CN220752388U

CN220752388U - Fixed focus lens and supervisory equipment

Info

Publication number: CN220752388U
Application number: CN202322477128.4U
Authority: CN
Inventors: 封文轩; 何剑炜
Original assignee: Dongguan Yutong Optical Technology Co Ltd
Current assignee: Dongguan Yutong Optical Technology Co Ltd
Priority date: 2023-09-12
Filing date: 2023-09-12
Publication date: 2024-04-09
Anticipated expiration: 2033-09-12

Abstract

The embodiment of the utility model discloses a fixed focus lens and monitoring equipment. The fixed-focus lens comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens which are sequentially arranged from an object plane to an image plane along an optical axis; the first lens and the fifth lens are of negative focal power, and the third lens, the fourth lens and the sixth lens are of positive focal power; wherein: -phi 1/phi 0.23; the phi is more than or equal to 0.15 and less than or equal to 0.4; phi 3/phi is more than or equal to 0.1 and less than or equal to 0.5; phi 4/phi is more than or equal to 0.65 and less than or equal to 1.3; the phi is more than or equal to 1 and less than or equal to 1.8. The fixed focus lens can realize the functions that the total optical length is smaller than 22.5mm, a SENSOR chip with a 1/2.7' inch target surface can be matched, the diagonal field angle reaches 45.3-50.3 degrees, the resolution ratio of 4K is 4K, the F number of the aperture is 1.6+/-5%, the focal length is about 8mm, and the day and night confocal function is realized.

Description

Fixed focus lens and supervisory equipment

Technical Field

The embodiment of the utility model relates to the technical field of optical lenses, in particular to a fixed-focus lens and monitoring equipment.

Background

The current security monitoring lens can monitor for a long time and multiple scenes, and a large amount of manpower and time cost are saved. Along with the development of security and protection monitoring industry, the requirements of the used optical lens gradually tend to miniaturization, high resolution, large aperture and day-night confocal, and even under some scenes, the requirement of long focus is also provided for the optical lens. However, the present fixed focus lens has the characteristics on the basis of low cost.

Disclosure of Invention

The utility model provides a fixed focus lens and monitoring equipment, which can achieve the effects of small volume, long focal length, high resolution and day-night confocal under lower cost.

In a first aspect, an embodiment of the present utility model provides a fixed focus lens, including a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens, which are sequentially arranged from an object plane to an image plane along an optical axis;

the first lens is of negative focal power, the second lens is of positive focal power or negative focal power, the third lens is of positive focal power, the fourth lens is of positive focal power, the fifth lens is of negative focal power, and the sixth lens is of positive focal power;

the focal power of the first lens isThe focal power of the second lens is +.>The third lens has optical power of +>The focal power of the fourth lens is +.>The focal power of the fifth lens is +.>The focal power of the sixth lens is +.>The focal power of the fixed focus lens is +.>Wherein:

optionally, the first lens, the second lens, the third lens, the fifth lens and the sixth lens are plastic aspheric lenses, and the fourth lens is a glass spherical lens.

Optionally, a surface of the first lens facing the object plane is a convex surface, and a surface of the first lens facing the image plane is a concave surface;

the surface of one side of the second lens, facing the object plane, is a concave surface, and the surface of one side of the second lens, facing the image plane, is a convex surface;

the surface of one side of the third lens, facing the object plane, is a concave surface, and the surface of one side of the third lens, facing the image plane, is a convex surface;

the surface of the fourth lens facing the object plane is a convex surface, and the surface of the fourth lens facing the image plane is a convex surface.

Optionally, the abbe number of the fourth lens is Vd4, wherein Vd4 is more than or equal to 70 and less than or equal to 95.

Optionally, a distance from an optical axis center of an image side surface of the sixth lens to an image plane is BFL, and a distance from an optical axis center of an object side surface of the first lens to an optical axis center of an image side surface of the sixth lens is TL, wherein 0.3+.bfl/TL <0.42.

Optionally, the focal length of the fixed focus lens is f, and the distance from the center of the optical axis of the object side surface of the first lens to the image plane is TTL, where TTL/f is less than or equal to 3.2.

