Measuring device and method for measuring a modulation transfer function of an afocal optical system

Abstract

Measuring device (100) for measuring a modulation transfer function (MTF) of an afocal optical system (105), wherein the measuring device (100) has the following features: a recording device (110) for recording the afocal optical system (105) in a recording plane (140); a light supply device (115) for supplying light (145) for illuminating the afocal optical system (105) in the receiving device (110) from a first side (150); a camera (120) for observing the afocal optical system (105) in the recording device (110) from a second side (155) opposite the first side (150), for producing a camera image (160), wherein in an operational state of the measuring device (100) the light supply device (115), the afocal optical system (105) and the camera (120) are arranged coaxially on or with measuring axes parallel to a surveying axis (162) which is oriented perpendicular to the recording plane (140); at least one further light supply device (125) for providing further light (165) for illuminating the afocal optical system (105) in the receiving device (110) from the first side (150), wherein the afocal optical system (105) is illuminated simultaneously by the light supply device (115) and the at least one further light supply device (125); at least one further camera (130) for observing the afocal optical system (105) in the recording device (110) from the second side (155), for producing a further camera image (170); wherein the camera image (160) and the further camera image (170) are produced simultaneously and wherein, in the operational state, the further light-providing device (125), the afocal optical system (105) and the further camera (130) are arranged coaxially on or with measuring axes parallel to an inclined measurement axis (175) which is oriented obliquely to the measurement axis (162) and / or recording plane (140); and a transmission interface (135) for transmitting the camera image (160) and further camera images (170) to an evaluation unit (180) which is configured to detect the modulation transfer function (MTF) of the afocal optical system (105) using at least the camera image (160) and / or further camera images (170).

Description

[0001] The present approach relates to a measuring device and a method for measuring a modulation transfer function of an afocal optical system.

[0002] US 2019 / 0238830A1 describes an optical testing device for testing cameras.

[0003] JP H10-68674A discloses a measuring device for lens systems and a method for measuring a modulation transfer function (MTF) of a lens system. Disclosure of the invention

[0004] Against this background, the present approach presents a measuring device for measuring a modulation transfer function of an afocal optical system and a method for measuring a modulation transfer function of an afocal optical system according to the main claims. Advantageous embodiments are described in the respective dependent claims and the following description.

[0005] The advantages achievable with the presented approach include the ability to test an afocal optical system, for example, with regard to its modulation transfer function. This allows the imaging quality of the afocal optical system to be verified.

[0006] A measuring device for measuring a modulation transfer function of an afocal optical system comprises a recording device, a light source, a camera, at least one further light source, at least one further camera, and a transmission interface. The recording device is configured to accommodate the afocal optical system in a recording plane. The light source is configured to provide light for illuminating the afocal optical system in the recording device from a first side.The camera is designed to observe the afocal optical system in the recording device from a second side opposite the first side and to create a camera image. In an operational state of the measuring device, the light supply device, the afocal optical system, and the camera are arranged coaxially on or with measuring axes parallel to a measurement axis that is oriented perpendicular to the recording plane. The additional light supply device is designed to provide further light for illuminating the afocal optical system in the recording device from the first side.The additional camera is configured to observe the afocal optical system in the recording device from the second side and to create a further camera image; wherein, in the operational state, the additional light-providing device, the afocal optical system, and the additional camera are arranged coaxially on or with measuring axes parallel to an oblique measurement axis, which is oriented obliquely to the measurement axis and / or recording plane. The transmission interface is configured to transmit the camera image and the additional camera image to an evaluation unit, which is configured to recognize the modulation transfer function of the afocal optical system using at least the camera image and / or the additional camera image.

[0007] An afocal optical system is characterized by the fact that, as a whole, it exhibits no converging or diverging effect on the light emitted from the optical system. The afocal optical system can be either a single element, such as an exit window for a laser, a haptically sensitive, transparent viewing window for a smartphone display, or an optical filter, or an optical system composed of several elements, such as a double-sided telecentric camera lens or binoculars. Measuring the modulation transfer function (MTF) allows conclusions to be drawn about the image quality of the optical system. Measuring the image quality of refracting optical systems, such as lenses, using the MTF is well known in the art.The measuring device presented here utilizes the approach of simultaneously measuring the image quality of an optical system at multiple field positions, wherein the optical system is advantageously, in particular, an afocal optical system that can be measured using the measuring device. The receiving device of the measuring device can be configured to receive the optical system within the recording plane at a fixed position or to move the optical system within the recording plane to the fixed position. The light supply device can be configured to provide the light as broadband light, and / or the additional light supply device can be configured to provide the additional light as broadband light. The light supply device and / or the additional light supply device can include at least one LED, for example, at least one white light LED.The measurement axis can be understood as the optical path from the light source through the optical system to the camera. Similarly, the oblique measurement axis can be understood as the optical path from the additional light source through the optical system to the additional camera. According to one embodiment, the evaluation unit can be part of the measuring device.

[0008] The measuring device can also include at least one third camera for observing the optical system in the recording device from the second side, configured to produce a third camera image, and at least one third light-providing device for providing third light to illuminate the optical system in the recording device from the first side. In the operational state of the measuring device, the third light-providing device, the optical system, and the third camera are arranged coaxially on or with measuring axes parallel to a further oblique measurement axis, which is oriented obliquely to the measurement axis and / or recording plane and / or oblique measurement axis. In this way, the MTF of the afocal optical system can advantageously be measured at several field angles to obtain a more detailed result for the MTF.The measuring device can also include any number of additional cameras and associated light-providing devices, which can be arranged with the optical system on different additional oblique measurement axes. For example, the measuring device can have a total of nine cameras and nine associated light-providing devices. In this way, the measurement axis and eight oblique measurement axes can be used to measure the MTF of the optical system. All oblique measurement axes can intersect the measurement axis at a common intersection point, which can be located, for example, on or within the afocal optical system.

