Large aperture distortion-free fixed-focus objective optical system

Abstract

The present invention belongs to the technical field of objective optical systems and provides a large-aperture, non-distortion, fixed-focus objective optical system adapted for a 1-inch low-light-level CMOS or CCD image plane. The system comprises a first lens group, an aperture, and a second lens group, arranged in sequence. The first lens group comprises a first lens, a second lens, and a third lens; and the second lens group comprises a fourth lens, a fifth lens, a sixth lens, and a seventh lens. The optical specifications achieved by the system are: a wavelength band of 480nm to 1000nm, a maximum distortion of no more than 0.5%, a pixel size of 800px × 600px, and a field of view of 35.5° × 27°. The present invention aims to address the problem of existing large-aperture objective optical systems, which suffers from large distortion indexes that cause image distortion and poor overall imaging quality. The system features high resolution, a large relative aperture, and a wide wavelength band design, achieving day and night confocality, and excellent imaging quality in extreme environments.

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] Optical instruments are increasingly being used in both military and civilian applications. Applications such as geographic surveying and mapping, architectural photography, and other specialized applications require the use of distortion-free low-light-level objectives. Existing large-aperture objective optical systems rarely consider distortion when designing. This is particularly true for objectives with a wide field of view (e.g., full field of view ≥ 40°), where distortion is often significant, resulting in distorted images. This results in significant recognition errors when used in measuring instruments, reducing the accuracy of the results.

[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 distortion index of the existing large-aperture objective optical system is large, which causes the image to be deformed 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-level CMOS or CCD image plane;

[0006] The optical system includes a first lens group, an aperture, 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 aperture is coplanar with the object side surface of 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] Furthermore, 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 along the optical axis from the object side to the image side;

[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, with a convex object side and a convex image side;

[0012] The fourth lens is a glass spherical lens with positive refractive power, with its object side being convex and its image side being 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 concave;

[0014] The sixth lens is a glass spherical lens with positive refractive power, with its object side being convex and its image side being 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] 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 satisfies the following condition: 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.

[0017] Furthermore, the optical system composed 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 A3; Φ A3 represents 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 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 relationship: Nd≥1.9, Vd≥30, and 33mm <f A1 <34mm, f A1 is the focal length of the first lens; the second lens satisfies the relationship: Nd ≥ 1.75, Vd ≥ 20, and -21mm <f A2 <-20mm, f A2 is the focal length of the second lens; the third lens satisfies the relationship: Nd≥1.9, Vd≥30, and 27mm <f A3 <28mm, f A3 is the focal length of the third lens; the fourth lens satisfies the relationship: Nd≥1.9, Vd≥30, and 16mm <f C1 <17mm, f C1 is the focal length of the fourth lens; the fifth lens satisfies the relationship: Nd ≥ 1.9, Vd ≤ 20, and -12mm <f C2 <-11mm, f C2 is the focal length of the fifth lens; the sixth lens satisfies the relationship: Nd≥2.0, Vd≥25, and 12mm <f C3 <13mm, f C3 is the focal length of the sixth lens; the seventh lens satisfies the relationship: Nd≥1.60, Vd≥30, and -18mm <f C4 <-17mm, f C4 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 23.2 mm, the surface spacing is 4.17 mm, and the effective aperture is set to 22.5 mm; the curvature radius of the image side is 86.1 mm, the surface spacing is 4.06, and the effective aperture is 21.2 mm.

[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 -37.7 mm, the surface spacing is 2.25 mm, and the effective aperture is 18.7 mm; the curvature radius of its image side is 30.3 mm, the surface spacing is 2.48, and the effective aperture is 17.3 mm.

[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 76.2 mm, the surface spacing is 4.78 mm, and the effective aperture is 17.6 mm; the curvature radius of its image side is -39.0 mm, the surface spacing is 0.23, and the effective aperture is 17.8 mm.

[0022] Furthermore, the glass refractive index Nd of the object side surface 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 surface 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 element is 2.0, and the glass Abbe number Vd is 25.5; its 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 element 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] Furthermore, 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 solutions of the present invention, the optical system of the present invention has high resolution, adopts a large relative aperture and a wide-band design, achieves 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 focal length 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 light on each mirror 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 in different drawings indicate the same or similar components or parts; and the drawings of the present invention are not necessarily drawn to scale.

[0030] In the attached figure:

[0031] Figure 1 is a schematic structural diagram 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 that these embodiments are intended to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Based on the embodiments provided by the present invention, all other embodiments obtained by those skilled in the art without creative effort should still fall within the scope of protection of the present invention.

