A coaxial telecentric lens and camera module

Abstract

Embodiments of the present application relate to the technical field of camera, and provide a coaxial telecentric lens and a camera module, the coaxial telecentric lens comprising a first lens group, a diaphragm, a light splitting element and a second lens group arranged from an object side to an image side; the first lens group has positive focal power; the second lens group has negative focal power; the combined focal length f2 of the second lens group and the focal length f of the coaxial telecentric lens satisfy the relationship: -0.52 < f2 / f < 0. The coaxial telecentric lens can well balance high resolution, uniform illumination and uniform image quality on the basis of low telecentricity.

Description

Technical Field

[0001] This application relates to the field of camera technology, and in particular to a coaxial telecentric lens and camera module. Background Technology

[0002] Machine vision inspection technology is widely used in all aspects of manufacturing. A coaxial telecentric lens is a type of industrial lens specially designed to correct parallax in traditional industrial lenses. Within a certain object distance range, it ensures that the magnification of the image remains constant regardless of the object distance. Coaxial telecentric lenses are widely used for surface imaging inspection of semiconductors, PCBs, and metal parts.

[0003] Coaxial telecentric lenses are mainly used with coaxial light sources to form camera modules. They can eliminate ghosting in the acquired images, have good uniformity, excel at imaging abnormal features on smooth surfaces, and have excellent performance in depicting local dents or scratches.

[0004] In related technologies, coaxial telecentric lenses can cause hot spots and ghosting on the detector when the object being detected is large and has diffuse reflection characteristics. This phenomenon is caused by the Lambertian property of diffuse scattering objects and the residual reflection of the surfaces of various optical elements in the optical system, which will result in decreased image contrast and stray light, seriously affecting the detection accuracy.

[0005] With the continuous improvement of industrial intelligence, the requirements for the accuracy of product defect detection are becoming increasingly stringent. Therefore, how to enable coaxial telecentric lenses to achieve a good balance of high resolution, low distortion, and uniform illumination at low light intensity has become an important issue in the industry. Summary of the Invention

[0006] Embodiments of this application provide a coaxial telecentric lens and camera module that can effectively balance high resolution, uniform illumination, and uniform image quality even in low light conditions.

[0007] To achieve the above objectives, the embodiments of this application adopt the following technical solutions:

[0008] In a first aspect, embodiments of this application provide a coaxial telecentric lens, comprising a first lens group, an aperture stop, a beam splitter, and a second lens group arranged along the object side to the image side; the first lens group has positive optical power; the second lens group has negative optical power; the combined focal length f2 of the second lens group and the focal length f of the coaxial telecentric lens satisfy the relationship: -0.52 <f2 / f<0。

[0009] By rationally allocating the optical power of each lens group in the coaxial telecentric lens, the combined focal length of the second lens group can be well balanced with that of the first lens group. This effectively corrects aberrations, reduces distortion, and ensures uniform illumination on the imaging plane, thereby improving image quality uniformity and resolution. When paired with a coaxial light source, the first lens group, with its positive optical power, has a certain light-gathering effect on large field-of-view rays on the object side, thus reducing telephoto power. Furthermore, when the combined focal length f2 of the second lens group satisfies the aforementioned relationship with the focal length f of the coaxial telecentric lens, stray light reflected from the beam-splitter on the object side of the second lens group converges at a point far from the image plane. This allows the coaxial telecentric lens to achieve high resolution, uniform illumination, and uniform image quality while maintaining low telephoto power. Additionally, compared to placing polarizers on the object side of the coaxial telecentric lens closer to the image side and on the image side closer to the object side, using beam-splitters in both the first and second lens groups allows the coaxial telecentric lens to meet optical performance requirements while relatively reducing costs.

[0010] In some embodiments, the magnification β2 of the second lens group and the magnification β of the coaxial telecentric lens satisfy the relationship: β2 / β>0.83.

