Large-aperture distortionless fixed-focus objective lens optical system

Abstract

The invention belongs to the technical field of objective lens optical systems, and provides a large-aperture distortionless fixed-focus objective lens optical system which is adaptive to a low-light CMOS (complementary metal oxide semiconductor) or CCD (charge coupled device) with the image surface size of 1 inch. The first lens group, the diaphragm and the second lens group are arranged in sequence; the first lens group comprises a first lens, a second lens and a third lens; the second lens group comprises a fourth lens, a fifth lens, a sixth lens and a seventh lens; the optical indexes that the wave band ranges from 480 nm to 1000 nm, the maximum distortion is not larger than 0.5%, the pixel is 800 px * 600 px, and the view field range is 35.5 degrees * 27 degrees are achieved. The invention aims to solve the problem that the overall imaging quality of the lens is poor due to the deformation of an imaged picture caused by the large distortion index of the existing large-aperture objective lens optical system, and has the advantages of high resolution, large relative aperture and broadband design, realization of day and night confocal, and good imaging quality in an extreme environment.

Description

Technical Field

[0001] The invention belongs to the technical field of objective optical systems, and specifically provides a large-aperture distortion-free fixed-focus objective optical system. Background Art

[0002] At present, optical instruments are increasingly used in military and civilian fields. For scenes such as geographic surveying and mapping, architectural photography, and other special requirements, there is a special demand for the use of distortion-free low-light objective lenses. Existing large-aperture objective optical systems rarely consider distortion when designing, especially for objectives with larger field of view (such as full field of view ≥ 40°), where distortion is generally large, resulting in deformation of the image after imaging. This results in large recognition errors when the lens is used in a measuring instrument, which reduces the accuracy of the results of the measuring instrument.

[0003] Therefore, there is an urgent need for a large-aperture, distortion-free objective optical system to solve the above problems. Summary of the invention

[0004] One purpose of the present invention is to solve the problem that the existing large-aperture objective optical system has a large distortion index, which causes deformation of the image after imaging and reduces the imaging quality.

[0005] To achieve the above object, the present invention provides a large-aperture, non-distortion, fixed-focus objective optical system, wherein the optical system is adapted to a 1-inch low-light CMOS or CCD image plane size;

[0006] The optical system comprises a first lens group, an aperture, and a second lens group which are arranged in sequence; the first lens group comprises a first lens, a second lens, and a third lens; the second lens group comprises a fourth lens, a fifth lens, a sixth lens, and a seventh lens; the aperture is coplanar with the fourth lens;

[0007] The optical indicators achieved by the optical system are: wavelength band 480nm to 1000nm, maximum distortion no more than 0.5%, pixel 800px×600px, and field of view range 35.5°×27°.

[0008] Further, the first lens, the second lens, the third lens, the aperture, the fourth lens, the fifth lens, the sixth lens and the seventh lens are sequentially arranged from the object side to the image side along the optical axis;

[0009] The first lens is a glass spherical lens with positive optical power, the object side of which is convex and the image side of which is concave;

[0010] The second lens is a glass spherical lens with negative optical power, the object side of which is concave and the image side of which is concave;

[0011] The third lens is a glass spherical lens with positive refractive power, the object side of which is convex, and the image side of which is convex;

[0012] The fourth lens is a glass spherical lens with positive refractive power, the object side of which is convex, and the image side of which is convex;

[0013] The fifth lens is a glass spherical lens with negative optical power, the fourth lens and the fifth lens are glued together by photosensitive adhesive, and the image side of the fifth lens is a concave surface;

[0014] The sixth lens is a glass spherical lens with positive refractive power, the object side of which is convex, and the image side of which is convex;

[0015] The seventh lens is a glass spherical lens with negative optical power, the object side of which is concave, and the image side of which is concave.

[0016] Further, the optical system consisting of the first lens, the second lens, the third lens, the aperture, the fourth lens, the fifth lens, the sixth lens and the seventh lens satisfies the following condition: f / L≥0.5, wherein f represents the focal length of the objective lens, and L represents the total optical length of the objective lens.

