CN218956903U

CN218956903U - Folding type fish-eye lens

Info

Publication number: CN218956903U
Application number: CN202223195303.2U
Authority: CN
Inventors: 杨铭; 李赐才; 范智宇; 张荣曜
Original assignee: Xiamen Leading Optics Co Ltd
Current assignee: Xiamen Leading Optics Co Ltd
Priority date: 2022-11-30
Filing date: 2022-11-30
Publication date: 2023-05-02
Anticipated expiration: 2032-11-30

Abstract

The patent relates to the field of fisheye lenses, in particular to a foldback fisheye lens, which sequentially comprises a first lens, a second lens, a third lens, a fourth lens, a diaphragm, a fifth lens, a sixth lens, a seventh lens, an eighth lens and a ninth lens from an object side to an image side along an optical axis; the first lens element to the ninth lens element each comprise an object side surface facing the object side and allowing the imaging light to pass therethrough, and an image side surface facing the image side and allowing the imaging light to pass therethrough; the first lens has positive focal power, the second lens has positive focal power, the third lens has negative focal power, the fourth lens and the fifth lens are isosceles right-angle reflecting prisms, and reflecting surfaces of the fourth lens and the fifth lens are mutually glued to form a prism group; the sixth lens has positive focal power, the seventh lens has positive focal power, the eighth lens has negative focal power, the ninth lens has positive focal power, the reentrant fisheye lens has good imaging quality, and a larger angle of view, and imaging is uniform.

Description

Folding type fish-eye lens

Technical Field

The patent relates to the field of fisheye lenses, and in particular relates to a foldback fisheye lens.

Background

Reflex lenses (reflexes), also known as Reflex lenses, are a special form of super-telephoto lenses. In a typical photographic lens, light enters from a first set of lenses as it passes through the lens, and reaches the film directly. The lens has large volume and weight which can be multiplied by several times when the focal length reaches 300mm-500mm or even 1000mm, and the catadioptric lens is inconvenient to use, and the catadioptric lens utilizes the principle of catadioptric light to lead the light to reach the film after being reflected instead of directly reaching the film when passing through the first group of lenses. The lens length can be effectively controlled. The existing foldback lens has poor imaging effect and smaller field angle.

Disclosure of Invention

In order to overcome the defects of the prior art, the utility model provides the foldback type fish-eye lens, which can solve the technical problems of poor imaging effect, small angle of view and the like of the conventional foldback lens.

In order to solve the technical problems, the utility model provides the following technical scheme:

the foldback fisheye lens is characterized by sequentially comprising a first lens, a second lens, a third lens, a fourth lens, a diaphragm, a fifth lens, a sixth lens, a seventh lens, an eighth lens and a ninth lens from an object side to an image side along an optical axis; the first lens element to the ninth lens element each comprise an object side surface facing the object side and allowing the imaging light to pass therethrough, and an image side surface facing the image side and allowing the imaging light to pass therethrough;

the first lens has positive focal power, the object side surface is a convex surface, and the image side surface is a concave surface;

the second lens has positive focal power, the object side surface is a convex surface, and the image side surface is a concave surface;

the third lens has negative focal power, the object side surface is a concave surface, and the image side surface is a concave surface;

the fourth lens and the fifth lens are isosceles right-angle reflecting prisms, and reflecting surfaces of the fourth lens and the fifth lens are mutually glued to form a prism group;

the sixth lens is provided with positive focal power, the object side surface is a convex surface, and the image side surface is a convex surface;

the seventh lens has positive focal power, the object side surface is a convex surface, and the image side surface is a convex surface;

the eighth lens is provided with negative focal power, the object side surface is a concave surface, and the image side surface is a concave surface;

the ninth lens has positive focal power, the object side surface is a convex surface, and the image side surface is a convex surface.

Further, the third lens, the sixth lens and the ninth lens are plastic aspheric lenses.

Further, the following conditional expressions, f1< |30|, f2< |20|, f3< |60|, f4> |0|, f5> |0|, f6< |20|, f7< |80|, f8< |20|, and f9< |30|, are satisfied, wherein f1 to f9 are focal lengths of the first lens to the ninth lens, respectively.

