Short TTL wide-angle monitoring lens and imaging method thereof

Abstract

The invention relates to the technical field of optical imaging, in particular to a short TTL wide-angle monitoring lens and an imaging method thereof.The optical system of the lens is composed of a first lens, a second lens, a third lens, a fourth lens, a diaphragm, a fifth lens, a sixth lens and a seventh lens which are sequentially arranged from the object side to the image side along the optical axis; wherein the first lens and the fifth lens are glass spherical lenses, and the second lens, the third lens, the fourth lens, the sixth lens and the seventh lens are plastic aspheric lenses. The total length of the lens is greatly shortened by reasonably distributing the focal power and the surface type of each lens, the central thickness of each lens, the axial distance between the lenses and the like, so that the lens can adapt to the structure requirement of compact equipment; the lens has the advantages of large aperture, large field angle and high resolution, is good in imaging performance, achieves day and night confocal, and corrects purple edges.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, and in particular to a short TTL wide-angle surveillance lens and its imaging method. Background Technology

[0002] With the rapid development of consumer electronics, especially smartphones, tablets, action cameras, and security monitoring devices, increasingly stringent requirements are being placed on their built-in camera modules. On the one hand, users are demanding thinner and lighter, more portable device designs, which requires camera modules to have smaller dimensions, especially shorter total track lengths (TTL). On the other hand, users are also constantly increasing their demands for image quality, hoping to obtain images with wider angles, less distortion, and higher resolution.

[0003] Wide-angle lenses, capable of capturing a wider field of view without increasing shooting distance, have become standard equipment in many devices. However, existing wide-angle lenses often compromise on several aspects, struggling to achieve a good balance between short TTL, wide angle, high environmental stability, and low cost.

[0004] Therefore, there is an urgent need for a short TTL wide-angle lens design solution. Summary of the Invention

[0005] The purpose of this invention is to provide a short TTL wide-angle surveillance lens and its imaging method. This lens meets the monitoring requirements of large aperture, high resolution, day and night confocal focus, and low temperature drift while ensuring miniaturization and low cost.

[0006] The technical solution of this invention is as follows: a short TTL wide-angle surveillance lens, the optical system of which consists of a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens arranged sequentially along the optical axis from the object side to the image side; without considering the curvature caused by the aspherical coefficient, the first lens is a meniscus lens with negative optical power, its object side is convex, and its image side is concave; the second lens is a biconcave lens with negative optical power, its object side is concave, and its image side is concave. The third lens is a biconvex lens with positive optical power, its object-side surface is convex, and its image-side surface is convex; the fourth lens is a meniscus lens with positive optical power, its object-side surface is concave, 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 biconcave lens with negative optical power, its object-side surface is concave, and its image-side surface is concave; the seventh lens is a biconvex lens with positive optical power, its object-side surface is convex, and its image-side surface is convex.

[0007] Furthermore, the first and fifth lenses are spherical lenses, while the second, third, fourth, sixth, and seventh lenses are aspherical lenses.

[0008] Furthermore, the first and fifth lenses are glass spherical lenses, while the second, third, fourth, sixth, and seventh lenses are plastic aspherical lenses.

[0009] Furthermore, the focal length of the optical system is f, and the focal lengths of the first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, and seventh lens are f1, f2, f3, f4, f5, f6, and f7, respectively, wherein f1, f2, f3, f4, f5, f6, and f7 satisfy the following ratio with f: -2.0 <f1 / f<-1.5,-3.5<f2 / f<-3.0,3.0<f3 / f<3.5,6.5<f4 / f<7.0,2.0<f5 / f<2.5,-2.0<f6 / f<-1.5,1.5<f7 / f<2.0。

[0010] Furthermore, the first lens satisfies the following relationships: 1.8≤Nd≤2.0, Vd≤50.0; the second lens satisfies the following relationship: 1.5≤Nd≤1.8, Vd≥50.0; the third lens satisfies the following relationship: 1.5≤Nd≤1.8, Vd≤50.0; the fourth lens satisfies the following relationship: 1.5≤Nd≤1.8, Vd≥50.0; the fifth lens satisfies the following relationship: 1.4≤Nd≤1.6, Vd≥50.0; the sixth lens satisfies the following relationship: 1.5≤Nd≤1.8, Vd≤50.0; and the seventh lens satisfies the following relationship: 1.5≤Nd≤1.8, Vd≥50.0; where Nd is the refractive index and Vd is the Abbe constant.

