Close-up lens and detection method for image quality detection of telephoto video surveillance camera lens

Abstract

This divisional application relates to a close-up lens and a detection method for detecting the image quality of a telephoto video surveillance camera lens, which is composed of a close-up lens three for detecting the telephoto video surveillance camera lens, wherein the close-up lens three is composed of a fifth lens and a sixth lens that forms a close-contact bonding group with the fifth lens. The close-up lens and the detection method can meet the requirements of image quality detection of video surveillance camera lenses with a focal length range of 20 to 75 mm. The addition of the close-up lens not only does not affect the calibrated imaging quality of the video surveillance camera lens, but the close-up lens can also lengthen the near object distance and shorten the far object distance, thereby realizing the miniaturization of the detection equipment.

Description

[0001] This application is a divisional application of the patent application with the filing date of August 10, 2017, the patent application number of 201710680696.0, and the invention title of a close-up lens and a detection method for assisting in the image quality detection of a video surveillance camera lens. Technical Field

[0002] The present invention relates to the field of optics, and particularly to a close-up lens and a detection method for the image quality detection of a long-focus video surveillance camera lens. Background Art

[0003] With the full entry of video camera technology into the era of high-definition image quality above one million total pixels, the imaging quality of the camera lens, as a key component supporting it, is also required to be greatly improved (currently, enterprises require it to reach about 5 million - 10 million). Since its output is very large, how to effectively detect the imaging quality of such lenses has become the focus of attention in the domestic and foreign optical communities. At present, from the perspective of having industry detection standards, being able to meet different focal length requirements, intuitiveness, and cost performance, the method using a resolution test chart is more applicable. Especially when directly combined with a camera, it can better reflect the imaging effect of the lens in the imaging system. By replacing the color test chart, it can also achieve the intuitive detection effect of the lens color restoration that is difficult to achieve by other methods. However, its difficulties are: when detecting an ultra-wide-angle short-focus lens, how to truly reflect the imaging effect at the practical distance; when detecting a long-focus lens, how to solve problems such as effective illumination, making a large-format resolution test chart, and miniaturization of the equipment. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned drawbacks, and provide a close-up lens and a detection method for the image quality detection of a long-focus video surveillance camera lens. The close-up lens and the detection method can meet the image quality detection of video surveillance camera lenses in the focal length range of 20 - 75 mm. The addition of this close-up lens not only does not affect the already calibrated imaging quality of the video surveillance camera lens, but also can lengthen the near object distance and shorten the far object distance, realizing the miniaturization of the detection equipment.

[0005] The present invention is implemented as follows:

[0006] Solution (1):

[0007] A close-up lens for image quality detection of a telephoto video surveillance camera lens, characterized in that it includes a close-up lens one, a close-up lens two, and a close-up lens three for detecting a short-focus video surveillance camera lens, a medium-focus video surveillance camera lens, and a telephoto video surveillance camera lens respectively. The close-up lens one includes a first lens and a second lens that form a close-contact cemented group with the first lens. The close-up lens two includes a third lens and a fourth lens that form a close-contact cemented group with the third lens. The close-up lens three includes a fifth lens and a sixth lens that form a close-contact cemented group with the fifth lens. The optical elements that make up each close-up lens must meet the following conditions:

[0008] 0.01 < Pcd12 - Pcd11 < 0.02; 20 < R12 / R11 < 26......①

[0009] 0.28 ≤ |Φ1 / R11 - Φ1 / R12|......②

[0010] 1.50 < n11 < 1.54; 60 < ν11 < 65......③

[0011] 1.60 < n12 < 1.626; 35 < ν12 < 38......④

[0012] 0.008 < Pcd22 - Pcd21 < 0.012; 4 < |R22 / R21| < 6......⑤

[0013] 0.4 ≤ |Φ2 / R21 - Φ2 / R22|......⑥

[0014] 1.50 < n21 < 1.54; 60 < ν21 < 65......⑦

[0015] 1.60 < n22 < 1.63; 56 < ν22 < 61......⑧

[0016] 0.001 < Pcd32 - Pcd31 < 0.006; 8 < |R32 / R31| < 12......⑨

[0017] 0.4 ≤ |Φ3 / R31 - Φ3 / R32|......⑩

[0018]

[0019]

[0020] Wherein, Pcd11, Pcd12, Pcd21, Pcd22, Pcd31, and Pcd32 are the relative dispersion coefficients of the first lens to the sixth lens respectively; R11, R12, R13, R21, R22, R23, R31, R32, and R33 are the radii of each surface of the first lens to the sixth lens respectively; Φ1 to Φ3 are the apertures of the first close-up lens to the third close-up lens respectively; n11, n12, n21, n22, n31, and n32 are the refractive indices of the first lens to the sixth lens respectively; ν11, ν12, ν21, ν22, ν31, and ν32 are the Abbe numbers of the first lens to the sixth lens respectively.