Optionally, a distance from an optical axis center of an object side surface of the first lens to an image plane is TTL, where TTL is less than 22.5mm.

Optionally, the field angle of the fixed focus lens is FOV, wherein FOV is more than or equal to 45.3 degrees and less than or equal to 50.3 degrees.

Optionally, the fixed focus lens further comprises a diaphragm, and the diaphragm is located in an optical path between the third lens and the fourth lens.

In a second aspect, an embodiment of the present utility model further provides a monitoring device, including a fixed focus lens as set forth in any one of the first aspects.

In the embodiment of the utility model, by adopting a structure that 1 glass spherical lens and 5 plastic aspherical lenses are mixed, and reasonably distributing the focal power, the surface number, the Abbe number and the like of each lens, the balance of the incidence angle of the front group lens and the rear group lens of the fixed focus lens can be ensured on the premise of low cost, the sensitivity of the lens is reduced, the fixed focus lens is ensured to have higher resolution, the imaging quality is improved, and the high-definition image quality requirement is met; meanwhile, the imaging capability of the lens under the low-light condition is ensured, and the consistency of the image quality under different conditions is realized. Therefore, the fixed-focus lens can realize the functions that the total optical length is smaller than 22.5mm, a SENSOR chip with a 1/2.7' inch target surface can be matched, the diagonal field angle reaches 45.3-50.3 degrees, the resolution ratio of 4K is 4K, the F number of F is 1.6+/-5%, the focal length is about 8mm, and day-night confocal is realized.

Drawings

Fig. 1 is a schematic structural diagram of a fixed focus lens according to a first embodiment of the present utility model;

FIG. 2 is a graph of the full frequency MTF of the visible band of the fixed focus lens of FIG. 1;

FIG. 3 is a graph of spherical aberration of the fixed focus lens of FIG. 1;

FIG. 4 is a graph of relative illuminance for the fixed focus lens of FIG. 1;

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

FIG. 6 is a graph of the full frequency MTF of the visible band for the fixed focus lens of FIG. 5;

FIG. 7 is a graph of spherical aberration of the fixed focus lens of FIG. 5;

FIG. 8 is a graph of relative illuminance for the fixed focus lens of FIG. 5;

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

FIG. 10 is a graph of the full frequency MTF of the visible band for the fixed focus lens of FIG. 9;

FIG. 11 is a graph of spherical aberration of the fixed focus lens of FIG. 9;

fig. 12 is a graph of relative illuminance for the fixed focus lens of fig. 9.

Detailed Description

The terminology used in the embodiments of the utility model is for the purpose of describing particular embodiments only and is not intended to be limiting of the utility model. It should be noted that, the terms "upper", "lower", "left", "right", and the like in the embodiments of the present utility model are described in terms of the angles shown in the drawings, and should not be construed as limiting the embodiments of the present utility model. In addition, in the context, it will also be understood that when an element is referred to as being formed "on" or "under" another element, it can be directly formed "on" or "under" the other element or be indirectly formed "on" or "under" the other element through intervening elements. The terms "first," "second," and the like, are used for descriptive purposes only and not for any order, quantity, or importance, but rather are used to distinguish between different components. The specific meaning of the above terms in the present utility model will be understood in specific cases by those of ordinary skill in the art.

The term "comprising" and variants thereof as used herein is intended to be open ended, i.e., including, but not limited to. The term "based on" is based at least in part on. The term "one embodiment" means "at least one embodiment".

It should be noted that the terms "first," "second," and the like herein are merely used for distinguishing between corresponding contents and not for defining a sequential or interdependent relationship.

It should be noted that references to "one", "a plurality" and "a plurality" in this disclosure are intended to be illustrative rather than limiting, and those skilled in the art will appreciate that "one or more" is intended to be construed as "one or more" unless the context clearly indicates otherwise.

