CN111897109A - Fixed focus lens - Google Patents

Abstract

The invention discloses a fixed focus lens, which comprises the following components in sequence from an object side to an imaging surface: the lens comprises a first lens with negative focal power, a second lens and a third lens, wherein the object side surface of the first lens is a convex surface, and the image side surface of the first lens is a concave surface; the second lens has positive focal power, the object side surface of the second lens is a convex surface, and the image side surface of the second lens is a plane; a diaphragm; a third lens having a positive optical power, the third lens having convex object and image side surfaces; the fourth lens is provided with negative focal power, and the object side surface of the fourth lens is a convex surface and the image side surface of the fourth lens is a concave surface; the fifth lens is provided with positive focal power, the object side surface of the fifth lens is a concave surface, and the image side surface of the fifth lens is a convex surface; a sixth lens having a negative optical power, an object-side surface and an image-side surface of the sixth lens being both concave at a paraxial region, the object-side surface and the image-side surface of the sixth lens each having an inflection point. The prime lens has the advantages of uniform pixel distribution in the full field angle, small volume, large imaging image surface, small distortion, good thermal stability, high image quality and the like.

Description

Fixed focus lens

Technical Field

The invention relates to the technical field of optical lenses, in particular to a fixed focus lens.

Background

All optical lenses have distortion, the distortion belongs to imaging geometric distortion, and is a picture distortion deformation phenomenon formed by different areas on a focal plane and different image magnification ratios, the degree of the deformation is gradually increased from the picture center to the picture edge, and the distortion is reflected obviously at the picture edge. The distortion is generally divided into two categories, barrel distortion and pincushion distortion; due to distortion of the lens, an image formed by a shot object projected on the imaging chip after passing through the optical system becomes barrel-shaped or pillow-shaped.

In order to reduce the image distortion caused by lens distortion, a circle around an imaging chip is generally cut by self-contained software in the camera, and the image is restored to a new image through an algorithm. Although this method of stretching an image can solve the problem of image distortion caused by distortion, the large stretching variation has a large influence on the image quality, for example, the definition and brightness around the image are reduced, and the problem that some pixels around the chip are not used can not be solved.

Disclosure of Invention

Therefore, the present invention is directed to a fixed focus lens for solving the above problems.

In order to achieve the purpose, the technical scheme of the invention is as follows:

the invention provides a fixed focus lens, which sequentially comprises the following components from an object side to an imaging surface: the lens comprises a first lens with negative focal power, a second lens and a third lens, wherein the object side surface of the first lens is a convex surface, and the image side surface of the first lens is a concave surface; the second lens with positive focal power, the object side surface of the second lens is a convex surface, and the image side surface of the second lens is a plane; the third lens has positive focal power, and the object side surface and the image side surface of the third lens are convex surfaces; the fourth lens with negative focal power, the object side surface of the fourth lens is a convex surface, and the image side surface of the fourth lens is a concave surface; the fifth lens has positive focal power, the object side surface of the fifth lens is a concave surface, and the image side surface of the fifth lens is a convex surface; the sixth lens with negative focal power, the object side surface of the sixth lens is a concave surface, and the image side surface of the sixth lens is a concave surface; a diaphragm is arranged between the second lens and the third lens; the image width L corresponding to the unit angle of the fixed focus lens, the field angle FOV of the fixed focus lens and the image plane size D satisfy the following conditional expression: 0.70< L/(D/FOV) < 1.50.

In addition, in the fixed focus lens system, the second lens element is a glass spherical lens element or an aspheric lens element, and the first lens element, the third lens element, the fourth lens element, the fifth lens element and the sixth lens element are plastic aspheric lens elements.

In addition, in the fixed focus lens, the fixed focus lens satisfies the following conditional expression:

0.20<Φa/Φ<0.40，

0.45<Φb/Φ<0.60；

wherein Φ represents an optical power of the fixed focus lens, Φ a represents a combined optical power of the first lens and the second lens, and Φ b represents a combined optical power of the third lens, the fourth lens, the fifth lens, and the sixth lens.

In addition, in the fixed focus lens, the fixed focus lens satisfies the following conditional expression:

Φ3>0，Φ4<0，Vd3-Vd4>30；

wherein Φ 3 represents an optical power of the third lens, Φ 4 represents an optical power of the fourth lens, Vd3 represents an abbe number of the third lens, and Vd4 represents an abbe number of the fourth lens.

