Fixed-focus optical system and vehicle-mounted lens

Abstract

The utility model discloses a fixed-focus optical system and a vehicle-mounted lens, and relates to the technical field of optics, and the fixed-focus optical system is provided with an object side and an image side which are oppositely arranged along the direction of an optical axis. The fixed-focus optical system is composed of a first lens, a diaphragm, a second lens, a third lens, a fourth lens and a photosensitive chip which are sequentially arranged from the object side to the image side. Wherein the focal power of the first lens is negative, the object side surface is a convex surface, and the image side surface is a concave surface; the focal power of the second lens is positive, the object side surface is a convex surface, and the image side surface is a convex surface; the focal power of the third lens is positive, the object side surface is a concave surface, and the image side surface is a convex surface; the focal power of the fourth lens is negative, the object side surface is a concave surface, and the image side surface is a concave surface; the fixed-focus optical system is high in resolution, low in temperature drift, small in size, bright in picture and better in imaging effect.

Description

Technical Field

[0001] The utility model relates to the technical field of optics, in particular to a fixed-focus optical system and a vehicle-mounted lens. Background Art

[0002] With the development of intelligent vehicles and autonomous driving technology, driver monitoring systems (DMS) have become an essential component of vehicle safety. Using cameras, DMS monitors the driver's status in real time, such as fatigue and distraction, and issues timely alerts to ensure driving safety. A core component of DMS is the camera lens, whose image quality directly impacts system performance and reliability.

[0003] Currently, most automotive DMS lenses are made of glass, and some are made of a glass-plastic hybrid design, which cannot guarantee optimal imaging quality in complex environments with large temperature differences. Utility Model Content

[0004] The main purpose of the utility model is to provide a fixed-focus optical system and a vehicle-mounted lens, aiming to improve the resolution, achieve miniaturization, low temperature drift, and better imaging effect.

[0005] To achieve the above-mentioned object, the present invention proposes a fixed-focus optical system, wherein the fixed-focus optical system has an object side and an image side arranged opposite to each other along the optical axis, and the fixed-focus optical system is composed of a first lens, an aperture, a second lens, a third lens, a fourth lens, and a photosensitive chip arranged in sequence from the object side to the image side;

[0006] The first lens has a negative optical power, a convex object-side surface, and a concave image-side surface;

[0007] The second lens has positive optical power, a convex object-side surface, and a convex image-side surface;

[0008] The third lens has positive optical power, a concave object-side surface, and a convex image-side surface;

[0009] The fourth lens has negative optical power, a concave object-side surface, and a concave image-side surface.

[0010] In one embodiment, the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, and the focal length of the fourth lens is f4. The focal lengths of the first lens, the second lens, the third lens, and the fourth lens satisfy the following relationship: 6mm<|f1|<10mm, 4mm<|f2|<7mm, 2mm<|f3|<4.5mm, and 3mm<|f4|<6.5mm.

[0011] In one embodiment, the refractive index of the first lens is n1, the refractive index of the second lens is n2, the refractive index of the third lens is n3, and the refractive index of the fourth lens is n4. The refractive indices of the first lens, the second lens, the third lens, and the fourth lens satisfy the following relationship: 1.60≤n1≤1.90, 1.80≤n2≤2.05, 1.70≤n3≤2.05, and 1.50≤n4≤1.70.

[0012] In one embodiment, the dispersion coefficient of the first lens is v1, the dispersion coefficient of the second lens is v2, the dispersion coefficient of the third lens is v3, and the dispersion coefficient of the fourth lens is v4. The dispersion coefficients of the first lens, the second lens, the third lens, and the fourth lens satisfy the following relationship: 40.0≤v1≤60.0, 18.0≤v2≤40.0, 25.0≤v3≤50.0, and 50≤v4≤75.

[0013] In one embodiment, the image plane diameter of the photosensitive chip is IC, wherein IC≤4.8mm.

[0014] In one embodiment, the first lens and the third lens are aspherical lenses, and the second lens and the fourth lens are spherical lenses.