Fig. 1 is a schematic structural diagram of a fixed focus lens according to a first embodiment of the present utility model, referring to fig. 1, the fixed focus lens includes a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, and a sixth lens 16 sequentially arranged from an object plane to an image plane along an optical axis;

the first lens 11 has negative focal power, the second lens 12 has positive or negative focal power, the third lens 13 has positive focal power, the fourth lens 14 has positive focal power, the fifth lens 15 has negative focal power, and the sixth lens 16 has positive focal power;

the first lens 11 has optical power ofThe second lens 12 has an optical power of +>The third lens 13 has the focal power ofThe fourth lens 14 has an optical power of +>The optical power of the fifth lens 15 is +.>The optical power of the sixth lens 16 is +.>The focal power of the fixed focus lens is +.>Wherein: />

First, for an optical lens, the optical power is equal to the difference between the image-side beam convergence and the object-side beam convergence, which characterizes the ability of the optical system to deflect light. The greater the absolute value of the optical power, the greater the ability to bend the light, the smaller the absolute value of the optical power, and the weaker the ability to bend the light. When the focal power is positive, the refraction of the light rays is convergent; when the optical power is negative, the refraction of the light is divergent. The optical power may be suitable for characterizing a refractive surface of a lens (i.e. a surface of a lens), for characterizing a lens, or for characterizing a system of lenses together (i.e. a lens group). In the fixed focus lens provided in this embodiment, each lens may be fixed in one lens barrel (not shown in fig. 1), as shown in fig. 1, the first lens 11 and the fifth lens 15 are both provided as negative power lenses, the second lens 12 is a positive power lens or a negative power lens, the third lens 13, the fourth lens 14 and the sixth lens 16 are both provided as positive power lenses, and the power ratio relationship between each lens and the entire system or between lenses is provided to satisfy a specific range condition, that is Can utilize the focal power of every lens to make them pass through every lensThe light rays are converged or diffused to different degrees in sequence, so that integral imaging is realized, and the purposes of reducing the volume, increasing the focal length, improving the resolution and improving the day and night confocal effect are achieved.

Optionally, the first lens 11, the second lens 12, the third lens 13, the fifth lens 15 and the sixth lens 16 are plastic aspherical lenses, and the fourth lens 14 is a glass spherical lens.

Wherein, the aspheric lens has the function of correcting the aberration such as field curvature, astigmatism, spherical aberration, coma and the like. The material of the plastic aspheric lens can be various plastics known to those skilled in the art, and the material of the glass spherical lens is various types of glass known to those skilled in the art, and the embodiments of the present utility model are not repeated and limited. Because the cost of the lens made of plastic is far lower than that of the lens made of glass, the fixed focus lens provided by the embodiment of the utility model can correct aberration, improve image quality and reduce preparation difficulty and material cost through the structure of mixing 1 glass sphere with 5 plastic aspherical lenses.

Optionally, as shown in fig. 1, a surface of the first lens 11 facing the object plane is a convex surface, and a surface of the first lens facing the image plane is a concave surface; the surface of the second lens 12 facing the object plane is concave, and the surface of the second lens facing the image plane is convex; the surface of the third lens 13 facing the object plane is concave, and the surface of the third lens facing the image plane is convex; the surface of the fourth lens 14 facing the object plane is convex, and the surface of the fourth lens facing the image plane is convex.

Referring to fig. 1, the first lens 11 is a meniscus negative lens with a convex front and concave back, and the first lens 11 is configured as the meniscus negative lens, which is beneficial to compressing the light aperture and balancing the off-axis aberration. For the second lens 12, the nature is a front concave back convex meniscus low-power lens, and the second lens 12 is arranged as the meniscus negative lens, which is favorable for enlarging the light height of the central chief ray at the diaphragm position and enlarging the aperture, thereby improving the imaging quality of the lens under the dim condition. For the third lens 13, the nature is a front concave back convex meniscus positive power lens, and the third lens 13 is set as a meniscus positive power lens, which is beneficial to balancing system aberration and improving imaging definition of the lens. For the fourth lens 14, the nature of the fourth lens is a biconvex positive lens, and the biconvex fourth lens 14 is beneficial to realizing the chromatic aberration on the axis of the correction system and realizing the day-night confocal function.