[0021] Preferably, the first lens is a convex-concave positive lens, and the second lens is a convex-concave negative lens; the third lens is a convex-concave positive lens, and the fourth lens is a convex-concave negative lens; the fifth lens is a concave-convex positive lens, and the sixth lens is a concave-convex negative lens.

[0022] Preferably, the focal length range of the short-focus video surveillance camera lens is 2.5 to 8 mm, the focal length range of the medium-focus video surveillance camera lens is 8 to 20 mm, and the focal length range of the long-focus video surveillance camera lens is 20 to 75 mm.

[0023] Preferably, the first lens and the third lens are made of H-K9L, the second lens and the fourth lens are made of H-F4, the fifth lens is made of H-ZK3, and the sixth lens is made of H-ZK10.

[0024] Solution (2):

[0025] A method for detecting the image quality of a video surveillance camera lens by using a close-up lens, characterized in that the method comprises the following steps:

[0026] a. Arrange a resolution test chart, a close-up lens, a video surveillance camera lens, and a camera target surface in sequence along the light incident direction. The resolution test chart is located within the front focal point of the close-up lens. The resolution test chart forms a virtual image at a relatively long distance in the object space through the close-up lens, and the virtual image is imaged on the camera target surface through the video surveillance camera lens. The close-up lens (R) is selected as follows according to the different focal length ranges of the video surveillance camera lens (T):

[0027] ① When the focal length range of the video surveillance camera lens is 2.5 to 8 mm, the first close-up lens is used as the close-up lens, and the positional relationship between the close-up lens and the video surveillance camera lens should satisfy 7 < Δ < 10;

[0028] ② When the focal length range of the video surveillance camera lens is 8 to 20 mm, the second close-up lens is used as the close-up lens, and the positional relationship between the close-up lens and the video surveillance camera lens should satisfy 15 < Δ < 30;

[0029] ③When the focal length range of the video surveillance camera lens is between 20 and 75 mm, the close-up lens III is used as the close-up lens, and the positional relationship between the close-up lens and the video surveillance camera lens should satisfy 15 < Δ < 30;

[0030] where Δ is the distance between the first surface of the video surveillance camera lens and the close-up lens;

[0031] b. The inspectors judge the imaging quality of the video surveillance camera lens according to the pattern of the test card presented on the camera target surface or use image intelligent software to read out the imaging quality of the video surveillance camera lens.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] (1) The close-up lens and the detection method for long focal length video surveillance camera lens image quality detection provided by the present invention can meet the detection of the image quality of video surveillance camera lenses with a focal length range of 2.5 to 75 mm. The addition of this close-up lens not only does not affect the already calibrated imaging quality of the video surveillance camera lens, but also can lengthen the near object distance and shorten the far object distance, realizing the miniaturization of the detection equipment;

[0034] (2) The method for using a close-up lens to assist in the image quality detection of a video surveillance camera lens provided by the present invention, under the premise that the corresponding camera device can achieve the full-screen test standard conditions and use fewer different specifications and overly large television test cards, when detecting a long focal length lens to be tested, the longest distance between the common television test card and the close-up lens can be no more than 2 meters; when detecting an ultra-wide angle short focal length lens to be tested, the shortest distance between the test card below version 2# and the close-up lens can be no less than 0.15 meters, which can make the detection equipment miniaturized while making the detection operation convenient;

[0035] (3) The close-up lens for long focal length video surveillance camera lens image quality detection provided by the present invention, by controlling the relative dispersion difference of the glass pair within an appropriate range, making the secondary spectrum of the close-up lens not too large, increasing the radius of the second surface and making it face the direction of the entrance pupil of the lens to be tested, plays a role in reducing the influence of off-axis aberration on the lens to be tested, and at the same time, is beneficial to the correction of on-axis spherical aberration and chromatic spherical aberration;

[0036] (4) The close-up lens for long focal length video surveillance camera lens image quality detection provided by the present invention, by selecting the refractive index difference of the glass pair within a certain range, is beneficial to controlling the secondary spectrum, chromatic spherical aberration and combined focal length value;

