An optical lens applicable to a vacuum environment

Abstract

The present invention discloses an optical lens applicable to a vacuum environment, which includes a lens group. The lens group is composed of a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens, and a sixth lens arranged in sequence from the object side to the image side. At least one of the first lens to the sixth lens is a doublet lens. The vacuum defocus amount d1 and the semi-focal depth d2 of the entire optical lens satisfy: |d1| < |d2|. Through the arrangement and combination of lenses with different optical powers and surface shapes, as well as the reasonable arrangement of the cemented lenses, while controlling the vacuum defocus amount of the optical lens to be less than the semi-focal depth of the optical lens, the influence brought by the change in the refractive index of the medium in the gap between the lenses after the optical lens enters the vacuum environment is reduced, and high resolution and low sensitivity of the optical lens imaging are achieved.

Description

Technical Field

[0001] The present invention relates to an optical lens, and in particular to an optical lens suitable for a vacuum environment. Background Art

[0002] Space cameras are based on aerospace vehicles and monitor ground and near-earth space targets. With the development of detection technology and the improvement of detection requirements, higher requirements are put forward for the optical lenses in space cameras:

[0003] 1) When the space camera lens works in a vacuum environment, the air layer between the lenses becomes a vacuum layer, the refractive index decreases, and the light path and the position of the best image plane will change. The Chinese invention patent application with the publication number CN116931259A provides a method for presetting the best image plane of a compensation lens by calculating the vacuum defocus amount, so that the best image plane, focal length and imaging quality of the compensated lens are all consistent with those in a vacuum environment, reducing the difficulty of lens vacuum performance image quality detection, but this method requires an additional compensation lens.

[0004] 2) Space cameras have requirements for volume and mass, so lightweight structural design of the lens is needed. The Chinese invention patent application with the publication number CN119200155A proposes a head-mounted low-light night vision optical system, which realizes an ultra-short optical back focal length of 1.1 mm through eight spherical lenses, controlling the miniaturization and lightweight of the optical system, but the imaging accuracy needs to be improved.

[0005] 3) After the space camera is assembled and tested on the ground under normal temperature and pressure, it works in a vacuum space environment. The environmental change causes an internal and external air pressure difference in the lens with a conventional structure, resulting in stress deformation of the lens and affecting the imaging quality of the lens. The Chinese invention patent application with the publication number CN113671659B proposes a structure with exhaust grooves provided on the inner side wall of the lens barrel and a plurality of exhaust holes provided on the exhaust grooves, enabling smooth air flow inside the lens and communicating with the outside to achieve the exhaust and ventilation functions; however, external light is likely to enter the lens through the exhaust holes, causing light pollution. The Chinese invention patent application with the publication number CN107861215B proposes a space transmission lens with a deflation structure, leaving square grooves on the internal pressure ring and the lens frame to connect the air inside the lens cavity, and opening a deflation hole in the middle of the lens barrel, reducing the risk of light pollution while realizing the deflation function; however, the structure of a single exhaust hole is not applicable to a multi-lens lens with multiple air gaps. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an optical lens suitable for a vacuum environment that can maintain consistent imaging performance in both vacuum and non-vacuum environments.

[0007] The technical solution adopted by the present invention to solve the above technical problems is as follows: An optical lens applicable to a vacuum environment, comprising a lens group. The lens group is composed of a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens, and a sixth lens arranged in sequence from the object side to the image side. The object side surface of the first lens is convex, and the image side surface is concave. The optical power of the second lens is negative, and the object side surface is concave. The optical power of the third lens is positive, and the object side surface is convex. The optical power of the fourth lens is positive, and the object side surface is convex. The fifth lens is a meniscus lens. The optical power of the sixth lens is negative. At least one of the first lens to the sixth lens is a doublet lens. The vacuum defocus amount d1 and the semi-focal depth d2 of the entire optical lens satisfy: |d1| < |d2|, where d1 = bfl1 - bfl2, d2 = 2λ(f / EPD). 2 , bfl1 is the distance from the image side surface of the sixth lens to the image plane of the optical lens in the non-vacuum state, bfl2 is the distance from the image side surface of the sixth lens to the image plane of the optical lens in the vacuum state, with the unit of mm. λ is the central wavelength, with the unit of um. f is the focal length of the optical lens, with the unit of mm, and satisfies: 4mm < f < 6mm. EPD is the entrance pupil diameter of the optical lens, with the unit of mm. The object distance U of the optical lens satisfies: U ≥ 10m. The total length TTL satisfies: 14mm < TTL < 18mm. The F number F# satisfies 2.5 < F# < 2.6.

