DEVICE AND METHOD FOR MEASURING IMAGE PROPERTIES OF AN OPTICAL SYSTEM

Description

[0001] The invention relates to a device for measuring imaging properties of an optical system, the device comprising: a test specimen holder configured to position the optical system to be tested at a predetermined test position, a rigid holding device, and a plurality of MTF measuring devices arranged at fixed, predeterminable positions of the holding device such that each of the MTF measuring devices can measure a modulation transfer function at mutually different, likewise fixed, angular positions in the image field of the optical system. Furthermore, the invention relates to a method for measuring imaging properties of an optical system using such a device.

[0002] Measuring the imaging properties of an optical system is often performed as part of quality control and / or to characterize imaging optical systems. A widely used measurement method for this purpose is the measurement of the modulation transfer function (MTF). MTF measurements are performed on a wide variety of optical systems. They are performed in large numbers in the mass production of lenses and also for the characterization of high-quality specialty optics.

[0003] A well-known MTF inspection device is offered by Trioptics GmbH under the name ImageMaster ®< PRO. The ImageMaster ®< PRO devices utilize a plurality of telescopic cameras, each mounted at a fixed angular position relative to the optical axis of the test piece and in the "line of sight" to the pupil of the test piece. This is achieved by using a dome-shaped or cap-shaped camera holder, with the cameras arranged on the inside of this dome. The cameras serve as MTF measuring devices and view the dome's center of curvature along their optical axes. At the same time, all telescopic cameras are aligned with the pupil of a single optical system, which is positioned as the test piece at a test position.Using such a measuring device, multiple MTF measurements can be performed simultaneously at different field positions, represented by different angular positions, within the image field of the optical system under test. For this purpose, for example, an illuminated reticle in the image plane of the optical system under test is imaged onto the camera sensor via the respective telescopic optics of the MTF testing device.

[0004] In order to determine the imaging quality of the optical system under test with high accuracy, it is desirable to achieve a high measurement point density. The measurement point density correlates directly with the number of MTF measuring devices used. The more MTF measuring devices are positioned in an angular range of the imaging optics under test, the higher the measurement point density in this angular range. However, each MTF measuring device, i.e. each individual camera including its imaging optics, has a finite spatial extent. For this reason, the measurement point density in an existing system cannot simply be increased. Once the mechanically tightest and thus densest possible arrangement of the MTF measuring devices has been reached, in which the MTF measuring devices touch each other, the limit for the number of possible measurement points has also been reached.

[0005] One way to increase the number of measurement points would be to increase the dimensions of the entire measuring device, arranging a larger number of MTF measuring devices on a dome with a larger radius. However, this approach would quickly make the measuring device unwieldy.

[0006] CN 104865047 A discloses an MTF measuring device whose cameras used for MTF measurements are attached to a pivoting dome. These cameras are configured to perform infinite measurements. After the infinite measurement, the dome is pivoted so that the MTF measuring devices attached to it move away from the optics to be tested, opening up a travel path. Along this travel path, additional image sensors arranged on a flat mounting plate are moved into the field area of ​​the optics to be tested. These cameras, arranged in a plane, are configured to perform a finite measurement. The entire dome-like structure, including the cameras, is designed to be pivotable, so that after the finite measurement, a measurement can be taken at a finite distance using the additional image sensors.

[0007] Between performing the infinite measurement and the finite measurement, it is therefore necessary to move the measuring device between two configurations. This is only possible with a mechanically movable structure that does not represent a rigid holding device as a whole. A holding device that includes moving parts inevitably has the design disadvantages associated with moving parts, which affect the measurement accuracy and speed. These include, among other things, greater design complexity and lower tolerances and accuracies, or tolerances that can only be achieved with considerable additional effort. In addition, with the known measurement, only either an infinite measurement or a measurement with a finite distance can be performed; simultaneous measurement with all available cameras is structurally impossible.

[0008] Another measuring device is known from CN 208751828 U. This comprises several MTF measuring devices arranged on a dome. In order to be able to record high-density measurement values ​​in a central imaging area of ​​an optical system under test, the device has image sensors arranged at a finite distance, with which a measurement can be carried out in the central area of ​​the optical system under test. These measuring devices arranged at a finite distance are sensors onto which the testing optics directly images and which determine the image quality using technology not disclosed in detail. While the cameras with attachment optics could be MTF measuring devices, this is technically only possible with limitations using the sensors, which capture a direct image of a test object imaged by the optical system under test.In order to capture a sharp image with a finite image, the selected distance between the sensor and the test object must be matched to the optics under test, and a sensor size must be selected that can capture the entire test structure. In contrast to a measurement performed based on an image at infinity, where the distance between the test object and the telescope is irrelevant, this condition severely limits the scope of application of the disclosed solution.

[0009] DE 10 2015 006 015 A1 discloses a device for measuring an imaging property of an optical system, which generates a light pattern in a focal plane of the optical system. The device comprises an arrangement of N separate cameras, each camera having a lens and a light sensor arranged in a focal plane of the lens. The cameras are arranged on a side opposite the light pattern generating device in such a way that each camera, with its light sensor, captures the image of exactly one section of the light pattern created with the cooperation of the optical system. At least one beam deflection element is arranged between the optical system and at least one of the cameras in such a way that it deflects the light incident on the at least one camera from a reference axis of the device, to which the optical system is aligned.

[0010] EP 3 410 091 A1 shows a device for detecting a modulation transfer function and a centering of an optical system.

