Automatic focusing lens

Abstract

The invention discloses an automatic focusing lens, and relates to the technical field of lenses, the lens sequentially comprises a first lens group, a second lens group, an iris diaphragm and a third lens group from an object side to an imaging side, the first lens group has positive focal power, and during focusing, the position of the first lens group relative to an image surface is kept unchanged; the second lens group has negative focal power, and the second lens group moves along the optical axis during focusing; the third lens group has positive focal power, and during focusing, the position of the third lens group relative to the image surface is kept unchanged; the lens satisfies a conditional expression of-2.3 lt; (f1 + f3) / f2lt; -1.6); according to the invention, the performance requirements of high resolution, large clear aperture, small chromatic aberration and small distortion can be met.

Description

Technical Field

[0001] This application relates to the technical field of lenses, and particularly to an autofocus lens. Background Art

[0002] With the development of society, people have an increasing demand for shooting with autofocus lenses, and the requirements for autofocus lenses are also getting higher and higher. However, the long-focus autofocus lenses commonly available in the market at present have disadvantages such as insufficient resolution, large distortion, small aperture, and large chromatic aberration, which cannot meet the high requirements for shooting with long-focus autofocus lenses.

[0003] Therefore, there is an urgent need to design a lens with high resolution, large aperture, small chromatic aberration, small distortion, and capable of meeting the shooting requirements of autofocus at the same time. Summary of the Invention

[0004] The main purpose of the embodiments of this application is to aim at solving at least one of the technical problems existing in the prior art, and to propose an autofocus lens that can meet the performance requirements of high resolution, large aperture, small chromatic aberration, and small distortion.

[0005] To achieve the above object, the embodiments of the present invention application propose an autofocus lens, which sequentially includes from the object side to the imaging side: a first lens group, a second lens group, a variable aperture, and a third lens group. The first lens group has a positive optical power. During focusing, the position of the first lens group relative to the image plane remains unchanged; the second lens group has a negative optical power. During focusing, the second lens group moves along the optical axis; the third lens group has a positive optical power. During focusing, the position of the third lens group relative to the image plane remains unchanged; the lens satisfies the following conditional formula:

[0006]

[0007] Wherein, f1 represents the focal length value of the first lens group, f2 represents the focal length value of the second lens group, and f3 represents the focal length value of the third lens group.

[0008] An autofocus lens provided according to an embodiment of the present invention has at least the following beneficial effects: First, the second lens group with negative optical power can efficiently adjust the focusing distance during movement, while the first lens group and the third lens group with positive optical power can stabilize the image plane position, suppress image plane shift during focusing, and improve imaging stability; Second, during the focusing process, the positions of the first lens group and the third lens group relative to the image plane remain unchanged, and autofocus is achieved only by moving the second lens group, enabling the motor to quickly achieve the autofocus function and improve the focusing efficiency; Immediately afterwards, the variable aperture is placed between the second lens group and the third lens group, which can not only optimize aberrations (such as field curvature and distortion) by adjusting the aperture position, but also dynamically balance the light input during focusing, improving the adaptability under complex lighting conditions; In addition, by satisfying the conditional expressions related to the focal length values of the first lens group, the second lens group, and the third lens group, the optimization of the lens structure is achieved, enabling the lens to meet the performance requirements of high resolution, large aperture, small chromatic aberration, small distortion, and short optical total length while achieving fast focusing.

[0009] In some embodiments, in the first lens group, at least two lenses with a refractive index greater than 1.4 and less than 1.5 are included.

[0010] In some embodiments, the first lens group includes, in order from the object side to the imaging side: a first lens with positive optical power, a second lens with positive optical power, a third lens with negative optical power, a fourth lens with positive optical power, and a fifth lens with negative optical power;

[0011] Among them, the refractive index of the second lens and the refractive index of the fourth lens are both greater than 1.4 and less than 1.5.

[0012] In some embodiments, the fourth lens and the fifth lens are combined into a doublet lens.

[0013] In some embodiments, the first lens, the second lens, and the third lens are all meniscus lenses.

[0014] In some embodiments, the second lens group includes: a sixth lens with negative optical power.

[0015] In some embodiments, the refractive index of the sixth lens is greater than 1.5 and less than 1.6.