[0011] When β2 / β satisfies the above relationship, the ghost spot generated by the optical element located on the object side of the second lens group can be magnified when passing through the second lens group, and the reflected image energy is diffused, making the energy at the periphery and center of the image plane more uniform.

[0012] In some embodiments, the first lens group includes a plurality of lenses arranged sequentially from the object side to the image side. The lens located at a first position in the direction from the object side to the image side is a first lens. The first lens has positive optical power. The refractive index nd1 of the first lens satisfies the relationship: nd1>1.8.

[0013] By reasonably selecting the refractive index of the first lens, when the above relationship is satisfied, that is, when the first lens is made of a material with a high refractive index, the first lens can collect light rays from a large field of view on the object side, which is beneficial for controlling the telecentricity.

[0014] In some embodiments, the first lens group includes a first lens, a second lens, and a third lens arranged sequentially from the object side to the image side; the second lens and the third lens form a cemented lens.

[0015] The above configuration not only helps to reduce tolerance sensitivity, thereby improving image quality, but also simplifies the assembly process of the first lens group by including cemented lenses.

[0016] In some embodiments, the Abbe number vd2 of the second lens and the Abbe number vd3 of the third lens satisfy the relationship: vd2-vd3>20; the refractive index nd2 of the second lens and the refractive index nd3 of the third lens satisfy the relationship: nd3-nd2>0.05.

[0017] When a coaxial telecentric lens satisfies the above relationship, the chromatic aberration of the coaxial telecentric lens can be effectively corrected, thus improving image quality.

[0018] In some embodiments, the second lens group includes at least a fourth lens and a fifth lens arranged sequentially from the object side to the image side, the fourth lens having positive optical power and the fifth lens having negative optical power.

[0019] By placing a fourth lens with positive optical power close to the first lens group, it is beneficial to balance the aberrations between the second lens group and the first lens group.

[0020] In some embodiments, the second lens group further includes a sixth lens located on the side of the fifth lens closer to the image side, the sixth lens having positive optical power.

[0021] With the above settings, the aberrations of the second lens group and the first lens group are balanced. When light passes through the second lens group, the light is smoother, thereby improving the image quality.

[0022] In some embodiments, the beam-splitting element is a non-polarizing beam-splitting prism, and the transmittance t and reflectance r of the beam-splitting surface of the beam-splitting element satisfy the relationship: t:r = 1:1.

[0023] In some embodiments, the beam splitter is composed of two right-angled prisms bonded together.

[0024] Secondly, embodiments of this application provide a camera module, including a light source and a coaxial telecentric lens as described in the first aspect, wherein the light source is located on the light-receiving surface of the beam-splitting element of the coaxial telecentric lens.

[0025] The coaxial telecentric lens in the camera module of this application embodiment has the same structure and technical effect as the coaxial telecentric lens in the first aspect, and will not be described again here.

[0026] In some embodiments, the camera module further includes a diffuser sheet located between the light source and the beam splitter.

[0027] By placing a diffuser between the light source and the beam splitter, the light becomes more uniform, which helps to improve the uniformity of image quality. Attached Figure Description

[0028] Figure 1This is a schematic diagram of the camera module provided in Embodiment 1 of this application;

[0029] Figure 2 MTF vs field diagram of the coaxial telecentric lens provided in Embodiment 1 of this application;

[0030] Figure 3 The distortion diagram is of the coaxial telecentric lens provided in Embodiment 1 of this application;

[0031] Figure 4 Illumination diagram of the imaging plane of the coaxial telecentric lens provided in Embodiment 1 of this application;

[0032] Figure 5 This is a schematic diagram of the same camera module provided in Embodiment 2 of this application;

[0033] Figure 6 MTF vs field diagram of the coaxial telecentric lens provided in Embodiment 2 of this application;

[0034] Figure 7 The distortion diagram is shown for the coaxial telecentric lens provided in Embodiment 2 of this application;

[0035] Figure 8 This is an illuminance diagram of the imaging plane of the coaxial telecentric lens provided in Embodiment 2 of this application.