[0011] It is an object of the invention to provide a device and a method for measuring imaging properties of an optical system, which can be implemented with little design effort, has compact dimensions and enables the acquisition of MTF measurement data in a central imaging area of ​​an optical system to be tested with a high measurement point density.

[0012] The object is achieved by a device for measuring imaging properties of an optical system, wherein the device comprises: a test specimen holder which is designed to position the optical system to be tested at a predetermined test position, a rigid holding device and a plurality of MTF measuring devices which are arranged at fixedly predeterminable positions of the holding device in such a way that with each of the MTF measuring devices a modulation transfer function can be measured at mutually different, likewise fixedly predeterminable angular positions in the image field of the optical system, wherein this device is further developed in that the holding device comprises at least a first and a second holder and the plurality of MTF measuring devices comprises a first and a second group of MTF measuring devices, wherein the first holder is configured to hold the MTF measuring devices of the first group at first positions such that the MTF measuring devices of the first group are arranged on a first spherical shell, the second holder is configured to hold the MTF measuring devices of the second group at second positions such that the MTF measuring devices of the second group are arranged on a second spherical shell, wherein the first and the second spherical shell have different radii and are arranged concentrically to one another.

[0013] In the context of this description, a rigid holding device is understood to mean a holding device without moving parts. The majority of the MTF measuring devices are arranged at fixed, predeterminable positions on the holding device, which means that they are located in fixed positions during measurement data acquisition and, in particular, are not moved. The MTF measuring devices can be attached to the holding device in a position that can be changed, in particular adjusted, for example for the purpose of adjustment. Such changeability can be realized, for example, by mounting the MTF measuring devices with the aid of screws guided through elongated holes.

[0014] The optical system whose imaging properties are measured is, in particular, a refractive optical system. In the context of the present description, a refractive optical system is understood to mean an optical system that comprises at least one refractive optical element; in particular, all optical elements of the optical system are refractive optical elements.

[0015] The MTF measuring devices are, in particular, measuring cameras designed to determine the modulation transfer function (MTF) of the optical system under test. For this purpose, the MTF measuring devices are equipped with suitable optics. The MTF measuring devices are, in particular, mounted on the holding device in such a way that their fields of view do not overlap. In other words, the MTF measuring devices are arranged so that they do not interfere with each other when performing the measurements.

[0016] The angular position of the MTF measuring devices determines a position of the MTF measuring devices in the image field of the optical system to be tested.

[0017] Advantageously, the device according to aspects of the invention enables simultaneous measurement of the optical imaging quality of an optical system to be tested on the basis of MTF measurements, whereby a high measurement point density can be obtained. The MTF measurements can advantageously be carried out simultaneously, which allows the optical system to be tested to be characterized at high speed. The mechanical design of the device advantageously does not have any moving parts, which benefits the precision and speed of the measurement carried out. The device is also very flexible because it can be used to characterize both optical systems with a large maximum field of view, i.e. a large field angle (FOV), and, in particular, optical systems with a small field angle. For this purpose, it is not necessary to convert, retool, or move the device.

[0018] MTF measuring devices, for example, are cameras equipped with suitable finite or infinity optics, allowing them to capture the test object imaged by the optical system under test, such as a cross-shaped aperture. It is also possible to equip the MTF measuring devices with collimators that offer focusing capabilities.

[0019] The device is particularly designed such that all MTF measuring devices comprised by the device are of the same design, i.e., they are configured for the same type of measurement. In particular, it is provided that all MTF measuring devices perform an infinite measurement.

[0020] The mechanical design of the device, which requires no moving parts, is extremely temperature-stable, which is particularly advantageous for mass testing of optical systems over extended periods. The holding device can, for example, be implemented by several mechanically rigid struts that connect the first and second holders or provide a suitable holding structure for these holders.

[0021] In MTF measuring devices as known from the prior art, the number of detectable measurement points, which is limited by the mechanical expansion of the MTF measuring devices, could be increased by arranging the MTF measuring devices at a greater distance from the optical system under test. It would then be possible to arrange a larger number of MTF measuring devices at a similarly large field angle of the optical system under test. However, this measure significantly increases the size of the devices for measuring the imaging properties of the optical system. This disadvantage is overcome with the help of the multi-stage design according to the invention. A solution is provided in which a large number of measurement points can be recorded per field angle, while at the same time the compact dimensions of the measuring devices can be largely retained.In a multi-stage arrangement, it is possible to arrange the MTF measuring devices on the first and second holders so that their fields of view do not overlap. This allows each individual MTF measuring device to acquire a corresponding MTF measurement value in the image field of the optical system under test.

[0022] The device is particularly refined in that the MTF measuring devices are arranged on the holder in such a way that the optical axes of the MTF measuring devices intersect in a plane of an aperture or pupil of the optical system to be tested. In particular, the centers of the spherical shells also lie in the plane of the aperture or pupil of the optical system to be tested.

[0023] According to a further advantageous embodiment, the device is further developed in that the holding device comprises a third holder and the plurality of MTF measuring devices comprises the first and second group and additionally a third group of MTF measuring devices, wherein the third holder is configured to hold the MTF measuring devices of the third group at third positions, so that the MTF measuring devices of the third group are arranged on a third spherical shell, wherein the third spherical shell has a third radius different from the first and second and is arranged concentrically to the first and second spherical shell.

[0024] By introducing a third plane, the measurement point density per field angle of the optical system under test can be further increased. By increasing the distance between the MTF measurement devices and the optical system under test, it is possible to provide an even larger number of MTF measurement devices per field angle.