[0008] Compared with the prior art, the advantages of the present invention are that through the arrangement and combination of lenses with different optical powers and surface shapes, and the reasonable arrangement of doublet lenses, while controlling the vacuum defocus amount of the entire optical lens to be less than the semi-focal depth of the entire optical lens, the influence brought by the change in the refractive index of the medium in the gap between the lenses after the optical lens enters the vacuum environment is reduced, thereby achieving high resolution and low sensitivity of the optical lens imaging.

[0009] Preferably, both the object side surface and the image side surface of the second lens are aspherical surfaces, and both the object side surface and the image side surface of the sixth lens are aspherical surfaces.

[0010] Preferably, the fourth lens is a doublet lens composed of a fifth singlet lens and a sixth singlet lens. The Abbe number Vd of the fifth singlet lens 05 , the Abbe number Vd of the sixth singlet lens 06 , the curvature radius R of the cemented surface between the fifth singlet lens and the sixth singlet lens 56 and the focal length f of the optical lens satisfy: 0.01 ≤ |(R 56 / (Vd 05 - Vd 06 )) / f| ≤ 0.07.

[0011] Preferably, the second lens is a doublet lens composed of a first singlet lens and a second singlet lens, and the Abbe number Vd of the first singlet lens 01 and the Abbe number Vd of the second singlet lens 02 satisfy: 18 ≤ |Vd 01 - Vd 02 | ≤ 22.

[0012] Preferably, the fifth lens is a doublet lens composed of a seventh singlet lens and an eighth singlet lens, and the Abbe number Vd of the seventh singlet lens 07 , the Abbe number Vd of the eighth singlet lens 08 , the radius of curvature R of the cemented surface between the seventh singlet lens and the eighth singlet lens 78 and the focal length f of the optical lens satisfy: 0.01 ≤ |(R 78 / (Vd 07 - Vd 08 )) / f| ≤ 0.07.

[0013] Preferably, the third lens is a doublet lens composed of a third singlet lens and a fourth singlet lens, and the Abbe number Vd of the third singlet lens 03 and the Abbe number Vd of the fourth singlet lens 04 satisfy: 18 ≤ |Vd 03 - Vd 04 | ≤ 22.

[0014] Preferably, the optical lens further includes a lens barrel for accommodating and mounting the lens group. An annular base is provided at the end of the lens barrel. A retaining ring is screwed to the open end of the lens barrel. The image side of the sixth lens abuts against the annular base. The retaining ring presses against the object side of the first lens. Spacer rings are provided between the respective lenses from the first lens to the sixth lens. An air vent groove is provided on the inner wall of the lens barrel. First air vent holes for communicating the gaps between the respective lenses with the air vent groove are provided on the spacer rings. Second air vent holes for communicating the outside with the air vent groove are provided on the retaining ring. The vacuum ventilation structure provided by the present invention: An air vent groove is provided on the inner wall of the lens barrel. First air vent holes for communicating the gaps between the respective lenses with the air vent groove are provided on the spacer rings. Second air vent holes for communicating the outside with the air vent groove are provided on the retaining ring. The gaps between the respective lenses communicate with each other, enabling smooth air flow inside the lens; realizing the ventilation function, enabling the lens to work normally in a vacuum; the ventilation work can be completed without drilling air holes on the lens barrel, and at the same time, light pollution is avoided.