[0009] According to one embodiment, the light-providing device can have a focusable or non-focusable collimator configured to provide collimated light. This allows the light output to be directed precisely, for example, to the optical system. Similarly, the further light-providing device can have a focusable or non-focusable collimator configured to provide further collimated light. The collimator can also have a structure to be imaged, for example, in the form of a reticle. The reticle can, for example, form a crosshair. The structure / reticle can be arranged between the light-providing device and the optical system. The position of the structure / reticle can be fixed or variable along the measurement axis.Each collimator can have its own such structure or reticle.

[0010] It is further advantageous if the measuring device according to one embodiment has at least one optical filter configured to modify light incident on the optical filter with a first wavelength range in order to provide light exiting the optical filter with a modified second wavelength range, and / or configured to modify light incident on the optical filter with a first polarization in order to provide light exiting the optical filter with a modified second polarization. Such an optical filter makes it possible to adapt the wavelength range or polarization of the light to a specific application. For example, a so-called V-lambda filter can be used as the optical filter if the optical system is intended to be a window for a mobile phone display or a waveguide for an augmented reality or virtual reality system, or AR system for short.This is a "VR system." This allows the light to be adapted to the sensitivity distribution of the human eye in daylight. A corresponding or other optical filter can also be arranged on the oblique measurement axis. The optical filter can be pivotable and / or rotatable, or it can be fixed. The optical filter can be arranged parallel to the recording plane, for example, between the camera and the recording device, or between the light supply device and the recording device. Additionally or alternatively, the measuring device can have a pivotable and / or rotatable or fixed optical filter arranged in the beam path of the collimator for changing or limiting a wavelength range of the light or changing or limiting a polarization of the light.

[0011] The measuring device can include a camera mounting device with receiving units for the cameras. Such a camera mounting device enables, for example, the simultaneous recording of all cameras in fixed positions relative to each other. The camera mounting device can be spherical, forming a camera spherical shell. The camera spherical shell can be linearly movable and / or tiltable about the X-axis and / or Y-axis along an X-axis perpendicular to the measurement axis and / or a Y-axis perpendicular to both the measurement axis and the X-axis. This mobility of the camera spherical shell allows for the measurement of an eyebox in an optical system, such as one shaped like a waveguide.

[0012] The measuring device can also include a light-supply holding device with mounting units for the light-supply devices. Such a light-supply holding device allows, for example, all light-supply holding devices to be measured together in fixed positions relative to each other. The light-supply holding device can be spherical in shape as a light-supply spherical shell. The light-supply spherical shell can be arranged to be linearly movable and / or tiltable about the X-axis and / or Y-axis on an X-axis perpendicular to the measurement axis and / or a Y-axis perpendicular to both the measurement axis and the X-axis. Such mobility of the light-supply spherical shell allows for the measurement of an eyebox in an optical system shaped, for example, as a waveguide.According to an advantageous embodiment, the camera ball mount and the recording device are fixed, and the light-providing ball mount is linearly movable and / or tiltable. According to an alternative embodiment, the light-providing ball mount and the recording device are fixed, and the camera ball mount is linearly movable and / or tiltable. In other words, the camera mounting device can be tilted or angled relative to the light-providing mounting device, or the light-providing mounting device can be tilted or angled relative to the camera mounting device. Thus, according to one embodiment, an offset between the light-providing ball mount and the camera ball mount is possible or has been implemented.

[0013] The camera mounting device and, additionally or alternatively, the light supply mounting device can be arranged to be laterally movable. This allows for a lateral offset along the X-axis and / or the Y-axis. A distinction can be made between the lateral offset of the cameras or collimators, or the associated dome, and the lateral offset of the receiving device (test specimen holder, tray). There are test specimens where, for example, the entrance pupil is much smaller than the exit pupil. These are, for instance, waveguides for AR / VR systems. The test specimen must therefore be in a fixed position so that the entrance pupil can be targeted. To scan the FOV or eyebox, the camera mount is moved laterally. Additionally, a lateral offset of the collimators can be implemented.

[0014] For example, the measuring device may further include a movement device configured to move the recording device transversely to the measurement axis. For instance, the recording device may be movable along an X-axis perpendicular to the measurement axis and / or a Y-axis perpendicular to both the measurement and X-axis using the movement device, and / or be tiltable about the X-axis and / or Y-axis. The movement device allows the afocal optical system to be moved onto the measurement axis between the camera and the light source, and / or to the intersection of the oblique measurement axis(es). A tiltable recording device enables field-of-view (FOV) measurement with optical systems configured as waveguides.

[0015] It is further advantageous if the measuring device, according to one embodiment, has at least one aperture for the light and / or additional light. The aperture can serve to create an effective pupil. For this purpose, the aperture can be arranged on the recording device, camera, or light supply device.

[0016] The measuring device may further include the evaluation unit, which is designed to detect a deviation in the modulation transfer function using the camera image and / or additional camera images, and to determine a correction value or a correction matrix for correcting the modulation transfer function to increase the image quality of the optical system using the deviation.

[0017] For example, the evaluation unit can be designed to detect deviations in the modulation transfer function from a predetermined desired modulation transfer function. Such deviations can be caused, for instance, by internal structuring, such as capacitive sensors used to create a touch-sensitive mobile phone display, within the optical system integrated into the mobile phone display. This structuring can negatively affect the image information transmitted by the mobile phone display, resulting in a reduction in image quality. Advantageously, the deviating modulation transfer function can be corrected using the correction value or correction matrix, thereby improving image quality.