Further, the following conditional expressions are satisfied, 3< |f1/f| <8,3< |f2/f| <15,5< |f3/f| <25,2< |f6/f| <5,7< |f7/f| <35,1.9< |f8/f| <2.5,4< |f9/f| <8, where f1, f2, f3, f6, f7, f8, and f9 are focal lengths of the first lens, the second lens, the third lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens, respectively, and f is a focal length of the fish-eye lens.

Further, the following conditional expressions are satisfied, 1.80< nd1<2.00,1.7< nd2<1.9,1.5< nd3<1.7,1.55< nd6<1.7,1.5< nd7<1.8,1.7< nd8<1.93,1.5< nd9<1.7, where nd1, nd2, nd3, nd6, nd7, nd8, and nd9 are refractive indices of the first lens, the second lens, the third lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens, respectively.

Further, the following conditional expressions are satisfied, 20< vd1<50, 45< vd2<60, 19< vd3<60, 50< vd6<60, 55< vd7<80, 20< vd8<50, 50< vd9<60, wherein vd1, vd2, vd3, vd6, vd7, vd8, and vd9 are abbe numbers of the first lens, the second lens, the third lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens, respectively.

Further, the following conditional expression is satisfied, where vd1+vd2+vd3<135, and vd1, vd2, and vd3 are abbe numbers of the first lens, the second lens, and the third lens, respectively.

Further, the following conditional expression is satisfied, wherein TTL/AAG is 5.0.ltoreq.TTL/AAG, TTL is the total length of the fisheye lens, and AAG is the sum of three air gaps on the optical axis between the first lens and the fourth lens.

Further, the following conditional expression is satisfied, ALT <14.55, alt=ct1+ct2+ct3+ct4, wherein CT1, CT2, CT3, CT4 are center thicknesses of the first lens, the second lens, the third lens, and the fourth lens, respectively.

Further, TTL/F is less than 18.5, wherein TTL is the total length of the fisheye lens, and F is the clear aperture size of the fisheye lens.

The beneficial effects of the utility model are as follows:

the design that four glass spheres and three plastic aspheric surfaces combined is adopted in this scheme, can effectually promote the formation of image quality, and the full visual angle MTF of reentrant fisheye lens when spatial frequency reaches 112 lp/mm all is greater than 0.30, has good formation of image quality, and the HFOV of reentrant fisheye lens reaches 178, has great angle of view, and RI is greater than 45% simultaneously, and formation of image is even, and the edge does not have the hidden angle.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present utility model, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some examples of the present utility model and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a light path diagram of a foldback fisheye lens according to an embodiment of the utility model;

FIG. 2 is a graph showing the MTF of a foldback fisheye lens according to an embodiment of the utility model;

FIG. 3 is a defocus graph of a foldback fisheye lens according to an embodiment of the utility model;

FIG. 4 is a diagram showing the relative illuminance of a foldback fisheye lens according to an embodiment of the utility model;

fig. 5 is a longitudinal chromatic diagram of a foldback fisheye lens according to an embodiment of the utility model;

FIG. 6 is a graph showing curvature of field and distortion of a foldback fisheye lens according to an embodiment of the utility model;

fig. 7 is a light path diagram of a foldback fisheye lens according to a second embodiment of the utility model;

FIG. 8 is a graph showing the MTF of a foldback fisheye lens according to the second embodiment of the utility model;

FIG. 9 is a defocus graph of a foldback fisheye lens according to the second embodiment of the utility model;

FIG. 10 is a diagram showing the relative illuminance of a foldback fisheye lens according to the second embodiment of the utility model;

fig. 11 is a longitudinal chromatic aberration diagram of a foldback fisheye lens according to a second embodiment of the utility model;

FIG. 12 is a graph showing curvature of field and distortion of a foldback fisheye lens according to a second embodiment of the utility model;

fig. 13 is a light path diagram of a foldback fisheye lens according to the third embodiment of the utility model;

fig. 14 is an MTF graph of a foldback fisheye lens according to the third embodiment of the utility model;

FIG. 15 is a defocus graph of a foldback fisheye lens according to the third embodiment of the utility model;

FIG. 16 is a diagram showing the relative illuminance of a foldback fisheye lens according to the third embodiment of the utility model;

fig. 17 is a longitudinal chromatic diagram of a foldback fisheye lens according to the third embodiment of the utility model;

fig. 18 is a graph showing curvature of field and distortion of a foldback fisheye lens according to the third embodiment of the utility model.

