Near-to-camera lens and detection method for detecting image quality of a medium-focus video monitoring camera lens

Abstract

The application relates to a close-up lens and a detection method for detecting the image quality of a medium-focus video monitoring camera lens, which comprises two close-up lenses for detecting the medium-focus video monitoring camera lens, wherein the close-up lens two is composed of a third lens and a fourth lens which are tightly bonded to form a close-up lens group, the close-up lens and the detection method can meet the image quality detection of the video monitoring camera lens with a focal length of 8-20 mm, the addition of the close-up lens does not affect the imaging quality of the video monitoring camera lens which has been corrected, the close-up lens can lengthen the near object distance and shorten the far object distance, and the miniaturization of the detection equipment is realized.

Description

[0001] This application is a divisional application of patent application No. 201710680696.0, with a filing date of August 10, 2017, and an invention title of a close-up lens and detection method for assisting video monitoring camera lens image quality detection. TECHNICAL FIELD

[0002] The present application relates to the field of optics, in particular to a close-up lens and detection method for mid-focus video monitoring camera lens image quality detection. BACKGROUND

[0003] With the advent of the era of video camera technology entering the all-megapixel high-definition image quality era, the imaging quality of the camera lens, as a key component, is also required to be greatly improved (currently enterprises require about 5-10 million). Since the yield is large, how to effectively detect the imaging quality of such lenses has become the focus of the optical community at home and abroad. At present, the resolution test card method is more suitable in terms of industry detection standards, adaptability to different focal length requirements, intuitiveness and cost performance. Especially when combined with a video camera, it can better reflect the imaging effect of the lens in the camera system. By replacing the color test card, it can also achieve the intuitive detection of the lens color reproduction effect which is difficult for other methods. However, its difficulties are: when detecting ultra-wide-angle short-focus lenses, how to truly reflect the imaging effect at a practical distance; when detecting long-focus lenses, how to solve the problems of effective illumination, large-format resolution test card production, and device miniaturization. SUMMARY

[0004] The purpose of the present application is to overcome the above-mentioned shortcomings, and to provide a close-up lens and detection method for mid-focus video monitoring camera lens image quality detection. The close-up lens and detection method can meet the detection of video monitoring camera lens image quality in the focal length range of 8-20mm. The addition of the close-up lens does not affect the imaging quality of the video monitoring camera lens which has been corrected, and the close-up lens can lengthen the near object distance and shorten the far object distance, thereby realizing the miniaturization of the detection device.

[0005] The present application is implemented as follows:

[0006] Scheme (I):

[0007] A near camera for detecting the image quality of a medium focal length video monitoring camera lens, characterized in that it comprises a near camera one, a near camera two and a near camera three for detecting a short focal length video monitoring camera lens, a medium focal length video monitoring camera lens and a long focal length video monitoring camera lens respectively, the near camera one comprises a first lens and a second lens which forms a close contact cemented group with the first lens, the near camera two comprises a third lens and a fourth lens which forms a close contact cemented group with the third lens, the near camera three comprises a fifth lens and a sixth lens which forms a close contact cemented group with the fifth lens, the optical elements of each near camera must satisfy 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] 1.57 < n31 < 1.1.63; 55 < ν31 < 59 … …

[0019] 1.60 < n32 < 1.63; 56 < ν32 < 61 … …

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

[0021] Preferably, the first lens is a convex-concave positive lens, the second lens is a convex-concave negative lens; the third lens is a convex-concave positive lens, 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 monitoring camera lens is 2.5-8mm, the focal length range of the medium-focus video monitoring camera lens is 8-20mm, and the focal length range of the long-focus video monitoring camera lens is 20-75mm.

