Infrared confocal optical lens and imaging device

Abstract

The application belongs to the field of optical imaging and security and intelligent transportation imaging equipment, and specifically discloses an infrared confocal optical lens, which comprises, from the object side to the image side, a first lens L1 with negative focal power, a second lens L2 with negative focal power, a third lens L3 with negative focal power, a fourth lens L4 with positive focal power, a fifth lens L5 with positive focal power, a sixth lens L6 with positive focal power, a seventh lens L7 with negative focal power, and an eighth lens L8 with positive focal power; an aperture stop STOP is arranged between the fourth lens L4 and the fifth lens L5; the image side of the eighth lens L8 is further provided with a color filter and an imaging surface. The infrared confocal optical lens can support a target imaging surface of up to 1 / 1.8 inches, and effectively realizes miniaturization of the lens structure while ensuring high-resolution imaging.

Description

Technical Field

[0001] This invention belongs to the field of optical imaging and security and intelligent transportation imaging equipment, specifically an infrared confocal optical lens and imaging device. Background Technology

[0002] In recent years, the security monitoring field has developed rapidly, and optical lenses are increasingly used in security applications, especially in intelligent buildings and intelligent transportation. The performance requirements for optical lenses, particularly in terms of pixel count and high-definition night vision, are becoming increasingly stringent. More R&D investment is being made in the development of large-aperture and infrared confocal lenses, with the aim of developing products with higher pixel counts and superior night vision performance. For optical lenses, the use of plastic lenses can significantly reduce lens size and lower product prices. More and more mass-produced lenses are moving towards a hybrid approach combining glass and plastic lenses. However, the following problems still exist in the optical imaging lenses currently on the market:

[0003] 1. Poor infrared confocal performance leads to blurred infrared imaging, and even blurred imaging in both visible and infrared light.

[0004] 2. Existing lenses have small imaging target sizes and low image resolution.

[0005] 3. The lens aperture is small, resulting in very dark camera images in low-light conditions, which reduces the product's adaptability.

[0006] 4. The large number of lenses and the large lens size make it impossible to design the entire camera in a miniaturized form.

[0007] 5. The lens has low resolution and the image quality is average.

[0008] 6. The performance stability is poor under high and low temperature conditions.

[0009] Chinese patent application CN103941395A discloses a low-temperature drift, low-cost, high-pixel infrared confocal optical system, which, from the object side, sequentially includes a first lens, a second lens, a third lens, an aperture stop, a fourth lens, a fifth lens, a sixth lens, a filter, and an image plane. The first lens is a meniscus spherical lens, the second lens is a biconcave aspherical lens, the third lens is a meniscus aspherical lens, the fourth lens is a biconvex spherical lens, the fifth lens is a meniscus aspherical lens, and the sixth lens is a biconvex aspherical lens. The object-side surface of the second lens is an elliptic aspherical, and the image-side surface is a hyperbolic aspherical. Both surfaces of the third lens are hyperbolic aspherical. Both surfaces of the fifth lens are hyperbolic aspherical. The object-side surface of the sixth lens is a hyperbolic aspherical, and the image-side surface is an oblate aspherical. The second, third, fifth, and sixth lenses are made of plastic. This patent application provides an infrared confocal lens, but the overall lens surface area is small, and the aperture value is relatively small. Moreover, the early lens designs, image quality, lens size, and overall performance have gradually become unable to meet the development needs of today's high-resolution applications.

[0010] The following technical problems still exist in the existing technology:

[0011] 1. Poor imaging characteristics, unable to support the high resolution requirements of today's surveillance;

[0012] 2. Poor infrared confocal performance, which cannot meet the requirements for high-definition infrared imaging;

[0013] 3. The lens structure is large in size, has a large number of lenses, poor processing characteristics, and high cost. Summary of the Invention

[0014] To address the aforementioned technical problems in the prior art, this invention provides an infrared confocal optical lens, comprising, from the object side to the image side: a first lens L1 with negative optical power, a second lens L2 with negative optical power, a third lens L3 with negative optical power, a fourth lens L4 with positive optical power, a fifth lens L5 with positive optical power, a sixth lens L6 with positive optical power, a seventh lens L7 with negative optical power, and an eighth lens L8 with positive optical power; an aperture stop (STOP) is provided between the fourth lens L4 and the fifth lens L5; and a color filter and an imaging surface are also provided on the image side of the eighth lens L8.

