A large aperture fixed focus lens

Abstract

The invention discloses a large aperture fixed focus lens, wherein the first lens group includes a first lens piece, a second lens piece, a third lens piece, a fourth lens piece and a fifth lens piece in order from the object side to the image side along the optical axis; the first lens piece has positive refractive power, and its object side curvature radius is R1, and its image side curvature radius is R2, wherein R1 and R2 are respectively greater than 0; the second lens piece has positive refractive power, and its object side curvature radius is R3, and its image side curvature radius is R4, and R3<R4; the third lens piece has negative refractive power, and is a plano-concave lens; the fourth lens piece has positive refractive power, and is a biconvex lens; the fifth lens piece has negative refractive power, and is a concave-convex lens. The large aperture fixed focus lens can not only realize a large aperture of 1.1, but also only needs 5 lens pieces to achieve good imaging quality, especially the imaging quality of the large aperture can be equal to or even exceed that of the existing fixed focus lenses on the market.

Description

Technical Field

[0001] The invention relates to the technical field of lens assemblies, and in particular to a large aperture fixed-focus lens. Background Art

[0002] Currently, most 50mm fixed-focus standard lenses use the multi-group lens combination method mentioned in optical design textbooks, and the aperture cannot be designed to be too large. This is because when there are more lens pieces, a smaller aperture design can improve the overall optical performance and imaging quality.

[0003] Currently, most fixed-focus standard lenses produced on the market have 8 to 15 lenses. Due to the large number of lenses used, the manufacturing cost of fixed-focus standard lenses remains high. For consumers in the market, their purchase expenses will also increase, which invisibly reduces consumers' purchasing intention.

[0004] But on the other hand, with the improvement of consumers' awareness and social progress, the majority of consumers are no longer satisfied with the conventional fixed-focus lenses in the existing market. Consumers need fixed-focus lenses with larger apertures and more affordable prices. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a low-cost large aperture fixed-focus lens.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a large aperture fixed focus lens, which includes a first lens group, a second lens group and a third lens group in sequence along the optical axis from the object side to the image side, the first lens group includes a first lens piece, a second lens piece and a third lens piece in sequence along the optical axis from the object side to the image side, the second lens group includes a fourth lens piece, and the third lens group includes a fifth lens piece;

[0007] The first lens has positive refractive power, and the radius of curvature of the object side surface is R1, and the radius of curvature of the image side surface is R2, wherein R1 and R2 are respectively greater than 0;

[0008] The second lens sheet has positive refractive power and is a positive meniscus lens, the object side curvature radius of which is R3, the image side curvature radius of which is R4, and R3<R4;

[0009] The third lens has negative refractive power and is a plano-concave lens, and the curvature radius of the image side surface is R6;

[0010] The fourth lens sheet has positive refractive power and is a biconvex lens, the object side curvature radius of which is R7, the image side curvature radius of which is R8, and R7=|R8|;

[0011] The fifth lens sheet has negative refractive power and is a meniscus lens, the object side curvature radius of which is R9, the image side curvature radius of which is R10, and |R9|<|R10|.

[0012] The beneficial effects of the present invention are as follows: Different from the arrangement of Crown Glass and Flint Glass in the existing fixed-focus lens in which the first and second lens pieces are Crown Glass, and the third, fourth and fifth lens pieces are Flint Glass, the structure is novel, breaking the inertial thinking in the industry, and this combination does not require glued pieces to improve the chromatic aberration of the lens, which not only facilitates the assembly of the lens but also reduces the manufacturing cost of the lens. More importantly, the present large-aperture fixed-focus lens can not only achieve a large aperture of 1.1, but also only requires 5 lens pieces to achieve good imaging quality, especially the imaging quality of the large aperture can be equal to or even exceed that of the existing fixed-focus lenses on the market. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a simplified schematic diagram of the structure of a large aperture fixed focus lens according to the first embodiment of the present invention;

[0014] Figure 2 This is a lateral chromatic aberration diagram of the large aperture fixed focus lens according to the first embodiment of the present invention (at aperture f1.4);

[0015] Figure 3 This is a graph showing the MTF test results of the large aperture fixed focus lens of the first embodiment of the present invention at the maximum aperture and the maximum field angle;

[0016] Figure 4 This is a graph showing the MTF test results of the central field angle of the large aperture fixed focus lens of Embodiment 1 of the present invention at the maximum aperture;

[0017] Figure 5 This is a graph showing the optical path difference of the central field of view of the large aperture fixed focus lens of the first embodiment of the present invention when the aperture is f1.1;