Description of the main reference signs

1. A first lens; 2. a second lens; 3. a third lens; 4. a fourth lens; 5. a fifth lens; 6. a sixth lens; 7. a seventh lens; 8. an eighth lens; 9. a ninth lens; 10. a diaphragm; 11. a protective sheet; 12. an imaging surface.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present utility model more apparent, the technical solutions of the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model, and it is apparent that the described embodiments are some embodiments of the present utility model, but not all embodiments. All other embodiments, based on the embodiments of the utility model, which are apparent to those of ordinary skill in the art without inventive faculty, are intended to be within the scope of the utility model. Thus, the following detailed description of the embodiments of the utility model, as presented in the figures, is not intended to limit the scope of the utility model, as claimed, but is merely representative of selected embodiments of the utility model. All other embodiments, based on the embodiments of the utility model, which are apparent to those of ordinary skill in the art without inventive faculty, are intended to be within the scope of the utility model.

Referring to fig. 1-18, the present utility model provides a foldback fisheye lens, which sequentially includes a first lens, a second lens, a third lens, a fourth lens, a diaphragm, a fifth lens, a sixth lens, a seventh lens, an eighth lens and a ninth lens along an optical axis from an object side to an image side; the first lens element to the ninth lens element each comprise an object side surface facing the object side and allowing the imaging light to pass therethrough, and an image side surface facing the image side and allowing the imaging light to pass therethrough;

the eighth lens has negative focal power, the object side surface is a concave surface, and the image side surface is a concave surface;

the ninth lens has positive focal power, the object side surface is a convex surface, and the image side surface is a convex surface;

the first lens, the second lens and the third lens are front group lenses, and the sixth lens, the seventh lens, the eighth lens and the ninth lens are rear group lenses. The third lens, the sixth lens and the ninth lens are plastic aspheric lenses, the first lens, the second lens, the seventh lens and the eighth lens are glass spherical lenses, and the design that four glass spherical surfaces and three plastic aspheric surfaces are combined is adopted, so that the imaging quality can be better improved, and meanwhile, the relative illumination can also be better improved. Meanwhile, the first lens is made of a high-hardness and wear-resistant glass material, can well meet the requirements of outdoor high-temperature and high-humidity use under friction and other environments, and has good imaging quality under the conditions of-40 ℃ to 105 ℃.

Preferably, the following conditional expressions, f1< |30|, f2< |20|, f3< |60|, f4> |0|, f5> |0|, f6< |20|, f7< |80|, f8< |20|, f9< |30|, are satisfied, wherein f1, f2, f3, f4, f5, f6, f7, f8 and f9 are focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens and the ninth lens, respectively.

Preferably, the following conditional expressions are satisfied, 3< |f1/f| <8,3< |f2/f| <15,5< |f3/f| <25,2< |f6/f| <5,7< |f7/f| <35,1.9< |f8/f| <2.5,4< |f9/f| <8, where f1, f2, f3, f6, f7, f8, and f9 are focal lengths of the first lens, the second lens, the third lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens, respectively, and f is a focal length of the fish-eye lens. The ratio between the focal length of the lens and the focal length of the lens is controlled, so that aberration correction is facilitated, and imaging quality is improved.

Preferably, the following conditional expressions are satisfied, 1.80< nd1<2.00,1.7< nd2<1.9,1.5< nd3<1.7,1.55< nd6<1.7,1.5< nd7<1.8,1.7< nd8<1.93,1.5< nd9<1.7, where nd1, nd2, nd3, nd6, nd7, nd8, and nd9 are refractive indices of the first lens, the second lens, the third lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens, respectively. The first lens and the second lens adopt high-refractive-index glass, so that light rays with a large wide angle can be gently deflected through the system, bending of the lens can not be severe, and large wide-angle aberration such as coma aberration and astigmatism can be corrected.

Preferably, the following conditional expressions, 20< vd1<50, 45< vd2<60, 19< vd3<60, 50< vd6<60, 55< vd7<80, 20< vd8<50, 50< vd9<60, vd1+vd2+vd3<135, are satisfied; wherein vd1, vd2, vd3, vd6, vd7, vd8, and vd9 are abbe numbers of the first lens, the second lens, the third lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens, respectively. The fourth lens and the sixth lens are made of high Abbe number materials for correcting chromatic aberration of magnification.

