Low-cost large-aperture day-and-night confocal fisheye lens

Abstract

The present application relates to a kind of low-cost large-aperture day and night confocal fisheye lens, the optical system of the lens is by first lens, second lens, third lens, fourth lens, fifth lens and sixth lens sequentially arranged from left to right along the light path of light incidence, diaphragm is arranged between third lens and fourth lens.Wherein first lens and third lens are glass spherical lens, second lens, fourth lens, fifth lens and sixth lens are all plastic aspheric lens.By reasonably distributing the optical power of each lens, surface type, the center thickness of each lens and the axial distance between each lens, etc., the lens meets the performance requirements of super wide angle, large aperture and high resolution imaging, while having day and night confocal, good thermal stability and purple edge correction ability;Adopt the glass-plastic hybrid system of four plastic aspheric lenses and two glass spherical lenses, the production cost is low, and the structure is reasonable, the assembly tolerance sensitivity is low, more suitable for large-scale high-yield mass production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical imaging technology, and particularly relates to a low-cost large-aperture day and night confocal fisheye lens. BACKGROUND

[0002] In recent years, with the rapid development of the Internet of Things and the progress of image sensing technology, more and more application fields require optical lenses not only to have high-definition imaging quality, but also to have a larger angle and a full range of field of view.

[0003] Among them, the fisheye lens generally has a field of view angle of more than 150 degrees, can simultaneously image and real-time extract information of the scene in a large field of view, and is favored by various industries in recent years due to its unique advantages, and is widely used in vehicle-mounted, security, machine vision, medical endoscopy and other fields, and has a very broad development prospect.

[0004] However, due to the large-angle oblique incidence of the fisheye lens system imaging light beam into the system, the off-axis imaging causes serious aberration, and the imaging quality also decreases; in addition, due to the super wide angle of the fisheye lens, the light flux of the image center and the edge of view is not uniform during lens design, so that the purple edge phenomenon becomes a prominent problem of the fisheye lens. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a low-cost large-aperture day and night confocal fisheye lens, which has the advantages of large aperture, high resolution, low temperature drift, day and night confocal and purple edge correction.

[0006] The fisheye lens of the present application can include, in order along the optical axis from the object side to the image side: a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens and a sixth lens.

[0007] Among them, the first lens is a negative meniscus lens with negative focal power, the object side is convex, and the image side is concave; the second lens is a double-concave negative lens with negative focal power, the object side is concave, and the image side is concave; the third lens and the fourth lens are both double-convex positive lenses with positive focal power, the object side and the image side are both convex; the fifth lens is a double-concave negative lens with negative focal power, the object side and the image side are both concave; and the sixth lens is a double-convex positive lens with positive focal power, the object side and the image side are both convex; the six lenses are made of glass or plastic material, wherein the first lens and the third lens are glass spherical lenses, and the second lens, the fourth lens, the fifth lens and the sixth lens are plastic aspherical lenses.

[0008] Preferably, the focal length of the optical system of the lens is f, and the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens are f1, f2, f3, f4, f5 and f6 respectively, wherein f1, f2, f3, f4, f5 and f6 satisfy the following ratios: -7.0 < f1 / f < -6.0, -2.0 < f2 / f < -1.0, 3.0 < f3 / f < 4.0, 2.0 < f4 / f < 3.0, -2.0 < f5 / f < -1.0, and 2 < f6 / f < 3.0.

[0009] Preferably, the first lens satisfies the relationship: 1.8 ≤ N d ≤ 2.0, and V d ≥ 50.0; the second lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, and V d ≥ 50.0; the third lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, and V d ≤ 50.0; the fourth lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, and V d ≥ 50.0; the fifth lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, and V d ≤ 50.0; and the sixth lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, and V d ≥ 50.0; wherein N d is the refractive index, and V d is the Abbe number.