[0018] Figure 6 This is a graph showing the optical path difference of the central field of view of the large aperture fixed focus lens of the first embodiment of the present invention when the aperture is f1.4;

[0019] Figure 7 This is a graph of the optical path difference of the edge field of view of the large aperture fixed focus lens of the first embodiment of the present invention when the aperture is f1.1;

[0020] Figure 8 This is a graph of the optical path difference of the edge field of view of the large aperture fixed focus lens of the first embodiment of the present invention when the aperture is f1.4;

[0021] Fig. 9This is a point diagram of the focusing of the central field light when the large aperture fixed focus lens of the first embodiment of the present invention is at an aperture of f1.1;

[0022] Fig.10 This is a point diagram of the focusing of the central field light when the large aperture fixed focus lens of the first embodiment of the present invention is at an aperture of f1.4;

[0023] Fig.11 This is a point diagram of the focusing of the edge field light when the large aperture fixed focus lens of the first embodiment of the present invention is at an aperture of f1.1;

[0024] Fig.12 This is a point diagram of the focusing of the edge field light when the large aperture fixed focus lens of the first embodiment of the present invention is at an aperture of f1.4;

[0025] Fig.13 The field curvature and distortion diagram of the main light ray when the large aperture fixed focus lens of the first embodiment of the present invention is at the maximum aperture;

[0026] Fig.14 The central field of view fan-shaped diagram of the large aperture fixed focus lens of the first embodiment of the present invention when the aperture is f1.1;

[0027] Fig.15 The central field of view fan-shaped diagram of the large aperture fixed focus lens of the first embodiment of the present invention when the aperture is f1.4;

[0028] Fig.16 The fan-shaped diagram of the edge field of view of the large aperture fixed focus lens of the first embodiment of the present invention when the aperture is f1.1;

[0029] Fig.17 This is a fan-shaped diagram of the edge field of view of the large aperture fixed focus lens of Example 1 of the present invention when the aperture is f1.4.

[0030] Description of labels:

[0031] 1. The first lens sheet;

[0032] 2. A second lens sheet;

[0033] 3. The third lens piece;

[0034] 4. The fourth lens sheet;

[0035] 5. Fifth lens sheet;

[0036] 6. Aperture diaphragm;

[0037] 7. Optical axis. DETAILED DESCRIPTION

[0038] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in conjunction with the implementation modes and the accompanying drawings.

[0039] Embodiment 1

[0040] Please refer to Figures 1 to 17 , Embodiment 1 of the present invention is: a large-aperture fixed-focus lens, which can be used in electronic device components such as mobile phone camera modules, tablet computer camera modules, notebook computer camera modules, and camera camera modules, and can achieve a large aperture of f1.4 or even f1.1.

[0041] As Figure 1 shown, the large-aperture fixed-focus lens sequentially includes a first lens group, a second lens group, and a third lens group along the optical axis 7 from the object side to the image side. The first lens group sequentially includes a first lens element 1, a second lens element 2, and a third lens element 3 along the optical axis 7 from the object side to the image side. The second lens group includes a fourth lens element 4, and the third lens group includes a fifth lens element 5. Among them, an aperture stop 6 is provided between the third lens element 3 and the fourth lens element 4;

[0042] The first lens element 1 has a positive refractive power, the curvature radius of its object side is R1, and the curvature radius of its image side is R2, where R1 and R2 are both greater than 0;

[0043] The second lens element 2 has a positive refractive power, it is a positive meniscus lens, the curvature radius of its object side is R3, and the curvature radius of its image side is R4, R3 < R4;

[0044] The third lens element 3 has a negative refractive power, it is a plano-concave lens, and the curvature radius of its image side is R6;

[0045] The fourth lens element 4 has a positive refractive power, it is a biconvex lens, the curvature radius of its object side is R7, and the curvature radius of its image side is R8, R7 = |R8|;

[0046] The fifth lens element 5 has a negative refractive power, it is a concave-convex lens, the curvature radius of its object side is R9, and the curvature radius of its image side is R10, |R9| < |R10|.

[0047] Specifically, the diameter of the first lens element 1 is D1, the gap between the first lens element 1 and the second lens element 2 is t1, and D1 and t1 satisfy the conditional formula 220 ≤ D1 / t1 < 250. The diameter of the second lens element 2 is D2, the thickness of the second lens element 2 is T2, and D2 and T2 satisfy the conditional formula 4 < D2 / T2 < 5. The diameter of the third lens element 3 is D3, the thickness of the third lens element 3 is T3, and D3 and T3 satisfy the conditional formula 21 < D3 / T3 < 23. The diameter of the fifth lens element 5 is D5, the gap between the fifth lens element 5 and the image side is t5, and D5 and t5 satisfy the conditional formula 1 < D5 / t5 < 2.

