CN112526728A

CN112526728A - Fixed focus lens

Info

Publication number: CN112526728A
Application number: CN202011577389.8A
Authority: CN
Inventors: 景姣; 张磊; 何剑炜
Original assignee: Dongguan Yutong Optical Technology Co Ltd
Current assignee: Dongguan Yutong Optical Technology Co Ltd
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2021-03-19

Abstract

The embodiment of the invention discloses a fixed focus lens, which comprises: the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are sequentially arranged from an object plane to an image plane along an optical axis; the first lens has negative focal power, the second lens has positive focal power, the third lens has negative focal power, the fourth lens has positive focal power, the fifth lens has positive focal power, the sixth lens has negative focal power and the seventh lens has positive focal power; the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, the focal length of the fourth lens is f4, the focal length of the fifth lens is f5, the focal length of the sixth lens is f6, the focal length of the seventh lens is f7, and the focal length of the optical system is f; wherein-1.91 < f1/f < -1.10, f2/f > 1.8, f3/f > -3.40, 1.70< f4/f <2.63, 1.78< f5/f <3.20, -1.88< f6/f < -1.01, and 1.16< f7/f < 2.33. On the premise of ensuring the ultra-large light transmission amount and low cost of the fixed focus lens, the imaging quality is improved, and the monitoring requirement under the low illumination condition is met.

Description

Fixed focus lens

Technical Field

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

Background

The existing solution for night shooting of a security camera is a dual-band confocal technology, namely, when light is sufficient in the daytime, the camera adopts a visible light receiving mode; when the camera is in a dim light environment at night, the camera adopts a mode of receiving visible light and infrared light (850nm) together for monitoring so as to ensure larger light entering amount; in order to realize this function, the lens is required to have the characteristic of common focus of the visible light band and the infrared band, i.e. the offset of the focus of the visible light and the infrared light is within the focal depth range of the infrared light. At night and when dusk, bigger logical light means better shooting effect, and the camera lens light ring of present mainstream is F2.0, and first piece of lens mostly is the plastic material, can not satisfy the requirement of customer to the camera lens outward appearance completely, and simultaneously, the purple limit phenomenon can appear at the in-process that uses of a lot of security protection cameras, and the imaging quality of shortwave department is relatively poor promptly, causes the shooting effect not good.

Therefore, it is necessary to develop a lens which is confocal day and night, has an ultra-large light transmission amount, has a wide angle and is good in purple margin.

Disclosure of Invention

The embodiment of the invention provides a fixed-focus lens, which ensures the ultra-large light flux, improves the imaging quality and meets the monitoring requirement under the low-illumination condition.

An embodiment of the present invention provides a fixed focus lens, including: the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are sequentially arranged from an object plane to an image plane along an optical axis;

the first lens has a negative optical power, the second lens has a positive optical power, the third lens has a negative optical power, the fourth lens has a positive optical power, the fifth lens has a positive optical power, the sixth lens has a negative optical power and the seventh lens has a positive optical power;

the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, the focal length of the fourth lens is f4, the focal length of the fifth lens is f5, the focal length of the sixth lens is f6, the focal length of the seventh lens is f7, and the focal length of the optical system is f;

wherein-1.91 < f1/f < -1.10, f2/f > 1.8, f3/f > -3.40, 1.70< f4/f <2.63, 1.78< f5/f <3.20, -1.88< f6/f < -1.01, and 1.16< f7/f < 2.33.

Optionally, the first lens and the fourth lens are both glass spherical lenses, and the second lens, the third lens, the fifth lens, the sixth lens and the seventh lens are all plastic aspheric lenses.

Optionally, the surface of the lens on the side close to the object plane is an object side surface, and the surface of the lens on the side close to the image plane is an image side surface;

the object side surface of the first lens is convex towards the object plane, and the image side surface of the first lens is convex towards the object plane; the object side surface of the second lens is convex towards the image plane, and the image side surface of the second lens is convex towards the image plane; the object side surface of the fourth lens is convex towards the object plane, and the image side surface of the fourth lens is convex towards the image plane; the object side surface of the fifth lens is convex towards the object plane, and the image side surface of the fifth lens is convex towards the image plane; the object side surface of the sixth lens is convex towards the image plane, and the image side surface of the sixth lens is convex towards the object plane; the object side surface of the seventh lens is convex towards the object plane, and the image side surface of the seventh lens is convex towards the image plane.

Optionally, the refractive index of the second lens is n 2; the refractive index of the third lens is n 3; the refractive index of the fourth lens is n 4; the refractive index of the fifth lens is n 5; the refractive index of the sixth lens is n 6; the refractive index of the seventh lens is n 7;

wherein 1.57< n2<1.68, 1.50< n3<1.55, 1.40< n4<1.64, 1.50< n5<1.55, 1.57< n6<1.68, 1.50< n7< 1.55.

