A visible near-infrared optical system with small-stroke focusing

Abstract

The present invention provides a visible-near-infrared optical system with a short-range focusing function. The system is suitable for wavelengths between 400 nm and 1100 nm and object distances from infinity to 50 mm. It can maintain a substantially unchanged focal length, achieve a short focusing range, effectively resolve chromatic aberration issues, and improve imaging quality to meet the needs of applications such as spectral analysis, high-precision imaging, and detection.

Description

Technical Field

[0001] The present invention relates to the technical field of optical lenses, and in particular to a visible near-infrared optical system with a small-stroke focusing form. Background Art

[0002] Current optical lens technology offers a variety of lens designs for different wavelength ranges and specific object distances. However, for applications with wavelengths between 400nm and 1100nm and object distances ranging from infinity to 50mm, traditional lenses have limitations. Existing lenses often cannot effectively focus light of different wavelengths simultaneously, resulting in chromatic aberration. This is particularly true in the short-wavelength (around 400nm) and long-wavelength (around 1100nm) regions, where chromatic aberration leads to image blur, compromising image quality and subsequent analysis. While internal focus lenses have addressed some of these focusing issues, existing technology remains insufficient for maintaining a nearly constant focal length and a short focusing stroke within this specific wavelength range and object distance. Existing lenses struggle to maintain a nearly constant focal length as the object distance varies from infinity to 50mm. This results in an unstable imaging plane during close-range photography or observation, degrading image quality and failing to meet the demands of high-precision observation. To achieve focusing within a variable object distance range, some lenses are designed with a long focusing stroke. This not only complicates the lens structure and increases its size, but also makes it unsuitable for space-critical applications and increases the difficulty of lens manufacturing and assembly. Therefore, by combining existing focusing technologies and material selection, developing a visible-near-infrared optical system with a narrow focusing stroke is of great practical significance. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a visible near-infrared optical system with a small-stroke focusing form.

[0004] The technical solution adopted by the present invention is as follows: a visible near-infrared optical system with a small-stroke internal focus, which is provided with a front fixed lens group, a front movable lens group, an intermediate fixed lens group, a rear compensating lens group, a rear fixed lens group and an aperture in sequence from the object plane to the image plane.

[0005] The front fixed lens group includes:

[0006] The first lens has positive refractive power, and both the object-side surface and the image-side surface are convex;

[0007] a second lens having negative optical power, a convex object-side surface and a concave image-side surface;

[0008] The front movable lens group comprises:

[0009] The third lens has positive optical power, with a concave object-side surface and a convex image-side surface;

[0010] The fourth lens element has negative optical power, a concave object-side surface and a convex image-side surface;

[0011] The intermediate fixed lens group includes:

[0012] The fifth lens has positive optical power and its object-side and image-side surfaces are both convex;

[0013] The rear compensation lens group includes:

[0014] a sixth lens element having negative optical power, a convex object-side surface and a concave image-side surface;

[0015] The seventh lens element has positive optical power, and both the object-side surface and the image-side surface are convex;

[0016] The eighth lens has positive optical power, and both the object-side surface and the image-side surface are convex;

[0017] The rear fixed lens group comprises:

[0018] The ninth lens element has negative optical power, and its object-side surface is concave and its image-side surface is convex.

[0019] Preferably, the front movable lens group and the rear compensation lens group are movable groups.

[0020] During the focusing process, the air gap D1 between the front fixed lens group and the front movable lens group varies in the range of 3.9mm≤D1≤5.6mm, and the air gap D2 between the front movable lens group and the middle fixed lens group varies in the range of 0.3mm≤D2≤2.0mm.

[0021] The air gap D3 between the intermediate fixed lens group and the rear compensation lens group varies in a range of 3.5 mm ≤ D3 ≤ 4.6 mm, and the air gap D4 between the rear compensation lens group and the rear fixed lens group varies in a range of 1.4 mm ≤ D4 ≤ 2.5 mm.

[0022] Preferably, in the front fixed lens group, the air gap between the first lens and the second lens is 0.7-0.8 mm.

[0023] In the front moving lens group, the air gap between the third lens and the fourth lens is 1.6-1.8mm.

[0024] In the rear compensation lens group, the air gap between the sixth lens and the seventh lens is 0.7-0.8 mm, and the air gap between the seventh lens and the eighth lens is 0.2-0.4 mm.