[0015] In one embodiment, the total optical length of the fixed-focus optical system is TTL, and the effective focal length of the fixed-focus optical system is EFL, wherein TTL / EFL≤2.3.

[0016] In one embodiment, the aperture value of the fixed-focus optical system is F, wherein 2.2≤F≤2.4.

[0017] In one embodiment, the fixed-focus optical system includes a filter, and the filter is arranged between the fourth lens and the photosensitive chip along the optical axis; and / or,

[0018] The fixed-focus optical system further includes a protective glass, which is disposed between the fourth lens and the photosensitive chip along the optical axis and close to the photosensitive chip.

[0019] The present invention also provides a vehicle-mounted lens, comprising a fixed-focus optical system, wherein the fixed-focus optical system has an object side and an image side disposed opposite to each other along an optical axis, and the fixed-focus optical system comprises a first lens, an aperture, a second lens, a third lens, a fourth lens, and a photosensitive chip, which are arranged in sequence from the object side to the image side;

[0020] The first lens has a negative optical power, a convex object-side surface, and a concave image-side surface;

[0021] The second lens has positive optical power, a convex object-side surface, and a convex image-side surface;

[0022] The third lens has positive optical power, a concave object-side surface, and a convex image-side surface;

[0023] The fourth lens has negative optical power, a concave object-side surface, and a concave image-side surface.

[0024] By combining a negative-power first lens and a positive-power second lens, this new lens design facilitates the control of thermal drift in the optical system and the collection and control of light entering the entire system. By comprehensively adjusting the focal power of each lens, the lens effectively controls light distribution, allowing for greater light flow while achieving a more compact structure. Furthermore, by combining different lenses and rationally allocating focal power, the lens achieves high resolution, low-temperature drift, a compact size, and a brighter image, resulting in superior imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0026] Figure 1 This is a structural schematic diagram of an embodiment of a fixed-focus optical system provided by the present utility model;

[0027] Figure 2 for Figure 1 A schematic diagram of an MTF curve of an embodiment of a medium fixed-focus optical system;

[0028] Figure 3 for Figure 1 A schematic diagram of an MTF curve of another embodiment of a medium-fixed-focus optical system.

[0029] Description of Figure Numbers:

[0030] 100. Fixed-focus optical system; 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Aperture; 6. Photosensitive chip; 7. Filter; 8. Protective glass.

[0031] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0033] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0034] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of such features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme in which A and B are satisfied at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0035] The present invention provides a fixed-focus optical system 100 .

[0036] First, it's important to understand that focal power is equal to the difference between the image-side and object-side beam convergences, and it characterizes an optical system's ability to deflect light. The larger the absolute value of the focal power, the greater the light-bending ability; the smaller the absolute value, the weaker the light-bending ability. When the focal power is a positive number, the light is refracted in a convergent manner; when the focal power is a negative number, the light is refracted in a divergent manner. Focal power can be applied to characterize a specific refractive surface of a lens, a single lens, or a system composed of multiple lenses.

[0037] See also Figure 1In one embodiment of the present invention, the fixed-focus optical system 100 has an object side and an image side that are opposite to each other along the optical axis. The fixed-focus optical system 100 is composed of a first lens 1, an aperture 5, a second lens 2, a third lens 3, a fourth lens 4, and a photosensitive chip 6, which are arranged in sequence from the object side to the image side; wherein, the first lens 1 has a negative optical power, a convex object-side surface, and a concave image-side surface; the second lens 2 has a positive optical power, a convex object-side surface, and a convex image-side surface; the third lens 3 has a positive optical power, a concave object-side surface, and a convex image-side surface; the fourth lens 4 has a negative optical power, a concave object-side surface, and a concave image-side surface.