Optionally, the abbe number of the second lens is v 2; the third lens has an abbe number v 3; the abbe number of the fourth lens is v 4; the abbe number of the fifth lens is v 5; the abbe number of the sixth lens is v 6; the abbe number of the seventh lens is v 7;

wherein 19.1< v2<30.4, 55.0< v3<57.1, 67.1< v4<97.0, 55.0< v5<57.1, 19.1< v6<30.4, 55.0< v7< 57.1.

Optionally, the fixed-focus lens further includes a diaphragm, and the diaphragm is disposed in a light path between the fourth lens and the fifth lens.

Optionally, a distance from the optical axis center of the image side surface of the seventh lens to the image plane is BFL, a distance from the object side surface of the first lens to the image plane is TTL, and BFL/TTL is greater than or equal to 0.17.

Optionally, the F-number F of the fixed focus lens satisfies that F is more than or equal to 1.4 and less than or equal to 1.6.

Optionally, the field angle of the fixed focus lens is an FOV, wherein the FOV is greater than or equal to 144 °.

According to the fixed-focus lens, the number of the lenses in the fixed-focus lens, the focal power of each lens and the relative relation between the focal lengths of the lenses are reasonably set, on the premise of low cost, the balance of the incident angles of the front and rear groups of lenses of the fixed-focus lens is ensured, the sensitivity of the lens is reduced, the production possibility is improved, the fixed-focus lens is ensured to have higher resolving power, the normal use at minus 40-80 ℃ is met, a shot picture has no purple edges, the ultra-large light flux is realized, the imaging quality is improved, and the requirement of high-definition image quality is met.

Drawings

To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief description will be given below of the drawings required for the embodiments or the technical solutions in the prior art, and it is obvious that the drawings in the following description, although being some specific embodiments of the present invention, can be extended and extended to other structures and drawings by those skilled in the art according to the basic concepts of the device structure, the driving method and the manufacturing method disclosed and suggested by the various embodiments of the present invention, without making sure that these should be within the scope of the claims of the present invention.

Fig. 1 is a schematic structural diagram of a fixed focus lens according to an embodiment of the present invention;

fig. 2 is a spherical aberration curve chart of a fixed focus lens according to an embodiment of the present invention;

fig. 3 is a chromatic aberration curve diagram of a fixed-focus lens according to an embodiment of the present invention;

fig. 4 is a field curvature distortion curve chart of a fixed focus lens according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of a fixed-focus lens according to a second embodiment of the present disclosure;

fig. 6 is a spherical aberration curve chart of a fixed focus lens according to a second embodiment of the present invention;

fig. 7 is a chromatic aberration curve diagram of a fixed-focus lens according to a second embodiment of the present invention;

fig. 8 is a field curvature distortion curve chart of a fixed focus lens according to a second embodiment of the present invention;

fig. 9 is a schematic structural diagram of a fixed-focus lens according to a third embodiment of the present invention;

fig. 10 is a spherical aberration curve chart of a fixed-focus lens according to a third embodiment of the present invention;

fig. 11 is a chromatic aberration curve diagram of a fixed-focus lens according to a third embodiment of the present invention;

fig. 12 is a field curvature distortion curve chart of a fixed focus lens according to a third embodiment of the present invention;

fig. 13 is a schematic structural diagram of a fixed-focus lens according to a fourth embodiment of the present invention;

fig. 14 is a spherical aberration curve chart of a fixed focus lens according to a fourth embodiment of the present invention;

fig. 15 is a chromatic aberration curve diagram of a fixed-focus lens according to a fourth embodiment of the present invention;

fig. 16 is a field curvature distortion curve chart of a fixed focus lens according to a fourth embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described through embodiments with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the basic idea disclosed and suggested by the embodiments of the present invention, are within the scope of the present invention.

Example one

Fig. 1 is a schematic structural diagram of a fixed-focus lens according to an embodiment of the present invention, as shown in fig. 1, the fixed-focus lens according to the embodiment of the present invention includes: a first lens 101, a second lens 102, a third lens 103, a fourth lens 104, a fifth lens 105, a sixth lens 106, and a seventh lens 107 arranged in this order from an object plane to an image plane along an optical axis;

the first lens 101 has a negative power, the second lens 102 has a positive power, the third lens 103 has a negative power, the fourth lens 104 has a positive power, the fifth lens 105 has a positive power, the sixth lens 106 has a negative power and the seventh lens 107 has a positive power;

the focal length of the first lens 101 is f1, the focal length of the second lens 102 is f2, the focal length of the third lens 103 is f3, the focal length of the fourth lens 104 is f4, the focal length of the fifth lens 105 is f5, the focal length of the sixth lens 106 is f6, the focal length of the seventh lens 107 is f7, and the focal length of the optical system is f;

