A method for adjusting image plane consistency of continuous zoom lens

Abstract

The present invention provides a method for adjusting the image plane consistency of a continuous zoom lens, which is used to solve the technical problems of existing methods for adjusting the image plane consistency of a continuous zoom system, such as large limitations, lack of theoretical guidance, high blindness, and cumbersome operation, which in turn lead to low adjustment efficiency. The present invention provides a method for adjusting the image plane consistency of a continuous zoom lens, which uses optical design theory analysis as a guide for the adjustment process, analyzes the normalized image plane defocus sensitivity of the short focus and long focus of each zoom component in the continuous zoom lens, and combines the relationship between the image plane defocus amount of the defocus-sensitive zoom component and the magnification ratio of the zoom component movement amount to find the zoom component to be adjusted and determine the axial movement amount and movement direction of the zoom component, thereby completing the image plane consistency adjustment. The adjustment is efficient and convenient and effectively guarantees the imaging quality of the continuous zoom lens. The method can be widely used in the image plane consistency adjustment of various zoom lenses.

Description

Technical Field

[0001] The present invention relates to a method for adjusting a zoom lens, and in particular to a method for adjusting the image plane consistency of a continuous zoom lens. Background Art

[0002] Currently, continuous zoom lenses are widely used in security, surveillance, Skynet, transportation, production safety, and forest fire prevention. These lenses consist of various zoom components. Because these components include both moving elements, such as the zoom and compensation groups, and fixed elements, such as the front, middle, and rear fixed groups, their overall assembly and adjustment are complex. However, fast and high-quality assembly and adjustment have always been a key factor restricting the application of continuous zoom lenses.

[0003] Currently, the assembly process of a continuous zoom lens primarily involves two adjustments: 1. Image quality adjustment of the continuous zoom lens. This adjustment should ensure that the system image quality at each focal length position, such as the system wavefront aberration or optical transfer function (MTF), meets the requirements. 2. Image consistency adjustment of the continuous zoom lens. Since the focal length of a continuous zoom lens changes continuously throughout the zoom range, image consistency must be ensured after the entire assembly is complete. This means that the image must be consistently clear throughout the entire zoom range. However, the image quality adjustment of a continuous zoom lens primarily controls assembly errors such as decentration and tilt within the optical lenses of each zoom component. The assembly process only considers whether the image quality at each focal length position meets the requirements, without considering the image quality throughout the entire zoom range. Furthermore, testing is performed only on the image plane corresponding to each focal length position to determine the system wavefront aberration or optical transfer function (MTF). However, during the initial assembly of a continuous zoom lens, due to the accumulation of assembly errors (zoom component spacing, cam curve errors, etc.), the image plane corresponding to each focal length position is not unique. Even if the imaging quality at the image plane corresponding to each focal length position meets the requirements, since the continuous zoom lens can only have one common image plane for placing the image detector at each focal length position, if the image plane consistency is not adjusted, the entire zoom process will not produce consistent and clear images. Therefore, image plane consistency adjustment of continuous zoom lenses is an issue that needs to be urgently addressed.

[0004] Currently, most zoom lens assembly and adjustment methods focus solely on adjusting the image quality. For example, Zhao Yue et al., in "Zoom Optical System Assembly Based on Aberration Characteristic Analysis," published in Volume 41, Issue 2 of Applied Optics, describe a zoom system coaxiality adjustment method based on aberration characteristic analysis. While this method primarily addresses zoom lens image quality adjustment, it fails to address image plane consistency adjustment for zoom lenses. Chinese Patent Publication No. CN 111650711A discloses a method for adjusting a zoom system's image plane consistency. This method achieves image plane consistency throughout the entire zoom range by repeatedly adjusting the axial position of the focusing group and image detector. However, this adjustment method has significant limitations. It is only applicable to zoom lenses with a fixed front group as the focusing group and no other fixed components between the moving components. It is not universally applicable to other zoom structures that include fixed components between the moving components. In addition, this method lacks theoretical guidance and is highly blind. It requires repeated attempts to adjust the position of the focusing group and the imaging detector. The operation is cumbersome and leads to low installation and adjustment efficiency. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problems of existing methods for adjusting the image plane consistency of continuous zoom systems, such as large limitations, lack of theoretical guidance, high blindness and cumbersome operation, which lead to low installation efficiency, and to provide a method for adjusting the image plane consistency of a continuous zoom lens.