[0038] The first lens 1 has a positive optical power, a convex object side surface, and a concave image side surface, which can introduce more light, thereby making the fixed-focus optical system 100 small in size; the aperture 5 is arranged between the first lens 1 and the second lens 2, and can adjust the field of view, block the far-axis light, and prevent the far-axis light from affecting the imaging quality, thereby improving the image quality and making the lens have a large light throughput; the object side surface of the second lens 2 is concave, and the image side surface is concave, and the object side surface of the third lens 3 is convex, and the image side surface is convex. Through such an arrangement, the concave and convex surfaces of the second lens 2 and the third lens 3 complement each other, fit more closely, and have a more compact structure; in addition, it is also ensured that the second lens 2 has a positive optical power and the third lens 3 has a positive optical power, which controls the light trend and improves the resolution.

[0039] In the technical solution of this utility model, by providing a first lens 1 with negative optical power and a second lens 2 with positive optical power, the overall focal length is maintained stable and thermal compensation is achieved, which facilitates the control of temperature drift of the optical system and the control and collection of light entering the entire optical system. By comprehensively adjusting the optical power of each lens, the lens can effectively control the direction of light, allowing more light to flow while achieving a more compact structure. Furthermore, by combining different lenses and rationally allocating optical power, the lens achieves high resolution, low temperature drift, compact size, bright images, and better imaging effects.

[0040] See also Figure 2In one embodiment of the present invention, it should be understood that the focal length refers to the distance from the rear surface of the lens to the image plane in an optical system. The focal length determines the magnification and viewing angle of the image. The optical power is the reciprocal of the focal length. The focal length of the first lens 1 is f1, the focal length of the second lens 2 is f2, the focal length of the third lens 3 is f3, and the focal length of the fourth lens is f4. The focal lengths of the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 satisfy the following relationship: 6mm<|f1|<10mm, 4mm<|f2|<7mm, 2mm<|f3|<4.5mm, and 3mm<|f4|<6.5mm. Through the mutual combination of different lenses and the reasonable distribution of optical power, the optical system has a small volume while improving the resolution of the fixed-focus optical system 100. In addition, by reasonably setting the focal length ratio, the lens does not defocus under environmental conditions of -40℃ to +105℃, and the working performance is more stable.

[0041] In one embodiment of the present invention, the refractive index of the first lens 1 is n1, the refractive index of the second lens 2 is n2, the refractive index of the third lens 3 is n3, and the refractive index of the fourth lens 4 is n4. The refractive indices of the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 satisfy the following relationship: 1.60≤n1≤1.90, 1.80≤n2≤2.05, 1.70≤n3≤2.05, and 1.50≤n4≤1.70. By controlling the refractive indices of the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4, the refraction angle and path of the light can be more precisely controlled, thereby ensuring that the light converges to the correct position and forms a clear, distortion-free image. This helps to improve the sharpness and color accuracy of the image.

[0042] In one embodiment of the present invention, the dispersion coefficient of the first lens 1 is v1, the dispersion coefficient of the second lens 2 is v2, the dispersion coefficient of the third lens 3 is v3, and the dispersion coefficient of the fourth lens 4 is v4. The dispersion coefficients of the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4 satisfy the following relationship: 40.0≤v1≤60.0, 18.0≤v2≤40.0, 25.0≤v3≤50.0, and 50≤v4≤75. It is understood that different colors of light will undergo different degrees of refraction when passing through the lens due to their different wavelengths, resulting in different focus positions, resulting in chromatic aberration, and affecting image clarity and color accuracy. By limiting the dispersion coefficients of the first lens 1, the second lens 2, the third lens 3, and the fourth lens 4, the refractive index differences of light of various wavelengths can be effectively balanced, chromatic aberration can be reduced, and image edges can be made clearer and color transitions more natural.

[0043] In one embodiment of the present invention, it can be understood that when the light-emitting surface is too large, the photosensitive chip 6 cannot collect all the light, affecting the imaging quality. For this reason, the image surface diameter of the photosensitive chip 6 is IC, where IC≤4.8mm, so that the fixed-focus optical system 100 can collect a complete image and improve the imaging effect.

[0044] See also Figure 1 In one embodiment of the present invention, the first lens 1 and the third lens 3 are aspherical lenses, and the second lens 2 and the fourth lens 4 are spherical lenses.

