A method for finding the vertex of the lens surface in the measurement of the lens mounting flange distance

Abstract

The present invention discloses a method for finding the vertex of a lens surface during lens mounting flange distance measurement, belonging to the field of optical measurement technology. The method aims to solve the problems existing in the prior art, such as the inability to accurately locate, misjudgment of focal position, increased system complexity, the need for frequent calibration, and increased equipment costs. The method comprises a light-emitting unit, a transmission optical path, an energy detection system, and a lens to be measured. Light emitted by the light-emitting unit is transmitted to the surface of the lens to be measured via the transmission optical path, and light reflected by the surface of the lens to be measured is transmitted to the energy detection system via the transmission optical path. The lens to be measured is moved along the X-axis direction, and the position of the lens to be measured and the measurement value of the energy detection system are recorded in real time, and the X-axis position at which the maximum detection value is located is recorded. The lens to be measured is moved along the Y-axis direction, and the position of the lens to be measured and the measurement value of the energy detection system are recorded in real time, and the Y-axis position at which the maximum detection value is located is recorded. The intersection of the recorded X-axis position and Y-axis position is used as the vertex position of the lens surface to be measured.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measurement, and in particular relates to a method for finding the vertex of a lens mirror surface in measuring the lens mounting flange distance. Background Art

[0002] Centering and adjustment is the core technology for achieving high-precision assembly of transmissive optical systems. It is achieved by customizing a dedicated lens mount for each lens and implementing double calibration: first, the coaxiality of the lens optical axis and the mechanical axis of the lens mount is precisely corrected; second, the axial distance from the end face of the lens mount to the apex of the lens spherical surface is strictly controlled, so that each lens assembly forms an independent optical-mechanical integrated module; during assembly, automatic centering is achieved by the precise fit between the outer circle of the lens mount and the inner hole of the lens barrel, and finally rigid fixation is completed by a pressing ring. This modular pre-calibration system effectively solves the accuracy bottleneck of the traditional spacer ring positioning method, significantly improves the batch assembly quality of transmissive optical systems, and has become a standardized solution in the field of high-precision optical instrument manufacturing.

[0003] Based on the principle of centering assembly, accurate measurement of the lens mounting flange focal distance is one of the key steps to ensure that different lens groups can be correctly docked. Deviations in the lens mounting flange focal distance directly affect the air gap between adjacent lenses. Errors in the air gap between lenses in an optical system can directly reduce image quality, leading to a decrease in MTF, loss of contrast, and aberrations such as spherical aberration and coma. Currently, there are two methods for measuring mirror spacing: contact and non-contact. The contact method for measuring lens spacing relies primarily on direct contact between a mechanical probe and the lens surface. Typically, the distance between the vertex of the preceding lens and the vertex of the following lens is measured, and the center thickness of the lens is subtracted from this distance. Non-contact lens spacing measurement typically uses interferometry. This involves focusing light on the vertex of the lens to be measured, moving a probe arm, and observing changes in the coherent light to measure the spacing. Alternatively, the measurement light is focused on the vertex of the lens to be measured, moving a measurement probe, and observing the energy reflected from the lens surface to the energy detector to determine the spacing. The method and device for measuring the thickness and spacing of optical elements disclosed in Chinese patent publication number CN1428627 focus the measuring light on the vertex of the lens surface to be measured when measuring the thickness and spacing of optical elements, and judge the thickness or spacing of the optical element by observing the interference between the reflected measuring light and the reference light. The integrated measurement optical path and measurement method for lens mounting flange distance and center offset disclosed in Chinese patent publication number CN119573611A focus the measuring light on the vertex of the lens surface to be measured to obtain the maximum reflected light energy when measuring the lens mounting flange distance, and then focus the measuring light on the end face of the lens seat to obtain the maximum reflected energy. The distance the measuring head moves is the lens mounting flange distance. The above-mentioned non-contact lens air spacing measurement methods all require that the measuring light be focused on the vertex of the lens surface to be measured.

[0004] Currently, when measuring the separation between lens surfaces, it is assumed that when the measuring light is focused on the vertex of the lens surface being measured or on the optical axis of the lens being measured, there is no decentering of the lens assembly being measured, meaning that the decentering has been calibrated. Methods for ensuring that the measuring light is focused on the vertex of the lens surface being measured or on the optical axis of the lens being measured include autofocus technology and interference fringe analysis technology. Autofocus technology uses a translation stage to move the lens and monitor the clarity of the reflected light spot in real time. When the reflected light spot is the clearest, the measuring light is focused on the vertex of the lens surface being measured or on the optical axis of the lens being measured. Interference fringe analysis technology determines the focal point position by observing the parallelism of the interference fringes formed by the light reflected from the lens surface being measured and the reference light. If the fringes are rotated or deformed, the lens position must be adjusted until the interference fringes are parallel.