[0015] Preferably, a third air vent hole for communicating the outside with the air vent groove is provided on the inner end face of the annular base.

[0016] Preferably, the materials of the lens barrel, the retaining ring, and the spacer are all titanium alloy. For the lens barrel, retaining ring, and spacer of this structure, titanium alloy is selected as the material without adding additional structures such as the frame, avoiding excessive lens volume and weight; achieving the effects of miniaturization and light weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the optical system of Example 1 of the present invention;

[0018] Figure 2 Graph of the transfer function of Example 1 of the present invention under non-vacuum conditions;

[0019] Figure 3 Graph of the transfer function of Example 1 of the present invention under vacuum conditions;

[0020] Figure 4 Schematic diagram of the optical system of Example 2 of the present invention;

[0021] Figure 5 Graph of the transfer function of Example 2 of the present invention under non-vacuum conditions;

[0022] Figure 6 Graph of the transfer function of Example 2 of the present invention under vacuum conditions;

[0023] Figure 7 Schematic diagram of the optical system of Example 3 of the present invention;

[0024] Figure 8 Graph of the transfer function of Example 3 of the present invention under non-vacuum conditions;

[0025] Figure 9 Graph of the transfer function of Example 3 of the present invention under vacuum conditions;

[0026] Figure 10 Schematic diagram of the optical system of Example 4 of the present invention;

[0027] Figure 11 Graph of the transfer function of Example 4 of the present invention under non-vacuum conditions;

[0028] Figure 12 Graph of the transfer function of Example 4 of the present invention under vacuum conditions;

[0029] Figure 13 Schematic diagram of the lens assembly structure of Example 2 of the present invention;

[0030] Figure 14 Schematic diagram of the lens barrel structure of Example 2 of the present invention;

[0031] Figure 15 Schematic diagram of the spacer structure of Example 1 of the present invention;

[0032] Figure 16 Schematic diagram of the retaining ring structure of Example 1 of the present invention;

[0033] Figure 17 Schematic diagram of the ventilation structure of Example 2 of the present invention.

[0034] Explanation of reference numerals:

[0035] 1, lens barrel; 11, annular base; 12, ventilation groove; 13, third ventilation through hole; 2, retaining ring; 21, second ventilation through hole; 3, spacer ring; 31, first ventilation through hole; L1, first lens; L2, second lens; L01, first singlet lens; L02, second singlet lens; L3, third lens; L03, third singlet lens; L04, fourth singlet lens; L4, fourth lens; L05, fifth singlet lens; L06, sixth singlet lens; L5, fifth lens; L07, seventh singlet lens; L08, eighth singlet lens; L6, sixth lens; STO, aperture stop; IMA, image plane. Detailed implementation manners

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0037] The exemplary embodiments of the present invention will be specifically illustrated below with reference to the accompanying drawings. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the protection scope of the present invention patent.

[0038] Example:

[0039] In the accompanying drawings, for the sake of clarity, the thickness, size and shape of the lenses have been slightly exaggerated. The accompanying drawings are only for illustration and are not drawn to an exact scale. The convexity and concavity of the lenses can be determined according to the vertex curvature radius of the lens surface. When the vertex curvature radius of the object side surface of the lens is greater than 0, this surface is a convex surface, and vice versa; when the vertex curvature radius of the image side surface of the lens is greater than 0, this surface is a concave surface, and vice versa.

[0040] The object of the present invention is to provide a lens that can maintain consistent imaging performance in both vacuum and non-vacuum environments without a compensation lens. Vacuum mainly refers to an ultra-high vacuum or high vacuum environment of 10 -8 Pa to 10 -2 Pa, and non-vacuum mainly refers to the ground environment under one standard atmosphere.