Optionally, the Abbe number of the fourth lens 14 is Vd4, wherein, vd4 is 70.ltoreq.Vd4.ltoreq.95.

Wherein the Abbe number is an index for representing the dispersion capability of the transparent medium, and the Abbe number is smaller as the medium dispersion is more serious; conversely, the more slightly the dispersion of the medium, the greater the Abbe number. Accordingly, in the embodiment of the present utility model, the abbe number of the fourth lens 14 is set to be greater than or equal to 70, which can improve the chromatic dispersion problem in the imaging process, and is favorable for correcting the chromatic aberration on the axis of the system, thereby realizing the day-night confocal function.

Optionally, the distance from the optical axis center of the image side surface of the sixth lens 16 to the image plane is BFL, and the distance from the optical axis center of the object side surface of the first lens 11 to the optical axis center of the image side surface of the sixth lens 16 is TL, wherein 0.3+.bfl/TL <0.42.

The distance from the optical axis center of the image side surface of the sixth lens element 16 to the image plane is BFL, which is the back focal length of the fixed-focus lens assembly, and the distance from the optical axis center of the object side surface of the first lens element 11 to the optical axis center of the image side surface of the sixth lens element 16 is TL, which is the total length of the lens assembly in the fixed-focus lens assembly. The total length of the back focus and the lens group of the fixed focus lens meets the condition that BFL/TL is less than or equal to 0.3 and less than or equal to 0.42, so that the fixed focus lens can obtain longer back focus on the basis of miniaturization, the imaging sensor and the flat optical filter are ensured to have enough installation space, the whole fixed focus lens can be ensured to have compact structure, the fixed focus lens has high integration level, and the fixed focus lens is convenient to install and practical and meets the miniaturization requirement.

Optionally, the focal length of the fixed focus lens is f, and the distance from the center of the optical axis of the object side surface of the first lens 11 to the image plane is TTL, where TTL/f is less than or equal to 3.2.

The distance from the center of the optical axis of the object side surface of the first lens 11 to the image plane is TTL, which is the total optical length of the fixed focus lens. The focal length f and the total optical length TTL of the fixed focus lens are set to be less than or equal to 3.2, so that the total lens length is compressed, the fixed focus lens has a larger target surface and a smaller volume, the fixed focus lens can be ensured to have better imaging quality, the picture is clearer, and meanwhile, the fixed focus lens has a smaller volume, and miniaturization is realized.

Optionally, the distance from the center of the optical axis of the object side surface of the first lens 11 to the image plane is TTL, where TTL < 22.5mm.

As described above, the distance from the optical axis center of the object side surface of the first lens 11 to the image plane is TTL, which is the total optical length of the fixed focus lens. The total length TTL of the fixed focus lens is smaller than 22.5mm, so that the whole fixed focus lens can be ensured to be compact in structure, the fixed focus lens has higher integration level, and the fixed focus lens can have smaller volume under the condition of the same image plane.

Optionally, the field angle of the fixed focus lens is FOV, wherein 45.3 ° or less FOV or less than 50.3 °. The fixed focus lens provided by the embodiment of the utility model is a long focus lens relatively, and the field angle of the fixed focus lens needs to meet the specific range requirement.

Optionally, the fixed focus lens further comprises a diaphragm 17, the diaphragm 17 being located in the optical path between the third lens 13 and the fourth lens 14.

The fixed focus lens provided by the embodiment of the utility model further comprises the diaphragm 17, and the propagation direction of the light beam can be adjusted by additionally arranging the diaphragm 17, so that the imaging quality is improved. The diaphragm 17 may be located in the optical path between the third lens 13 and the fourth lens 14, but the embodiment of the present utility model does not limit the specific arrangement position of the diaphragm 10, and by arranging the diaphragm 10 at an appropriate position, it is helpful to increase the relative illuminance and reduce CRA.