Preferably, the following conditional expression is satisfied, wherein TTL/AAG is 5.0.ltoreq.TTL/AAG, TTL is the total length of the fisheye lens, and AAG is the sum of three air gaps on the optical axis between the first lens and the fourth lens. The air gaps between the front group lenses and the fourth lens are controlled, so that the size of the lens can be effectively shortened, and the lens is more convenient to install and use.

Preferably, the following conditional expression is satisfied, ALT <14.55, alt=ct1+ct2+ct3+ct4, wherein CT1, CT2, CT3, CT4 are center thicknesses of the first lens, the second lens, the third lens, and the fourth lens, respectively.

Preferably, TTL/F is less than 18.5 according to the following conditional expression, wherein TTL is the total length of the fisheye lens, and F is the clear aperture size of the fisheye lens.

The foldback fisheye lens of the present utility model will be described in detail with reference to specific examples.

Example 1

Referring to fig. 1-6, the present utility model provides a foldback fisheye lens, which sequentially includes a first lens, a second lens, a third lens, a fourth lens, a diaphragm, a fifth lens, a sixth lens, a seventh lens, an eighth lens and a ninth lens along an optical axis from an object side to an image side; the first lens element to the ninth lens element each comprise an object side surface facing the object side and allowing the imaging light to pass therethrough, and an image side surface facing the image side and allowing the imaging light to pass therethrough;

the detailed optical data of this embodiment are shown in table 1.

Table 1 detailed optical data for example one

Surface of the body		Caliber size	Radius of curvature	Thickness of (L)	Material of material	Refractive index	Coefficient of dispersion	Focal length
									0		Infinity	Infinity	Infinity
1		21.172	19.000	0.500
									2	First lens 1	18.999	19.095	2.074	2.0000,25.4584	2.01	25.46	-9.211
3		10.426	5.906	2.060
									4	Second lens 2	10.094	11.291	1.100	1.7725,49.5990	1.78	49.60	-7.621
5		6.626	3.714	2.990
									6	Third lens 3	6.524	-8.842	3.074	1.6714,19.2758	1.68	19.28	18.380
7		6.926	-5.897	0.402
									8	Fourth lens 4	6.080	Infinity	2.800	1.5168,64.1987	1.52	64.20	Infinity
9	Fifth lens 5	5.021	Infinity	2.800	1.5168,64.1987	1.51830	64.199	Infinity
									10		3.963	Infinity	0.518
11	Diaphragm 10	3.660	Infinity	0.120
									12	Sixth lens 6	3.921	6.043	1.731	1.5445,56.0033	1.55	56.00	5.412
13		4.143	-5.203	0.120
									14	Seventh lens 7	4.016	7.759	1.961	1.5928,68.3420	1.59	68.34	51.168
15	Eighth lens 8	3.922	-3.108	1.300	1.7847,25.7200	1.79	25.72	-4.200
									16		4.270	4.720	0.254
17	Ninth lens 9	4.525	6.722	2.397	1.5445,56.0033	1.55	56.00	10.420
									18		5.682	-32.486	1.000
19	Protective sheet 11	6.356	Infinity	0.700	1.5168,64.1987	1.52	64.20	Infinity
									20		6.6641	Infinity	0.342
21	Imaging surface 12	6.9066	Infinity	0

In this embodiment, the third lens 3, the sixth lens 6 and the ninth lens 9 are all plastic aspheric lenses, and the aspheric parameters of the third lens 3, the sixth lens 6 and the ninth lens 9 are shown in table 2 below;

table 2: aspheric coefficient

Face number	K	A4	A6	A8	A10	A12	A14	A16
										6	0	-0.001400112	-0.000117613	3.65885E-05	-8.39959E-06	1.02705E-06	-6.31588E-08	1.52687E-09
7	0	0.000352029	-6.26112E-06	4.58073E-06	-1.0303E-06	1.48314E-07	-9.84756E-09	2.66966E-10
									11	0	-0.000652319	0.000131755	-0.00026601	0.000107113	-3.06524E-05	4.71594E-06	-3.57243E-07
12	0	0.002062581	-0.000422323	6.02674E-05	-3.10226E-05	5.41659E-06	-6.19846E-07	8.52835E-09
									13	0	0.004587828	-0.000807279	0.000172631	-9.54874E-05	2.66996E-05	-3.67792E-06	1.83597E-07
14	0	0.006188935	-0.000524464	0.000145624	-4.80139E-05	7.42835E-06	-6.23932E-07	2.11415E-08
									15	0	-0.001400112	-0.000117613	3.65885E-05	-8.39959E-06	1.02705E-06	-6.31588E-08	1.52687E-09
16	0	0.000352029	-6.26112E-06	4.58073E-06	-1.0303E-06	1.48314E-07	-9.84756E-09	2.66966E-10

The folded fisheye lens of this embodiment has a TTL of 27.74mm, an F number of 1.9, and an HFOV of 178.