[0018] The camera and / or additional cameras can have a fixed or adjustable focus position. Adjusting the focus position can be achieved by moving the camera sensor axially along the optical axis relative to the camera's focusing lens. Alternatively or additionally, the camera's focusing lens can have a variable focal length.

[0019] According to a further embodiment, the measuring device can have a structure recognition camera arranged facing the second side, which is configured to detect a predefined structure on the recording plane or in a defined area around the recording plane, wherein the evaluation device is configured to determine a lateral position of the optical system using the detected predefined structure. This makes it possible to detect a position of the optical system within the recording plane in order to, for example, effect a movement of the optical system to the measurement axis and / or the intersection of the oblique measurement axis(es) using the movement device.

[0020] The afocal optical system can be a single element, such as an exit window for a laser, a display window for a mobile phone, a waveguide for an AR system, or an optical filter. Alternatively, the afocal optical system can also be a composite optical system consisting of multiple optical elements, such as a camera lens or binoculars.

[0021] A method for measuring a modulation transfer function of an afocal optical system comprises a light-providing step, a further light-providing step, a camera-image-generating step, a further camera-image-generating step, and a detection step. In the light-providing step, light is supplied from a first side using a light-providing device to illuminate the optical system, which is captured in a recording plane of a recording device. In the further light-providing step, additional light is supplied from the first side using a further light-providing device to illuminate the optical system, which is captured in the recording plane of the recording device.In the step of generating a camera image, a camera image of a reticle is generated via the afocal optical system in the recording device from a second side opposite the first side using a camera, wherein the light-providing device, the optical system, and the camera are arranged coaxially on or with measuring axes parallel to a surveying axis that is oriented perpendicular to the recording plane. In the step of generating another camera image, another camera image of a further reticle is generated via the afocal optical system in the recording device from the second side using another camera, wherein the further light-providing device, the optical system, and the further camera are arranged coaxially on or with measuring axes parallel to an oblique surveying axis that is oriented obliquely to the surveying axis and / or recording plane.In the recognition step, the modulation transfer function of the optical system is recognized using the camera image and / or additional camera images.

[0022] In the step of generating the camera image, the camera image can be generated from the reticle, which is imaged by the camera using a collimator, afocal system, and camera optics. Similarly, in the step of generating the second camera image, the second camera image can be generated from the second reticle, which is imaged by the second camera using a collimator, afocal system, and camera optics.

[0023] In the step of generating the camera image and / or in the step of generating the subsequent camera image, a sequence of camera images and / or further camera images can be generated. For example, a first intermediate image of the reticle(s) is generated by the collimator, this is modified by the afocal optical system (test object) and then imaged onto the sensor via a converging lens of the camera / further camera.

[0024] The approach is explained in more detail below using the attached drawings as examples. They show: Fig. 1 a schematic representation of a measuring device for measuring a modulation transfer function of an afocal optical system according to an exemplary embodiment; Fig. 2 a perspective view of a measuring device according to an exemplary embodiment; Fig. 3 a schematic representation of a measuring device according to an exemplary embodiment; Fig. 4 a schematic representation of a camera image of a measuring device according to an exemplary embodiment; Fig. 5 a schematic lateral cross-sectional view of a collimator of a measuring device according to an exemplary embodiment; Fig. 6 a perspective view of a camera holding device of a measuring device according to an embodiment; Fig. 7 a lateral cross-sectional view of a camera holding device of a measuring device according to an embodiment; Fig. 8 a perspective view of a light supply holding device of a measuring device according to an embodiment; Fig. 9 a lateral cross-sectional view of a light supply holding device of a measuring device according to an exemplary embodiment; and Fig. 10 a flowchart of a method for measuring a modulation transfer function of an afocal optical system according to an embodiment.

[0025] In the following description of favorable embodiments of the present approach, the same or similar reference numerals are used for the elements shown in the various figures and which have a similar effect, without repeating these elements.

[0026] Fig. Figure 1 shows a schematic representation of a measuring device 100 for measuring a modulation transfer function MTF of an afocal optical system 105 according to an exemplary embodiment.

[0027] The measuring device 100 comprises a receiving device 110, a light supply device 115, a camera 120, at least one further light supply device 125, at least one further camera 130, and a transmission interface 135. The receiving device 115 is configured to receive the afocal optical system 105 in a receiving plane 140. The light supply device 115 is configured to provide light 145 for illuminating the afocal optical system 105 in the receiving device 110 from a first side 150.The camera 120 is designed to observe the afocal optical system 105 in the recording device 110 from a second side 155 opposite the first side 150 and to create a camera image 160, wherein, in an operational state of the measuring device 100 shown here, the light supply device 115, the afocal optical system 105 and the camera 120 are arranged coaxially on or with measuring axes parallel to a measurement axis 162, which is oriented perpendicular to the recording plane 140. The additional light supply device 125 is designed to provide further light 165 for illuminating the afocal optical system 105 in the recording device 110 from the first side 150.The additional camera 130 is configured to observe the afocal optical system 105 in the recording device 110 from the second side 155 and to create a further camera image 170; wherein, in the operational state, the additional light supply device 125, the afocal optical system 105, and the additional camera 130 are arranged coaxially on or with measuring axes parallel to an inclined measurement axis 175, which is oriented obliquely to the measurement axis 162 and / or obliquely to the recording plane 140. The transmission interface 135 is configured to transmit the camera image 160 and the additional camera image 170 to an evaluation unit 180, which is configured to recognize the modulation transfer function (MTF) of the afocal optical system 105 using at least the camera image 160 and / or the additional camera image 170.