[0015] Furthermore, the first lens L1 is a meniscus lens; the second lens L2 is a biconcave lens; the third lens L3 is a meniscus lens; the fourth lens L4 is a biconvex lens; the fifth lens L5 is a biconvex lens; the sixth lens L6 is a biconvex lens; the seventh lens L7 is a biconcave lens; and the eighth lens L8 is a meniscus lens.

[0016] Furthermore, the fifth lens L5 is a single lens or a cemented lens group G1, which consists of lens L5-1 and lens L5-2.

[0017] Furthermore, the focal length of the third lens L3 is f3, the system focal length of the lens is f, and the field of view is FOV, satisfying the following relationship:

[0018]

[0019] Furthermore, the sixth lens L6 has a convex surface on both the object side and the image side.

[0020] Furthermore, the eighth lens L8 has a convex surface on the object side and a concave surface on the image side.

[0021] Furthermore, the central radius of curvature R8 of the image side of the fourth lens L4 and the central radius of curvature R9 of the object side of the fifth lens L5 satisfy the following:

[0022]

[0023] Furthermore, the system focal length f of the infrared confocal optical lens and the total optical length TTL of the optical lens satisfy the following relationship:

[0024] 6.1≤TTL / f≤6.5 (3).

[0025] Furthermore, the focal lengths f1 of the first lens L1, f2 of the second lens L2, and f4 of the fourth lens L4 of the infrared confocal optical lens satisfy the following formula:

[0026] f1≤-12 (4)

[0027] f2≤-13 (5)

[0028] f4≤31 (6).

[0029] An imaging device, the imaging device comprising the aforementioned infrared confocal optical lens.

[0030] Beneficial effects

[0031] The infrared confocal optical lens of this invention can support an imaging target surface of up to 1 / 1.8 inches, effectively achieving lens structure miniaturization while ensuring high-resolution imaging. It also has the following characteristics:

[0032] 1. Excellent confocal characteristics;

[0033] 2. The total mechanical length of the lens shall not exceed 31.3mm;

[0034] 3. The MTF value across the entire field of view reaches above 0.6 at 100 lp / mm;

[0035] 4. The lens has fewer elements and is easier to manufacture, resulting in lower costs;

[0036] 5. With a large aperture of F-number 1.0, it is particularly suitable for security needs under low-light conditions;

[0037] 6. Stable optical performance, meeting the requirements of high and low temperature operation from -30 to +70℃. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structure of an optical lens in the prior art;

[0039] Figure 2 This is a schematic diagram of the structure of the optical lens of this application;

[0040] Figure 3 This is an optical transfer function (MTF) curve of Embodiment 1 of the optical lens provided in this application at room temperature in the visible light band;

[0041] Figure 4 This is an optical transfer function (MTF) curve of Embodiment 1 of the optical lens provided in this application at room temperature in the infrared light band;

[0042] Figure 5a and Figure 5b This is a field curvature and distortion diagram of Embodiment 1 of the optical lens provided in this application in the visible light band;

[0043] Figure 6 This is a lateral fan pattern in the visible light band of Embodiment 1 of the optical lens provided in this application;

[0044] Figure 7 This is a dot plot of Embodiment 1 of the optical lens provided in this application in the visible light band;

[0045] Figure 8 This is an optical transfer function (MTF) curve of Embodiment 2 of the optical lens provided in this application at room temperature in the visible light band;

[0046] Figure 9 This is an optical transfer function (MTF) curve of Embodiment 1 of the optical lens provided in this application at room temperature in the infrared light band;

[0047] Figure 10a and Figure 10b This is a field curvature and distortion diagram in the visible light band of Embodiment 2 of the optical lens provided in this application;

[0048] Figure 11This is a lateral fan pattern in the visible light band of Embodiment 2 of the optical lens provided in this application;

[0049] Figure 12 This is a dot plot of Embodiment 2 of the optical lens provided in this application in the visible light band;

[0050] Figure 13 This is a schematic diagram of a specific embodiment of the imaging device provided in this application. Detailed Implementation

[0051] 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 a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0052] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0053] like Figure 2 As shown, the infrared confocal optical lens of the present invention comprises, from the object side to the image side, the following elements in sequence: a first lens L1 with negative optical power, a second lens L2 with negative optical power, a third lens L3 with negative optical power, a fourth lens L4 with positive optical power, a fifth lens L5 with positive optical power, a sixth lens L6 with positive optical power, a seventh lens L7 with negative optical power, and an eighth lens L8 with positive optical power.