[0011] Furthermore, the total optical length TTL of the optical system and the focal length f of the optical system satisfy the following condition: 6.5 ≤ TTL / f ≤ 7.0.

[0012] Furthermore, the F-number of the optical system is ≤1.9; the image height H of the optical system and the focal length f of the optical system satisfy the condition: H / f≥3.0.

[0013] Furthermore, the aperture stop of the optical system is located between the fourth lens and the fifth lens.

[0014] Furthermore, an equivalent flat glass is provided between the seventh lens and the imaging surface.

[0015] An imaging method for a short TTL wide-angle surveillance lens, wherein light rays pass sequentially from the object side to the image side along the incident direction through a first lens, a second lens, a third lens, a fourth lens, an aperture stop, a fifth lens, a sixth lens, and a seventh lens before forming an image on the imaging plane.

[0016] Compared with the prior art, the present invention has the following advantages: 1. This lens adopts a glass-plastic hybrid optical system, consisting of two glass spherical lenses and five plastic aspherical lenses. By rationally allocating the optical power of each lens and adjusting the surface shape and on-axis distance of each lens, the lens can achieve a large aperture, a wide field of view and high resolution while greatly compressing the overall length and realizing lens miniaturization and weight reduction. It has good imaging performance, and at the same time achieves day and night confocal focus and corrects purple fringing.

[0017] 2. The lens exhibits minimal image plane shift under high and low temperature conditions, is insensitive to temperature changes, provides uniform image plane illumination, has strong stray light suppression capabilities, and boasts a large manufacturing tolerance, ensuring good environmental reliability and enabling high-definition imaging within an operating temperature range of -40℃ to 85℃. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the optical system structure of the present invention; Figure 2 This is the transverse chromatic aberration diagram of the entire working band of the present invention; Figure 3 This is the axial chromatic aberration diagram of the entire working band of the present invention; Figure 4 This is the field curvature distortion diagram of the entire working band of the present invention; Figure 5 This is the MTF curve diagram of the entire operating band of this invention; Figure 6 This is the MTF curve of the infrared operating band of the present invention; Figure 7 This is the defocused MTF curve of the present invention at a low operating temperature of -40℃; Figure 8 This is the defocused MTF curve of the present invention at a high operating temperature of 85°C; In the diagram: STO - aperture stop; L1 - first lens; L2 - second lens; L3 - third lens; L4 - fourth lens; L5 - fifth lens; L6 - sixth lens; L7 - seventh lens; L8 - equivalent glass plate; IMA - imaging plane. Detailed Implementation

[0019] To make the above features and advantages of the present invention more readily understood, specific embodiments are described below in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0020] refer to Figures 1 to 8 A short TTL wide-angle surveillance lens, the optical system of which consists of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a fifth lens L5, a sixth lens L6, and a seventh lens L7 arranged sequentially along the optical axis from the object side to the image side; the first lens L1 and the fifth lens L5 are glass spherical lenses, and the second lens L2, the third lens L3, the fourth lens L4, the sixth lens L6, and the seventh lens L7 are plastic aspherical lenses.

[0021] In this embodiment, the equations for the aspherical curves of the second lens L2, the third lens L3, the fourth lens L4, the sixth lens L6, and the seventh lens L7 are as follows: Where Z is the distance from the vertex of the aspherical surface to the optical axis at a height of r; c is the paraxial curvature of the aspherical surface; r = 1 / c; k is the conic constant; α1, α2, α3, α4, α5, α6, α7, and α8 are all higher-order coefficients.

[0022] In this embodiment, without considering the curvature caused by the aspherical coefficient, the first lens L1 is a meniscus lens with negative optical power, its object side is convex and its image side is concave; the second lens L2 is a biconcave lens with negative optical power, its object side is concave and its image side is concave; the third lens L3 is a biconvex lens with positive optical power, its object side is convex and its image side is convex; the fourth lens L4 is a meniscus lens with positive optical power, its object side is concave and its image side is convex; the fifth lens L5 is a biconvex lens with positive optical power, its object side is convex and its image side is convex; the sixth lens L6 is a biconcave lens with negative optical power, its object side is concave and its image side is concave; and the seventh lens L7 is a biconvex lens with positive optical power, its object side is convex and its image side is convex.