Further, in the fixed focus lens described above, the fifth lens and the sixth lens are made of the same material and satisfy the following conditional expressions:

|Φc/Φ|<0.20；

wherein Φ c represents a combined focal power of the fifth lens and the sixth lens, and Φ represents a focal power of the fixed-focus lens.

In addition, in the fixed focus lens, the fixed focus lens satisfies the following conditional expression:

70°<FOV<90°；

7mm<D<9mm；

wherein FOV represents an angle of view of the fixed focus lens, and D represents an image plane size of the fixed focus lens.

In addition, in the fixed focus lens, the fixed focus lens satisfies the following conditional expression:

0.98<IH/(f*tan(FOV/2))<1.04；

wherein IH represents an actual image height of the fixed focus lens, f represents a focal length of the fixed focus lens, and FOV represents a field angle of the fixed focus lens.

In addition, in the fixed focus lens, the fixed focus lens satisfies the following conditional expression:

|DIST|<2％；

wherein DIST represents distortion of the fixed focus lens.

In addition, in the fixed focus lens, the fixed focus lens satisfies the following conditional expression:

|Φ3*(dn/dt)3+Φ4*(dn/dt)4+Φ5*(dn/dt)5+Φ6*(dn/dt)6|<2.5；

wherein Φ 3 represents a power of the third lens, Φ 4 represents a power of the fourth lens, Φ 5 represents a power of the fifth lens, Φ 6 represents a power of the sixth lens, (dn/dt)3 represents a temperature coefficient of refractive index of the third lens, (dn/dt)4 represents a temperature coefficient of refractive index of the fourth lens, (dn/dt)5 represents a temperature coefficient of refractive index of the fifth lens, and (dn/dt)6 represents a temperature coefficient of refractive index of the sixth lens.

Compared with the prior art, the prime lens provided by the invention has the advantages that through the collocation among the lenses and the limitation of parameters, the high image quality of the lens in high and low temperature environments is met, and the weight and the cost of the lens are effectively reduced; the imaging surface of the lens is large, and the imaging requirement of a 1/2-inch large target surface CMOS chip can be met; the distortion of the lens is small, so that the influence of camera software on the image quality deterioration after the image stretching processing can be reduced; the unit angle image width of the lens is uniform, so that the center and the periphery of an imaging picture of the lens are uniform. The prime lens provided by the invention meets the use requirements of the market on cameras with small volume, low weight, low cost and high-definition imaging.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a schematic structural diagram of a fixed-focus lens according to a first embodiment of the present invention;

fig. 2 is a normal-temperature MTF graph of a fixed-focus lens according to a first embodiment of the present invention;

fig. 3 is a distortion diagram of a fixed-focus lens according to a first embodiment of the present invention;

FIG. 4 is a diagram of image width per unit angle of a conventional lens in the prior art (horizontal axis coordinate: angle, vertical axis coordinate: mm in the figure);

FIG. 5 is a unit angle image width diagram of the fixed focus lens according to the first embodiment of the present invention (horizontal axis coordinate: angle, vertical axis coordinate: mm in the figure);

fig. 6 is a vertical axis chromatic aberration diagram of a fixed focus lens according to a first embodiment of the present invention;

fig. 7 is a schematic structural diagram of a fixed-focus lens according to a second embodiment of the present invention;

fig. 8 is a normal-temperature MTF graph of a fixed-focus lens according to a second embodiment of the present invention;

fig. 9 is a distortion diagram of a fixed-focus lens according to a second embodiment of the present invention;

FIG. 10 is a unit angle image width diagram of a fixed focus lens according to a second embodiment of the present invention (horizontal axis coordinate: angle, vertical axis coordinate: mm in the figure);

fig. 11 is a vertical axis chromatic aberration diagram of a fixed focus lens according to a second embodiment of the present invention.