[0025] Within the scope of further embodiments, it is also envisaged to provide further levels in addition to the three levels mentioned above, so that a device according to such an embodiment has more than three levels. The design can be easily continued systematically with a fourth, fifth, sixth level, etc., as described above for the first three levels, without requiring any special design measures deviating from the described concept.

[0026] The additional levels are provided by additional holders of the holding device and are designed to hold the MTF measuring devices held on the corresponding level arranged on an additional spherical shell. The spherical shells of all holders are arranged concentrically to each other, meaning the centers of the spherical shells all coincide at a single point.

[0027] According to a further advantageous embodiment, the device is further developed in that the first radius of the first spherical shell is greater than the second radius of the second spherical shell and in particular the second radius of the second spherical shell is greater than the third radius of the third spherical shell, so that the MTF measuring devices of the first group each have a greater distance to the optical system to be tested than the MTF measuring devices of the second group and in particular the MTF measuring devices of the second group each have a greater distance to the optical system to be tested than the MTF measuring devices of the third group.

[0028] The MTF measuring devices of the first group are used to capture a high density of measurement points in a central imaging area of ​​the optical system under test. The MTF measuring devices of the second and third groups are used to capture more peripheral areas of the field of view of the optical system under test, i.e., the edge areas of the field of view. Depending on the size of the viewing angle / field of view of the optical system under test, it may also be possible to use only individual groups of MTF measuring devices to characterize the optical system under test. For example, if the device is configured to measure optical systems with an image angle of 200° (using the MTF measuring devices of the first and second groups), optical systems with an image angle of, for example, up to 50° can be measured using only the MTF measuring devices of the first group.

[0029] The device is further developed in that for all MTF measuring devices of the first group, a first lateral angle between an optical axis of the optical system to be tested and an optical axis of the MTF measuring device is smaller than a second lateral angle between the optical axis of the optical system to be tested and an optical axis of any MTF measuring device of the second group and in particular for all MTF measuring devices of the second group, a second lateral angle between an optical axis of the optical system to be tested and an optical axis of the MTF measuring device is smaller than a lateral angle between the optical axis of the optical system to be tested and an optical axis of any MTF measuring device of the third group.

[0030] The central arrangement of the MTF measuring devices in the first group can be clearly determined by the angle between their optical axes and the optical axis of the optical system under test. An angular interval, which typically includes the axes of the MTF measuring devices in the second group and the optical axis of the optical system under test, lies above the interval for the first group.

[0031] The first group typically includes an axial MTF measuring device whose optical axis coincides with the optical axis of the optical system under test (assuming ideal orientation of the optical system under test).

[0032] According to a further advantageous embodiment, the device is further developed in that a lateral angle between two adjacently arranged MTF measuring devices of the first group is smaller than a lateral angle between two adjacently arranged MTF measuring devices of the second group and in particular the second lateral angle is smaller than a third lateral angle between two adjacently arranged MTF measuring devices of the third group.

[0033] The aforementioned lateral angles between the adjacent MTF measuring devices are determined as follows. Depending on whether the MTF measuring devices belong to the first, second, or third group, a great circle is marked off on the first, second, or third spherical shell, on which the adjacent MTF measuring devices lie. The angle is then determined in the plane of this great circle. By definition, the center of the corresponding spherical shell also lies in the plane of the great circle. This definition of the lateral angle corresponds to that commonly used for a field angle of an image area, whereby in this case, reference is made to the optical system under test.

[0034] Advantageously, such a measuring device can be used to obtain MTF measurement values ​​in a central image field area of ​​the optical system to be tested with a high measurement point density.

[0035] The first lateral angle, for industry-standard camera dimensions, lies in particular in a range between 2.7° and 3.1°, furthermore in particular in a range between 2.8° and 3.0° and furthermore is in particular at least approximately 2.9°. The second lateral angle lies, for example, in a range between 3.0° and 9°, in particular in a range between 3.1° and 7° and furthermore is in particular at least approximately 3.3°. The third lateral angle lies, for example, in particular in a range between 9° and 13°, furthermore in particular in a range between 10° and 12° and furthermore is in particular at least approximately 11°.

[0036] According to a further advantageous embodiment, the device is further developed in that the holders of the holding device extend at least in sections along the corresponding spherical shell.

[0037] In the context of this description, the term "extend along" means that the corresponding holders of the holding device extend at a constant distance from the respective spherical shell. In other words, this means that the holders do not necessarily have the same radius as the corresponding spherical shell.

[0038] According to a further advantageous embodiment, the device is further developed in that the first holder is designed as a spherical cap and the second and / or the third holder are / is designed as a spherical cap with a central opening, wherein in particular the second and / or the third holder are / is annular, and furthermore wherein in particular the second and / or the third holder are / is designed in the form of a spherical zone.

[0039] A spherical zone, also referred to as a spherical layer or spherical disk, is a portion of a spherical surface cut out by two parallel planes. The cut-out curved surface portion is usually called the spherical zone of the corresponding spherical layer or spherical disk. The second or third holder is particularly designed such that its surface extends along such a spherical zone. This allows the cameras of the next higher level to view through the central opening of the underlying annular holder. This provides a mechanically stable mount for the MTF measuring devices without the MTF measuring devices interfering with each other or restricting the viewing angle.