[0025] The air gap between the rear fixed lens group and the aperture is 11.5-12.0 mm.

[0026] Preferably, the curvature radius R1 of the object side surface of the first lens satisfies 355mm≤R1≤405mm, and the curvature radius R2 of the image side surface of the first lens satisfies -45mm≤R2≤-35mm;

[0027] The curvature radius R3 of the object side surface of the second lens satisfies 55mm≤R3≤65mm, and the curvature radius R4 of the image side surface of the second lens satisfies 5mm≤R4≤15mm;

[0028] The curvature radius R5 of the object side of the third lens satisfies -25mm≤R5≤-15mm, and the curvature radius R6 of the image side of the third lens satisfies -20mm≤R6≤-10mm;

[0029] The curvature radius R7 of the object side surface of the fourth lens satisfies -15 mm ≤ R7 ≤ -5 mm, and the curvature radius R8 of the image side surface of the fourth lens satisfies -20 mm ≤ R8 ≤ -10 mm;

[0030] The curvature radius R9 of the object side surface of the fifth lens satisfies 15 mm ≤ R9 ≤ 25 mm, and the curvature radius R10 of the image side surface of the fifth lens satisfies -25 mm ≤ R10 ≤ -15 mm;

[0031] The curvature radius R11 of the object side surface of the sixth lens element satisfies 30 mm ≤ R11 ≤ 40 mm, and the curvature radius R12 of the image side surface of the sixth lens element satisfies 5 mm ≤ R12 ≤ 15 mm;

[0032] The curvature radius R13 of the object side surface of the seventh lens element satisfies 5 mm ≤ R13 ≤ 15 mm, and the curvature radius R14 of the image side surface of the seventh lens element satisfies -45 mm ≤ R14 ≤ -35 mm;

[0033] The curvature radius R15 of the object side surface of the eighth lens element satisfies 35 mm ≤ R15 ≤ 45 mm, and the curvature radius R16 of the image side surface of the eighth lens element satisfies -15 mm ≤ R16 ≤ -5 mm;

[0034] The curvature radius R17 of the object side surface of the ninth lens element satisfies -15 mm ≤ R17 ≤ -5 mm, and the curvature radius R18 of the image side surface of the ninth lens element satisfies -15 mm ≤ R18 ≤ -5 mm.

[0035] Preferably, the center thickness of the first lens is 3-4 mm;

[0036] The center thickness of the second lens is 2-3mm;

[0037] The center thickness of the third lens is 3-5mm;

[0038] The center thickness of the fourth lens is 3-4mm;

[0039] The center thickness of the fifth lens is 2-4 mm;

[0040] The center thickness of the sixth lens is 1-2 mm;

[0041] The center thickness of the seventh lens is 2-3 mm;

[0042] The center thickness of the eighth lens is 1-3 mm;

[0043] The center thickness of the ninth lens is 1-2 mm.

[0044] Preferably, both the object-side surface and the image-side surface of the first lens are aspherical surfaces.

[0045] Preferably, the material of the first lens is HQK3L_CDGM.

[0046] Preferably, the object-side surface and the image-side surface of the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, and the ninth lens are all spherical surfaces.

[0047] Preferably, the Abbe coefficient of the first lens and the second lens is greater than 70.

[0048] The beneficial effects of the present invention are as follows:

[0049] 1. The present invention is applicable to wavelengths ranging from 400nm to 1100nm and object distances from infinity to 50mm. It can maintain a substantially unchanged focal length, achieve a short focusing stroke, effectively resolve chromatic aberration issues, and improve imaging quality to meet the needs of applications such as spectral analysis, high-precision imaging, and detection.

[0050] 2. To accommodate a wide wavelength range, the front fixed lens group utilizes special optical materials and an aspheric design. This design utilizes materials with high Abbe numbers (greater than 70; generally, an Abbe number above 50 is considered high. Common optical glass materials typically have an Abbe number between 30 and 60, with materials with an Abbe number above 50 exhibiting relatively low dispersion and superior imaging quality) and low dispersion to minimize chromatic aberration of both short and long wavelengths. The aspheric shape helps correct spherical aberration and improve light convergence efficiency.

[0051] 3. The front movable lens group and the rear compensating lens group are key components in achieving the internal focusing function. By adopting a movable lens unit design, it moves on high-precision rails within the lens barrel. The material and curvature design of the front movable lens group and the rear compensating lens group have been optimized to effectively compensate for the differences in light propagation caused by changes in object distance when moving within a small range, while maintaining a relatively constant focal length.