[0005] When using autofocus technology for focusing, the clarity of the reflected light spot is highly dependent on the reflectivity and cleanliness of the lens surface being measured. If the reflectivity of the lens surface is too low or there is surface contamination, the intensity or shape of the reflected light spot may change, making it impossible to accurately locate the lens. When there is a lot of background interference on the lens surface, the light spot contrast is reduced, and the autofocus system may misjudge the focus position. Especially in low-light conditions, it is necessary to rely on highly sensitive detectors or enhanced light sources, which increases the complexity of the system. Moreover, the system cannot accurately quantify the clarity of the reflected pattern, which will cause certain errors and affect the measurement of the mirror separation.

[0006] Interference fringe analysis requires extremely high light source coherence, requiring a short-coherence light source with a coherence length greater than the optical path difference to be measured. If the light source's spectral width is too wide or if ambient temperature fluctuations cause wavelength drift, the interference fringes will blur or even disappear, necessitating frequent calibration. Furthermore, the interferometer system requires precision optical components and high-speed signal processing, which increases equipment costs. Summary of the Invention

[0007] The purpose of the present invention is to propose a method for finding the vertex of a lens surface during lens mounting flange distance measurement, so as to solve the problems existing in the prior art such as inability to accurately locate, misjudgment of focus position, increased system complexity, need for frequent calibration and increased equipment cost.

[0008] To achieve the above objectives, the present invention provides a method for finding the vertex of a lens surface during lens mounting flange focal distance measurement, comprising a light emitting unit, a transmission optical path, an energy detection system, and a lens to be measured. The lens to be measured is mounted on a two-dimensional electric translation stage, and the two-dimensional electric translation stage drives the lens to be measured to move in the X-axis and Y-axis directions of a plane perpendicular to the optical axis. Light emitted by the light emitting unit is transmitted to the surface of the lens to be measured via the transmission optical path, and light reflected by the surface of the lens to be measured is transmitted to the energy detection system via the transmission optical path.

[0009] Move the lens to be tested along the X-axis direction by a two-dimensional electric translation stage, record the position of the lens to be tested and the measurement value of the energy detection system in real time, and record the X-axis position where the maximum value of the energy detection system in the X-axis direction is detected;

[0010] Move the lens to be tested along the Y-axis direction by a two-dimensional electric translation stage, record the position of the lens to be tested and the measurement value of the energy detection system in real time, and record the Y-axis position where the maximum value of the energy detection system is detected in the Y-axis direction;

[0011] The intersection of the recorded X-axis position and Y-axis position is used as the vertex position of the lens to be measured.

[0012] The transmission optical path includes a beam splitter prism and a focusing objective lens; the parallel light incident through the light-emitting unit is reflected by the beam splitter prism and then focused onto the mirror surface of the lens to be measured by the focusing objective lens; the light reflected by the lens to be measured is reversely collimated into parallel light by the focusing objective lens and propagates through the beam splitter prism to the energy detection system.

[0013] The light-emitting unit includes a light source, a light-homogenizing sheet, an exit pinhole sheet and a collimating cemented lens; the light emitted by the light source forms a light-emitting circular hole through the light-homogenizing sheet and the exit pinhole sheet, generating a circular indicator image, which is collimated into parallel light by the collimating cemented lens and incident on the transmission light path.

[0014] The light source is a monochromatic LED light source or a laser light source.

[0015] The collimating doublet lens is replaced by a collimating off-axis parabolic mirror.

[0016] The energy detection system includes a focusing cemented lens, an incident pinhole plate and an optical power detector; the light reflected by the lens to be measured passes through a beam splitter prism and propagates to the focusing cemented lens, is focused by the focusing cemented lens, passes through the incident pinhole plate and enters the optical power detector.

[0017] The focusing cemented lens is replaced by a focusing off-axis parabolic mirror.

[0018] The method further includes a lens holder for a lens to be tested, wherein the lens to be tested is mounted on the two-dimensional electric translation stage via the lens holder for a lens to be tested.