[0006] In order to achieve the above object, the technical solution provided by the present invention is as follows:

[0007] A method for adjusting image plane consistency of a continuous zoom lens is characterized in that it includes the following steps:

[0008] Step 1: Adjust the distance between each zoom element of the continuous zoom lens to meet the design requirements;

[0009] Step 2: Analyze the image plane defocus amount and the magnification ratio between the image plane defocus amount and the zoom component movement amount caused by independently changing the axial position of each zoom component at the short focus position and the long focus position of the continuous zoom lens by the same amount, and obtain the normalized image plane defocus sensitivity of each zoom component at the short focus and long focus positions; based on the normalized image plane defocus sensitivity of each zoom component at the short focus and long focus positions, select the zoom component that is sensitive to long focus image plane defocus and has the largest difference in defocus sensitivity between the long focus image plane and the short focus image plane as the most sensitive component at long focus;

[0010] Step 3: Image plane consistency test;

[0011] Step 3.1, constructing an image plane consistency test device; the image plane consistency test device includes a collimator, a resolution plate placed at the focal plane of the collimator, and a reading microscope coaxially placed behind the collimator; during the test, the continuous zoom lens is coaxially placed between the collimator and the reading microscope;

[0012] Step 3.2: Move the zoom lens to the short focal length position, and then adjust the axial position of the reading microscope until the image of the discrimination plate is clearest.

[0013] Step 3.3: Move the zoom lens to the telephoto position and observe with a reading microscope whether the image clarity of the resolution plate at the telephoto position meets the preset requirements. If so, the image plane consistency meets the preset requirements, and the image plane consistency adjustment is completed. Otherwise, adjust the axial position of the reading microscope until the image clarity of the resolution plate at the telephoto position meets the preset requirements. Record the axial movement amount and movement direction of the reading microscope, and proceed to step 4.

[0014] Step 4: image plane consistency adjustment;

[0015] Step 4.1, based on the axial movement and movement direction of the reading microscope recorded in step 3.3, combined with the magnification ratio between the image plane defocus amount corresponding to the most sensitive telephoto component and the movement amount of the zoom component in step 2, calculate the axial movement of the most sensitive telephoto component and determine the movement direction;

[0016] In step 4.2, adjust the axial position of the most sensitive telephoto component according to the axial movement amount and movement direction of the most sensitive telephoto component. Return to step 3.2 and repeat the adjustment cycle until the image clarity of the discrimination plate at the telephoto position observed by the reading microscope when the continuous zoom lens moves to the telephoto position in step 3.3 meets the preset requirements, completing the image plane consistency adjustment.

[0017] Furthermore, step A is further included before step 1:

[0018] The distance between the center point of the pin on each moving component barrel in the continuous zoom lens and the axial vertex of the first lens in the corresponding moving component barrel is adjusted to a preset range.

[0019] Furthermore, in step A, the distance tolerance between the center point of the pin on each moving component barrel in the continuous zoom lens and the axial vertex of the first lens in the corresponding moving component barrel is less than or equal to 0.05 mm.

[0020] Furthermore, step 1 is specifically as follows:

[0021] The interval between two adjacent fixed components and the interval between adjacent moving components and the fixed component are adjusted according to the design tolerance requirements of the optical system, and the interval between two adjacent moving components is constrained according to the cam curve.

[0022] Furthermore, in step 2, optical design software CODE V or ZEMAX is used to analyze the image plane defocus amount and the magnification ratio between the image plane defocus amount and the zoom component movement amount caused when the axial position of each zoom component of the continuous zoom lens is independently changed by a certain same movement amount at the short focus position and the long focus position.

[0023] Furthermore, in step 2, the movement amount is a positive value or a negative value; the movement amount is ±0.05 mm or ±0.1 mm.

[0024] Furthermore, in step 3.1, the focal length of the collimator is greater than 3 times the telephoto focal length of the continuous zoom lens; and the numerical aperture of the reading microscope is greater than the maximum numerical aperture of the continuous zoom lens.

