A fixed focus lens

Abstract

The utility model discloses a fixed focus lens, including the first lens, second lens, third lens, fourth lens and fifth lens that light axis is arranged in order from object plane to image plane, the first lens includes the first image side of the side close to image plane, the sag of first image side is SAGY21, wherein, 1.250<=SAGY21<=1.450. Adopt above -mentioned technical features, through setting fixed focus lens includes five lenses with refractive power, the setting mode of five lenses guarantees the number setting of lens in optical system is reasonable, will not because lens quantity is too much to cause lens volume is bigger, also will not because lens quantity is too few to cause single lens because of assuming bigger refractive power to cause bigger aberration, guarantees the imaging aberration to be small while guaranteeing the miniaturization of optical system, and the imaging quality is high. Further, the utility model embodiment restricts the sag of first image side SAGY21 to satisfy 1.250<=SAGY21<=1.450, is favorable to reduce the aberration of system off -axis field of view, improves system visible light off -axis field of view resolving.

Description

Technical Field

[0001] This utility model relates to the field of optical device technology, and in particular to a fixed-focus lens. Background Technology

[0002] As the industry develops, various unique lenses are playing their distinctive roles in the market. Currently, the resolution of conventional medium and short telephoto lenses on the market varies greatly, and different scenarios also have certain requirements for lens size, making the design of compact lenses a challenge. Therefore, designing a high-resolution, compact lens can be considered a technological innovation. Utility Model Content

[0003] This invention provides a fixed-focus lens that achieves both small size and high image quality by rationally setting the number of lenses and the image-side sagitta of the first lens.

[0004] This utility model embodiment provides a fixed-focus lens, including a first lens, a second lens, a third lens, a fourth lens, and a fifth lens arranged sequentially along the optical axis from the object plane to the image plane; The first lens includes a first image-side surface near the image plane, and the sagitta of the first image-side surface is SAGY21, wherein 1.250≤SAGY21≤1.450.

[0005] Optionally, the fixed-focus lens further includes an aperture stop, which is disposed in the optical path between the second lens and the third lens; The combined optical power of the first lens and the second lens is φ12, and the optical power of the fixed-focus lens is φ; wherein, -0.600≤φ12 / φ≤-0.280.

[0006] Optionally, the first lens includes a first object-side surface near the object plane, and the fifth lens includes a fifth image-side surface near the image plane. The distance from the first object side to the aperture is S. 1O The distance from the aperture to the side of the fifth image is S. O5 Where -0.500≤S 1O / S O5 ≤0.700.

[0007] Optionally, the aperture number of the fixed-focus lens is F, where F≤1.70.

[0008] Optionally, the total optical length of the fixed-focus lens is TTL, wherein TTL < 18.100 mm.

[0009] Optionally, the center thickness of the second lens is TH12, the center thickness of the third lens is TH13, and the Abbe number of the third lens is vd3; Among them, 0.320≤(THI2+THI3) / TTL≤0.350, 42.00≤vd3≤85.00.

[0010] Optionally, the infrared defocusing amount corresponding to 0.850μm of the fixed-focus lens is less than 12μm.

[0011] Optionally, the Abbe number of the first lens is vd1, the Abbe number of the third lens is vd3, and the Abbe number of the fourth lens is vd4. Among them, 50.00≤vd1≤62.00, 18.00≤vd4≤25.00, and 2.100≤vd3 / vd4≤3.700.

[0012] Optionally, the first lens further includes a first object-side surface near the object surface, wherein the first object-side surface is convex and the first image-side surface is concave. The second lens includes a second object-side surface near the object plane and a second image-side surface near the image plane. The second object-side surface is concave, and the second image-side surface is convex. The third lens includes a third object-side surface near the object plane and a third image-side surface near the image plane. The third object-side surface is convex, and the third image-side surface is convex. The fourth lens includes a fourth object-side surface near the object plane and a fourth image-side surface near the image plane. The fourth object-side surface is convex, and the fourth image-side surface is concave. The fifth lens includes a fifth object-side surface near the object plane and a fifth image-side surface near the image plane. The fifth object-side surface is convex, and the fifth image-side surface is convex.

[0013] Optionally, the first lens, the second lens, the fourth lens, and the fifth lens are all plastic aspherical lenses, and the third lens is a glass spherical lens.