[0052] 4. The rear fixed lens is responsible for accurately focusing the light adjusted by the front moving lens group and the rear compensating lens group onto the imaging plane. Its design takes into account the light propagation characteristics of the entire wavelength range, ensuring clear images within the 400nm - 1100nm range.

[0053] 5. The post-aperture system allows light to pass through the front lens group and then be filtered by the aperture, allowing light rays of different heights to be better converged on the image plane. This post-aperture design optimizes the light propagation path, allowing the image across the entire field of view to be more flattened on the detector plane, reducing blur at the edges of the field of view, making distant images clearer and more symmetrical, and improving image clarity. The post-aperture system can rationally select the range of the light beam entering the system based on parameters such as detector size and the focal length of the optical system, preventing excessive stray light from entering the system and thus improving the utilization of light energy on the detector. In the visible and near-infrared bands, the refractive index of some optical materials changes with temperature, affecting the performance of the optical system. The post-aperture system can reduce this effect to a certain extent by making the light propagation path of the optical system relatively more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, other drawings obtained based on these drawings still fall within the scope of the present invention.

[0055] Figure 1 is a schematic diagram of the optical system of the present invention when it is at infinite object distance;

[0056] Figure 2 Schematic diagram of the optical system of the present invention when it is at an object distance of 50 mm;

[0057] Figure 3 The figure shows a transfer function curve diagram of the system of this embodiment when the object distance is infinite;

[0058] Figure 4 The figure shows the transfer function curve of the system of this embodiment at an object distance of 50mm;

[0059] Figure 5 FIG2 is a schematic diagram of field curvature aberration of the system of this embodiment at infinite object distance;

[0060] Figure 6 FIG2 is a schematic diagram of field curvature aberration of the system of this embodiment at an object distance of 50 mm;

[0061] In the figure, 1-first lens, 2-second lens, 3-third lens, 4-fourth lens, 5-fifth lens, 6-sixth lens, 7-seventh lens, 8-eighth lens, 9-ninth lens, 10-aperture stop. DETAILED DESCRIPTION

[0062] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0063] like Figure 1-2 The figure shows a visible near-infrared optical system with a small-stroke internal focusing mode. From the object plane to the image plane, a front fixed lens group, a front movable lens group, an intermediate fixed lens group, a rear compensating lens group, a rear fixed lens group, and a stop 10 are sequentially arranged.

[0064] The front fixed lens group includes:

[0065] A first lens 1 having positive refractive power, wherein both the object-side surface and the image-side surface are convex;

[0066] The second lens 2 has a negative optical power, a convex object-side surface and a concave image-side surface;

[0067] The front movable lens group comprises:

[0068] The third lens element 3 has positive refractive power, a concave object-side surface and a convex image-side surface;

[0069] The fourth lens element 4 has a negative optical power, a concave object-side surface, and a convex image-side surface;

[0070] The intermediate fixed lens group includes:

[0071] The fifth lens element 5 has positive refractive power, and both the object-side surface and the image-side surface are convex;

[0072] The rear compensation lens group includes:

[0073] The sixth lens element 6 has a negative optical power, and its object-side surface is convex and its image-side surface is concave;

[0074] The seventh lens element 7 has positive refractive power, and both the object-side surface and the image-side surface are convex;

[0075] The eighth lens element 8 has positive refractive power, and both the object-side surface and the image-side surface are convex;

[0076] The rear fixed lens group comprises:

[0077] The ninth lens element 9 has negative optical power, and its object-side surface is concave and its image-side surface is convex.

[0078] The front movable lens group and the rear compensation lens group are movable groups.

[0079] During the focusing process, the air gap D1 between the front fixed lens group and the front movable lens group varies in the range of 3.9mm≤D1≤5.6mm, and the air gap D2 between the front movable lens group and the middle fixed lens group varies in the range of 0.3mm≤D2≤2.0mm.

[0080] The air gap D3 between the intermediate fixed lens group and the rear compensation lens group varies in a range of 3.5 mm ≤ D3 ≤ 4.6 mm, and the air gap D4 between the rear compensation lens group and the rear fixed lens group varies in a range of 1.4 mm ≤ D4 ≤ 2.5 mm.

[0081] In the front fixed lens group, the air gap between the first lens 1 and the second lens 2 is 0.7-0.8 mm.