[0019] The beneficial effects of the present invention are as follows: a method for finding the vertex of a lens mirror surface in the measurement of the lens mounting flange distance of the present invention scans the lens mirror surface by the focus point of light in the measurement of the lens group mirror interval to find the vertex of the lens mirror surface. The position of the focus point relative to the vertex of the lens mirror surface can be determined only by measuring the energy of the light reflected by the lens mirror surface. The vertex of the lens mirror surface can be found without adding other additional devices; there is no requirement for the coherence of the light source; by moving the X-axis and Y-axis of the lens to be measured respectively, the energy will show a trend of first increasing and then decreasing, and the vertex of the lens mirror surface can be determined by the maximum energy of the X-axis and Y-axis. The energy size is a quantitative indicator, and there is no subjective interference such as the clarity of human eye observation, thereby ensuring measurement accuracy. This method can effectively reduce the measurement process of finding the vertex of the lens mirror surface in the measurement of the lens group mirror interval. The measurement process is all non-contact measurement, and a monochromatic LED light source can be used. The scanning process is simple, and while ensuring measurement accuracy, the process difficulty and equipment cost are effectively reduced. Finding the vertex of the mirror surface by the energy size reflected by the lens mirror surface effectively reduces the process difficulty. Independent scanning of the X / Y axes reduces system complexity and avoids multi-dimensional coupling errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is an overall optical path diagram of a method for finding the vertex of a lens surface in measuring the flange focal distance of a lens installation according to the present invention;

[0021] Figure 2 This is the light path diagram when the focus point does not coincide with the mirror vertex;

[0022] Figure 3 Schematic diagram of the X-axis scanning process;

[0023] Figure 4 Schematic diagram of the Y-axis scanning process;

[0024] Figure 5 is the X-axis scanning result;

[0025] Figure 6 It is the Y-axis scanning result;

[0026] The components include: 1. Light source, 2. Light homogenizer, 3. Exit pinhole, 4. Collimating doublet lens, 5. Beam splitter, 6. Focusing objective lens, 7. Lens mount to be tested, 8. Lens to be tested, 9. Two-dimensional electric translation stage, 10. Focusing doublet lens, 11. Entrance pinhole, 12. Optical power detector. DETAILED DESCRIPTION

[0027] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0028] The energy detection system is combined with the system to be tested to find the vertex of the lens surface. After locating the vertex of the lens surface, the energy detection system is used to measure the lens mounting flange distance. After obtaining the accurate lens mounting flange distance, the lens surface spacing can be calculated.

[0029] See also Figure 1 The present invention provides a method for finding the vertex of a lens surface in measuring the flange focal distance of a lens installation, comprising a light source 1, a light homogenizer 2, an exit pinhole plate 3, a collimating cemented lens 4, a beam splitter 5, a focusing objective lens 6, a lens holder to be measured 7, a lens to be measured 8, a two-dimensional electric translation stage 9, a focusing cemented lens 10, an incident pinhole plate 11, and an optical power detector 12.

[0030] Light source 1 is a monochromatic LED light source with a divergent angle. After passing through the light-homogenizing plate 2 and the exit pinhole plate 3, it emits light equivalent to the pinhole in the pinhole plate, producing a circular indicator image. The divergent light emitted by the pinhole is collimated into parallel light by the collimating doublet lens 4. The parallel light is reflected by the beam splitter prism 5 to the focusing objective lens 6. The focusing objective lens 6 focuses the light on the mirror surface of the lens to be measured 8. The light is then reflected back by the lens to be measured 8 and returned to the focusing objective lens 6. After being reverse-collimated by the focusing objective lens 6, it passes through the rear beam splitter prism 5 and propagates to the focusing doublet lens 10. After being converged by the focusing doublet lens 10, it passes through the incident pinhole plate 11 and finally enters the optical power detector 12.

[0031] When the light is focused by the focusing lens 6 and converges on the vertex of the lens 8 to be measured, all the light will be reflected and collimated by the focusing lens 6 and finally propagate to the optical power detector 12. At this time, the energy detected by the optical power detector 12 is the maximum. Figure 2 When the convergence point of the light after being focused by the focusing objective lens 6 is not at the mirror vertex of the lens to be measured 8, the reflection angle of the light changes, causing part of the light to be reversely collimated by the focusing objective lens 6 and finally enter the optical power detector 12, while the reflection angle of the other part of the light is larger than the field of view of the focusing objective lens 6 and is not received and collimated by it, resulting in a decrease in the energy detected by the optical power detector 12.

[0032] Based on this principle, the lens 8 under test can be translated using the two-dimensional motorized translation stage 9, and the energy detected by the optical power detector 12 can be observed to determine the location of the light focus. The vertex of the lens 8 under test can be accurately found by simply scanning the X and Y axes.