[0040] According to a further advantageous embodiment, the device is further developed in that the first holder is designed as a spherical cap and the second and / or the third holder are / is each designed as at least one bracket, wherein the brackets are each fastened to the first holder at a first end close to the first holder and extend along great circles of the first or second spherical shell in the direction of a distal free end, wherein the great circles run within planes that intersect along an optical axis of the optical system to be tested.

[0041] A bracket design of the holder allows for a particularly lightweight and material-saving construction of the holder in question. Furthermore, a fastening element between the first holder and the second holder can be omitted if the first and second holders are fastened directly to one another, or a structurally small and thus efficiently designed component can be used. The brackets from which, for example, the second holder is constructed can, for example, advantageously be fastened at their first end directly to the first holder, which is a spherical cap. According to a preferred exemplary embodiment, this spherical cap only accommodates one axial MTF measuring device, which is arranged centrally in the spherical cap. The other MTF measuring devices are held on brackets.

[0042] According to a further embodiment, the device is further developed in that the holders of the holding device are configured such that a displacement of the MTF measuring devices on the associated spherical shell is possible. The MTF measuring devices of the first group are thus arranged displaceably on the first spherical shell, the MTF measuring devices of the second group are arranged on the second spherical shell, and the MTF measuring devices of the third group are arranged displaceably on the third spherical shell. This is achieved, for example, by attaching the MTF measuring devices to the holders using elongated holes. The elongated holes preferably extend along great circles on the spherical shells.

[0043] According to a further advantageous embodiment, the connection between the spherical cap and the brackets is realized using elongated holes, so that the brackets can be moved along these elongated holes, which preferably run along great circles. This allows for flexible adaptation of the field angle of the device to the given measurement task.

[0044] Furthermore, the great circles preferably extend in planes that intersect at a common axis. This axis preferably coincides with the optical axis of the optical system under test.

[0045] The object is further achieved by a method for measuring imaging properties of an optical system using a device according to one or more of the aforementioned embodiments. The method according to the invention comprises the steps of arranging the optical system to be tested in the test specimen holder and simultaneously performing MTF measurements with all MTF measuring devices.

[0046] This method advantageously allows for very rapid characterization of the optical system under test, as all MTF measurements can be performed simultaneously. The method is also very flexible, as both optical systems with a large field angle and optical systems with a small field angle can be characterized on the same device.

[0047] Further features of the invention will become apparent from the description of embodiments of the invention together with the claims and the accompanying drawings. Embodiments of the invention may incorporate individual features or a combination of several features.

[0048] Within the scope of the invention, features marked with "in particular" or "preferably" are to be understood as optional features.

[0049] The invention is described below, without limiting the general inventive concept, using exemplary embodiments with reference to the drawings, whereby express reference is made to the drawings for all details of the invention not explained in more detail in the text. They show: Fig. 1 and 2 each show a schematic and simplified perspective view of a device for measuring imaging properties of an optical system according to a first embodiment, Fig. 3 a view of this device from the bottom, Fig. 4 a side view of this device, Fig. 5 a top view of this device, Fig. 6 and 7 each show a schematic and simplified perspective view of a device for measuring imaging properties of an optical system according to a second embodiment, Fig. 8 a view of this device from the bottom, Fig. 9 a first side view of this device and Fig. 10 a further side view of this device, wherein only some of the MTF measuring devices are shown, Fig. 11 a top view of the device according to the second embodiment, Fig.12 and 13 each show a schematic and simplified perspective view of a device for measuring imaging properties of an optical system according to a third exemplary embodiment, Fig. 14 shows a top view of this device, Fig. 15 shows a view from below of this system, Fig. 16 shows a schematic and simplified perspective detailed view of this system, wherein only some of the MTF measuring devices are shown, Fig. 17 shows a schematic and simplified sectional view of a device for measuring imaging properties of an optical system according to a fourth exemplary embodiment.

[0050] In the drawings, identical or similar elements and / or parts are provided with the same reference numbers, so that a repeated presentation is omitted.

[0051] Fig. 1 shows a schematic and simplified perspective view of a device 2 for measuring imaging properties of an optical system 4. The optical system 4 is, in particular, a refractive optical system 4. In the following description, reference is made to such a refractive optical system 4 merely by way of example. The refractive optical system 4 is shown in a highly schematic manner; it is, for example, an imaging optic, such as a lens or the like. The device 2 comprises a test specimen holder 6, which is designed to position the optical system 4 to be tested at a predetermined test position. The device 2 further comprises a rigid holding device 8, which, in the illustrated embodiment, comprises a first holder 10, a second holder 12, and struts 14 connecting the two holders 10, 12, only one of which is provided with a reference numeral for reasons of clarity.By way of example, the first holder 10 is designed as a spherical cap (also referred to as a dome). The second holder is ring-shaped and is also designed as a spherical cap but has a central opening 16. The second holder 12 is designed as a spherical zone, i.e. its surfaces extend along two concentric spherical zones. The first holder 10 also extends along a first spherical shell, which, however, has a larger radius than a second spherical shell, along which the second holder 12 extends. The first spherical shell and the second spherical shell are arranged concentrically to one another. The centers of these two spherical shells lie on the area marked with a cross in . Fig. 1 marked sphere center 18. This sphere center 18 preferably lies in the plane of an aperture of the optical system 4 to be tested.

[0052] A plurality of MTF measuring devices 20 are attached to the holding device 8. The MTF measuring devices 20, of which only one is provided with a reference numeral for reasons of clarity, are, for example, cameras equipped with suitable optics. The MTF measuring devices 20 are attached to the holding device 8 in such a way that they are located in a fixed, predeterminable position on the holding device 8. With each of the MTF measuring devices 20, a modulation transfer function (MTF) can be measured at a fixed, predeterminable angular position in the image field of the optical system 4.