[0014] The fixed-focus lens provided in this embodiment of the invention comprises five lenses with optical power, a relatively small number of which ensures a miniaturized fixed-focus lens configuration. Furthermore, the arrangement of five lenses ensures a reasonable number of lenses in the optical system, preventing excessive lens size due to an excessive number of lenses, and avoiding excessive aberrations caused by a single lens bearing a large optical power due to an insufficient number of lenses. This ensures both miniaturization of the optical system and low imaging aberrations, resulting in high image quality. Moreover, a certain sag value indirectly reflects the aberrations borne on a single surface of the lens. In this embodiment of the invention, the sag SAGY21 of the first image side is constrained to satisfy 1.250≤SAGY21≤1.450, which helps reduce aberrations in the system's off-axis field of view and improves the system's resolution in the visible light off-axis field of view.

[0015] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this utility model, nor is it intended to limit the scope of this utility model. Other features of this utility model will become readily apparent from the following description. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 1 of this utility model; Figure 2 This is a schematic diagram of the visible light defocus MTF of a fixed-focus lens provided in Embodiment 1 of this utility model; Figure 3 This is a schematic diagram of the 0.850μm infrared defocus MTF of a fixed-focus lens provided in Embodiment 1 of this utility model; Figure 4 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 2 of this utility model; Figure 5 This is a schematic diagram of the visible light defocus MTF of a fixed-focus lens provided in Embodiment 2 of this utility model; Figure 6 This is a schematic diagram of the 0.850μm infrared defocus MTF of a fixed-focus lens provided in Embodiment 2 of this utility model; Figure 7 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 3 of this utility model; Figure 8This is a schematic diagram of the visible light defocus MTF of a fixed-focus lens provided in Embodiment 3 of this utility model; Figure 9 This is a schematic diagram of the 0.850μm infrared defocus MTF of a fixed-focus lens provided in Embodiment 3 of this utility model. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0019] Example 1 Figure 1 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 1 of this utility model, as shown below. Figure 1 As shown, the fixed-focus lens provided in this embodiment of the present invention includes a first lens 101, a second lens 102, a third lens 103, a fourth lens 104 and a fifth lens 105 arranged sequentially along the optical axis from the object plane to the image plane; the first lens 101 includes a first image-side surface near the image plane, and the sagitta of the first image-side surface is SAGY21, wherein 1.250≤SAGY21≤1.450.

[0020] Specifically, the fixed-focus lens provided in this embodiment includes five lenses with optical power: a first lens 101, a second lens 102, a third lens 103, a fourth lens 104, and a fifth lens 105. The arrangement of the five lenses ensures that the number of lenses in the optical system is reasonable. Too many lenses will result in a large lens size, and too few lenses will result in a large aberration due to a single lens bearing a large optical power. This ensures that the optical system is miniaturized while maintaining small imaging aberrations and high imaging quality.

[0021] Furthermore, the first lens 101 includes a first image-side surface near the image plane. The sag of the first image-side surface, SAGY21, satisfies 1.250≤SAGY21≤1.450. A certain sag value indirectly reflects the aberration carried on a single surface of the lens. By constraining the sag of the first lens image-side surface, it is beneficial to reduce the aberration in the off-axis field of view of the system and improve the resolution of the off-axis field of view of the visible light of the system.

[0022] In summary, by setting a fixed-focus lens including five lenses with optical power, the number of lenses in the optical system is reasonably set. Too many lenses result in excessively large lens sizes, while too few lenses cause significant aberrations due to individual lenses bearing too much optical power. This ensures both miniaturization of the optical system and low imaging aberrations, resulting in high image quality. Furthermore, constraining the sag SAGY21 of the first image side to satisfy 1.250≤SAGY21≤1.450 helps reduce off-axis aberrations and improve the system's off-axis resolution in the visible light field.

[0023] Based on the above embodiments, continue to refer to Figure 1 As shown, the fixed-focus lens also includes an aperture stop STO, which is disposed in the optical path between the second lens 102 and the third lens 103; the combined optical power of the first lens 101 and the second lens 102 is φ12, and the optical power of the fixed-focus lens is φ; wherein, -0.600≤φ12 / φ≤-0.280.

[0024] Specifically, the optical system provided in this embodiment may further include an aperture stop STO. Setting an aperture stop STO can adjust the propagation direction of the light beam, which is beneficial to improving image quality. Furthermore, the aperture stop STO can be set in the optical path between the second lens 102 and the third lens 103, that is, the aperture stop STO is set in the optical system, which is beneficial to reducing the aperture value and achieving a large aperture.