[0025] The beneficial effects of the present invention compared to the prior art are as follows:

[0026] 1. The present invention provides a method for adjusting the image plane consistency of a continuous zoom lens. This method uses optical design theory analysis as a guide for the adjustment process. By analyzing the normalized image plane defocus sensitivity of each zoom component at short and long focal lengths in the continuous zoom lens, and combining the magnification relationship between the image plane defocus amount of the defocus-sensitive zoom component and the zoom component movement amount, the zoom component that needs adjustment is identified and the axial movement amount and movement direction of the zoom component are determined. This method avoids the technical difficulties of existing methods for adjusting the image plane consistency of continuous zoom lenses, such as a lack of theoretical guidance, high operational complexity, and low zoom lens adjustment efficiency. The method can be widely applied to the image plane consistency adjustment of various continuous zoom lenses.

[0027] 2. The present invention provides a method for adjusting the image plane consistency of a continuous zoom lens. This method essentially studies the factors that affect the image plane consistency of a continuous zoom lens, provides guidance for assembly and adjustment, and avoids aimless and repeated disassembly and assembly during lens assembly. This method not only ensures the final imaging quality of the zoom lens but also saves assembly time. It is of great significance to improving the assembly efficiency of the continuous zoom lens and has the characteristics of simple operation, high efficiency, and practicality.

[0028] 3. The image plane consistency adjustment method for a continuous zoom lens provided by the present invention is not limited by the structure of the continuous zoom lens. It is applicable to both continuous zoom lenses with no other fixed components between moving components and continuous zoom lenses with fixed components, thereby improving the versatility and universality of the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a flow chart of an embodiment of a method for adjusting image plane consistency of a continuous zoom lens according to the present invention;

[0030] Figure 22. The optical path diagram of the continuous zoom lens in the embodiment of the present invention;

[0031] Figure 3 Schematic diagram of the structure of the image plane consistency testing device in an embodiment of the present invention;

[0032] Figure 4 Graph showing the normalized image plane defocus sensitivity of the short and long focal lengths of each zoom component in the continuous zoom lens according to an embodiment of the present invention.

[0033] The specific reference numerals are as follows:

[0034] 1-collimator; 2-discriminator plate; 3-continuous zoom lens; 4-reading microscope; 5-human eye observation point; 6-front fixed group, 7-zoom group, 8-intermediate fixed group, 9-compensation group, 10-rear fixed group. DETAILED DESCRIPTION

[0035] In order to make the advantages and features of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] A method for adjusting the image plane consistency of a continuous zoom lens, such as Figure 1 As shown, the specific steps are as follows:

[0037] Step 1: Adjust the intervals between each moving element and the corresponding pin in the continuous zoom lens 3.

[0038] like Figure 2 As shown, the zoom lens 3 in this embodiment includes a front fixed group 6, a zoom group 7, an intermediate fixed group 8, a compensating group 9, and a rear fixed group 10. The zoom lens 3 has a focal length range of 15 mm to 300 mm, an operating wavelength of 450 nm to 650 nm, and an F-number range of F4.5 to F5.5.

[0039] Each zoom element in the continuous zoom lens 3 is mounted within its own lens barrel. For the moving element, a pin is mounted on the outside of its barrel. This pin is constrained by a cam groove in the cam barrel, thereby achieving the desired motion pattern for zooming. During assembly of each moving element, the distance between the center point of the pin on each moving element's barrel and the axial vertex (along the optical axis) of the first lens in the corresponding moving element's barrel is controlled. Based on experience, the tolerance for this distance is generally controlled within 0.05 mm.

[0040] Step 2: Adjust the intervals between the zoom components of the continuous zoom lens 3.

[0041] During the assembly of the continuous zoom lens 3, the distance between each zoom component needs to be adjusted. The interval between two adjacent fixed components and the interval between an adjacent moving component and a fixed component both meet the design tolerance requirements of the optical system. The interval between two adjacent moving components is constrained according to the cam curve.

[0042] In this embodiment, the total length of the continuous zoom lens 3 is based on the telephoto position. When in the telephoto position, the total length of the continuous zoom lens 3 must be consistent with the design value. When in the short focal position, the total length of the continuous zoom lens 3 is allowed to deviate from the design value to a certain extent, and the total length deviation is generally controlled to be ≤0.2mm.