[0053] The holding device 8 is rigid, meaning it has no moving parts. The MTF measuring devices 20 are located at fixed positions. However, they can be flexibly positioned, for example, during an initial adjustment of the device 2. For this purpose, the first holder has elongated holes 22 along which the MTF measuring devices 20 can be moved. The MTF measuring devices 20 are fixed via knurled screws that are visible on the top side of the first holder 10. The elongated holes 22 preferably extend along great circles of the first spherical shell, along which the first holder 10 extends.

[0054] The device 2 is designed to accommodate a plurality of MTF measuring devices 20. This plurality of MTF measuring devices 20 is divided into a first and a second group of MTF measuring devices 20. The first group of MTF measuring devices 20 is attached to the first holder 10. This first group is in Fig. 1 A second group of MTF measuring devices 20, which are Fig. 2 not shown, is attached to the second holder 12. The same applies to these MTF measuring devices 20 as was previously stated with regard to the MTF measuring devices 20 of the first group. They are located at fixed, predeterminable positions. However, their position can be adjusted. For this purpose, the second holder 12 also has elongated holes 22, of which, again for reasons of clarity, only one is provided with a reference numeral. The elongated holes 22 of the second holder 12 preferably extend along great circles of the second spherical shell, along which the second holder 12 extends. Similar to the MTF measuring devices 20 held by the first holder 10 in Fig. 1 As shown, the MTF measuring devices 20 of the second group are located in Fig. 1 below the second holder 12. The MTF measuring devices 20 of the first and second groups are arranged on the first and second holders 10, 12, respectively, such that the optical axes of the MTF measuring devices 20 intersect at the sphere center 18. In other words, the MTF measuring devices 20 are mounted on the holder 8 such that their optical axes intersect in a plane of the aperture of the optical system 4 to be tested.

[0055] The MTF measuring devices 20 of the first group are arranged on a first spherical shell, which means that, in particular, the sensors of the cameras used as MTF measuring devices 20 are located within this first spherical shell. The first holder 10 extends along this first spherical shell, but this does not mean that the holder 10 runs within this spherical shell with the same radius. The first holder 10 extends at a constant distance from this first spherical shell, so that the desired arrangement of the first group of MTF measuring devices 20 can be provided. This construction allows the use of simple camera holders 24 to accommodate the MTF measuring devices 20, which maintain the directional orientation predetermined by the dome-like construction of the first holder 10 and merely position the MTF measuring device 20 radially further inward, i.e., closer to the optical system 4.The same applies to the inclusion of the MTF measuring devices 20 of the second group, which are shown in . Fig. 1 are not shown.

[0056] The MTF measuring devices 20 of the first group are configured to perform MTF measurements in a central region of the image field of the optical system 4. Since these MTF measuring devices 20 are arranged at a greater distance from the optical system 4 to be tested, more MTF measuring devices 20 can be arranged per field angle of the optical system 4 compared to the second group. This means that MTF measurement values ​​can be acquired with a higher measurement point density in a central region of the image field of the optical system 4. At the same time, the device 2 makes it possible to cover a large field angle during the MTF measurement; MTF measurements at large field angles can be performed with the MTF measuring devices 20 of the second group. This allows the testing of optical systems 4 that have a large image or field angle, whereby the entire image field of the optical system 4 can be tested.At the same time, the device 2 can also be used to test optical systems 4 which have a small field angle, such as telephoto lenses. It is advantageously not necessary to convert the device 2 between testing, for example, a wide-angle lens with a large field angle and a telephoto lens with a small field angle. It is also possible, for example, to use only the MTF measuring devices 20 of the first group to test telephoto lenses. For this purpose, the MTF measuring devices 20 are advantageously arranged such that their image areas do not overlap. During the measurement, the MTF measuring devices 20 of the first group look through the central opening 16 provided in the second holder 12. At the same time, the values ​​shown in . Fig. 1 not shown MTF measuring devices 20 of the second group are arranged so that they do not obstruct the image field of the MTF measuring devices 20 of the first group.

[0057] Fig. 2 shows the already Fig. 1 known device 2 in a further schematic and simplified perspective view. The refractive optical system 4 to be measured and the test piece holder 6 are shown in Fig. 2 not shown for reasons of clarity, only the sphere center 18 is indicated, which lies in the plane of the test specimen aperture. Fig. 2 shows the device 2 viewed from below. It is clearly visible how the MTF measuring devices 20 are mounted on corresponding camera mounts 24 on the first holder 10. The illustrated MTF measuring devices 20 of the first group look through the opening 16 of the second holder 12 onto the optical system 4 to be tested. The optical axes of the MTF measuring devices 20 intersect at the sphere center 18.

[0058] Fig. 3 shows a view of the device 2 from its underside. Visible are the MTF measuring devices 20 of the first group, which face the sphere center 18. A central MTF measuring device 20 is used to perform an on-axis measurement, while the four MTF measuring devices 20 grouped around it perform off-axis MTF measurements. For reasons of clarity, the optical system 4 to be tested is again not shown.

[0059] Fig. 4 shows the device 2 in a schematic and simplified side view. For reasons of clarity, the optical system 4 is also not shown in this figure. The optical axis of the central MTF measuring device 20 for performing the on-axis measurement is shown in a dashed line, as is the optical axis of an MTF measuring device 20 for performing the off-axis measurement. The optical axis of the on-axis MTF measuring device 20 coincides with the optical axis of the optical system 4 to be tested (not shown).