In this embodiment, the light path diagram of the folded fisheye lens is shown in fig. 1. Referring to fig. 2, the MTF graphs of different focal lengths of the foldback fisheye lens disclosed in the embodiment under the visible light 435nm-660nm wave band show that when the spatial frequency of the foldback fisheye lens reaches 112 lp/mm, the full-view MTF is greater than 0.48, and the foldback fisheye lens has better imaging quality. Referring to fig. 3, different curves represent defocus curves of meridian direction and sagittal direction under different fields of view, and as can be seen from fig. 3, almost all the peaks of the curves are near the zero offset vertical axis, and at this time, the defocus characteristic of the foldback fisheye lens is excellent, so that a larger effective focal depth range can be obtained. Referring to fig. 4, it can be seen that the refractive fisheye lens disclosed in the embodiment has RI > 58% under the maximum field of view, high relative illuminance, high uniformity of image and good imaging effect. Referring to fig. 5, the longitudinal chromatic aberration curve of the foldback fisheye lens under the visible light 435nm-660nm wave band disclosed in the embodiment can be seen from fig. 5 that the maximum longitudinal chromatic aberration of the foldback fisheye lens working in the visible light wave band is 0.02mm, and the longitudinal chromatic aberration of the foldback fisheye lens is well corrected. Referring to fig. 6, the field curvature distortion curve of the foldback fisheye lens disclosed in the embodiment under the visible light 435nm-660nm wave band can be seen from fig. 6 that the optical distortion of the foldback fisheye lens is less than 6%, the imaging quality is good, and the later correction difficulty is reduced.

Example two

Referring to fig. 7-12, the present utility model provides a foldback fisheye lens, which sequentially includes a first lens, a second lens, a third lens, a fourth lens, a diaphragm, a fifth lens, a sixth lens, a seventh lens, an eighth lens and a ninth lens along an optical axis from an object side to an image side; the first lens element to the ninth lens element each comprise an object side surface facing the object side and allowing the imaging light to pass therethrough, and an image side surface facing the image side and allowing the imaging light to pass therethrough;

the detailed optical data of this embodiment are shown in table 3.

Table 3 detailed optical data for example two

Surface of the body		Caliber size	Radius of curvature	Thickness of (L)	Material of material	Refractive index	Coefficient of dispersion	Focal length
									0		Infinity	Infinity	Infinity
1		26.977	25.000	0.500
									2	First lens 1	21.363	20.777	2.000	2.0000,25.4584	2.01	25.46	-10.523
3		12.027	6.682	2.180
									4	Second lens 2	11.702	10.871	1.100	1.7292,53.8512	1.73	53.85	-11.005
5		7.972	4.428	3.979
									6	Third lens 3	7.840	-6.512	2.322	1.6714,19.2758	1.68	19.28	55.928
7		8.002	-6.357	0.120
									8	Fourth lens 4	6.060	Infinity	2.800	1.5168,64.1987	1.52	64.20	Infinity
9	Fifth lens 5	5.073	Infinity	2.800	1.5168,64.1987	1.51830	64.199	Infinity
									10		5.588	Infinity	1.208
11	Diaphragm 10	5.000	Infinity	0.120
									12	Sixth lens 6	5.956	6.892	2.297	1.5350,55.7107	1.54	55.71	7.148
13		6.333	-7.666	1.321
									14	Seventh lens 7	6.445	8.284	2.929	1.6180,63.4058	1.62	63.41	77.133
15	Eighth lens 8	6.155	-4.348	1.300	1.9228,20.8799	1.93	20.88	-5.832
									16		6.417	9.762	0.483
17	Ninth lens 9	6.958	8.265	2.512	1.5350,55.7107	1.54	55.71	15.140
									18		8.058	-459.449	1.000
19	Protective sheet 11	8.548	Infinity	0.700	1.5168,64.1987	1.52	64.20	Infinity
									20		8.8352	Infinity	0.546
21	Imaging surface 12	9.1844	Infinity	0

