CN209842201U - Fixed focus lens - Google Patents

Abstract

The embodiment of the utility model provides a fixed focus lens, including first lens, second lens, third lens, fourth lens, fifth lens and the sixth lens that arrange in proper order along object plane directional image plane direction; the first lens, the second lens, the fifth lens and the sixth lens are plastic aspheric lenses, and the third lens and/or the fourth lens are glass aspheric lenses. An embodiment of the utility model provides a tight shot to realize providing a big light ring, small, with low costs tight shot.

Description

Fixed focus lens

Technical Field

The embodiment of the utility model provides a relate to the camera lens technique, especially relate to a tight shot.

Background

The large-aperture lens has larger light transmission amount than a common lens, has higher image brightness than the common lens in the same environment, and can also present a better effect in a dark environment, so the large-aperture lens is popular in the security monitoring industry. Nowadays, the security industry is fully high-definition and miniaturized, so that higher requirements are put forward on the resolution and the volume of a large-aperture lens.

However, the large aperture brings more difficult-to-correct aberration, so that the large aperture lens designed and manufactured by using the traditional all-glass spherical structure generally has low resolution or large volume, and thus has the problems of large volume and high cost.

SUMMERY OF THE UTILITY MODEL

An embodiment of the utility model provides a tight shot to realize providing a big light ring, small, with low costs tight shot.

The embodiment of the utility model provides a fixed focus lens, including first lens, second lens, third lens, fourth lens, fifth lens and the sixth lens that arrange in proper order along object plane directional image plane direction;

the first lens, the second lens, the fifth lens and the sixth lens are plastic aspheric lenses, and the third lens and/or the fourth lens are glass aspheric lenses.

Optionally, the third lens is a glass aspheric lens, and the fourth lens is a plastic aspheric lens;

or, the third lens is a plastic aspheric lens, and the fourth lens is a glass aspheric lens.

Optionally, the third lens and the fourth lens have positive optical power.

Optionally, the first lens and the fifth lens have negative focal power; the second lens and the sixth lens have positive optical power.

Optionally, the surface of the lens adjacent to the object plane is a front surface, and the surface of the lens adjacent to the image plane is a rear surface;

the front surface of the first lens is convex towards the image plane, or the front surface of the first lens is convex towards the object plane, or the front surface of the first lens is a plane; the rear surface of the first lens is convex towards the object plane;

the front surface and the rear surface of the second lens are convex towards the image surface;

the front surface of the third lens is convex towards the object plane, and the rear surface of the third lens is convex towards the image plane; or the front surface of the third lens is a plane, and the rear surface of the third lens is convex towards the image plane; or the front surface and the rear surface of the third lens are convex towards the object plane;

the front surface of the fourth lens is convex towards the object plane, and the rear surface of the fourth lens is convex towards the image plane; or the front surface of the fourth lens is a plane, and the rear surface of the fourth lens is convex towards the image plane; or the front surface and the rear surface of the fourth lens are convex towards the object plane;

the front surface of the fifth lens is convex towards the image plane, or the front surface of the fifth lens is convex towards the object plane, or the front surface of the fifth lens is a plane; the rear surface of the fifth lens is convex towards the object plane;

the front surface of the sixth lens is convex towards the object plane, and the rear surface of the sixth lens is convex towards the image plane; or the front surface of the sixth lens is a plane, and the rear surface of the sixth lens is convex towards the image plane; or, the front surface and the rear surface of the sixth lens are both convex towards the object plane.

Optionally, a focal length of the third lens is f3, a focal length of the fourth lens is f4, a focal length of the fifth lens is f5, a focal length of the sixth lens is f6, and a focal length of the prime lens is f, so that:

1.4＜|f3/f|＜6.6；0.7＜|f4/f|＜3.8；0.6＜|f5/f|＜4；1.9＜|f6/f|＜9.5。

optionally, the focal length of the third lens is f3, the focal length of the fourth lens is f4, and the focal length of the fifth lens is f5, so that:

0.7＜|f3/f5|＜3.9；0.5＜|f4/f5|＜2。

optionally, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens satisfy:

	focal length (mm)	Refractive index
			First lens	-16.5～-3.5	1.43～1.66
Second lens	15～200	1.43～1.72
			Third lens	4.9～23.5	1.43～2.11
Fourth lens	2.5～15.6	1.43～2.11
			Fifth lens element	-13.8～-3.1	1.43～1.66
Sixth lens element	7.2～-32.5	1.45～1.72

Optionally, the optical module further comprises a diaphragm, and the diaphragm is located between the second lens and the third lens.