[0017] Furthermore, the optical system consisting of the first lens, the second lens, the third lens, the aperture, the fourth lens, the fifth lens, the sixth lens and the seventh lens further satisfies the following condition: 2≥f A1 / Φ A1 ≥1, where f A1 represents the focal length of the first lens A1; Φ A1 represents the effective aperture of the first lens A1; 2≥f A2 / Φ A2 ≥1, where f A2 represents the focal length of the second lens A2; Φ A2 represents the effective aperture of the second lens A2; 2≥f A3 / Φ A3 ≥1, where f A3 represents the focal length of the third lens A1; Φ A3 represents the effective aperture of the third lens A1; 2≥f C1 / Φ C1 ≥1, where f C1 represents the focal length of the fourth lens C1; Φ C1 represents the effective aperture of the fourth lens C1; 1≥f C2 / Φ C2 ≥0.5, where f C2 represents the focal length of the fifth lens C2; Φ C2 represents the effective aperture of the fifth lens C2; 1≥fC3 / Φ C3 ≥0.5, where f C3 represents the focal length of the sixth lens C3; Φ C3 represents the effective aperture of the sixth lens C3; 2≥f C4 / Φ C4 ≥1, where f C4 represents the focal length of the seventh lens C4; Φ C4 represents the effective aperture of the seventh lens C4.

[0018] Furthermore, the first lens satisfies the relational expressions: Nd≥1.9, Vd≥30, and 33mm < f1 < 34mm, where f1 is the focal length of the first lens; the second lens satisfies the relational expressions: Nd≥1.75, Vd≥20, and -21mm < f2 < -20mm, where f2 is the focal length of the second lens; the third lens satisfies the relational expressions: Nd≥1.9, Vd≥30, and 27mm < f3 < 28mm, where f3 is the focal length of the third lens; the fourth lens satisfies the relational expressions: Nd≥1.9, Vd≥30, and 16mm < f4 < 17mm, where f4 is the focal length of the fourth lens; the fifth lens satisfies the relational expressions: Nd≥1.9, Vd≤20, and -12mm < f5 < -11mm, where f5 is the focal length of the fifth lens; the sixth lens satisfies the relational expressions: Nd≥2.0, Vd≥25, and 12mm < f6 < 13mm, where f6 is the focal length of the sixth lens; the seventh lens satisfies the relational expressions: Nd≥1.60, Vd≥30, and -18mm < f7 < -17mm, where f7 is the focal length of the seventh lens.

[0019] Furthermore, the glass refractive index Nd of the first lens is 1.91, and the glass Abbe number Vd is 35.2; the curvature radius of its object side is 23.2mm, the surface interval is 4.17mm, and the effective aperture is set to 22.5mm; the curvature radius of its image side is 86.1mm, the surface interval is 4.06, and the effective aperture is 21.2mm.

[0020] Furthermore, the glass refractive index Nd of the second lens is 1.78, and the glass Abbe number Vd is 25.7; the curvature radius of its object side is -37.7mm, the surface interval is 2.25mm, and the effective aperture is 18.7mm; the curvature radius of its image side is 30.3mm, the surface interval is 2.48, and the effective aperture is 17.3mm.

[0021] Furthermore, the glass refractive index Nd of the third lens is 1.95, and the glass Abbe number Vd is 32.3; the curvature radius of its object side is 76.2mm, the surface interval is 4.78mm, and the effective aperture is 17.6mm; the curvature radius of its image side is -39.0mm, the surface interval is 0.23, and the effective aperture is 17.8mm.

[0022] Furthermore, the glass refractive index Nd of the object side of the fourth lens is 1.91, the glass Abbe number Vd is 35.2; the radius of curvature is 20.0 mm, the surface spacing is 6.54 mm, and the effective aperture is 16.4 mm; the glass refractive index Nd of the image side of the fourth lens is 1.95, the glass Abbe number Vd is 18; the radius of curvature is 48.9 mm, the surface spacing is 3.97 mm, and the effective aperture is 14.2 mm.

[0023] Furthermore, the curvature radius of the fifth lens is 15.0 mm, the surface spacing is 0.79 mm, and the effective aperture is 12.4 mm.

[0024] Furthermore, the glass refractive index Nd of the sixth lens is 2.0, and the glass Abbe number Vd is 25.5; the object side curvature radius is 26.3 mm, the surface spacing is 7.66 mm, and the effective aperture is 12.6 mm; the image side curvature radius is -20.8 mm, the surface spacing is 0.52 mm, and the effective aperture is 13.5 mm.