[0033] The specific process of the present invention is as follows: the lens 8 to be tested is moved by a two-dimensional electric translation stage 9, so that the focus of the light scans the mirror surface of the lens 8 to be tested, and the position of the system to be tested and the measured value of the optical power detector 12 are recorded in real time. Only when the light converges at the vertex of the mirror surface of the lens 8 to be tested, the energy detected by the optical power detector 12 is the maximum; see Figure 3, move the lens 8 to be tested along the X-axis direction by the two-dimensional electric translation stage 9, record the position of the lens 8 to be tested and the measurement value of the energy detection system in real time, and record the X-axis position where the maximum value of the energy detection system in the X-axis direction is detected; Figure 3 (a), (b), (c), (d), and (e) are schematic diagrams of the mirror-reflected light of the lens 8 to be tested during its translation in the X-axis direction; Figure (c) shows that the focal point of the light is exactly at the vertex of the mirror of the lens 8 to be tested. At this time, all the reflected light will be reversely collimated by the focusing objective 6 and eventually enter the optical power detector 12, and the optical power detector 12 detects the highest energy; (a), (b), (d), and (e) are schematic diagrams of light reflection when there is a deviation between the focal point of the light and the vertex of the mirror of the lens 8 to be tested. In the figure, X1 and X2 are different positions, and the distance deviation between the optical axis and the axis where the vertex is located is symmetrically distributed with the vertex and the optical axis coinciding as the axis; it can be seen from the figure that the deviation between the focal point of the light and the vertex of the mirror of the lens 8 to be tested will affect the angle of the light reflected by the mirror. The larger the deviation, the more light will exceed the field of view of the focusing objective 6 and cannot be collimated by it, and thus cannot be finally detected by the optical power detector 12. Since the deviation between the focus point of the light and the vertex of the lens 8 to be measured is relatively small compared to the focal length of the focusing lens 6, it is assumed that the scanning point is always at the focus of the focusing lens 6 during the scanning process, and the influence of the curvature radius of the lens 8 to be measured during the scanning process is ignored. Figure 4 , is the X-axis scanning result. The image is symmetrically distributed, and the position corresponding to the highest energy point in the middle is the optimal position.

[0034] See also Figure 5 , move the lens 8 to be tested along the Y-axis direction by the two-dimensional electric translation stage 9, record the position of the lens 8 to be tested and the measurement value of the energy detection system in real time, and record the Y-axis position where the maximum value of the energy detection system in the Y-axis direction is detected; Figure 5(f), (g), (h), (i), and (j) are schematic diagrams of the mirror-reflected light of the lens 8 to be tested during its translation in the Y-axis direction; Figure (h) shows that the focal point of the light is exactly at the vertex of the mirror of the lens 8 to be tested. At this time, all the reflected light will be reversely collimated by the focusing objective lens 6 and eventually enter the optical power detector 12, and the optical power detector 12 detects the highest energy; (f), (g), (i), and (j) are schematic diagrams of light reflection when there is a deviation between the focal point of the light and the vertex of the mirror of the lens 8 to be tested. In the figure, Y1 and Y2 are different positions, and the distance deviation between the optical axis and the axis where the vertex is located is symmetrically distributed with the vertex and the optical axis coinciding as the axis; it can be seen from the figure that the deviation between the focal point of the light and the vertex of the mirror of the lens 8 to be tested will affect the angle of the light reflected by the mirror. The larger the deviation, the more light will exceed the field of view of the focusing objective lens 6 and cannot be collimated by it, and thus cannot be finally detected by the optical power detector 12. Since the deviation between the focus point of the light and the vertex of the lens 8 to be measured is relatively small compared to the focal length of the focusing lens 6, it is assumed that the scanning point is always at the focus of the focusing lens 6 during the scanning process, and the influence of the curvature radius of the lens 8 to be measured during the scanning process is ignored. Figure 6 , is the Y-axis scanning result. The image is symmetrically distributed, and the position corresponding to the highest energy point in the middle is the optimal position.

[0035] The whole system has two translation directions, X-axis and Y-axis. Scan the X-axis direction to determine the point with the highest energy in the X-axis direction; scan the Y-axis direction to determine the point with the highest energy in the Y-axis direction. The final vertex position of the lens 8 to be tested can be determined through the intersection of the two axes.