[0037] (5) The method for detecting the image quality of a video surveillance camera lens assisted by a close-up lens provided by the present invention adopts the concept of "central focal length". A close-up lens is used to adapt to video surveillance camera lenses within a certain focal length range, which can not only ensure the image quality but also avoid the trouble of frequently replacing the close-up lens. Only three close-up lenses can meet the detection of the image quality of video surveillance camera lenses within the focal length range of 2.5 - 75 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0039] Figure 1 is a schematic structural diagram of the first close-up lens of the present invention;

[0040] Figure 2 is a schematic structural diagram of the second close-up lens of the present invention;

[0041] Figure 3 is a schematic structural diagram of the third close-up lens of the present invention;

[0042] Figure 4 is a schematic optical principle diagram of the method for detecting the image quality of a video surveillance camera lens assisted by a close-up lens of the present invention;

[0043] Figure 5 are the MTF curve graph and geometric aberration graph after adding the first close-up lens to the video surveillance camera lens with a focal length ft' = 4 mm, where Figure 5 a is the MTF curve graph, Figure 5 b - Figure 5 e are the geometric aberration graphs;

[0044] Figure 6 is the MTF curve graph (l = 2300 mm) after removing the first close-up lens from the video surveillance camera lens with a focal length ft' = 4 mm;

[0045] Figure 7 are the MTF curve graphs after adding and removing the first close-up lens to the video surveillance camera lens with a focal length ft' = 6 mm, where Figure 7 a is the MTF curve graph after adding the first close-up lens, Figure 7 b is the MTF curve graph after removing the first close-up lens;

[0046] Figure 8 are the MTF curve graphs after adding and removing the first close-up lens to the video surveillance camera lens with a focal length ft' = 2.8 mm, where Figure 8 a is the MTF curve graph after adding the first close-up lens, Figure 8 b is the MTF curve graph after removing the first close-up lens;

[0047] Figure 9It is the MTF curve graph and geometric aberration graph of the video surveillance camera lens with a focal length of ft′ = 12 mm after adding the close-up lens II, where Figure 9 a is the MTF curve graph, Figure 9 b~ Figure 9 e are the geometric aberration graphs;

[0048] Figure 10 It is the MTF curve graph (l = 8430 mm) of the video surveillance camera lens with a focal length of ft′ = 12 mm after removing the close-up lens II;

[0049] Figure 11 It is the MTF curve graphs of the video surveillance camera lens with a focal length of ft′ = 16 mm after adding and removing the close-up lens II, where Figure 11 a is the MTF curve graph after adding the close-up lens II, Figure 11 b is the MTF curve graph after removing the close-up lens II;

[0050] Figure 12 It is the MTF curve graphs of the video surveillance camera lens with a focal length of ft′ = 8 mm after adding and removing the close-up lens II, where Figure 12 a is the MTF curve graph after adding the close-up lens II, Figure 12 b is the MTF curve graph after removing the close-up lens II;

[0051] Figure 13 It is the MTF curve graph and geometric aberration graph of the video surveillance camera lens with a focal length of ft′ = 35 mm after adding the close-up lens III, where Figure 13 a is the MTF curve graph, Figure 13 b~ Figure 13 e are the geometric aberration graphs;

[0052] Figure 14 It is the MTF curve graph (l = 1980 mm) of the video surveillance camera lens with a focal length of ft′ = 35 mm after removing the close-up lens III;

[0053] Figure 15 It is the MTF curve graphs of the video surveillance camera lens with a focal length of ft′ = 25 mm after adding and removing the close-up lens III, where Figure 15 a is the MTF curve graph after adding the close-up lens III, Figure 15 b is the MTF curve graph after removing the close-up lens III;

[0054] Figure 16 It is the MTF curve graphs of the video surveillance camera lens with a focal length of ft′ = 70 mm after adding and removing the close-up lens III, where Figure 16 a is the MTF curve graph after adding the close-up lens III, Figure 16 b is the MTF curve graph after removing the close-up lens III.

[0055] In the above figures: For the MTF curve, the abscissa is the characteristic frequency, and its coordinate unit is: line pairs / mm; the ordinate curve is the MTF values of the fields of view (0ω, 0.7ω, 1ω) at the full aperture and different characteristic frequencies. For the geometric aberration diagram, for the spherical aberration curve and the astigmatism curve, the unit of the abscissa is: mm; the unit of the abscissa of the longitudinal chromatic aberration curve is: μm; the abscissa of the meridional and sagittal characteristic curves is the tangent value of the aperture angle, with a maximum of 1; the ordinate is the maximum value of the dispersion value being ±20μm in Figure 5 and the maximum value being ±100μm in Figure 9 and the maximum value being ±10μm in Figure 13 .