[0016] In some embodiments, in the third lens group, at least three lenses with an Abbe number greater than 30 and less than 40 are included.

[0017] In some embodiments, the third lens group sequentially includes, from the object side to the imaging side: a seventh lens with positive optical power, an eighth lens with negative optical power, a ninth lens with positive optical power, a tenth lens with negative optical power, an eleventh lens with positive optical power, a twelfth lens with negative optical power, a thirteenth lens with positive optical power, and a fourteenth lens with negative optical power;

[0018] Wherein, the Abbe number of the ninth lens, the Abbe number of the tenth lens, and the Abbe number of the eleventh lens are all greater than 30 and less than 40.

[0019] In some embodiments, the seventh lens, the eighth lens, the ninth lens, and the tenth lens are combined into a four-cemented lens. Description of the Drawings

[0020] The drawings are used to provide a further understanding of the technical solutions of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the technical solutions of the present invention, and do not constitute a limitation to the technical solutions of the present invention.

[0021] The present invention will be further described below in conjunction with the drawings and embodiments;

[0022] Figure 1 is a schematic diagram of the overall structure of an autofocus lens provided by the present invention;

[0023] Figure 2 is a schematic diagram of longitudinal chromatic aberration of an autofocus lens provided by the present invention;

[0024] Figure 3 is a schematic diagram of field curvature and distortion of an autofocus lens provided by the present invention;

[0025] Figure 4 is a schematic diagram of the circle of confusion of an autofocus lens provided by the present invention;

[0026] Figure 5 is a schematic diagram of MTF of an autofocus lens provided by the present invention;

[0027] Figure 6 is a schematic diagram of the MTF defocus curve of an autofocus lens provided by the present invention. Detailed Embodiments

[0028] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0029] It should be noted that the terms "first", "second", etc. in the specification, claims and the above-mentioned drawings are used to distinguish similar objects and do not necessarily describe a specific order or sequence.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used herein are only for the purpose of describing embodiments of this application and are not intended to limit this application.

[0031] Embodiments of the present invention provide an autofocus lens that can meet the performance requirements of high resolution, large aperture, small chromatic aberration, and small distortion.

[0032] The following further elaborates on the embodiments of the present invention with reference to the drawings.

[0033] Refer to Figure 1 , embodiments of the present invention application propose an autofocus lens, which sequentially includes, from the object side to the imaging side: a first lens group G1, a second lens group G2, a variable aperture STO, and a third lens group G3. The first lens group G1 has a positive optical power, and during focusing, the position of the first lens group G1 relative to the image plane remains unchanged; the second lens group G2 has a negative optical power, and during focusing, the second lens group G2 moves along the optical axis; the third lens group G3 has a positive optical power, and during focusing, the position of the third lens group G3 relative to the image plane remains unchanged; the lens satisfies the following conditional expressions:

[0034]

[0035] Wherein, 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 f3 represents the focal length value of the third lens group G3.

[0036] An autofocus lens according to an embodiment of the present invention, first, the second lens group G2 with negative optical power can efficiently adjust the focusing distance during movement, while the first lens group G1 and the third lens group G3 with positive optical power can stabilize the image plane position, suppress image plane shift during focusing, and improve imaging stability; second, during the focusing process, the positions of the first lens group G1 and the third lens group G3 relative to the image plane remain unchanged, and autofocus is achieved only by moving the second lens group G2, which can enable the motor to quickly achieve the autofocus function and improve the focusing efficiency; immediately afterwards, the variable aperture STO is placed between the second lens group G2 and the third lens group G3, which can not only optimize aberrations (such as field curvature and distortion) by adjusting the aperture position, but also dynamically balance the light input amount during focusing, improving adaptability under complex lighting conditions; in addition, by satisfying the conditional formula related to the focal length values of the first lens group G1, the second lens group G2, and the third lens group G3, the optimization of the lens structure is realized, so that the lens can meet the performance requirements of high resolution, large aperture, small chromatic aberration, small distortion, and short optical total length while achieving fast focusing.