[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] Scheme (two):

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

[0026] a. The resolution test card, the close-up lens, the video monitoring camera lens, and the camera target surface are arranged in sequence along the light incident direction, the resolution test card is located in the front focal point of the close-up lens, the resolution test card forms a virtual image at a far distance in the object field through the close-up lens, and the virtual image is imaged on the camera target surface through the video monitoring camera lens; the close-up lens (R) is selected according to the focal length range of the video monitoring camera lens (T) as follows:

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

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

[0029] ③When the focal length range of the video monitoring camera lens is 20-75mm, the close-up lens uses close-up lens three, and the positional relationship of the close-up lens and the video monitoring camera lens should satisfy 15< Δ <30;

[0030] Wherein, Δ is the interval from the first surface of the video monitoring camera lens to the close-up lens;

[0031] b. The imaging quality of the video monitoring camera lens is judged by a tester according to the test card pattern presented on the target surface of the camera or is read out by image intelligent software.

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

[0033] (1) The close-up lens and the detection method for middle focal length video monitoring camera lens image quality detection provided by the present application can meet the detection of the image quality of the video monitoring camera lens with a focal length range of 2.5-75mm. The addition of the close-up lens does not affect the corrected imaging quality of the video monitoring camera lens, and the close-up lens can lengthen the near object distance and shorten the far object distance, so that the detection equipment is miniaturized.

[0034] (2) The method for video monitoring camera lens image quality detection assisted by the close-up lens provided by the present application can realize the full-screen test standard condition and the use of less different specifications and oversized television test cards under the premise that the corresponding camera device can realize the full-screen test standard condition and the use of less different specifications and oversized television test cards. When the long focal length to-be-detected lens is detected, the longest distance between the commonly used television test card and the close-up lens is not more than 2 meters. When the ultra-wide angle and short focal length to-be-detected lens is detected, the shortest distance between the 2# version or below test card and the close-up lens is not less than 0.15 meters. The detection equipment is miniaturized, and the detection operation is convenient.

[0035] (3) The close-up lens for middle focal length video monitoring camera lens image quality detection provided by the present application controls the relative dispersion difference of the glass pair in a proper range, increases the radius of the second surface and makes it face the direction of the entrance pupil of the to-be-detected lens, so that the influence of the off-axis aberration on the to-be-detected lens is reduced under the condition that the second spectrum of the close-up lens is not too large, and the on-axis spherical aberration and chromatic spherical aberration are corrected.

[0036] (4) The close-up lens for middle focal length video monitoring camera lens image quality detection provided by the present application selects the refractive index difference of the glass pair in a certain range, which is beneficial to the control of the second spectrum, the chromatic spherical aberration and the combined focal length value.

[0037] (5) The method for detecting image quality of video monitoring camera lens with the aid of close-up lens provided by the present application adopts the concept of "central focal length", and uses one close-up lens to adapt to video monitoring camera lens with certain focal length range, which can ensure image quality and avoid the trouble of frequently changing close-up lens, and only three close-up lenses can meet the detection of image quality of video monitoring camera lens with focal length range of 2.5-75mm. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

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

[0042] Figure 4 is an optical principle schematic diagram of the method for detecting image quality of video monitoring camera lens with the aid of close-up lens of the present application;

[0043] Figure 5 is the MTF curve diagram and geometric aberration diagram of video monitoring camera lens with focal length ft'=4mm after adding the close-up lens one, wherein Figure 5 a is the MTF curve diagram, Figure 5 b is the geometric aberration diagram, Figure 5 e is the geometric aberration diagram;

[0044] Figure 6 is the MTF curve diagram of video monitoring camera lens with focal length ft'=4mm after removing the close-up lens one (l=2300mm);

[0045] Figure 7 is the MTF curve diagram of video monitoring camera lens with focal length ft'=6mm after adding and removing the close-up lens one, wherein Figure 7 a is the MTF curve diagram after adding the close-up lens one, Figure 7 b is the MTF curve diagram after removing the close-up lens one;

[0046] Figure 8 is the MTF curve diagram of video monitoring camera lens with focal length ft'=2.8mm after adding and removing the close-up lens one, wherein Figure 8 a is the MTF curve diagram after adding the close-up lens one, Figure 8 b is the MTF curve diagram after removing the close-up lens one;

[0047] Figure 9is the MTF curve plot and the geometric aberration plot of the video monitoring camera lens with focal length ft' = 12 mm with the second close-up lens added, where Figure 9 a is the MTF curve plot, Figure 9 b ~ Figure 9 e is the geometric aberration plot;

