Optical lens suitable for vacuum environment

Abstract

The invention discloses an optical lens suitable for a vacuum environment, which comprises 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 which are arranged in sequence from an object space to an image space, at least one of the first lens to the sixth lens is a doublet lens, and at least one of the second lens, the third lens, the diaphragm, the fourth lens, the fifth lens and the sixth lens is a doublet lens. The vacuum defocusing amount d1 and the semi-focal depth d2 of the whole optical lens meet the condition that d1 is smaller than d2, and the vacuum defocusing amount of the optical lens is controlled to be smaller than the semi-focal depth of the optical lens through permutation and combination of the lenses with different focal powers and surface shapes and reasonable arrangement of the bonding lens. The influence caused by the change of the refractive index of the medium in the gap between the lenses after the optical lens enters a vacuum environment is reduced, and high resolution and low sensitivity of imaging of the optical lens are achieved.

Description

Technical Field

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

[0002] Space cameras use aerospace vehicles as platforms to monitor ground and near-Earth space targets. With the development of detection technology and the increase in detection needs, higher requirements are placed on the optical lenses in space cameras: 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 trend and the position of the best image plane change. The Chinese invention patent application with publication number CN116931259A provides a method for presetting the best image plane of the compensation lens by calculating the vacuum defocus amount, so that the best image plane, focal length and imaging quality of the compensated lens are consistent with those in the vacuum environment, reducing the difficulty of lens vacuum performance image quality detection, but this method requires an additional compensation lens.

[0003] 2) Space cameras have certain requirements on volume and mass, so a lightweight structural design of the lens is needed. The Chinese invention patent application with publication number CN119200155A proposes a head-mounted low-light night vision optical system, which achieves an ultra-short optical back focus of 1.1mm through eight spherical lenses, controls the miniaturization and lightweight of the optical system, but the imaging accuracy needs to be improved.

[0004] 3) After the space camera is assembled and tested on the ground at normal temperature and pressure, it works in a vacuum space environment. The environmental change causes the conventional structure lens to produce an internal and external pressure difference, resulting in lens stress deformation, affecting the lens imaging quality. The Chinese invention patent application with publication number CN113671659B proposes a structure in which an exhaust groove is set on the inner wall of the lens barrel, and multiple exhaust holes are set on the exhaust groove. The airflow inside the lens is smooth and connected to the outside to realize the exhaust ventilation function; however, the outside light easily enters the lens through the exhaust hole to cause light pollution. The Chinese invention patent application with publication number CN107861215B proposes a space transmission lens with a venting structure, leaving a square groove on the internal pressure ring and the lens frame to connect the air in the lens cavity, and a venting hole is opened in the middle of the lens barrel to realize the venting function while reducing the risk of light pollution; however, the structure of a single exhaust hole is not suitable for multi-lens lenses with multiple air gaps. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an optical lens suitable for a vacuum environment and capable of maintaining consistent imaging performance in a vacuum environment and a non-vacuum environment.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: an optical lens suitable for a vacuum environment, comprising a lens group, wherein the lens group is composed of a first lens, a second lens, a third lens, an aperture, 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 a convex surface, and the image side surface is a concave surface, the optical power of the second lens is negative, and the object side surface is a concave surface, the optical power of the third lens is positive, and the object side surface is a convex surface, the optical power of the fourth lens is positive, and the object side surface is a convex surface, the fifth lens is a meniscus lens, and the optical power of the sixth lens is negative, at least one of the first lens to the sixth lens is a double cemented lens, and the vacuum defocus amount d1 and the semi-focal depth d2 of the entire optical lens satisfy: |d1|<|d2|, wherein 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 a 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 a vacuum state, the unit is mm, λ is the central wavelength, the unit is um, f is the focal length of the optical lens, the unit is mm, and satisfies: 4mm<f<6mm, EPD is the entrance pupil diameter of the optical lens, the unit is 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.

[0007] Compared with the prior art, the advantage of the present invention lies in that through the arrangement and combination of lenses with different optical focal lengths and surface shapes, and the reasonable arrangement of cemented lenses, the vacuum defocus of the entire optical lens is controlled to be smaller than the semi-focal depth of the entire optical lens, thereby reducing the influence of the change in the refractive index of the medium in the gap between the lenses after the optical lens enters the vacuum environment, thereby achieving high resolution and low sensitivity of optical lens imaging.