[0037] It can be understood that when the conditional formula related to the focal length values of the first lens group G1, the second lens group G2, and the third lens group G3 is satisfied, first, the focal length value of the second lens group G2 is controlled within a reasonable range, so that only a small displacement is required during focusing to achieve rapid focus switching, effectively improving the focusing efficiency; second, if the negative optical power of the second lens group G2 is too strong, that is, the absolute value of the focal length value of the second lens group G2 is too small, it will cause deterioration of field curvature, and through the constraint of the conditional formula, it can be ensured that the positive optical powers of the first lens group G1 and the third lens group G3 are sufficient to offset the deterioration of the field area caused by the second lens group G2 to improve the resolution; immediately afterwards, by restricting the focal length ratio, the intensity matching of chromatic aberration compensation can be ensured, which is beneficial to reducing chromatic aberration; in addition, distortion is mainly caused by the asymmetric propagation of the chief ray before and after the variable aperture STO. By restricting the focal length ratio, the positive optical powers of the first lens group G1 and the third lens group G3 and the negative optical power of the second lens group G2 form an approximately symmetric structure, making the deflection angles of the chief ray before and after the variable aperture STO close to symmetric, significantly reducing distortion.

[0038] Preferably, the overall focal length of the lens is 85 mm.

[0039] Preferably, the optical total length of the autofocus lens is limited to the range between 115 mm and 120 mm.

[0040] It can be understood that by controlling the optical total length of the autofocus lens within the range of 115 mm to 120 mm, it is possible to avoid the optical total length being too long, reduce the lens cost, and at the same time reduce the assembly sensitivity.

[0041] In some embodiments, in the first lens group G1, there are at least two lenses with a refractive index greater than 1.4 and less than 1.5.

[0042] It can be understood that by selecting at least two lenses with a moderate refractive index to form the first lens group G1, while maintaining good imaging quality, the thickness and weight of the lenses can be relatively reduced, which helps to reduce the volume and weight of the entire optical system.

[0043] In some embodiments, the first lens group G1 includes, in order from the object side to the imaging side: a first lens 1 with positive optical power, a second lens 2 with positive optical power, a third lens 3 with negative optical power, a fourth lens 4 with positive optical power, and a fifth lens 5 with negative optical power;

[0044] Among them, the refractive index of the second lens 2 and the refractive index of the fourth lens 4 are both greater than 1.4 and less than 1.5.

[0045] It should be noted that by controlling the refractive index of the second lens 2 and the refractive index of the fourth lens 4 within the range of 1.4 to 1.5, the propagation path of light can be kept from being overly disturbed, and the propagation path of light in the optical element can be accurately controlled.

[0046] In some embodiments, the fourth lens 4 and the fifth lens 5 are combined into a doublet lens.

[0047] It can be understood that the fourth lens 4 with positive optical power and the fifth lens 5 with negative optical power, two lenses with different dispersion characteristics, are combined into a doublet lens. Their dispersions can compensate each other, effectively optimizing and reducing chromatic aberration; the reduction of chromatic aberration helps different wavelengths of light to be focused more accurately on the image plane, thus restoring the true picture color; at the same time, it reduces the sensitivity to assembly tolerances on the production line; in addition, there is no need to worry about the relative position change between the lenses during the assembly of the doublet lens, which helps to improve the production yield.

[0048] In some embodiments, the first lens 1, the second lens 2, and the third lens 3 are all meniscus lenses.

[0049] It can be understood that the meniscus lens can more precisely control the focusing position of light, reduce the scattering of light inside the lens and the influence of stray light, which helps to improve the contrast and clarity of the image, thus optimizing the MTF value; in addition, the meniscus lens can correct the deflection of light when passing through the lens, so that the light can be focused more accurately on the image plane, which helps to reduce image distortion caused by light deflection.

[0050] In some embodiments, the second lens group G2 includes: a sixth lens 6 with negative optical power.

[0051] Preferably, the weight of the sixth lens 6 is less than 6.7 grams.

[0052] It can be understood that by using a lightweight lens group composed of a single lens as the focusing group in the second lens group G2, the required driving force is smaller, and the motor can drive to quickly achieve the autofocus function.

[0053] In some embodiments, the refractive index of the sixth lens 6 is greater than 1.5 and less than 1.6.

[0054] It should be noted that by controlling the refractive index of the sixth lens 6 within the range of 1.5 to 1.6, the propagation path of light can be kept from being overly interfered, and the propagation path of light in the lens can be precisely controlled.