[0048] Figure 10 is the MTF curve plot (l = 8430 mm) of the video monitoring camera lens with focal length ft' = 12 mm without the second close-up lens;

[0049] Figure 11 is the MTF curve plot of the video monitoring camera lens with focal length ft' = 16 mm with and without the second close-up lens, where Figure 11 a is the MTF curve plot with the second close-up lens added, Figure 11 b is the MTF curve plot without the second close-up lens;

[0050] Figure 12 is the MTF curve plot of the video monitoring camera lens with focal length ft' = 8 mm with and without the second close-up lens, where Figure 12 a is the MTF curve plot with the second close-up lens added, Figure 12 b is the MTF curve plot without the second close-up lens;

[0051] Figure 13 is the MTF curve plot and the geometric aberration plot of the video monitoring camera lens with focal length ft' = 35 mm with the third close-up lens added, where Figure 13 a is the MTF curve plot, Figure 13 b ~ Figure 13 e is the geometric aberration plot;

[0052] Figure 14 is the MTF curve plot (l = 1980 mm) of the video monitoring camera lens with focal length ft' = 35 mm without the third close-up lens;

[0053] Figure 15 is the MTF curve plot of the video monitoring camera lens with focal length ft' = 25 mm with and without the third close-up lens, where Figure 15 a is the MTF curve plot with the third close-up lens added, Figure 15 b is the MTF curve plot without the third close-up lens;

[0054] Figure 16 is the MTF curve plot of the video monitoring camera lens with focal length ft' = 70 mm with and without the third close-up lens, where Figure 16 a is the MTF curve plot with the third close-up lens added, Figure 16 b is the MTF curve plot without the third close-up lens.

[0055] In the above figures: the horizontal coordinate of the MTF curve is characteristic frequency, the coordinate unit is: line pair / mm; the vertical coordinate curve is the MTF value of the field of view (0ω, 0.7ω, 1ω) in the full aperture at different characteristic frequencies. The spherical aberration curve and the astigmatism curve of the geometric aberration diagram, the horizontal coordinate unit is: mm; the horizontal coordinate unit of the lateral chromatic aberration curve is: μm; the horizontal coordinate of the meridian and sagittal characteristic curves is the tangent value of the aperture angle, the maximum is 1; the vertical coordinate is the maximum value of the dispersion value in Figure 5 ±20 μm in Figure 9 ±100 μm in Figure 13 ±10 μm in

[0056] Figure symbol explanation: 1, close-up mirror one, 11, first lens, 12, second lens, 2, close-up mirror two, 21, third lens, 22, fourth lens, 3, close-up mirror three, 31, fifth lens, 32, sixth lens, A, resolution test card, B, virtual image, R, close-up mirror, T, video monitoring camera lens, P, camera target surface. DETAILED DESCRIPTION

[0057] The content of the application will be described in detail below in combination with the drawings and specific embodiments of the specification: Specific embodiment (one):

[0059] As shown in Figure 1 - Figure 3 Fig. 1 is a close-up mirror for detecting the image quality of a medium focal length video monitoring camera lens provided by the present application, characterized by: comprising a close-up mirror one 1, a close-up mirror two 2 and a close-up mirror three 3 for detecting a short focal length video monitoring camera lens, a medium focal length video monitoring camera lens and a long focal length video monitoring camera lens respectively, the close-up mirror one 1 comprises a first lens 11 and a second lens 12 which forms a close contact cemented group with the first lens 11, the close-up mirror two 2 comprises a third lens 21 and a fourth lens 22 which forms a close contact cemented group with the third lens 21, and the close-up mirror three 3 comprises a fifth lens 31 and a sixth lens 32 which forms a close contact cemented group with the fifth lens 31, the optical elements of each close-up mirror must satisfy 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 < v21 < 65...... (7)

[0067] 1.60 < n22 < 1.63; 56 < v22 < 61...... (8)

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

[0069] 0.4 ≦ |Φ3 / R31 - Φ3 / R32|...... (10)

[0070] 1.57 < n31 < 1.63; 55 < v31 < 59...... (11)

[0071] 1.60 < n32 < 1.63; 56 < v32 < 61...... (12)

[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 the surfaces of the first lens 11 to the sixth lens 32 respectively; Φ1-Φ3 are the apertures of the close-up lens 1 to the 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; v11, v12, v21, v22, v31, v32 are the Abbe coefficients of the first lens 11 to the sixth lens 32 respectively.