[0041] It should be noted that in the description of the present invention, terms such as "center," "upper," "lower," "top," "bottom," "left," "right," "vertical," "horizontal," "inner," and "outer" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. These are merely for ease of description and do not indicate or imply that the device or element described must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed 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 structural diagram 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 closely related (directly or indirectly related) to the technical problem and / or technical concept to be solved by the present invention, and does not describe the technical features that are less closely related to the technical problem and / or technical concept to be solved by the invention. Since such technical features with a lesser degree of relevance are common knowledge in the field, even if the present invention does not describe such features with a lesser degree of relevance, it will not result in insufficient disclosure of the present invention.

[0045] like Figure 1 As shown, in some embodiments of the present invention, a large-aperture, distortion-free, fixed-focus objective optical system 100 is provided. Optical system 100 includes a first lens group A, an aperture B, and a second lens group C, with aperture B disposed between first lens group A and second lens group C. First lens group A includes a first lens A1, a second lens A2, and a third lens A3, and second lens group C includes a fourth lens C1, a fifth lens C2, a sixth lens C3, and a seventh lens C4. Optical system 100 of the present invention is compatible with a 1-inch low-light-level CMOS or CCD image plane. Optical system 100 achieves the following optical specifications: a wavelength band of 480 nm to 1000 nm, 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, its object side and image side surfaces are convex. The second lens A2 is a glass spherical lens with negative focal power, its object side and image side surfaces are concave and convex. The third lens A3 is a glass spherical lens with positive focal power, its object side and image side surfaces are convex and concave. The aperture B is coplanar with the object side surface of the fourth lens C1. The fourth lens C1 is a glass spherical lens with positive focal power, and its image side surface is convex. The fifth lens C2 is a glass spherical lens with negative focal power. The fourth and fifth lenses C1 and C2 are bonded together with photosensitive adhesive, and the image side surface of the fifth lens C2 is convex. The sixth lens C3 is a glass spherical lens with positive focal power, its object side and image side surfaces are concave and concave. The seventh lens C4 is a glass spherical lens with positive focal power, its object side and image side surfaces are convex and flat.

[0048] The optical system 100 consisting 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, where 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; Φ A1 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 fC4 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 following relationship: Nd≥1.9, Vd≥30, and 33mm <f A1 <34mm, f A1 is the focal length of the first lens A1.

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

[0060] The third lens A3 satisfies the following relationship: Nd≥1.9, Vd≥30, and 27mm <f A3 <28mm, f A3 is the focal length of the third lens A3.

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

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

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

[0064] The seventh lens C4 satisfies the relationship: Nd ≥ 1.60, Vd ≥ 30, and -18mm <f C4 <-17mm, f C4 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, Figure 1As 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 B is set on 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; and surface S13 is the image-side surface of the seventh lens C4.

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

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

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

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

[0072] The radius of curvature 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 element C3 is 2.0, and its Abbe number Vd is 25.5. The radius of curvature of the object-side surface S10 of the sixth lens element C3 is 26.3mm, the surface separation is 7.66mm, and the effective aperture is 12.6mm. The radius of curvature of the image-side surface S11 is -20.8mm, the surface separation is 0.52mm, and the effective aperture is 13.5mm.

[0074] The refractive index Nd of the glass of the seventh lens element C4 is 1.78, and the Abbe number Vd is 25.7. The radius of curvature of the object-side surface S12 of the seventh lens element C4 is -15.5mm, the surface separation is 2.03mm, and the effective aperture is 13.5mm. The radius of curvature of the image-side surface S13 of the seventh lens element C4 is 148.4mm, the surface separation 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 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, and the second lens A2, the fifth lens C2 and the seventh lens C4 are all made of flint glass.

[0077] Those skilled in the art will appreciate that the present invention achieves parfocality day and night by complementing the aberrations of the first lens group A and the second lens group C, complementing the correction of spherical and chromatic aberrations by the cemented lens in the second lens group C, and rationally calculating the focal power of each lens to ensure focal plane offset at both high and low temperatures. This achieves high-definition imaging at an ultra-low cost, with a relatively large aperture and zero distortion. High-definition image quality is achieved during the day, while also maintaining high-definition image quality at night or in low-light conditions. Furthermore, the camera remains usable in environments with varying temperatures.

[0078] The entire lens ensures a balanced distribution of refractive index and focal power, ensuring balanced angles of incidence between the front and rear lens elements to avoid sensitive aberrations and reduce assembly and adjustment difficulties. By rationally allocating the focal lengths of each lens element, the imaging system's spherical aberration and field curvature are minimized, ensuring high image quality both on-axis and off-axis. This effectively addresses the problem of high distortion and poor imaging performance in existing large-aperture objective optical systems.

[0079] So far, the technical solutions of the present invention have been described in conjunction with the above multiple embodiments. However, it is easy for those skilled in the art to understand that the scope of protection 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 may split and combine the technical solutions in the above various embodiments, and may 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 scope of protection of the present invention.