[0055] In some embodiments, in the third lens group G3, it includes at least three lenses with an Abbe number greater than 30 and less than 40.

[0056] It can be understood that by selecting at least three lenses with a high Abbe number to form the third lens group G3, the focusing ability of the third lens group G3 for light of different wavelengths can be more precisely controlled, thereby effectively optimizing chromatic aberration and improving imaging quality.

[0057] In some embodiments, the third lens group G3 includes, in order from the object side to the imaging side: a seventh lens 7 with positive optical power, an eighth lens 8 with negative optical power, a ninth lens 9 with positive optical power, a tenth lens 10 with negative optical power, an eleventh lens 11 with positive optical power, a twelfth lens 12 with negative optical power, a thirteenth lens 13 with positive optical power, and a fourteenth lens 14 with negative optical power;

[0058] Among them, the Abbe numbers of the ninth lens 9, the tenth lens 10, and the eleventh lens 11 are all greater than 30 and less than 40.

[0059] It should be noted that by controlling the Abbe numbers of the ninth lens 9, the tenth lens 10, and the eleventh lens 11 within the range of 30 to 40, the focusing ability of the ninth lens 9, the tenth lens 10, and the eleventh lens 11 for light of different wavelengths can be more precisely controlled, thereby effectively optimizing chromatic aberration and improving imaging quality.

[0060] In some embodiments, the seventh lens 7, the eighth lens 8, the ninth lens 9, and the tenth lens 10 are combined into a four-cemented lens.

[0061] It can be understood that by combining four positive and negative lenses, namely the seventh lens 7 with a positive refractive power, the eighth lens 8 with a negative refractive power, the ninth lens 9 with a positive refractive power, and the tenth lens 10 with a negative refractive power, into a four-cemented lens, chromatic dispersion can be compensated for each other, further reducing chromatic aberration, which helps to restore the true picture color; at the same time, it reduces the sensitivity to assembly tolerances in the production line; in addition, there is no need to worry about the relative position change between the lenses during the assembly of the four-cemented lens, which helps to improve the mass production yield.

[0062] In some embodiments, the first lens group G1 sequentially includes, from the object side to the imaging side: a first lens 1 with a positive refractive power, a second lens 2 with a positive refractive power, a third lens 3 with a negative refractive power, a fourth lens 4 with a positive refractive power, and a fifth lens 5 with a negative refractive power; the second lens group G2 includes: a sixth lens 6 with a negative refractive power; the third lens group G3 sequentially includes, from the object side to the imaging side: a seventh lens 7 with a positive refractive power, an eighth lens 8 with a negative refractive power, a ninth lens 9 with a positive refractive power, a tenth lens 10 with a negative refractive power, an eleventh lens 11 with a positive refractive power, a twelfth lens 12 with a negative refractive power, a thirteenth lens 13 with a positive refractive power, and a fourteenth lens 14 with a negative refractive power.

[0063] It should be noted that the specific data of the above structural embodiments are shown in Table 1:

[0064] Table 1

[0065] Surface number Surface type Radius of curvature Thickness Refractive index Abbe number Object Spherical surface Infinity Infinity 1 Spherical surface 56.395721 7.6 2.000689 25.435062 2 Spherical surface 137.760968 1.850056 3 Spherical surface 41.289478 8.8 1.496998 81.594687 4 Spherical surface 158.901548 3.150668 5 Spherical surface 137.029148 1 1.740773 27.761693 6 Spherical surface 27.492796 2.234981 7 Spherical surface 34.698561 9.6 1.496998 81.594687 8 Spherical surface -79.509437 1 1.846666 23.787324 9 Spherical surface 1053.028593 2.58935 10 Spherical surface 1000.00173 1 1.516797 64.212351 11 Spherical surface 37.740252 18.616668 STO Spherical surface Infinity 0.682319 13 Spherical surface 84.239429 7 1.603001 65.45962 14 Spherical surface -31.070911 1 1.761823 26.613203 15 Spherical surface 42.506585 6.4 1.953749 32.318108 16 Spherical surface -76.689724 1.2 1.647693 33.842283 17 Spherical surface 61.284056 5.206638 18 Spherical surface 58.047873 9.1 1.850136 30.060435 19 Spherical surface -59.780155 0.15 20 Spherical surface -184.399532 1 1.617998 63.405767 21 Spherical surface 49.55537 1.064393 22 Spherical surface 67.489847 4.75 1.846666 23.787324 23 Spherical surface -549.25125 4.968094 24 Spherical surface -36.335599 1 1.487491 70.41964 25 Spherical surface 500 12.698307 26 Spherical surface Infinity 2.5 1.516797 64.212351 27 Spherical surface Infinity 1 IMA Spherical surface Infinity

