of a wide-angle zoom lens provided in Example 2 of the present invention.

[0049] Figure 4 These are the spherical aberration, field curvature, distortion, and lateral chromatic aberration at infinity and minimum shooting distance in Example 2. DETAILED DESCRIPTION

[0050] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0051] Example 1

[0052] like Figure 1 As shown, the wide-angle zoom lens includes, from the object side to the image side, 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;

[0053] 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 side, the movement amount is S2, the third lens group G3 first moves from the object side to the image side, then turns back and moves from the image side to the object side, the total movement amount is S3, and the fourth lens group moves from the image side to the object side;

[0054] Among them, 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. The focal length of the first lens group G1 at infinity is F1. The negative refractive power front group G1a consists of three negative lenses with a focal length of F1a, and the middle group G1b consists of two positive lenses with a focal length of F1b. When the object moves from infinity to a close distance, the positive refractive power middle group G1b of the first lens group G1 moves from the object side to the image side to achieve focus, and the fifth lens group G5 moves to adjust the change in back focal length BF.

[0055] The spherical aberration, field curvature, distortion and lateral chromatic aberration at infinity and the minimum photographic distance of Example 1 are as follows: Figure 2 shown.

[0056] Focus distance: 17.52~33.01~48.31;

[0057] Fno: 2.85~2.85~2.85;

[0058] Half-frame angle ω: 42.33~24.66~17.21;

[0059] The data of Example 1 are as follows:

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066] Where, R (mm): radius of curvature of each surface;

[0067] D (mm): the distance between lenses and the thickness of the lenses;

[0068] Nd: refractive index of each glass at d line;

[0069] Vd: Abbe number of glass.

[0070] The adjustment amount of the 5th group G5 is: G5S = +0.2;

[0071] The change in back focal length is: ΔBF = 25.1361 - 25.0304 = +0.1057;

[0072] D(37)-0.2 2.4006 14.5130 19.1284 2.4006 14.5130 19.1284 D(41)+0.2 1.2000 1.2000 1.2000 1.2000 1.2000 1.2000 BF 24.9244 24.9244 24.9244 24.9244 24.9244 24.9244

[0073] The adjustment amount of the 5th group G5 is: G5S = -0.2;

[0074] The change in back focal length is: ΔBF=24.9244-25.0304=-0.106.

[0075] Example 2

[0076] like Figure 3 As shown, the wide-angle zoom lens includes, from the object side to the image side, 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;

[0077] 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 side, the movement amount is S2, the third lens group G3 first moves from the object side to the image side, then turns back and moves from the image side to the object side, the total movement amount is S3, and the fourth lens group moves from the image side to the object side;

[0078] Among them, 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. The focal length of the first lens group G1 at infinity is F1. The negative refractive power front group G1a consists of three negative lenses with a focal length of F1a, and the middle group G1b consists of two positive lenses with a focal length of F1b. When the object moves from infinity to a close distance, the positive refractive power middle group G1b of the first lens group G1 moves from the object side to the image side to achieve focus, and the fifth lens group G5 moves to adjust the change in back focal length BF.

[0079] The spherical aberration, field curvature, distortion and lateral chromatic aberration at infinity and the minimum photographic distance in Example 2 are as follows: Figure 4 shown.

[0080] Focus distance: 29.01~50.01~72.50;

[0081] Fno: 2.85~2.85~2.85;

[0082] Half picture angle ω: 37.81~23.09~16.24;

[0083]

[0084]

[0085]

[0086]

[0087]

[0088] Where, R (mm): radius of curvature of each surface;

[0089] D (mm): the distance between lenses and the thickness of the lenses;

[0090] Nd: refractive index of each glass at d line;

[0091] Vd: Abbe number of glass.

[0092] The adjustment amount of the 5th group G5 is: G5S = +0.2;

[0093] The change in back focal length is: ΔBF = 36.8532 - 36.7529 = +0.1003

[0094] D(37)-0.2 3.0506 15.6940 27.4814 3.0506 15.6940 27.4814 D(41)+0.2 1.2000 1.2000 1.2000 1.2000 1.2000 1.2000 BF 36.6571 36.6571 36.6571 36.6571 36.6571 36.6571

[0095] The adjustment amount of the 5th group G5 is: G5S = -0.2;

[0096] The change in back focal length is: ΔBF=36.6571-36.7529=-0.0958.

[0097] Conditional summary table:

[0098] Example 1 Example 2 Conditional formula (1): 0.3≤|F1a / F1|≤1; 0.691 0.512 Conditional expression (2): 1≤F1 / Fw≤3; 1.904 2.163 Conditional formula (3): 8≤WL / (tan(ωw)×WI)≤16; 11.493 13.231 Conditional formula (4): 0.3≤|F1a / F1bc|≤1.2; 0.893 0.832 Conditional expression (5): 0.3≤F5 / WL≤1.2; 0.605 0.684 Conditional expression (6): 0.2≤ΔBF / G5S≤1.5; 0.530 0.502 Conditional formula (7): 1.5≤ENPW / (WI×tan(ωw))≤3.0; 2.194 2.234

[0099] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A wide-angle zoom lens, characterized in that: The lens system includes, from the object side to the image side, 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 is composed 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 a close distance, the positive refractive power middle group G1b of the first lens group G1 moves from the object side to the image side to achieve focus, and the following conditions (1), (2), and (3) are satisfied: 0.3≤|F1a / F1|≤1 (1); 1≤F1 / Fw≤3 (2); 8≤WL / (tan(ωw) ×WI)≤16 (3); in, WL: total optical length of the lens; F1: focal length of the first lens group G1 at infinity; F1a: focal length of the front lens group G1a of the first lens group G1; Fw: focal length of the entire optical system at the wide-angle end at infinity; ωw: half field of view at the wide-angle end; WI: Maximum paraxial image height at the wide-angle end, expressed as WI = tan(ωw) × Fw.

2. The wide-angle zoom lens according to claim 1, wherein: The first lens group G1 has a focal length of F1 at infinity, the negative refractive power front group G1a consists of three negative lenses with a focal length of F1a, and the middle group G1b consists of two positive lenses with a focal length of F1b, and satisfies conditional equation (4); 0.3≤|F1a / F1bc|≤1.2 (4); in, F1a: focal length of the front lens group G1a in the first lens group G1; F1bc: the combined focal length of lens G1b and lens G1c in the first lens group G1 at infinity.

3. The wide-angle zoom lens according to claim 1 or 2, wherein: In order to conveniently adjust the back focal length BF, the ratio of the movement amount G5S of the fifth lens group G5 with positive refractive power to the back focal length change ΔBF satisfies the conditions (5) and (6); 0.3 ≤F5 / WL≤1.2 (5); 0.2≤ΔBF / G5S≤1.5 (6); in, F5: focal length of the fifth lens group G5; WL: The total length of the optical system from the first surface on the object side to the image plane; ΔBF: The change in back focal length BF when moving the fifth lens group G5; G5S: Adjustment movement of the fifth lens group G5.

4. The wide-angle zoom lens according to any one of claims 1 to 3, wherein: In order to achieve a wide-angle field angle greater than 70° and a zoom ratio of more than 2 times, while miniaturizing the first lens group G1, the entrance pupil distance ENPW at the wide-angle end satisfies the conditional equation (7); 1.5≤ENPW / (WI×tan(ωw))≤ 3.0 (7); in, ENPW: entrance pupil distance of the entire optical system at infinity at the wide-angle end; ωw: half field of view at the wide-angle end; WI: Maximum paraxial image height at the wide-angle end, expressed as WI = tan(ωw) × Fw.

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