[0056] Explanation of symbols in the figures: 1. Close-up lens one, 11. First lens, 12. Second lens, 2. Close-up lens two, 21. Third lens, 22. Fourth lens, 3. Close-up lens three, 31. Fifth lens, 32. Sixth lens, A. Resolution test chart, B. Virtual image, R. Close-up lens, T. Video surveillance camera lens, P. Camera target surface. Specific implementation mode

[0057] The following will specifically describe the content of the present invention in conjunction with the accompanying drawings of the specification and specific embodiments: Specific implementation mode (1):

[0059] As shown in Figure 1 - Figure 3 , a close-up lens for image quality detection of a long-focus video surveillance camera lens provided by the present invention is characterized in that: it includes close-up lens one 1, close-up lens two 2, and close-up lens three 3 respectively used for detecting short-focus video surveillance camera lenses, medium-focus video surveillance camera lenses, and long-focus video surveillance camera lenses. The close-up lens one 1 includes a first lens 11 and a second lens 12 that forms a close-contact cemented group with the first lens 11. The close-up lens two 2 includes a third lens 21 and a fourth lens 22 that forms a close-contact cemented group with the third lens 21. The close-up lens three 3 includes a fifth lens 31 and a sixth lens 32 that forms a close-contact cemented group with the fifth lens 31. The optical elements forming each close-up lens must meet the following conditions:

[0060] 0.01 < Pcd12 - Pcd11 < 0.02; 20 < R12 / R11 < 26 ‥‥‥ ①

[0061] 0.28 ≤ |Φ1 / R11 - Φ1 / R12| ‥‥‥ ②

[0062] 1.50 < n11 < 1.54; 60 < ν11 < 65 ‥‥‥ ③

[0063] 1.60 < n12 < 1.626; 35 < ν12 < 38 ‥‥‥ ④

[0064] 0.008 < Pcd22 - Pcd21 < 0.012; 4 < |R22 / R21| < 6......⑤

[0065] 0.4 ≤ |Φ2 / R21 - Φ2 / R22|......⑥

[0066] 1.50 < n21 < 1.54; 60 < ν21 < 65......⑦

[0067] 1.60 < n22 < 1.63; 56 < ν22 < 61......⑧

[0068] 0.001 < Pcd32 - Pcd31 < 0.006; 8 < |R32 / R31| < 12......⑨

[0069] 0.4 ≤ |Φ3 / R31 - Φ3 / R32|......⑩

[0070]

[0071]

[0072] Wherein, Pcd11, Pcd12, Pcd21, Pcd22, Pcd31, Pcd32 are the relative dispersion coefficients of the first lens 11 to the sixth lens 32 respectively; R11, R12, R13, R21, R22, R23, R31, R32, R33 are the radii of each surface of the first lens 11 to the sixth lens 32 respectively; Φ1 to Φ3 are the apertures of the first close-up lens 1 to the third close-up lens 3 respectively; n11, n12, n21, n22, n31, n32 are the refractive indices of the first lens 11 to the sixth lens 32 respectively; ν11, ν12, ν21, ν22, ν31, ν32 are the Abbe numbers of the first lens 11 to the sixth lens 32 respectively.

[0073] The purpose of setting condition ① is to control the relative dispersion difference of the glass pair within an appropriate range, increase the radius of the second surface and make it face the entrance pupil of the lens to be measured when the secondary spectrum of the short focal length close-up lens is not too large, so as to reduce the influence of off-axis aberration on the lens to be measured (especially the ultra-wide-angle short focal length). At the same time, it is beneficial to the correction of on-axis spherical aberration and chromatic spherical aberration.

[0074] The purpose of setting condition ② is to ensure a certain edging coefficient, which is beneficial to the processing of the first lens of the short focal length close-up lens.

[0075] The purpose of setting conditions ③ and ④ is to control the secondary spectrum, chromatic spherical aberration and combined focal length value by selecting the refractive index difference of the glass pair within a certain range.

[0076] The purpose of setting condition ⑤ is to control the relative dispersion difference of the glass pair within an appropriate range, so that when the secondary spectrum of the close-up lens in the medium focal length range is not too large, the radius of the second surface is increased and it faces the entrance pupil direction of the lens under test, which can reduce the influence of off-axis aberration on the lens under test. At the same time, it is beneficial to the correction of on-axis spherical aberration and chromatic spherical aberration.