[0010] Preferably, the distance of each lens on the optical axis of the lens satisfies the following relationships: the air gap between the first lens and the second lens is 5.0-6.0 mm; the air gap between the second lens and the third lens is 1.5-2.0 mm; the air gap between the third lens and the diaphragm is 1.5-2.0 mm; the air gap between the diaphragm and the fourth lens is -0.1-0 mm; the air gap between the fourth lens and the fifth lens is 0-0.1 mm; and the air gap between the fifth lens and the sixth lens is 0-0.5 mm.

[0011] Preferably, the second lens, the fourth lens, the fifth lens and the sixth lens are all aspherical lenses, and the aspherical curve equation is expressed as:

[0012]

[0013] wherein Z is the sagittal height of the aspherical surface at a height of h on the optical axis from the vertex of the aspherical surface; c is the paraxial curvature of the aspherical surface; k is the conic constant; and α1, α2, α3, α4, α5, α6, α7 and α8 are all high-order coefficients.

[0014] Preferably, the total track length TTL of the optical system and the focal length f of the optical system satisfy: 16≤TTL / f≤17.

[0015] Preferably, the F number of the optical system is ≤2.1.

[0016] Preferably, the image height H of the optical system and the focal length f of the optical system satisfy: H / f≥3.5.

[0017] Preferably, the stop of the optical system is located between the third lens and the fourth lens.

[0018] Preferably, the rear side of the sixth lens is provided with a filter.

[0019] Compared with the prior art, the present application has the following advantages:

[0020] The fisheye lens provided by the present application adopts six lenses, and an optical imaging system is formed by two glass spherical lenses and four plastic aspherical lenses.

[0021] 1. Six lenses with specific focal lengths are adopted, and specific surface shapes are matched and reasonable focal length distribution is allocated, so that the lens has a large aperture and an ultra-large field of view angle of more than 180 degrees, and ensures high resolution imaging clarity in both day and night, and realizes day and night co-focusing functions.

[0022] 2. A plurality of aspherical plastic lenses with negative correlation of refractive index temperature coefficient are matched with glass spherical lenses to balance temperature drift, so that the lens realizes athermalization while having lower production cost.

[0023] 3. The surface shape of the aspherical lens is adjusted to correct chromatic aberration in the optical system, so that the imaging picture does not appear purple edge chromatic aberration.

[0024] The present application will be further described in detail below in combination with the drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a schematic diagram of the optical structure of the present application;

[0026] Figure 2 is an axial chromatic aberration diagram of the full working waveband of the present application;

[0027] Figure 3 is a field curvature distortion diagram of the full working waveband of the present application;

[0028] Figure 4 is an MTF curve diagram of the full working waveband of the present application;

[0029] In the figure: STO - diaphragm; L1 - first lens; L2 - second lens; L3 - third lens; L4 - fourth lens; L5 - fifth lens; L6 - sixth lens; L7 - equivalent glass flat plate; IMA - imaging plane. DETAILED DESCRIPTION

[0030] The application will be further described below in conjunction with the drawings and specific implementation methods.

[0031] As shown in the figure, the fish-eye optical lens of the application is sequentially provided with a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens from the object side to the image side, and a diaphragm is arranged between the third lens and the fourth lens; the first lens and the third lens are glass spherical lenses, and the second lens, the fourth lens, the fifth lens and the sixth lens are plastic aspherical lenses. Figure 1

[0032] The first lens and the second lens are both lenses with negative focal length, the object side of the first lens is a convex surface, and the image side is a concave surface, and the object side and the image side of the second lens are both concave surfaces; the surface shape and the interval of the first lens and the second lens are beneficial to adjusting the large-angle light, and the glass lens of the first lens can make the lens have adaptability to complex environments and effectively reduce the damage of the external environment to the lens.