[0045] It can be understood that the characteristics of aspherical lenses are: the curvature changes continuously from the center of the lens to the periphery of the lens. Unlike spherical lenses with a constant curvature from the center of the lens to the periphery of the lens, aspherical lenses have better curvature radius characteristics and have the advantages of improving distortion and astigmatism. After using aspherical lenses, the aberrations that occur during imaging can be eliminated as much as possible, thereby improving the imaging quality of the lens.

[0046] Specifically, in one embodiment of the present invention, the aspheric lens in the projection optical system

[0047]

[0048] Where c is the curvature corresponding to the radius; y is the radial coordinate (its unit is the same as the lens length unit); k is the conic coefficient, and A, B, C, D, E, F, G... represent the fourth-order, sixth-order, eighth-order, tenth-order, twelfth-order, fourteenth-order, sixteenth-order... aspheric coefficients, respectively.

[0049] Specifically, in one embodiment of the present invention, the focal length of the fixed-focus optical system is f=3.9 mm, the aperture value is F=2.4, the image plane diameter is 4.8 mm, and the diagonal field angle is 69.0°. The parameters of the fixed-focus optical system are shown in Table 1 below, and the even-order coefficients of each aspheric surface are shown in Table 2 below.

[0050] The above parameters can be used to accurately set the shape and size of the lens's aspherical surface to correct distortion and eliminate aberrations that occur during imaging as much as possible, thereby improving the imaging quality of the lens. They can also be used to correct pupil aberrations caused by large apertures, thereby improving the imaging quality of the system. At the same time, the number of spherical lenses set up can be greatly reduced, reducing the system volume.

[0051] Table 1

[0052]

[0053]

[0054] Table 2

[0055]

[0056] Figure 2 The figure shows the MTF curve of an embodiment of the present invention. Figure 2 It can be seen that the fixed-focus lens provided in this embodiment has good imaging capabilities.

[0057] In addition, in another embodiment of the present invention, the focal length of the fixed-focus optical system is f=4.85 mm, the aperture value is F=2.4, the image plane diameter is 4.8 mm, and the diagonal field angle is 69.0°. The parameters of the fixed-focus optical system are shown in Table 3 below, and the even-order coefficients of each aspheric surface are shown in Table 4 below.

[0058] The above parameters can be used to accurately set the shape and size of the lens's aspherical surface to correct distortion and eliminate aberrations that occur during imaging as much as possible, thereby improving the imaging quality of the lens. They can also be used to correct pupil aberrations caused by large apertures, thereby improving the imaging quality of the system. At the same time, the number of spherical lenses set up can be greatly reduced, reducing the system volume.

[0059] Table 3

[0060]

[0061] Table 4

[0062]

[0063] Figure 3 The figure shows the MTF curve of another embodiment of the present invention. Figure 3 It can be seen that the fixed-focus lens provided in this embodiment also has good imaging capabilities.

[0064] In one embodiment of the present invention, the total optical length of the fixed-focus optical system 100, that is, the distance from the object-side vertex of the first lens 1 to the photosensitive chip 6 is TTL, and the effective focal length of the fixed-focus optical system 100 is EFL, wherein TTL / EFL≤2.3; by limiting the total optical length, the volume of the fixed-focus lens can be further reduced, which is conducive to the miniaturization of the fixed-focus lens.

[0065] In one embodiment of the present invention, the aperture value of the fixed-focus optical system 100 is F, where 2.2≤F≤2.4; when the aperture value F of the fixed-focus optical system 100 is within this range, the resolution and contrast of the lens are optimal, the lens transmits a large amount of light, the picture brightness is high, and the imaging effect is better.

[0066] In one embodiment of the present invention, the fixed-focus optical system 100 includes a filter 7, which is arranged between the fourth lens 4 and the photosensitive chip 6 along the optical axis; and / or, the fixed-focus optical system 100 also includes a protective glass 8, which is arranged between the fourth lens 4 and the photosensitive chip 6 along the optical axis and is arranged close to the photosensitive chip 6.