[0041] Such as Figure 13 and Figure 17As shown in the figure, an optical lens applicable to a vacuum environment includes a lens group and a lens barrel 1 for accommodating and mounting the lens group. An annular base 11 is provided at the end of the lens barrel 1. A retaining ring 2 is screwed to the open end of the lens barrel 1. The lens barrel 1 and the retaining ring 2 are made of titanium alloy. The lens group includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6. The image side of the sixth lens L6 abuts against the annular base 11, and the retaining ring 2 is pressed against the object side of the first lens L1. Spacer rings 3 are provided between the respective lenses from the first lens L1 to the sixth lens L6. The spacer rings 3 are made of titanium alloy, as Figure 14 shown, an air vent groove 12 is provided on the inner wall of the lens barrel 1, and a third air vent hole 13 for communicating the outside with the air vent groove 12 is provided on the inner end surface of the annular base 11, as Figure 15 shown, a first air vent hole 31 for communicating the gap between the respective lenses with the air vent groove 12 is provided on the spacer ring 3, as Figure 16 shown, a second air vent hole 21 for communicating the outside with the air vent groove 12 is provided on the retaining ring 2; for convenience of processing, both the first air vent hole 31 and the second air vent hole 21 adopt a half-hole structure.

[0042] The lens group of the present invention is as Figure 1 、 Figure 4 、 Figure 7 and Figure 10 shown. It can be seen that in the figure, from the object side to the image side in sequence are the first lens L1, the second lens L2, the third lens L3, the aperture stop STO, the fourth lens L4, the fifth lens L5, the sixth lens L6, and the image plane IMA. An imaging chip is placed on the image plane IMA to record the imaging picture. When the best focal plane of the optical lens coincides with the imaging chip, the imaging quality is better; otherwise, the imaging quality will be reduced.

[0043] After the optical lens enters the vacuum environment from the ground environment, the air medium in the gap between the lenses becomes vacuum, and the refractive index will change; at this time, the best focal plane of the optical lens moves, which will affect the imaging quality and interfere with the operation of the optical lens. According to the description of the performance changes of the lens in the vacuum and non-vacuum in paragraphs

[0065] to

[0071] of the specification of the Chinese invention patent with the patent publication number CN116931259A, in this example, the vacuum defocus amount of the entire optical lens is set as d1, and the half focal depth of the entire optical lens is set as d2, satisfying: |d1| < |d2|, where d1 = bfl1 - bfl2, d2 = 2λ(f / EPD) 2, bfl1 is the distance from the image side of the sixth lens L6 to the image plane IMA of the optical lens in a non-vacuum state, bfl2 is the distance from the image side of the sixth lens L6 to the image plane IMA of the optical lens in a vacuum state, with the unit of mm, λ is the central wavelength with the unit of um, f is the focal length of the optical lens with the unit of mm, and EPD is the entrance pupil diameter of the optical lens with the unit of mm.

[0044] It can be obtained from the above formula that when the optical system of the optical lens is designed and completed, if |d1| > |d2| and the imaging requirements in vacuum are not satisfied, the focal length f and the entrance pupil diameter EPD of the optical lens can be adjusted as needed, thereby changing the paraxial depth of focus d2 of the entire optical lens to satisfy the above formula.

[0045] The object distance U of the optical lens satisfies: U ≥ 10 m, enabling spatial imaging within a relatively long distance range; the wavelength range of the incident light is 486 - 656 nm, and the central wavelength λ = 588 nm; the focal length f of the optical lens satisfies: 4 mm < f < 6 mm; the overall length TTL of the optical lens satisfies: 14 mm < TTL < 18 mm; the F-number F# of the optical lens satisfies 2.5 < F# < 2.6.

[0046] There are four single lenses on the image side of the aperture STO, and at least one set of doublet lenses.