[0028] For illustrative purposes only, the afocal optical system 105 according to this embodiment is mounted in the receiving device 110 of the measuring device 100 and thus arranged in the recording plane 140.

[0029] In this exemplary embodiment, the afocal optical system 105 is, by way of example, a single optical element, here in the form of a display window for, say, a mobile phone. According to an alternative embodiment, the afocal optical system 105 is configured as another single optical element, such as an exit window for a laser, a waveguide for, say, an AR / VR system, or an optical filter, or as an optical system composed of several optical elements, such as a double-sided telecentric camera lens or binoculars. The measuring device 100 presented here is designed, according to one embodiment, to simultaneously measure the modulation transfer function (MTF) / image quality of the afocal optical system 105 at several field positions.The measurement axis 162 can be understood as the optical path of the light supply device 115 through the optical system 105 to the camera 120. Similarly, the oblique measurement axis 175 can be understood as the optical path of the further light supply device 125 through the optical system 105 to the further camera 130. According to one embodiment, the evaluation unit 180 is part of the measuring device 100.

[0030] According to this embodiment, the light-providing device 115 has a focusable or non-focusable collimator configured to provide the light 145 as collimated light. Similarly, according to this embodiment, the further light-providing device 125 has a focusable or non-focusable collimator configured to provide the further light 165 as collimated further light. The collimator is in Fig. Figure 5 shows and describes in more detail. According to this embodiment, the collimator(s) has / have a structure to be imaged, here for example in the form of a reticle 185, which here merely forms an example crosshair. According to one embodiment, the reticle 185 is arranged between the light-providing device 115 and the optical system 105. The position of the structure / reticle 185 is fixed or can be changed along the measurement axis 162 / oblique measurement axis 175. According to one embodiment, the additional light-providing device 125 has its own additional reticle 185.

[0031] According to one embodiment, the measuring device 100 has at least one optical filter configured to modify light 145 incident on the optical filter with a first wavelength range in order to provide light 145 with a modified second wavelength range exiting the optical filter, and / or configured to modify light 145 incident on the optical filter with a first polarization in order to provide light 145 with a modified second polarization exiting the optical filter. Such an optical filter makes it possible to adapt the wavelength range or the polarization of the light to a specific application. According to one embodiment, a corresponding or other optical filter is also arranged on the inclined measurement axis 175. According to one embodiment, the optical filter is pivotable and / or rotatable, or fixedly arranged.According to one embodiment, the optical filter is arranged parallel to the recording plane 140, for example between the camera 120 and the recording device 110, or according to another embodiment, between the light-supplying device 115 and the recording device 110. Additionally or alternatively, according to one embodiment, the measuring device 100 has a pivotable and / or rotatable or fixed optical filter arranged in the beam path of the collimator of the light-supplying device 115 for changing or limiting a wavelength of the light 145 or changing or limiting a polarization of the light 145.Additionally or alternatively, the measuring device 100 according to an embodiment has a pivotable and / or rotatable or fixed optical filter arranged in the beam path of the collimator of the further light supply device 125 for changing or limiting a wavelength of the further light 165 or changing or limiting a polarization of the further light 165.

[0032] According to one embodiment, the measuring device 100 further comprises a movement device 190 configured to move the recording device 110 transversely to the measurement axis 162. For example, the recording device 110 is movable and / or tiltable about the X-axis and / or Y-axis along an X-axis and / or a Y-axis perpendicular to both the measurement axis 162 and the X-axis using the movement device 190. According to one embodiment, the optical system 105 can be moved within the recording plane 140 along the measurement axis 162 between the camera 120 and the light-providing device 115 and / or to an intersection of the measurement axis 162 with the oblique measurement axis 175 by means of the movement device 190.

[0033] According to this embodiment, the measuring device 100 has at least one aperture 192 for the light 145 and / or further light 165. According to this embodiment, the aperture 192 is designed to create an effective pupil. For this purpose, according to this embodiment, the aperture 192 is arranged on the recording device 110, or according to an alternative embodiment, on or in the camera 120 and / or further camera 130 or the light supply device 115 and / or further light supply device 125.

[0034] According to this embodiment, the measuring device 100 further comprises the evaluation unit 180, which is configured to detect a deviation in the modulation transfer function (MTF) using the camera image 160 and / or another camera image 170, and to determine a correction value or a correction matrix for correcting the MTF to improve the image quality of the optical system 105. Such a deviation in the MTF is caused, for example, by an internal structuring 195, such as capacitive sensors for generating a touch-sensitive mobile phone display, in the afocal optical system 105 shaped as a mobile phone display window. The structuring 195 can therefore have a negative impact on the image information transmitted by the mobile phone display, resulting in a reduction in image quality.Using the correction value or correction matrix, the deviating modulation transfer function can advantageously be corrected, thus improving the imaging quality. For example, the evaluation unit 180 is designed to detect deviations in the modulation transfer function (MTF) from a predetermined desired modulation transfer function.

[0035] According to different embodiments, the camera 120 and / or further camera 130 has either a fixed or an adjustable focus position. According to this embodiment, the camera 120 and / or further camera 130 has an adjustable focus position in that the image sensor is movable relative to the camera's focusing lens along its optical axis, and / or is, for example, designed as a telescopic camera with a variable focal length.

[0036] According to this embodiment, the measuring device 100 further comprises a structure recognition camera 197 arranged facing the second side 155, which is configured to detect a predefined structure on the recording plane 140 or in a defined area around the recording plane 140, wherein the evaluation device 180 is configured to determine a lateral position of the optical system 105 using the detected predefined structure. According to one embodiment, the movement device 190 is configured to effect a movement of the optical system 105 to the measurement axis 162 and / or the intersection of the measurement axis 162 with the oblique measurement axis 175 using the lateral position of the optical system 105.