[0054] An aperture stop (STOP) is provided between the fourth lens L4 and the fifth lens L5; the image side of the eighth lens L8 is also provided with a color filter and an imaging surface.

[0055] Optionally, the first lens L1 is a meniscus lens; the second lens L2 is a biconcave lens; the third lens L3 is a meniscus lens; the fourth lens L4 is a biconvex lens; the fifth lens L5 is a biconvex lens; the sixth lens L6 is a biconvex lens; the seventh lens L7 is a biconcave lens; and the eighth lens L8 is a meniscus lens.

[0056] The fifth lens L5 can be a single lens or a cemented lens group G1, which consists of lens L5-1 and lens L5-2.

[0057] The third lens L3 has a focal length of f3, the system focal length of the lens is f, and the field of view is FOV, satisfying the following relationship:

[0058]

[0059] The sixth lens L6 has a convex surface on both the object side and the image side.

[0060] The eighth lens L8 has a convex surface on the object side and a concave surface on the image side.

[0061] The central radius of curvature R8 of the image side of the fourth lens L4 and the central radius of curvature R9 of the object side of the fifth lens L5 satisfy the following:

[0062]

[0063] The system focal length f of the infrared confocal optical lens and the total optical length TTL of the optical lens satisfy the following relationship:

[0064] 6.1≤TTL / f≤6.5 (3).

[0065] The focal lengths f1 of the first lens L1, f2 of the second lens L2, and f4 of the fourth lens L4 of the infrared confocal optical lens satisfy the following formula:

[0066] f1≤-12 (4)

[0067] f2≤-13 (5)

[0068] f4≤31 (6).

[0069] Example 1

[0070] The radius of curvature R, center thickness Tc, refractive index Nd, Abbe constant Vd, and conic coefficient k of each lens in the infrared confocal optical lens of this embodiment 1 satisfy the conditions listed in Table 1:

[0071]

[0072]

[0073] Table 1 Lens Parameter Table

[0074] It should be noted that the mirror serial numbers in Table 1 are Figure 2 The diagram of the infrared confocal optical lens structure shown has the lens face numbers from left to right.

[0075] Lens L1, L2, L3, L6, L7, and L8 are aspherical lenses, and their equations satisfy the following formula:

[0076]

[0077] The aspherical coefficients are as follows:

[0078]

[0079] Table 2 Aspherical Coefficients

[0080] The infrared confocal optical lens provided in this embodiment 1 has the following optical technical specifications:

[0081] Total optical length (TTL) ≤ 31.3 mm;

[0082] Lens focal length f: 4.7mm;

[0083] Lens field of view: 120.8°;

[0084] Lens optical distortion: -47.1%;

[0085] The aperture of the lens system is Fn. 1.0;

[0086] Lens image size: 1 / 1.8".

[0087] In this embodiment 1, the focal length f3 of the third lens L3 of the infrared confocal optical lens, the system focal length f of the lens, and the field of view (FOV) satisfy the following: The central radius of curvature R8 of the image side of the fourth lens L4 and the central radius of curvature R9 of the object side of the fifth lens L5 satisfy the following: The system focal length f of the optical lens and the total optical length TTL of the optical lens satisfy the following relationship: The focal length of the first lens L1 of the optical lens is f1 = -14.91, the focal length of the second lens L2 is f2 = -13.36, and the focal length of the fourth lens L4 is f4 = 30.08.

[0088] Example 2

[0089] The radius of curvature R, center thickness Tc, refractive index Nd, Abbe constant Vd, and conic coefficient k of each lens in the infrared confocal optical lens of this embodiment 2 satisfy the conditions listed in Table 2:

[0090]

[0091] Table 3 Lens Parameter Table

[0092] It should be noted that the mirror serial numbers in Table 3 are... Figure 2 The optical lens structure diagram shown shows the lens face numbers from left to right. This embodiment includes a set of cemented lens groups.