[0047] In a preferred embodiment, the fourth lens L4 is a doublet lens, including a fifth single lens L05 and a sixth single lens L06. The Abbe number Vd of the fifth single lens L05 05 , the Abbe number Vd of the sixth single lens L06 06 , the radius of curvature R of the cemented surface between the fifth single lens L05 and the sixth single lens L06 56 and the focal length f of the optical lens satisfy: 0.01 ≤ |R 56 / (Vd 05 - Vd 06 ) / f| ≤ 0.07. Controlling the formula not to exceed the lower limit can balance chromatic aberration at higher light levels and limit the length of the optical system, while controlling the formula not to exceed the upper limit can avoid overcorrection and limit the field of view of the optical system.

[0048] In the above preferred embodiment, there can be three single lenses on the object side of the aperture STO without doublet lenses, which can reduce material and processing costs and decrease the lens volume.

[0049] However, it can also be chosen to set four single lenses on the object side of the aperture STO, with at least one doublet lens, which can make the light path more stable, reduce the lens sensitivity, and improve the imaging quality.

[0050] Further, the second lens L2 is a doublet lens, including a first singlet lens L01 and a second singlet lens L02, and the Abbe number Vd of the first singlet lens L01 01 and the Abbe number Vd of the second singlet lens L02 02 satisfy: 18 ≤ |Vd 01 - Vd 02 | ≤ 22. Controlling the formula not to exceed the lower limit can balance chromatic aberration at higher light levels, and controlling the formula not to exceed the upper limit can avoid overcorrection.

[0051] In another preferred embodiment, the fifth lens L5 is a doublet lens, including a seventh singlet lens L07 and an eighth singlet lens L08, and the Abbe number Vd of the seventh singlet lens L07 07 , the Abbe number Vd of the eighth singlet lens L08 08 , the radius of curvature R of the cemented surface between the seventh singlet lens L07 and the eighth singlet lens L08 78 and the focal length f of the optical lens satisfy: 0.01 ≤ |R 78 / (Vd 07 - Vd 08 ) / f | ≤ 0.07. Controlling the formula not to exceed the lower limit can balance chromatic aberration at higher light levels and limit the length of the optical system, and controlling the formula not to exceed the upper limit can avoid overcorrection and limit the field of view of the optical system.

[0052] At this time, the third lens L3 can be selected as a doublet lens, including a third singlet lens L03 and a fourth singlet lens L04, and the Abbe number Vd of the third singlet lens L03 03 and the Abbe number Vd of the fourth singlet lens L04 04 satisfy: 18 ≤ |Vd 03 - Vd 04 | ≤ 22. Controlling the formula not to exceed the lower limit can balance chromatic aberration at higher light levels, and controlling the formula not to exceed the upper limit can avoid overcorrection.

[0053] In an exemplary embodiment, to improve the imaging quality of the lens and reduce the aberration in the imaging system, an aspherical lens can be used, and its surface profile satisfies the following equation: , where y represents the radial coordinate value of the lens perpendicular to the optical axis, Z is the sagitta of the aspherical lens along the optical axis at the position with height y, c = 1 / R, R represents the radius of curvature of the center of the aspherical lens surface profile, k represents the conic coefficient, and the parameters A, B, C, D, E are the coefficients of the 2nd, 4th, 6th, 8th, and 10th order terms of the high-order aspherical polynomial in sequence.

[0054] The object side of the first lens L1 is convex and the image side is concave, collecting light and controlling axial chromatic aberration.

[0055] The second lens L2 has a negative optical power, and the object side is concave. It further collects light and adjusts the light path, converges the light to control the field of view angle, increases the semi-focal depth, and provides subsequent lenses to correct aberrations while controlling the lens size. The object side and the image side of the second lens L2 can be aspherical surfaces to adjust the light path of different fields of view and correct aberrations while reducing the number of lenses.

[0056] The third lens L3 has a positive optical power, and the object side is convex. It further converges the light, controls the field of view angle, increases the semi-focal depth, makes the light transition smoothly, reduces the lens sensitivity, and controls the lens size at the same time.