[0048] The focal length fA of the first lens group satisfies the conditional expression: 120 < fA < 140. The focal length fB of the second lens group and the diameter D2 of the second lens 2 satisfy the conditional expression: 1 < D2 / fB < 3, and fA / fB > 5. The focal length fC of the third lens group satisfies the conditional expression: -50 < fC < -40.

[0049] Furthermore, the refractive index of the first lens 1 is the same as that of the second lens 2, and the refractive indices of any two of the second lens 2, the third lens 3, the fourth lens 4, and the fifth lens 5 are different from each other.

[0050] As a specific implementation mode

[0051] R1 = 32, R2 = 550, R3 = 23, R4 = 50, R6 = 17, R7 = 38, R8 = -38, R9 = -28, R10 = -150;

[0052] The focal length f1 of the first lens 1 is 51 mm, the refractive index N1 is 1.6, and the diameter D1 is 44 mm. The focal length f2 of the second lens 2 is 58 mm, the refractive index N2 is 1.6, and the diameter D2 is 34 mm. The focal length f3 of the third lens 3 is -20 mm, the refractive index N3 is 1.9, and the diameter D3 is 34 mm. The focal length f4 of the fourth lens 4 is 24 mm, the refractive index N4 is 1.8, and the diameter D4 is 24 mm. The focal length f5 of the fifth lens 5 is -48 mm, the refractive index N5 is 1.7, and the diameter D5 is 22 mm;

[0053] The focal length fA of the first lens group is 137 mm, the focal length fB of the second lens group is 24 mm, and the focal length fC of the third lens group is -48 mm;

[0054] The thickness T1 of the first lens 1 is 10.5 mm, the thickness T2 of the second lens 2 is 7.2 mm, the thickness T3 of the third lens 3 is 1.5 mm, the thickness T4 of the fourth lens 4 is 8.2 mm, and the thickness T5 of the fifth lens 5 is 1.4 mm; It should be noted that the thickness of the lens refers to the distance from the intersection point of the object side of a single lens and the optical axis 7 to the intersection point of its image side and the optical axis 7.

[0055] The gap t1 between the first lens piece 1 and the second lens piece 2 is 0.2mm, the gap t2 between the second lens piece 2 and the third lens piece 3 is 2.2mm, the gap t3 between the third lens piece 3 and the fourth lens piece 4 is 16.2mm, wherein the spacing t31 between the third lens piece 3 and the aperture stop 6 is 6.9mm, the spacing t32 between the fourth lens piece 4 and the aperture stop 6 is 9.3mm, the gap t4 between the fourth lens piece 4 and the fifth lens piece 5 is 3.9mm, and the gap t5 between the fifth lens piece 5 and the image side is 14mm. It is easy to understand that t1 is the distance from the intersection of the image side surface of the first lens piece 1 and the optical axis 7 to the intersection of the object side surface of the second lens piece 2 and the optical axis 7, t2 is the distance from the intersection of the image side surface of the second lens piece 2 and the optical axis 7 to the intersection of the object side surface of the third lens piece 3 and the optical axis 7, t3 is the distance from the intersection of the image side surface of the third lens piece 3 and the optical axis 7 to the intersection of the object side surface of the fourth lens piece 4 and the optical axis 7, t31 is the distance from the intersection of the image side surface of the third lens piece 3 and the optical axis 7 to the aperture stop 6, t32 is the distance from the intersection of the object side surface of the fourth lens piece 4 and the optical axis 7 to the aperture stop 6, t4 is the distance from the intersection of the image side surface of the fourth lens piece 4 and the optical axis 7 to the intersection of the object side surface of the fifth lens piece 5 and the optical axis 7, and t5 is the distance from the intersection of the image side surface of the fifth lens piece 5 and the optical axis 7 to the image side.

[0056] The first and second lens pieces of the large aperture fixed focus lens are Crown Glass, and the third, fourth, and fifth lens pieces are Flint Glass. The arrangement of the Crown Glass and the Flint Glass in the existing fixed focus lens in a cross arrangement is changed, so that the fixed focus lens does not need to use a cemented piece to improve the chromatic aberration. The lateral chromatic aberration diagram of the large aperture fixed focus lens of this embodiment at an aperture of f1.4 is shown in FIG. Figure 2 As shown, the lateral chromatic aberration data results of the large aperture fixed focus lens of this embodiment at the aperture of f1.4 are shown in Table 1.