[0093] Lens L1, L2, L3, L6, L7, and L8 are aspherical lenses, and their equations satisfy the following formula:

[0094]

[0095] The aspherical coefficients are as follows:

[0096]

[0097] Table 4 Aspherical Coefficients

[0098] The infrared confocal optical lens provided in this embodiment 2 has the following optical technical specifications:

[0099] Total optical length (TTL) ≤ 30.3 mm;

[0100] Lens focal length f: 4.7mm;

[0101] Lens field of view: 115.8°;

[0102] Lens optical distortion: -41.2%;

[0103] The aperture of the lens system is Fn. 1.0;

[0104] Lens image size: 1 / 1.8".

[0105] In this embodiment 2, the focal length f3 of the third lens L3 of the infrared confocal optical lens, the system focal length f of the lens, and the field of view (FOV) satisfy the following: The central radius of curvature R8 of the image side of the fourth lens L4 and the central radius of curvature R9 of the object side of the fifth lens L5 satisfy the following: The system focal length f of the optical lens and the total optical length TTL of the optical lens satisfy the following relationship: The focal length of the first lens L1 of the optical lens is f1 = -12.61, the focal length of the second lens L2 is f2 = -17.76, and the focal length of the fourth lens L4 is f4 = 16.04.

[0106] In summary, Examples 1 to 2 satisfy the relationships shown in Table 5 below.

[0107]

[0108] Table 5: Comprehensive Table of Parameter Relationships

[0109] The optical transfer function is a relatively accurate, intuitive, and common way to evaluate the imaging quality of an imaging system. The higher and smoother the curve, the better the imaging quality of the system and the better it corrects various aberrations (such as spherical aberration, coma, astigmatism, field curvature, axial chromatic aberration, and transverse chromatic aberration).

[0110] like Figure 3 As shown, the optical transfer function (MTF) curve of this infrared confocal optical lens at room temperature in the visible light region is relatively smooth and concentrated, and the average MTF value of the entire field of view (half-image height Y' = 4.4 mm) reaches more than 0.60; it can be seen that the infrared confocal optical lens provided in this embodiment can achieve high imaging requirements.

[0111] like Figure 4 As shown, the optical transfer function (MTF) curve of the infrared confocal optical lens at room temperature in the infrared region is also relatively smooth and concentrated, with an average MTF value of over 0.25 across the entire field of view (half-image height Y' = 4.4 mm). It can be seen that the imaging system provided in this embodiment can meet high imaging requirements and satisfy the design of infrared confocal imaging.

[0112] like Figure 8 As shown, the optical transfer function (MTF) curve of the infrared confocal optical lens in the visible light region at room temperature is relatively smooth and concentrated, and the average MTF value of the entire field of view (half-image height Y' = 4.4 mm) reaches more than 0.60; it can be seen that the infrared confocal optical lens provided in this embodiment can achieve high imaging requirements.

[0113] like Figure 9 As shown, the optical transfer function (MTF) curve of the infrared confocal optical lens at room temperature in the infrared region is also relatively smooth and concentrated, with an average MTF value of over 0.25 across the entire field of view (half-image height Y' = 4.4 mm). It can be seen that the imaging system provided in this embodiment can meet high imaging requirements and satisfy the design of infrared confocal imaging.

[0114] like Figure 5a and Figure 10aAs shown, the field curvature of this infrared confocal lens is controlled within ±0.1mm. Field curvature is also known as "image field curvature." When a lens has field curvature, the intersection of the entire beam does not coincide with the ideal image point. Although a sharp image point can be obtained at each specific point, the entire image plane is a curved surface. T represents meridional field curvature, and S represents sagittal field curvature. The field curvature curve shows the distance from the current focal plane or image plane to the paraxial focal plane as a function of the field of view coordinates. The meridional field curvature data is the distance from the currently determined focal plane to the paraxial focal plane measured along the Z-axis, and is measured on the meridional (YZ plane). The sagittal field curvature data is the distance measured on a plane perpendicular to the meridional plane. The baseline in the schematic diagram is on the optical axis, and the top of the curve represents the maximum field of view (angle or height). No units are set on the vertical axis because the curve is always normalized using the maximum radial field of view.