[0008] 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.

[0009] Preferably, the fourth lens is a doublet lens consisting of a fifth single lens and a sixth single lens, and the Abbe number Vd of the fifth single lens is 05 , the Abbe number Vd of the sixth single lens 06 , the curvature radius R of the bonding surface of the fifth single lens and the sixth single lens 56 The focal length f of the optical lens satisfies: 0.01≤|(R 56 / (Vd 05 -Vd 06 )) / f|≤0.07.

[0010] Preferably, the second lens is a doublet lens consisting of a first single lens and a second single lens, and the Abbe number Vd of the first single lens is 01 The Abbe number Vd of the second single lens 02 Satisfy: 18≤|Vd 01 -Vd 02 |≤22.

[0011] Preferably, the fifth lens is a doublet lens consisting of a seventh single lens and an eighth single lens, and the Abbe number Vd of the seventh single lens is 07 , the Abbe number Vd of the eighth single lens 08 , the curvature radius R of the bonding surface of the seventh single lens and the eighth single lens 78 The focal length f of the optical lens satisfies: 0.01≤|(R 78 / (Vd 07 -Vd 08 )) / f|≤0.07.

[0012] Preferably, the third lens is a doublet lens consisting of a third single lens and a fourth single lens, and the Abbe number Vd of the third single lens is 03 The Abbe number Vd of the fourth single lens 04 Satisfy: 18≤|Vd 03 -Vd 04 |≤22.

[0013] Preferably, the optical lens also includes a lens barrel for accommodating and installing the lens group, the end of the lens barrel is provided with an annular base, the open end of the lens barrel is screwed with a pressing ring, the image side of the sixth lens abuts on the annular base, the pressing ring is pressed on the object side of the first lens, a spacer is provided between each lens from the first lens to the sixth lens, the inner wall of the lens barrel is provided with a ventilation groove, the spacer is provided with a first ventilation hole connecting the gap between each lens with the ventilation groove, and the pressing ring is provided with a second ventilation hole connecting the outside with the ventilation groove. The vacuum ventilation structure provided by the present invention: the ventilation groove is provided on the inner wall of the lens barrel, the first ventilation hole connecting the gap between each lens with the ventilation groove is provided on the spacer, and the second ventilation hole connecting the outside with the ventilation groove is provided on the pressing ring, the gaps between each lens are connected to each other, so that the airflow inside the lens is smooth; the ventilation function is realized, so that the lens can work normally in a vacuum; the ventilation work can be completed without opening a ventilation hole on the lens barrel, and light pollution is avoided at the same time.

[0014] Preferably, the inner end surface of the annular base is provided with a third ventilation hole connecting the outside with the ventilation groove.

[0015] Preferably, the lens barrel, the pressure ring and the spacer are all made of titanium alloy. In this structure, the lens barrel, the pressure ring and the spacer are all made of titanium alloy, and no additional structures such as a lens frame are added, so as to avoid the lens being too large and heavy, and achieve the effect of miniaturization and lightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of an optical system of Example 1 of the present invention; Figure 2 This is a transfer function curve diagram of Example 1 of the present invention under non-vacuum conditions; Figure 3 This is a transfer function curve diagram of Example 1 of the present invention under vacuum; Figure 4 Schematic diagram of an optical system of Example 2 of the present invention; Figure 5 This is a transfer function curve diagram of Example 2 of the present invention under non-vacuum conditions; Figure 6 is a transfer function curve diagram of Example 2 of the present invention under vacuum; Figure 7 is a schematic diagram of an optical system of Example 3 of the present invention; Figure 8 This is a transfer function curve diagram of Example 3 of the present invention under non-vacuum conditions; Fig. 9 This is a transfer function curve diagram of Example 3 of the present invention under vacuum; Fig.10 is a schematic diagram of an optical system of Example 4 of the present invention; Fig.11 This is a transfer function curve diagram of Example 4 of the present invention under non-vacuum conditions; Fig.12 is a transfer function curve diagram of Example 4 of the present invention under vacuum; Fig.13 This is a schematic diagram of the lens assembly structure of Example 2 of the present invention; Fig.14 Schematic diagram of the lens barrel structure of Example 2 of the present invention; Fig.15 This is a schematic diagram of the spacer structure of Example 1 of the present invention; Fig.16 This is a schematic diagram of the pressing ring structure of Example 1 of the present invention; Fig.17 This is a schematic diagram of the ventilation structure of Example 2 of the present invention.