In this embodiment, the third lens 3, the sixth lens 6 and the ninth lens 9 are all plastic aspheric lenses, and the aspheric parameters of the third lens 3, the sixth lens 6 and the ninth lens 9 are shown in the following table 4;

table 4: aspheric coefficient

Face number

K

A4

A6

A8

A10

A12

A14

A16

6

0

-0.000738472

2.56728E-05

-1.48088E-06

9.95608E-08

9.53923E-09

-5.92511E-10

7.88323E-12

7

0

0.00023566

3.44561E-05

-2.67028E-06

2.61902E-07

-3.31197E-09

-3.7323E-10

1.72608E-11

11

0

-0.000174015

1.65212E-05

-1.01904E-05

1.3476E-06

-1.13469E-07

5.01272E-09

-3.18985E-10

12

0

0.000793621

-5.62132E-05

1.26324E-05

-2.40933E-06

2.19227E-07

-9.69429E-09

-3.43145E-11

13

0

0.000195909

2.68912E-05

-3.26069E-05

5.8425E-06

-6.35721E-07

3.60064E-08

-8.84315E-10

14

0

0.002357712

7.57206E-06

-1.16356E-05

1.51887E-06

-1.50001E-07

6.70016E-09

-1.14558E-10

15

0

-0.000738472

2.56728E-05

-1.48088E-06

9.95608E-08

9.53923E-09

-5.92511E-10

7.88323E-12

16

0

0.00023566

3.44561E-05

-2.67028E-06

2.61902E-07

-3.31197E-09

-3.7323E-10

1.72608E-11

The folded fisheye lens of this embodiment has a TTL of 32.22mm, an F number of 1.9, and an HFOV of 178.

In this embodiment, the light path diagram of the folded fisheye lens is shown in fig. 7. Referring to fig. 8, the MTF graphs of different focal lengths of the foldback fisheye lens disclosed in the embodiment under the visible light 435nm-660nm wave band show that when the spatial frequency of the foldback fisheye lens reaches 112 lp/mm, the full-view MTF is greater than 0.46, and the foldback fisheye lens has better imaging quality. Referring to fig. 9, the defocus curves of the foldback fisheye lens in the visible light 435nm-660nm band disclosed in this embodiment represent defocus curves in the meridian direction and the sagittal direction under different fields, and as can be seen from fig. 9, almost all the peaks of the curves are near the zero offset vertical axis, and at this time, the defocus characteristic of the foldback fisheye lens is excellent, and a larger effective focal depth range can be obtained. Referring to fig. 10, it can be seen that the refractive fisheye lens disclosed in the embodiment has RI > 46% under the maximum field of view, high relative illuminance, high uniformity of image and good imaging effect. Referring to fig. 11, the longitudinal chromatic aberration curve of the foldback fisheye lens under the visible light 435nm-660nm wave band disclosed in the embodiment is shown, and it can be seen from fig. 11 that the maximum longitudinal chromatic aberration of the foldback fisheye lens working in the visible light wave band is 0.02mm, and the longitudinal chromatic aberration of the foldback fisheye lens is well corrected. Referring to fig. 12, the field curvature distortion curve of the foldback fisheye lens disclosed in the embodiment under the visible light 435nm-660nm wave band can be seen from fig. 12 that the optical distortion of the foldback fisheye lens is less than 5%, the imaging quality is good, and the later correction difficulty is reduced.

Example III

Referring to fig. 13-18, the present utility model provides a foldback fisheye lens, which sequentially includes a first lens, a second lens, a third lens, a fourth lens, a diaphragm, a fifth lens, a sixth lens, a seventh lens, an eighth lens and a ninth lens along an optical axis from an object side to an image side; the first lens element to the ninth lens element each comprise an object side surface facing the object side and allowing the imaging light to pass therethrough, and an image side surface facing the image side and allowing the imaging light to pass therethrough;

the detailed optical data of this embodiment are shown in table 5.