[0036] The following are the labeling elements in the figure:

[0037] First lens group G1; Second lens group G2; First lens L1; Second lens L2; ​​Third lens L3; Fourth lens L4; Fifth lens L5; Sixth lens L6; Optical element LL1; Aperture stop STOP. Detailed Implementation

[0038] For ease of understanding, the English abbreviations and related technical terms used in the embodiments of this application will be explained and described below.

[0039] Focal power is equal to the difference between the convergence of the image-side beam and the convergence of the object-side beam. It characterizes the ability of a coaxial telecentric lens to deflect light rays.

[0040] A lens or lens group with positive optical power, having a positive focal length, and having the effect of converging light.

[0041] A lens or lens group with negative optical power has a negative focal length and has the effect of diverging light.

[0042] Focal length, also known as focal length, is a measure of the convergence or divergence of light in a coaxial telecentric lens. It refers to the perpendicular distance from the optical center of a lens or lens group to the focal plane when a distant object is focused into a sharp image. For prime lenses, the position of their optical center remains constant; for telephoto lenses, changes in the optical center result in changes in the focal length.

[0043] The effective focal length (EFL) of a lens refers to the distance from the center of the lens to the focal point.

[0044] The combined focal length is the combination of the focal lengths of the individual lenses in a lens group.

[0045] The object side is defined by the lens; the side where the object is located is called the object side, and the surface of the lens closest to the object side is called the object side surface.

[0046] The image side is the side on which the image of the object is located, with the lens as the boundary. The surface of the lens closest to the image side is called the image side surface.

[0047] An aperture diaphragm is a device used to control the amount of light passing through the lens and entering the sensor inside the camera body; it is usually located inside the lens.

[0048] The imaging plane is located on the image side of all lenses in a coaxial telecentric lens, and the plane on which the image is formed after light rays pass through each lens in the coaxial telecentric lens in sequence.

[0049] The optical axis is a vertical axis that passes through the center of a lens. The lens optical axis is the axis that passes through the centers of each lens in the lens.

[0050] The focal point is the point where parallel light rays converge after being refracted by a lens or lens group.

[0051] The Abbe number, also known as the dispersion coefficient, is the ratio of the difference in refractive index of an optical material at different wavelengths, representing the degree of dispersion of the material.

[0052] Magnification β is equal to the sensor diameter / field of view diameter. When selecting a lens, the sensor surface that the lens is compatible with must be larger than or equal to the matching camera surface; otherwise, it will result in a waste of resolution.

[0053] Aberrations: A lens has the property of an ideal optical system at the optical axis, where a near-axis ray emitted from a point on an object intersects the image plane at a point (i.e., the optical axis image point). However, in reality, light rays passing through different apertures of the lens rarely intersect perfectly at a single point, but rather deviate from the position of the near-axis image point. These differences are collectively referred to as aberrations.

[0054] Distortion, also known as image distortion, refers to the degree of distortion of the image formed by a coaxial telecentric lens relative to the object itself. Distortion is caused by the spherical aberration of the aperture; the height of the intersection point between the principal ray from different fields of view and the Gaussian image plane after passing through the coaxial telecentric lens is not equal to the ideal image height, and the difference between the two is the distortion.

[0055] Illuminance, simply put, is the amount of light (luminous flux) emitted by a light source that is incident on a surface, such as the imaging surface of a lens, in a certain direction with a certain intensity (light intensity). The illuminance of this surface can then be measured.

[0056] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0057] In the embodiments of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "multiple" means two or more.

[0058] like Figure 1 As shown, some embodiments of this application provide a camera module. The camera module includes a coaxial telecentric lens and a photosensitive element, with the photosensitive element located on the image side of the coaxial telecentric lens.

[0059] The working principle of the camera module is as follows: the light reflected from the subject passes through the coaxial telecentric lens to generate an optical image, which is then projected onto the photosensitive surface of the photosensitive element. The photosensitive element converts the optical image into an electrical signal, i.e., an analog image signal, and transmits it to the processor.