Illustratively, the optical power is equal to the difference between the image-side and object-side beam convergence, which characterizes the ability of the optical system to deflect light. The larger the absolute value of the focal power is, the stronger the bending ability to the light ray is, and the smaller the absolute value of the focal power is, the weaker the bending ability to the light ray is. When the focal power is positive, the refraction of the light is convergent; when the focal power is negative, the refraction of the light is divergent. The optical power can be suitable for representing a certain refractive surface of a lens (namely, a surface of the lens), can be suitable for representing a certain lens, and can also be suitable for representing a system (namely a lens group) formed by a plurality of lenses together. In the fixed focus lens provided in this embodiment, each lens may be fixed in a lens barrel (not shown in fig. 1), and the first lens 101 is set to be a negative power lens for controlling the incident angle of the light rays of the optical system; the second lens 102 is a positive focal length lens, the third lens 103 is a negative focal length lens, and the second lens 102 and the third lens 103 adopt a positive and negative focal length combination form, so that the focal power of the whole system can be shared, the tolerance of the whole structure can be facilitated, and the assembly sensitivity can be reduced; the fourth lens 104 is a positive power lens for focusing a light beam; the third lens 103 and the sixth lens 106 are negative focal power lenses, and the second lens 102, the fifth lens 105 and the seventh lens 107 are positive focal power lenses, and are used for correcting high-order aberrations including aberrations such as field curvature, coma aberration and astigmatism. The focal power of the whole fixed-focus lens is distributed according to a certain proportion, and the balance of the incident angles of the front and rear lens groups is ensured, so that the sensitivity of the lens is reduced, and the production possibility is improved. Meanwhile, the focal lengths among the lenses are reasonably distributed, so that the spherical aberration and the field curvature of the imaging system are small at the same time, the on-axis and off-axis field-of-view image quality is ensured, and infrared can be imaged clearly without focusing under the condition that visible light is focused clearly.

Optionally, the first lens 101 and the fourth lens 104 are both glass spherical lenses, and the second lens 102, the third lens 103, the fifth lens 105, the sixth lens 106, and the seventh lens 107 are all plastic aspheric lenses.

The aspheric lens has the function of correcting aberrations such as field curvature, astigmatism, spherical aberration, coma aberration and the like. Because the cost of the lens made of plastic is far lower than that of the lens made of glass, the prime lens provided by the embodiment of the invention has good image quality and low cost by arranging 5 pieces of plastic aspheric lenses. And because the two materials have the mutual compensation function, the prime lens can still be normally used in high and low temperature environments.

Optionally, the prime lens further includes a diaphragm, and the diaphragm is disposed in an optical path between the fourth lens 104 and the fifth lens 105.

By arranging the diaphragm in the optical path between the fourth lens 104 and the fifth lens 105, the propagation direction of the light beam can be adjusted, and the incident angle of the light beam can be adjusted, which is beneficial to further improving the imaging quality.

the object side surface of the first lens is convex towards the object plane, and the image side surface of the first lens is convex towards the object plane; the object side surface of the second lens is convex towards the image surface, and the image side surface of the second lens is convex towards the image surface; the object side surface of the fourth lens is convex towards the object plane, and the image side surface of the fourth lens is convex towards the image plane; the object side surface of the fifth lens is convex towards the object plane, and the image side surface of the fifth lens is convex towards the image plane; the object side surface of the sixth lens is convex towards the image plane, and the image side surface of the sixth lens is convex towards the object plane; the object side surface of the seventh lens is convex towards the object plane, and the image side surface of the seventh lens is convex towards the image plane.

Furthermore, by reasonably setting the surface type of each lens, the focal power and the focal length of each lens can meet the focal power and the focal length requirement in the embodiment, and the whole fixed-focus lens can also be ensured to be compact in structure.

Optionally, the refractive index of the second lens 102 is n 2; the refractive index of the third lens 103 is n 3; the refractive index of the fourth lens 104 is n 4; the refractive index of the fifth lens 105 is n 5; the refractive index of the sixth lens 106 is n 6; the refractive index of the seventh lens 107 is n 7;

Optionally, the abbe number of the second lens 102 is v 2; the abbe number of the third lens 103 is v 3; the abbe number of the fourth lens 104 is v 4; the abbe number of the fifth lens 105 is v 5; the abbe number of the sixth lens 106 is v 6; the abbe number of the seventh lens 107 is v 7;

Specifically, the refractive index is the ratio of the propagation speed of light in vacuum to the propagation speed of light in the medium, and is mainly used to describe the refractive power of materials to light, and the refractive indices of different materials are different. The abbe number is an index for expressing the dispersion capability of the transparent medium, and the more severe the dispersion of the medium is, the smaller the abbe number is; conversely, the more slight the dispersion of the medium, the greater the abbe number. Therefore, the refractive index and the Abbe number of each lens in the fixed-focus lens are matched and arranged, so that the miniaturization design of the fixed-focus lens is facilitated; meanwhile, the method is favorable for realizing higher pixel resolution and larger aperture.