[0023] In this embodiment, the focal length of the optical system is f, and the focal lengths of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, the sixth lens L6, and the seventh lens L7 are f1, f2, f3, f4, f5, f6, and f7, respectively. The ratio of f1, f2, f3, f4, f5, f6, and f7 to f satisfies the following condition: -2.0 <f1 / f<-1.5,-3.5<f2 / f<-3.0,3.0<f3 / f<3.5,6.5<f4 / f<7.0,2.0<f5 / f<2.5,-2.0<f6 / f<-1.5,1.5<f7 / f<2.0。

[0024] In this embodiment, the first lens L1 satisfies the following relationship: 1.8≤Nd≤2.0, Vd≤50.0; the second lens L2 satisfies the following relationship: 1.5≤Nd≤1.8, Vd≥50.0; the third lens L3 satisfies the following relationship: 1.5≤Nd≤1.8, Vd≤50.0; the fourth lens L4 satisfies the following relationship: 1.5≤Nd≤1.8, Vd≥50.0; the fifth lens L5 satisfies the following relationship: 1.4≤Nd≤1.6, Vd≥50.0; the sixth lens L6 satisfies the following relationship: 1.5≤Nd≤1.8, Vd≤50.0; and the seventh lens L7 satisfies the following relationship: 1.5≤Nd≤1.8, Vd≥50.0; where Nd is the refractive index and Vd is the Abbe constant.

[0025] In this embodiment, the on-axis distances of the optical system satisfy the following relationships: the air gap between the first lens L1 and the second lens L2 is 1.5~2.0mm; the air gap between the second lens L2 and the third lens L3 is 0~0.5mm; the air gap between the third lens L3 and the fourth lens L4 is 0~0.5mm; the air gap between the fourth lens L4 and the fifth lens L5 is 0~0.5mm; the air gap between the fifth lens L5 and the sixth lens L6 is 0~0.5mm; and the air gap between the sixth lens L6 and the seventh lens L7 is 0~0.5mm.

[0026] In this embodiment, the total optical length (TTL) of the optical system and the focal length (f) of the optical system satisfy the following condition: 6.5 ≤ TTL / f ≤ 7.0.

[0027] In this embodiment, the F-number of the optical system is ≤1.9; the image height H of the optical system and the focal length f of the optical system satisfy the condition: H / f≥3.0.

[0028] In this embodiment, an equivalent flat glass L8 is also provided between the seventh lens L7 and the imaging surface IMA.

[0029] In this embodiment, as Figures 2 to 8 As shown, by rationally combining the optical power and surface shape of the seven lenses and using five plastic aspherical surfaces, the optical system possesses excellent aberration correction and resolution capabilities.

[0030] In this embodiment, the technical specifications achieved by the optical system are as follows: (1) Focal length: 2.0≤EFFL≤2.5mm; (2) Aperture F≤1.9; (3) Field of view: 2w ≥ 170°; (4) Operating bands: visible light and short-wave infrared bands.

[0031] To achieve the above design parameters, the specific design of the optical system is shown in the table below: .

[0032] In this embodiment, the aspherical coefficients of each aspherical lens in the optical system are shown in the following table: .

[0033] An imaging method for a short TTL wide-angle surveillance lens, wherein light rays pass sequentially from the object side to the image side along the incident direction through a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an equivalent flat glass L8 before forming an image on the imaging surface IMA.

[0034] The optical system of this invention achieves the design requirements of short TTL, large aperture, and wide-angle by rationally allocating the optical power, surface shape, center thickness of each lens, and on-axis distance between each lens. The design employs five aspherical lenses to correct chromatic aberration in the optical system, effectively correcting the chromatic aberration between ultraviolet and infrared wavelengths, achieving day and night confocal focus without noticeable purple fringing. Simultaneously, this wide-angle lens has high resolution, and by using multiple lenses with negative refractive index temperature coefficients, it corrects high- and low-temperature image plane drift, enabling high-definition imaging even in environments ranging from -40℃ to 85℃.