[0060] A photosensitive element (also known as an image sensor) is a semiconductor chip containing hundreds of thousands to millions of photodiodes on its surface. When illuminated by light, these photodiodes generate electrical charges. Photosensitive elements can be charge-coupled devices (CCDs) or complementary metal-oxide-semiconductor (CMOS) devices. CCDs are made of a highly sensitive semiconductor material that converts light into electrical charges. A charge-coupled device consists of many photosensitive units, typically measured in megapixels. When light illuminates the surface of the photosensitive element, each photosensitive unit reflects a charge onto the component. The signals generated by all the photosensitive units are added together to form a complete image.

[0061] Coaxial telecentric lenses primarily utilize the refraction principle of lenses for imaging. Light rays from a scene pass through the coaxial telecentric lens, forming a clear image on the focal plane, which is then recorded by a photosensitive element located on the focal plane. These coaxial telecentric lenses can be, but are not limited to, industrial lenses.

[0062] like Figure 1 As shown, this application embodiment provides a coaxial telecentric lens, including a first lens group G1, an aperture stop, a beam splitter LL1, and a second lens group G2 arranged along the object side to the image side; the first lens group G1 has positive optical power; the second lens group G2 has negative optical power; the combined focal length f2 of the second lens group G2 and the focal length f of the coaxial telecentric lens satisfy the relationship: -0.52 <f2 / f<0。

[0063] The aforementioned beam splitter LL1 primarily functions to split light. When a light source is placed on the light-inlet surface of the beam splitter LL1, the light emitted by the light source is deflected by 90 degrees after passing through the beam splitter LL1, thus achieving coaxial illumination.

[0064] By rationally allocating the optical power of each lens group in the coaxial telecentric lens, the aberrations of the second lens group G2 can be well balanced with those of the first lens group G1, thereby effectively correcting aberrations, reducing distortion, and ensuring uniform illumination on the imaging plane, which in turn helps improve image quality uniformity and resolution. When paired with a coaxial light source, the first lens group G1, with its positive optical power, has a certain light-gathering effect on the large field of view of the object side, thus reducing telephoto power. Furthermore, when the combined focal length f2 of the second lens group G2 and the focal length f of the coaxial telecentric lens satisfy the above relationship, the stray light reflected by the beam splitter LL1 on the object side of the second lens group G2 converges at a point far from the image plane IMA after passing through the second lens group G2. This allows the coaxial telecentric lens to achieve high resolution, uniform illumination, and uniform image quality while maintaining low telephoto power. In addition, compared to setting polarizers on the object plane near the image side and the image plane IMA near the object side of the coaxial telecentric lens, by setting beam-splitting element LL1 in the first lens group G1 and the second lens group G2, the cost of the coaxial telecentric lens is relatively reduced while meeting the optical performance requirements.

[0065] It should be noted that the above-mentioned beam splitting element LL1 can be a non-polarizing beam splitting prism, which is composed of two right-angle prisms cemented together. The transmittance t and reflectance r of the beam splitting surface of the beam splitting element LL1 satisfy the relationship: t:r = 1:1.

[0066] With the above setup, a coaxial telecentric lens paired with a light source enables coaxial illumination.

[0067] In some embodiments, the magnification β2 of the second lens group G2 and the magnification β of the coaxial telecentric lens satisfy the relationship: β2 / β>0.83.

[0068] If β2 / β is too small, the ghosting spot produced by the optical element LL1 on the object side of the second lens group G2 will be more obvious, resulting in a more concentrated energy in the center of the imaging plane of the coaxial telecentric lens, while the energy in the periphery will be less.

[0069] When β2 / β satisfies the above relationship, the ghost spot generated by the optical element on the object side of the second lens group G2 can be magnified when passing through the second lens group G2, and the reflected image energy is diffused, making the energy at the periphery and center of the image plane more uniform.