According to the fixed focus lens provided by the embodiment of the utility model, through adopting a structure that 1 glass spherical lens and 5 plastic aspherical lenses are mixed, and through reasonably distributing the focal power, the surface shape, the Abbe number and the like of each lens, on the premise of low cost, the balance of the incidence angle of the front and rear groups of lenses of the fixed focus lens can be ensured, the sensitivity of the lens is reduced, the fixed focus lens is ensured to have higher resolution, the imaging quality is improved, and the high-definition image quality requirement is met; meanwhile, the imaging capability of the lens under the low-light condition is ensured, and the consistency of the image quality under different conditions is realized. Therefore, the fixed-focus lens can realize the functions that the total optical length is smaller than 22.5mm, a SENSOR chip with a 1/2.7' inch target surface can be matched, the diagonal field angle reaches 45.3-50.3 degrees, the resolution ratio of 4K is 4K, the F number of F is 1.6+/-5%, the focal length is about 8mm, and day-night confocal is realized.

Based on the same conception, the embodiment of the utility model also provides monitoring equipment, which comprises any one of the fixed-focus lenses provided by the embodiment. In addition, since the monitoring device includes the fixed-focus lens in the above embodiment, the same or similar beneficial effects as those of the fixed-focus lens are provided, and the description thereof is omitted.

Based on the same conception, the utility model provides three different embodiments, wherein the focal power relation and the design range of the related physical optical parameters are shown in table 1:

table 1 design values of the power relationships and related physical optical parameters of each lens in three embodiments

Referring to fig. 1, in a first embodiment of the present utility model, the fixed focus lens includes a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, and a sixth lens 16, which are sequentially arranged from an object plane to an image plane along an optical axis;

The first lens 11, the second lens 12, the third lens 13, the fifth lens 15 and the sixth lens 16 are plastic aspherical lenses, and the fourth lens 14 is a glass spherical lens.

The surface of the first lens 11 facing the object plane is a convex surface, and the surface of the first lens facing the image plane is a concave surface; the surface of the second lens 12 facing the object plane is concave, and the surface of the second lens facing the image plane is convex; the surface of the third lens 13 facing the object plane is concave, and the surface of the third lens facing the image plane is convex; the surface of the fourth lens 14 facing the object plane is convex, and the surface of the fourth lens facing the image plane is convex.

With continued reference to fig. 1, further, in the first embodiment, the fifth lens 15 is a concave-convex negative lens, and the sixth lens 16 is a biconvex positive lens.

It should be noted that, in the first embodiment, abbe numbers of the lenses, ranges of mirror distances of the lenses, and the like are shown in table 1, and are not described herein.

In the first embodiment, by adopting a structure in which 1 glass spherical lens and 5 plastic aspherical lenses are mixed, and by reasonably distributing the optical power, the surface shape, the abbe number, etc. of each lens, the following design values can be realized: the angle of view is 50.3 °, f# is 1.61, the optical back focus BFL is 6.362mm, the total optical length TTL is 22.496mm, and the lens focal length F is 7.357mm.

The parameter design values of each lens in the fixed focus lens of the first embodiment shown in fig. 1 are shown in table 2:

table 2 a design value of each lens of the fixed focus lens in the first embodiment

The surface numbers in table 2 are numbered according to the surface order of the respective lenses, where "S1" represents the front surface of the first lens 11, "S2" represents the rear surface of the first lens 11, and so on; "STO" represents the stop 17 of the fixed focus lens; the radius of curvature represents the degree of curvature of the lens surface, a positive value represents the surface curved to the image plane side, a negative value represents the surface curved to the object plane side, wherein "PL" represents the surface as a plane and the radius of curvature is infinity; thickness represents the center axial distance from the current surface to the next surface, and the radius of curvature and thickness are in millimeters (mm). Refractive index represents the ability of the material between the current surface and the next surface to deflect light, space represents the current position as air, and refractive index is 1; the k value represents the magnitude of the best fit conic coefficient for the aspheric surface.

The aspherical cone coefficients can be defined by the following aspherical formula, but are not limited to the following representation:

wherein Z is the axial sagittal height of the aspheric surface in the Z direction; r is the height of the aspheric surface; c is the curvature of the fitting sphere, and the numerical value is the reciprocal of the curvature radius; k is a fitting cone coefficient; a-G are 4 th, 6 th, 8 th, 10 th, 12 th, 14 th, 16 th order polynomial coefficients of the aspherical polynomial.