[0060] In The side view clearly shows that the first radius of the first spherical shell, in which the MTF measuring devices 20 of the first group are arranged, is larger than the second radius, in which the Fig. 4 MTF measuring devices 20 of the second group (not shown) can be arranged. This results directly from a comparison of the different radii of curvature of the first holder 10 and the second holder 12.

[0061] Fig. 5 shows the device 2 in a schematically simplified plan view. In The top view shown shows the compact dimensions of the measuring device 2 in the lateral direction. The first holder 10 and the second holder 12 have only slightly different diameters (see also Fig. 4 ), whereby the maximum dimensions are determined by the holding device 8.

[0062] In addition, Fig. 5 visible that the slots 22 of the first holder 10 and the second holder 12, oriented along the main axes, are aligned with each other. These are the slots in Fig. 5 horizontally or vertically extending elongated holes 22. To increase the measuring point density, the elongated holes 22 not used in the illustrated embodiment, which run along the 45° division between the horizontal and the vertical, could be equipped with additional MTF measuring devices 20. In this respect, the device 2 is flexible and can be adapted to the desired measuring task.

[0063] Fig. 6 shows a schematic and simplified perspective view of a device 2 for measuring imaging properties of a refractive optical system 4, according to a further embodiment. Again, the optical system 4 is shown in a highly schematic manner. It is arranged on a test specimen holder 6, with which the optical system 4 is positioned at a predetermined test position. Also in Fig. 6 the sphere center 18 is shown, which preferably lies in a plane of the aperture of the optical system 4 to be tested.

[0064] The device 2 shown again comprises a spherical cap or dome-shaped first holder 10, which, together with an annular, but otherwise also spherical cap or dome-shaped second holder 12 and the struts 14 connecting them, forms a holding device 8 for the MTF measuring devices 20 of this device 2. The second holder 12 again comprises a central opening 16 through which the MTF measuring devices 20 of the first group look through. In the illustrated embodiment, MTF measuring devices 20 of the second group are also shown, which are received on the second holder 12.

[0065] Fig. 7 shows the Fig. 6 known device 2 in a further perspective view, in this case more from its underside. Clearly visible are the MTF measuring devices 20 of the second group, whose optical axes, like the optical axes of the MTF measuring devices 20 of the first group, intersect at the sphere center 18. The MTF measuring devices 20 of the second group allow MTF measurements to be performed on the optical system 4 to be tested at a large field angle. Also clearly visible is the high measurement point density in a central image area of ​​the optical system 4 provided by the large number of MTF measuring devices 20 of the first group. Fig. 7 Clearly visible is the mounting of the MTF measuring devices 20 of both the first and second groups with corresponding camera mounts 24. As already mentioned, these offset the MTF measuring devices 20 radially inward, so that the MTF measuring devices 20 of the first group are arranged on the first spherical shell, and the MTF measuring devices 20 of the second group are arranged on a second spherical shell with a second radius. The first radius is visibly larger than the second radius of the second spherical shell.

[0066] The MTF measuring devices 20 are mounted at fixed, predefined positions on the holding device 8. However, for adjustment purposes, they can be moved along the elongated holes 22. Similarly, the radial spacing of the MTF measuring devices 20 along the camera holders 24 can also be changed. These also have elongated holes 22 for this purpose.

[0067] Fig. 8 shows the Fig. 6 and7 known device 2 from its underside. For reasons of clarity, the optical system 4 to be tested is again not shown; only the sphere center 18 is shown. The MTF measuring devices 20 of the first group look through the opening 16 of the second holder 12. Their noticeably denser arrangement ensures the high measurement point density in the central image area of ​​the optical system 4 to be tested.

[0068] Fig. 9 shows the device 2 according to the second exemplary embodiment in a schematically simplified side view. It is clearly visible that the MTF measuring devices 20 of the first group are arranged on a first spherical shell with a larger radius than the MTF measuring devices 20 of the second group (held by the second holder 12), which are arranged on a second spherical shell with a smaller radius. By way of example, the optical axis 26 of an MTF measuring device 20 of the first group is shown in a dash-dotted line. An optical axis 26 for an MTF measuring device 20 of the second group is also shown in a dash-dotted line. The optical axes 26 of all MTF measuring devices meet at the sphere center 18, which, by way of example, lies in the aperture of the optical system 4 to be tested.

[0069] Fig. 10 shows a schematically simplified side view of the device 2 according to the second exemplary embodiment, wherein only one on-axis MTF measuring device 203, one of the MTF measuring devices 201 of the first group, and one MTF measuring device 202 of the second group are shown. The respective optical axes 263, 261, and 262 intersect at the sphere center 18. The optical axis 263 of the on-axis MTF measuring device 203 corresponds to an optical axis of the optical system 4 to be tested (not shown).

[0070] A first lateral angle α1 between the optical axis 263 of the optical system 4 to be tested and the optical axis 261 of the MTF measuring device 201 of the first group is smaller than a second lateral angle α2, measured between the optical axis 263 of the optical system 4 to be tested and the optical axis 262 of the MTF measuring device 202 of the second group. This applies to all MTF measuring devices 201 of the first group, each of which encloses a smaller lateral angle with the optical axis 263 of the optical system 4 to be tested than any MTF measuring device 202 of the second group. In other words, this means that the MTF measuring devices 201 of the first group are configured to acquire measured values ​​in a central imaging area of ​​the optical system 4 to be tested.

