A medium focal length, large aperture, long flange video lens with a focal length of 50mm

Abstract

The present invention relates to a medium focal length large aperture long flange video lens with a focal length of 50 mm, which includes a first lens group, a variable aperture, and a second lens group arranged in sequence along the light incident direction of the optical path; wherein the first lens group is a non-movable fixed group with a positive optical power, and is composed of lenses L11 to L17 arranged in sequence along the light incident direction of the optical path, including two groups of doublet lenses and one group of triplet lenses; the second lens group is a movable focusing group with a positive optical power, and is composed of lenses L21 to L27 arranged in sequence along the light incident direction of the optical path, including two groups of doublet lenses and one glass aspherical lens; moreover, the focal length value f1 of the first lens group and the focal length value f2 of the second lens group satisfy 0.47 < f2 / f1 < 0.56. This lens realizes a large aperture, high MTF resolution, small distortion, and reduced achromatism, and has a relatively short overall optical length, meeting the requirements of a camera module with a long flange back focus.

Description

Technical Field

[0001] The invention belongs to the technical field of photographic lenses, and in particular relates to a medium-focus, large-aperture, long-flange video lens with a focal length of 50 mm. Background Art

[0002] With the rapid development of social economy, people's demand for film and television and self-media is increasing, and the demand for video shooting scenes is increasing, which has led to higher requirements for the index parameters of video lenses. Among them, the important indicators for mid-focus video lenses are large aperture, high MTF resolution, low chromatic aberration, small distortion and short total optical length.

[0003] However, the applicant has found that the mid-focus video lenses currently on the market generally have the following disadvantages: the MTF resolution is not high enough, the distortion is large, the aperture is small, the chromatic aberration effect is poor, the total optical length is long (the total optical length is 165 mm to 185 mm), and the flange back focus is too short (the optical back focus is 23 mm to 31 mm). These disadvantages cannot meet the high requirements of the market demand for mid-focus video shooting with a long flange back focus, especially for video lenses with a focal length of 50 mm. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a medium focal length, large aperture and long flange video lens with a focal length of 50 mm.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a medium focal length large aperture long flange video lens with a focal length of 50 mm, the lens comprises a first lens group, a variable aperture and a second lens group which are sequentially arranged along the incident direction of light along the optical path; wherein,

[0007] The first lens group is an immovable fixed group with positive optical power. The first lens group is composed of lenses L11 to L17 arranged in sequence along the incident direction of the light path, including two groups of doublets and one group of triplet;

[0008] The second lens group is a movable focusing group with positive focal power. The second lens group is composed of lenses L21 to L27 arranged in sequence along the incident direction of the light path, including two groups of double-cemented lenses and one glass aspherical lens;

[0009] And the focal lengths of the first lens group and the second lens group satisfy the following equation:

[0010] 0.47 <f2 / f1<0.56

[0011] Where f1 is the focal length of the first lens group, and f2 is the focal length of the second lens group.

[0012] Furthermore, the lens L11 and the lens L12 of the first lens group constitute a first group of double-cemented lenses, the lenses L13 to L15 constitute a triple-cemented lens, and the lens L16 and the lens L17 constitute a second group of double-cemented lenses; the lens L22 and the lens L23 of the second lens group constitute a third group of double-cemented lenses, the lens L24 and the lens L25 constitute a fourth group of double-cemented lenses, and the lens L26 is a glass aspherical lens.

[0013] Furthermore, the refractive indexes of lens L11, lens L14, lens L15 and lens L17 in the first lens group are greater than 1.8 and less than 1.9, and the refractive indexes of lens L23, lens L24, lens L25 and lens L26 in the second lens group are greater than 1.6 and less than 1.7.

[0014] Furthermore, the Abbe numbers of lens L11 and lens L15 in the first lens group are greater than 35 and less than 45, and the Abbe number of lens L22 in the second lens group is greater than 80 and less than 85.