The distance from the optical axis center of the image space surface of the seventh lens 107 to the image plane can be understood as the back focal length of the fixed-focus lens, and the compact structure of the whole fixed-focus lens can be ensured by reasonably setting the back focal length of the fixed-focus lens.

Optionally, F number F of the fixed focus lens satisfies that F is more than or equal to 1.4 and less than or equal to 1.6. The fixed-focus lens provided by the embodiment of the invention is a large-aperture fixed-focus lens, meets the ultra-large throughput, and is suitable for the monitoring requirement under the low-illumination condition.

Optionally, the field angle of the fixed focus lens is FOV, wherein, FOV is larger than or equal to 144 °.

The fixed-focus lens provided by the embodiment of the invention is an ultra-large field angle fixed-focus lens, and meets the requirement of a large field angle.

For example, table 1 illustrates specific setting parameters of each lens in a fixed focus lens provided in a first embodiment of the present invention in a feasible implementation manner, where the fixed focus lens in table 1 corresponds to the fixed focus lens described in fig. 1.

TABLE 1 design values of optical parameters of fixed-focus lenses

With continued reference to fig. 1, the fixed focus lens provided by the embodiment of the present invention includes a first lens 101, a second lens 102, a third lens 103, a fourth lens 104, a fifth lens 105, a sixth lens 106, and a seventh lens 107, which are arranged in order from an object plane to an image plane along an optical axis. Table 1 shows optical physical parameters such as a curvature radius, a thickness, and a material of each lens in the fixed focus lens provided in the embodiment. Wherein, the surface numbers are numbered according to the surface sequence of each lens, for example, "1" represents the object surface of the first lens 101, "2" represents the image surface of the first lens 101, "STO/9" represents the object surface of the fifth lens 105, "10" represents the image surface of the fifth lens 105, and so on; the curvature radius represents the bending degree of the surface of the lens, a positive value represents that the surface is bent to the image surface side, and a negative value represents that the surface is bent to the object surface side; thickness represents the central axial distance from the current surface to the next surface, and the radius of curvature and thickness are both in millimeters (mm).

In addition to the above implementation, optionally, the first lens 101 and the fourth lens 104 are both glass spherical lenses, and the second lens 102, the third lens 103, the fifth lens 105, the sixth lens 106, and the seventh lens 107 are all plastic aspheric lenses. The prime lens provided by the embodiment of the invention also comprises a diaphragm (STO), and the propagation direction of the light beam can be adjusted by additionally arranging the diaphragm, so that the imaging quality is favorably improved. A diaphragm may be located in the optical path between the fourth lens 104 and the fifth lens 105, but the embodiment of the present invention does not limit the specific location of the diaphragm, and by locating the diaphragm at a suitable location, it is helpful to improve the relative illuminance.

The aspherical surface shape equation Z of the second lens 102, the third lens 103, the fifth lens 105, the sixth lens 106, and the seventh lens 107 satisfies:

wherein Z is the distance rise from the vertex of the aspheric surface when the aspheric surface is at the position with the height of y along the optical axis direction; c is 1/R, R represents the paraxial radius of curvature of the mirror surface; k is the cone coefficient; A. b, C, D, E, F is a high-order aspheric coefficient, where Z, R and y are both in mm.

Illustratively, table 2 details the aspheric parameters of the first embodiment in one possible implementation.

TABLE 2 design value of aspheric coefficients in fixed-focus lens

wherein-2.1642E-03 indicates that the coefficient A with the face number of 3 is-2.1642E 10^-3And so on.

The prime lens of the first embodiment achieves the following technical indexes:

focal length: f is 3.3 mm;

f-number: f is 1.6;

the field angle: 2w is more than or equal to 144.5 degrees (the image space 2 eta is more than or equal to phi 7 mm);

resolution ratio: up to 800 ten thousand pixel resolution CCD or CMOS cameras.

Fig. 2 is a spherical aberration curve of the fixed focus lens according to the first embodiment of the present invention, as shown in fig. 2, the spherical aberration of the fixed focus lens at different wavelengths (0.486 μm, 0.588 μm, 0.656 μm, 0.850 μm, and 0.436 μm) is within 0.05mm, and the curves at different wavelengths are relatively concentrated, which indicates that the axial aberration of the fixed focus lens is small, so that the fixed focus lens according to the first embodiment of the present invention can better correct the aberration.

Fig. 3 is a chromatic aberration graph of a fixed-focus lens according to an embodiment of the present invention, as shown in fig. 3, a vertical direction indicates a field of view, 0 indicates on an optical axis, and a vertex in the vertical direction indicates a maximum radius of the field of view; the horizontal direction is the distance in μm from the intersection point of the principal rays of the shortest wavelength to the intersection point of the principal rays of the longest wavelength on the image plane. As can be seen from fig. 3, the vertical axis chromatic aberration is better corrected.