[0082] In the front moving lens group, the air gap between the third lens 3 and the fourth lens 4 is 1.6-1.8 mm.

[0083] In the rear compensation lens group, the air gap between the sixth lens 6 and the seventh lens 7 is 0.7-0.8 mm, and the air gap between the seventh lens 7 and the eighth lens 8 is 0.2-0.4 mm.

[0084] The air gap between the rear fixed lens group and the aperture 10 is 11.5-12.0 mm.

[0085] The curvature radius R1 of the object side surface of the first lens 1 satisfies 355 mm ≤ R1 ≤ 405 mm, and the curvature radius R2 of the image side surface of the first lens 1 satisfies -45 mm ≤ R2 ≤ -35 mm;

[0086] The curvature radius R3 of the object side surface of the second lens 2 satisfies 55 mm ≤ R3 ≤ 65 mm, and the curvature radius R4 of the image side surface of the second lens 2 satisfies 5 mm ≤ R4 ≤ 15 mm;

[0087] The curvature radius R5 of the object side surface of the third lens 3 satisfies -25mm≤R5≤-15mm, and the curvature radius R6 of the image side surface of the third lens 3 satisfies -20mm≤R6≤-10mm;

[0088] The curvature radius R7 of the object side surface of the fourth lens 4 satisfies -15 mm ≤ R7 ≤ -5 mm, and the curvature radius R8 of the image side surface of the fourth lens 4 satisfies -20 mm ≤ R8 ≤ -10 mm;

[0089] The curvature radius R9 of the object side surface of the fifth lens 5 satisfies 15 mm ≤ R9 ≤ 25 mm, and the curvature radius R10 of the image side surface of the fifth lens 5 satisfies -25 mm ≤ R10 ≤ -15 mm;

[0090] The curvature radius R11 of the object-side surface of the sixth lens 6 satisfies 30 mm ≤ R11 ≤ 40 mm, and the curvature radius R12 of the image-side surface of the sixth lens 6 satisfies 5 mm ≤ R12 ≤ 15 mm;

[0091] The curvature radius R13 of the object-side surface of the seventh lens 7 satisfies 5 mm ≤ R13 ≤ 15 mm, and the curvature radius R14 of the image-side surface of the seventh lens 7 satisfies -45 mm ≤ R14 ≤ -35 mm.

[0092] The curvature radius R15 of the object side surface of the eighth lens 8 satisfies 35 mm ≤ R15 ≤ 45 mm, and the curvature radius R16 of the image side surface of the eighth lens 8 satisfies -15 mm ≤ R16 ≤ -5 mm;

[0093] The curvature radius R17 of the object-side surface of the ninth lens 9 satisfies -15 mm ≤ R17 ≤ -5 mm, and the curvature radius R18 of the image-side surface of the ninth lens 9 satisfies -15 mm ≤ R18 ≤ -5 mm.

[0094] The center thickness of the first lens 1 is 3-4 mm;

[0095] The center thickness of the second lens 2 is 2-3 mm;

[0096] The center thickness of the third lens 3 is 3-5 mm;

[0097] The center thickness of the fourth lens 4 is 3-4 mm;

[0098] The center thickness of the fifth lens 5 is 2-4 mm;

[0099] The center thickness of the sixth lens 6 is 1-2 mm;

[0100] The center thickness of the seventh lens 7 is 2-3 mm;

[0101] The center thickness of the eighth lens 8 is 1-3 mm;

[0102] The center thickness of the ninth lens 9 is 1-2 mm.

[0103] The object-side surface and the image-side surface of the first lens 1 are both aspherical surfaces.

[0104] The material of the first lens 1 is HQK3L_CDGM.

[0105] The object-side surfaces and image-side surfaces of the second lens 2 , the third lens 3 , the fourth lens 4 , the fifth lens 5 , the sixth lens 6 , the seventh lens 7 , the eighth lens 8 , and the ninth lens 9 are all spherical surfaces.

[0106] The Abbe coefficients of the first lens 1 and the second lens 2 are greater than 70.

[0107] Example 1

[0108] This embodiment provides a visible near-infrared optical system with a small range of focus. The system parameters are as follows:

[0109] Image-side F-number: 4; field of view: 48.6°-53.5°; operating wavelength: 400nm-1100nm, achieving high-definition imaging through internal focusing; total optical length: 50mm; resolution: 1920×1080, 3.45μm pixel, compatible with high-definition detectors.