[0057] Table 1 Lateral chromatic aberration data of large aperture fixed focus lens at aperture f1.4

[0058] Rel.Field Lateral Color 0 0.00E+00 0.05 -1.82E-01 0.1 -3.24E-01 0.15 -4.25E-01 0.2 -4.81E-01 0.25 -4.87E-01 0.3 -5.86E-01 0.35 -6.57E-01 0.4 -6.97E-01 0.45 -7.03E-01 0.5 -6.69E-01 0.55 -7.35E-01 0.6 -7.75E-01 0.65 -7.89E-01 0.7 -7.76E-01 0.75 -7.35E-01 0.8 -7.41E-01 0.85 -7.43E-01 0.9 -7.54E-01 0.95 -7.98E-01 1 -9.07E-01

[0059] It can be seen from Table 1 that when the aperture is f1.4 (a common large aperture lens specification on the market), the Lateral Color value of the large aperture fixed focus lens of this embodiment at 0.7F is -0.776um, which meets the industry specification.

[0060] In this embodiment, the intervals between the first lens sheet 1, the second lens sheet 2 and the third lens sheet 3 are small and the thickness of the fifth lens sheet 5 is also relatively thin, which effectively improves the problems of spherical aberration and astigmatism. Preferably, the side of the second lens sheet 2 close to the image side contacts the side of the third lens close to the object side.

[0061] When the aperture is f1.1, the Sider aberration simulation results of the large aperture fixed focus lens of this embodiment are shown in Table 2.

[0062] Table 2 Aberration simulation results of the large aperture fixed focus lens at f1.1

[0063]

[0064]

[0065] It can be seen from Table 2 that when the aperture is f1.1, the large aperture fixed focus lens of this embodiment can well balance the problems of field curvature (CURV), defocus (SPHA), coma (COMA), distortion, MTF, etc., and achieve the background blur effect.

[0066] When the aperture is f1.4, the Sider aberration simulation results of the large aperture fixed focus lens of this embodiment are shown in Table 3.

[0067] Table 3 Simulation results of the aberration of the large aperture fixed focus lens at f1.4

[0068] Surf SPHA S1 COMA S2 ASTI S3 FCUR S4 DIST S5 CLA(CL) CTR(CT) 1 0 0 0 0 0 0 0 2 0.467147 -0.116454 0.029031 0.25919 -0.07185 -0.060744 0.015143 3 0.195534 -0.372746 0.710562 -0.014989 -1.325968 -0.029573 0.056374 4 -0.057454 -0.026908 -0.012602 0.357674 0.161608 -0.030549 -0.014307 5 0.370249 -0.674499 1.228763 -0.163717 -1.94024 -0.028287 0.051531 6 -1.116981 1.496706 -2.00552 0 2.687308 0.100306 -0.134406 7 -0.087996 -0.069519 -0.054921 -0.558095 -0.484293 0.072752 0.057475 STO 0 0 0 0 0 0 0 9 -0.001452 -0.011573 -0.092237 0.249652 1.254593 -0.007679 -0.061199 10 0.615696 -0.107186 0.01866 0.249652 -0.04671 -0.041816 0.00728 11 -0.435631 -0.00421 -0.000041 -0.310611 -0.003002 0.037865 0.000366 12 0.099799 -0.118674 0.14112 0.058569 -0.237457 -0.02131 0.025341 IMA 0 0 0 0 0 0 0 TOT 0.048909 -0.005062 -0.037184 0.127326 -0.006011 -0.009035 0.003597

[0069] It can be seen from Table 3 that, compared with the aperture of f1.1, at the aperture of f1.4, all data of the large aperture fixed focus lens of this embodiment are significantly improved, and the blur effect of the depth of field of the APS-C lens can be maintained.

[0070] Figure 3 This is a graph showing the MTF test results of the large aperture fixed focus lens of this embodiment at the maximum field angle when the aperture is maximum;

[0071] Figure 4 This is a graph showing the MTF test results of the central field angle of the large aperture fixed focus lens of this embodiment at the maximum aperture;

[0072] Figure 5 This is a central field optical path difference curve (OPD) of the large aperture fixed focus lens of this embodiment at an aperture of f1.1. In this figure, the wavelength is 486um (blue light), PX-0.998, PY-0.998; the wavelength is 587um (green light), PX 0.001, PY 0.001; the wavelength is 656um (red light), PX-4.181, PY-4.181.