Description of the main element symbols:

first lens	L1	Second lens	L2
				Third lens	L3	Fourth lens	L4
Fifth lens element	L5	Sixth lens element	L6
				Diaphragm	ST	Optical filter	G1
Object side surface of the first lens	S1	Image side surface of the first lens	S2
				Object side surface of the second lens	S3	Image side surface of the second lens	S4
Object side of the third lens	S5	Image side surface of the third lens	S6
				Object side of the fourth lens	S7	Image side surface of the fourth lens	S8
Object side surface of fifth lens	S9	Image side surface of the fifth lens element	S10
				Object side surface of sixth lens	S11	Image side surface of sixth lens element	S12
Object side of optical filter	S13	Image side of optical filter	S14
				Image plane	S15	Fixed focus lens	100、200

Detailed Description

In order to make the objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. Several embodiments of the invention are presented in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The invention provides a fixed focus lens, which comprises the following components in sequence from an object side to an imaging surface: the lens comprises a first lens, a second lens, a diaphragm, a third lens, a fourth lens, a fifth lens, a sixth lens and an optical filter.

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

the second lens has positive focal power, the object side surface of the second lens is a convex surface, and the image side surface of the second lens is a plane; the second lens can be a glass lens, and the image side surface of the second lens is set to be a plane, so that the tolerance sensitivity of the plane is better than that of a spherical surface on one hand, and the production and processing are convenient on the other hand;

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

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

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

the sixth lens has negative focal power, the object side surface and the image side surface of the sixth lens are both concave surfaces, and the object side surface and the image side surface of the sixth lens are both provided with inflection points.

The diaphragm can be made of shading paper with a light through hole in the center, and the light through aperture of the diaphragm is smaller than the space ring, so that the light through amount of the fixed-focus lens is determined by the light through aperture of the diaphragm. The diaphragm is arranged between the second lens and the third lens, so that the field angle of the fixed-focus lens can be improved, and the incidence angle of the chip can be better matched; the shading paper with the light through hole in the center is used as the diaphragm, so that the requirement of the light through hole of the lens cone can be reduced, the forming difficulty of the light through hole of the lens cone is reduced, the production efficiency is improved, and the production cost is reduced.

In some embodiments, in order to reduce the weight of the lens and the single-item price of the lens, the fixed-focus lens is made of five plastic lenses and one glass lens, so that the weight of the lens is greatly reduced, the single-item price of the lens is relatively low, and the fixed-focus lens is suitable for mass production.

In some embodiments, in order to improve the resolution of the lens and reduce the vertical axis chromatic aberration of the lens, the five lenses of the fixed focus lens use aspheric lenses, one of the five lenses uses a spherical lens or the six lenses use aspheric lenses, and the aspheric lenses can better correct the aberration of the lens, improve the resolution of the lens and enable the image to be clearer.

In some embodiments, to correct distortion of the lens and ray aberrations at different apertures, the object-side surface and the image-side surface of the sixth lens have inflection points.

In some embodiments, in order to make the image quality of the center and the periphery of the imaging picture of the lens more uniform, the fixed-focus lens satisfies the following conditional expression:

0.70<L/(D/FOV)<1.50；(1)

where FOV indicates the field angle of the fixed focus lens, D indicates the image plane size of the fixed focus lens, and L indicates the image width size corresponding to the unit angle of the fixed focus lens.

The condition formula (1) reasonably distributes the image width corresponding to the unit angle in the angle of view, so that the image width corresponding to each degree of the central and peripheral fields of view does not differ too much from the average value, the image quality of the central and peripheral fields of view can be balanced, and the phenomenon that the difference between the central resolution and the peripheral resolution of an imaging picture is large can not occur.

In some embodiments, to properly distribute the optical power of the lens, the fixed focus lens satisfies the following conditional expression:

0.20<Φa/Φ<0.40；(2)

0.45<Φb/Φ<0.60；(3)

where Φ represents the focal power of the fixed-focus lens, Φ a represents the combined focal power of the first lens and the second lens, and Φ b represents the combined focal power of the third lens, the fourth lens, the fifth lens, and the sixth lens.

The lenses (the first lens and the second lens) before the diaphragm form a front group of lenses, and the lenses (the third lens, the fourth lens, the fifth lens and the sixth lens) after the diaphragm form a rear group of lenses; the front group of lenses of the lens mainly plays a role in converging light beams, the focal power is not too large, otherwise too much aberration is introduced, and the focal power is too small, so that the light beams cannot be converged; the rear group lens of the lens mainly bears most of focal power of the lens, and meanwhile, the aberration introduced by the front group lens is corrected; the conditional expressions (2) and (3) reasonably distribute the focal power of each lens, so that the lens has a good imaging effect, and the resolving power of the lens is effectively improved.