[0035] The above description is only a preferred embodiment of the present invention. For those skilled in the art, designing different forms of short TTL wide-angle surveillance lenses according to the teachings of the present invention does not require creative labor. All equivalent changes, modifications, substitutions and variations made in accordance with the scope of the patent application of the present invention without departing from the principles and spirit of the present invention shall be covered by the present invention.

Claims

1. A short-TTL wide-angle surveillance lens characterized in that, The optical system of the lens is composed of a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens arranged in sequence along the optical axis from the object side to the image side; without considering the reverse bending caused by the aspherical surface coefficient, the first lens is a meniscus lens with negative focal power, the object side surface of which is convex, and the image side surface of which is concave; the second lens is a double-concave lens with negative focal power, the object side surface of which is concave, and the image side surface of which is concave; the third lens is a double-convex lens with positive focal power, the object side surface of which is convex, and the image side surface of which is convex; the fourth lens is a meniscus lens with positive focal power, the object side surface of which is concave, and the image side surface of which is convex; the fifth lens is a double-convex lens with positive focal power, the object side surface of which is convex, and the image side surface of which is convex; the sixth lens is a double-concave lens with negative focal power, the object side surface of which is concave, and the image side surface of which is concave; and the seventh lens is a double-convex lens with positive focal power, the object side surface of which is convex, and the image side surface of which is convex.

2. The short-TTL wide-view surveillance lens of claim 1, wherein, The first lens and the fifth lens are spherical lenses, and the second lens, the third lens, the fourth lens, the sixth lens and the seventh lens are aspherical lenses.

3. A short-TTL wide-angle surveillance lens according to claim 1 or 2, characterized in that The first lens and the fifth lens are glass spherical lenses, and the second lens, the third lens, the fourth lens, the sixth lens and the seventh lens are plastic aspherical lenses.

4. The short-TTL wide-view surveillance lens of claim 1, wherein, The focal length of the optical system is f, and the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are f1, f2, f3, f4, f5, f6 and f7 respectively, wherein f1, f2, f3, f4, f5, f6 and f7 and f satisfy the following ratios: -2.0 < f1 / f < -1.5, -3.5 < f2 / f < -3.0, 3.0 < f3 / f < 3.5, 6.5 < f4 / f < 7.0, 2.0 < f5 / f < 2.5, -2.0 < f6 / f < -1.5, and 1.5 < f7 / f < 2.

0.

5. The short TTL wide-angle monitoring lens according to claim 1, 2 or 4, characterized in that, The first lens satisfies the relationship: 1.8 ≤ Nd ≤ 2.0, and Vd ≤ 50.0; the second lens satisfies the relationship: 1.5 ≤ Nd ≤ 1.8, and Vd ≥ 50.0; the third lens satisfies the relationship: 1.5 ≤ Nd ≤ 1.8, and Vd ≤ 50.0; the fourth lens satisfies the relationship: 1.5 ≤ Nd ≤ 1.8, and Vd ≥ 50.0; the fifth lens satisfies the relationship: 1.4 ≤ Nd ≤ 1.6, and Vd ≥ 50.0; the sixth lens satisfies the relationship: 1.5 ≤ Nd ≤ 1.8, and Vd ≤ 50.0; and the seventh lens satisfies the relationship: 1.5 ≤ Nd ≤ 1.8, and Vd ≥ 50.0; wherein Nd is the refractive index, and Vd is the Abbe number.

6. The short-TTL wide-view surveillance lens of claim 1, wherein, The total optical length TTL of the optical system and the focal length f of the optical system satisfy: 6.5 ≤ TTL / f ≤ 7.

0.

7. The short-TTL wide-view surveillance lens of claim 1, wherein, The F number of the optical system is ≤1.9; the image height H of the optical system and the focal length f of the optical system satisfy: H / f ≥ 3.

0.

8. The short-TTL wide-view surveillance lens of claim 1, wherein, The stop of the optical system is located between the fourth lens and the fifth lens.

9. The short-TTL wide-view surveillance lens of claim 1, wherein, An equivalent flat glass is further arranged between the seventh lens and the imaging surface.

10. An imaging method applied to the short-TTL wide-angle monitoring lens according to claims 1-9, characterized in that, Light rays sequentially pass through the first lens, the second lens, the third lens, the fourth lens, the diaphragm, the fifth lens, the sixth lens and the seventh lens from the object side to the image side in the direction of incidence, and then are imaged on the imaging plane.

Images