[0025] Continue to refer to Figure 2 As shown, the optical system may further include a filter 106, which is disposed in the optical path between the fifth lens 105 and the image plane to filter out stray light and improve imaging performance. Furthermore, the fixed-focus lens provided in this embodiment may also include a protective glass, which may be disposed on the image side of the filter to protect the optical system.

[0026] Furthermore, the combined optical power φ12 of the first lens 101 and the second lens 102 satisfies -0.600≤φ12 / φ≤-0.280 with respect to the optical power φ of the fixed-focus lens. The negative optical power anti-telephoto structure of the front lens group with aperture stop STO can effectively improve the relative aperture of the system, which is beneficial for the system to achieve the characteristics of a large aperture.

[0027] Based on the above embodiments, the first lens 101 includes a first object-side surface near the object plane, and the fifth lens 105 includes a fifth image-side surface near the image plane; the distance from the first object-side surface to the aperture stop STO is S. 1O The distance from the aperture STO to the side of the fifth image is S. O5 Where -0.500≤S 1O / S O5≤0.700.

[0028] Specifically, the distance from the side of the first object to the aperture stop STO can be understood as the lens size before the aperture stop STO, and the distance from the side of the first object to the aperture stop STO can be understood as the lens size after the aperture stop STO. By setting -0.500≤S 1O / S O5 ≤0.70, can be -0.500≤S 1O / S O5 A aperture of ≤0.70 allows for a compact lens group structure before and after the aperture stop. Furthermore, the negative optical power anti-telephoto structure of the front lens group with an STO aperture stop enables the large aperture characteristic of the optical system in one step. The fixed-focus lens provided in this embodiment satisfies F≤1.70, and the larger aperture ensures sufficient light intake, guaranteeing the imaging effect of the optical system. Moreover, the compact lens group structure also helps to reduce the size of the optical system. In this embodiment, the TTL of the optical assembly of the fixed-focus lens meets TTL<18.100mm, achieving the design requirement of miniaturization for fixed-focus lenses.

[0029] Based on the above embodiment, the center thickness of the second lens 102 is TH12, the center thickness of the third lens 103 is TH13, and the Abbe number of the third lens 103 is vd3; wherein, 0.320≤(THI2+THI3) / TTL≤0.350, 42.00≤vd3≤85.00.

[0030] Specifically, the center thickness of the lens can be understood as the thickness of the lens along the optical axis. By controlling the proportion of the total thickness of the lenses before and after the aperture stop to the total length of the entire optical system, the optical path difference of light rays in a certain range before and after the aperture stop can be optimized. Combined with the high Abbe number of the third lens 103, the axial chromatic aberration of the system can be effectively reduced, thereby improving the resolution of the on-axis field of view of the visible light. At the same time, good axial chromatic aberration is a prerequisite for reducing infrared defocus. Constraining the above conditions can effectively improve the amount of infrared defocus in the optical system. Specifically, in this embodiment of the invention, the infrared defocus amount corresponding to 0.850 μm of the fixed-focus lens is less than 12 μm, which fully ensures that the optical system has high resolution capability and guarantees imaging effect.

[0031] Based on the above embodiments, the Abbe number of the first lens 101 is vd1, the Abbe number of the third lens 103 is vd3, and the Abbe number of the fourth lens 104 is vd4; wherein, 50.00≤vd1≤62.00, 18.00≤vd4≤25.00, and 2.100≤vd3 / vd4≤3.700. The high Abbe number lens material of the first lens 101 prevents excessive dispersion of light across different wavelengths when object-side light enters the optical system, while the low Abbe number lens material of the fourth lens 104 balances the chromatic aberration of adjacent lenses. The Abbe numbers of these two lenses affect the transverse chromatic aberration of the system, which is beneficial for improving the resolution of the system's visible light off-axis field of view. Furthermore, based on the above description of the effect of the Abbe number of the third lens 103 and the effectiveness of the Abbe number of the fourth lens 104, by controlling the ratio of the Abbe numbers of the third lens 103 and the fourth lens 104, the resolution of the infrared off-axis field of view can also be improved.