In some embodiments, to correct axial chromatic aberration of the lens, the fixed-focus lens satisfies the conditional expression:

Φ3>0，Φ4<0；(4)

Vd3-Vd4>30；(5)

where Φ 3 denotes the refractive power of the third lens, Φ 4 denotes the refractive power of the fourth lens, Vd3 denotes the abbe number of the third lens, and Vd4 denotes the abbe number of the fourth lens.

The abbe number is an index indicating the dispersive power of the transparent medium. Generally, the smaller the abbe number of the lens, the more severe the dispersion; conversely, the larger the abbe number of the lens, the more slight the dispersion. The positive lens can generate positive chromatic aberration, and the negative lens can generate negative chromatic aberration, so that the chromatic aberration generated by the positive lens can be compensated only by the chromatic aberration generated by the negative lens, and the chromatic aberration can be corrected as far as possible by adopting a structure of matching the positive lens and the negative lens. The conditional expression (5) limits the abbe number difference of the third lens and the fourth lens, so that the third lens generates a small negative chromatic aberration, the fourth lens generates a large positive chromatic aberration, and then chromatic aberration compensation is performed on other lenses in the lens. Satisfying the above conditional expression (5), the chromatic aberration generated by each lens can be compensated reasonably, and the picture shot by the lens has higher color reduction degree.

In some embodiments, in order to reduce the aberration of the lens barrel, the fifth lens and the sixth lens are made of the same material, and the following conditional expression is satisfied:

|Φc/Φ|<0.20； (6)

where Φ c represents the combined focal power of the fifth lens and the sixth lens, and Φ represents the focal power of the fixed-focus lens.

The fifth lens and the sixth lens are made of the same material, and the conditional expression (6) is satisfied, so that the focal power of the fifth lens and the sixth lens after combination is smaller, the astigmatism of the lens is favorably reduced, the resolving power of the lens in the horizontal direction and the vertical direction is close, the image distortion degree is reduced, and the reduction degree of the real-shot object is higher.

In some embodiments, the prime lens satisfies the following conditional expression:

70°<FOV<90°， (7)

7mm<D<9mm； (8)

where FOV represents the angle of view of the fixed focus lens, and D represents the image plane size of the fixed focus lens.

The condition formulas (7) and (8) are met, the lens can be ensured to have a larger imaging surface, and the imaging requirement of a 1/2-inch large target surface CMOS chip can be matched.

In some embodiments, the prime lens satisfies the following conditional expression:

0.98<IH/(f*tan(FOV/2))<1.04； (9)

where IH denotes the actual image height of the fixed focus lens, f denotes the focal length of the fixed focus lens, and FOV denotes the angle of view of the fixed focus lens.

Satisfying the above conditional expression (9), the lens can have smaller distortion, so that the image surface cut by the camera software can fill the effective imaging area of the whole chip as far as possible without excessive pixel loss, and the peripheral definition and brightness reduction of the stretched image by the software can be reduced.

In some embodiments, the prime lens satisfies the following conditional expression:

|DIST|<2％； (10)

herein, DIST represents the distortion magnitude of the fixed focus lens.

Satisfying the above conditional expression (10) indicates that the distortion of the fixed focus lens is small.

In some embodiments, to improve the thermal stability of the lens, the prime lens satisfies the following conditional expression:

|Φ3*(dn/dt)3+Φ4*(dn/dt)4+Φ5*(dn/dt)5+Φ6*(dn/dt)6|<2.5； (11)

where Φ 3 represents the refractive power of the third lens, Φ 4 represents the refractive power of the fourth lens, Φ 5 represents the refractive power of the fifth lens, Φ 6 represents the refractive power of the sixth lens, (dn/dt)3 represents the temperature coefficient of refractive index of the third lens, (dn/dt)4 represents the temperature coefficient of refractive index of the fourth lens, (dn/dt)5 represents the temperature coefficient of refractive index of the fifth lens, and (dn/dt)6 represents the temperature coefficient of refractive index of the sixth lens.

The focal power of the first lens is small, the influence of temperature on the first lens is small, the second lens is made of glass, the thermal stability of the glass is much better than that of plastic, and therefore the thermal stability of the lens mainly refers to the influence of high and low temperature of the rear 4 plastic lenses (the third lens, the fourth lens, the fifth lens and the sixth lens). The conditional expression (11) reasonably distributes the focal power of the rear 4 lenses, and limits the temperature coefficient of the refractive index of the corresponding lens, so that the rear 4 lenses can compensate each other in high and low temperature environments, and the thermal stability of the lens is improved; meanwhile, the lens is ensured to have small focus offset in high-temperature and low-temperature working environments, and has good imaging quality.