[0036] This method obtains the returned energy value by scanning the mirror surface of the lens 8 to be tested, and determines the position of the lens mirror vertex by the magnitude of the returned energy value. Compared with the interference fringe method for finding the lens mirror vertex, this method does not require a high-coherence light source and can use a monochromatic LED or a low-cost laser as a light source. The interference fringe method requires the human eye to judge whether the shape of the fringe is deformed to find the lens mirror vertex, which has certain subjective errors. However, the energy detected by this method is an objective quantity and does not have subjective errors. While ensuring measurement accuracy, this method effectively reduces the process difficulty and equipment cost.

[0037] The collimating cemented lens 4 in the present invention can be replaced by a collimating off-axis parabolic mirror or other types of lenses.

[0038] The focusing cemented lens 10 in the present invention can be replaced by a focusing off-axis parabolic mirror or other types of lenses.

[0039] The monochromatic LED light source 1 can be replaced by a laser light source.

[0040] The circular shape of the exit pinhole plate 3 can be replaced with other openings with shapes that meet energy detection conditions.

[0041] The energy detection system of the present invention can also be used to measure the flange focal distance of a lens.

Claims

1. A method for finding the vertex of a lens surface during lens mounting flange focal length measurement, characterized in that: The invention comprises a light emitting unit, a transmission optical path, an energy detection system and a lens to be measured (8), wherein the lens to be measured (8) is mounted on a two-dimensional electric displacement stage (9), and the lens to be measured (8) is driven by the two-dimensional electric displacement stage (9) to move in the X-axis and Y-axis directions of the plane where the vertical optical axis is located; light emitted by the light emitting unit is transmitted to the surface of the lens to be measured (8) via the transmission optical path, and light reflected by the surface of the lens to be measured (8) is transmitted to the energy detection system via the transmission optical path; The lens to be tested (8) is moved along the X-axis direction by a two-dimensional electric displacement stage (9), and the position of the lens to be tested (8) and the measurement value of the energy detection system are recorded in real time, and the X-axis position where the maximum value detected by the energy detection system in the X-axis direction is recorded; The lens to be tested (8) is moved along the Y-axis direction by a two-dimensional electric displacement stage (9), and the position of the lens to be tested (8) and the measurement value of the energy detection system are recorded in real time, and the Y-axis position where the maximum value detected by the energy detection system in the Y-axis direction is recorded; The intersection of the recorded X-axis position and Y-axis position is used as the vertex position of the lens (8) to be tested; The transmission optical path comprises a beam splitter prism (5) and a focusing objective lens (6); parallel light incident through the light-emitting unit is reflected by the beam splitter prism (5) and then focused onto the mirror surface of the lens to be measured (8) through the focusing objective lens (6); the light reflected by the lens to be measured (8) is reversely collimated into parallel light through the focusing objective lens (6), and propagates through the beam splitter prism (5) to the energy detection system.

2. The method for finding the vertex of a lens surface in measuring the lens mounting flange focal distance according to claim 1, characterized in that: The light-emitting unit comprises a light source (1), a light-homogenizing sheet (2), an exit pinhole sheet (3), and a collimating cemented lens (4); light emitted by the light source (1) passes through the light-homogenizing sheet (2) and the exit pinhole sheet (3) to form a light-emitting circular hole, thereby generating a circular indicating image; the circular indicating image is collimated into parallel light by the collimating cemented lens (4) and incident on a transmission light path.

3. The method for finding the vertex of a lens surface in measuring the lens mounting flange focal distance according to claim 2, characterized in that: The light source (1) is a monochromatic LED light source (1) or a laser light source (1).

4. The method for finding the vertex of a lens surface in measuring the lens mounting flange focal distance according to claim 2, wherein: The collimating cemented lens (4) is replaced by a collimating off-axis parabolic mirror.

5. The method for finding the vertex of a lens surface in measuring the lens mounting flange focal distance according to claim 1, characterized in that: The energy detection system comprises a focusing cemented lens (10), an incident pinhole plate (11) and an optical power detector (12); light reflected by the lens to be measured (8) passes through a beam splitter prism (5) and propagates to the focusing cemented lens (10), is focused by the focusing cemented lens (10), passes through the incident pinhole plate (11), and then enters the optical power detector (12).

6. The method for finding the vertex of a lens surface in measuring the lens mounting flange focal distance according to claim 5, characterized in that: The focusing cemented lens (10) is replaced by a focusing off-axis parabolic mirror.

7. The method for finding the vertex of a lens surface in measuring the lens mounting flange focal distance according to claim 1, characterized in that: The method further comprises a lens holder (7) to be tested, and the lens (8) to be tested is mounted on the two-dimensional electric displacement stage (9) via the lens holder (7) to be tested.

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