[0070] In the design of coaxial telecentric lenses, the refractive index and Abbe number of each lens in the lens are important parameters in the optical design process, especially the refractive index and Abbe number of each lens in the first lens group.

[0071] In some embodiments, the first lens group G1 includes a first lens L1, a second lens L2, and a third lens L3 arranged sequentially from the object side to the image side; the first lens L1 has positive optical power; the refractive index nd1 of the first lens L1 satisfies the relationship: nd1>1.8.

[0072] In a coaxial telecentric lens, the refractive index nd1 of the first lens L1 is crucial to the optical performance of the lens. If the refractive index nd1 of the first lens L1 is too small, the first lens L1 will have a poor light collection effect on the large field of view on the object side, which is not conducive to reducing the telecentricity of the coaxial telecentric lens.

[0073] By reasonably selecting the refractive index nd1 of the first lens L1, when the refractive index nd1 of the first lens L1 satisfies the above relationship, that is, when the first lens L1 is made of a high refractive index material, the first lens L1 can collect light from a large field of view in the object side, which is beneficial to controlling the telecentricity.

[0074] In some embodiments, the Abbe number vd2 of the second lens L2 and the Abbe number vd3 of the third lens L3 satisfy the relationship: vd2-vd3>20; the refractive index nd2 of the second lens L2 and the refractive index nd3 of the third lens L3 satisfy the relationship: nd3-nd2>0.05.

[0075] When the refractive index nd2 of the second lens L2 and the refractive index nd3 of the third lens L3 in the first lens group G1 satisfy the above relationship, and the Abbe number vd2 of the second lens L2 and the Abbe number vd3 of the third lens L3 satisfy the above relationship, the chromatic aberration of the coaxial telecentric lens can be effectively corrected and the image quality can be improved.

[0076] Figure 1 A structural diagram of the camera module according to Embodiment 1 is shown. The camera module includes a coaxial telecentric lens and a light source. The coaxial telecentric lens includes a first lens group G1, an optical element LL1, an aperture stop, a second lens group G2, and a photosensitive element (located on the imaging plane IMA) arranged from the object side to the image side. The first lens group G1 includes a first lens L1, a second lens L2, and a third lens L3 arranged sequentially from the object side to the image side. The second lens L2 and the third lens L3 are combined to form a cemented lens. The second lens group G2 includes a fourth lens L4, a fifth lens L5, and a sixth lens L6 arranged sequentially from the object side to the image side.

[0077] A diffuser is also provided between the light source and the optical element LL1. This makes the light more uniform, thus improving the uniformity of the image. The light source mentioned above is a coaxial light source, located on the light-inlet surface of the beam-splitting element LL1.

[0078] Tables 1a to 1d respectively provide the specific parameter values ​​of each lens of the coaxial telecentric lens in an optional embodiment of Embodiment 1 of this application.

[0079] Table 1a

[0080] Face number Surface type R value thickness Refractive index nd Abbe number vd Sur1 Standard 166.67 4.39 1.95 32.20 Sur2 Standard -193.16 57.61 Sur3 Standard 19.30 4.23 1.59 68.90 Sur4 Standard -35.07 5.00 1.74 28.30 Sur5 Standard 13.69 11.89 Sur6 Standard infinity 10.00 1.52 64.20 Stop Standard infinity 1.72 Sur7 Standard 29.14 2.12 1.60 60.00 Sur8 Standard -37.85 7.94 Sur9 Standard -11.39 1.20 1.49 70.30 Sur10 Standard 90.57 1.55 Sur11 Standard 38.93 2.71 2.01 28.40 Sur12 Standard -86.59 17.7 Image Standard Infinity -

[0081] It should be noted that in Table 1a, "Surface Number" refers to the number of each surface arranged sequentially from the object side to the image side. The radius R value is the lens corresponding to the surface number, that is, the radius of curvature of the object side or image side of the lens corresponding to each surface number at the optical axis. "Infinite" in the "Radius of Curvature" parameter series means that the object side or image side of the lens is a plane. The first value in the "Thickness / Spacing" parameter series for each lens is the thickness of the lens on the optical axis, and the second value is the distance on the optical axis from the image side of the lens to the object side of the next lens. The value of the stop STOP in the "Thickness" parameter series is the distance on the optical axis from the center of the stop STOP to the object side of the next lens.