[0071] Furthermore, a further lateral angle between two adjacently arranged MTF measuring devices 201 of the first group is always smaller than a lateral angle between two adjacently arranged MTF measuring devices 202 of the second group. In other words, this means that the MTF measuring devices of the first group are arranged closer together than those of the second group.

[0072] Fig. 11 shows the device 2 according to the second embodiment in a schematically simplified top view. In this view, too, the higher density of the MTF measuring devices 20 of the first group is evident, recognizable by their rear fastening elements, which are, for example, knurled screws, which are each provided on the top side of the first and second holders 10, 12. The arrangement of the MTF measuring devices 20 is merely exemplary; their density can be increased or decreased by adding and / or removing corresponding MTF measuring devices 20 on the first and / or second holders 10, 12 in the first or second group. Such adaptation of the device 2 can be carried out flexibly depending on the measuring task, whereby the MTF measuring devices 20 again remain in fixed, predetermined positions for the respective measuring task.For flexible mounting of the MTF measuring devices 20, elongated holes 22 are provided in the first and second holders 10, 12. Along the axis shown in . Fig. 10 In horizontal and vertical directions, the elongated holes 22 of the first and second holders 10, 12 can again be arranged in alignment with one another.

[0073] Fig. 12 shows, in a schematic and simplified perspective view, a device 2 for measuring imaging properties of a refractive optical system 4 according to a third exemplary embodiment. The device 2 comprises a first holder 10, which is designed as a spherical cap. Directly attached to this dome-shaped first holder 10 is only a single MTF measuring device 20, which performs an on-axis measurement. The associated knurled screw 28, with which this MTF measuring device 20 is attached to the dome-shaped first holder 10, is shown in Fig. 12 centrally visible on the first holder 10. The remaining MTF measuring devices 20 are attached to the second holder 12, which is designed in the form of a plurality of brackets 30. These brackets 30 are attached to the dome-shaped first holder 10 via cylindrical connecting pieces 32.

[0074] The brackets 30 from which the second holder 12 is constructed extend along great circles of the second spherical shell, starting from a first end 34 toward a distal free end 36. The brackets 30 are each connected to the first holder 10 at their first ends 34 via the connecting pieces 32. The second holder 12, constructed from brackets 30, is flexible in that the connection to the first holder 10 can be changed along the elongated holes 22 present in the first holder 10 along a great circle. For example, the bracket 30a can be attached closer to the center of the first holder 10, while another bracket 30b can be attached further to the edge of the first holder 10. The MTF measuring devices 20 are also adjustably attached to the brackets 30. For this purpose, the brackets 30 are also provided with elongated holes 22 that run in the direction of a longitudinal extension of the respective bracket 30.

[0075] Fig. 13 shows the device 2 according to the third exemplary embodiment in a further schematic and simplified perspective view, more from the bottom. The MTF measuring devices 20 are all aligned such that their optical axes intersect at the sphere center 18, which in turn can be located in an opening aperture of an optical system 4 to be tested. The optical system 4 is not shown for reasons of clarity. The exemplary embodiment shown is particularly suitable for testing optical systems 4 with extremely large field angles. MTF measurements can be recorded over a very wide field angle range.

[0076] Fig. 14 shows this device 2 in a top view. The compact dimensions of the device 2 are evident. The second holder 12, constructed from the brackets 30, protrudes only slightly beyond the outer edge of the first holder 10; only the free ends 36 of the brackets 30 are visible. Clearly visible are the elongated holes 22 in the first holder 10. These elongated holes run in a star shape from the center of the holder 10 toward its edge and along which the brackets 30 of the second holder 12 can be moved.

[0077] Fig. 15 shows the device 2 from the bottom. Three or two MTF measuring devices 20 are alternately mounted on the brackets 30 of the second holder 12. All MTF measuring devices 20 are directed toward the sphere center 18. The MTF measuring device 20 for performing the on-axis measurement is located centrally.

[0078] Fig. 16 shows the device 2 according to the third exemplary embodiment in a schematically simplified perspective view, wherein only two brackets 30 of the second holder 12 are shown. A first bracket 30a, which is received relatively centrally on the first holder 10 via the connecting piece 32, accommodates, for example, two MTF measuring devices 20. The second bracket 30b, which is attached relatively far outwardly on the first holder 10 via its connecting piece 32, accommodates, for example, three MTF measuring devices 20. The MTF measuring devices 20 are, as already described in the context of the other exemplary embodiments, fastened to the second holder 12, formed by the brackets 30 and the connecting pieces 32, by means of corresponding camera holders 24.

[0079] Fig. 17 shows, in a highly schematic and simplified sectional view, another device 2 for measuring imaging properties of a refractive optical system 4, according to a fourth exemplary embodiment. This device 2 comprises a first holder 10, which is again designed as a spherical cap. This is configured to fasten the MTF measuring devices 20 of a first group on a spherical shell with a first radius R1. In particular, the image sensors 38 of the cameras used as MTF measuring devices 20 are arranged on this first spherical shell. The device 2 further comprises a second holder 12, which is ring-shaped and has a central opening 16. This is configured to hold MTF measuring devices 20 of a second group on a spherical shell with a second radius R2. The image sensors 38 of these MTF measuring devices 20 are again arranged on this second spherical shell.The device 2 further comprises a third holder 40, which holds MTF measuring devices 20 of a third group arranged such that their image sensors 38 are located on a third spherical shell with a third radius R3. R3 ≤ R2 ≤ R1. Bezugszeichenliste