[0025] Furthermore, the glass refractive index Nd of the seventh lens is 1.78, and the glass Abbe number Vd is 25.7; its object side curvature radius is -15.5 mm, the surface spacing is 2.03 mm, and the effective aperture is 13.5 mm; the image side curvature radius is 148.4 mm, the surface spacing is 3.22 mm, and the effective aperture is 14.8 mm.

[0026] Furthermore, the mirror surfaces of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are all made of white light glass, and all the lenses are coated to the near-infrared band.

[0027] Further, the first lens, the third lens, the fourth lens and the sixth lens are all made of heavy lanthanum flint glass material; and the second lens, the fifth lens and the seventh lens are all made of flint glass material.

[0028] Based on the foregoing description, those skilled in the art will understand that, in the aforementioned technical solution of the present invention, the optical system of the present invention has high resolution, adopts a large relative aperture and a wide-band design, realizes day and night confocality, and has good imaging quality in extreme environments such as -30°C -50°C; all spherical lenses and environmentally friendly materials are used, which are low in cost, simple to install and adjust, and convenient for mass production; through reasonable glass material matching and lens optical power distribution, the axial chromatic aberration and lateral chromatic aberration of the entire optical system are well corrected, and the reasonable surface design also enables the high-order aberrations of the entire optical system to be effectively corrected. At the same time, the incident angle of each mirror light is small, and the overall imaging quality of the system is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solution of the present invention, some embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood by those skilled in the art that the same reference numerals indicate the same or similar components or parts in different drawings; the drawings of the present invention are not necessarily drawn to scale.

[0030] In the attached figure:

[0031] Figure 1 is a schematic diagram of the structure of an objective optical system in some embodiments of the present invention;

[0032] Figure 2 yes Figure 1 Diagram of the light propagation path of the objective optical system;

[0033] Figure 3 yes Figure 1 Optical transfer function diagram of the objective optical system;

[0034] Figure 4 yes Figure 1 Optical point diagram of the objective optical system;

[0035] Figure 5 yes Figure 1 Schematic diagram of the optical field curvature and distortion of the objective optical system.

[0036] Description of reference numerals:

[0037] 100. Optical system;

[0038] A, first lens group; A1, first lens; A2, second lens; A3, third lens; B, aperture; C, second lens group; C1, fourth lens; C2, fifth lens; C3, sixth lens; C4, seventh lens;

[0039] S1 is the object side surface of the first lens; S2 is the image side surface of the first lens; S3 is the object side surface of the second lens; S4 is the image side surface of the second lens; S5 is the object side surface of the third lens; S6 is the image side surface of the third lens; S7 is the aperture surface; S8 is the image side surface of the fourth lens; S9 is the image side surface of the fifth lens; S10 is the object side surface of the sixth lens; S11 is the image side surface of the sixth lens; S12 is the object side surface of the seventh lens; S13 is the image side surface of the seventh lens. DETAILED DESCRIPTION

[0040] It should be understood by those skilled in the art that the embodiments described below are only some embodiments of the present invention, rather than all embodiments of the present invention, and these embodiments are intended to explain the technical principles of the present invention, rather than to limit the protection scope of the present invention. Based on the embodiments provided by the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should still fall within the protection scope of the present invention.

[0041] It should be noted that in the description of the present invention, the terms "center", "upper", "lower", "top", "bottom", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings, which are only for the convenience of description, and do not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0042] Refer to the following Figures 1 to 5 , to describe in detail the schematic diagram of the objective optical system in some embodiments of the present invention. Figure 1 is a schematic diagram of the structure of an objective optical system in some embodiments of the present invention;

[0043] Figure 2 yes Figure 1 Diagram of the light propagation path of the objective optical system; Figure 3 yes Figure 1 Optical transfer function diagram of the objective optical system; Figure 4 yes Figure 1 Optical point diagram of the objective optical system; Figure 5 yes Figure 1 Schematic diagram of the optical field curvature and distortion of the objective optical system.

[0044] It should be noted that, for the convenience of description and to enable those skilled in the art to quickly understand the technical solution of the present invention, the following text only describes the technical features that are strongly related (directly or indirectly related) to the technical problem and / or technical concept to be solved by the present invention, and will not describe the technical features that are weakly related to the technical problem and / or technical concept to be solved by the invention. Since the technical features with a weaker degree of correlation belong to the common knowledge in the field, even if the present invention does not describe the features with a weaker degree of correlation, it will not lead to insufficient disclosure of the present invention.