Fig. 4 is a field curvature distortion curve graph of a fixed focus lens according to a first embodiment of the present invention, as shown in fig. 4, in a left coordinate system, a horizontal coordinate represents a size of field curvature, and a unit is mm; the vertical coordinate represents the normalized image height, with no units; wherein T represents meridian and S represents sagittal; as can be seen from fig. 4, the fixed focus lens provided by this embodiment is effectively controlled in curvature of field from light with a wavelength of 436nm to light with a wavelength of 850nm, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small; in the right-hand coordinate system, the horizontal coordinate represents the magnitude of distortion in units; the vertical coordinate represents the normalized image height, with no units; as can be seen from fig. 4, the field curvature of the fixed-focus lens provided by this embodiment is well corrected, and the imaging quality is effectively improved.

In summary, the fixed focus lens provided by this embodiment has the advantages of an ultra-large field angle, high image quality and a small volume under a low-light-level condition, and the design adopts a 7-piece structure, so that the requirement of 8MP image quality can be met under the condition of low cost and the collocation of different focal powers, and the use requirement under the environment of-40 ℃ to 80 ℃ can be met by adopting a glass-plastic mixed structure.

Example two

Fig. 5 is a schematic structural diagram of a fixed focus lens according to a second embodiment of the present invention, as shown in fig. 5, the fixed focus lens according to the second embodiment of the present invention includes: a first lens 201, a second lens 202, a third lens 203, a fourth lens 204, a fifth lens 205, a sixth lens 206, and a seventh lens 207 arranged in this order from an object plane to an image plane along an optical axis;

the first lens 201 has negative optical power, the second lens 202 has positive optical power, the third lens 203 has negative optical power, the fourth lens 204 has positive optical power, the fifth lens 205 has positive optical power, the sixth lens 206 has negative optical power and the seventh lens 207 has positive optical power;

the focal length of the first lens 201 is f1, the focal length of the second lens 202 is f2, the focal length of the third lens 203 is f3, the focal length of the fourth lens 204 is f4, the focal length of the fifth lens 205 is f5, the focal length of the sixth lens 206 is f6, the focal length of the seventh lens 207 is f7, and the focal length of the optical system is f;

The focal power, refractive index, abbe number, surface shape, material and stop position of the prime lens are the same as those in the first embodiment, and are not described herein again.

Table 3 details specific setting parameters of each lens in the fixed-focus lens provided in the second embodiment of the present invention, in another feasible implementation manner, and the black light lens in table 3 corresponds to the fixed-focus lens described in fig. 5.

TABLE 3 design values of optical parameters of fixed-focus lens

With continued reference to fig. 5, the fixed focus lens provided by the embodiment of the present invention includes a first lens 201, a second lens 202, a third lens 203, a fourth lens 204, a fifth lens 205, a sixth lens 206, and a seventh lens 207, which are arranged in order from an object plane to an image plane along an optical axis. Table 3 shows optical physical parameters such as a curvature radius, a thickness, and a material of each lens in the fixed focus lens provided in the embodiment. The surface numbers are numbered according to the surface sequence of the lenses, for example, "1" represents the object surface of the first lens 201, "2" represents the image surface of the first lens 201, "STO/9" represents the object surface of the fifth lens 205, "10" represents the image surface of the fifth lens 205, and so on; the curvature radius represents the bending degree of the surface of the lens, a positive value represents that the surface is bent to the image surface side, and a negative value represents that the surface is bent to the object surface side; thickness represents the central axial distance from the current surface to the next surface, and the radius of curvature and thickness are both in millimeters (mm).

Based on the above implementation, optionally, the first lens 201 and the fourth lens 204 are both glass spherical lenses, and the second lens 202, the third lens 203, the fifth lens 205, the sixth lens 206, and the seventh lens 207 are all plastic aspheric lenses. The prime lens provided by the embodiment of the invention also comprises a diaphragm (STO), and the propagation direction of the light beam can be adjusted by additionally arranging the diaphragm, so that the imaging quality is favorably improved. A diaphragm may be located in an optical path between the fourth lens 204 and the fifth lens 205, but the embodiment of the present invention does not limit a specific location of the diaphragm, and by locating the diaphragm at a suitable location, it is helpful to improve relative illuminance.

The aspherical surface shape equation Z of the second lens 202, the third lens 203, the fifth lens 205, the sixth lens 206, and the seventh lens 207 satisfies:

Illustratively, table 4 details the aspheric surface type parameters of the second embodiment in a possible implementation manner.

TABLE 4 design value of aspheric surface coefficient in fixed focus lens

wherein-6.3366E-03 indicates that the coefficient A with the face number of 3 is-6.3366E 10^-3And so on.

The fixed-focus lens of the second embodiment achieves the following technical indexes:

focal length: f is 3.3 mm;

f-number: f is 1.6;

the field angle: 2w is more than or equal to 144.3 degrees (the image space 2 eta is more than or equal to phi 7 mm);

resolution ratio: up to 800 ten thousand pixel resolution CCD or CMOS cameras.