[0080] 2 Fixture 4 Optical system 6 Test specimen holder 8 Holding device 10 First holder 12 Second holder 14 Struts 16 Opening 18 Sphere center 20 MTF measuring device 20 1 MTF measuring device first group 20 2 MTF measuring device second group 20 3 On-axis MTF measuring device 22 Slotted hole 24 Camera holder 26 Optical axis 26 1 First optical axis 26 2 Second optical axis 26 3 Optical axis of the optical system 28 Knurled screw 30 Bracket 30, 30b Bracket 32 ​​Connecting piece 34 First end 36 Free end 38 Image sensors 40 Third holder α1first angle α2second angle R1first radius R2second radius R3third radius

Claims

1. Device (2) for measuring imaging properties of an optical system (4), wherein the device (2) comprises: a test-object holder (6), which is configured to position the optical system (4) to be tested at a predefined testing position, a rigid holding device (8), and a plurality of MTF measuring devices (20), which are arranged at firmly predefinable positions of the holding device (8) such that, by means of each of the MTF measuring devices (20), a modulation transfer function can be measured at respective different, likewise firmly predefinable, angular positions in the image field of the optical system (4), characterized in that the holding device (8) comprises at least a first and a second holder (10, 12), and the plurality of MTF measuring devices (20) comprises a first and a second group of MTF measuring devices (20), wherein the first holder (10) is configured to hold the MTF measuring devices (20) of the first group at first positions so that the MTF measuring devices (20) of the first group are arranged on a first spherical shell, the second holder (12) is configured to hold the MTF measuring devices (20) of the second group at second positions so that the MTF measuring devices (20) of the second group are arranged on a second spherical shell, wherein the first and the second spherical shells have different radii and are arranged so as to be mutually concentric.

2. Device (2) according to claim 1, characterized in that the MTF measuring devices (20) are arranged on the holding device (8) in such a way that the optical axes of the MTF measuring devices (20) intersect in a plane of an aperture of the optical system (4) to be tested.

3. Device (2) according to either claim 1 or 2, characterized in that the holding device (8) comprises a third holder (40) and the plurality of MTF measuring devices comprises the first and second group and additionally a third group of MTF measuring devices, wherein the third holder (40) is configured to hold the MTF measuring devices of the third group at third positions so that the MTF measuring devices of the third group are arranged on a third spherical shell, wherein the third spherical shell has a third radius that is different from the first and second radii and is arranged so as to be concentric to the first and second spherical shell.

4. Device (2) according to any of claims 1 to 3, characterized in that the first radius of the first spherical shell is greater than the second radius of the second spherical shell, and in particular the second radius of the second spherical shell is greater than the third radius of the third spherical shell, such that the MTF measuring devices (20) of the first group have in each case a greater distance from the optical system (4) to be tested than the MTF measuring devices (20) of the second group, and in particular the MTF measuring devices (20) of the second group have in each case a greater distance from the optical system (4) to be tested than the MTF measuring devices (20) of the third group.

5. Device (2) according to any of claims 1 to 4, characterized in that, for all the MTF measuring devices (201) of the first group, a first lateral angle (α1) between an optical axis (263) of the optical system (4) to be tested and an optical axis (261) of the MTF measuring device (201) is smaller than a second lateral angle (α2) between the optical axis (263) of the optical system (4) to be tested and an optical axis (262) of any MTF measuring device (202) of the second group, and in particular for all the MTF measuring devices (202) of the second group a second lateral angle between an optical axis (262) of the optical system (4) to be tested and an optical axis of the MTF measuring device is smaller than a lateral angle between the optical axis (263) of the optical system (4) to be tested and an optical axis of any MTF measuring device of the third group.

6. Device (2) according to any of claims 1 to 5, characterized in that a lateral angle between two adjacently arranged MTF measuring devices (20) of the first group is smaller than a lateral angle between two adjacently arranged MTF measuring devices (20) of the second group, and in particular the second lateral angle is smaller than a third lateral angle between two adjacently arranged MTF measuring devices of the third group.

7. Device (2) according to any of claims 1 to 6, characterized in that the holders (10, 12) of the holding device (8) extend, at least in portions, along the corresponding spherical shell.

8. Device (2) according to any of claims 1 to 7, characterized in that the first holder (10) is configured as a spherical cap, and the second and / or the third holder (12, 40) is / are configured as a spherical cap having a central opening (16), wherein in particular the second and / or the third holder (12, 40) is / are annular, and wherein more particularly the second and / or the third holder (12, 40) is / are configured in the form of a spherical zone.

9. Device (2) according to any of claims 1 to 8, characterized in that the first holder (10) is configured as a spherical cap and the second and / or the third holder (12, 40) is / are configured in each case as at least one bracket (30), wherein the brackets (30) are in each case fastened to the first holder (10) at a first end (34) close to the first holder (10) and extend along great circles of the first or second spherical shell in the direction of a distal free end (36), wherein the great circles extend within planes that intersect along an optical axis of the optical system (4) to be tested.

10. Device (2) according to any of claims 1 to 9, characterized in that the holders (10) of the holding device (8) are configured in such a way that a displacement of the MTF measuring devices (20) on the associated spherical shell is possible.

11. Method for measuring imaging properties of an optical system (4) using a device (2) according to any of claims 1 to 10, comprising the following steps: arranging the optical system (4) to be tested in the test-object holder (6), simultaneously carrying out MTF measurements using all the MTF measuring devices (20).