[0073] The purpose of condition ① is to control the relative dispersion difference of the glass pair within a proper range, to increase the radius of the second surface and make it towards the direction of the entrance pupil of the to-be-tested lens under the condition that the second spectrum of the close-up lens in the short-focus section is not too large, so as to reduce the influence of the off-axis aberration on the to-be-tested lens (especially the ultra-wide-angle short-focus lens). Meanwhile, it is beneficial to the correction of the on-axis spherical aberration and chromatic spherical aberration.

[0074] The purpose of condition ② 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 short-focus section.

[0075] The purposes of conditions ③ and ④ are to control the second spectrum, chromatic spherical aberration and combined focal length value by selecting the refractive index difference of a certain range of glass pairs.

[0076] The purpose of condition ⑤ is to control the relative dispersion difference of the glass pair within a proper range, to increase the radius of the second surface and direct it towards the entrance pupil of the lens to be tested, so as to reduce the influence of the off-axis aberration on the lens to be tested, under the condition that the secondary spectrum of the close-up lens in the middle focal length section is not too large. Meanwhile, it is beneficial to the correction of the on-axis spherical aberration and chromatic spherical aberration.

[0077] The purpose of 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 middle focal length section.

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

[0079] The purpose of condition ⑨ is to make the secondary spectrum very small by controlling the relative dispersion difference of the glass pair due to the very long focal length of the close-up lens in the long focal length section. Since the field angle of the long focal length section is very small, the radius of each surface does not need to be directed towards the entrance pupil of the lens to be tested, so the radius of the second surface can be reduced, which is beneficial to the processing and is also beneficial to the correction of the on-axis spherical aberration and chromatic spherical aberration.

[0080] The purpose of 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 section.

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

[0082] Preferably, the first lens 11 is a convex-concave positive lens, the second lens 12 is a convex-concave negative lens; the third lens 21 is a convex-concave positive lens, 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 monitoring camera lens is 2.5-8mm, the focal length range of the middle focal length video monitoring camera lens is 8-20mm, and the focal length range of the long focal length video monitoring camera lens is 20-75mm.

[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. DETAILED DESCRIPTION (II):

[0086] As Figure 4The present invention illustrates a method for image quality detection of a video surveillance camera lens using a close-up lens, characterized by the following steps:

[0087] a. Arrange the resolution test card A, close-up lens R, video surveillance camera lens T, and camera target surface P sequentially along the direction of light incidence. 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 far distance on the object side through the close-up lens R. The virtual image B is imaged onto the camera target surface P through the video surveillance camera lens T. The close-up lens (R) is selected according to the different focal length ranges of the video surveillance camera lens (T) as follows:

[0088] ① When the focal length of the video surveillance camera lens T is in the range of 2.5 to 8 mm, the close-up lens R should be 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 of the video surveillance camera lens T is in the range of 8 to 20 mm, the close-up lens R should be close-up lens 2. 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 of the video surveillance camera lens T is in the range of 20 to 75 mm, the close-up lens R should be a close-up lens 3. 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 from the first surface of the video surveillance camera lens T to the close-up lens R;

[0092] b. The testing personnel judge the imaging quality of the video surveillance camera lens T based on the test card pattern presented on the camera target surface P, or use image intelligence software to interpret the imaging quality of the video surveillance camera lens T.