[0066] Among them, the surface serial number represents the surface serial number of each lens from the object side to the image side. Further, the lenses in the first lens group G1, the second lens group G2, the variable aperture STO, and the third lens group G3 are set according to the data in Table 1 and experiments are carried out. The experimental results can be referred to Figures 2 to 6 , and it can be seen from the figure that the lens can better meet the performance requirements of good aberration correction, small distortion, and high resolution; specifically, refer to Figure 2 , Figure 2 is a schematic diagram of longitudinal chromatic aberration. It can be seen that the chromatic aberration focal shift at the center is less than 50 microns, which can ensure no chromatic aberration before and after the focus; refer to Figure 3 , Figure 3 is a schematic diagram of field curvature distortion. It can be seen that the optical distortion of this optical system is less than 0.5%, and the distortion effect in the actual shooting is very small, and there is no distortion effect when viewed with the naked eye; refer to Figure 5 and Figure 6 , Figure 5 is a schematic diagram of MTF, Figure 6It is a schematic diagram of the MTF defocus curve. It can be seen that the MTF opposite the 30th line is greater than 0.48. In this area, the two characteristics of high resolution and defocus are highly concentrated, which facilitates rapid focusing.

[0067] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention.

Claims

1. An autofocus lens, characterized in that: From the object side to the imaging side, it includes: a first lens group, the first lens group having positive refractive power, and when focusing, the position of the first lens group relative to the image plane remains unchanged; a second lens group, the second lens group having negative optical power, and the second lens group moving along the optical axis during focusing; Variable aperture; a third lens group, the third lens group having positive refractive power, and when focusing, the position of the third lens group relative to the image plane remains unchanged; The lens satisfies the following conditional formula: Wherein, f1 represents the focal length value of the first lens group, f2 represents the focal length value of the second lens group, and f3 represents the focal length value of the third lens group.

2. The autofocus lens according to claim 1, characterized in that: The first lens group includes at least two lenses having a refractive index greater than 1.4 and less than 1.

5.

3. The autofocus lens according to claim 2, characterized in that: The first lens group includes, from the object side to the image side, a first lens with positive power, a second lens with positive power, a third lens with negative power, a fourth lens with positive power, and a fifth lens with negative power; Wherein, the refractive index of the second lens and the refractive index of the fourth lens are both greater than 1.4 and less than 1.

5.

4. The autofocus lens according to claim 3, characterized in that: The fourth lens and the fifth lens are combined into a doublet lens.

5. The autofocus lens according to claim 3, characterized in that: The first lens, the second lens and the third lens are all meniscus lenses.

6. The autofocus lens according to claim 1, wherein: The second lens group includes a sixth lens having negative optical power.

7. The autofocus lens according to claim 6, characterized in that: The refractive index of the sixth lens is greater than 1.5 and less than 1.

6.

8. The autofocus lens according to claim 1, wherein: The third lens group includes at least three lenses having an Abbe number greater than 30 and less than 40.

9. The autofocus lens according to claim 8, characterized in that: The third lens group includes, from the object side to the image side, a seventh lens having positive power, an eighth lens having negative power, a ninth lens having positive power, a tenth lens having negative power, an eleventh lens having positive power, a twelfth lens having negative power, a thirteenth lens having positive power, and a fourteenth lens having negative power; Wherein, the Abbe number of the ninth lens, the Abbe number of the tenth lens, and the Abbe number of the eleventh lens are all greater than 30 and less than 40.

10. The autofocus lens according to claim 9, characterized in that: The seventh lens, the eighth lens, the ninth lens and the tenth lens are combined into a quadruple lens.

Images