Table 5 detailed optical data for example three

Surface of the body		Caliber size	Radius of curvature	Thickness of (L)	Material of material	Refractive index	Coefficient of dispersion	Focal length
									0		Infinity	Infinity	Infinity
1		29.018	25.000	0.500
									2	First lens 1	26.936	24.895	2.953	2.0000,25.4584	2.01	25.46	-19.809
3		16.412	10.419	2.249
									4	Second lens 2	15.795	17.614	1.100	1.7725,49.5990	1.78	49.60	-10.991
5		10.133	5.587	2.266
									6	Third lens 3	9.961	8.294	1.000	1.5350,55.7107	1.54	55.71	-21.461
7		7.856	4.621	2.133
									8	Fourth lens 4	7.079	Infinity	2.800	1.5168,64.1987	1.52	64.20	Infinity
9	Fifth lens 5	6.350	Infinity	2.800	1.5168,64.1987	1.51830	64.199	Infinity
									10		6.350	Infinity	2.994
11	Diaphragm 10	5.156	Infinity	0.120
									12	Sixth lens 6	6.377	6.607	2.683	1.5350,55.7107	1.54	55.71	7.428
13		6.768	-8.650	2.272
									14	Seventh lens 7	7.212	6.549	3.389	1.6180,63.4058	1.62	63.41	21.999
15	Eighth lens 8	6.796	-5.070	1.300	1.9229,20.8799	1.93	20.88	-5.307
									16		6.687	7.626	0.255
17	Ninth lens 9	6.928	6.685	2.568	1.5168,64.1987	1.54	55.71	12.238
									18		7.778	-346.152	1.000
19	Protective sheet 11	8.412	Infinity	0.700	H-K9L	1.52	64.20	Infinity
									20		8.775	Infinity	0.526
21	Imaging surface 12	9.2069	Infinity	0

In this embodiment, the third lens 3, the sixth lens 6 and the ninth lens 9 are all plastic aspheric lenses, and the aspheric parameters of the third lens 3, the sixth lens 6 and the ninth lens 9 are shown in the following table 6;

table 6: aspheric coefficient

Face number

K

A4

A6

A8

A10

A12

A14

A16

6

0

-8.18E-04

-3.57E-06

-2.49E-07

8.23E-09

0.00E+00

7

0

-8.03E-04

1.91E-05

-3.17E-06

1.44E-07

0.00E+00

11

0

-4.24E-04

-6.19E-06

1.06E-06

-7.08E-08

0.00E+00

12

0

6.34E-04

-1.36E-05

2.26E-06

-1.03E-07

0.00E+00

13

0

-6.74E-04

-1.01E-04

1.17E-05

-1.26E-06

3.97E-08

0.00E+00

14

0

2.21E-03

-1.06E-04

1.08E-05

-1.03E-06

3.00E-08

0.00E+00

15

0

-8.18E-04

-3.57E-06

-2.49E-07

8.23E-09

0.00E+00

16

0

-8.03E-04

1.91E-05

-3.17E-06

1.44E-07

0.00E+00

The folded fisheye lens of this embodiment has a TTL of 35.11mm, an F number of 1.9, and an HFOV of 178 °.

In this embodiment, the light path diagram of the folded fisheye lens is shown in fig. 13. Referring to fig. 14, the MTF graphs of different focal lengths of the foldback fisheye lens disclosed in the embodiment under the visible light 435nm-660nm wave band show that when the spatial frequency of the foldback fisheye lens reaches 112 lp/mm, the full-view MTF is greater than 0.30, and the foldback fisheye lens has better imaging quality. Referring to fig. 15, the defocus curves of the foldback fisheye lens in the visible light 435nm-660nm band disclosed in this embodiment represent defocus curves in the meridian direction and the sagittal direction under different fields, and as can be seen from fig. 15, almost all the peaks of the curves are near the zero offset vertical axis, and at this time, the defocus characteristic of the foldback fisheye lens is excellent, and a larger effective focal depth range can be obtained. Referring to fig. 16, it can be seen that the refractive fisheye lens disclosed in the embodiment has RI > 45% under the maximum field of view, high relative illuminance, high uniformity of image and good imaging effect. Referring to fig. 17, the longitudinal chromatic aberration curve of the foldback fisheye lens under the visible light 435nm-660nm wave band disclosed in the embodiment is shown, and it can be seen from fig. 17 that the maximum longitudinal chromatic aberration of the foldback fisheye lens working in the visible light wave band is 0.04mm, and the longitudinal chromatic aberration of the foldback fisheye lens is well corrected. Referring to fig. 18, the field curvature distortion curve of the foldback fisheye lens disclosed in the embodiment under the visible light 435nm-660nm wave band can be seen from fig. 18 that the optical distortion of the foldback fisheye lens is less than 6%, the imaging quality is good, and the later correction difficulty is reduced.