The even term coefficients of the aspherical surfaces in the first embodiment are shown in table 3:

table 3 aspherical parameters

Wherein 5.729258E-05 represents a coefficient A of 5.7292583×10 with a surface number S1 ^-5 And so on.

Fig. 2 is a graph of full-frequency MTF of the visible light band of the fixed focus lens shown in fig. 1, in which the modulation transfer function (Modulation Transfer Function, MTF) is used to evaluate the imaging quality of an optical system in a more accurate, intuitive and common manner, and the higher and smoother the curve, the better the imaging quality of the system, the better the correction of various aberrations, and the clearer the imaging. The MTF is an important index and means for showing the resolution of the imaging system, and the higher the MTF value, the clearer the imaging, wherein, as shown in fig. 2, the abscissa Spatial Frequency in cycles per mm represents the spatial frequency in terms of cycles per mm, the ordinate Modulus of the OTF represents the OTF coefficient, and the MTF value of the fixed focus lens in the first embodiment at each position in the range of 22.75 ° of view angle is not lower than 0.5 at 120lp/mm, and the MTF value at the position of 25.13 ° of view angle is also above 0.45, which indicates that the fixed focus lens has good resolution, can realize high resolution imaging, and meets the required image quality requirement.

Fig. 3 is a spherical aberration diagram of the fixed focus lens shown in fig. 1, the vertical axis in fig. 3 being dimensionless, showing normalized entrance pupil radii, and the horizontal axis showing distances from the image sensor surface to focal points on the respective wavelength axes. As shown by the spherical aberration graph, the abscissa values of all wavelengths are within the range of +/-0.07 mm, which indicates that the axial chromatic aberration of the optical system is well corrected, and the fixed focus lens can also have day-night confocal function.

Fig. 4 is a graph of relative illuminance of the fixed focus lens shown in fig. 1, wherein the relative illuminance refers to a ratio of illuminance at different coordinate points of an image plane to illuminance at a center point, an ordinate represents a normalized illuminance value, and an abscissa represents a field angle of the lens. Under the same condition, the smooth transition of the relative illuminance curves of the fields of view represents that the illuminance in the projection picture is uniform, and the closer the relative illuminance value of the fields of view is to 1, the higher the final projection brightness is. As shown in fig. 4, the relative illuminance of the fixed focus lens of the first embodiment at each position within the 25.1 ° field angle range is above 0.45, which indicates that the fixed focus lens has high uniformity of illuminance on the image plane, and can also be inferred that the system has the characteristics of high efficiency and high brightness.

Fig. 5 is a schematic structural diagram of a fixed-focus lens according to a second embodiment of the present utility model, referring to fig. 5, in the second embodiment of the present utility model, the fixed-focus lens includes a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, and a sixth lens 16, which are sequentially arranged from an object plane to an image plane along an optical axis;

With continued reference to fig. 5, further in the second embodiment, the fifth lens 15 is a biconcave negative lens, and the sixth lens 16 is a biconvex positive lens.

It should be noted that, in the second embodiment, abbe numbers of the lenses, ranges of distances between the various mirrors, and the like are shown in table 1, and are not described herein.

In the second embodiment, by adopting a structure in which 1 glass spherical lens and 5 plastic aspherical lenses are mixed, and by reasonably distributing the optical power, the surface shape, the abbe number, and the like of each lens, the following design values can be realized: the angle of view is 45.3 °, f# is 1.6, the optical back focus BFL is 6.621mm, the total optical length TTL is 22.495mm, and the lens focal length F is 8.515mm.