[0045] like Figure 1As shown, in some embodiments of the present invention, a large aperture non-distortion fixed-focus objective optical system 100 is provided, and the optical system 100 includes a first lens group A, an aperture B and a second lens group C, and the aperture B is arranged between the first lens group A and the second lens group C. The first lens group A includes a first lens A1, a second lens A2 and a third lens A3, and the second lens group C includes a fourth lens C1, a fifth lens C2, a sixth lens C3 and a seventh lens C4. The optical system 100 in the present invention is adapted to an image plane size of 1 inch low-light CMOS or CCD. The optical indicators achieved by the optical system 100 are: a wavelength band of 480nm to 1000nm, a maximum distortion of no more than 0.5%, a pixel setting of 800×600, and a field of view of 35.5°×27°.

[0046] Specifically, the optical system includes, in order from the object side to the image side, a first lens A1, a second lens A2, a third lens A3, a stop B, a fourth lens C1, a fifth lens C2, a sixth lens C3 and a seventh lens C4.

[0047] The first lens A1 is a glass spherical lens with positive focal power, whose object side is convex and whose image side is convex. The second lens A2 is a glass spherical lens with negative focal power, whose object side is concave and whose image side is convex. The third lens A3 is a glass spherical lens with positive focal power, whose object side is convex and whose image side is concave. The aperture B is coplanar with the fourth lens C1, and the fourth lens C1 is a glass spherical lens with positive focal power, and whose image side is convex. The fifth lens C2 is a glass spherical lens with negative focal power, and the fourth lens C1 and the fifth lens C2 are glued together by photosensitive adhesive, and the image side of the fifth lens C2 is convex. The sixth lens C3 is a glass spherical lens with positive focal power, whose object side is concave and whose image side is concave. The seventh lens C4 is a glass spherical lens with positive focal power, whose object side is convex and whose image side is flat.

[0048] The optical system 100 composed of the first lens A1, the second lens A2, the third lens A3, the aperture B, the fourth lens C1, the fifth lens C2, the sixth lens C3 and the seventh lens C4 satisfies the following conditions:

[0049] f / L≥0.5, wherein f represents the focal length of the objective lens, and L represents the total optical length of the objective lens.

[0050] The optical system 100 composed of the first lens A1, the second lens A2, the third lens A3, the aperture B, the fourth lens C1, the fifth lens C2, the sixth lens C3 and the seventh lens C4 also satisfies the following conditions:

[0051] 2≥f A1 / Φ A1 ≥1, where f A1 represents the focal length of the first lens A1; ΦA1 Represents the effective aperture of the first lens A1;

[0052] 2 ≥ f A2 / Φ A2 ≥ 1, where f A2 represents the focal length of the second lens A2; Φ A2 represents the effective aperture of the second lens A2;

[0053] 2 ≥ f A3 / Φ A3 ≥ 1, where f A3 represents the focal length of the third lens A3; Φ A3 represents the effective aperture of the third lens A3;

[0054] 2 ≥ f C1 / Φ C1 ≥ 1, where f C1 represents the focal length of the fourth lens C1; Φ C1 represents the effective aperture of the fourth lens C1;

[0055] 1 ≥ f C2 / Φ C2 ≥ 0.5, where f C2 represents the focal length of the fifth lens C2; Φ C2 represents the effective aperture of the fifth lens C2;

[0056] 1 ≥ f C3 / Φ C3 ≥ 0.5, where f C3 represents the focal length of the sixth lens C3; Φ C3 represents the effective aperture of the sixth lens C3;

[0057] 2 ≥ f C4 / Φ C4 ≥ 1, where f C4 represents the focal length of the seventh lens C4; Φ C4 represents the effective aperture of the seventh lens C4.

[0058] The first lens A1 satisfies the relational expressions: Nd ≥ 1.9, Vd ≥ 30, and 33 mm < f1 < 34 mm, where f1 is the focal length of the first lens A1.

[0059] The second lens A2 satisfies the relational expressions: Nd ≥ 1.75, Vd ≥ 20, and -21 mm < f2 < -20 mm, where f2 is the focal length of the second lens A2.

[0060] The third lens A3 satisfies the relational expressions: Nd ≥ 1.9, Vd ≥ 30, and 27 mm < f3 < 28 mm, where f3 is the focal length of the third lens A3.