[0073] Figure 6This is a central field optical path difference curve (OPD) of the large aperture fixed focus lens of this embodiment at an aperture of f1.4. In this figure, the wavelength is 486um (blue light), PX 1.036, PY 1.036; the wavelength is 587um (green light), PX-0.278, PY-0.278; the wavelength is 656um (red light), PX-3.182, PY-3.182.

[0074] Combination Figure 5 and Figure 6 It can be seen that, in the case of apertures of f1.1 and f1.4, the values ​​of some blue, green and red wavelengths in the optical path difference curve of the large aperture fixed focus lens of this embodiment are quite close, indicating that the aberration of the central field of view is not much different from the theoretical value.

[0075] Figure 7 This is a graph of the optical path difference (OPD) of the edge field of view of the large aperture fixed focus lens of this embodiment at an aperture of f1.1; in this graph, the wavelength is 486um (blue light), PX-14.535, and PY 31.064; the wavelength is 587um (green light), PX-13.530, and PY16.719; the wavelength is 656um (red light), PX-15.348, and PY 10.779.

[0076] Figure 8 This is a graph of the optical path difference (OPD) of the edge field of view of the large aperture fixed focus lens of this embodiment at an aperture of f1.4. In this graph, the wavelength is 486um (blue light), PX-2.524, and PY 16.088; the wavelength is 587um (green light), PX-3.518, and PY8.399; the wavelength is 656um (red light), PX-5.187, and PY 4.965.

[0077] Combination Figure 7 and Figure 8 It can be seen that when the aperture of the large aperture fixed focus lens of this embodiment is f1.1, the wavelength difference of the three colors is relatively large, and there is obvious aberration, but this is within the reasonable range of lens design. At this time, the image field is already in the range of image 0.9 to 1.0, and it is easy to obtain a significant background blur effect (large aperture shallow depth of field and background blur effect).

[0078] Fig. 9 This is the spot diagram (SPOT) of the central field of view light focused when the large aperture fixed focus lens of this embodiment is at an aperture of f1.1; RMS 7.765um.

[0079] Fig.10 This is the spot diagram (SPOT) of the central field of view light focused when the large aperture fixed focus lens of this embodiment is at an aperture of f1.4; RMS 5.463um.

[0080] Fig.11This is the spot diagram (SPOT) of the edge field of view light focusing when the large aperture fixed focus lens of this embodiment is at aperture f1.1; RMS 106.273um.

[0081] Fig.12 This is the spot diagram (SPOT) of the edge field light focusing when the large aperture fixed focus lens of this embodiment is at aperture f1.4; RMS 47.663um.

[0082] Combination Figures 9 to 12 It can be seen that when the aperture is f1.1 and f1.4, the shape of this large aperture fixed focus lens is almost circular, and the center field of view of the entire RMS diameter is only one percent of the main wavelength (0.587um), and the edge field of view (1.1 aperture) is only one quarter of the main wavelength (0.587um), which is already a very good optical design.

[0083] Fig.13 This is the field curvature and distortion diagram of the main light when the large aperture fixed focus lens of this embodiment is at the maximum aperture; wavelength 587um (green light), (S) horizontal offset 0.017mm, (T) vertical offset -0.478mm, maximum optical distortion -1.25%. Combined Fig.13 It can be seen that when the aperture of the large aperture fixed focus lens of this embodiment is f1.1, its vertical offset is relatively large (-0.478mm), and the edge part will be defocused, but this is within the reasonable range of lens design. Its maximum optical distortion is -1.25%, which is less than -2%, which is less than the distortion that can be recognized by the human eye, and is close to the ideal state of no distortion.

[0084] Fig.14 This is a central field fan diagram (Ray Fan) of the large aperture fixed focus lens of this embodiment when the aperture is f1.1. In this diagram, the wavelength is 486um (blue light), PX 17.341, PY 17.341; the wavelength is 587um (green light), PX-0.312, PY-0.312; the wavelength is 656um (red light), PX 9.639, PY 9.639.

[0085] Fig.15 This is a central field fan diagram (Ray Fan) of the large aperture fixed focus lens of this embodiment when the aperture is f1.4. In this diagram, the wavelength is 486um (blue light), PX-1.271, PY-1.271; the wavelength is 587um (green light), PX-6.960, PY-6.960; the wavelength is 656um (red light), PX 2.728, PY 2.728.