[0043] Step 3: Analyze the normalized image plane defocus sensitivity of each zoom component at short focus and long focus.

[0044] If image plane uniformity does not meet requirements, image plane defocus sensitivity analysis is required. In the optical design software CODE V or ZEMAX, analyze the image plane defocus amount and the magnification ratio between the image plane defocus amount and the zoom component movement amount when the axial position of each zoom component of the continuous zoom lens 3 is independently changed by the same amount at the short and long focal positions, thereby obtaining the normalized image plane defocus sensitivity of each zoom component at short and long focal positions.

[0045] When analyzing the image plane defocus caused by independently varying the axial position of each zoom component of the continuous zoom lens 3 by the same amount at both the short and long focal positions, the shift can be either positive or negative, and is generally performed by a small amount, such as ±0.05mm or ±0.1mm, to maintain relative stability in the magnification ratio between the image plane defocus and the zoom component shift. Furthermore, when analyzing the normalized image plane defocus sensitivity of each zoom component at both the short and long focal positions, the present invention primarily shifts the axial position of each zoom component in the continuous zoom lens 3, such as the front fixed group 6, the zoom group 7, the intermediate fixed group 8, the compensation group 9, and the rear fixed group 10. Lenses within each zoom component are not adjusted.

[0046] In this embodiment, each zoom component of the continuous zoom lens 3 moves 0.1 mm respectively, and the corresponding normalized image plane defocus sensitivities of short focus and long focus are shown in Table 1.

[0047] Table 1 Image plane defocus sensitivity of each zoom component

[0048]

[0049] According to the normalized image plane defocus sensitivity of short focus and long focus in Table 1, the following is formed: Figure 4 The normalized image plane defocus sensitivity diagram of each zoom component at short focus and long focus is shown in Table 1. Through this diagram, the normalized image plane defocus sensitivity of each zoom component at short focus and long focus can be observed. Figure 4It can be seen that in this embodiment, the front fixed group 6 is most sensitive to the defocus of the long-focus image plane, and is extremely insensitive to the defocus of the short-focus image plane. The zoom group 7 is the second most sensitive to the defocus of the long-focus image plane, and has a relatively low sensitivity to the defocus of the short-focus image plane. The middle fixed group 8, the compensation group 9 and the rear fixed group 10 are all equally sensitive to the defocus of the long-focus image plane and the defocus of the short-focus image plane of the continuous zoom lens 3.

[0050] Table 2 shows the axial magnification ratio between the image plane defocus amount and the movement amount of each zoom component at short and long focal lengths. + indicates that the image plane defocus direction is the same as the movement direction of each zoom component, and – indicates that the image plane defocus direction is opposite to the movement direction of each zoom component.

[0051] Table 2 Axial magnification ratio between image plane defocus amount and movement amount of each zoom component

[0052]

[0053] As can be seen from Table 2, the long-focus axial magnification of the front fixed group 6 in the continuous zoom lens 3 is much higher than the short-focus axial magnification. In other words, when the continuous zoom lens 3 is in the long-focus position, the short-focus image plane defocus caused by adjusting the position of the front fixed group 6 can be basically ignored.

[0054] Therefore, in this embodiment, the zoom component that is sensitive to long-focus image plane defocus and has the largest difference in sensitivity between long-focus image plane defocus and short-focus image plane defocus is the front fixed group 6, that is, the front fixed group 6 is the most sensitive component for long-focus.

[0055] Step 4: Image plane consistency test.

[0056] Step 4.1: Image plane consistency test of continuous zoom lens 3 requires the help of Figure 3 The image plane consistency test device shown in the figure is implemented. The image plane consistency test device mainly consists of a collimator 1, a resolution plate 2, and a reading microscope 4. The resolution plate 2 is placed at the focal plane of the collimator 1, and the reading microscope 4 is coaxially placed behind the collimator 1. During the test, a continuous zoom lens 3 is coaxially placed between the collimator 1 and the reading microscope 4. The continuous zoom lens 3 is used to image the resolution plate 2 at the focal plane of the collimator 1. The operator observes the image of the resolution plate 2 through the reading microscope 4 from the human eye observation point 5 throughout the zoom range from short to long focus and analyzes it.