Table 7 shows the values of relevant important parameters for three embodiments of the present utility model:

table 7: relevant important parameters of various embodiments

In the present utility model, unless expressly stated or limited otherwise, a first feature "above" or "below" a second feature may include both the first and second features being in direct contact, as well as the first and second features not being in direct contact but being in contact with each other through additional features therebetween. Moreover, a first feature being "above," "over" and "on" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly under and obliquely below the second feature, or simply means that the first feature is less level than the second feature.

The foregoing has shown and described the basic principles, principal features and advantages of the utility model. It will be understood by those skilled in the art that the present utility model is not limited to the above-described embodiments, and that the above-described embodiments and descriptions are only preferred embodiments of the present utility model, and are not intended to limit the utility model, and that various changes and modifications may be made therein without departing from the spirit and scope of the utility model as claimed. The scope of the utility model is defined by the appended claims and equivalents thereof.

Claims

1. The foldback fisheye lens is characterized by sequentially comprising a first lens, a second lens, a third lens, a fourth lens, a diaphragm, a fifth lens, a sixth lens, a seventh lens, an eighth lens and a ninth lens from an object side to an image side along an optical axis; the first lens element to the ninth lens element each comprise an object side surface facing the object side and allowing the imaging light to pass therethrough, and an image side surface facing the image side and allowing the imaging light to pass therethrough;

2. The fold-back fisheye lens of claim 1 wherein: the third lens, the sixth lens and the ninth lens are plastic aspheric lenses.

3. The fold-back fisheye lens of claim 1 wherein: the following conditional expressions, f1< |30|, f2< |20|, f3< |60|, f4> |0|, f5> |0|, f6< |20|, f7< |80|, f8< |20|, f9< |30|, are satisfied, wherein f1 to f9 are focal lengths of the first lens to the ninth lens, respectively.

4. The fold-back fisheye lens of claim 1 wherein: the following conditional expressions are satisfied, 3< |f1/f| <8,3< |f2/f| <15,5< |f3/f| <25,2< |f6/f| <5,7< |f7/f| <35,1.9< |f8/f| <2.5,4< |f9/f| <8, where f1, f2, f3, f6, f7, f8, and f9 are focal lengths of the first lens, the second lens, the third lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens, respectively, and f is a focal length of the fish-eye lens.

5. The fold-back fisheye lens of claim 1 wherein: the following conditional expressions are satisfied, 1.80< nd1<2.00,1.7< nd2<1.9,1.5< nd3<1.7,1.55< nd6<1.7,1.5< nd7<1.8,1.7< nd8<1.93,1.5< nd9<1.7, where nd1, nd2, nd3, nd6, nd7, nd8, and nd9 are refractive indices of the first lens, the second lens, the third lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens, respectively.

6. The fold-back fisheye lens of claim 1 wherein: the following conditional expressions are satisfied, 20< vd1<50, 45< vd2<60, 19< vd3<60, 50< vd6<60, 55< vd7<80, 20< vd8<50, 50< vd9<60, where vd1, vd2, vd3, vd6, vd7, vd8, and vd9 are abbe numbers of the first lens, the second lens, the third lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens, respectively.

7. The fold-back fisheye lens of claim 1 wherein: and the following conditional expression is satisfied, wherein vd1+vd2+vd3 is <135, and vd1, vd2 and vd3 are abbe numbers of the first lens, the second lens and the third lens respectively.

8. The fold-back fisheye lens of claim 1 wherein: the following conditional expression is satisfied, wherein TTL/AAG is 5.0.ltoreq.TTL/AAG, TTL is the total length of the fish-eye lens, AAG is the sum of three air gaps on the optical axis between the first lens and the fourth lens.

9. The fold-back fisheye lens of claim 1 wherein: the following conditional expression is satisfied, ALT <14.55, alt=ct1+ct2+ct3+ct4, wherein CT1, CT2, CT3, CT4 are center thicknesses of the first lens, the second lens, the third lens, and the fourth lens, respectively.

10. The fold-back fisheye lens of claim 1 wherein: the TTL/F is less than 18.5, wherein TTL is the total length of the fisheye lens, and F is the clear aperture size of the fisheye lens.