[0082] In Example 1, as shown in Table 1a, the refractive index nd1 of the first lens L1 of the coaxial telecentric lens is 1.95; the refractive index nd2 of the second lens L2 is 1.59; the refractive index nd3 of the third lens L3 is 1.74; the Abbe number vd2 of the second lens L2 is 68.9; and the Abbe number vd3 of the third lens L3 is 28.3.

[0083] The parameters of the coaxial telecentric lens in Example 1 satisfy the relationship shown in Table 1b.

[0084] Table 1b

[0085] Relationship <![CDATA[f2 / f]]> <![CDATA[β2 / β]]> numerical values -0.31 1.1

[0086] Note: The following annotations explain the relationship between the coaxial telecentric lenses in the various embodiments:

[0087] f is the focal length of the coaxial telecentric lens;

[0088] f2 is the combined focal length of the second lens group, that is, the combined focal length of all the lenses in the second lens group;

[0089] The positive and negative values ​​of the optical power of each lens in the coaxial telecentric lens in Example 1 are shown in Table 1c.

[0090] Table 1c

[0091]

[0092] It should be noted that the "+" and "-" in Table 1c represent the positive and negative optical power of each lens in the coaxial telecentric lens of Example 1. "+" indicates that the lens has positive optical power; "-" indicates that the lens has negative optical power.

[0093] The concavity or convexity of the object side or image side of each lens in the coaxial telecentric lens of Example 1 at the optical axis is shown in Table 1d.

[0094] Table 1d

[0095]

[0096] It should be noted that in Table 1d, "+-" and "-+" represent the concavity or convexity of the object-side or image-side of each lens at the optical axis. "+-" indicates that both the object-side and image-side of the lens are convex towards the object at the optical axis, i.e., a biconvex structure / biconvex lens; "-+" indicates that both the object-side and image-side of the lens are concave towards the object at the optical axis, i.e., a biconcave structure / biconcave lens. Of course, in addition to the concave and convex configurations mentioned above, the lenses in a coaxial telecentric lens can also include any one or more of the following: "++", "∞-", "-∞", "∞+", "+∞", and "--". "++" represents that both the object-side and image-side surfaces of the lens are convex towards the object; "∞-" represents that the object-side surface of the lens is flat at the optical axis, and the image-side surface is concave towards the object; "-∞" represents that the object-side surface of the lens is concave towards the object, and the image-side surface is flat at the optical axis; "∞+" represents that the object-side surface of the lens is flat at the optical axis, and the image-side surface is convex towards the object; "+∞" represents that the object-side surface of the lens is convex towards the object, and the image-side surface is flat at the optical axis; and "--" represents that both the object-side and image-side surfaces of the lens are concave towards the object. No specific limitations are imposed here.

[0097] Combination Figure 1 The diagram shows the structure of the coaxial telecentric lens in the camera module of Embodiment 1, and Tables 1a to 1d show that the main parameters of the coaxial telecentric lens in Embodiment 1 satisfy the relationship in Table 1b, as well as the concavity and convexity of each lens at the optical axis. Simulation results were obtained for the coaxial telecentric lens of Embodiment 1. Figures 2-4 .

[0098] in: Figure 2The MTF vs field plot of the coaxial telecentric lens provided in Embodiment 1 of this application is also called the MTH plot. MTF is short for Modulation Transfer Function, which is a function that describes the modulation degree as a function of spatial frequency. Both the MTH plot and the MTF plot are curves reflecting the contrast (fidelity) reproduction of the optical lens. The horizontal axis of the MTF plot is the distance from the center to the edge, while the vertical axis of the MTF plot reflects the quality of contrast, or in other words, the quality of fidelity. However, the horizontal axis of the MTH plot is the normalized field of view, and the vertical axis is the same as that of the MTF plot. Higher values ​​on the vertical axis of both the MTH and MTF plots indicate better fidelity and higher resolution of the optical lens.