[0017] Description of reference numerals: 1. Lens barrel; 11. Ring base; 12. Ventilation groove; 13. Third vent hole; 2. Pressing ring; 21. Second vent hole; 3. Spacer; 31. First vent hole; L1. First lens; L2. Second lens; L01. First single lens; L02. Second single lens; L3. Third lens; L03. Third single lens; L04. Fourth single lens; L4. Fourth lens; L05. Fifth single lens; L06. Sixth single lens; L5. Fifth lens; L07. Seventh single lens; L08. Eighth single lens; L6. Sixth lens; STO, aperture; IMA, image plane. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to the accompanying drawings.

[0019] The following is a detailed description of an example embodiment of the present invention in conjunction with the accompanying drawings. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention.

[0020] Example: In the drawings, the thickness, size and shape of the lens are slightly exaggerated for ease of explanation. The drawings are for illustration only and are not drawn strictly to scale. The concave and convex of the lens can be determined according to the vertex curvature radius of the lens surface. When the vertex curvature radius of the object side of the lens is greater than 0, the surface is convex, otherwise it is concave; when the vertex curvature radius of the image side of the lens is greater than 0, the surface is concave, otherwise it is convex.

[0021] The purpose of the present invention is to provide a lens that can maintain consistent imaging performance in vacuum and non-vacuum environments without requiring a compensation lens. The vacuum mainly refers to 10 -8 Pa to 10 -2 Pa ultra-high vacuum or high vacuum environment; non-vacuum mainly refers to the ground environment under a standard atmospheric pressure.

[0022] like Fig.13 and Fig.17 As shown, an optical lens suitable for a vacuum environment comprises a lens group and a lens barrel 1 for accommodating and installing the lens group, an annular base 11 is arranged at the end of the lens barrel 1, a pressing ring 2 is screwed at the open end of the lens barrel 1, and the lens barrel 1 and the pressing ring 2 are made of titanium alloy, the lens group comprises 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 surface of the sixth lens L6 abuts against the annular base 11, the pressing ring 2 is pressed against the object side surface of the first lens L1, and spacers 3 are arranged between the lenses from the first lens L1 to the sixth lens L6, and the spacers 3 are made of titanium alloy, as shown in FIG. Fig.14 As shown, the inner wall of the lens barrel 1 is provided with a ventilation groove 12, and the inner end surface of the annular base 11 is provided with a third ventilation hole 13 that connects the outside with the ventilation groove 12. Fig.15As shown, the spacer 3 is provided with a first ventilation hole 31 which connects the gap between each lens with the ventilation groove 12. Fig.16 As shown, the pressing ring 2 is provided with a second ventilation hole 21 connecting the outside with the ventilation groove 12; for the convenience of processing, the first ventilation hole 31 and the second ventilation hole 21 both adopt a half-hole structure.

[0023] The lens assembly of the present invention is as follows Figure 1 , Figure 4 , Figure 7 and Fig.10 As shown. It can be seen that the first lens L1, the second lens L2, the third lens L3, the aperture STO, the fourth lens L4, the fifth lens L5, the sixth lens L6 and the image plane IMA are shown in the figure from the object side to the image side. 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.

[0024] When the optical lens enters the vacuum environment from the ground environment, the air medium in the gap between the lenses becomes a vacuum, and the refractive index changes; at this time, the optimal 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 change of the lens in vacuum and non-vacuum in paragraphs

[0065] to

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

[0025] It can be concluded from the above formula that when the optical system design of the optical lens is completed, when |d1|>|d2| does not meet the imaging requirements in a vacuum, the lens can be adjusted as needed to change the focal length f and entrance pupil diameter EPD of the optical lens, thereby changing the semi-focal depth d2 of the entire optical lens so that the above formula is satisfied.

[0026] The object distance U of the optical lens satisfies: U ≥ 10m, which can achieve spatial imaging within a long distance range; the wavelength range of the incident light is 486~656nm, and the central wavelength λ=588nm; the focal length f of the optical lens satisfies: 4mm<f<6mm; the total length TTL of the optical lens satisfies: 14mm<TTL<18mm; the F number F# of the optical lens satisfies 2.5<F#<2.6.

[0027] The image side of the aperture STO has four single lenses, of which at least one is a set of doublets.