[0077] The purpose of setting condition ⑥ is to ensure a certain edge grinding coefficient, which is beneficial to the processing of the first lens of the close-up lens in the medium focal length range.

[0078] The purpose of setting conditions ⑦ and ⑧ is to control the secondary spectrum, chromatic spherical aberration and combined focal length value by selecting the refractive index difference of the glass pair within a certain range.

[0079] The purpose of setting condition ⑨ is that since the focal length of the close-up lens in the long focal length range is very long, the secondary spectrum is made very small by controlling the relative dispersion difference of the glass pair. Since the field angle in the long focal length range is very small, it is not necessary for the radius of each surface to face the entrance pupil direction of the lens under test. In this way, the radius of the second surface can be reduced, which is beneficial to processing and is also beneficial to the correction of on-axis spherical aberration and chromatic spherical aberration.

[0080] The purpose of setting condition ⑩ is to ensure a certain edge grinding coefficient, which is beneficial to the processing of the first lens of the close-up lens in the long focal length range.

[0081] Condition The purpose of setting is to control the secondary spectrum, chromatic spherical aberration and combined focal length value by selecting the refractive index difference of the glass pair within a certain range.

[0082] Preferably, the first lens 11 is a convex-concave positive lens, and the second lens 12 is a convex-concave negative lens; the third lens 21 is a convex-concave positive lens, and the fourth lens 22 is a convex-concave negative lens; the fifth lens 31 is a concave-convex positive lens, and the sixth lens 32 is a concave-convex negative lens.

[0083] Preferably, the focal length range of the short focal length video surveillance camera lens is 2.5 - 8 mm, the focal length range of the medium focal length video surveillance camera lens is 8 - 20 mm, and the focal length range of the long focal length video surveillance camera lens is 20 - 75 mm.

[0084] Preferably, the first lens 11 and the third lens 21 are made of H-K9L, the second lens 12 and the fourth lens 22 are made of H-F4, the fifth lens 31 is made of H-ZK3, and the sixth lens 32 is made of H-ZK10. Specific embodiment (two):

[0086] As Figure 4 shown is a method for detecting the image quality of a video surveillance camera lens using a close-up lens provided by the present invention, which is characterized in that: the method includes the following steps:

[0087] a. Arrange the resolution test card A, the close-up lens R, the video surveillance camera lens T, and the camera target surface P in sequence along the light incident direction. The resolution test card A is located within the front focal point of the close-up lens R. The resolution test card A forms a virtual image B at a relatively long distance in the object space through the close-up lens R, and the virtual image B is imaged on the camera target surface P through the video surveillance camera lens T. The close-up lens (R) is selected as follows according to different focal length ranges of the video surveillance camera lens (T):

[0088] ① When the focal length range of the video surveillance camera lens T is between 2.5 and 8 mm, the close-up lens R uses the first close-up lens 1, and the positional relationship between the close-up lens R and the video surveillance camera lens T should satisfy 7 < Δ < 10;

[0089] ② When the focal length range of the video surveillance camera lens T is between 8 and 20 mm, the close-up lens R uses the second close-up lens 2, and the positional relationship between the close-up lens R and the video surveillance camera lens T should satisfy 15 < Δ < 30;

[0090] ③ When the focal length range of the video surveillance camera lens T is between 20 and 75 mm, the close-up lens R uses the third close-up lens 3, and the positional relationship between the close-up lens R and the video surveillance camera lens T should satisfy 15 < Δ < 30;

[0091] Where Δ is the distance between the first surface of the video surveillance camera lens T and the close-up lens R;

[0092] b. The detection personnel judge the imaging quality of the video surveillance camera lens T according to the pattern of the test card presented on the camera target surface P or use image intelligent software to read out the imaging quality of the video surveillance camera lens T.

[0093] As Figure 4 shown, where A is the scene of the close-up lens (the resolution test card in the present invention), which is placed within the front focal point of the close-up lens R, and B is the "virtual object surface" formed by the scene A through the close-up lens R. T is the lens to be detected, and through it, the "virtual object surface" B is imaged on the camera target surface P at a distance of Xt' from its rear focal point. Let the focal length of the close-up lens be f', 近 , the focal length of the lens T to be detected is ft'; the distance from the scene A to the close-up lens is |L 近 |; the distances from the first surface of the lens D to the virtual image B, to the close-up lens, and to its front principal plane are |Lt|, Δ, and OHt respectively. Since |Lt| >> OHt, it can be considered that |Lt| + OHt is approximately equal to |Lt|. Let the size of the object surface be ΦA, the size of the "virtual object surface" of the close-up lens be ΦB, and the size of the camera target surface be ΦC. The relationships between their magnification factors are set as |M| = |ΦA| / |ΦB|, |MR| = |ΦA| / |ΦP|, and |MT| = |ΦB| / |ΦP|