Optionally, an f-number of the fixed focus lens is less than or equal to 1.0.

The embodiment of the utility model provides an in, adopt 6 lenses, the quantity of lens is less, under the condition that satisfies the imaging quality requirement, has reduced the volume and the cost of tight shot. The plastic aspheric lens has smaller mass and lower cost, so most lenses in the embodiment of the present invention are configured as plastic aspheric lenses (at least 4 lenses out of 6 lenses are plastic aspheric lenses). Simultaneously, in order to realize the confocal high low temperature, the embodiment of the utility model provides a set up third lens and/or fourth lens for glass aspheric lens in the intermediate position of tight shot, and glass aspheric lens has bigger refracting index for plastics aspheric lens, consequently uses the volume that glass aspheric lens can reduce tight shot. Furthermore, compared with a plastic aspheric lens, the glass aspheric lens has the advantages of good aberration eliminating capability and small temperature deformation. Consider glass aspherical lens's cost simultaneously and be higher than plastics aspherical lens, consequently the embodiment of the utility model provides an in, set up most lens into plastics aspherical lens, set up third lens and/or fourth lens into glass aspherical lens to the realization provides a big light ring, small, with low costs tight shot.

Drawings

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

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.

Fig. 1 is a schematic structural diagram of a fixed focus lens provided in an embodiment of the present invention, referring to fig. 1, the fixed focus lens includes a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5 and a sixth lens 6, which are sequentially arranged along an object plane OB pointing to an image plane IM direction. The first lens 1, the second lens 2, the fifth lens 5 and the sixth lens 6 are plastic aspherical lenses, and the third lens 3 and/or the fourth lens 4 are glass aspherical lenses. That is, the third lens 3 is a glass aspherical lens, and the fourth lens 4 is a glass aspherical lens, or both the third lens 3 and the fourth lens 4 are glass aspherical lenses. Two surfaces of the plastic aspheric lens are aspheric surfaces, and two surfaces of the glass aspheric lens are aspheric surfaces.

The embodiment of the utility model provides an in, adopt 6 lenses, the quantity of lens is less, under the condition that satisfies the imaging quality requirement, has reduced the volume and the cost of tight shot. The plastic aspheric lens has smaller mass and lower cost, so most lenses in the embodiment of the present invention are configured as plastic aspheric lenses (at least 4 lenses out of 6 lenses are plastic aspheric lenses). Simultaneously, in order to realize the confocal high low temperature, the embodiment of the utility model provides a set up third lens and/or fourth lens for glass aspheric lens in the intermediate position of tight shot, and glass aspheric lens has bigger refracting index for plastics aspheric lens, consequently uses the volume that glass aspheric lens can reduce tight shot. Furthermore, compared with a plastic aspheric lens, the glass aspheric lens has the advantages of good aberration eliminating capability and small temperature deformation. Consider glass aspherical lens's cost simultaneously and be higher than plastics aspherical lens, consequently the embodiment of the utility model provides an in, set up most lens into plastics aspherical lens, set up third lens and/or fourth lens into glass aspherical lens to the realization provides a big light ring, small, with low costs tight shot. It should be noted that "glass" and "plastic" are known materials, and the embodiment of the present invention is to apply materials known in the prior art to products having shapes and structures, and is not an improvement on the materials, but an improvement on the focusing ability and the positional relationship of each lens in a fixed focus lens, which belongs to an improvement on the structure of the fixed focus lens.

Alternatively, referring to fig. 1, the third lens 3 is a glass aspherical lens, and the fourth lens 4 is a plastic aspherical lens. The embodiment of the utility model provides an in, be glass aspherical lens through setting up third lens 3, fourth lens 4 is plastics aspherical lens, includes a glass aspherical lens and five plastics aspherical lens in the tight shot, and plastics aspherical lens has less weight and lower cost for glass aspherical lens to reduced the tight shot volume, reduced the cost of tight shot. In other embodiments, the third lens 3 may be a glass aspheric lens, and the fourth lens 4 may be a plastic spherical lens or a glass spherical lens, which is not limited in the embodiments of the present invention.