Claims

1. A large aperture, non-distortion, fixed-focus objective optical system, characterized in that: The optical system is suitable for an image plane size of 1-inch low-light CMOS or CCD; The optical system comprises a first lens group, an aperture, and a second lens group, which are arranged in sequence from the object side to the image side along the optical axis; 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 object side surface of the fourth lens; The optical indicators achieved by the optical system are: wavelength band 480nm to 1000nm, maximum distortion no more than 0.5%, pixel size 800px×600px, and field of view range 35.5°×27°; 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; 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; The third lens is a glass spherical lens with positive refractive power, with a convex object side and a convex image side; The fourth lens is a glass spherical lens with positive refractive power, with its object side being convex and its image side being convex; 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 concave; The sixth lens is a glass spherical lens with positive refractive power, with its object side being convex and its image side being convex; 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; The optical system consisting of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens further 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 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 A3; Φ A3 represents 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 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≥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; 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.

2. The large-aperture, non-distortion, fixed-focus objective optical system according to claim 1, wherein: 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 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.

3. The large-aperture, non-distortion, fixed-focus objective optical system according to claim 1, wherein: The first lens satisfies the relationship: Nd≥1.9, Vd≥30, and 33mm <f A1 <34mm, f A1 is the focal length of the first lens; The second lens satisfies the relationship: Nd≥1.75, Vd≥20, and -21mm <f A2 <-20mm, f A2 is the focal length of the second lens; The third lens satisfies the relationship: Nd≥1.9, Vd≥30, and 27mm <f A3 <28mm, f A3 is the focal length of the third lens; The fourth lens satisfies the relationship: Nd≥1.9, Vd≥30, and 16mm <f C1 <17mm, f C1 is the focal length of the fourth lens; The fifth lens satisfies the relationship: Nd≥1.9, Vd≤20, and -12mm <f C2 <-11mm, f C2 is the focal length of the fifth lens; The sixth lens satisfies the relationship: Nd≥2.0, Vd≥25, and 12mm <f C3 <13mm, f C3 is the focal length of the sixth lens; The seventh lens satisfies the relationship: Nd≥1.60, Vd≥30, and -18mm <f C4 <-17mm, f C4 is the focal length of the seventh lens.

4. The large-aperture, non-distortion, fixed-focus objective optical system according to claim 3, wherein: 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 23.2 mm, the surface spacing is 4.17 mm, and the effective aperture is set to 22.5 mm; the curvature radius of the image side is 86.1 mm, the surface spacing is 4.06, and the effective aperture is 21.2 mm.

5. The large-aperture, non-distortion, fixed-focus objective optical system according to claim 3, wherein: 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 -37.7 mm, the surface spacing is 2.25 mm, and the effective aperture is 18.7 mm; the curvature radius of its image side is 30.3 mm, the surface spacing is 2.48, and the effective aperture is 17.3 mm.

6. The large-aperture, non-distortion, fixed-focus objective optical system according to claim 3, wherein: 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 76.2 mm, the surface spacing is 4.78 mm, and the effective aperture is 17.6 mm; the curvature radius of its image side is -39.0 mm, the surface spacing is 0.23, and the effective aperture is 17.8 mm.

7. The large-aperture, non-distortion, fixed-focus objective optical system according to claim 3, wherein: 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 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.

8. The large-aperture, non-distortion, fixed-focus objective optical system according to claim 3, wherein: The curvature radius of the image side surface of the fifth lens is 15.0 mm, the surface spacing is 0.79 mm, and the effective aperture is 12.4 mm.

9. The large-aperture, non-distortion, fixed-focus objective optical system according to claim 3, wherein: The glass refractive index Nd of the sixth lens element is 2.0, and the glass Abbe number Vd is 25.

5. The object side surface has a curvature radius of 26.3 mm, a surface spacing of 7.66 mm, and an effective aperture of 12.6 mm. The image side surface has a curvature radius of -20.8 mm, a surface spacing of 0.52 mm, and an effective aperture of 13.5 mm.

10. The large-aperture, non-distortion, fixed-focus objective optical system according to claim 3, wherein: The glass refractive index Nd of the seventh lens element is 1.78, and the glass Abbe number Vd is 25.

7. The object side surface has a curvature radius of -15.5 mm, a surface spacing of 2.03 mm, and an effective aperture of 13.5 mm. The image side surface has a curvature radius of 148.4 mm, a surface spacing of 3.22 mm, and an effective aperture of 14.8 mm.

11. The large-aperture, non-distortion, fixed-focus objective optical system according to claim 1, wherein: 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.

12. The large-aperture, non-distortion, fixed-focus objective optical system according to claim 11, wherein: The first lens, the third lens, the fourth lens and the sixth lens are all made of heavy lanthanum flint glass; and The second lens, the fifth lens and the seventh lens are all made of flint glass.

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