[0057] The focal length of the collimator 1 should generally be greater than about 3 times the telephoto focal length of the zoom lens 3. For example, if the telephoto focal length of the zoom lens 3 is 300 mm, the focal length of the collimator 1 should be 900 mm.

[0058] Step 4.2: Move the zoom lens 3 to the short focal position. At this time, adjust the axial position of the reading microscope 4 until the image of the discrimination plate 2 is clearest.

[0059] Step 4.3, rotate the zoom cam of the continuous zoom lens 3 to move the continuous zoom lens 3 to the telephoto position, and observe through the reading microscope 4 whether the imaging clarity of the discrimination plate 2 at the telephoto position meets the preset requirements. If so, it proves that the image surface consistency meets the preset requirements, and the image surface consistency adjustment is completed; otherwise, it proves that the image surface consistency does not meet the preset requirements, and adjust the axial position of the reading microscope 4 until the imaging clarity of the discrimination plate 2 at the telephoto position meets the preset requirements. At this time, record the axial movement amount and movement direction of the reading microscope 4 at the telephoto position, and execute step 5.

[0060] It is worth noting that the numerical aperture of the reading microscope 4 should be larger than the maximum numerical aperture of the continuous zoom lens 3, that is, larger than F4.5.

[0061] Step 5: Image plane consistency adjustment.

[0062] Step 5.1, based on the axial movement and movement direction of the reading microscope 4 recorded in step 4.3, combined with the magnification ratio between the image plane defocus amount corresponding to the most sensitive component of the telephoto lens in step 2 and the movement amount of the zoom component, calculate the axial movement of the most sensitive component of the telephoto lens and determine the movement direction.

[0063] The axial movement of the most sensitive component of the telephoto lens is the ratio of the axial movement of the reading microscope 4 to the magnification. The direction of movement is determined according to the positive or negative sign of the magnification. When the magnification is positive, the direction of movement of the most sensitive component of the telephoto lens is opposite to the direction of movement of the reading microscope 4 in step 4.3. When the magnification is negative, the two move in the same direction.

[0064] In step 5.2, after adjusting the axial position of the most sensitive component at telephoto according to the axial movement amount and movement direction of the most sensitive component at telephoto, return to step 4.2 for cyclic adjustment until the image clarity of the discrimination plate 2 at the telephoto position observed by the reading microscope 4 when the continuous zoom lens 3 moves to the telephoto position in step 4.3 meets the preset requirements, and the image plane consistency adjustment is completed.

[0065] In order to take into account all possible situations that may not have been considered, when the adjusted zoom component is sensitive to short focus but insensitive to long focus, the continuous zoom lens 3 can also be moved to the long focus position in step 4.2, and the axial position of the reading microscope 4 is adjusted until the image of the discrimination plate 2 is clearest. Correspondingly, in step 4.3, the axial position of the reading microscope 4 needs to be adjusted until the imaging clarity of the discrimination plate 2 at the short focus position meets the preset requirements, that is, the axial movement amount and movement direction of the reading microscope 4 at the short focus position are recorded at this time, and the most sensitive component of short focus also needs to be found.

[0066] It is worth noting that the present invention mainly solves the problem of rapid adjustment of the image plane consistency of a continuous zoom lens. Before the image plane consistency adjustment, the imaging quality adjustment of the continuous zoom lens has been completed, that is, the system wave aberration or optical transfer function (MTF) at the image plane at each focal length position has met the requirements. However, the imaging quality adjustment of a continuous zoom lens is a prior art and is not part of the content involved in the present invention.

[0067] The above description is only used to illustrate the technical solution of the present invention, rather than to limit it. For ordinary professional and technical personnel in this field, the specific technical solutions recorded in the above embodiments can be modified, or some of the technical features therein can be replaced by equivalents. These modifications or replacements do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solution protected by the present invention.