[0028] In a preferred embodiment, the fourth lens L4 is a doublet lens, including a fifth single lens L05 and a sixth single lens L06, and the Abbe number Vd of the fifth single lens L05 is 05 , Abbe number Vd of the sixth single lens L06 06 , the curvature radius R of the cemented surface of the fifth single lens L05 and the sixth single lens L06 56 The focal length f of the optical lens satisfies: 0.01≤|R 56 / (Vd 05 -Vd 06 ) / f|≤0.07. Controlling the formula not to exceed the lower limit can balance chromatic aberration and limit the length of the optical system in places with higher light. Controlling the formula not to exceed the upper limit can avoid over-correction and limit the field of view of the optical system.

[0029] In the above preferred embodiment, the object side of the aperture STO can have three single lenses without double cemented lenses, which can reduce material and processing costs and reduce the size of the lens.

[0030] However, it is also possible to set four single lenses on the object side of the aperture STO, at least one of which is a double-cemented lens, so as to make the light trend smoother, reduce the sensitivity of the lens and improve the imaging quality.

[0031] Furthermore, the second lens L2 is a doublet lens, including a first single lens L01 and a second single lens L02, and the Abbe number Vd of the first single lens L01 is 01 and the Abbe number Vd of the second single lens L02 02 Satisfy: 18≤|Vd 01 -Vd 02 |≤22, controlling the formula not to exceed the lower limit can balance the chromatic aberration in places with higher light, and controlling the formula not to exceed the upper limit can avoid over-correction.

[0032] In another preferred embodiment, the fifth lens L5 is a doublet lens, including a seventh single lens L07 and an eighth single lens L08, and the Abbe number Vd of the seventh single lens L07 is 07 , Abbe number Vd of the eighth single lens L08 08, the curvature radius R of the cemented surface of the seventh single lens L07 and the eighth single lens L08 78 The focal length f of the optical lens satisfies: 0.01≤|R 78 / (Vd 07 -Vd 08 ) / f|≤0.07. Controlling the formula not to exceed the lower limit can balance chromatic aberration and limit the length of the optical system in places with higher light. Controlling the formula not to exceed the upper limit can avoid over-correction and limit the field of view of the optical system.

[0033] At this time, the third lens L3 can be selected as a double cemented lens, including a third single lens L03 and a fourth single lens L04. The Abbe number Vd of the third single lens L03 is 03 and the Abbe number Vd of the fourth single lens L04 04 Satisfy: 18≤|Vd 03 -Vd 04 |≤22, controlling the formula not to exceed the lower limit can balance the chromatic aberration in places with higher light, and controlling the formula not to exceed the upper limit can avoid over-correction.

[0034] In an exemplary embodiment, in order to improve the imaging quality of the lens and reduce the aberration in the imaging system, an aspherical lens may be used, the surface shape of which satisfies the following equation: , where y represents the radial coordinate value of the lens perpendicular to the optical axis, Z is the vector height of the aspheric lens from the aspheric vertex when it is at a height of y along the optical axis, c=1 / R, R represents the radius of curvature of the corresponding aspheric lens surface center, k represents the cone coefficient, and the parameters A, B, C, D, and E are the coefficients of the 2nd, 4th, 6th, 8th, and 10th order terms of the high-order aspheric polynomial respectively.

[0035] The object side surface of the first lens L1 is convex, and the image side surface is concave, which collects light and controls axial chromatic aberration.

[0036] The second lens L2 has a negative focal length and a concave object side surface, which further collects light and adjusts the light trend, converges the light to control the field angle, increases the semi-focal depth, and allows subsequent lenses to adjust aberrations while controlling the size of the lens. The object surface and image side surface of the second lens L2 can be aspherical, which adjusts the trend of light in different fields of view, and corrects aberrations while reducing the number of lenses.

[0037] The third lens L3 has positive optical power and a convex object side surface, which 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.

[0038] The fourth lens L4 has a positive optical power and a convex object side surface, which converges light and increases the semi-focal depth, making the light transition smooth and reducing the lens sensitivity and aberration.

[0039] The fifth lens L5 is a meniscus lens, which makes the light transition smoothly, reduces the sensitivity and aberration of the lens, and at the same time converges the light for subsequent imaging, increases the semi-focal depth, and controls the length of the optical system.