Alternatively, referring to fig. 1, the third lens 3 is a plastic aspherical lens, and the fourth lens 4 is a glass aspherical lens. The embodiment of the utility model provides an in, be plastics aspherical lens through setting up third lens 3, fourth lens 4 is glass aspherical lens, includes a glass aspherical lens and five plastics aspherical lens in the tight shot, and plastics aspherical lens has less weight and lower cost for glass aspherical lens to reduced the tight shot volume, reduced the cost of tight shot. In other embodiments, the third lens 3 may be a plastic spherical lens or a glass spherical lens, and the fourth lens 4 may be a glass aspheric lens, which is not limited in the embodiments of the present invention.

Alternatively, referring to fig. 1, the third lens 3 and the fourth lens 4 have positive optical power. Wherein the focal power is equal to the difference between the image-side and object-side convergence, which characterizes the ability of the optical system to deflect light rays. 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. Since the plastic aspherical lens is deformed with a change in temperature, which causes a focal length shift, in general, the sum of the total power of the positive lens and the total power of the negative lens in the plastic aspherical lens is less than 0. The embodiment of the utility model provides an in have positive focal power through setting up third lens 3 and fourth lens 4, third lens 3 and/or fourth lens 4 are glass aspheric lens, and glass aspheric lens takes place deformation less along with the change of temperature, has compensated the focus skew that plastics aspheric lens took place along with the temperature, has guaranteed that the high low temperature of tight shot is confocal.

Alternatively, referring to fig. 1, the first lens 1, the fifth lens 5 have negative power, and the second lens 2 and the sixth lens 6 have positive power. The first lens 1, the second lens 2, the fifth lens 5 and the sixth lens 6 are plastic aspheric lenses, 2 negative lenses and 2 positive lenses are arranged in the 4 plastic aspheric lenses, and the sum of the total focal power of the positive lenses and the total focal power of the negative lenses in the plastic aspheric lenses is less than 0, so that the fixed-focus lens has good aberration elimination capability and high-low temperature confocal compensation capability. It will be appreciated that the arrangement and combination of lenses of different powers in an optical design constitute different types of lenses. The embodiment of the utility model provides an in focal power of lens be the focus of lens promptly, the embodiment of the utility model provides an in focal power combination of lens be applicable to the tight shot.

Alternatively, referring to fig. 1, the surface of the lens on the side adjacent to the object plane OB is a front surface, and the surface of the lens on the side adjacent to the image plane IM is a rear surface. The front surface of the first lens 1 protrudes towards the image plane IM, or the front surface of the first lens 1 protrudes towards the object plane OB, or the front surface of the first lens 1 is a plane; the rear surface of the first lens 1 is convex toward the object plane OB. That is, the first lens 1 may be one of a biconcave lens, a plano-concave lens, or a convex-concave lens. The front surface and the rear surface of the second lens 2 are both convex toward the image plane IM. That is, the second lens 2 may be a meniscus lens. The front surface of the third lens 3 is convex towards the object plane OB, and the rear surface of the third lens 3 is convex towards the image plane IM; or the front surface of the third lens 3 is a plane, and the rear surface of the third lens 3 is convex toward the image plane IM; alternatively, both the front surface and the rear surface of the third lens 3 are convex toward the object plane OB. That is, the third lens 3 may be one of a biconvex lens, a plano-convex lens, or a convex-concave lens. The front surface of the fourth lens 4 is convex towards the object plane OB, and the rear surface of the fourth lens 4 is convex towards the image plane IM; or the front surface of the fourth lens 4 is a plane, and the rear surface of the fourth lens 4 is convex toward the image plane IM; alternatively, both the front surface and the rear surface of the fourth lens 4 are convex toward the object plane OB. That is, the fourth lens 4 may be one of a biconvex lens, a plano-convex lens, or a convex-concave lens. The front surface of the fifth lens 5 is convex towards the image plane IM, or the front surface of the fifth lens 5 is convex towards the object plane OB, or the front surface of the fifth lens 5 is a plane; the rear surface of the fifth lens 5 is convex toward the object plane OB. That is, the fifth lens 5 may be one of a biconcave lens, a plano-concave lens, or a convex-concave lens. The front surface of the sixth lens 6 is convex toward the object plane OB, and the rear surface of the sixth lens 6 is convex toward the image plane IM; or the front surface of the sixth lens 6 is a plane, and the rear surface of the sixth lens 6 is convex toward the image plane IM; alternatively, both the front surface and the rear surface of the sixth lens 6 are convex toward the object plane OB. That is, the sixth lens 6 may be one of a biconvex lens, a plano-convex lens, or a convex-concave lens.