[0057] The fourth lens L4 has a positive optical power, and the object side is convex. It converges the light to increase the semi-focal depth, makes the light transition smoothly, and reduces the lens sensitivity and aberrations.

[0058] The fifth lens L5 is a meniscus lens, which makes the light transition smoothly, reduces the lens sensitivity and aberrations, converges the light for subsequent imaging, increases the semi-focal depth, and controls the length of the optical system.

[0059] The sixth lens L6 has a negative optical power, further converges the light to form an image, and controls the image plane size. Both the object side and the image side of the sixth lens L6 are aspherical surfaces, which can adjust the light path of different fields of view and correct aberrations while reducing the number of lenses.

[0060] The following are four specific examples of the lens group in the optical lens of the embodiment of the present invention, and the main design parameters are shown in Table 1. In each lens of the following examples, the value of the curvature radius corresponding to the convex object side is positive, the value of the curvature radius corresponding to the concave object side is negative, the value of the curvature radius corresponding to the convex image side is negative, the value of the curvature radius corresponding to the concave image side is positive, and the positive value of the cemented surface indicates that the image side of the lens close to the object side is concave, and the negative value of the cemented surface indicates that the image side of the lens close to the object side is convex.

[0061] Table 1

[0062]

[0063] Example 1:

[0064] The structure of this Example 1 is as Figure 1 shown, and the physical optical parameters are shown in Table 2.

[0065] From the object side to the image side, it is composed of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6.

[0066] The first lens L1 has a positive optical power, the object side is convex, and the image side is concave.

[0067] The second lens L2 has a negative optical power, with the object side being concave and the image side being concave;

[0068] The third lens L3 has a positive optical power, with the object side being convex and the image side being convex;

[0069] The fourth lens L4 has a positive optical power, with the object side being convex and the image side being convex;

[0070] The fifth lens L5 has a negative optical power, with the object side being concave and the image side being convex;

[0071] The sixth lens L6 has a negative optical power, with the object side being convex and the image side being concave;

[0072] The fifth lens L5 is a doublet lens, the seventh singlet lens L07 is a biconcave negative lens, and the eighth singlet lens L08 is a biconvex positive lens.

[0073] Both the object side and the image side of the second lens L2 and the sixth lens L6 are aspherical surfaces.

[0074] Table 2

[0075]

[0076] Since the radius of curvature of the image side of the third lens L3 is relatively large, Figure 1 the image side of the third lens L3 in

[0077] is approximately planar.

[0078] Table 3

[0079]

[0080] The transfer function curve of this Example 1 is as shown in Figure 2 and Figure 3 and the specific values are shown in Table 1. At 200 line pairs, the MTF value of the central field of view (where 0.00° meridian and 0.00° sagittal coincide) is greater than 0.5, and the MTF value of the marginal field of view (32.00° meridian, 32.00° sagittal) is greater than 0.3, with relatively high resolution. The imaging performance of the lens in non-vacuum and vacuum environments is close, and the difference is basically within 5%.

[0081] Example 2:

[0082] The structure of this Example 2 is as shown in Figure 4 shown.

[0083] This Example 2 is based on Example 1. Mainly, the two surfaces of the second lens L2 are changed to spherical surfaces to reduce the manufacturing cost of the process. At the same time, the third lens L3 is changed from a single lens to a doublet lens. The third single lens L03 is a meniscus negative lens, and the fourth single lens L04 is a biconvex positive lens. The curvature radii of the two sides of the first lens L1 are modified to increase the difference between them, reducing the manufacturing difficulty of the process.

[0084] The physical optical parameters of this Example 2 are shown in Table 4.

[0085] Table 4

[0086]

[0087] The aspherical surface type parameters of this Example 2 are shown in Table 5.