The parameter design values of each lens in the fixed-focus lens of the second embodiment shown in fig. 5 are shown in table 4:

table 4 design values of lenses of the fixed-focus lens in the second embodiment

The surface numbers in table 4 are numbered according to the surface order of the respective lenses, where "S1" represents the front surface of the first lens 11, "S2" represents the rear surface of the first lens 11, and so on; "STO" represents the stop 17 of the fixed focus lens; the radius of curvature represents the degree of curvature of the lens surface, a positive value represents the surface curved to the image plane side, a negative value represents the surface curved to the object plane side, wherein "PL" represents the surface as a plane and the radius of curvature is infinity; thickness represents the center axial distance from the current surface to the next surface, and the radius of curvature and thickness are in millimeters (mm). Refractive index represents the ability of the material between the current surface and the next surface to deflect light, space represents the current position as air, and refractive index is 1; the k value represents the magnitude of the best fit conic coefficient for the aspheric surface.

The even term coefficients of the aspherical surfaces in the second embodiment are shown in table 5:

table 5 aspherical parameters

Wherein, -2.109233E-03 shows that the coefficient A with the surface number S1 is-2.109233 x 10 ^-3 And so on.

Fig. 6 is a full-frequency MTF chart of the visible light band of the fixed focus lens shown in fig. 5, and as shown in fig. 6, the fixed focus lens of the second embodiment has MTF values of about 0.5 and above at each position in the 22.63 ° field angle range at 120lp/mm, which indicates that the fixed focus lens has good resolution, can realize high resolution imaging, and meets the required image quality requirement.

Fig. 7 is a spherical aberration diagram of the fixed focus lens shown in fig. 5, and it can be seen from the spherical aberration diagram that the abscissa values of all wavelengths are within ±0.06mm, which indicates that the axial chromatic aberration of the optical system is well corrected, and also indicates that the fixed focus lens has a day-night confocal function.

Fig. 8 is a graph of relative illuminance of the fixed focus lens shown in fig. 5, and as shown in fig. 8, the relative illuminance of the fixed focus lens of the second embodiment at each position in the 22.63 ° field angle range is above 0.55, which indicates that the fixed focus lens has high uniformity of illuminance on the image plane, and can also be inferred that the system has the characteristics of high efficiency and high brightness.

Fig. 9 is a schematic structural view of a fixed focus lens according to a third embodiment of the present utility model, referring to fig. 9, in the third embodiment of the present utility model, the fixed focus lens includes a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, and a sixth lens 16 sequentially arranged from an object plane to an image plane along an optical axis;

the first lens 11Optical power isThe second lens 12 has an optical power of +>The third lens 13 has the focal power ofThe fourth lens 14 has an optical power of +>The optical power of the fifth lens 15 is +.>The optical power of the sixth lens 16 is +.>The focal power of the fixed focus lens is +.>Wherein: />

With continued reference to fig. 9, further, in the third embodiment, the fifth lens 15 is a concave-front convex-back negative lens, and the sixth lens 16 is a biconvex positive lens.

It should be noted that, in the third embodiment, abbe numbers of the lenses, ranges of mirror distances of the lenses, and the like are shown in table 1, and are not described herein.

In the third embodiment, by adopting a structure in which 1 glass spherical lens and 5 plastic aspherical lenses are mixed, and by reasonably distributing the optical power, the surface shape, the abbe number, and the like of each lens, the following design values can be realized: the angle of view is 48 °, f# is 1.6, the optical back focus BFL is 6.259mm, the total optical length TTL is 22.491mm, and the lens focal length F is 7.957mm.

The parameter design values of each lens in the fixed focus lens of the third embodiment shown in fig. 9 are shown in table 6:

table 6 design values of lenses of the fixed-focus lens in the third embodiment

The surface numbers in table 6 are numbered according to the surface order of the respective lenses, where "S1" represents the front surface of the first lens 11, "S2" represents the rear surface of the first lens 11, and so on; "STO" represents the stop 17 of the fixed focus lens; the radius of curvature represents the degree of curvature of the lens surface, a positive value represents the surface curved to the image plane side, a negative value represents the surface curved to the object plane side, wherein "PL" represents the surface as a plane and the radius of curvature is infinity; thickness represents the center axial distance from the current surface to the next surface, and the radius of curvature and thickness are in millimeters (mm). Refractive index represents the ability of the material between the current surface and the next surface to deflect light, space represents the current position as air, and refractive index is 1; the k value represents the magnitude of the best fit conic coefficient for the aspheric surface.