[0033] The third lens is a lens with positive focal length, and the object side and the image side are both convex surfaces, which is beneficial to converging the light passing through the front system and smoothly transitioning the light into the rear system; the diaphragm is arranged between the third lens and the fourth lens, which can balance the positive and negative focal lengths of the lens groups before and after the diaphragm, effectively reduce the aberration of the optical system, and improve the imaging performance of the lens.

[0034] The fourth lens is a plastic aspherical lens with positive focal length, and the image side and the object side are both convex surfaces; the fifth lens is a plastic aspherical lens with negative focal length, and the image side and the object side are both concave surfaces; through the reasonable matching of the fourth lens and the fifth lens, the spherical aberration in the optical system is effectively corrected; the sixth lens is a lens with positive focal length, and the object side and the image side are both convex surfaces.

[0035] The focal length of the optical system of the lens is f, and the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens are f1, f2, f3, f4, f5 and f6 respectively, wherein f1, f2, f3, f4, f5 and f6 satisfy the following proportions: -7.0 < f1 / f < -6.0, -2.0 < f2 / f < -1.0, 3.0 < f3 / f < 4.0, 2.0 < f4 / f < 3.0, -2.0 < f5 / f < -1.0, and 2 < f6 / f < 3.0.

[0036] ​The first lens satisfies the relationship: 1.8≤N d ≤2.0, V d ≥50.0; the second lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≥50.0; the third lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≤50.0; the fourth lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≥50.0; the fifth lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≤50.0; the sixth lens satisfies the relationship: 1.5≤N d ≤1.8, V d ≥50.0; wherein N d is the refractive index, and V d is the Abbe number.

[0037] The distance of each lens of the lens on the optical axis satisfies the following relationship: the air gap between the first lens and the second lens is 5.0-6.0mm; the air gap between the second lens and the third lens is 1.5-2.0mm; the air gap between the third lens and the diaphragm is 1.5-2.0mm; the air gap between the diaphragm and the fourth lens is -0.1-0mm; the air gap between the fourth lens and the fifth lens is 0-0.1mm; and the air gap between the fifth lens and the sixth lens is 0-0.5mm.

[0038] The second lens, the fourth lens, the fifth lens, and the sixth lens are all aspherical lenses, and the aspherical curve equation expression is:

[0039]

[0040] wherein Z is the sagittal height of the aspherical surface at a height of h along the optical axis from the vertex of the aspherical surface; c is the paraxial curvature of the aspherical surface; k is the conic constant; and α1, α2, α3, α4, α5, α6, α7, and α8 are all high-order coefficients.

[0041] The total optical length TTL of the optical system and the focal length f of the optical system satisfy: 16≤TTL / f≤17; the F number of the optical system is ≤2.1; the image height H of the optical system and the focal length f of the optical system satisfy: H / f≥3.5; and the rear side of the sixth lens is provided with a filter.

[0042] The technical indexes achieved by the optical system of the embodiment are as follows:

[0043] (1) focal length: 1.0≤EFFL≤2.0mm;

[0044] (2) Focal ratio F≤2.1;

[0045] (3) Field of view: 2w≥185°;

[0046] (4) Working waveband: visible waveband and short wave infrared waveband.

[0047] To realize the above design parameters, the specific design of the optical system of the embodiment is shown in the following table:

[0048]

[0049] The aspheric coefficients of each aspheric lens of the optical system of the embodiment are shown in the following table:

[0050]

[0051] The optical system of the embodiment makes the fisheye lens meet the imaging performance requirements of large aperture and high resolution, and has day and night confocal, good thermal stability and purple edge correction ability by reasonably distributing the focal power of each lens, the surface shape, the central thickness of each lens and the axial distance between each lens. The glass-plastic hybrid system of four plastic aspheric lenses and two glass spherical lenses has low production cost, reasonable structure, low assembly tolerance sensitivity and is more suitable for large-scale high-yield production.

[0052] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any skilled person in the art can modify or change the above disclosed technical content to obtain equivalent embodiments. However, any simple modification, equivalent change and modification made according to the technical essence of the present application to the above embodiments without departing from the technical solution of the present application still falls within the protection scope of the present application.