[0037] Fig. Figure 2 shows a perspective view of a measuring device 100 according to an exemplary embodiment. This could be the device shown in Fig. The measuring device 100 described in section 1 differs in that the measuring device 100 according to this embodiment has at least a third camera 200, at least a third light supply device 205, a camera holding device 210 with receiving units 215 for receiving the cameras 120, 130, 200 and / or a light supply holding device 220 with receiving units 225 for receiving the light supply devices 115, 125, 205.

[0038] The third camera 200 is designed to observe the optical system 105 in the recording device 110 from the second side and to create a third camera image. The third light supply device 205 is designed to provide third light for illuminating the optical system 105 in the recording device 110 from the first side, wherein, in the operational state of the measuring device 100 shown here, the third light supply device 205, the optical system 105, and the third camera 200 are arranged coaxially on or with measuring axes parallel to a further inclined measurement axis, which is oriented at an angle to the measurement axis and / or recording plane and / or inclined measurement axis.According to one embodiment, the measuring device 100 has any number of additional cameras and associated light-providing devices, each arranged on different, additional oblique measurement axes with the optical system 105. According to the embodiment shown here, the measuring device 100 has a total of nine cameras 120, 130, 200 and nine light-providing devices 115, 125, 205 associated with the cameras 120, 130, 200. The measurement axis and eight oblique measurement axes serve to measure the MTF of the optical system 105. According to this embodiment, all oblique measurement axes intersect the measurement axis at a common intersection point, which is, for example, located on or within the optical system 105.

[0039] According to this embodiment, the camera mounting device 210 is spherically shaped as a camera spherical cup. In one embodiment, the camera spherical cup is arranged so as to be linearly movable and / or tiltable about the X-axis and / or Y-axis on an X-axis and / or Y-axis perpendicular to the measurement axis. According to this embodiment, the light supply mounting device 220 is spherically shaped as a light supply spherical cup. In one embodiment, the light supply spherical cup is arranged so as to be linearly movable and / or tiltable about the X-axis and / or Y-axis on an X-axis and / or Y-axis perpendicular to the measurement axis.According to an alternative embodiment, the camera ball cup and the receiving device 110 are fixed, and the light-providing ball cup is designed to be linearly movable and / or tiltable. According to an alternative embodiment, the light-providing ball cup and the receiving device 110 are fixed, and the camera ball cup is designed to be linearly movable and / or tiltable.

[0040] According to this embodiment, the camera holding device 210, light supply holding device 220 and recording device 110 are mounted in a workbench, here by way of example in the form of a trolley 230.

[0041] In Fig. 1 and Fig. Figure 2 illustrates the measuring principle and structure of the measuring device 100 for afocal optical systems 105 using the example of a structured display. For illustrative purposes, the beam paths off-axis with respect to the measurement axis are not shown. Fig. Figure 2 shows the technical implementation in the finished measuring device. The measuring device 100 makes it possible, as with known measuring systems, to simultaneously measure the image quality of optical components, hereinafter also referred to as "test specimens," at different field positions. However, unlike in known measuring systems, the test specimens to be measured are afocal optical systems 105. In one application example, the test specimen is illuminated from below with collimated light. This light is generated using the collimator, which in turn contains a structure to be imaged, for example, a reticle. Fig. Figure 2 shows a collimator with a fixed reticle. For example, a white LED is used as the light source for each of the light-providing devices 115, 125, and 205. Depending on the application, other light sources are conceivable. Additionally, according to one embodiment, optical filters are used to adapt the wavelength range to the application. For example, when measuring mobile phone display windows or waveguides for AR / VR systems, a Photopic-Eye filter is used to adapt the wavelength range of the light 145 to the sensitivity distribution of the human eye in daylight. Additionally or alternatively, according to one embodiment, a fixed or rotatable polarizing filter is arranged in the beam path of the collimator. The use of filters is also relevant, for example, when measuring the wavelength-dependent image quality (MTF).

[0042] To enable simultaneous measurement of the test specimen at various field positions, the collimators on the light supply holding device 220 are arranged in a dome shape, and the cameras 120, 130, and 200 on the camera holding device 210 are also arranged in a dome shape. These domes are located in the Fig. 6, Fig. 7, Fig. 8 and Fig. Figure 9 shows in more detail. The two dome structures are positioned below and above the test specimen, respectively, in the operational state of the measuring device 100 shown here. The assembled measuring device 100 is shown here in Fig. Figure 2 shows that each dome consists of a spherical shell to whose surface mounting devices are attached. These mounting devices, in turn, serve to attach the cameras 120, 130, 200 and the collimators, respectively. The cameras 120, 130, 200 and the collimators are mounted such that their optical axes intersect at a single point. The camera 120 and the collimator of the light supply unit 115 are mounted in the center of the dome. This axial camera 120 and this axial collimator are oriented such that its optical axis is perpendicular to the plane of the test specimen, previously referred to as the recording plane. The intersection point of all optical axes of the cameras 120, 130, 200 and the collimators lies on the optical axis of the axial camera 120 and the axial collimator, respectively. In the finished measuring device 100, the dome structures are arranged opposite each other.According to one embodiment, the centers of curvature coincide, while in another embodiment they are offset from one another. This may be necessary, for example, if the optical element / system 105 under test generates a parallel offset in the beam path, as can be the case with a planar waveguide or a prismatic system. Additionally, an effective pupil is created in the beam path of the cameras 120, 130, and 200. According to one embodiment, this is achieved using an aperture near the test object, as shown in [reference]. Fig. 1 or Fig. Figure 3 is shown. According to an alternative embodiment, an individual aperture is arranged in front of each collimator or in front of each camera 120, 130, 200.

