Apparatus and method for measuring imaging properties of an optical system

Abstract

The invention relates to a device (2) for measuring imaging properties of an optical system (4), wherein the device (2) comprises a test specimen holder (6) which is arranged for positioning the optical system (4) to be tested at a predetermined test position, a rigid holding device (8) and a plurality of MTF measuring devices (20) which are arranged at fixably predetermined positions of the holding device (8) in such a way that the modulation transfer function can be measured with each of the MTF measuring devices at respectively mutually different likewise fixably predetermined angular positions in the image field of the optical system (4). The improvement of the device is that the holding device (8) comprises at least one first holder (10) and at least one second holder (12) and the plurality of MTF measuring devices comprises a first group of MTF measuring devices (20) and a second group of MTF measuring devices (20), wherein the first holder (10) is arranged for holding the first group of MTF measuring devices (20) at a first position in such a way that the first group of MTF measuring devices (20) is arranged on a first spherical shell surface and the second holder (12) is arranged for holding the second group of MTF measuring devices (20) at a second position in such a way that the second group of MTF measuring devices (20) is arranged on a second spherical shell surface, wherein the first spherical shell surface and the second spherical shell surface have different radii and are arranged concentrically relative to each other.

Description

Technical Field

[0001] This invention relates to an apparatus for measuring the imaging characteristics of an optical system, comprising: a specimen holder configured to position the optical system under test at a predetermined test position; a rigid holding device; and a plurality of MTF measuring devices arranged at a fixed, predetermined position on the holding device such that the modulation transfer function can be measured in the image field of the optical system at different, equally fixed, predetermined angular orientations using each of the MTF measuring devices. Furthermore, this invention relates to a method for measuring the imaging characteristics of an optical system using such an apparatus. Background Technology

[0002] Imaging characteristics of optical systems are frequently measured within quality control limits and / or to characterize them. A well-known measurement method for this purpose is the measurement of the modulation transfer function (MTF), also known as the modulation transfer function. MTF measurements are performed on various optical systems. They are also extensively performed in the mass production of objectives and to characterize high-quality special optical components.

[0003] Trioptics GmbH sells a product called PRO's known MTF testers. The PRO tester uses multiple telescopic cameras, each mounted at a fixed, predetermined angular orientation relative to the optical axis of the specimen and along the "viewing direction" towards the pupille of the specimen. This is achieved using a dome-shaped or dome-shaped camera holder, with the cameras positioned inside the dome. The cameras serve as MTF measurement devices and observe the center of curvature of the dome along their optical axes. Simultaneously, all telescopic cameras are aligned with the pupille of a single optical system, which is placed as the specimen at the test position. With this measurement device, multiple MTF measurements can be performed simultaneously at various field positions, represented by different angular orientations, within the image field of the optical system under test. For example, for this purpose, the corresponding telescopic optics of the MTF tester image an illuminated lattice plate in the image plane of the optical system under test on its camera sensor.

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

[0005] One possible solution to increase the number of measurement points is to increase the size of the entire measuring device, in which a larger number of MTF measuring devices can be arranged on a dome with a larger radius. However, in this solution the measuring device quickly becomes too large to handle.

[0006] From CN 104865047 A a MTF measuring device is known, whose cameras for MTF measurement are fastened at a pivotable dome. These cameras are provided for performing an infinit measurement. After the infinit measurement has been carried out, the dome is pivoted so that the MTF measuring devices fastened there are moved away from the optics to be tested and release a travel path. On this travel path, further image sensors arranged on a flat holding plate are introduced into the field area of the optics to be tested. These cameras arranged in one plane are provided for performing a finite measurement. Thus, the complete dome-like structure including the cameras is implemented pivotable, so that after the finite measurement has been carried out, the finite measurement can be performed with the further image sensors at a finite distance.

[0007] Thus, between the performance of the infinit measurement and the performance of the finite measurement, a changeover of the measuring device between the two configurations is necessary. This is only possible with a mechanically movable structure, which as a whole does not show a rigid holding device. A holding device including movable components inevitably has constructional disadvantages related to the movable components, which affect the measurement accuracy and the measurement speed. This is in particular a higher constructional complexity and lower tolerances and accuracies or only achievable with significantly more expenditure. Furthermore, with the known measuring method only an infinit measurement or a measurement with a finite distance can always be carried out, while a way of simultaneously carrying out a measurement with all available cameras is excluded from a constructional point of view.

[0008] A further measuring device is known from CN 2087518128 U. This measuring device comprises a plurality of MTF measuring devices arranged on a dome. In order to be able to record a high density of measurement values in the central imaging region of the optical system to be tested, the device has image sensors arranged at a limited distance, with which measurements can be performed in the central region of the optical system to be tested. These measuring devices arranged at a limited distance are sensors on which the optical means to be tested are imaged directly and which determine the imaging quality using a technology not further disclosed. Although a camera with additional optical means can be an MTF measuring device, this is technically only possible in a limited way by means of the sensor, which detects the direct imaging of the test object imaged by the optical system to be tested. In order to be able to detect mainly sharp images when imaging at a limited distance, the chosen spacing between the sensor and the test piece must be matched to the optical means to be tested and the sensor size with which the complete test structure can be detected must be chosen. Unlike measurements based on imaging at an infinite distance and the spacing between the test piece and the telescopic camera not having an influence, this condition greatly limits the range of application of the disclosed solution.