[0110] Table 1 below shows the parameters of each optical element in this embodiment:

[0111] Table 1 Parameters of optical components in Example 1

[0112]

[0113] The focus interval changes of the optical system of this embodiment are shown in Table 2 below:

[0114] Table 2 Focus interval change table of Example 1

[0115]

[0116] The aspheric coefficients of the first lens in the optical system of this embodiment are shown in Table 3 below:

[0117] Table 3 Aspheric coefficients of the first lens in Example 1

[0118]

[0119] Among them, surface 1 and surface 2 in the above table may represent the object plane side and the image plane side of the first lens, surface 3 and surface 4 may represent the object plane side and the image plane side of the second lens, surface 5 and surface 6 may represent the object plane side and the image plane side of the third lens, surface 7 and surface 8 may represent the object plane side and the image plane side of the fourth lens, surface 9 and surface 10 may represent the object plane side and the image plane side of the fifth lens, surface 11 and surface 12 may represent the object plane side and the image plane side of the sixth lens, surface 13 and surface 14 may represent the object plane side and the image plane side of the seventh lens, surface 15 and surface 16 may represent the object plane side and the image plane side of the eighth lens, and surface 17 and surface 18 may represent the object plane side and the image plane side of the ninth lens.

[0120] The thickness of surface 1 can represent the center thickness of the first lens, and the thickness of surface 2 can represent the vertical distance between the side of the first lens close to the image plane and the side of the second lens close to the object plane. The same applies to surfaces 3-18.

[0121] like Figure 3-4 Figures 2 and 3 show transfer function curves for the system of this embodiment at infinite and 50mm object distances, respectively. The MTF curves represent the overall resolution of an optical system. This system operates in the visible and near-infrared bands. After balancing performance and aberrations at different object distances, the four-way MTF is greater than 0.6 at 36 Lp / mm, and the two-way MTF is greater than 0.3 at 72 Lp / mm, resulting in high resolution.

[0122] like Figure 5-6 Figures 2 and 3 show schematic diagrams of the field curvature aberration of the system of this embodiment at infinite object distance and 50mm object distance, respectively. The figures indicate that both axial chromatic aberration and astigmatism field curvature are within ±0.05mm, and distortion is within -2%. The aberrations are well corrected, which is conducive to high-quality imaging.

[0123] The above disclosure is merely a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A visible near-infrared optical system with a small-stroke focusing mode, characterized by: A front fixed lens group, a front movable lens group, an intermediate fixed lens group, a rear compensation lens group, a rear fixed lens group and a stop (10) are sequentially arranged from the object plane to the image plane. The front fixed lens group is composed of a first lens (1) and a second lens (2) in sequence from the object plane to the image plane. The first lens (1) has positive optical power, and both the object side surface and the image side surface are convex; The second lens (2) has a negative optical power, a convex object side surface, and a concave image side surface; The front movable lens group is composed of a third lens (3) and a fourth lens (4) in sequence from the object plane to the image plane. The third lens (3) has positive optical power, the object side surface is concave, and the image side surface is convex; The fourth lens (4) has a negative optical power, a concave object side surface, and a convex image side surface; The intermediate fixed lens group consists of a fifth lens (5), The fifth lens (5) has positive optical power, and both the object side surface and the image side surface are convex; The rear compensation lens group is composed of a sixth lens (6), a seventh lens (7), and an eighth lens (8) in sequence from the object plane to the image plane. The sixth lens (6) has a negative optical power, a convex object side surface, and a concave image side surface; The seventh lens (7) has positive optical power, and both the object side surface and the image side surface are convex; The eighth lens (8) has positive optical power, and both the object side surface and the image side surface are convex; The rear fixed lens group is composed of a ninth lens (9), The ninth lens (9) has a negative optical power, a concave object side surface, and a convex image side surface; The curvature radius R1 of the object side surface of the first lens (1) satisfies 355 mm ≤ R1 ≤ 405 mm, and the curvature radius R2 of the image side surface of the first lens (1) satisfies -45 mm ≤ R2 ≤ -35 mm; The curvature radius R3 of the object side surface of the second lens (2) satisfies 55 mm ≤ R3 ≤ 65 mm, and the curvature radius R4 of the image side surface of the second lens (2) satisfies 5 mm ≤ R4 ≤ 15 mm; The curvature radius R5 of the object side surface of the third lens (3) satisfies -25mm≤R5≤-15mm, and the curvature radius R6 of the image side surface of the third lens (3) satisfies -20mm≤R6≤-10mm; The curvature radius R7 of the object side surface of the fourth lens (4) satisfies -15mm≤R7≤-5mm, and the curvature radius R8 of the image side surface of the fourth lens (4) satisfies -20mm≤R8≤-10mm; The curvature radius R9 of the object side surface of the fifth lens (5) satisfies 15 mm ≤ R9 ≤ 25 mm, and the curvature radius R10 of the image side surface of the fifth lens (5) satisfies -25 mm ≤ R10 ≤ -15 mm; The curvature radius R11 of the object side surface of the sixth lens (6) satisfies 30 mm ≤ R11 ≤ 40 mm, and the curvature radius R12 of the image side surface of the sixth lens (6) satisfies 5 mm ≤ R12 ≤ 15 mm; The curvature radius R13 of the object side surface of the seventh lens (7) satisfies 5 mm ≤ R13 ≤ 15 mm, and the curvature radius R14 of the image side surface of the seventh lens (7) satisfies -45 mm ≤ R14 ≤ -35 mm; The curvature radius R15 of the object side surface of the eighth lens (8) satisfies 35 mm ≤ R15 ≤ 45 mm, and the curvature radius R16 of the image side surface of the eighth lens (8) satisfies -15 mm ≤ R16 ≤ -5 mm; The curvature radius R17 of the object side surface of the ninth lens (9) satisfies -15 mm ≤ R17 ≤ -5 mm, and the curvature radius R18 of the image side surface of the ninth lens (9) satisfies -15 mm ≤ R18 ≤ -5 mm.