[0067] The filter 7 can filter out stray light, preventing stray light from reaching the photosensitive chip 6 and interfering with normal visible light imaging, thereby improving imaging quality. The protective glass 8 is arranged close to the photosensitive chip 6 to provide effective protection for the photosensitive chip 6.

[0068] It can be understood that the filter 7 and the protective glass 8 can be set separately, and in order to provide a better imaging effect, the filter 7 and the protective glass 8 can also be set at the same time, and the light carrying the information of the subject can pass through the first lens 1, the aperture 5, the second lens 2, the third lens 3, the fourth lens 4, the filter 7 and the protective glass 8 in sequence and finally be imaged on the photosensitive chip 6.

[0069] The present invention also provides a vehicle-mounted lens, which includes a fixed-focus optical system. The specific structure of the fixed-focus optical system refers to the above-mentioned embodiment. Since the vehicle-mounted lens adopts all the technical solutions of all the above-mentioned embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above-mentioned embodiments, which will not be described one by one here.

[0070] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A fixed-focus optical system, characterized in that: The fixed-focus optical system has an object side and an image side that are oppositely arranged along the optical axis, and the fixed-focus optical system is composed of a first lens, an aperture, a second lens, a third lens, a fourth lens, and a photosensitive chip arranged in sequence from the object side to the image side; The first lens has a negative optical power, a convex object-side surface, and a concave image-side surface; The second lens has positive optical power, a convex object-side surface, and a convex image-side surface; The third lens has positive optical power, a concave object-side surface, and a convex image-side surface; The fourth lens has negative optical power, a concave object-side surface, and a concave image-side surface.

2. The fixed-focus optical system according to claim 1, wherein: The focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, and the focal length of the fourth lens is f4. The focal lengths of the first lens, the second lens, the third lens, and the fourth lens satisfy the following relationship: 6mm<|f1|<10mm, 4mm<|f2|<7mm, 2mm<|f3|<4.5mm, and 3mm<|f4|<6.5mm.

3. The fixed-focus optical system according to claim 1, wherein: The refractive index of the first lens is n1, the refractive index of the second lens is n2, the refractive index of the third lens is n3, and the refractive index of the fourth lens is n4. The refractive indices of the first lens, the second lens, the third lens, and the fourth lens satisfy the following relationship: 1.60≤n1≤1.90, 1.80≤n2≤2.05, 1.70≤n3≤2.05, and 1.50≤n4≤1.

70.

4. The fixed-focus optical system according to claim 1, wherein: The dispersion coefficient of the first lens is v1, the dispersion coefficient of the second lens is v2, the dispersion coefficient of the third lens is v3, and the dispersion coefficient of the fourth lens is v4. The dispersion coefficients of the first lens, the second lens, the third lens, and the fourth lens satisfy the following relationship: 40.0≤v1≤60.0, 18.0≤v2≤40.0, 25.0≤v3≤50.0, and 50≤v4≤75.

5. The fixed-focus optical system according to claim 1, wherein: The image plane diameter of the photosensitive chip is IC, where IC≤4.8mm.

6. The fixed-focus optical system according to claim 1, wherein: The first lens and the third lens are aspherical lenses, and the second lens and the fourth lens are spherical lenses.

7. The fixed-focus optical system according to claim 1, wherein: The total optical length of the fixed-focus optical system is TTL, and the effective focal length of the fixed-focus optical system is EFL, wherein TTL / EFL≤2.

3.

8. The fixed-focus optical system according to claim 1, wherein: The aperture value of the fixed-focus optical system is F, wherein 2.2≤F≤2.

4.

9. The fixed-focus optical system according to claim 1, wherein: The fixed-focus optical system includes a filter, and the filter is arranged between the fourth lens and the photosensitive chip along the optical axis; and / or, The fixed-focus optical system further includes a protective glass, which is disposed between the fourth lens and the photosensitive chip along the optical axis and close to the photosensitive chip.

10. A vehicle-mounted lens, characterized in that: The fixed-focus optical system comprises the fixed-focus optical system according to any one of claims 1 to 9.

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