The even term coefficients of the aspherical surfaces in the third embodiment are shown in table 7:

table 7 aspherical parameters

Wherein, -2.458330E-03 represents that the coefficient A with the surface number S1 is-2.458330 x 10 ^-3 And so on.

Fig. 10 is a full-frequency MTF chart of the visible light band of the fixed focus lens shown in fig. 9, and as shown in fig. 10, the fixed focus lens of the third embodiment has MTF values above 0.45 at each position in the 24.01 ° field angle range at 120lp/mm, which indicates that the fixed focus lens has good resolution, can realize high resolution imaging, and meets the required image quality requirement.

Fig. 11 is a spherical aberration diagram of the fixed focus lens shown in fig. 9, and it is clear from the spherical aberration diagram that the abscissa values of all wavelengths are within the range of ±0.065mm, which indicates that the axial chromatic aberration of the optical system is well corrected, and also that the fixed focus lens has a day-night confocal function.

Fig. 12 is a graph of relative illuminance of the fixed focus lens shown in fig. 9, and as shown in fig. 12, the fixed focus lens of the third embodiment has relative illuminance at each position within the 24.01 ° field angle range of 0.42 or more, which indicates that the fixed focus lens has high uniformity of illuminance on the image plane, and can also be inferred that the system has the characteristics of high efficiency and high brightness.

Note that the above is only a preferred embodiment of the present utility model and the technical principle applied. It will be understood by those skilled in the art that the present utility model is not limited to the particular embodiments described herein, and that various obvious changes, rearrangements, combinations, and substitutions can be made by those skilled in the art without departing from the scope of the utility model. Therefore, while the utility model has been described in connection with the above embodiments, the utility model is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the utility model, which is set forth in the following claims.

Claims

1. The fixed focus lens is characterized by comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens which are sequentially arranged from an object plane to an image plane along an optical axis;

the focal power of the first lens is phi 1, the focal power of the second lens is phi 2, the focal power of the third lens is phi 3, the focal power of the fourth lens is phi 4, the focal power of the fifth lens is phi 5, the focal power of the sixth lens is phi 6, and the focal power of the fixed lens is phi, wherein:

-0.48≤φ1/φ≤-0.23；

0.15≤|φ2/φ|≤0.4；

0.1≤φ3/φ≤0.5；

0.65≤φ4/φ≤1.3；

1≤|φ5/φ6|≤1.8。

2. the fixed focus lens of claim 1, wherein the first lens, the second lens, the third lens, the fifth lens, and the sixth lens are plastic aspherical lenses, and the fourth lens is a glass spherical lens.

3. The fixed focus lens of claim 1, wherein,

the surface of one side of the first lens, facing the object plane, is a convex surface, and the surface of one side of the first lens, facing the image plane, is a concave surface;

4. The fixed focus lens of claim 1, wherein the fourth lens has an abbe number Vd4, wherein Vd4 is 70-95.

5. The fixed focus lens of claim 1, wherein a distance from an optical axis center of an image side surface of the sixth lens to an image plane is BFL, and a distance from an optical axis center of an object side surface of the first lens to an optical axis center of an image side surface of the sixth lens is TL, wherein 0.3+_bfl/TL <0.42.

6. The fixed focus lens of claim 1, wherein a focal length of the fixed focus lens is f, and a distance from an optical axis center of an object side surface of the first lens to an image plane is TTL, wherein TTL/f is less than or equal to 3.2.

7. The fixed focus lens of claim 1, wherein a distance from an optical axis center of an object side surface of the first lens to an image plane is TTL, wherein TTL < 22.5mm.

8. The fixed focus lens of claim 1, wherein the field angle of the fixed focus lens is FOV, wherein 45.3 ° or less FOV or less than 50.3 °.

9. The fixed focus lens of claim 1, further comprising a stop in an optical path between the third lens and the fourth lens.

10. A monitoring device comprising a fixed focus lens as claimed in any one of claims 1 to 9.