[0061] The fourth lens C1 satisfies the relationships: Nd ≥ 1.9, Vd ≥ 30, and 16 mm < f4 < 17 mm, where f4 is the focal length of the fourth lens C1.

[0062] The fifth lens C2 satisfies the relationships: Nd ≥ 1.9, Vd ≤ 20, and -12 mm < f5 < -11 mm, where f5 is the focal length of the fifth lens C2.

[0063] The sixth lens C3 satisfies the relationships: Nd ≥ 2.0, Vd ≥ 25, and 12 mm < f6 < 13 mm, where f6 is the focal length of the sixth lens C3.

[0064] The seventh lens C4 satisfies the relationships: Nd ≥ 1.60, Vd ≥ 30, and -18 mm < f7 < -17 mm, where f7 is the focal length of the seventh lens C4.

[0065] Table 1 shows the parameter values of each lens in some embodiments of the optical system 100 of the present invention.

[0066]

[0067] Among them, as Figure 1 shown, surface S1 is the object side surface of the first lens A1; surface S2 is the image side surface of the first lens A1; surface S3 is the object side surface of the second lens A2; surface S4 is the image side surface of the second lens A2; surface S5 is the object side surface of the third lens A3; surface S6 is the image side surface of the third lens A3; surface S7 is the object side surface of the fourth lens C1, and the aperture stop B is disposed at surface S7; surface S8 is the image side surface of the fourth lens C1; surface S9 is the image side surface of the fifth lens C2; surface S10 is the object side surface of the sixth lens C3; surface S11 is the image side surface of the sixth lens C3; surface S12 is the object side surface of the seventh lens C4; surface S13 is the image side surface of the seventh lens C4.

[0068] As shown in Table 1, in a specific embodiment of the present invention, the glass refractive index Nd of the first lens A1 is 1.91, and the glass Abbe number Vd is 35.2. The radius of curvature of the object side surface S1 of the first lens A1 is 23.2 mm, the surface interval is 4.17 mm, and the effective aperture is set to 22.5 mm. The radius of curvature of the image side surface S2 of the first lens A1 is 86.1 mm, the surface interval is 4.06, and the effective aperture is 21.2 mm.

[0069] The glass refractive index Nd of the second lens A2 is 1.78, and the glass Abbe number Vd is 25.7. The radius of curvature of the object side surface S3 of the second lens A2 is -37.7 mm, the surface interval is 2.25 mm, and the effective aperture is 18.7 mm. The radius of curvature of the image side surface S4 of the second lens A2 is 30.3 mm, the surface interval is 2.48, and the effective aperture is 17.3 mm.

[0070] The glass refractive index Nd of the third lens A3 is 1.95, and the glass Abbe number Vd is 32.3. The radius of curvature of the object side S5 of the third lens A3 is 76.2 mm, the surface interval is 4.78 mm, and the effective aperture is 17.6 mm. The radius of curvature of the image side S6 of the third lens A3 is -39.0 mm, the surface interval is 0.23, and the effective aperture is 17.8 mm.

[0071] The glass refractive index Nd of the object side surface S7 of the fourth lens C1 is 1.91, the glass Abbe number Vd is 35.2, the curvature radius is 20.0 mm, the surface interval is 6.54 mm, and the effective aperture is 16.4 mm. The glass refractive index Nd of the image side surface S8 of the fourth lens C1 is 1.95, the glass Abbe number Vd is 18, the curvature radius is 48.9 mm, the surface interval is 3.97 mm, and the effective aperture is 14.2 mm.

[0072] The curvature radius of the image-side surface S9 of the fifth lens C2 is 15.0 mm, the surface spacing is 0.79 mm, and the effective aperture is 12.4 mm.

[0073] The glass refractive index Nd of the sixth lens C3 is 2.0, and the glass Abbe number Vd is 25.5. The curvature radius of the object side surface S10 of the sixth lens C3 is 26.3 mm, the surface interval is 7.66 mm, and the effective aperture is 12.6 mm; the curvature radius of the image side surface S11 is -20.8 mm, the surface interval is 0.52 mm, and the effective aperture is 13.5 mm.

[0074] The glass refractive index Nd of the seventh lens C4 is 1.78, and the glass Abbe number Vd is 25.7. The curvature radius of the object side S12 of the seventh lens C4 is -15.5mm, the surface interval is 2.03mm, and the effective aperture is 13.5mm. The curvature radius of the image side S13 of the seventh lens C4 is 148.4mm, the surface interval is 3.22mm, and the effective aperture is 14.8mm.