[0043] The test specimen itself is placed in a suitable holder, the mounting device 110, which is located between the upper and lower domes. The holder is movable in the x- and y-directions, allowing the test specimen to be measured at different positions. According to one embodiment, the holder is designed to accommodate several test specimens, which are measured sequentially. Furthermore, according to another embodiment, an optical filter is arranged above or below the test specimen, which modifies the wavelength and / or polarization of the light rays passing through the test specimen. According to another embodiment, the size of the filter is adjustable as needed. This represents an alternative design for cases where collimators without corresponding filters are used.

[0044] According to one embodiment, the struts of the upper dome are equipped with additional cameras in the form of those shown in Fig. The device is equipped with structure recognition cameras as described in section 1 to determine the lateral position (x, y position) of the test specimen. For this purpose, these structure recognition cameras are designed according to one embodiment to detect known structures in the plane of the test specimen or additional structures that are arranged at a defined distance from the test specimen and are located, for example, on the test specimen holder.

[0045] An important application of the measuring device 100 presented here is the measurement of mobile phone display windows. These have the special feature of having an internal structure, which, for example, makes the displays touch-sensitive. A section of such a structured display is shown in Fig. 1 and Fig. Figure 3 is shown schematically. Such an introduced structure has a negative impact on the image information transmitted by the display. According to one embodiment, the measuring device 100 presented here also has an evaluation unit that makes it possible to determine a reduction in image quality caused by the structuring and to calculate a correction factor or a correction matrix based on this value. The correction factor or correction matrix calculated in this way is then applied within the framework of image processing to correct an image that was captured through the display with a camera 120, 130, or 200. A specific application would be image capture via the front camera of a smartphone.

[0046] Another important application of the measuring device 100 presented here is the measurement of waveguides, especially those used in VR / AR headsets. In optical systems for VR / AR applications, it is important to measure the area of ​​the so-called "eyebox." This area can generally be defined as the volume within which the pupil of the eye must be located to meet certain defined criteria regarding image perception. One such criterion could be, for example, that an image generated by the headset remains completely visible within the eyebox.In order to measure a corresponding waveguide at different positions within the eyebox using the measuring device 100 proposed here, it is designed in a corresponding variant such that the test specimen and optionally the lower or upper dome are fixed and the other dome can be changed in its lateral position.

[0047] Another important measurement parameter for optics used in AR / VR systems is their field of view (FOV). It is necessary that the angle between the test object plane and the optical axes of the cameras 120, 130, 200 or the collimators can be changed, so that, for example, the angle between the test object plane and the axial camera 120 / axial collimator is different from 90°. According to various embodiments, this is achieved either by making the test object holder tiltable around the x-axis or y-axis, or alternatively, by making the upper or lower dome tiltable.

[0048] According to an exemplary embodiment, the main features of the measuring device 100 presented here for measuring the MTF of afocal optical systems 105 are the following components: - the receiving device 110 in the form of a test specimen holder, which according to an exemplary embodiment is able to move the afocal optical system 105 to be tested into a fixedly defined position; - several cameras 120, 130, which are arranged above the test object in, for example, a fixed structure such that the image planes of the cameras 120, 130 are distributed on the surface of a spherical shell and that the optical axes of the cameras 120, 130 intersect at least approximately at a point, and that furthermore one of the cameras 120 is arranged in the center of the surface of the spherical shell such that the optical axis of the one camera 120 can be perpendicular to the plane of the test object, and that furthermore the intersection point of the optical axes of all cameras 120, 130 lies on the optical axis of the one camera 120; - several light-providing devices 115, 125, for example with collimators, which are arranged below the test specimen in, for example, a fixed structure such that the object planes of the collimators are distributed on the surface of a spherical shell and that the optical axes of the collimators intersect at least approximately at one point, and furthermore, that one of the collimators is arranged in the center of the surface of the spherical shell such that the optical axis of that one collimator can be perpendicular to the plane of the test specimen, and furthermore, that the intersection point of the optical axes of all collimators lies on the optical axis of that one collimator; and - the evaluation unit in the form of a control unit for evaluating the camera images recorded by cameras 120 and 130.

[0049] Other optional components or features of the measuring device 100 presented here, in any combination, are: - that the cameras 120, 130 either have a fixed or adjustable focus position; - that each collimator / lighting device 115, 125, 205 has a broadband light source and / or that fixed or rotatable or swiveling optical filters are arranged within the beam path of the collimator / lighting device 115, 125, 205 and / or that the optical filters serve to limit or change the wavelength range and / or the polarization of the light 145 emitted from the light source; - that in the beam path of each collimator / light supply device 115, 125, 205 there is a reticle which is illuminated by the light source and whose position along the optical axis in the beam path of the collimator / light supply device 115, 125, 205 is either fixed or variable; - that in a plane parallel to the plane of the test object, a fixed or rotatable or pivotable optical filter is arranged and serves to influence the wavelength and / or polarization of the light rays passing through the test object; - that an effective pupil is produced in at least one beam of radiation passing through the test object, which is realized in the form of at least one physical aperture; - that the test specimen holder is fixedly connected to the camera holding device 210 in the form of a fixed camera structure located above the test specimen holder, and that the light supply holding device 220 in the form of a fixed collimator structure located below the test specimen holder is adjustable in its lateral position relative to the test specimen holder; - that the specimen holder is rigidly connected to the rigid collimator structure located below the specimen holder, and that the rigid camera structure located above the specimen holder is adjustable in its lateral position relative to the specimen holder; - that it is possible to change the angle between the test object plane and the optical axes of the cameras 120, 130 within the fixed camera structure and / or the collimators within the fixed collimator structure; - that at least one structure recognition camera is arranged above the test object and serves to recognize known structures in the test object plane or at a distance defined from the test object plane, and that the control unit is further designed in such a way that a lateral position of the test object is determined on the basis of the images recognized by the at least one structure recognition camera; - that the control unit is further designed in such a way that it is able to determine a reduction in image quality caused by a structure in the test object and furthermore to determine a correction factor or a correction matrix with which the previously determined reduction can be computationally compensated within the framework of image processing.