[0040] The sixth lens L6 has a negative focal length, which further converges the light to form an image and controls the size of the image plane. The object side and image side of the sixth lens L6 are both aspherical, which can adjust the trend of light in different fields of view, and correct aberrations while reducing the number of lenses.

[0041] The following are four specific examples of lens groups 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 surface of the object side surface is positive, the value of the curvature radius corresponding to the concave surface of the object side surface is negative, the value of the curvature radius corresponding to the convex surface of the image side surface is negative, the value of the curvature radius corresponding to the concave surface of the image side surface is positive, the value of the cemented surface is positive, indicating that the image side surface of the lens close to the object side is concave, and the value of the cemented surface is negative, indicating that the image side surface of the lens close to the object side is convex.

[0042] Table 1

[0043] Example 1: The structure of Example 1 is as follows Figure 1 The physical and optical parameters are shown in Table 2.

[0044] 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. The first lens L1 has a positive refractive power, a convex object-side surface, and a concave image-side surface; The second lens L2 has a negative refractive power, a concave object-side surface, and a concave image-side surface; The third lens L3 has a positive refractive power, a convex object-side surface, and a convex image-side surface; The fourth lens L4 has a positive refractive power, a convex object-side surface, and a convex image-side surface; The fifth lens L5 has a negative refractive power, a concave object-side surface, and a convex image-side surface; The sixth lens L6 has a negative refractive power, a convex object-side surface, and a concave image-side surface; The fifth lens L5 is a doublet lens, the seventh single lens L07 is a double concave negative lens, and the eighth single lens L08 is a double convex positive lens.

[0045] The object-side surfaces and image-side surfaces of the second lens L2 and the sixth lens L6 are both aspherical surfaces.

[0046] Table 2

[0047] Since the curvature radius of the image side surface of the third lens L3 is large, Figure 1 The image-side surface of the third lens L3 is approximately a plane.

[0048] The aspheric surface parameters of Example 1 are shown in Table 3.

[0049] Table 3

[0050] The transfer function curve of Example 1 is as follows Figure 2 and Figure 3 The specific values ​​are shown in Table 1. Under 200 line pairs, the MTF value of the center field of view (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 relatively high, and the imaging performance of the lens in non-vacuum and vacuum environments is close, and the difference is basically within 5%.

[0051] Example 2: The structure of Example 2 is as follows Figure 4 shown.

[0052] This Example 2 is based on Example 1, mainly changing the two surfaces of the second lens L2 into spherical surfaces to reduce the process manufacturing cost, and at the same time changing the third lens L3 from a single lens to a double cemented lens, the third single lens L03 is a meniscus negative lens, and the fourth single lens L04 is a double convex positive lens. The curvature radius of the two sides of the first lens L1 is modified to increase the difference, which reduces the difficulty of process manufacturing.

[0053] The physical optical parameters of this example 2 are shown in Table 4.

[0054] Table 4

[0055] The aspheric surface parameters of Example 2 are shown in Table 5.

[0056] Table 5

[0057] The transfer function curve of Example 2 is as follows Figure 5 and Figure 6 The specific values ​​are shown in Table 1. Under 200 line pairs, the MTF value of the center field of view (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 the imaging illumination is also improved. The imaging performance of the lens in non-vacuum and vacuum environments is close, and the difference is basically within 5%.

[0058] Example 3: The structure of Example 3 is as follows Figure 7 The physical and optical parameters are shown in Table 6.

[0059] Compared with Example 1, Example 3 mainly changes the positive and negative refractive 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.

[0060] Table 6

[0061] Since the curvature radius of the image side surface of the fifth lens L5 is large, Figure 7 The image-side surface of the fifth lens L5 is approximately a plane.

[0062] The aspheric surface parameters of Example 3 are shown in Table 7: Table 7

[0063] The transfer function curve of Example 3 is as follows Figure 8 and Fig. 9 The specific values ​​are shown in Table 1. Under 200 line pairs, the MTF value of the central field of view (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 0.4. The resolution and illumination are slightly improved, and the field curvature and RMS of the imaging diffuse spot radius are reduced. The imaging performance of the optical lens in non-vacuum and vacuum environments is close, and the difference in most parameters is within 5%.

[0064] Example 4: The structure of Example 4 is as follows Fig.10 shown.

[0065] This Example 4 is based on Example 3, except that the second lens L2 is mainly changed to a doublet lens, the first single lens L01 is a biconcave negative lens, and the second single lens L02 is a biconvex positive lens.