[0009] A device for measuring imaging properties of an optical system is known from DE 10 2015 006 015 A1, which generates a light pattern in the focal plane of the optical system. The device comprises an arrangement of N cameras separated from one another, wherein each camera has an objective and a light sensor arranged in the focal plane of the objective. The cameras are arranged on the side opposite the light pattern generating means, so that each camera detects an image of exactly one part of the generated light pattern under the participation of the optical system with its light sensor. At least one beam deflection element is arranged between the optical system and at least one of the cameras, so that it deflects the light impinging on the at least one camera relative to a reference axis to which the optical system of the device is aligned. SUMMARY

[0010] It is an object of the present invention to give a device and a method for measuring imaging properties of an optical system, which can be realized with low constructional complexity, have a compact size and are able to detect MTF measurement data in the central imaging region of the optical system to be tested with a high measurement point density.

[0011] This object is achieved by a device for measuring imaging properties of an optical system, wherein the device comprises:

[0012] a test specimen holder, which is provided for positioning an 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 fixably predetermined positions of the holding device in such a way that the modulation transfer function can be measured in the image field of the optical system at respectively mutually different likewise fixably predetermined angular positions with each of the MTF measuring devices, wherein the improvement consists in that

[0013] the holding device comprises at least one first holder and at least one second holder and the plurality of MTF measuring devices comprises a first group of MTF measuring devices and a second group of MTF measuring devices, wherein

[0014] the first holder is provided for holding the first group of MTF measuring devices at a first position in such a way that the first group of MTF measuring devices is arranged on a first Kugelschale,

[0015] the second holder is provided for holding the second group of MTF measuring devices at a second position in such a way that the second group of MTF measuring devices is arranged on a second Kugelschale, wherein

[0016] the first Kugelschale and the second Kugelschale have different radii and are arranged concentrically relative to one another.

[0017] In the context of the present specification, a rigid holding device is to be understood as a holding device without movable parts. The plurality of MTF measuring devices is arranged at fixably predetermined positions of the holding device, which means that they are at fixed positions during the measurement value detection and in particular do not move. The MTF measuring devices can be mounted at the holding device in a way that their position is variable, in particular adjustable, for example for adjustment purposes. Such variability can be achieved, for example, by receiving the MTF measuring devices by means of a screw joint guided by a long hole.

[0018] The optical system whose imaging properties are measured is in particular a refractive optical system. A refractive optical system is to be understood in the context of the present specification as an optical system comprising at least one refractive optical element, in particular an optical system in which all optical elements are refractive optical elements.

[0019] The MTF measuring devices are in particular measuring cameras, which are provided for determining the modulation transfer function (MTF) of the optical system as test specimen. To this end, the MTF measuring devices are equipped with suitable optics. The MTF measuring devices are in particular received at the holding device in such a way that their fields of view do not overlap. In other words, the MTF measuring devices are arranged in such a way that they do not interfere with one another when performing measurements.

[0020] The angular orientation determines the position of the MTF measurement device in the image field of the optical system to be tested.

[0021] Advantageously, it is possible with the device according to aspects of the application to measure the optical imaging quality of the optical system to be tested synchronously based on the MTF measurement, wherein a high density of measurement points can be achieved. The MTF measurement can advantageously be performed synchronously, which enables a high speed characterization of the optical system to be tested. The mechanical structure of the device advantageously has no movable components, which is beneficial for the precision and speed of the measurements performed. The device is also very flexible, since it can be used both for characterizing optical systems having a large maximum field of view, i.e. a large field angle (English: Field of View: FOV), and for characterizing optical systems having a small field angle, among others. There is no need to adapt, rebuild or transform the device for this purpose.

[0022] The MTF measurement devices are, for example, cameras equipped with suitable finite distance or infinite distance optics, so that they can detect test objects imaged by the optical system to be tested, for example a crosshair or the like. It is also possible to equip the MTF measurement devices with a collimator that can be focused.

[0023] The device is designed in particular such that all MTF measurement devices included in the device are constructed similarly, i.e. are set up for the same type of measurement. It is in particular provided that all MTF measurement devices perform infinite distance measurements.

[0024] The mechanical structure of the device has no movable components, which has a very high temperature stability, which is advantageous in particular for large-scale testing of optical systems over longer periods of time. The holding of the device can be achieved, for example, by means of a plurality of mechanically rigid braces, which connect the first holder and the second holder to one another or provide a suitable holding structure for these holders.