[0032] Based on the above embodiments, the first lens 101 further includes a first object-side surface near the object surface, the first object-side surface being convex and the first image-side surface being concave; the second lens 102 includes a second object-side surface near the object surface and a second image-side surface near the image surface, the second object-side surface being concave and the second image-side surface being convex; the third lens 103 includes a third object-side surface near the object surface and a third image-side surface near the image surface, the third object-side surface being convex and the third image-side surface being convex; the fourth lens 104 includes a fourth object-side surface near the object surface and a fourth image-side surface near the image surface, the fourth object-side surface being convex and the fourth image-side surface being concave; the fifth lens 105 includes a fifth object-side surface near the object surface and a fifth image-side surface near the image surface, the fifth object-side surface being convex and the fifth image-side surface being convex.

[0033] Specifically, the object-side surface of a lens can be understood as the surface of the lens closest to the object plane, and the image-side surface of a lens can be understood as the surface of the lens closest to the image plane.

[0034] The object side of the first lens 101 is convex, and the image side is concave. This can be understood as the object side of the first lens 101 convex towards the object surface near the optical axis, and the image side is concave towards the image surface near the optical axis. In other words, the first lens 101 is a lens with a convex-concave structure.

[0035] The object side of the second lens 102 is concave, and the image side is convex. This can be understood as the object side of the second lens 102 being concave towards the object surface near the optical axis, and the image side being convex towards the image surface near the optical axis. In other words, the second lens 102 is a lens with a concave-convex structure.

[0036] The object-side surface of the third lens 103 is convex, and the image-side surface is also convex. This can be understood as the object-side surface of the third lens 103 convex towards the object surface near the optical axis, and the image-side surface convex towards the image surface near the optical axis. In other words, the third lens 103 is a lens with a biconvex structure.

[0037] The object side of the fourth lens 104 is convex, and the image side is concave. This can be understood as the object side of the fourth lens 104 convex towards the object surface near the optical axis, and the image side concave towards the image surface near the optical axis. In other words, the fourth lens 104 is a lens with a convex-concave structure.

[0038] The object-side surface of the fifth lens 105 is convex, and the image-side surface is also convex. This can be understood as the object-side surface of the fifth lens 105 convex towards the object surface near the optical axis, and the image-side surface convex towards the image surface near the optical axis. In other words, the fifth lens 105 is a lens with a biconvex structure.

[0039] By rationally setting the concave and convex surfaces of each lens, and further modulating the direction of light propagation through these surfaces, an optical design with a large aperture and small overall length can be achieved.

[0040] Based on the above embodiments, the first lens 101, the second lens 102, the fourth lens 104 and the fifth lens 105 are all plastic aspherical lenses, and the third lens 103 is a glass spherical lens.

[0041] Specifically, aspherical lenses are characterized by a continuous change in curvature from the center to the periphery, unlike spherical lenses which have a constant curvature from the center to the periphery. Aspherical lenses have better curvature radius characteristics, which improves distortion aberrations and astigmatism. The first lens 101, second lens 102, fourth lens 104, and fifth lens 105 are all plastic aspherical lenses. Using plastic aspherical lenses helps to simplify the manufacturing process and reduces the cost of the optical system.

[0042] A spherical lens is characterized by a constant curvature from its center to its periphery, ensuring a simple lens configuration. Furthermore, due to the low coefficient of thermal expansion and good stability of glass lenses, the third lens 103 is a glass spherical lens. The thermal properties of glass spherical lenses are more stable, ensuring good resolving power over a wide temperature range when handling higher optical powers. Moreover, the range of glass materials available is wider, and the choice of refractive index and Abbe number is relatively flexible, allowing for better control of higher aberrations and chromatic aberration, meeting the needs of use under complex conditions. Therefore, the fixed-focus lens provided in this embodiment can employ a combination of glass spherical lenses and plastic aspherical lenses, effectively controlling the cost of the fixed-focus lens while ensuring its optical performance. Simultaneously, the different lens materials have mutual compensatory effects, ensuring normal operation even in high and low temperature environments.

[0043] As a feasible implementation method, the parameters of each lens in the fixed-focus lens will be explained next.