[0015] Further, the object side coefficients of the lens L26 are: K=0.000000000, E4=0.000018695271718920, E6=-0.0000000011933790389, E8=0.000000000013805153, E10=0.0000000000000010980, R1=-24.170112744;

[0016] The image side coefficients of the lens L26 are: K=0.067706757, E4=0.000016083612725860, E6=-0.000000013519105358, E8=0.000000000008676814, E10=-0.0000000000000002846, R2=-40.737432563.

[0017] Furthermore, the focal length adjustment range of the optical system composed of the first lens group and the second lens group is 49.04mm~50.98mm, and during the focal length adjustment range adjustment process of the optical system, the adjustment range of the relative aperture is 1.43mm~1.35mm, the adjustment range of the half field angle is 22.736°~22.913°, the adjustment range of the object distance is 394mm~infinity, the adjustment range of the distance between the variable aperture surface and the image side surface of the lens L19 is 1.350264mm~8.2072mm, and the adjustment range of the back focus is 43.899736mm~37.0428mm.

[0018] Furthermore, the total length of the optical system formed by the first lens group and the second lens group is greater than 155 mm and less than 162 mm.

[0019] Furthermore, the structure of the optical system composed of the first lens group and the second lens group is specifically as shown in the following table:

[0020] .

[0021] Beneficial effects of the present invention:

[0022] 1. The present invention adopts an optimized combination of 13 standard glass spherical lenses and 1 glass aspherical lens to obtain a medium-focus video lens with a focal length of 50 mm, which achieves a large clear aperture, high MTF resolution, small distortion, reduced achromatism and long flange back focus.

[0023] 2. The present invention optimizes the total optical length by adopting a compact optical structure, so that the total length of the optical system composed of the first lens group G1 and the second lens group G2 is greater than 155 mm and less than 162 mm, and the total optical length is reduced; at the same time, it can also meet the requirements of matching camera modules with longer flange back focus. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of a medium focal length, large aperture, long flange video lens with a focal length of 50 mm according to the present invention;

[0025] Figure 2 It is a longitudinal aberration diagram of a test of a medium focal length, large aperture, long flange video lens with a focal length of 50 mm according to an embodiment of the present invention;

[0026] Figure 3 This is a lateral chromatic aberration diagram of a medium focal length, large aperture, long flange video lens with a focal length of 50 mm as described in an embodiment of the present invention;

[0027] Figure 4 This is a field curvature distortion diagram of a test of a medium focal length, large aperture, long flange video lens with a focal length of 50 mm according to an embodiment of the present invention;

[0028] Figure 5 is a relative illumination curve diagram of a test of a medium focal length, large aperture, long flange video lens with a focal length of 50 mm according to an embodiment of the present invention;

[0029] Figure 6 It is an MTF curve diagram of the test of the medium focal length, large aperture and long flange video lens with a focal length of 50 mm described in the embodiment of the present invention;

[0030] Figure 7 It is a spot diagram of a test of a medium focal length, large aperture, long flange video lens with a focal length of 50 mm according to an embodiment of the present invention;

[0031] Figure 8 is a lateral chromatic aberration diagram of the video lens test described in Comparative Example 1 of the present invention;

[0032] Fig. 9 is a relative illumination curve diagram of the video lens test described in Comparative Example 1 of the present invention;

[0033] Fig.10 is an MTF curve diagram of the video lens test described in Comparative Example 1 of the present invention;

[0034] Fig.11 is a point diagram of the video lens test described in Comparative Example 1 of the present invention;

[0035] Fig.12 is a lateral chromatic aberration diagram of the video lens test described in Comparative Example 2 of the present invention;

[0036] Fig.13 is a field curvature distortion diagram of the video lens test described in Comparative Example 2 of the present invention;

[0037] Fig.14 This is a relative illumination curve of the video lens test described in Comparative Example 2 of the present invention.