Fig. 6 is a spherical aberration curve diagram of a fixed focus lens according to a second embodiment of the present invention, as shown in fig. 6, the spherical aberration of the fixed focus lens at different wavelengths (0.486 μm, 0.588 μm, 0.656 μm, 0.850 μm, and 0.436 μm) is within 0.05mm, and the curves at different wavelengths are relatively concentrated, which indicates that the axial aberration of the fixed focus lens is small, so that the fixed focus lens according to the second embodiment of the present invention can better correct the aberration.

Fig. 7 is a chromatic aberration graph of a fixed-focus lens according to a second embodiment of the present invention, as shown in fig. 7, a vertical direction indicates a field of view, 0 indicates on an optical axis, and a vertex in the vertical direction indicates a maximum radius of the field of view; the horizontal direction is the distance in μm from the intersection point of the principal rays of the shortest wavelength to the intersection point of the principal rays of the longest wavelength on the image plane. As can be seen from fig. 7, the vertical axis chromatic aberration is better corrected.

Fig. 8 is a field curvature distortion curve graph of a fixed focus lens according to a second embodiment of the present invention, as shown in fig. 8, in a left coordinate system, a horizontal coordinate represents a size of field curvature, and a unit is mm; the vertical coordinate represents the normalized image height, with no units; wherein T represents meridian and S represents sagittal; as can be seen from fig. 8, the fixed focus lens provided by this embodiment is effectively controlled in curvature of field from light with a wavelength of 436nm to light with a wavelength of 850nm, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small; in the right-hand coordinate system, the horizontal coordinate represents the magnitude of distortion in units; the vertical coordinate represents the normalized image height, with no units; as can be seen from fig. 8, the field curvature of the fixed-focus lens provided by this embodiment is well corrected, and the imaging quality is effectively improved.

EXAMPLE III

Fig. 9 is a schematic structural diagram of a fixed focus lens according to a third embodiment of the present invention, and as shown in fig. 9, the fixed focus lens according to the third embodiment of the present invention includes: a first lens 301, a second lens 302, a third lens 303, a fourth lens 304, a fifth lens 305, a sixth lens 306, and a seventh lens 307 arranged in this order from the object plane to the image plane along the optical axis;

the first lens 301 has a negative power, the second lens 302 has a positive power, the third lens 303 has a negative power, the fourth lens 304 has a positive power, the fifth lens 305 has a positive power, the sixth lens 306 has a negative power and the seventh lens 307 has a positive power;

the focal length of the first lens 301 is f1, the focal length of the second lens 302 is f2, the focal length of the third lens 303 is f3, the focal length of the fourth lens 304 is f4, the focal length of the fifth lens 305 is f5, the focal length of the sixth lens 306 is f6, the focal length of the seventh lens 307 is f7, and the focal length of the optical system is f;

Table 5 details specific setting parameters of each lens in the fixed-focus lens provided in the third embodiment of the present invention in another feasible implementation manner, and the black light lens in table 5 corresponds to the fixed-focus lens described in fig. 9.

TABLE 5 design values of optical parameters of fixed-focus lens

With continued reference to fig. 9, the fixed focus lens provided by the embodiment of the present invention includes a first lens 301, a second lens 302, a third lens 303, a fourth lens 304, a fifth lens 305, a sixth lens 306, and a seventh lens 307, which are arranged in order from the object plane to the image plane along the optical axis. Table 5 shows optical physical parameters such as the radius of curvature, thickness, and material of each lens in the fixed focus lens provided in the embodiment. Wherein, the surface numbers are numbered according to the surface sequence of each lens, for example, "1" represents the object surface of the first lens 301, "2" represents the image surface of the first lens 301, "STO/9" represents the object surface of the fifth lens 305, "10" represents the image surface of the fifth lens 305, and so on; the curvature radius represents the bending degree of the surface of the lens, a positive value represents that the surface is bent to the image surface side, and a negative value represents that the surface is bent to the object surface side; thickness represents the central axial distance from the current surface to the next surface, and the radius of curvature and thickness are both in millimeters (mm).

In addition to the above implementation, optionally, the first lens 301 and the fourth lens 304 are both glass spherical lenses, and the second lens 302, the third lens 303, the fifth lens 305, the sixth lens 306 and the seventh lens 307 are all plastic aspheric lenses. The prime lens provided by the embodiment of the invention also comprises a diaphragm (STO), and the propagation direction of the light beam can be adjusted by additionally arranging the diaphragm, so that the imaging quality is favorably improved. A diaphragm may be located in an optical path between the fourth lens 304 and the fifth lens 305, but the embodiment of the present invention does not limit a specific location of the diaphragm, and by locating the diaphragm at a suitable location, it is helpful to improve relative illuminance.