[0093] like Figure 4 As shown, A is the scene in the close-up lens (in this invention, it is the resolution test card), which is placed within the front focal point of the close-up lens R. B is the "virtual object surface" formed by the scene A through the close-up lens R. T is the lens to be tested, which images the "virtual object surface" B onto the camera target surface P, which is a distance Xt′ from its rear focal point. Let the focal length of the close-up lens be f′. 近 The focal length ft′ of the lens T to be tested; the distance from the scene A to the close-up lens is |L 近|Lt|, △, OHt. Since |Lt| » OHt, |Lt| + OHt can be considered approximately equal to |Lt|. Let the size of the object plane be ΦA, the size of the "virtual object plane" of the close-up lens be ΦB, and the size of the target plane of the camera be ΦC. Let the magnification between them be |M| = |ΦA| / |ΦB|, |MR| = |ΦA| / |ΦP|, and |MT| = |ΦB| / |ΦP|

[0094] According to the optical imaging relationship, the following formulas can be derived:

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

[0096] (2) The magnification relationship: |MR| = |M| * |MT|

[0097] (3) The focal length of the close-up lens: f' 近 = |MR| * (|Lt| - △) * ft' / [(|Lt| - ft') - |MR| * ft']

[0098] (4) The distance between the close-up lens and the object (the object is actually a television resolution test card):

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

[0100] In the above formulas, |Lt|, △, and ft' are all known quantities. According to actual detection requirements, when the focal length ft' of the lens T to be detected is 2 to 6 mm, |Lt| can be 2 to 3.5 m; when ft' is 8 to 16 mm, |Lt| can be 2.5 to 4.5 m; and when ft' is 25 mm or more, |Lt| can be 3.5 m or more. △ is generally about 7 to 10 mm for a short focal length lens to be detected, because a large field angle would result in a large aperture of the close-up lens, which is not conducive to processing, but taking it too small would also not be conducive to the installation and removal of the lens to be detected. For ft' of 8 mm or more, △ can be 15 mm or more. A necessary condition for the television resolution test card testing method is that the image of the television resolution test card formed by the lens to be detected on the target plane of the camera device must fill the target plane, so |MR| can be calculated from the relationship between the selected test card and the size of the camera device. In this way, the required f' close and |L 近| Generally, the different focal lengths of the lens ft', the different sizes of the camera device |￠P|, the different sizes of the television resolution test card |ΦA| and the different distances |Lt| from the first surface of the lens to the virtual image surface can be shown by the list method to find the appropriate f' 近 and |L 近 | initial value. For example, a commonly used 4:3 specification 1# television resolution test card has a size of 280mm*220mm and a diagonal length of 356mm. The CMOS size is 1 / 3"(Φ6mm), 1 / 2.7"(Φ6.6mm), 1 / 2.5"(Φ7.2mm), 1 / 2"(Φ8mm), 1 / 1.8"(Φ8.9mm), and 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 camera device increases, the near camera lens focal length f' near and |L near | need to be reduced; but as the focal length of the lens to be tested increases, the near camera lens focal length f' near and |L near | also increase, and even become negative. For large field of view and large target surface of the lens to be tested, it is beneficial to select a large test card; while for long focal length lenses to be tested, it is more beneficial to select a small size test card, but attention should be paid to prevent |L near | from being too long (which will affect the miniaturization of the equipment).

[0106] 2. From the table, under the condition that the object A and the "virtual object surface" B form a positive image relationship, the calculated f' near is much larger than ft', so the near camera lens bears a small axial and off-axis angle, and therefore it has little effect on the image quality of the lens to be tested which has been corrected. Since the f' near value is large, the chromatic aberration (especially the second spectrum) is definitely large, and attention should be paid when correcting the near camera lens aberration.

[0107] Since the separately optimized close-up lens is difficult to reflect the imaging effect of the combination of the close-up lens and the rear lens to be tested, the method adopted by the application is to combine the initial design of the close-up lens structure with the lens to be tested with the same focal length, different fields of view, different apertures, different lens structures, and then optimize the calculation, that is, under the condition that the parameters of the lens to be tested are unchanged, the aberration is balanced by changing the back distance and the parameters of the close-up lens, and the new structure of the optimized close-up lens is obtained; then, under the condition that the new back distance is unchanged, the close-up lens is removed, the object distance is adjusted again, and the imaging quality of the lens to be tested at this time is calculated, if the imaging quality is good and the object distance meets the design requirements, it can be considered that the close-up lens suitable for the detection of various types of lenses to be tested with the same focal length is selected. The method is simple and clear, and it is proved to be feasible, which not only solves the problem that the separately optimized close-up lens is difficult to reflect the imaging effect of the combination of the close-up lens and the rear lens to be tested, but also avoids the problem of the change of aberration and other parameters caused by the different front main surfaces of different lens structures.