[0044] Table 1. Optical design values ​​for a fixed-focus lens in Example 1 Table 2 Design values ​​of optical physical parameters for fixed-focus lenses The surface number is determined by the order of the lenses. For example, surface number "S1" represents the object side of the first lens, surface number "S2" represents the image side of the first lens, and so on. "STO" represents the aperture stop of the lens. The radius of curvature represents the curvature of the lens surface in mm. A positive value means that the surface bends towards the image plane with the center closer to the image plane, and a negative value means that the surface bends towards the object plane with the center closer to the object plane. "Infinity" means that the surface is flat and the radius of curvature is infinite. The thickness represents the axial distance between the center of the current surface and the next surface in mm. Due to the different number of digits for each parameter, there may be focusing errors. Therefore, the thickness of the 13th surface is not given a specific value. The value can be adjusted as needed to achieve a clear focus. nd represents the refractive index, which is the ability of the material between the current surface and the next surface to deflect light. A space indicates that the current position is air and the refractive index is 1. vd represents the Abbe number, which is the dispersion characteristic of the material between the current surface and the next surface. A space indicates that the current position is air.

[0045] The formula for aspherical surfaces is shown below: Where Z is the sag of the aspherical surface. Let be the fundamental curvature at the vertex. For conic section constants, The radial coordinate is perpendicular to the optical axis. For higher-order terms, For aspherical surfaces, the term is of higher order.

[0046] Table 3 Design values ​​for the aspherical coefficient of a fixed-focus lens Where -5.174E-04 indicates All other parameters can be represented in this way.

[0047] This embodiment satisfies the following parameters: Focal length: 3.269mm; Aperture: F1.70; Total optical length: 17.411mm.

[0048] Figure 2 This is a schematic diagram of the visible light defocus MTF of a fixed-focus lens according to Embodiment 1 of this utility model. The horizontal axis represents the focal position of the lens, in mm. A horizontal axis of 0 indicates the current actual focal position of the lens as the reference, while other values ​​represent the offset between the current actual focal position and the actual focal position. The vertical axis represents the optical transfer function (MTF) value. The imaging uses the visible light band of 436-656nm, with a spatial frequency of 125 cycles per millimeter. The curves in the diagram represent different fields of view; the horizontal axis corresponding to the highest point of the curve represents the ideal focal position for that field of view. T / S represents the meridional and sagittal directions within the same field of view. As can be seen from the diagram, with a wavelength of 436-656nm and a spatial frequency of 125 cycles per millimeter, different fields of view have different MTF values ​​near the actual focal position. The closer the curves converge, the higher the MTF at the actual focal position, indicating better lens image quality. As shown in the figure, the MTF value of the ideal image point on the axis represented by the vertical coordinate corresponding to the actual focal position (horizontal coordinate is 0) of each field of view of this lens is greater than 0.3, which indicates that the overall image is clear and reflects that the lens has good imaging quality.

[0049] Figure 3This is a schematic diagram of the 0.850μm infrared defocus MTF of a fixed-focus lens according to Embodiment 1 of this utility model. The horizontal axis represents the focal position of the lens, in mm. A horizontal axis of 0 indicates the current actual focal position of the lens as the reference, while other values ​​represent the offset between the current actual focal position and the focal position. The vertical axis represents the optical transfer function (MTF). The imaging uses an infrared wavelength of 0.850μm, with a spatial frequency of 125 cycles per millimeter. The curves in the diagram represent different fields of view; the horizontal axis corresponding to the highest point of the curve represents the ideal focal position for that field of view. T / S represents the meridional and sagittal directions within the same field of view. As shown in the diagram, after focusing under visible light, at a wavelength of 0.850μm and a spatial frequency of 125 cycles per millimeter, different fields of view have different MTF values ​​near the actual focal position. The closer the curves converge, the higher the MTF at the actual focal position, indicating better lens image quality. As shown in the figure, this lens uses 0.850μm infrared light for imaging. The highest point of its 0 field of view curve deviates from the actual focal position by less than 12μm, which meets the requirements of day and night confocal focus and reflects the good imaging quality of the lens.

[0050] In summary, the fixed-focus lens provided by this utility model embodiment adopts a glass-plastic hybrid lens and features day and night confocality, high resolution, large aperture, low cost, and small size. The final fixed-focus lens has the characteristics of infrared defocus within 12μm at 0.850μm, visible light MTF above 0.3 at 125lp / mm, aperture below F1.7, and total length of 17.411mm. It can be used with a 1 / 2.7” chip.

[0051] Example 2 Figure 4 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 2 of this utility model, as shown below. Figure 4 As shown, the fixed-focus lens provided in Embodiment 2 of this utility model includes a first lens 101, a second lens 102, a third lens 103, a fourth lens 104 and a fifth lens 105 arranged sequentially along the optical axis from the object plane to the image plane; the first lens 101 includes a first image-side surface near the image plane, and the sagitta of the first image-side surface is SAGY21, wherein 1.250≤SAGY21≤1.450.