The invention is further illustrated below in the following examples. In each embodiment, the thickness, the curvature radius, and the material selection part of each lens in the fixed-focus lens are different, and the specific difference can be referred to the parameter table of each embodiment. The following examples are only preferred embodiments of the present invention, but the embodiments of the present invention are not limited only by the following examples, and any other changes, substitutions, combinations or simplifications which do not depart from the innovative points of the present invention should be construed as being equivalent substitutions and shall be included within the scope of the present invention.

In the embodiments of the present invention, when the lens in the fixed focus lens is an aspheric lens, each aspheric surface type may satisfy the following equation:

wherein z is the distance rise from the aspheric surface vertex when the aspheric surface is at the position with the height h along the optical axis direction, c is the paraxial curvature radius of the surface, k is the conic coefficient, A_2iIs the aspheric surface type coefficient of 2i order.

First embodiment

Referring to fig. 1, which is a structural diagram of a fixed focus lens 100 according to a first embodiment of the present invention, the fixed focus lens 100 includes, in order from an object side to an image plane, a first lens L1, a second lens L2, a stop ST, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a filter G1.

The first lens L1 has negative power, and has a convex object-side surface S1 and a concave image-side surface S2; the second lens L2 has positive focal power, the object-side surface S3 of the second lens is convex, and the image-side surface S4 of the second lens is plane; the third lens L3 has positive focal power, and has a convex object-side surface S5 and a convex image-side surface S6; the fourth lens element L4 has negative power, and has a convex object-side surface S7 and a concave image-side surface S8; the fifth lens L5 has negative power, and the fifth lens has a concave object-side surface S9 and a convex image-side surface S10; the sixth lens L6 has positive power, an object-side surface S11 of the sixth lens is concave at the paraxial region, an image-side surface S12 is concave at the paraxial region, and inflection points are present on both the object-side surface S11 and the image-side surface S12 of the sixth lens.

Table 1 shows relevant parameters of each lens of the fixed focus lens 100 according to this embodiment.

TABLE 1

The relevant parameters of the aspherical lens of the fixed focus lens 100 in the present embodiment are shown in table 2.

TABLE 2

Flour mark

k

a4

a6

a8

a10

a12

a14

S1

-0.62

1.07E-02

-2.12E-03

2.74E-04

-2.85E-05

1.79E-06

-5.49E-08

S2

-0.95

2.51E-02

-1.07E-03

-7.33E-05

9.44E-05

-1.86E-05

0

S5

2.96

-2.75E-02

-2.80E-02

1.48E-02

-2.60E-02

4.93E-05

0

S6

6.08

1.17E-02

-1.28E-02

-2.60E-02

2.19E-02

-8.14E-03

0

S7

250.00

3.35E-03

1.96E-02

-3.07E-02

1.62E-02

-3.06E-03

0

S8

-23.03

5.31E-02

-1.23E-02

5.07E-03

-1.97E-03

2.64E-04

0

S9

-43.39

-1.87E-02

7.85E-03

-4.97E-03

-7.09E-04

9.21E-04

-2.36E-04

S10

-6.24

-3.76E-02

2.32E-02

-5.45E-03

1.30E-04

1.21E-04

-1.51E-05

S11

-0.34

2.22E-03

4.25E-03

-1.33E-04

-3.57E-05

2.71E-06

9.33E-09

S12

-22.03

-1.67E-02

2.38E-03

-1.96E-04

1.58E-05

9.13E-07

-1.95E-08

Referring to fig. 2, an MTF graph of the fixed-focus lens 100 in the present embodiment is shown, and it can be seen from the graph that the MTF value of the full field of the lens is above 0.2 and the MTF value of the central field of the lens is as high as above 0.5 at a spatial frequency of 200lp/mm, which indicates that the fixed-focus lens 100 has a higher resolution.

Referring to fig. 3, a distortion diagram of the fixed-focus lens 100 in the present embodiment is shown, and it can be seen from the diagram that the distortion of the lens is very small and is within-2%.