[0075] Among them, the mirror surfaces of the first lens A1, the second lens A2, the third lens A3, the fourth lens C1, the fifth lens C2, the sixth lens C3 and the seventh lens C4 are all set to be white light glass material, and all lenses are coated to the near-infrared band.

[0076] Preferably, the first lens A1, the third lens A3, the fourth lens C1 and the sixth lens C3 are all made of heavy lanthanum flint glass material, and the second lens A2, the fifth lens C2 and the seventh lens C4 are all made of flint glass material.

[0077] Those skilled in the art can understand that, in the present invention, the aberrations of the first lens group A and the second lens group C are complemented, the cemented lens in the second lens group C is complementarily corrected for spherical aberration and chromatic aberration, and the focal power of each lens is reasonably calculated to meet the requirement of no focal plane offset at high and low temperatures, so as to achieve the effect of parfocality during the day and night. High-definition videography is achieved at an ultra-low cost, with a relatively large aperture and no distortion. While achieving high-quality pixels during the day, it also has high-definition image quality at night or in low light conditions. And it can still meet the requirements of use in environments with different temperatures.

[0078] The entire lens ensures that the refractive index and focal length of the lens are reasonably distributed, and the incident angle of the front and rear lens groups is balanced to avoid sensitive aberrations and reduce the difficulty of installation and adjustment. By reasonably distributing the focal lengths of each lens, the spherical aberration and field curvature of the imaging system are both small, ensuring high imaging quality both on and off the axis. This effectively solves the problem of large distortion values ​​in existing large-aperture objective optical systems, which leads to poor imaging effects.

[0079] So far, the technical solution of the present invention has been described in combination with the above multiple embodiments, but it is easy for those skilled in the art to understand that the protection scope of the present invention is not limited to these specific embodiments. Without departing from the technical principles of the present invention, those skilled in the art can split and combine the technical solutions in the above embodiments, and can also make equivalent changes or replacements to the relevant technical features. Any changes, equivalent replacements, improvements, etc. made within the technical concept and / or technical principles of the present invention will fall within the protection scope of the present invention.

Claims

1. A large aperture, non-distortion, fixed-focus objective optical system, characterized in that: The optical system is adapted to an image plane size of 1-inch low-light CMOS or CCD; The optical system includes a first lens group, a diaphragm, and a second lens group arranged in sequence; the first lens group includes a first lens, a second lens, and a third lens; the second lens group includes a fourth lens, a fifth lens, a sixth lens, and a seventh lens; the diaphragm is coplanar with the fourth lens; The optical indicators achieved by the optical system are as follows: the wavelength band is from 480 nm to 1000 nm, the maximum distortion is not greater than 0.5%, the pixel is 800 px × 600 px, and the field of view range is 35.5° × 27°.

2. The large aperture non-distortion fixed-focus objective optical system according to claim 1, characterized in that: The first lens, the second lens, the third lens, the diaphragm, the fourth lens, the fifth lens, the sixth lens, and the seventh lens are arranged in sequence along the optical axis from the object side to the image side; The first lens is a glass spherical lens with positive optical power, its object side is convex, and its image side is concave; The second lens is a glass spherical lens with negative optical power, its object side is concave, and its image side is concave; The third lens is a glass spherical lens with positive optical power, its object side is convex, and its image side is convex; The fourth lens is a glass spherical lens with positive optical power, its object side is convex, and its image side is convex; The fifth lens is a glass spherical lens with negative optical power, the fourth lens and the fifth lens are glued together with photosensitive glue, and the image side of the fifth lens is concave; The sixth lens is a glass spherical lens with positive optical power, its object side is convex, and its image side is convex; The seventh lens is a glass spherical lens with negative optical power, its object side is concave, and its image side is concave.

3. The large aperture non-distortion fixed-focus objective optical system according to claim 2, characterized in that: The optical system composed of the first lens, the second lens, the third lens, the diaphragm, the fourth lens, the fifth lens, the sixth lens, and the seventh lens satisfies the following conditions: f / L≥0.5, where f represents the focal length of the objective lens and L represents the total optical length of the objective lens.