[0086] Fig.16This is the edge field fan diagram (Ray Fan) of the large aperture fixed focus lens of this embodiment when the aperture is f1.1; in this diagram, the wavelength is 486um (blue light), PX 138.410, PY 312.435; the wavelength is 587um (green light), PX 136.890, PY205.470; the wavelength is 656um (red light), PX 148.237, PY 161.806.

[0087] Fig.17 This is a fan-shaped diagram (Ray Fan) of the edge field of view of the large aperture fixed focus lens of this embodiment when the aperture is f1.4; in this diagram, the wavelength is 486um (blue light), PX 36.935, PY 185.903; the wavelength is 587um (green light), PX 40.090, PY124.821; the wavelength is 656um (red light), PX 50.238, PY 95.427.

[0088] Combination Fig.12 , Fig.13 , Fig.16 and Fig.17 It can be seen that the large aperture fixed focus lens of this embodiment comprehensively considers defocus, coma (COMA), distortion, MTF and large aperture blur effect, finds a balance point, and achieves the background blur effect.

[0089] In summary, the large aperture fixed focus lens provided by the present invention has the first and second lens pieces as Crown Glass, and the third, fourth, and fifth lens pieces as Flint Glass. The structure is novel and breaks the inertial thinking in the industry. Moreover, this combination does not require glued pieces to improve the chromatic aberration of the lens, which not only facilitates the assembly of the lens but also reduces the manufacturing cost of the lens. More importantly, the large aperture fixed focus lens can not only achieve a large aperture of 1.1, but also only requires 5 lens pieces to achieve good imaging quality, especially the imaging quality of the large aperture can be equal to or even exceed the existing fixed focus lenses on the market. At the same time, it is conducive to reducing the purchase cost of users and promoting the development of the industry.

[0090] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A large aperture fixed focus lens, characterized by: The first lens group includes a first lens group, a second lens group and a third lens group in order from the object side to the image side along the optical axis. The first lens group includes a first lens piece, a second lens piece and a third lens piece in order from the object side to the image side along the optical axis. The second lens group includes a fourth lens piece. The third lens group includes a fifth lens piece. The first lens has positive refractive power, and the radius of curvature of the object side surface is R1, and the radius of curvature of the image side surface is R2, wherein R1 and R2 are respectively greater than 0; The second lens sheet has positive refractive power and is a positive meniscus lens, the object side surface curvature radius is R3, the image side surface curvature radius is R4, R3<R4; The third lens has negative refractive power and is a plano-concave lens, and the curvature radius of the image side surface is R6; The fourth lens sheet has positive refractive power and is a biconvex lens, the object side curvature radius of which is R7, the image side curvature radius of which is R8, and R7=|R8|; The fifth lens sheet has negative refractive power and is a meniscus lens, the object side surface curvature radius is R9, the image side surface curvature radius is R10, |R9|<|R10|; An aperture stop is provided between the third lens sheet and the fourth lens sheet; The diameter of the second lens sheet is D2, the thickness of the second lens sheet is T2, D2 and T2 satisfy the conditional expression: <D2 / T2<5; The diameter of the third lens piece is D3, the thickness of the third lens piece is T3, D3 and T3 satisfy the conditional expression: 21 <D3 / T3<23。 2. The large aperture fixed focus lens according to claim 1, characterized in that: The diameter of the first lens sheet is D1, the gap between the first lens sheet and the second lens sheet is t1, and D1 and t1 satisfy the condition: 220≤D1 / t1<250.

3. The large aperture fixed focus lens according to claim 1, characterized in that: The focal length fA of the first lens group satisfies the conditional expression: 120 <fA<140。 4. The large aperture fixed focus lens according to claim 3, characterized in that: The focal length fB of the second lens group and the diameter D2 of the second lens sheet satisfy the conditional expressions: 1<D2 / fB<3, and fA / fB>5.

5. The large aperture fixed focus lens according to claim 4, characterized in that: The focal length fC of the third lens group satisfies the conditional expression, -50 <fC<-40。 6. The large aperture fixed focus lens according to claim 1, characterized in that: The diameter of the fifth lens sheet is D5, the gap between the fifth lens sheet and the image side is t5, D5 and t5 satisfy the conditional expression: <D5 / t5<2。 7. The large aperture fixed focus lens according to claim 1, characterized in that: The refractive index of the first lens sheet is the same as the refractive index of the second lens sheet, and the refractive indexes of any two of the second lens sheet, the third lens sheet, the fourth lens sheet, and the fifth lens sheet are different.

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