[0050] Fig. Figure 3 shows a schematic representation of a measuring device 100 according to an exemplary embodiment. This could be the one described in Fig. 1 or Fig. 2 described measuring device 100 act.

[0051] In Fig. Figure 3 shows the axial beam path of the measuring device 100. The corresponding axial camera image is shown in Fig. Figure 4 shows that, according to one embodiment, the imaging system used is a camera 120 with, for example, an axially variable sensor position and / or an adjustable focal length. Alternatively, it is possible to use a collimator with a movable reticle and a fixed camera 120, or a focusable collimator and a camera 120 whose focus position can be adjusted.

[0052] Fig. Figure 4 shows a schematic representation of a camera image 160 of a measuring device 100 according to an exemplary embodiment. This can be the camera image 160 of the camera 120 of the in Fig. 3 described measuring device 100, which can also be referred to as an axial camera image.

[0053] Fig. Figure 5 shows a schematic side cross-sectional view of a collimator 500 of a measuring device according to an exemplary embodiment. This can be the collimator shown in one of the Fig. 1, Fig. 2, Fig. 3 to Fig. The measuring device 100 described in section 4 is shown. The general operating principle of a focusable collimator 500 is illustrated.

[0054] Fig. Figure 6 shows a perspective view of a light supply holding device 220 of a measuring device according to an exemplary embodiment. This can be the one shown in Fig. The light supply holding device 220 described in section 2 is located here. The light supply holding device 220 can also be referred to as a collimator dome. A section line AA is shown.

[0055] Fig. Figure 7 shows a side cross-sectional view of a light supply holding device 220 of a measuring device according to an exemplary embodiment. Section AA is shown. Thus, it can be the one described in Fig. 6 described light provision holding device 220, in which in Fig. The 5 described collimators are included.

[0056] Fig. Figure 8 shows a perspective view of a camera holding device 210 of a measuring device according to an exemplary embodiment. This can be the one shown in Fig. The camera mounting device 210 described in Figure 2 is located there. The camera mounting device 210 can also be referred to as a telescopic dome. A further section line AA is shown.

[0057] Fig. Figure 9 shows a lateral cross-sectional view of a camera holding device 210 of a measuring device according to an exemplary embodiment. Section AA is shown. Thus, it can be the one described in Fig. 8 described camera holding device 210, into which cameras are included.

[0058] Fig.Figure 10 shows a flowchart of a method 1000 for measuring a modulation transfer function of an afocal optical system according to an exemplary embodiment. This can be the afocal optical system described in one of the preceding figures. The method 1000 can be controlled or carried out by the measuring device described in one of the preceding figures.

[0059] Method 1000 comprises a step 1005 of providing light, a step 1010 of providing further light, a step 1015 of generating a camera image, a step 1020 of generating another camera image, and a step 1025 of detecting. In step 1005 of providing light, light for illuminating the afocal optical system, which is captured in a recording plane of a recording device, is provided from a first side using a light-providing device. In step 1010 of providing further light, further light for illuminating the afocal optical system, which is captured in the recording plane of the recording device, is provided from the first side using another light-providing device.In step 1015 of generating a camera image, a camera image of the reticle is generated via the afocal optical system in the recording device from a second side opposite the first side using a camera, wherein the light-providing device, the afocal optical system, and the camera are arranged coaxially on a measurement axis or have parallel measurement axes oriented perpendicular to the recording plane. In step 1020 of generating another camera image, another camera image of another reticle is generated via the afocal optical system in the recording device from the second side using another camera, wherein the further light-providing device, the afocal optical system, and the further camera are arranged coaxially on or with measurement axes parallel to an oblique measurement axis that is oriented obliquely to the measurement axis and / or recording plane.In step 1025 of the recognition process, the modulation transfer function of the afocal optical system is detected or calculated using the camera image and / or additional camera images. Optionally, a correction factor or correction matrix can also be calculated during this step.

[0060] According to one embodiment, step 1005 of providing light and step 1010 of providing further light are executed simultaneously. According to another embodiment, step 1015 of generating a camera image and step 1020 of generating another camera image are executed simultaneously.

[0061] In step 1015 of the generation process, the camera image can be generated from the reticle, which is imaged by the camera using a collimator, afocal system, and camera optics. Similarly, in step 1020 of the generation process, the second camera image can be generated from the second reticle, which is imaged by the second camera using a collimator, afocal system, and camera optics.

[0062] In step 1015 and / or step 1020 of the generation process, a sequence of camera images and / or further camera images can be generated. For example, a first intermediate image of the reticle is generated by the collimator, this is modified by the afocal optical system (test object) and then imaged onto the sensor via a converging lens of the camera / further camera.