[0052] Other parameters are the same as in Example 1, and will not be repeated here.

[0053] As another feasible implementation method, the specific parameters of the fixed-focus lens are explained below.

[0054] Table 4. Optical design values ​​for a fixed-focus lens in Example 2 Table 5 Design values ​​of optical physical parameters for fixed-focus lenses The surface number is determined by the order of the lenses. For example, surface number "S1" represents the object side of the first lens, surface number "S2" represents the image side of the first lens, and so on. "STO" represents the aperture stop of the lens. The radius of curvature represents the curvature of the lens surface in mm. A positive value means that the surface bends towards the image plane with the center closer to the image plane, and a negative value means that the surface bends towards the object plane with the center closer to the object plane. "Infinity" means that the surface is flat and the radius of curvature is infinite. The thickness represents the axial distance between the center of the current surface and the next surface in mm. Due to the different number of digits for each parameter, there may be focusing errors. Therefore, the thickness of the 13th surface is not given a specific value. The value can be adjusted as needed to achieve a clear focus. nd represents the refractive index, which is the ability of the material between the current surface and the next surface to deflect light. A space indicates that the current position is air and the refractive index is 1. vd represents the Abbe number, which is the dispersion characteristic of the material between the current surface and the next surface. A space indicates that the current position is air.

[0055] The formula for aspherical surfaces is shown below: Where Z is the sag of the aspherical surface. Let be the fundamental curvature at the vertex. For conic section constants, The radial coordinate is perpendicular to the optical axis. For higher-order terms, For aspherical surfaces, the term is of higher order.

[0056] Table 6 Design values ​​for the aspherical coefficient of a fixed-focus lens Where -1.372E-04 indicates All other parameters can be represented in this way.

[0057] This embodiment satisfies the following parameters: Focal length: 3.255mm; Aperture: F1.66; Total optical length: 17.341mm.

[0058] Figure 5This is a schematic diagram of the visible light defocus MTF of a fixed-focus lens according to Embodiment 2 of this utility model. The horizontal axis represents the focal position of the lens, in mm. A horizontal axis of 0 indicates the current actual focal position of the lens as the reference, while other values ​​represent the offset between the current focal position and the actual focus position. The vertical axis represents the optical transfer function (MTF) value. The imaging uses the visible light band of 436-656nm, with a spatial frequency of 125 cycles per millimeter. The curves in the diagram represent different fields of view; the horizontal axis corresponding to the highest point of the curve represents the ideal focal position for that field of view. T / S represents the meridional and sagittal directions within the same field of view. As can be seen from the diagram, with a wavelength of 436-656nm and a spatial frequency of 125 cycles per millimeter, different fields of view have different MTF values ​​near the actual focus position. The closer the curves converge, the higher the MTF at the actual focal position, indicating better lens image quality. As shown in the figure, the MTF value of the ideal image point on the axis represented by the vertical coordinate corresponding to the actual focal position (horizontal coordinate is 0) of each field of view of this lens is greater than 0.3, which indicates that the overall image is clear and reflects that the lens has good imaging quality.

[0059] Figure 6 This is a schematic diagram of the 0.850μm infrared defocus MTF of a fixed-focus lens according to Embodiment 2 of this utility model. The horizontal axis represents the focal position of the lens, in mm. A horizontal axis of 0 indicates the current actual focal position of the lens as the reference, while other values ​​represent the offset between the current actual focus position and the focal position. The vertical axis represents the optical transfer function (MTF). The imaging uses an infrared wavelength of 0.850μm, with a spatial frequency of 125 cycles per millimeter. The curves in the diagram represent different fields of view; the horizontal axis corresponding to the highest point of the curve represents the ideal focal position for that field of view. T / S represents the meridional and sagittal directions within the same field of view. As can be seen from the diagram, after focusing under visible light, at a wavelength of 0.850μm and a spatial frequency of 125 cycles per millimeter, different fields of view have different MTF values ​​near the actual focus position. The closer all the curves converge, the higher the MTF at the actual focal position, indicating better lens image quality. As shown in the figure, this lens uses 0.850μm infrared light for imaging. The highest point of its 0 field of view curve deviates from the actual focal position by less than 12μm, which meets the requirements of day and night confocal focus and reflects the good imaging quality of the lens.