[0094] The following formulas can be derived based on the optical imaging relationship:

[0095] ⑴ Magnification between the object and image planes of the close-up lens: |M| = |1 - (|Lt| - △) / f′ 近 |

[0096] ⑵ Magnification ratio relationship: |MR| = |M| * |MT|

[0097] ⑶ Focal length of the close-up lens: f′ 近 = |MR| * (|Lt| - △) * ft′ / [(|Lt| - ft′) - |MR| * ft′]

[0098] (4) Distance between the close-up lens and the scene (the scene is actually a TV resolution test card):

[0099] |L 近 | = |(-|Lt| + △) * f′ 近 / (-|Lt| + △ + f′ 近 )|

[0100] In the above formulas, |Lt|, △, and ft′ are all known quantities that can be set. According to the actual detection requirements, when the focal length ft′ of the lens T to be detected is between 2 and 6 mm, |Lt| can be taken as 2 to 3.5 m; when ft′ is between 8 and 16 mm, |Lt| can be taken as 2.5 to 4.5 m; when ft′ is above 25 mm, |Lt| can be taken as above 3.5 m. When the focal length of the lens to be detected is relatively short, due to the large field of view angle, the aperture of the close-up lens will be very large, which is not conducive to processing, but if it is taken too small, it will not be conducive to the loading and unloading of the lens to be detected. Generally, it is taken as about 7 to 10 mm; for the lens to be detected with ft′ above 8 mm, it can be taken as above 15 mm. A necessary condition for the method of using a TV resolution test card for testing is that the image of the TV resolution test card formed on the target surface of the imaging device by the lens to be detected must fill the target. Therefore, |MR| can be calculated from the relationship formula of the selected test card and the size of the imaging device. In this way, the required f′ near and |L 近 | can be obtained according to the above formulas. Generally, by listing, different focal lengths of the lens to be detected ft′, different sizes of the imaging device |￠P|, different sizes of the TV resolution test card |ΦA|, and different distances |Lt| from the first surface of the lens to be detected to the virtual image plane can be shown, and the appropriate f′ 近 and |L 近Initial value of |. Taking the commonly used 4:3 standard 1# TV resolution test card as an example, its size is 280mm * 220mm, and the diagonal length is 356mm. CMOS sizes: 1 / 3″ (Φ6mm), 1 / 2.7″ (Φ6.6mm), 1 / 2.5″ (Φ7.2mm), 1 / 2″ (Φ8mm), 1 / 1.8″ (Φ8.9mm), 2 / 3″ (Φ11mm). Some of the calculated results are shown in Table 1:

[0101] Table 1 Unit: mm

[0102]

[0103]

[0104] From the analysis of the calculation results in the above table, it can be concluded that:

[0105] 1. As the imaging device increases, the focal length f′near of the close-up lens and |Lnear| to be selected need to decrease; however, as the focal length of the lens under test increases, the focal length f′near of the close-up lens and |Lnear| to be selected also increase, and may even become negative. For the lens under test with a large field of view and a large target surface, it is beneficial to select a larger test card accordingly; for the long-focus lens under test, it is more beneficial to select a test card with a small size, but attention should be paid to preventing |Lnear| from being too long (which will affect the miniaturization of the equipment).

[0106] 2. From the table, under the condition that the scene A and the "virtual object plane" B are required to be in a positive image relationship with each other, the calculated f′near is much larger than ft′. It can be seen that the axial and off-axis deflection angles borne by the close-up lens are not large, so its impact on the already corrected image quality of the lens under test will not be too great. Due to the large value of fnear, the spherical aberration (especially the secondary spectrum) is definitely large, which is worthy of attention when correcting the aberration of the close-up lens.

[0107] Since it is difficult for a separately optimized close-up lens to reflect the imaging effect of it combined with the subsequent lens under test, the method adopted in the present invention is to connect the initially designed close-up lens structure with the lenses under test with the same focal length, different fields of view, different apertures, and different lens structures for optimization calculation. That is, under the condition that the parameters of the lens under test remain unchanged, the aberration balance is carried out by changing the back intercept of the combined lens and the parameters of the close-up lens to obtain a new structure of the optimized close-up lens; then, under the condition of keeping the new back intercept unchanged, the close-up lens is removed, the object distance is readjusted, and the imaging quality of the lens under test at this time is calculated. If its imaging quality is good and the object distance also meets the design requirements, it can be considered that a close-up lens suitable for detecting various types of lenses under test with the same focal length has been selected from the best. The method is simple and clear, and proven to be feasible in practice. It not only solves the problem that it is difficult for a separately optimized close-up lens to reflect the imaging effect combined with the subsequent lens under test, but also avoids the problems of aberration and other parameter changes caused by different front principal planes of different lenses under test.