[0108] Theoretically, a close-up lens has the best imaging effect on the lens to be tested with the same focal length, the same relative aperture and the same "virtual object plane" B distance, but it is not reasonable from the perspective of processing cost. From the formula for calculating the focal length of the close-up lens:

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

[0110] It can be derived that: ft′ = f′near * |Lt| / [(|Lt| - Δ + f′near) * |MR| + f′near] (where, |MR| = |ΦA| / |ΦP|). In the above formula, if the same close-up lens is used, as long as the values of |MR| and |Lt| are changed, it is also possible to detect the lens to be measured with different focal lengths. That is, when the size of the camera's target surface is determined, the size of the test chart and the value of |Lt| can be changed to achieve the purpose of detecting the lens to be measured with different focal lengths. However, based on our extensive calculations, when trying to use a designed close-up lens to adapt to the aberration of the lens to be measured with a large range of focal lengths, the image quality will change significantly. Therefore, it is not appropriate to use a single close-up lens to detect the aberration of the lens to be measured with a large range of focal lengths. However, it is feasible to use a single close-up lens to adapt to the detection of the lens to be measured within a certain focal length range, which can achieve multiple uses of a single lens. When selecting the appropriate focal length range of the close-up lens, the concept of "central focal length" is adopted. For example, the central focal length ft′ selected for short focal length is 4 mm, which can meet the detection of the lens to be measured with a focal length of 2.5 - 8 mm; the central focal length ft′ selected for medium focal length is 12 mm, which can meet the detection of the lens to be measured with a focal length of 8 - 20 mm; the central focal length ft′ selected for long focal length is 35 mm, which can meet the detection of the lens to be measured with a focal length of 20 - 75 mm. When balancing aberration, correction should be carried out based on the selected central focal length. In this way, we only used three groups of doublet lens combinations to meet the detection of the imaging quality of the lens to be measured with a focal length from 2.5 mm to 75 mm.

[0111] Embodiment 1:

[0112] The close-up lens of the present invention includes close-up lens 1, close-up lens 2, and close-up lens 3, which are respectively arranged at the front ends of the video surveillance camera lenses to be measured with short, medium, and long focal lengths, and are used to assist in detecting the image quality of the video surveillance camera lenses.

[0113] The close-up lens 1 applicable to the short focal length range is composed of two convex-concave lenses with a focal length of f′ 近 = 337.8 mm, and the front and rear lenses have focal lengths of 103 and -140.1 mm respectively. The radii of the lenses are R11, R12, and R13; the thicknesses are d11 and d12; the optical materials are H-K9L and H-F4 respectively. Among them, the selected R12 is approximately 20 - 26 times that of R11, and the orientations of 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 correct the imaging quality while solving 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 focal length lens to be measured, and its D / f = 1:2; the image surface 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 geometric parameter changes of several short focal range lenses with and without the close-up lens.

[0115] Table 2: f' = 337.8 mm unit: mm

[0116]

[0117]

[0118] The close-up lens two 2 for the middle focal range is made of two lenses with a focal length of f' close = 1033 mm and a convex-concave shape. The focal lengths of the front and rear lenses are 297.5 and -408.7 mm, respectively. The radii of the lenses are R 21, R 22, and R 23, respectively. The thicknesses of the lenses are d 21 and d 22, respectively. The optical materials of the lenses are H-K9L and H-F4, respectively. In this case, R 22 is about 4-6 times R 21. This scheme corrects the imaging quality and solves the problem of too small edge grinding coefficient. Figure 2 The center focal length of the middle focal range lens is ft' = 12 mm, D / f = 1:2, and the image size is Φ6.6 mm. Figure 6 The MTF curve of the middle focal range lens at an object distance of 8430 mm is shown in Fig. 3. Table 3 lists the changes of several middle focal range lenses with and without the close-up lens.