Alternatively, referring to fig. 1, the focal length of the third lens 3 is f3, the focal length of the fourth lens 4 is f4, the focal length of the fifth lens 5 is f5, the focal length of the sixth lens 6 is f6, and the focal length of the prime lens is f, which satisfies:

1.4＜∣f3/f∣＜6.6；0.7＜∣f4/f∣＜3.8；0.6＜∣f5/f∣＜4；1.9＜∣f6/f∣＜9.5。

it can be understood that in the optical design, the focal length of the lens is determined by the structures of the front and rear surfaces of the lens, and the focal length of the lens reflects the overall situation of the combination of the front and rear surfaces of the lens, which is a structural parameter of the lens. In the embodiment of the present invention, 1.4 < | f3/f | < 6.6 is set; 0.7 < | f4/f | < 3.8; 0.6 < | f5/f | < 4; 1.9 < | f6/f | < 9.5, the absolute value of the ratio of the focal length of the third lens 3, the fourth lens 4, the fifth lens 5 and the sixth lens 6 to the fixed-focus lens is limited, the absolute value of the focal length of the third lens 3, the fourth lens 4, the fifth lens 5 and the sixth lens 6 is controlled in a certain range, and the miniaturization of the fixed-focus lens is ensured.

Alternatively, referring to fig. 1, the focal length of the third lens 3 is f3, the focal length of the fourth lens 4 is f4, and the focal length of the fifth lens 5 is f5, which satisfy: 0.7 < | f3/f5 | < 3.9; 0.5 < | f4/f5 | 2. In the embodiment of the utility model, 0.7 < | f3/f5 | 3.9 is set; 0.5 < | f4/f5 | 2, which ensures the prime lens to have good confocal performance of high and low temperature.

Alternatively, referring to fig. 1, the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, and the sixth lens 6 satisfy:

	focal length (mm)	Refractive index
			First lens	-16.5～-3.5	1.43～1.66
Second lens	15～200	1.43～1.72
			Third lens	4.9～23.5	1.43～2.11
Fourth lens	2.5～15.6	1.43～2.11
			Fifth lens element	-13.8～-3.1	1.43～1.66
Sixth lens element	7.2～-32.5	1.45～1.72

That is, the focal length of the first lens 1 is-16.5 mm to-3.5 mm (i.e. the focal length of the first lens 1 is greater than or equal to-16.5 mm and less than or equal to-3.5 mm), and the refractive index of the first lens 1 is 1.43 to 1.66. The focal length of the second lens 2 is 15 mm-200 mm, and the refractive index of the second lens 2 is 1.43-1.72. The focal length of the third lens 3 is 4.9 mm-23.5 mm, and the refractive index of the third lens 3 is 1.43-2.11. The focal length of the fourth lens 4 is 2.5 mm-15.6 mm, and the refractive index of the fourth lens 4 is 1.43-2.11. The focal length of the fifth lens 5 is-13.8 mm to-3.1 mm, and the refractive index of the fifth lens 5 is 1.43 to 1.66. The focal length of the sixth lens 6 is 7.2mm to-32.5 mm, and the refractive index of the sixth lens 6 is 1.45-1.72.

Optionally, referring to fig. 1, the fixed focus lens further includes a diaphragm 7, and the diaphragm 7 is located between the second lens 2 and the third lens 3. The diaphragm 7 is an entity that plays a role in limiting a light beam in an optical system. The diaphragm 7 may be a screen, for example. Diaphragm 7 has certain influence to the size of formation of image visual field to and the aberration, the embodiment of the utility model provides an in, set up diaphragm 7 between second lens 2 and third lens 3 to set up third lens and/or fourth lens into the condition of glass aspheric lens in the adaptation tight shot, eliminate the aberration, in order to improve like quality.