[0038] Fig.15 It is an MTF curve diagram of the video lens test described in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] like Figure 1 As shown, the medium focal length large aperture long flange video lens with a focal length of 50 mm described in the present invention is provided with a first lens group G1, a variable aperture S and a second lens group G2 in sequence along the incident direction of the light path. Among them,

[0041] The first lens group G1, as an immovable fixed group, has positive optical focal length. The first lens group G1 is composed of lenses L11 to L17 arranged in sequence along the light incident direction of the optical path, including two groups of double-cemented lenses and one group of triple-cemented lenses. Specifically, the lens L11 and the lens L12 constitute a first group of double-cemented lenses, the lenses L13 to L15 constitute a triple-cemented lens, and the lens L16 and the lens L17 constitute a second group of double-cemented lenses; the refractive index of the lens L11, the lens L14, the lens L15 and the lens L17 is greater than 1.8 and less than 1.9, and the Abbe number of the lens L11 and the lens L15 is greater than 35 and less than 45.

[0042] The second lens group G2, as a movable focusing group, has positive optical power. The second lens group G2 is composed of lenses L21 to L27 arranged in sequence along the incident direction of light along the optical path, including two groups of double-cemented lenses and one glass aspherical lens. Specifically, the lens L22 and the lens L23 constitute a third group of double-cemented lenses, the lens L24 and the lens L25 constitute a fourth group of double-cemented lenses, the lens L26 is a glass aspherical lens, and the coefficient of the lens L26 of the glass aspherical lens is shown in Table 1 below; the refractive indices of the lenses L23, L24, L25 and L26 are greater than 1.6 and less than 1.7, and the Abbe number of the lens L22 is greater than 80 and less than 85.

[0043] Table 1

[0044]

[0045] Moreover, the first lens group G1 and the second lens group G2 of the medium focal length large aperture long flange video lens with a focal length of 50 mm of the present invention satisfy the following formula:

[0046] 0.47 <f2 / f1<0.56

[0047] Among them, f1 is the focal length value of the first lens group G1, and f2 is the focal length value of the second lens group G2; this formula expresses the corresponding relationship between the optical focal lengths of the first lens group G1 and the second lens group G2. If this formula is not satisfied, the back focus working distance of the optical system is too short and cannot meet the requirements of matching the camera module with a long flange back focus.

[0048] Through experimental tests, the total length of the optical system of the medium-focus large aperture long flange video lens with a focal length of 50 mm described in the present invention, which is composed of the above-mentioned first lens group G1 and the second lens group G2, is greater than 155 mm and less than 162 mm, which meets the requirements of matching the camera module 100 with a longer flange back focus. The focal length adjustment range of the optical system is 49.04 mm to 50.98 mm, and in the process of adjusting the focal length adjustment range, its relative aperture is adjusted in the range of 1.43 mm to 1.35 mm, the half field of view angle is adjusted in the range of 22.736° to 22.913°, the object distance is adjusted in the range of 394 mm to infinity, the distance between the variable aperture surface and the image side surface of the lens L19 is adjusted in the range of 1.350264 mm to 8.2072 mm, and the back focus is adjusted in the range of 43.899736 mm to 37.0428 mm.

[0049] When the medium-focus large aperture long flange video lens with a focal length of 50 mm described in the present invention is working, the first lens group G1 is fixed when the object moves from infinity to a close distance, and the second lens group G2 moves toward the object when the object moves from infinity to a close distance to achieve focusing.

[0050] The present invention adopts an optimized combination of 13G1GM (13 standard glass spherical lenses and 1 glass aspherical lens) to obtain a medium - focal - length video lens with a focal length of 50 mm, achieving the advantages of a large aperture, high MTF resolution, small distortion, and reduced achromatism. Specifically: when the focal - length values of the first lens group G1 and the second lens group G2 of the present invention satisfy 0.47 < f2 / f1 < 0.56, the first lens group G1 all adopts the form of a cemented lens group to optimize and improve the MTF resolution and reduce chromatic aberration, so as to better match high - pixel cameras. At the same time, by setting two groups of doublet lenses and one aspherical lens in the second lens group G2, achromatism is effectively optimized, dispersion is reduced, MTF resolution is improved, and distortion is reduced.

