Athermal day and night confocal high-definition telephoto lens and imaging method

Abstract

The invention relates to an athermal day-night confocal high-definition telephoto lens and an imaging method, and the lens comprises an optical system which is composed of a first lens, a second lens, a diaphragm, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens which are sequentially arranged from left to right along a light incident path. Wherein the first lens and the second lens form a balsaming lens group, the third lens and the fourth lens form a balsaming lens group, and the sixth lens and the seventh lens form a balsaming lens group. According to the lens, the design of seven glass spherical lenses is adopted, the optical performance of large aperture, high resolution and day and night confocal is met by optimizing parameters and materials of the lenses, the relative illumination is high, and all-weather high-definition imaging is achieved; a glass material with a negative refractive index temperature coefficient is matched, so that passive athermalization design is realized, and good imaging quality is kept in a wide temperature range; the lens is low in tolerance sensitivity and easy to assemble.

Description

Technical Field

[0001] This invention relates to the field of lens technology, and in particular to a heat-free, day-night confocal high-definition telephoto lens and its imaging method. Background Technology

[0002] In large-scale, long-distance security monitoring fields such as safe cities, border defense, airports and ports, and large infrastructure, telephoto lenses have become core optical components because they can focus the monitoring field of view on targets hundreds of meters or even kilometers away, enabling detailed observation and accurate identification. As security monitoring systems develop towards high definition, intelligence, and all-weather operation, stringent requirements are placed on the performance of telephoto lenses, requiring them to integrate calorie-free operation, day and night focus, high resolution, and high illumination.

[0003] In telephoto optical systems, achieving the aforementioned performance indicators presents technical challenges amplified by focal length characteristics. First, the challenge of calorific resolution is exacerbated. Telephoto lenses typically have a larger overall optical length and more lens elements, leading to greater focus drift due to changes in the refractive index of lens materials caused by ambient temperature variations and thermal expansion and contraction of mechanical structures. This effect is significantly greater than in short-focal-length lenses. Second, achieving day-night confocal focusing is more difficult. To enable 24-hour continuous monitoring, the lens needs to provide excellent imaging across a broad spectral range of 400nm-940nm (covering visible to near-infrared). Telephoto lenses are more sensitive to chromatic aberration. While conventional optical systems correct chromatic aberration in the visible light band, significant focus shift often occurs in the near-infrared band. This results in severe defocusing of distant targets during day-night transitions, necessitating motorized refocusing and creating monitoring blind spots and response delays. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a thermal-free day and night confocal high-definition telephoto lens and imaging method, which deeply integrates passive thermal technology, achromatic technology and high-resolution large aperture design. It can automatically maintain focus and image clarity in a wide temperature range and wide spectral range without any mechanical or electronic focusing compensation, so as to meet the market demand for long-distance, high-precision, all-weather security systems.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is: a heat-free, day-night confocal high-definition telephoto lens, wherein the optical system of the lens consists of a first lens, a second lens, an aperture stop, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens arranged sequentially from left to right along the incident light path; the first lens is a biconcave lens with negative optical power, its object-side surface being concave and its image-side surface being concave; the second lens is a biconvex lens with positive optical power, its object-side surface being convex and its image-side surface being convex. The third lens is a biconcave lens with negative optical power, its object-side surface is concave, and its image-side surface is concave; the fourth lens is a biconvex lens with positive optical power, its object-side surface is convex, and its image-side surface is convex; the fifth lens is a biconvex lens with positive optical power, its object-side surface is convex, and its image-side surface is convex; the sixth lens is a biconvex lens with positive optical power, its object-side surface is convex, and its image-side surface is convex; the seventh lens is a biconcave lens with negative optical power, its object-side surface is concave, and its image-side surface is concave.

[0006] Preferably, the focal length of the optical system is The focal lengths of the first lens, second lens, third lens, fourth lens, fifth lens, and sixth lens are respectively , , , , , , ,in , , , , , , and Meets the following ratio: -1.0 < / -0.5, 0.5< / <1.0, -1.0< / <-0.5, 0.5< / <1.0, 1.5< / <2.0, 1.0< / <1.5, -1.5< / <-1.0.

[0007] Preferably, the first lens satisfies the relationship: 1.5 ≤ ≤1.8, ≥50.0; The second lens satisfies the relationship: 1.8≤ ≤2.1, ≤50.0; The third lens satisfies the relationship: 1.5≤ ≤1.8, ≤50.0; The fourth lens satisfies the relationship: 1.5≤ ≤1.8, ≥50.0; The fifth lens satisfies the relationship: 1.8≤ ≤2.1, ≤50.0; The sixth lens satisfies the relation: 1.8≤ ≤2.1, ≤50.0; The seventh lens satisfies the relation: 1.8≤ ≤2.1, ≤50.0; where For refractive index, Let be Abbe's constant.