Alternatively, referring to fig. 1, the f-number of the fixed-focus lens is less than or equal to 1.0. The F-number, also called the aperture value, or F-number, is the ratio of the focal length of the lens to the clear diameter of the lens. The larger the numerical value of the diaphragm number is, the smaller the diaphragm is, and the smaller the light flux amount is; the smaller the numerical value of the diaphragm number, the larger the diaphragm and the larger the amount of light transmitted. The embodiment of the utility model provides a tight shot's diaphragm number is less than or equal to 1.0, has great light ring, is favorable to providing the light flux of tight shot.

TABLE 1 design values for lenses in fixed-focus lens

Serial number	Surface type	Radius of curvature (mm)	Thickness (mm)	Refractive index	Value of K
						1	Aspherical surface	-59.2	1.0	1.54	55.5
2	Aspherical surface	4.37	2.37		-0.1
						3	Aspherical surface	-10.58	3.26	1.66	3.98
4	Aspherical surface	-8.75	2.35		-5.1
						Diaphragm	Plane surface
5	Aspherical surface	294.31	4.03	1.54	-36.4
						6	Aspherical surface	-5.92	0.08		-0.25
7	Aspherical surface	5.96	2.61	1.62	-3.2
						8	Aspherical surface	-11.22	0.15		3.8
9	Aspherical surface	5.25	0.8	1.66	-11.8
						10	Aspherical surface	26.45	0.65		-80.9
11	Aspherical surface	-51.21	1.61	1.54	54.1
						12	Aspherical surface	-7.45			-10.6

Table 1 shows a design value of a lens in a fixed focus lens, and the specific value can be adjusted according to the product requirement, which is not a limitation of the embodiment of the present invention. The fixed focus lens shown in table 1 may be that shown in fig. 1. A lens generally comprises two surfaces, each of which is a refractive surface. The numbers in table 1 are numbered according to the surface of each lens. Here, the number "1" indicates the front surface of the first lens 1, the number "2" indicates the rear surface of the first lens 1, and so on, which is not described herein again. Note that "aperture" in the column of "serial number" represents an aperture. In the column of "radius of curvature", a positive value of radius of curvature means that the center of curvature is on the side of the surface closer to the image plane IM, and a negative value of radius of curvature means that the center of curvature is on the side of the surface farther from the image plane IM. The numerical value in the column of "thickness" indicates the on-axis distance from the current surface to the next surface. The column "refractive index" indicates the refractive index of the medium between the current surface to the next surface. The spaces in the column "refractive index" are the refractive index of air. The column "k value" shows the numerical magnitude of the conic coefficient of the best fit cone for the aspheric surface.

Optionally, the surface of the aspheric lens satisfies the formula:

wherein Z is the axial rise of the surface in the Z direction, the radial distance on the diagonal line of r, k is the conic coefficient of the best fitting cone, C is the curvature of the best fitting sphere, C is the reciprocal of the curvature radius, and A, B, C, D, E, F, G and H are aspheric coefficients.

TABLE 2 design values of aspheric coefficients of lenses in fixed-focus lens

Serial number	A	B	C	D	E	F	G	H
									1	0	5.258E-004	-9.111E- 007	-9.291E- 007	1.271E-007	-9.173E- 009	0	0
2	0	2.313E-004	1.251E-005	-5.571E- 007	8.294E-009	2.524E-010	0	0
									3	0	-5.113E- 005	-2.211E- 005	-6.531E- 007	7.634E-009	8.954E-009	0	0
4	0	-9.121E- 005	-2.842E- 005	2.481E-007	1.474E-007	-2.238E- 009	0	0
									5	0	6.641E-004	2.231E-006	-3.534E- 007	-2.114E- 007	-3.274E- 008	0	0
6	0	5.524E-004	1.241E-005	6.617E-008	-2.604E- 008	-8.126E- 009	0	0
									7	0	-5.431E- 004	1.131E-005	7.564E-007	2.291E-008	-2.514E- 009	0	0
8	0	-7.534E- 004	3.381E-005	-1.717E- 007	3.291E-008	-5.134E- 009	0	0
									9	0	3.4131E- 003	-3.131E- 004	8.164E-006	1.531E-008	-6.264E- 009	0	0
10	0	9.634E-003	-6.311E- 004	2.735E-006	2.451E-006	-1.136E- 008	0	0
									11	0	1.471E-004	1.837E-004	-2.564E- 005	3.251E-006	-2.613E- 008	0	0
12	0	-3.036E- 003	6.331E-004	-8.017E- 005	9.211E-006	-7.332E- 008	0	0