Claims

1. A method for adjusting image plane consistency of a continuous zoom lens, characterized in that: The following steps are involved: Step 1, adjusting the distance between each zoom component of the continuous zoom lens (3) to meet the design requirements; Step 2, analyzing the image plane defocus amount and the magnification ratio between the image plane defocus amount and the zoom component movement amount caused when the axial position of each zoom component of the continuous zoom lens (3) changes independently by a certain same movement amount at the short focus position and the long focus position, and obtaining the normalized image plane defocus sensitivity of each zoom component at the short focus and long focus; according to the normalized image plane defocus sensitivity of each zoom component at the short focus and long focus, the zoom component that is sensitive to the long focus image plane defocus and has the largest difference in defocus sensitivity between the long focus image plane defocus and the short focus image plane defocus is taken as the most sensitive component at the long focus; Step 3: Image plane consistency test; Step 3.1, constructing an image plane consistency test device; the image plane consistency test device comprises a collimator (1), a resolution plate (2) placed at the focal plane position of the collimator (1), and a reading microscope (4) coaxially placed behind the collimator (1); during the test, the continuous zoom lens (3) is coaxially placed between the collimator (1) and the reading microscope (4); Step 3.2, move the continuous zoom lens (3) to the short focal position, and then adjust the axial position of the reading microscope (4) until the image of the discrimination plate (2) is clearest; Step 3.3, move the continuous zoom lens (3) to the telephoto position, and observe through the reading microscope (4) whether the image clarity of the discrimination plate (2) at the telephoto position meets the preset requirements. If so, the image plane consistency meets the preset requirements, and the image plane consistency adjustment is completed; otherwise, adjust the axial position of the reading microscope (4) until the image clarity of the discrimination plate (2) at the telephoto position meets the preset requirements, record the axial movement amount and movement direction of the reading microscope (4), and execute step 4; Step 4: image plane consistency adjustment; Step 4.1, based on the axial movement amount and movement direction of the reading microscope (4) recorded in step 3.3, combined with the magnification ratio between the image plane defocus amount corresponding to the most sensitive telephoto component and the movement amount of the zoom component in step 2, calculate the axial movement amount of the most sensitive telephoto component and determine the movement direction; In step 4.2, the axial position of the most sensitive component of the telephoto lens is adjusted according to the axial movement amount and movement direction of the most sensitive component of the telephoto lens, and the adjustment is repeated in step 3.2 until the image clarity of the discrimination plate (2) at the telephoto position observed by the reading microscope (4) when the continuous zoom lens (3) moves to the telephoto position in step 3.3 meets the preset requirements, and the image plane consistency adjustment is completed.

2. The method for adjusting image plane consistency of a continuous zoom lens according to claim 1, wherein: Before step 1, also include step A: The distance between the center point of the pin on each moving element barrel in the continuous zoom lens (3) and the axial vertex of the first lens in the corresponding moving element barrel is adjusted to within a preset range.

3. The method for adjusting image plane consistency of a continuous zoom lens according to claim 2, wherein: In step A, the distance tolerance between the center point of the pin on each moving element barrel in the continuous zoom lens (3) and the axial vertex of the first lens in the corresponding moving element barrel is less than or equal to 0.05 mm.

4. The method for adjusting image plane consistency of a continuous zoom lens according to any one of claims 1 to 3, wherein: Step 1 is as follows: The interval between two adjacent fixed components and the interval between adjacent moving components and the fixed component are adjusted according to the design tolerance requirements of the optical system, and the interval between two adjacent moving components is constrained according to the cam curve.

5. The method for adjusting image plane consistency of a continuous zoom lens according to claim 4, wherein: In step 2, optical design software CODE V or ZEMAX is used to analyze the image plane defocus amount and the magnification ratio between the image plane defocus amount and the zoom component movement amount when the axial position of each zoom component of the continuous zoom lens (3) is independently changed by the same movement amount at the short focus position and the long focus position.

6. The method for adjusting image plane consistency of a continuous zoom lens according to claim 5, wherein: In step 2, the movement amount is a positive value or a negative value; the movement amount is ±0.05 mm or ±0.1 mm.

7. The method for adjusting image plane consistency of a continuous zoom lens according to claim 1, wherein: In step 3.1, the focal length of the collimator (1) is greater than three times the telephoto focal length of the continuous zoom lens (3); and the numerical aperture of the reading microscope (4) is greater than the maximum numerical aperture of the continuous zoom lens (3).

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