[0108] Theoretically, a close-up lens with the same focal length, relative aperture, and distance B from the "virtual object plane" will produce the best imaging effect, but this is unreasonable from the perspective of processing cost. The formula for calculating focal length from a close-up lens is:

[0109] f′ 近 =|MR|*(|Lt|-△)*ft′ / [(|Lt|-ft′)-|MR|*ft′]

[0110] It can be derived that: ft′=f′Close*|Lt| / [(|Lt|-△+f′Close)*|MR|+f′Close] (where, |MR|=|ΦA| / |ΦP|). In the above formula, if the same close-up lens is used, as long as the |MR| and |Lt| values ​​are changed, lenses with different focal lengths can also be tested. That is, when the target size of the camera is determined, the size of the test card and the |Lt| value can be changed to achieve the purpose of testing lenses with different focal lengths. However, according to our large number of calculations, when we want to use a designed close-up lens to adapt to the aberration of the lens to be tested with a larger range of focal lengths, the image quality will change greatly. Therefore, it is not appropriate to use a close-up lens to detect the aberration of the lens to be tested with a larger range of focal lengths. However, it is feasible to use a close-up lens to adapt to the detection of lenses with a certain focal length range, so that one lens can be used for multiple purposes. When selecting the appropriate focal length range of the close-up lens, the concept of "center focal length" is used. For example, the center focal length ft'=4mm selected for the short focus lens can meet the test of the lens with a focal length of 2.5-8mm; the center focal length ft'=12mm selected for the medium focus lens can meet the test of the lens with a focal length of 8-20mm; the center focal length ft'=35mm selected for the long focus lens can meet the test of the lens with a focal length of 20-75mm. When balancing the aberration, the correction should be based on the selected center focal length. In this way, we only use three groups of double-cemented lens combinations to meet the test of the imaging quality of the lens with a focal length from 2.5mm to 75mm.

[0111] Example 1:

[0112] The close-up lens of the present invention comprises a close-up lens 1, a close-up lens 2 and a close-up lens 3, which are respectively arranged at the front end of the short, medium and long focal length video surveillance camera lenses to be tested, and are used to assist the image quality detection of the video surveillance camera lenses.

[0113] The close-up lens 1 for the short focal length range is composed of a focal length of f′. 近 ​​​= 337.8 mm, and is composed of two convex-concave lenses glued together. The focal lengths of the front and rear lenses are 103 and -140.1 mm respectively. The radii of the lenses are R11, R12, R13; the thicknesses are d11 and d12; the optical materials are H-K9L and H-F4 respectively. Among them, the selected R12 is about 20 - 26 times that of R11. All the radii face the entrance pupil of the lens to be measured, which is beneficial to reducing the influence of off-axis aberration. Such a scheme can not only correct the imaging quality but also solve the problem of too small edging coefficient. As Figure 1 shown. The present invention selects ft′ = 4 mm as the central focal length of the short-focus lens to be measured, and its D / f = 1:2; the image plane size is Φ6.6 mm, Figure 6 and this is its MTF curve when the object distance is 2300 mm.

[0114] Table 2 lists the changes in the geometric parameters of several lenses to be measured in the short-focus range when adding and removing the close-up lens.

[0115] Table 2: f′ = 337.8 mm Unit: mm

[0116]

[0117]

[0118] The close-up lens 2 applicable to the medium-focus range is composed of two lenses with a focal length of f′near = 1033 mm and both having a convex-concave shape glued together. The focal lengths of the front and rear lenses are 297.5 and -408.7 mm respectively. The radii of the lenses are R21, R22, R23; the thicknesses are d21 and d22; the optical materials are H-K9L and H-F4 respectively. Among them, the selected R22 is about 4 - 6 times that of R21. Such a scheme can correct the imaging quality while solving the problem of too small edging coefficient. (As Figure 2 shown). The present invention selects ft′ = 12 mm as the central focal length of the medium-focus lens to be measured, and its D / f = 1:2; the image plane size is Φ6.6 mm, Figure 6 and this is its MTF curve when the object distance is 8430 mm. Table 3 lists the changes in several lenses to be measured in the medium-focus range when adding and removing the close-up lens:

[0119] Table 3: f′near = 1033 mm Unit: mm

[0120]

[0121] The close-up lens three 3 applicable to the long focal length range is composed of two lenses with a focal length of f′near = 2084.8 mm and a concave-convex shape, which are glued together. The focal lengths of the front and rear lenses are 111.9 and -119.03 mm respectively. The radii of the lenses are R31, R32, and R33; the thicknesses are d31 and d32 respectively; the optical materials are H-ZK3 and H-ZK10 respectively. Among them, the selected R31 is about 8-12 times that of R32. Due to the long focal length, the radii of its front and rear surfaces are very large. If the design method of short and medium focal lengths is adopted, the radius of the glued surface will be very large, making the edging coefficient very small. The close-up lens applicable to the long focal length range of the present invention adopts the scheme that neither the front nor the rear surface faces the entrance pupil of the lens to be measured, so that the radius of the glued surface can be made very small, and while the imaging quality is corrected, the problem of too small edging coefficient is solved. (As Figure 3 shown). The present invention selects ft′ = 35 mm as the central focal length of the long focal length lens to be measured, and its D / f = 1:2; the image plane size is Φ6.6 mm, Figure 6 is its MTF curve when the object distance is 1980 mm. Table 4 lists the changes in several lenses to be detected in the short focal length range when the close-up lens is added and removed:

[0122] Table 4: f′near = 2084.8 mm Unit: mm

[0123]

[0124] The above specific embodiments only explain the technical solution of the present invention in detail. The present invention is not only limited to the above embodiments. Any improvement or replacement based on the principle of the present invention shall be within the protection scope of the present invention.

Claims

1. A close-up lens for detecting image quality of a telephoto video surveillance camera lens, characterized in that it is composed of a close-up lens three (3) for detecting a telephoto video surveillance camera lens, wherein the close-up lens three (3) is composed of a fifth lens (31) and a sixth lens (32) forming a close-contact glued group with the fifth lens (31), and the optical elements of the close-up lens three (3) must meet the following conditions: 0.001<Pcd32-Pcd31<0.006;8<|R32 / R31|<12 ‥‥‥⑨ 0.4 ≦ |Φ3 / R31-Φ3 / R32 | ‥‥‥⑩ 1.57<n31<1.63; 55<ν31<59 ‥‥‥11 1.60<n32<1.63; 56<ν32<61 ‥‥‥12 in, Pcd31 and Pcd32 are the relative dispersion coefficients of the fifth lens (31) and the sixth lens (32), respectively; R31, R32 and R33 are the radii of the surfaces of the fifth lens (31) and the sixth lens (32), respectively; Φ3 is the aperture of the close-up lens 3 (3); n31 and n32 are the refractive indices of the fifth lens (31) and the sixth lens (32), respectively; ν31 and ν32 are the Abbe coefficients of the fifth lens (31) and the sixth lens (32), respectively; The focal length of the close-up lens three (3) is 2084.8 mm, the focal length range of the telephoto video surveillance camera lens is 20-75 mm, and the positional relationship between the close-up lens three (3) and the telephoto video surveillance camera lens should satisfy 15 < Δ < 30; wherein Δ is the interval from the first surface of the telephoto video surveillance camera lens to the close-up lens three (3); The fifth lens (31) is a meniscus positive lens, and the sixth lens (32) is a meniscus negative lens.

2. The close-up lens for image quality detection of a telephoto video surveillance camera lens according to claim 1, characterized in that: The fifth lens (31) is made of H-ZK3, and the sixth lens (32) is made of H-ZK10.

3. A method for detecting image quality of a video surveillance camera lens using a close-up lens as claimed in any one of claims 1 to 2, characterized in that: The method comprises the following steps: a. Arrange a resolution test card (A), a close-up lens (R), a video surveillance camera lens (T), and a camera target surface (P) in sequence along the incident direction of light, wherein the resolution test card (A) is located within the front focus of the close-up lens (R), and the resolution test card (A) forms a virtual image (B) at a relatively long distance from the object through the close-up lens (R), and the virtual image (B) is formed on the camera target surface (P) through the video surveillance camera lens (T), and the close-up lens (R) is a close-up lens three (3); b. The inspector judges the imaging quality of the video surveillance camera lens (T) based on the test card pattern presented on the camera target surface (P) or uses image intelligence software to read out the imaging quality of the video surveillance camera lens (T).

Images