[0008] Preferably, the on-axis distances between the lenses satisfy the following relationships: the first lens and the second lens are cemented lenses with an air gap of 0 mm; the air gap between the second lens and the third lens is 1.5~2.0 mm; the third lens and the fourth lens are cemented lenses with an air gap of 0 mm; the air gap between the fourth lens and the fifth lens is 0~0.5 mm; the air gap between the fifth lens and the sixth lens is 0~0.5 mm; and the sixth lens and the seventh lens are cemented lenses with an air gap of 0 mm.

[0009] Preferably, the total optical length (TTL) of the optical system and the focal length (f) of the optical system satisfy the following condition: TTL / f ≤ 3.0.

[0010] Preferably, the F-number of the optical system is ≤2.0.

[0011] Preferably, the image height H of the optical system and the focal length f of the optical system satisfy the following condition: H / f ≥ 0.9.

[0012] Preferably, the first lens, second lens, third lens, fourth lens, fifth lens, sixth lens and seventh lens are all glass spherical lenses, and the aperture stop of the optical system is located between the second lens and the third lens.

[0013] An imaging method for a thermal confocal high-definition telephoto lens for day and night is performed according to the following steps: light rays pass through a first lens, a second lens, an aperture stop, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens from left to right before forming an image on the imaging plane.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The athermalized day-night confocal high-definition telephoto lens of this invention uses only seven spherical glass lenses to meet the optical performance requirements of large aperture, high resolution, and day-night confocality, while providing high relative illumination for all-weather high-definition and bright imaging. It employs multiple glass lenses with negative refractive index temperature coefficients to achieve a passive athermalized design, maintaining good image quality over a wide temperature range. The lens structure is compact, and the optical back focal length is long, facilitating module assembly. Furthermore, the system exhibits extremely low sensitivity to processing and assembly tolerances, making assembly easy and contributing to improved production yield and reduced manufacturing costs.

[0016] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the optical structure according to an embodiment of the present invention;

[0018] Figure 2 This is an axial chromatic aberration diagram of the entire working band of this invention.

[0019] Figure 3 This is a transverse chromatic aberration diagram of the entire working band of this invention.

[0020] Figure 4 This is a field curvature distortion diagram of the entire working band of this invention embodiment;

[0021] Figure 5 This is a relative illumination diagram according to an embodiment of the present invention;

[0022] Figure 6 This is a visible light operating band MTF defocus curve diagram of an embodiment of the present invention;

[0023] Figure 7 This is an MTF defocus curve diagram of the 850nm working band according to an embodiment of the present invention;

[0024] Figure 8 This is an MTF defocus curve diagram of an embodiment of the present invention at an operating temperature of -40℃;

[0025] Figure 9 This is an MTF defocus curve diagram of an embodiment of the present invention at an operating temperature of 85°C;

[0026] In the diagram: L1 - first lens; L2 - second lens; STO - aperture stop; L3 - third lens; L4 - fourth lens; L5 - fifth lens; L6 - sixth lens; L7 - sixth lens; L8 - equivalent glass plate; IMA - imaging plane. Detailed Implementation

[0027] To make the above features and advantages of the present invention more apparent and understandable, specific embodiments are described below in conjunction with the accompanying drawings for detailed explanation.

[0028] like Figures 1-9 As shown, a heat-free, day-and-night confocal high-definition telephoto lens includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7 arranged sequentially from left to right along the incident light path. An aperture stop is positioned between the second and third lenses. The first and second lenses form a cemented lens group, the third and fourth lenses form a cemented lens group, and the sixth and seventh lenses form a cemented lens group. All seven lenses are spherical glass lenses. The first lens is a biconcave lens with negative optical power, having a concave object-side surface and a concave image-side surface; the second lens is a biconvex lens with positive optical power, having a convex object-side surface and a convex image-side surface; the third lens is a biconcave lens with negative optical power, having a concave object-side surface and a concave image-side surface; the fourth lens is a biconvex lens with positive optical power, having a convex object-side surface and a convex image-side surface; the fifth lens is a biconvex lens with positive optical power, having a convex object-side surface and a convex image-side surface; the sixth lens is a biconvex lens with positive optical power, having a convex object-side surface and a convex image-side surface; and the seventh lens is a biconcave lens with negative optical power, having a concave object-side surface and a concave image-side surface.