[0066] Compared with Example 2, the positions of the two doublets in Example 4 are different, which makes the transfer function value of the lens full field of view more concentrated. The positive and negative combinations of the doublets on the image side of the aperture STO are reversed, closer to the aperture, and the light passing through is higher, giving full play to the achromatic function of the doublets.

[0067] The physical optical parameters of this example 4 are shown in Table 8.

[0068] Table 8

[0069] Since the curvature radius of the image side surface of the third lens L3 is large, Fig.10The image-side surface of the third lens L3 is approximately a plane.

[0070] The aspheric surface parameters of Example 4 are shown in Table 9.

[0071] Table 9

[0072] The transfer function curve of Example 4 is as follows Fig.11 and Fig.12 The specific values ​​are shown in Table 1. Under 200 line pairs, the MTF value of the central field of view (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 illumination are slightly improved, and the field curvature and RMS of the imaging diffuse spot radius are reduced. The imaging performance of the optical lens in non-vacuum and vacuum environments is close, and the difference in most parameters is within 5%.

[0073] The above are only individual examples of the present invention and cannot limit the scope of protection of the present invention. 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 suitable for a vacuum environment, comprising a lens group, wherein the lens group is composed of a first lens, a second lens, a third lens, an aperture, a fourth lens, a fifth lens and a sixth lens arranged in sequence from the object side to the image side, characterized in that: 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, and the image side surface is concave, at least one of the first lens to the sixth lens is a doublet lens, and the vacuum defocus amount d1 and the semi-focal depth d2 of the entire optical lens satisfy: |d1|<|d2|, wherein, 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 a 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 a vacuum state, the unit is mm, λ is the central wavelength of the incident light, the unit is um, f is the focal length of the optical lens, the unit is mm, and satisfies: 4mm<f<6mm, EPD is the entrance pupil diameter of the optical lens, the unit is 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. An optical lens suitable for a vacuum environment as claimed in claim 1, characterized in that: The object side surface and the image side surface of the second lens are both aspherical surfaces, and the object side surface and the image side surface of the sixth lens are both aspherical surfaces.

3. The optical lens suitable for a vacuum environment as claimed in claim 1, characterized in that: The fourth lens is a doublet lens composed of a fifth single lens and a sixth single lens, and the Abbe number Vd of the fifth single lens is 05 , the Abbe number Vd of the sixth single lens 06 , the curvature radius R of the bonding surface of the fifth single lens and the sixth single lens 56 The focal length f of the optical lens satisfies: 0.01≤|R 56 / (Vd 05 -Vd 06 ) / f|≤0.

07.

4. An optical lens suitable for a vacuum environment as claimed in claim 3, characterized in that: The second lens is a doublet lens consisting of a first single lens and a second single lens, and the Abbe number Vd of the first single lens is 01 The Abbe number Vd of the second single lens 02 Satisfy: 18≤|Vd 01 -Vd 02 |≤22.

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

07.

6. An optical lens suitable for a vacuum environment as claimed in claim 5, characterized in that: The third lens is a doublet lens consisting of a third single lens and a fourth single lens. The Abbe number Vd of the third single lens is 03 The Abbe number Vd of the fourth single lens 04 Satisfy: 18≤|Vd 03 -Vd 04 |≤22.

7. The optical lens suitable for a vacuum environment as claimed in claim 1, characterized in that: The optical lens also includes a lens barrel for accommodating and installing the lens group, the end of the lens barrel is provided with an annular base, the open end of the lens barrel is screwed with a pressing ring, the image side surface of the sixth lens abuts against the annular base, the pressing ring is pressed on the object side surface of the first lens, spacers are provided between each lens from the first lens to the sixth lens, the inner wall of the lens barrel is provided with a ventilation groove, the spacer is provided with a first ventilation hole connecting the gap between each lens with the ventilation groove, and the pressing ring is provided with a second ventilation hole connecting the outside with the ventilation groove.

8. An optical lens suitable for a vacuum environment as claimed in claim 7, characterized in that: The inner end surface of the annular base is provided with a third ventilation hole which connects the outside with the ventilation groove.

9. The optical lens suitable for a vacuum environment as claimed in claim 7, characterized in that: The lens barrel, the pressure ring and the spacer ring are all made of titanium alloy.

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