[0088] Table 5

[0089]

[0090] The transfer function curve of this Example 2 is as Figure 5 and Figure 6 shown. The specific values are shown in Table 1. At 200 line pairs, the MTF value of the central field of view (where the 0.00° meridian and 0.00° sagittal coincide) is greater than 0.5, and the MTF value of the edge field of view (32.00° meridian, 32.00° sagittal) is greater than 0.3. The resolution is improved, and at the same time, the imaging illuminance is also improved. The imaging performance of the lens in non-vacuum and vacuum environments is close, and the difference is basically within 5%.

[0091] Example 3:

[0092] The structure of this Example 3 is as Figure 7 shown, and the physical optical parameters are shown in Table 6.

[0093] This Example 3 relative to Example 1 mainly changes the positive and negative of the optical powers of the first lens L1 and the fifth lens L5, and changes the position of the doublet lens from the fifth lens L5 to the fourth lens L4.

[0094] Table 6

[0095]

[0096] Since the curvature radius of the image side of the fifth lens L5 is relatively large, therefore Figure 7 the image side of the fifth lens L5 in

[0097] is approximately planar.

[0098] Table 7

[0099]

[0100] The transfer function curve of Example 3 is as follows Figure 8 and Figure 9 shown. The specific values are shown in Table 1. At 200 line pairs, the MTF value of the central field of view (where 0.00° meridian and 0.00° sagittal coincide) is greater than 0.5, and the MTF value of the marginal field of view (32.00° meridian, 32.00° sagittal) is greater than 0.4. The resolution and illuminance are slightly improved, the field curvature and the radius RMS of the imaging blur spot decrease. The imaging performance of the optical lens in non-vacuum and vacuum environments is similar, and the difference in most parameters is within 5%.

[0101] Example 4:

[0102] The structure of Example 4 is as follows Figure 10 shown.

[0103] Example 4 is based on Example 3, mainly making the second lens L2 a doublet, the first singlet lens L01 a biconcave negative lens, and the second singlet lens L02 a biconvex positive lens.

[0104] Compared with Example 2, the positions of the two doublets in Example 4 are different, making the transfer function values of the entire field of view of the lens more concentrated. The positive and negative combination of the doublet on the image side of the aperture stop STO is reversed, closer to the aperture stop, and the height of the passing light rays is higher, giving full play to the achromatic function of the doublet.

[0105] The physical optical parameters of Example 4 are shown in Table 8.

[0106] Table 8

[0107]

[0108] Since the radius of curvature of the image side of the third lens L3 is relatively large, therefore Figure 10 the image side of the third lens L3 in

[0109] is approximately planar. The aspheric surface type parameters of Example 4 are shown in Table 9.

[0110] Table 9

[0111]

[0112] The transfer function curve of Example 4 is as follows Figure 11 and Figure 12As shown, the specific values are shown in Table 1. At 200 line pairs, the MTF value of the central field of view (where 0.00° meridian and 0.00° sagittal coincide) is greater than 0.6, and the MTF value of the edge field of view (32.00° meridian, 32.00° sagittal) is greater than 0.4. The resolution and illuminance are slightly improved, while the field curvature and the RMS radius of the imaging blur spot decrease. The imaging performance of the optical lens in non-vacuum and vacuum environments is similar, and the difference in most parameters is within 5%.

[0113] The individual examples shown above only represent the invention and cannot limit the scope of the invention's patent protection. Therefore, equivalent changes made according to the scope of the patent application of the present invention still fall within the scope covered by the present invention.