[0051] The following further illustrates the medium - focal - length large - aperture long - flange video lens with a focal length of 50 mm of the present invention through examples and comparative examples. Example

[0052] The video lens described in the embodiment of the present invention includes a first lens group G1, a variable aperture S, and a second lens group G2 as shown in Figure 1 . The structures of the first lens group G1 and the second lens group G2 are as described above and will not be repeated here. Among them, the ratio of the focal - length value f1 of the first lens group G1 to the focal - length value f2 of the second lens group G2 in this embodiment is: f2 / f1 = 0.53, and the optical back - focal length is 40.0428 mm; the structure of the optical system composed of the first lens group G1 and the second lens group G2 is specifically as shown in Table 2 below.

[0053] Table 2

[0054] ;

[0055] The coefficients of the lens L26 (glass aspherical lens) are as shown in Table 1 above.

[0056] The overall specifications of the optical system composed of the first lens group G1 and the second lens group G2 in the embodiment of the present invention are as shown in Table 3 below.

[0057] Table 3

[0058]

[0059] When the object moves from infinity to a short distance, in this embodiment, the first lens group G1 remains stationary, and the second lens group G2 moves towards the object direction to achieve focus, and this lens has a large aperture (see Figure 5 , this figure is the relative illuminance curve diagram of the video lens of the embodiment of the present invention for testing a light source with a wavelength of 0.546000 μm ), high MTF resolution (see Figure 6 and Figure 7 ), small distortion (see Figure 4 and Figure 7 ,in Figure 4 The field curvature distortion diagram of the video lens of the embodiment of the present invention under the maximum field of view of 21.5000 mm for the light sources with wavelengths of 0.435μm, 0.486μm, 0.546μm, 0.587μm and 0.656μm) and the reduction of achromatism (see Figure 2 and Figure 3 ,in Figure 2 This is a longitudinal aberration diagram of the video lens of the embodiment of the present invention when the pupil radius is 14.2578 mm and the wavelength is 0.435 μm. Figure 3 This is a diagram of the lateral chromatic aberration of the video lens of an embodiment of the present invention tested with a light source of wavelength 0.546000 μm at a maximum field of view of 21.5000 mm). Comparative Example 1

[0060] This comparative example 1 is basically the same as the video lens described in the embodiment, and includes a first lens group G1, a variable aperture S, and a second lens group G2. The difference is that in this comparative example 1, the ratio of the focal length value f1 of the first lens group G1 to the focal length value f2 of the second lens group G2 is: f2 / f1=0.47, f1 represents the focal length value of the first lens group G1, f2 represents the focal length value of the second lens group G2, and the structure of the optical system composed of the first lens group G1 and the second lens group G2 is specifically shown in Table 4 below.

[0061] Table 4

[0062]

[0063] The coefficients of lens L26 (glass aspherical lens) are shown in Table 5.

[0064] Table 5

[0065]

[0066] The same method as in the embodiment was used for testing. From the test results of Comparative Example 1 ( Figure 8-11 ) compared with the embodiment found that:

[0067] 1. The total optical length of Example 1 increases by 16.40mm, resulting in increased costs, while the optical back focus decreases by 12.03mm, making it impossible to match the long flange camera module;

[0068] 2. The lateral chromatic aberration of Example 1 becomes larger, the relative illumination decreases, the MTF resolution decreases, and the spot array becomes larger. Comparative Example 2

[0069] This Comparative Example 2 is basically the same as the video lens described in the embodiment, including a first lens group G1, an iris diaphragm S, and a second lens group G2. The difference is that in this Comparative Example 2, the ratio of the focal length value f1 of the first lens group G1 to the focal length value f2 of the second lens group G2 is: f2 / f1 = 0.56, where f1 represents the focal length value of the first lens group G1 and f2 represents the focal length value of the second lens group G2, and the structure of the optical system composed of the first lens group G1 and the second lens group G2 is specifically as shown in Table 6 below.

[0070] Table 6

[0071]

[0072] Among them, the coefficients of the lens L26 (glass aspherical lens) are as shown in Table 7 below.