The aspherical surface shape equation Z of the second lens 302, the third lens 303, the fifth lens 305, the sixth lens 306, and the seventh lens 307 satisfies:

Illustratively, table 6 details the aspheric parameters of the third embodiment in a possible implementation.

TABLE 6 design value of aspheric surface coefficient in fixed-focus lens

wherein-2.4159E-03 indicates that the coefficient A with the face number of 3 is-2.4159E 10^-3And so on.

The prime lens in the third embodiment achieves the following technical indexes:

focal length: f is 3.3 mm;

f-number: f is 1.6;

resolution ratio: up to 800 ten thousand pixel resolution CCD or CMOS cameras.

Fig. 10 is a spherical aberration curve diagram of a fixed focus lens provided in the third embodiment of the present invention, as shown in fig. 10, the spherical aberrations of the fixed focus lens at different wavelengths (0.486 μm, 0.588 μm, 0.656 μm, 0.850 μm, and 0.436 μm) are all within 0.05mm, and the curves at different wavelengths are relatively concentrated, which indicates that the axial aberration of the fixed focus lens is small, so that it can be known that the fixed focus lens provided in the third embodiment of the present invention can better correct the aberration.

Fig. 11 is a chromatic aberration graph of a fixed-focus lens according to a third embodiment of the present invention, as shown in fig. 11, where a vertical direction represents a field of view, 0 represents on an optical axis, and a vertex in the vertical direction represents a maximum radius of the field of view; the horizontal direction is the distance in μm from the intersection point of the principal rays of the shortest wavelength to the intersection point of the principal rays of the longest wavelength on the image plane. As can be seen from fig. 11, the vertical axis chromatic aberration is better corrected.

Fig. 12 is a field curvature distortion curve graph of a fixed-focus lens according to a third embodiment of the present invention, as shown in fig. 12, in a left-side coordinate system, a horizontal coordinate represents a size of field curvature, and a unit is mm; the vertical coordinate represents the normalized image height, with no units; wherein T represents meridian and S represents sagittal; as can be seen from fig. 12, the fixed focus lens provided by this embodiment is effectively controlled in curvature of field from light with a wavelength of 436nm to light with a wavelength of 850nm, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small; in the right-hand coordinate system, the horizontal coordinate represents the magnitude of distortion in units; the vertical coordinate represents the normalized image height, with no units; as can be seen from fig. 12, the field curvature of the fixed-focus lens provided by this embodiment is well corrected, and the imaging quality is effectively improved.

Example four

Fig. 13 is a schematic structural diagram of a fixed focus lens according to a fourth embodiment of the present invention, and as shown in fig. 13, the fixed focus lens according to the fourth embodiment of the present invention includes: a first lens 401, a second lens 402, a third lens 403, a fourth lens 404, a fifth lens 405, a sixth lens 406, and a seventh lens 407 arranged in this order from an object plane to an image plane along an optical axis;

the first lens 401 has a negative power, the second lens 402 has a positive power, the third lens 403 has a negative power, the fourth lens 404 has a positive power, the fifth lens 405 has a positive power, the sixth lens 406 has a negative power and the seventh lens 407 has a positive power;

the focal length of the first lens 401 is f1, the focal length of the second lens 402 is f2, the focal length of the third lens 403 is f3, the focal length of the fourth lens 404 is f4, the focal length of the fifth lens 405 is f5, the focal length of the sixth lens 406 is f6, the focal length of the seventh lens 407 is f7, and the focal length of the optical system is f;

Table 7 details specific setting parameters of each lens in the fixed-focus lens provided in the fourth embodiment of the present invention in another possible implementation manner, and the black light lens in table 7 corresponds to the fixed-focus lens described in fig. 13.

TABLE 7 design values of optical parameters of fixed-focus lens

With continued reference to fig. 13, the fixed focus lens provided by the embodiment of the present invention includes a first lens 401, a second lens 402, a third lens 403, a fourth lens 404, a fifth lens 405, a sixth lens 406, and a seventh lens 407, which are arranged in order from the object plane to the image plane along the optical axis. Table 7 shows optical physical parameters such as a curvature radius, a thickness, and a material of each lens in the fixed focus lens provided in the embodiment. Wherein, the surface numbers are numbered according to the surface sequence of each lens, for example, "1" represents the object surface of the first lens 401, "2" represents the image surface of the first lens 401, "STO/9" represents the object surface of the fifth lens 405, "10" represents the image surface of the fifth lens 405, and so on; the curvature radius represents the bending degree of the surface of the lens, a positive value represents that the surface is bent to the image surface side, and a negative value represents that the surface is bent to the object surface side; thickness represents the central axial distance from the current surface to the next surface, and the radius of curvature and thickness are both in millimeters (mm).