Referring to fig. 4, a unit angle image width diagram of a conventional lens in the prior art is shown, generally speaking, the image width ratio of the unit angle is decreasing from the central field to the peripheral field, which is also illustrated from the side: the distortion of the edge of the lens is large, so that the difference of the resolving power of the edge view field and the central view field is large. Referring to fig. 5, a unit angle image width diagram of the fixed focus lens 100 in this embodiment is shown, and it can be seen from the diagram that the deviation of the image width from the average value is small for each angle of the lens, which means that the pixel distribution is relatively uniform, and the ratio of the image width of the unit angle is continuously increased from the central field to the peripheral field, which means that the peripheral resolution of the fixed focus lens is relatively high, and the phenomenon of relatively large difference between the central resolution and the peripheral resolution of the image frame does not occur.

Referring to fig. 6, a vertical axis chromatic aberration diagram of the fixed focus lens 100 in the present embodiment is shown, and it can be seen from the diagram that the vertical axis chromatic aberration difference of different wavelengths is within 2um, which indicates that the chromatic aberration of the lens is small.

In this embodiment, the image plane diameter of the fixed focus lens 100 is 8mm, the field angle FOV is 82 °, and the total optical length TTL is 9 mm.

Second embodiment

Referring to fig. 7, in a structure diagram of a fixed focus lens 200 provided in the present embodiment, the surface type of each lens of the fixed focus lens 200 in the present embodiment is substantially the same as that of each lens of the fixed focus lens 100 in the first embodiment, and the difference is that: the second lens L2 uses a glass aspheric lens, and there are differences in the relevant parameters and air space of each lens.

The relevant parameters of each lens of the fixed focus lens 200 in the present embodiment are shown in table 3.

TABLE 3

The relevant parameters of the aspherical lens of the fixed focus lens 200 in the present embodiment are shown in table 4.

TABLE 4

Flour mark

k

a4

a6

a8

a10

a12

a14

S1

-0.03

1.80E-02

-3.12E-03

1.93E-04

-3.02E-06

-1.01E-06

-2.28E-09

S2

-0.05

2.76E-02

-4.54E-04

-1.78E-03

5.77E-04

-1.01E-04

0

S3

-0.46

-1.29E-03

-3.05E-03

6.30E-04

-3.88E-04

1.83E-04

0

S4

198.09

-1.47E-02

-5.24E-03

3.62E-03

-3.98E-04

1.04E-11

0

S5

2.83

-3.46E-02

-2.26E-02

3.84E-03

-1.35E-02

4.93E-05

0

S6

5.68

-7.40E-03

-8.67E-03

-2.30E-02

2.18E-02

-8.14E-03

0

S7

197.14

-6.33E-03

1.83E-02

-2.37E-02

1.44E-02

-3.06E-03

0

S8

-18.07

4.19E-02

2.70E-04

8.00E-04

-1.48E-03

2.64E-04

0

S9

-95.35

-1.87E-02

-1.38E-03

-1.93E-03

-1.45E-03

9.53E-04

-2.36E-04

S10

-4.83

6.12E-03

2.15E-03

-1.90E-03

1.94E-04

2.17E-05

-4.02E-06

S11

-7.64

-5.01E-03

9.02E-04

1.80E-04

-1.97E-05

1.55E-07

1.63E-08

S12

-18.94

-1.39E-02

1.54E-03

-1.92E-04

8.50E-06

9.89E-07

-1.49E-08

Referring to fig. 8, an MTF graph of the fixed-focus lens 200 in the present embodiment is shown, and it can be seen from the graph that the MTF value of the full field of the lens is above 0.2 and the MTF value of the central field of the lens is as high as above 0.5 at a spatial frequency of 200lp/mm, which indicates that the fixed-focus lens 100 has a higher resolution.

Referring to fig. 9, a distortion diagram of the fixed focus lens 200 in the present embodiment is shown, and it can be seen from the diagram that the distortion of the lens is very small and is within-1%.

Referring to fig. 10, a unit angle image width diagram of the fixed focus lens 100 in this embodiment is shown, and it can be seen from the diagram that the deviation of the image width from the average value is small for each angle of the lens, which means that the pixel distribution is relatively uniform, and the ratio of the image width of the unit angle is continuously increased from the central field to the peripheral field, which means that the peripheral resolution of the fixed focus lens is relatively high, and the phenomenon of relatively large difference between the central resolution and the peripheral resolution of the image frame does not occur.