[0073] Table 7

[0074]

[0075] The same method as in the embodiment is used for testing. From the comparison between the test results of Comparative Example 2 ( Figure 12-15 ) and the embodiment, it is found that:

[0076] 1. The overall optical length of Comparative Example 2 increases by 54.01 mm, resulting in an increase in cost. At the same time, the optical back focal length decreases by 12.07 mm, resulting in an inability to match the long flange camera module;

[0077] 2. The lateral chromatic aberration of Comparative Example 2 becomes larger, the distortion becomes larger, the relative illumination decreases, and the MTF resolution decreases.

[0078] Therefore, from the above embodiments and Comparative Examples 1 and 2, it can be seen that if the focal length value f1 of the first lens group and the focal length value f2 of the second lens group of the lens described in the present invention do not satisfy 0.47 < f2 / f1 < 0.56, it will result in too short a back focal working distance of the optical system, an inability to meet the requirements of matching the camera module with a long flange back focal length, and defects such as attenuation of optical performance such as MTF, relative illumination, chromatic aberration, or distortion.

[0079] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A medium focal length, large aperture, long flange video lens with a focal length of 50 mm, characterized in that: The lens is composed of a first lens group, a variable aperture and a second lens group which are sequentially arranged along the incident direction of light along the optical path; wherein, The first lens group is an immovable fixed group with positive focal power. The first lens group is composed of lenses L11 to L17 arranged in sequence along the incident direction of the light path, including two groups of doublets and one group of triplet. Specifically, the lens L11 and the lens L12 of the first lens group constitute a first group of doublets, the lenses L13 to L15 constitute a triplet, the lens L16 and the lens L17 constitute a second group of doublets, the focal power of the lenses L11, L14, L15 and L16 is positive, and the focal power of the lenses L12, L13 and L17 is negative; The second lens group is a movable focusing group with positive focal power. The second lens group is composed of lenses L21 to L27 arranged in sequence along the incident direction of the light path, including two groups of double-cemented lenses and one glass aspherical lens. Specifically, the lens L22 and the lens L23 of the second lens group constitute a third group of double-cemented lenses, the lens L24 and the lens L25 constitute a fourth group of double-cemented lenses, the lens L26 is a glass aspherical lens, the focal power of the lenses L21, L22, L25 and L27 is positive, and the focal power of the lenses L23, L24 and L26 is negative; And the focal lengths of the first lens group and the second lens group satisfy the following equation: 0.47 <f2 / f1<0.56 Where f1 is the focal length of the first lens group, and f2 is the focal length of the second lens group; The focal length adjustment range of the optical system composed of the first lens group and the second lens group is 49.04mm~50.98mm, and during the focal length adjustment range adjustment process of the optical system, the adjustment range of the relative aperture is 1.43mm~1.35mm, the adjustment range of the half field angle is 22.736°~22.913°, the adjustment range of the object distance is 394mm~infinity, the adjustment range of the distance between the variable aperture surface and the image side surface of the lens L19 is 1.350264mm~8.2072mm, and the adjustment range of the back focus is 43.899736mm~37.0428mm.

2. The medium focal length, large aperture, long flange video lens with a focal length of 50 mm according to claim 1, characterized in that: The refractive indexes of lens L11, lens L14, lens L15 and lens L17 in the first lens group are greater than 1.8 and less than 1.9, and the refractive indexes of lens L23, lens L24, lens L25 and lens L26 in the second lens group are greater than 1.6 and less than 1.

7.

3. The medium focal length, large aperture, long flange video lens with a focal length of 50 mm according to claim 2, characterized in that: The Abbe numbers of lens L11 and lens L15 in the first lens group are greater than 35 and less than 45, and the Abbe number of lens L22 in the second lens group is greater than 80 and less than 85.

4. The medium focal length, large aperture, long flange video lens with a focal length of 50 mm according to claim 1, characterized in that: The total length of the optical system formed by the first lens group and the second lens group is greater than 155 mm and less than 162 mm.

5. The medium focal length, large aperture, long flange video lens with a focal length of 50 mm according to any one of claims 1 to 4, characterized in that: The structure of the optical system composed of the first lens group and the second lens group is specifically shown in the following table: 。

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