In addition to the above implementation, optionally, the first lens 401 and the fourth lens 404 are both glass spherical lenses, and the second lens 402, the third lens 403, the fifth lens 405, the sixth lens 406, and the seventh lens 407 are all plastic aspheric lenses. The prime lens provided by the embodiment of the invention also comprises a diaphragm (STO), and the propagation direction of the light beam can be adjusted by additionally arranging the diaphragm, so that the imaging quality is favorably improved. A diaphragm may be located in an optical path between the fourth lens 404 and the fifth lens 405, but the embodiment of the present invention does not limit a specific location of the diaphragm, and by locating the diaphragm at a suitable location, it is helpful to improve the relative illuminance.

The aspherical surface shape equation Z of the second lens 402, the third lens 403, the fifth lens 405, the sixth lens 406, and the seventh lens 407 satisfies:

Illustratively, table 8 details the aspheric parameters of the fourth embodiment in a possible implementation.

TABLE 8 design value of aspheric surface coefficient in fixed-focus lens

wherein-4.48E-03 indicates that the coefficient A with the face number of 3 is-4.48E 10^-3And so on.

The fixed-focus lens in the fourth embodiment achieves the following technical indexes:

focal length: f is 3.3 mm;

f-number: f is 1.4;

the field angle: 2w is more than or equal to 144.7 degrees (the image space 2 eta is more than or equal to phi 7 mm);

resolution ratio: up to 800 ten thousand pixel resolution CCD or CMOS cameras.

Fig. 14 is a spherical aberration curve diagram of a fixed focus lens according to a fourth embodiment of the present invention, as shown in fig. 14, the spherical aberration of the fixed focus lens at different wavelengths (0.486 μm, 0.588 μm, 0.656 μm, 0.850 μm, and 0.436 μm) is within 0.05mm, and the curves at different wavelengths are relatively concentrated, which indicates that the axial aberration of the fixed focus lens is small, so that the fixed focus lens according to the fourth embodiment of the present invention can better correct the aberration.

Fig. 15 is a chromatic aberration graph of a fixed-focus lens according to a fourth embodiment of the present invention, as shown in fig. 15, where a vertical direction represents a field of view, 0 represents on an optical axis, and a vertex in the vertical direction represents a maximum radius of the field of view; the horizontal direction is the distance in μm from the intersection point of the principal rays of the shortest wavelength to the intersection point of the principal rays of the longest wavelength on the image plane. As can be seen from fig. 15, the vertical axis chromatic aberration is better corrected.

Fig. 16 is a graph of field curvature distortion of a fixed focus lens according to a fourth embodiment of the present invention, as shown in fig. 16, in a left coordinate system, a horizontal coordinate represents the size of field curvature, and the unit is mm; the vertical coordinate represents the normalized image height, with no units; wherein T represents meridian and S represents sagittal; as can be seen from fig. 16, the fixed focus lens provided by this embodiment is effectively controlled in curvature of field from light with a wavelength of 436nm to light with a wavelength of 850nm, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small; in the right-hand coordinate system, the horizontal coordinate represents the magnitude of distortion in units; the vertical coordinate represents the normalized image height, with no units; as can be seen from fig. 16, the field curvature of the fixed-focus lens provided by this embodiment is well corrected, and the imaging quality is effectively improved.

TABLE 9 summary of the parameters of the examples

As can be seen from the parameters of the embodiment shown in table 9, the first lens can be made of a high refractive index material or a low refractive index material, and thus the refractive index and abbe number of the first lens are not limited.

It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious modifications, rearrangements, combinations and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A prime lens, comprising: the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are sequentially arranged from an object plane to an image plane along an optical axis;

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

3. The prime lens according to claim 1, wherein the surface of the lens adjacent to the object plane is an object side surface, and the surface of the lens adjacent to the image plane is an image side surface;

4. The prime lens according to claim 1, wherein the refractive index of the second lens is n 2; the refractive index of the third lens is n 3; the refractive index of the fourth lens is n 4; the refractive index of the fifth lens is n 5; the refractive index of the sixth lens is n 6; the refractive index of the seventh lens is n 7;

5. The prime lens according to claim 1, wherein the abbe number of the second lens is v 2; the third lens has an abbe number v 3; the abbe number of the fourth lens is v 4; the abbe number of the fifth lens is v 5; the abbe number of the sixth lens is v 6; the abbe number of the seventh lens is v 7;

6. The prime lens according to claim 1, further comprising a diaphragm disposed in an optical path between the fourth lens and the fifth lens.

7. The fixed-focus lens system as claimed in claim 1, wherein a distance from an optical axis center of the image-side surface of the seventh lens element to the image plane is BFL, and a distance from the object-side surface of the first lens element to the image plane is TTL, wherein BFL/TTL is greater than or equal to 0.17.

8. The prime lens according to claim 1, wherein F-number F of the prime lens satisfies 1.4 ≤ F ≤ 1.6.

9. The prime lens according to claim 1, wherein the field angle of the prime lens is FOV, wherein FOV is greater than or equal to 144 °.