Referring to fig. 11, a vertical axis chromatic aberration diagram of the fixed focus lens 100 in the present embodiment is shown, and it can be seen from the diagram that the vertical axis chromatic aberration difference of different wavelengths is within 2um, which indicates that the chromatic aberration of the lens is small.

In this embodiment, the image plane diameter of the fixed focus lens 200 is 8mm, the field angle FOV is 82 °, and the total optical length TTL is 9 mm.

Referring to table 5, the optical characteristics corresponding to the fixed-focus lens provided in each of the above 2 embodiments include the focal length F, F # and total optical length TTL of the fixed-focus lens, and also include the corresponding correlation values of each conditional expression in the above conditional expressions.

TABLE 5

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (9)

1. A prime lens is characterized by comprising an object side and an imaging surface in sequence;

the lens comprises a first lens with negative focal power, a second lens and a third lens, wherein the object side surface of the first lens is a convex surface, and the image side surface of the first lens is a concave surface;

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

a third lens having a positive optical power, the third lens having convex object and image side surfaces;

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

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

a sixth lens element having a negative optical power, wherein an object-side surface and an image-side surface of the sixth lens element are both concave at a paraxial region, and both the object-side surface and the image-side surface of the sixth lens element have inflection points;

a diaphragm is arranged between the second lens and the third lens;

the prime lens meets the following conditional expression:

0.70<L/(D/FOV)<1.50；

wherein, FOV represents the field angle of the fixed focus lens, D represents the image plane size of the fixed focus lens, and L represents the image width size corresponding to the unit angle of the fixed focus lens.

2. The prime lens according to claim 1, wherein the second lens is a glass spherical lens or an aspheric lens, and the first lens, the third lens, the fourth lens, the fifth lens and the sixth lens are plastic aspheric lenses.

3. The fixed focus lens according to claim 1, wherein the fixed focus lens satisfies the following conditional expression:

0.20<Φa/Φ<0.40，

0.45<Φb/Φ<0.60；

wherein Φ represents an optical power of the fixed focus lens, Φ a represents a combined optical power of the first lens and the second lens, and Φ b represents a combined optical power of the third lens, the fourth lens, the fifth lens, and the sixth lens.

4. The fixed focus lens according to claim 1, wherein the fixed focus lens satisfies the following conditional expression:

Φ3>0，Φ4<0，Vd3-Vd4>30；

wherein Φ 3 represents an optical power of the third lens, Φ 4 represents an optical power of the fourth lens, Vd3 represents an abbe number of the third lens, and Vd4 represents an abbe number of the fourth lens.

5. The prime lens according to claim 1, wherein the fifth lens and the sixth lens are made of the same material and satisfy the following conditional expression:

|Φc/Φ|<0.20；

wherein Φ c represents a combined focal power of the fifth lens and the sixth lens, and Φ represents a focal power of the fixed-focus lens.

6. The fixed focus lens according to claim 1, wherein the fixed focus lens satisfies the following conditional expression:

70°<FOV<90°；

7mm<D<9mm；

wherein FOV represents an angle of view of the fixed focus lens, and D represents an image plane size of the fixed focus lens.

7. The fixed focus lens according to claim 1, wherein the fixed focus lens satisfies the following conditional expression:

0.98<IH/(f*tan(FOV/2))<1.04；

wherein IH represents an actual image height of the fixed focus lens, f represents a focal length of the fixed focus lens, and FOV represents a field angle of the fixed focus lens.

8. The fixed focus lens according to claim 1, wherein the fixed focus lens satisfies the following conditional expression:

|DIST|<2％；

wherein DIST represents distortion of the fixed focus lens.

9. The fixed focus lens according to claim 1, wherein the fixed focus lens satisfies the following conditional expression:

|Φ3*(dn/dt)3+Φ4*(dn/dt)4+Φ5*(dn/dt)5+Φ6*(dn/dt)6|<2.5；

wherein Φ 3 represents a power of the third lens, Φ 4 represents a power of the fourth lens, Φ 5 represents a power of the fifth lens, Φ 6 represents a power of the sixth lens, (dn/dt)3 represents a temperature coefficient of refractive index of the third lens, (dn/dt)4 represents a temperature coefficient of refractive index of the fourth lens, (dn/dt)5 represents a temperature coefficient of refractive index of the fifth lens, and (dn/dt)6 represents a temperature coefficient of refractive index of the sixth lens.

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