Claims

1. An optical lens applicable to a vacuum environment, comprising a lens group, wherein the lens group is composed of a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens and a sixth lens sequentially arranged from the object side to the image side, and is characterized in that, The object side of the first lens is convex and the image side is concave. The second lens has a negative optical power, with the object side being concave. The third lens has a positive optical power, with the object side being convex. The fourth lens has a positive optical power, with the object side being convex. The fifth lens is a meniscus lens. The sixth lens has a negative optical power, with the image side being concave. At least one of the first lens to the sixth lens is a doublet lens. The vacuum defocus amount d1 and the semi-focal depth d2 of the entire optical lens satisfy: |d1| < |d2|, where d1 = bfl1 - bfl2, d2 = 2λ(f / EPD) 2 , bfl1 is the distance from the image side of the sixth lens to the image plane of the optical lens in the non-vacuum state, bfl2 is the distance from the image side of the sixth lens to the image plane of the optical lens in the vacuum state, with the unit being mm, λ is the central wavelength of the incident light, with the unit being um, f is the focal length of the optical lens, with the unit being mm, satisfying: 4mm < f < 6mm, EPD is the entrance pupil diameter of the optical lens, with the unit being mm, the object distance U of the optical lens satisfies: U ≥ 10m, the total length TTL satisfies: 14mm < TTL < 18mm, and the F number F# satisfies 2.5 < F# < 2.

6.

2. The optical lens applicable to a vacuum environment according to claim 1, wherein The object side and the image side of the second lens are both aspherical surfaces, and the object side and the image side of the sixth lens are both aspherical surfaces.

3. An optical lens applicable to a vacuum environment according to claim 1, characterized in that, The fourth lens is a doublet lens composed of a fifth singlet lens and a sixth singlet lens. The Abbe number Vd of the fifth singlet lens 05 , the Abbe number Vd of the sixth singlet lens 06 , the radius of curvature R of the cemented surface between the fifth singlet lens and the sixth singlet lens 56 and the focal length f of the optical lens satisfy: 0.01 ≤ |R 56 / (Vd 05 - Vd 06 ) / f| ≤ 0.

07.

4. The optical lens applicable to a vacuum environment according to claim 3, characterized in that The second lens described is a doublet lens composed of a first singlet lens and a second singlet lens, and the Abbe number Vd of the first singlet lens 01 and the Abbe number Vd of the second singlet lens 02 satisfy: 18 ≤ |Vd 01 - Vd 02 | ≤ 22.

5. An optical lens applicable to a vacuum environment as claimed in claim 1, characterized in that, The fifth lens is a doublet lens composed of a seventh singlet lens and an eighth singlet lens. The Abbe number Vd of the seventh singlet lens 07 , the Abbe number Vd of the eighth singlet lens 08 , the radius of curvature R of the cemented surface between the seventh singlet lens and the eighth singlet lens 78 and the focal length f of the optical lens satisfy: 0.01 ≤ |R 78 / (Vd 07 - Vd 08 ) / f| ≤ 0.

07.

6. The optical lens applicable to a vacuum environment according to claim 5, characterized in that, The third lens is a doublet lens composed of a third singlet lens and a fourth singlet lens, and the Abbe number Vd of the third singlet lens 03 and the Abbe number Vd of the fourth singlet lens 04 satisfy: 18 ≤ |Vd 03 - Vd 04 | ≤ 22.

7. An optical lens applicable to a vacuum environment as described in claim 1, characterized in that, The optical lens further includes a lens barrel for accommodating and mounting the lens group. An annular base is provided at the end of the lens barrel. A retaining ring is screwed to the open end of the lens barrel. The image side of the sixth lens abuts against the annular base. The retaining ring presses against the object side of the first lens. Spacer rings are provided between the respective lenses from the first lens to the sixth lens. An air vent groove is provided on the inner wall of the lens barrel. The spacer rings are provided with first air vent through holes for communicating the gaps between the respective lenses with the air vent groove. The retaining ring is provided with second air vent through holes for communicating the outside with the air vent groove.

8. An optical lens applicable to a vacuum environment according to claim 7, characterized in that, The inner end face of the annular base is provided with third air vent through holes for communicating the outside with the air vent groove.

9. An optical lens applicable to a vacuum environment as claimed in claim 7, characterized in that, The lens barrel, the retaining ring and the spacer rings are all made of titanium alloy.

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