Claims

[1] Measuring device (100) for measuring a modulation transfer function (MTF) of an afocal optical system (105), wherein the measuring device (100) has the following features: a recording device (110) for recording the afocal optical system (105) in a recording plane (140); a light supply device (115) for supplying light (145) for illuminating the afocal optical system (105) in the receiving device (110) from a first side (150); a camera (120) for observing the afocal optical system (105) in the recording device (110) from a second side (155) opposite the first side (150), for producing a camera image (160), wherein in an operational state of the measuring device (100) the light supply device (115), the afocal optical system (105) and the camera (120) are arranged coaxially on or with measuring axes parallel to a surveying axis (162) which is oriented perpendicular to the recording plane (140); at least one further light supply device (125) for providing further light (165) for illuminating the afocal optical system (105) in the receiving device (110) from the first side (150), wherein the afocal optical system (105) is illuminated simultaneously by the light supply device (115) and the at least one further light supply device (125); at least one further camera (130) for observing the afocal optical system (105) in the recording device (110) from the second side (155), for producing a further camera image (170); wherein the camera image (160) and the further camera image (170) are produced simultaneously and wherein, in the operational state, the further light-providing device (125), the afocal optical system (105) and the further camera (130) are arranged coaxially on or with measuring axes parallel to an inclined measurement axis (175) which is oriented obliquely to the measurement axis (162) and / or recording plane (140); and a transmission interface (135) for transmitting the camera image (160) and further camera images (170) to an evaluation unit (180) which is configured to detect the modulation transfer function (MTF) of the afocal optical system (105) using at least the camera image (160) and / or further camera images (170). [2] Measuring device (100) according to claim 1, wherein the light supply device (115) has a focusable or non-focusable collimator (500) configured to supply the light (145) as collimated light. [3] Measuring device (100) according to one of the preceding claims, comprising at least one third camera (200) for observing the optical system (105) in the recording device (110) from the second side (155), for producing a third camera image, and at least one third light supply device (205) for providing third light for illuminating the optical system (105) in the recording device (110) from the first side (150), wherein in the operational state of the measuring device (100) the third light supply device (205), the optical system (105) and the third camera (200) are arranged coaxially on or with measuring axes parallel to a further oblique measurement axis, which is oriented obliquely to the measurement axis (162) and / or recording plane (140) and / or oblique measurement axis (175). [4] Measuring device (100) according to one of the preceding claims, comprising at least one optical filter configured to modify light (145) incident on the optical filter with a first wavelength range in order to provide the light (145) with a modified second wavelength range exiting the optical filter, and / or configured to modify light (145) incident on the optical filter with a first polarization in order to provide the light (145) with a modified second polarization exiting the optical filter. [5] Measuring device (100) according to one of the preceding claims, with a camera holding device (210) which has recording units (215) for receiving the cameras (120, 130, 200). [6] Measuring device (100) according to one of the preceding claims, with a light provision holding device (220) which has receiving units (225) for receiving the light provision devices (115, 125, 205). [7] Measuring device (100) according to claims 5 and 6, in which the camera holding device (210) is arranged to be tiltable or tilted relative to the light supply holding device (220) or the light supply holding device (220) is arranged to be tiltable or tilted relative to the camera holding device (210). [8] Measuring device (100) according to one of claims 5 to 7, wherein the camera holding device (210) and / or the light supply holding device (220) is arranged to be laterally movable. [9] Measuring device (100) according to one of the preceding claims, comprising a movement device (190) configured to move the receiving device (110) transversely to the measurement axis (162). [10] Measuring device (100) according to one of the preceding claims, comprising at least one aperture (192) for the light (145) and / or further light (165). [11] Measuring device (100) according to one of the preceding claims, comprising the evaluation unit (180) which is configured to detect a deviation in the modulation transfer function (MTF) using the camera image (160) and / or further camera image (170) and to determine a correction value or a correction matrix for correcting the modulation transfer function (MTF) to increase the image quality of the optical system (105) using the deviation. [12] Measuring device (100) according to one of the preceding claims, wherein the camera (120) and / or further camera (130) has a fixed or adjustable focus position. [13] Measuring device (100) according to one of the preceding claims, with a structure recognition camera (197) arranged facing the second side (155), which is configured to detect a predefined structure on the recording plane (140) or in a defined area around the recording plane (140), wherein the evaluation device is configured to determine a lateral position of the optical system (105) using the detected predefined structure. [14] Measuring device (100) according to one of the preceding claims, wherein the optical system (105) is configured as an exit window, display element, waveguide, optical filter, camera lens or binoculars. [15] Method (1000) for measuring a modulation transfer function (MTF) of an afocal optical system (105), wherein the method (1000) comprises the following steps: Providing (1005) light (145) to illuminate the afocal optical system (105) which is received in a recording plane (140) in a recording device (110), from a first side (150) using a light provision device (115); Providing (1010) further light (165) to illuminate the afocal optical system (105) which is recorded in the recording plane (140) in the recording device (110) from the first side (150) using a further light-providing device (125), wherein the afocal optical system (105) is illuminated simultaneously by the light-providing device (115) and the at least one further light-providing device (125); Generating (1015) a camera image (160) of a reticle (185) via the afocal optical system (105) in the recording device (110) from a second side (155) opposite the first side (150) using a camera (120), wherein the light supply device (115), the afocal optical system (105) and the camera (120) are arranged coaxially on or with measuring axes parallel to a surveying axis (162) which is oriented perpendicular to the recording plane (140); Generating (1020) a further camera image (170) of a further reticle (185) via the afocal optical system (105) in the recording device (110) from the second side (155) using a further camera (130), wherein the further camera image (170) is generated simultaneously with the camera image (160) and wherein the further light-providing device (125), the afocal optical system (105) and the further camera (130) are arranged coaxially on or with measuring axes parallel to an oblique measurement axis (175) which is oriented obliquely to the measurement axis (162) and / or recording plane (140); and Detect (1025) or calculate the modulation transfer function (MTF) of the afocal optical system (105) using the camera image (160) and / or additional camera image (170).

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