4. The large aperture non-distortion fixed-focus objective optical system according to claim 2, characterized in that: The optical system composed of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens also satisfies the following conditions: 2≥f A1 / Φ A1 ≥1, where f A1 represents the focal length of the first lens A1; Φ A1 represents the effective aperture of the first lens A1; 2≥f A2 / Φ A2 ≥1, where f A2 represents the focal length of the second lens A2; Φ A2 denotes the effective aperture of the second lens A2; 2≥f A3 / Φ A3 ≥1, where f A3 represents the focal length of the third lens A3; Φ A3 denotes the effective aperture of the third lens A3; 2≥f C1 / Φ C1 ≥1, where f C1 represents the focal length of the fourth lens C1; Φ C1 denotes the effective aperture of the fourth lens C1; 1≥f C2 / Φ C2 ≥0.5, where f C2 represents the focal length of the fifth lens C2; Φ C2 denotes the effective aperture of the fifth lens C2; 1≥f C3 / Φ C3 ≥0.5, where f C3 Φ represents the focal length of the sixth lens C3; Φ C3 denotes the effective aperture of the sixth lens C3; 2≥f C4 / Φ C4 ≥1, where f C4 represents the focal length of the seventh lens C4; Φ C4 Denotes the effective aperture of the seventh lens C4.

5. The large aperture non-distortion fixed-focus objective optical system according to claim 4, characterized in that: The first lens satisfies the relational expressions: Nd≥1.9, Vd≥30, and 33 mm < f1 < 34 mm, where f1 is the focal length of the first lens; The second lens satisfies the relational expressions: Nd≥1.75, Vd≥20, and -21 mm < f2 < -20 mm, where f2 is the focal length of the second lens; The third lens satisfies the relational expressions: Nd≥1.9, Vd≥30, and 27 mm < f3 < 28 mm, where f3 is the focal length of the third lens; The fourth lens satisfies the relational expressions: Nd≥1.9, Vd≥30, and 16 mm < f4 < 17 mm, where f4 is the focal length of the fourth lens; The fifth lens satisfies the relational expressions: Nd≥1.9, Vd≤20, and -12 mm < f5 < -11 mm, where f5 is the focal length of the fifth lens; The sixth lens satisfies the relational expressions: Nd≥2.0, Vd≥25, and 12 mm < f6 < 13 mm, where f6 is the focal length of the sixth lens; The seventh lens satisfies the relational expressions: Nd≥1.60, Vd≥30, and -18mm < f7 < -17mm, where f7 is the focal length of the seventh lens.

6. The large aperture non-distortion fixed-focus objective optical system according to claim 5, characterized in that: The glass refractive index Nd of the first lens is 1.91, and the glass Abbe number Vd is 35.2; the curvature radius of its object side is 23.2mm, the surface interval is 4.17mm, and the effective aperture is set to 22.5mm; the curvature radius of its image side is 86.1mm, the surface interval is 4.06, and the effective aperture is 21.2mm.

7. The large aperture non-distortion fixed-focus objective optical system according to claim 5, characterized in that: The glass refractive index Nd of the second lens is 1.78, and the glass Abbe number Vd is 25.7; the curvature radius of its object side is -37.7mm, the surface interval is 2.25mm, and the effective aperture is 18.7mm; the curvature radius of its image side is 30.3mm, the surface interval is 2.48, and the effective aperture is 17.3mm.

8. The large aperture non-distortion fixed-focus objective optical system according to claim 5, characterized in that: The glass refractive index Nd of the third lens is 1.95, and the glass Abbe number Vd is 32.3; the curvature radius of its object side is 76.2mm, the surface interval is 4.78mm, and the effective aperture is 17.6mm; the curvature radius of its image side is -39.0mm, the surface interval is 0.23, and the effective aperture is 17.8mm.

9. The large aperture non-distortion fixed-focus objective optical system according to claim 5, characterized in that: The glass refractive index Nd of the object side of the fourth lens is 1.91, and the glass Abbe number Vd is 35.2; the curvature radius is 20.0mm, the surface interval is 6.54mm, and the effective aperture is 16.4mm; the glass refractive index Nd of the image side of the fourth lens is 1.95, the glass Abbe number Vd is 18, the curvature radius is 48.9mm, the surface interval is 3.97mm, and the effective aperture is 14.2mm.

10. The large aperture non-distortion fixed-focus objective optical system according to claim 5, characterized in that: The curvature radius of the image side of the fifth lens is 15.0mm, the surface interval is 0.79mm, and the effective aperture is 12.4mm.

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