Claims

1. A low-cost, large-aperture day-and-night confocal fisheye lens, characterized in that: The lens sequentially comprises, along the optical axis from the object side to the image side, a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens, and a sixth lens; the number of lenses with optical power in the lens is 6 pieces; The first lens is a negative meniscus lens with negative optical power, the object side surface of which is a convex surface and the image side surface of which is a concave surface; the second lens is a double-concave negative lens with negative optical power, the object side surface of which is a concave surface and the image side surface of which is a concave surface; the third lens and the fourth lens are both double-convex positive lenses with positive optical power, the object side surface and the image side surface of each of which are convex surfaces; the fifth lens is a double-concave negative lens with negative optical power, the object side surface and the image side surface of which are concave surfaces; and the sixth lens is a double-convex positive lens with positive optical power, the object side surface and the image side surface of which are convex surfaces; wherein the first lens and the third lens are glass spherical lenses, and the second lens, the fourth lens, the fifth lens, and the sixth lens are plastic aspherical lenses; the focal length of the optical system of the lens is f, and the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are f1, f2, f3, f4, f5, and f6 respectively, wherein f1, f2, f3, f4, f5, and f6 and f satisfy the following ratios: -7.0 < f1 / f < -6.0, -2.0 < f2 / f < -1.0, 3.0 < f3 / f < 4.0, 2.0 < f4 / f < 3.0, -2.0 < f5 / f < -1.0, and 2 < f6 / f < 3.0; and the technical indexes achieved by the optical system of the lens are as follows: (1) focal length: 1.0 mm ≤ f ≤ 2.0 mm; (2) aperture F number ≤ 2.1; (3) field of view angle ≥ 185°; (4) working waveband: visible light waveband and short-wave infrared waveband.

2. The low-cost, large-aperture day-and-night confocal fisheye lens of claim 1, wherein: The first lens satisfies the relationship: 1.8 ≤ N d ≤ 2.0, V d ≤ 50.0; the second lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, V d ≥ 50.0; the third lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, V d ≤ 50.0; the fourth lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, V d ≥ 50.0; the fifth lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, V d ≤ 50.0; the sixth lens satisfies the relationship: 1.5 ≤ N d ≤ 1.8, V d ≥ 50.0; wherein N d is the refractive index, and V d is the Abbe number.

3. The low-cost, large-aperture day-and-night confocal fisheye lens of claim 2, wherein: The distance of each lens of the lens on the optical axis satisfies the following relationship: the air gap between the first lens and the second lens is 5.0-6.0 mm; the air gap between the second lens and the third lens is 1.5-2.0 mm; the air gap between the third lens and the diaphragm is 1.5-2.0 mm; the air gap between the diaphragm and the fourth lens is -0.1-0 mm; the air gap between the fourth lens and the fifth lens is 0-0.1 mm; and the air gap between the fifth lens and the sixth lens is 0-0.5 mm.

4. The low-cost, large-aperture day-and-night confocal fisheye lens of claim 3, wherein: The second lens, the fourth lens, the fifth lens, and the sixth lens are all aspherical lenses, and the aspherical curve equation expression is as follows: wherein z is the sagittal height of the aspherical surface at a height of h along the optical axis; c is the paraxial curvature of the aspherical surface; k is the conic constant; α1, α2, α3, α4, α5, α6, α7, and α8 are high-order coefficients; and r: 1 / c.

5. The low-cost, large-aperture day-and-night confocal fisheye lens of claim 4, wherein: The optical total length TTL of the optical system of the lens and the focal length f of the optical system satisfy: 16 ≤ TTL / f ≤ 17; the F number of the optical system is ≤ 2.1; the image height H of the optical system and the focal length f of the optical system satisfy: H / f ≥ 3.5; and a filter is arranged on the rear side of the sixth lens.

Images