[0060] In summary, the fixed-focus lens provided by this utility model embodiment adopts a glass-plastic hybrid lens and features day and night confocality, high resolution, large aperture, low cost, and small size. The final fixed-focus lens has the characteristics of infrared defocus within 12μm at 0.850μm, visible light MTF above 0.3 at 125lp / mm, aperture below F1.70, and total length of 17.341mm. It can be used with a 1 / 2.7” chip.

[0061] Example 3 Figure 7 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 3 of this utility model, as shown below. Figure 7 As shown, the fixed-focus lens provided in Embodiment 3 of this utility model includes a first lens 101, a second lens 102, a third lens 103, a fourth lens 104 and a fifth lens 105 arranged sequentially along the optical axis from the object plane to the image plane; the first lens 101 includes a first image-side surface near the image plane, and the sagitta of the first image-side surface is SAGY21, wherein 1.250≤SAGY21≤1.450.

[0062] The rest is the same as in Example 1, and will not be repeated here.

[0063] As another feasible implementation method, the specific parameters of the fixed-focus lens are explained below.

[0064] Table 7. Optical design values ​​for a fixed-focus lens in Example 3 Table 8 Design values ​​of optical physical parameters for fixed-focus lenses The surface number is determined by the order of the lenses. For example, surface number "S1" represents the object side of the first lens, surface number "S2" represents the image side of the first lens, and so on. "STO" represents the aperture stop of the lens. The radius of curvature represents the curvature of the lens surface in mm. A positive value means that the surface bends towards the image plane with the center closer to the image plane, and a negative value means that the surface bends towards the object plane with the center closer to the object plane. "Infinity" means that the surface is flat and the radius of curvature is infinite. The thickness represents the axial distance between the center of the current surface and the next surface in mm. Due to the different number of digits for each parameter, there may be focusing errors. Therefore, the thickness of the 13th surface is not given a specific value. The value can be adjusted as needed to achieve a clear focus. nd represents the refractive index, which is the ability of the material between the current surface and the next surface to deflect light. A space indicates that the current position is air and the refractive index is 1. vd represents the Abbe number, which is the dispersion characteristic of the material between the current surface and the next surface. A space indicates that the current position is air.

[0065] The formula for aspherical surfaces is shown below: Where Z is the sag of the aspherical surface. Let be the fundamental curvature at the vertex. For conic section constants, The radial coordinate is perpendicular to the optical axis. For higher-order terms, For aspherical surfaces, the term is of higher order.

[0066] Table 9 Design values ​​for the aspherical coefficient of a fixed-focus lens Where -3.795E-04 indicates All other parameters can be represented in this way.

[0067] This embodiment satisfies the following parameters: Focal length: 3.278mm; Aperture: F1.70; Total optical length: 17.351mm.

[0068] Figure 8 This is a schematic diagram of the visible light defocus MTF of a fixed-focus lens according to Embodiment 3 of this utility model. The horizontal axis represents the focal position of the lens, in mm. A horizontal axis of 0 indicates the current actual focal position of the lens as the reference, while other values ​​represent the offset between the current actual focal position and the actual focal position. The vertical axis represents the optical transfer function (MTF) value. The light wave used for imaging is the 436-656nm visible light band, with a spatial frequency of 125 cycles per millimeter. The curves in the diagram represent different fields of view. The horizontal axis corresponding to the highest point of the curve represents the ideal focal position for that field of view. T / S represents the meridional and sagittal directions within the same field of view. As can be seen from the diagram, with a wavelength of 436-656nm and a spatial frequency of 125 cycles per millimeter, different fields of view have different MTF values ​​near the actual focal position. The closer the curves converge, the higher the MTF at the actual focal position, indicating better lens image quality. As shown in the figure, the MTF value of the ideal image point on the axis represented by the vertical coordinate corresponding to the actual focal position (horizontal coordinate is 0) of each field of view of this lens is greater than 0.3, which indicates that the overall image is clear and reflects that the lens has good imaging quality.