[0099] Figure 3 This is a distortion diagram of a coaxial telecentric lens provided in Embodiment 1 of this application. The distortion diagram represents the percentage distortion of the coaxial telecentric lens as the field of view changes, where the horizontal axis represents the percentage distortion and the vertical axis represents the normalized field of view height.

[0100] Figure 4 Illumination diagram of the imaging plane of the coaxial telecentric lens provided in Embodiment 1 of this application.

[0101] The above descriptions of the MTF vs field plot, distortion plot, and illuminance plot are the same as those in other embodiments, and will not be repeated below.

[0102] from Figure 2 It can be seen that the 0-1.0 field-of-view lens has an MTF greater than 0.9 at 10 lp / mm, and the 0-1.0 field-of-view lens has an MTF greater than 0.7 at 40 lp / mm, indicating good color reproduction, high resolution, and excellent imaging.

[0103] from Figure 3 It can be seen that the absolute value of distortion of the coaxial telecentric lens is less than 0.1%.

[0104] from Figure 4 It can be seen that the highest energy of the image on the imaging plane IMA is 1.3E~0.8 W / cm^2, the lowest energy is 0.72E~0.8 W / cm^2, and the uniformity reaches 55%.

[0105] Figure 5 A structural diagram of the camera module in Embodiment 2 is shown. The main difference between the camera module in Embodiment 2 and the camera module in Embodiment 1 is the difference in the parameters and conditions satisfied by each lens in the coaxial telecentric lens, and the concavity or convexity of the object side or image side of each lens at the optical axis.

[0106] Of course, in addition to six lenses, the number of lenses in a coaxial telecentric lens can also be five, seven, eight, or other numbers, provided that the optical performance requirements are met. No specific limitation is made here.

[0107] Tables 2a to 2d provide the specific parameter values ​​for each lens of the coaxial telecentric lens in one of the optional embodiments of Embodiment 2 of this application.

[0108] Table 2a

[0109] Face number Surface type R value thickness Refractive index nd Abbe number vd Sur1 Standard 86.95 5.18 1.81 41.20 Sur2 Standard -376.53 56.78 Sur3 Standard 16.18 5.00 1.59 68.90 Sur4 Standard -41.45 5.00 1.65 33.90 Sur5 Standard 8.47 7.52 Sur6 Standard infinity 10.00 1.52 64.20 STOP Standard infinity 7.00 Sur7 Standard 176.01 2.41 1.60 60.00 Sur8 Standard -17.44 20.00 Sur9 Standard -14.02 5.00 1.74 35.00 Sur10 Standard -34.94 8.97 Sur11 Standard 56.96 2.93 1.91 35.30 Sur12 Standard -111.95 31.50 Image Standard Infinity -

[0110] In Example 2, as shown in Table 2a, the refractive index nd1 of the first lens L1 of the coaxial telecentric lens is 1.81; the refractive index nd2 of the second lens L2 is 1.59; the refractive index nd3 of the third lens L3 is 1.65; the Abbe number vd2 of the second lens L2 is 68.9; and the Abbe number vd3 of the third lens L3 is 33.9.

[0111] The parameters of the coaxial telecentric lens in Example 2 satisfy the relationship shown in Table 2b.

[0112] Table 2b

[0113] Relationship <![CDATA[f2 / f]]> <![CDATA[β2 / β]]> numerical values -0.33 0.95

[0114] The optical power of each lens in the coaxial telecentric lens in Example 2 is shown in Table 2c.

[0115] Table 2c

[0116]

[0117] The concavity or convexity of the object side or image side of each lens in the coaxial telecentric lens of Example 2 at the optical axis is shown in Table 2d.