2. The visible-near-infrared optical system with a small-stroke focusing mode according to claim 1, characterized in that: The front movable lens group and the rear compensation lens group are movable groups. During the focusing process, the air gap D1 between the front fixed lens group and the front movable lens group varies in the range of 3.9mm≤D1≤5.6mm, and the air gap D2 between the front movable lens group and the middle fixed lens group varies in the range of 0.3mm≤D2≤2.0mm. The air gap D3 between the intermediate fixed lens group and the rear compensation lens group varies in a range of 3.5 mm ≤ D3 ≤ 4.6 mm, and the air gap D4 between the rear compensation lens group and the rear fixed lens group varies in a range of 1.4 mm ≤ D4 ≤ 2.5 mm.

3. A visible near-infrared optical system with a short-range focusing function according to claim 1 or 2, characterized in that: In the front fixed lens group, the air gap between the first lens (1) and the second lens (2) is 0.7-0.8 mm. In the front moving lens group, the air gap between the third lens (3) and the fourth lens (4) is 1.6-1.8 mm. In the rear compensation lens group, the air gap between the sixth lens (6) and the seventh lens (7) is 0.7-0.8 mm, and the air gap between the seventh lens (7) and the eighth lens (8) is 0.2-0.4 mm. The air gap between the rear fixed lens group and the diaphragm (10) is 11.5-12.0 mm.

4. The visible-near-infrared optical system with a short-range focusing mode according to claim 1, characterized in that: The center thickness of the first lens (1) is 3-4 mm; The center thickness of the second lens (2) is 2-3 mm; The center thickness of the third lens (3) is 3-5 mm; The center thickness of the fourth lens (4) is 3-4 mm; The center thickness of the fifth lens (5) is 2-4 mm; The center thickness of the sixth lens (6) is 1-2 mm; The center thickness of the seventh lens (7) is 2-3 mm; The center thickness of the eighth lens (8) is 1-3 mm; The center thickness of the ninth lens (9) is 1-2 mm.

5. The visible-near-infrared optical system with a small-stroke focusing mode according to claim 1, characterized in that: The object side surface and the image side surface of the first lens (1) are both aspherical surfaces.

6. The visible-near-infrared optical system with a small-stroke focusing mode according to claim 1, characterized in that: The material of the first lens (1) is HQK3L_CDGM.

7. The visible-near-infrared optical system with a short-range focusing mode according to claim 1, characterized in that: The object side surfaces and image side surfaces of the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5), the sixth lens (6), the seventh lens (7), the eighth lens (8), and the ninth lens (9) are all spherical surfaces.

8. The visible-near-infrared optical system with a small-stroke focusing mode according to claim 1, characterized in that: The dispersion coefficients of the first lens (1) and the second lens (2) are greater than 70.

Images