[0115] like Figure 5b and Figure 10b As shown, the infrared confocal optical lens exhibits good distortion control, within -50%. Figure 5b The curves at multiple wavelengths (0.436 μm, 0.486 μm, 0.546 μm, 0.587 μm, and 0.656 μm) are referenced. Figure 5b The images overlapped. Generally speaking, lens distortion is actually a general term for the inherent perspective distortion of optical lenses, that is, distortion caused by perspective. This distortion is very detrimental to the image quality of a photograph, since the purpose of photography is reproduction, not exaggeration. However, because this is an inherent characteristic of lenses (convex lenses converge light rays, concave lenses diverge light rays), it cannot be eliminated, only improved. Figure 5b and Figure 10b As can be seen, the distortion of the lens provided in Embodiment 1 of the present invention is -47.1%; the distortion of the lens provided in Embodiment 2 of the present invention is -41.2%. This distortion setting is to balance the focal length, field of view and the size of the corresponding camera target surface. The deformation caused by the distortion can be corrected by post-image processing.

[0116] like Figure 6 and Figure 11 As shown, the curves in the optical sector diagram are relatively concentrated, indicating that the spherical aberration and dispersion of this imaging system are well controlled.

[0117] like Figure 7 and Figure 12 As shown, the imaging system has a small and concentrated spot radius, and the corresponding aberrations and coma are also relatively good.

[0118] In summary, embodiments 1 and 2 of this invention provide a high-resolution infrared confocal optical lens with a large target area, large aperture, and low cost. By employing eight optical lenses with specific structural shapes, arranged sequentially from the object side to the image side, and through the specific allocation and combination of the optical power of each optical lens, the imaging system achieves excellent imaging characteristics.

[0119] like Figure 13 As shown, the imaging device 10 of this application embodiment includes at least one infrared confocal optical lens 11. Specifically, the infrared confocal optical lens 11 can be the optical lens of the above embodiments 1 and 2, and its specific structure will not be described in detail here.

[0120] In this embodiment, the imaging device 10 can be applied to the security field, for example, it can be installed on smart buildings to provide high-definition environmental information for building security systems. In other embodiments, the imaging device 10 can also be applied to other devices, such as security equipment, drones, and robotic vacuum cleaners.

Claims

1. An infrared confocal optical lens, comprising, from the object side to the image side: The infrared confocal optical lens comprises eight lenses: a first lens L1 with negative optical power, a second lens L2 with negative optical power, a third lens L3 with negative optical power, a fourth lens L4 with positive optical power, a fifth lens L5 with positive optical power, a sixth lens L6 with positive optical power, a seventh lens L7 with negative optical power, and an eighth lens L8 with positive optical power. The lens is characterized by: an aperture stop (STOP) between the fourth lens L4 and the fifth lens L5; and a color filter and an imaging surface on the image side of the eighth lens L8. The first lens L1 is a meniscus lens; the second lens L2 is a biconcave lens; the third lens L3 is a meniscus lens; the fourth lens L4 is a biconvex lens; the fifth lens L5 is a biconvex lens; the sixth lens L6 is a biconvex lens; the seventh lens L7 is a biconcave lens; and the eighth lens L8 is a meniscus lens. The system focal length of the infrared confocal optical lens is: The following conditions must be met between the total optical length (TTL) of the optical lens and the total optical length (TTL) of the optical lens: （3） The focal lengths f1 of the first lens L1, f2 of the second lens L2, and f4 of the fourth lens L4 of the infrared confocal optical lens satisfy the following formula: -14.91≤f1≤-12 （4） -17.76≤f2≤-13 （5） （6）。 2. The infrared confocal optical lens according to claim 1, characterized in that: The fifth lens L5 is either a single lens or a cemented lens group G1, which consists of lens L5-1 and lens L5-2.

3. The infrared confocal optical lens according to claim 1, characterized in that: The focal length of the third lens L3 is The system focal length of the lens is The field of view is It satisfies the following relationship: （1）。 4. The infrared confocal optical lens according to claim 1, characterized in that: The sixth lens L6 has a convex surface on both the object side and the image side.

5. The infrared confocal optical lens according to claim 1, characterized in that: The eighth lens L8 has a convex surface on the object side and a concave surface on the image side.

6. The infrared confocal optical lens according to claim 1, characterized in that: The central radius of curvature R8 of the image side of the fourth lens L4 and the central radius of curvature R9 of the object side of the fifth lens L5 satisfy the following: （2）。 7. An imaging device, characterized in that, The imaging device includes the infrared confocal optical lens as described in any one of claims 1 to 6.

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