[0118] Table 2d

[0119]

[0120] Combination Figure 5 The diagram shows the structure of the coaxial telecentric lens in the camera module of Example 2, and Tables 2a to 2d show that the main parameters of the coaxial telecentric lens in Example 2 satisfy the relationship in Table 2b, as well as the concavity and convexity of each lens at the optical axis. The MTF vs field diagram, distortion diagram, and illuminance diagram of the coaxial telecentric lens of Example 2 are obtained through simulation.

[0121] from Figure 6It can be seen that the 0-1.0 field-of-view lens has an MTF greater than 0.9 at 10 lp / mm, and the 0-1.0 field-of-view lens has an MTF greater than 0.7 at 40 lp / mm, indicating good color reproduction, high resolution, and excellent imaging.

[0122] from Figure 7 It can be seen that the absolute value of distortion of the coaxial telecentric lens is less than 0.1%.

[0123] from Figure 8 It can be seen that the highest energy of the image in the IMA on the imaging plane is 2E~0.8w / cm^2, the lowest energy is 1E~0.8w / cm^2, and the uniformity reaches 50%.

[0124] In summary, the coaxial telecentric lens of this application achieves a telecentricity of less than or equal to 0.1, a target area of ​​up to 19mm, an MTF greater than or equal to 0.7, an absolute distortion value of less than 0.1%, and an image uniformity of 50% or more on the imaging plane IMA, thereby achieving the goal of balancing high resolution, low distortion, and uniform illumination.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A coaxial telecentric lens, characterized in that, It includes a first lens group, an aperture, a beam splitter, and a second lens group arranged from the object side to the image side; The first lens group consists of a first lens, a second lens, and a third lens arranged from the object side to the image side. The second lens group consists of a fourth lens, a fifth lens, and a sixth lens arranged from the object side to the image side. The coaxial telecentric lens has six lenses with optical power. The first lens has positive optical power, the second lens has positive optical power, the third lens has negative optical power, the fourth lens has positive optical power, the fifth lens has negative optical power, and the sixth lens has positive optical power, so that the first lens group has positive optical power. The second lens group has negative optical power; The first lens is a biconvex lens, the second lens is a biconvex lens, the third lens is a biconcave lens, the fourth lens is a biconvex lens, the sixth lens is a biconvex lens, and the object surface of the fifth lens is concave towards the object side at the optical axis; The combined focal length f2 of the second lens group and the focal length f of the coaxial telecentric lens satisfy the following relationship: -0.52 <f2 / f<0。 2. The coaxial telecentric lens according to claim 1, characterized in that, The magnification β2 of the second lens group and the magnification β of the coaxial telecentric lens satisfy the following relationship: β2 / β>0.

83.

3. The coaxial telecentric lens according to claim 1, characterized in that, The first lens has positive optical power; the refractive index nd1 of the first lens satisfies the relationship: nd1>1.

8.

4. The coaxial telecentric lens according to any one of claims 1 to 3, characterized in that, The second lens and the third lens together form a cemented lens; And / or, the Abbe number vd2 of the second lens and the Abbe number vd3 of the third lens satisfy the relationship: vd2-vd3>20; the refractive index nd2 of the second lens and the refractive index nd3 of the third lens satisfy the relationship: nd3-nd2>0.

05.

5. The coaxial telecentric lens according to any one of claims 1 to 3, characterized in that, The beam splitting element is a non-polarizing beam splitting prism, and the transmittance t and reflectance r of the beam splitting surface of the beam splitting element satisfy the relationship: t:r=1:

1.

6. The coaxial telecentric lens according to claim 5, characterized in that, The beam splitter is composed of two right-angled prisms bonded together.

7. A camera module, characterized in that, include: The coaxial telecentric lens according to any one of claims 1 to 6; A light source, wherein the light source is located on the light-receiving surface of the beam-splitting element of the coaxial telecentric lens.

8. The camera module according to claim 7, characterized in that, It also includes a diffuser sheet located between the light source and the beam splitter.

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