[0069] Figure 9This is a schematic diagram of the 0.850μm infrared defocus MTF of a fixed-focus lens according to Embodiment 3 of this utility model. The horizontal axis represents the focal position of the lens, in mm. A horizontal axis of 0 indicates the current actual focal position of the lens as the reference, and the other values ​​represent the offset between the current actual focus position and the focal position. The vertical axis represents the optical transfer function (MTF). The imaging uses the 0.850μm infrared wavelength band, with a spatial frequency of 125 cycles per millimeter. The curves in the diagram represent different fields of view; the horizontal axis corresponding to the highest point of the curve represents the ideal focal position for that field of view. T / S represents the meridional and sagittal directions within the same field of view. As can be seen from the diagram, after focusing under visible light, at a wavelength of 0.850μm and a spatial frequency of 125 cycles per millimeter, different fields of view have different MTF values ​​near the actual focus position. The closer all the curves converge, the higher the MTF at the actual focal position, indicating better lens image quality. As shown in the figure, this lens uses 0.850μm infrared light for imaging. The highest point of its 0 field of view curve deviates from the actual focal position by less than 12μm, which meets the requirements of day and night confocal focus and reflects the good imaging quality of the lens.

[0070] In summary, the fixed-focus lens provided by this utility model embodiment adopts a glass-plastic hybrid lens and features day and night confocality, high resolution, large aperture, low cost, and small size. The final fixed-focus lens has the characteristics of infrared defocus within 12μm at 0.850μm, visible light MTF above 0.3 at 125lp / mm, aperture below F1.70, and total length of 17.351mm. It can be used with a 1 / 2.7” chip.

[0071] The specific embodiments described above do not constitute a limitation on the scope of protection of this utility model. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. A fixed focus lens characterized by, It includes a first lens, a second lens, a third lens, a fourth lens, and a fifth lens arranged sequentially along the optical axis from the object plane to the image plane; The first lens includes a first image-side surface near the image plane, and the sagitta of the first image-side surface is SAGY21, wherein 1.250≤SAGY21≤1.

450.

2. The fixed focus lens of claim 1, wherein The fixed-focus lens also includes an aperture stop, which is disposed in the optical path between the second lens and the third lens; The combined optical power of the first lens and the second lens is φ12, and the optical power of the fixed-focus lens is φ; wherein, -0.600≤φ12 / φ≤-0.

280.

3. The fixed-focus lens according to claim 2, characterized in that, The first lens includes a first object-side surface near the object plane, and the fifth lens includes a fifth image-side surface near the image plane. The distance from the first object side surface to the stop is S 1O The distance from the stop to the fifth image side surface is S O5 where -0.500 ≤ S 1O / S O5 ≤ 0.

700.

4. The fixed focus lens of claim 3, wherein, The aperture number of the fixed-focus lens is F, where F≤1.

70.

5. The fixed focus lens of claim 3, wherein, The total optical length of the fixed-focus lens is TTL, where TTL < 18.100 mm.

6. The fixed focus lens of claim 1, wherein, The center thickness of the second lens is TH12, the center thickness of the third lens is TH13, and the Abbe number of the third lens is vd3; Among them, 0.320≤(THI2+THI3) / TTL≤0.350, 42.00≤vd3≤85.

00.

7. The fixed focus lens of claim 5, wherein, The fixed-focus lens has an infrared defocus of less than 12μm at 0.850μm.

8. The fixed lens according to claim 1, characterized in that, The Abbe number of the first lens is vd1, the Abbe number of the third lens is vd3, and the Abbe number of the fourth lens is vd4. Among them, 50.00≤vd1≤62.00, 18.00≤vd4≤25.00, and 2.100≤vd3 / vd4≤3.

700.

9. The fixed focus lens of claim 1, wherein, The first lens also includes a first object-side surface near the object surface, the first object-side surface being convex and the first image-side surface being concave; The second lens includes a second object-side surface near the object plane and a second image-side surface near the image plane. The second object-side surface is concave, and the second image-side surface is convex. The third lens includes a third object-side surface near the object plane and a third image-side surface near the image plane. The third object-side surface is convex, and the third image-side surface is convex. The fourth lens includes a fourth object-side surface near the object plane and a fourth image-side surface near the image plane. The fourth object-side surface is convex, and the fourth image-side surface is concave. The fifth lens includes a fifth object-side surface near the object plane and a fifth image-side surface near the image plane. The fifth object-side surface is convex, and the fifth image-side surface is convex.

10. The fixed lens according to claim 1, characterized in that, The first lens, the second lens, the fourth lens, and the fifth lens are all plastic aspherical lenses, and the third lens is a glass spherical lens.

Images