Table 2 is a design value of the aspheric coefficient of lens in the fixed focus lens, and its specific value can be adjusted according to the product requirement, and is not right the embodiment of the utility model provides a restriction. The fixed focus lens shown in table 2 may be that shown in fig. 1. The column of "number" in table 2 corresponds to the meaning of "number" in table 1, and for example, the number "1" also indicates the front surface of the first lens 1. "E" in various embodiments of the present invention represents an index with a base 10, for example, a value of 5.258E-004 is 0.0005258.

It should be noted that the foregoing is only a preferred embodiment of the present invention and the technical principles applied. 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 with reference to the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the scope of the present invention.

Claims (10)

1. A prime 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 along the direction of an object plane pointing to an image plane;

the first lens, the second lens, the fifth lens and the sixth lens are plastic aspheric lenses, and the third lens and/or the fourth lens are glass aspheric lenses.

2. The fixed focus lens as claimed in claim 1, wherein the third lens is a glass aspheric lens, and the fourth lens is a plastic aspheric lens;

or, the third lens is a plastic aspheric lens, and the fourth lens is a glass aspheric lens.

3. The prime lens according to claim 1, wherein the third lens and the fourth lens have positive optical power.

4. The prime lens according to claim 3, wherein the first lens and the fifth lens have negative optical power; the second lens and the sixth lens have positive optical power.

5. The prime lens according to claim 4, wherein the surface of the lens adjacent to the object plane is a front surface, and the surface of the lens adjacent to the image plane is a rear surface;

the front surface of the first lens is convex towards the image plane, or the front surface of the first lens is convex towards the object plane, or the front surface of the first lens is a plane; the rear surface of the first lens is convex towards the object plane;

the front surface and the rear surface of the second lens are convex towards the image surface;

the front surface of the third lens is convex towards the object plane, and the rear surface of the third lens is convex towards the image plane; or the front surface of the third lens is a plane, and the rear surface of the third lens is convex towards the image plane; or the front surface and the rear surface of the third lens are convex towards the object plane;

the front surface of the fourth lens is convex towards the object plane, and the rear surface of the fourth lens is convex towards the image plane; or the front surface of the fourth lens is a plane, and the rear surface of the fourth lens is convex towards the image plane; or the front surface and the rear surface of the fourth lens are convex towards the object plane;

the front surface of the fifth lens is convex towards the image plane, or the front surface of the fifth lens is convex towards the object plane, or the front surface of the fifth lens is a plane; the rear surface of the fifth lens is convex towards the object plane;

the front surface of the sixth lens is convex towards the object plane, and the rear surface of the sixth lens is convex towards the image plane; or the front surface of the sixth lens is a plane, and the rear surface of the sixth lens is convex towards the image plane; or, the front surface and the rear surface of the sixth lens are both convex towards the object plane.

6. The prime lens according to claim 1, wherein 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, and the focal length of the prime lens is f, so that:

1.4＜∣f3/f∣＜6.6；0.7＜∣f4/f∣＜3.8；0.6＜∣f5/f∣＜4；1.9＜∣f6/f∣＜9.5。

7. the prime lens according to claim 1, wherein the focal length of the third lens is f3, the focal length of the fourth lens is f4, and the focal length of the fifth lens is f5, so that:

0.7＜∣f3/f5∣＜3.9；0.5＜∣f4/f5∣＜2。

8. the prime lens according to claim 6, wherein the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens satisfy:

focal length (mm) Refractive index First lens -16.5～-3.5 1.43～1.66 Second lens 15～200 1.43～1.72 Third lens 4.9～23.5 1.43～2.11 Fourth lens 2.5～15.6 1.43～2.11 Fifth lens element -13.8～-3.1 1.43～1.66 Sixth lens element 7.2～-32.5 1.45～1.72

。

9. The prime lens according to claim 1, further comprising a diaphragm positioned between the second lens and the third lens.

10. The prime lens according to claim 1, wherein an f-number of the prime lens is less than or equal to 1.0.