[0119] Table 3: f' close = 1033 mm unit: mm

[0120]

[0121] The close-up lens three 3 for the long focal range is made of two lenses with a focal length of f' close = 2085 mm and a concave-convex shape. The focal lengths of the front and rear lenses are 111.9 and -119.03 mm, respectively. The radii of the lenses are R 31, R 32, and R 33, respectively. The thicknesses of the lenses are d 31 and d 32, respectively. The optical materials of the lenses are H-ZK3 and H-ZK 10, respectively. In this case, R 31 is about 8-12 times R 32. Since the focal length is long, the radii of the front and rear surfaces are large. If the short or middle focal range design method is used, the radii of the bonding surfaces will be large, and the edge grinding coefficient will be small. The close-up lens for the long focal range of the present application uses a scheme in which neither the front surface nor the rear surface faces the entrance pupil of the lens to be tested. This makes the radii of the bonding surfaces small, corrects the imaging quality, and solves the problem of too small edge grinding coefficient. Figure 3 The center focal length of the long focal range lens is ft' = 35 mm, D / f = 1:2, and the image size is Φ6.6 mm. Figure 6is its MTF curve at an object distance of 1980 mm. Table 4 lists the changes in the short-focus range for several lenses to be tested with and without the addition of a teleconverter:

[0122] Table 4: f' near = 2084.8 mm Units: mm

[0123]

[0124] The above detailed description is only a detailed explanation of the technical solutions of the present application, and the present application is not limited to the above examples only, any improvement or replacement according to the principle of the present application shall be within the protection scope of the present application.

Claims

1. A close-up lens for image quality testing of a medium-focus video surveillance camera lens, characterized in that: it comprises a second close-up lens (2) for testing a medium-focus video surveillance camera lens, wherein the second close-up lens (2) comprises a third lens (21) and a fourth lens (22) forming a close-fitting cemented group with the third lens (21), and the optical elements of the second close-up lens (2) must meet the following conditions: 0.008<Pcd22-Pcd21<0.012; 4<|R22 / R21|<6‥‥‥⑤ 0.4≦|Φ2 / R21-Φ2 / R22|‥‥‥⑥ 1.50<n21<1.54; 60<ν21<65‥‥‥⑦ 1.60<n22<1.63; 56<ν22<61‥‥‥⑧ Where Pcd21 and Pcd22 are the relative dispersion coefficients of the third lens (21) and the fourth lens (22), respectively; R21, R22, and R23 are the radii of each surface of the third lens (21) and the fourth lens (22), respectively; Φ2 is the aperture of the close-up lens 2 (2); n21 and n22 are the refractive indices of the third lens (21) and the fourth lens (22), respectively; and ν21 and ν22 are the Abbe coefficients of the third lens (21) and the fourth lens (22), respectively. The focal length of the second close-up lens (2) is 1033mm, and the focal length range of the medium-focus video surveillance camera lens is 8-20mm. The positional relationship between the second close-up lens (2) and the medium-focus video surveillance camera lens should satisfy 15 < Δ < 30; where Δ is the distance from the first surface of the medium-focus video surveillance camera lens to the second close-up lens (2). The third lens (21) is a convex-concave positive lens, and the fourth lens (22) is a convex-concave negative lens.

2. The close-up lens for image quality detection of a medium-range video surveillance camera lens according to claim 1, characterized in that: The third lens (21) is made of H-K9L and the fourth lens (22) is made of H-F4.

3. A method for image quality detection of a video surveillance camera lens assisted by a close-up lens as described in any one of claims 1-2, characterized in that: The method includes the following steps: a. The resolution test card (A), the close-up lens (R), the video surveillance camera lens (T), and the camera target surface (P) are arranged in sequence along the direction of light incidence. The resolution test card (A) is located in the front focal point of the close-up lens (R). The resolution test card (A) forms a virtual image (B) at a relatively far distance from the object through the close-up lens (R). 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 a second close-up lens (2). b. The testing personnel judge the imaging quality of the video surveillance camera lens (T) based on the test card pattern presented on the camera target surface (P) or use image intelligence software to interpret the imaging quality of the video surveillance camera lens (T).

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