[0029] The technical specifications achieved by the optical system in this embodiment are as follows:

[0030] (1) Focal length: 7.5≤EFFL≤8.5mm;

[0031] (2) Aperture F≤2.0;

[0032] (3) Field of view: 2w ≥ 56°;

[0033] (4) Operating bands: visible light band and near-infrared band.

[0034] To achieve the above design parameters, the specific design of the optical system adopted in this embodiment is shown in the table below:

[0035]

[0036] The optical system of this invention, by rationally allocating the optical power, surface shape, center thickness of each lens, and on-axis distance between each lens, can reduce the overall length of the lens and the radial dimensions of each lens element while meeting the lens imaging performance requirements, thereby miniaturizing the lens assembly and reducing costs.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An athermalized day and night confocal high definition long focus lens comprising an optical system, characterized in that: The optical system of the lens is composed of a first lens, a second lens, a diaphragm, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens arranged in sequence along the light path of the incident light from left to right, wherein, without considering the reverse bending caused by the aspherical coefficient, the first lens is a double-concave lens with negative focal power; the second lens is a double-convex lens with positive focal power; the third lens is a double-concave lens with negative focal power; the fourth lens is a double-convex lens with positive focal power; the fifth lens is a double-convex lens with positive focal power; the sixth lens is a double-convex lens with positive focal power; and the seventh lens is a double-concave lens with negative focal power.

2. Athermalized day and night confocal high definition long focus lens according to claim 1 characterized in that: The object side surface of the first lens is a concave surface, and the image side surface is a concave surface; the object side surface of the second lens is a convex surface, and the image side surface is a convex surface; the object side surface of the third lens is a concave surface, and the image side surface is a concave surface; the object side surface of the fourth lens is a convex surface, and the image side surface is a convex surface; the object side surface of the fifth lens is a convex surface, and the image side surface is a convex surface; the object side surface of the sixth lens is a convex surface, and the image side surface is a convex surface; and the object side surface of the seventh lens is a concave surface, and the image side surface is a concave surface.

3. The athermal day and night confocal high definition long focus lens according to claim 1, characterized in that: The focal length of the optical system is , the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are , , , , , , , wherein , , , , , , and satisfy the following ratios: -1.0 / -0.5, 0.5 / <1.0, -1.0 / <-0.5, 0.5 / <1.0, 1.5 / <2.0, 1.0 / <1.5, -1.5 / <-1.

0.

4. The athermal day and night confocal high definition long focus lens according to claim 1, characterized in that: the first lens satisfies the relation: 1.5 ≤ ≤ 1.8, ≥ 50.0; the second lens satisfies the relation: 1.8 ≤ ≤ 2.1, ≤ 50.0; the third lens satisfies the relation: 1.5 ≤ ≤ 1.8, ≤ 50.0; the fourth lens satisfies the relation: 1.5 ≤ ≤ 1.8, ≥ 50.0; the fifth lens satisfies the relation: 1.8 ≤ ≤ 2.1, ≤ 50.0; the sixth lens satisfies the relation: 1.8 ≤ ≤ 2.1, ≤ 50.0; the seventh lens satisfies the relation: 1.8 ≤ ≤ 2.1, ≤ 50.0; wherein is the refractive index, is the Abbe number.

5. The athermal day and night confocal high definition long focus lens according to claim 1, characterized in that: The on-axis distance between each lens satisfies the following relationship: the first lens and the second lens are cemented lenses, and the air gap is 0 mm; the air gap between the second lens and the third lens is 1.5-2.0 mm; the third lens and the fourth lens are cemented lenses, and the air gap is 0 mm; the air gap between the fourth lens and the fifth lens is 0-0.5 mm; the air gap between the fifth lens and the sixth lens is 0-0.5 mm; and the sixth lens and the seventh lens are cemented lenses, and the air gap is 0 mm.

6. Athermalized day and night confocal high definition long focus lens according to claim 1 characterized in that: The total optical length TTL of the optical system and the focal length f of the optical system satisfy TTL / f≤3.

0.

7. The athermal day and night confocal high definition long focus lens according to claim 1, characterized in that: The F number of the optical system is ≤2.

0.

8. The athermal day and night confocal high definition long focus lens according to claim 1, characterized in that: The image height H of the optical system and the focal length f of the optical system satisfy H / f≥0.

9.

9. The athermal day and night confocal high definition long focus lens according to claim 1, characterized in that: The first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are all glass spherical lenses.

10. An imaging method applied to the athermal day and night confocal high definition long focus lens of claim 2, characterized in that, The light rays pass through the first lens, the second lens, the diaphragm, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens in sequence from left to right and then are imaged on the imaging plane.

Images