[0025] In the case of MTF measuring devices, as is known from the prior art, the number of detectable measurement points limited by the mechanical dimensions of the MTF measuring device can be increased by arranging the MTF measuring devices at a greater distance from the optical system to be tested. A greater number of MTF measuring devices can then be arranged in the likewise greater field angle of the optical system to be tested. This measure, however, makes the device for measuring the imaging properties of the optical system significantly larger. This disadvantage is overcome by means of the multi-stage arrangement according to the application. The application provides a solution in which a large number of measurement points per field angle can be recorded, wherein at the same time the compact size of the resulting measuring device can be largely maintained. In the multi-stage arrangement, the MTF measuring devices can be arranged on the first holder and the second holder in such a way that their fields of view do not coincide. Thus, with each individual MTF measuring device, a corresponding MTF measurement value can be detected in the image field of the optical system to be tested.

[0026] The improvement of the device is particularly in that the MTF measuring devices are arranged at the holder in such a way that their optical axes intersect in the plane of the aperture or the eye of the optical system to be tested. Furthermore, particularly, the center of the spherical shell surface also lies in the plane of the aperture or the eye of the optical system to be tested.

[0027] According to a further advantageous embodiment, the improvement of the device is in that the holding device comprises a third holder and the plurality of MTF measuring devices comprises a first group of MTF measuring devices and a second group of MTF measuring devices and an additional third group of MTF measuring devices, wherein the third holder is provided for holding the third group of MTF measuring devices at a third position in such a way that the third group of MTF measuring devices is arranged on a third spherical shell surface, wherein the third spherical shell surface has a third radius which is different from the first and the second radius and is arranged concentrically to the first and the second spherical shell surface.

[0028] By introducing a third plane, the density of measurement points per field angle of the optical system to be tested can be further increased. Since the MTF measuring devices are even further away from the optical system to be tested, a greater number of MTF measuring devices can be provided per field angle.

[0029] It is likewise provided within the scope of further embodiments that further planes are provided in addition to the three planes described above, so that the device according to this embodiment has more than three planes. The structure for the first three planes described above can be continued without any problems in a systematic manner with a fourth, a fifth, a sixth plane, etc., without having to take specific structural measures for this which deviate from the described concept.

[0030] The further planes are provided by further holders of the holding device and are arranged to hold the MTF measuring devices held on the respective planes arranged on the further spherical shells. The spherical shells of all holders are arranged concentrically with respect to one another, so that the centers of the spherical shells all coincide in one point.

[0031] According to a further advantageous embodiment, the holding device is improved 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 first group of MTF measuring devices is arranged at a greater distance from the optical system to be tested than the second group of MTF measuring devices, and in particular the second group of MTF measuring devices is arranged at a greater distance from the optical system to be tested than the third group of MTF measuring devices.

[0032] The first group of MTF measuring devices serves to detect a high density of measuring points in the central imaging region of the optical system to be tested. The second group of MTF measuring devices and the third group of MTF measuring devices serve to detect regions of the field region of the optical system to be tested which are located more peripherally, i.e. edge regions of the field of view. Depending on the size of the angle of view / field region of the optical system to be tested, it can also be provided that only the respective group of MTF measuring devices is used for characterizing the optical system to be tested. For example, if the holding device is set up for measuring optical systems having an image angle of 200° (in the case of the use of the first group of MTF measuring devices and the second group of MTF measuring devices), it is possible to measure optical systems having an image angle of, for example, a maximum of 50° only with the first group of MTF measuring devices.

[0033] The holding device is further improved in that, for all MTF measuring devices of the first group, a first lateral angle between the optical axis of the optical system to be tested and the 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 the 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 the optical axis of the optical system to be tested and the 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 the optical axis of any MTF measuring device of the third group.

[0034] The central arrangement of the MTF measuring devices of the first group can be seen very well from the angle between the optical axis of the MTF measuring devices of the first group and the optical axis of the optical system to be tested. The angular interval (Winkelintervall) between the optical axis of the MTF measuring devices of the second group and the optical axis of the optical system to be tested is generally greater than this interval for the MTF measuring devices of the first group.

[0035] The first group of MTF measuring devices usually comprises an axial MTF measuring device, the optical axis of which coincides with the optical axis of the optical system to be tested (provided that the orientation of the optical system to be tested is ideal).

[0036] According to a further advantageous embodiment, the device is improved in that the lateral angle between two adjacently arranged MTF measuring devices of the first group of MTF measuring devices is smaller than the lateral angle between two adjacently arranged MTF measuring devices of the second group of MTF measuring devices, 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 of MTF measuring devices.

[0037] The mentioned lateral angles between adjacently arranged MTF measuring devices are determined in the following way. Depending on whether it is the first group of MTF measuring devices, the second group of MTF measuring devices or the third group of MTF measuring devices, a great circle is taken (abgeschlagen) on the first, second or third spherical shell surface, on which the adjacent MTF measuring devices lie. The angle is now determined in the plane of this great circle. By definition, the center point of the respective spherical shell surface also lies in the plane of the great circle. This definition of the lateral angle corresponds to the definition usually made for the field angle of an imaging region, in which case the optical system to be tested is referred to in this case.

[0038] Advantageously, it is possible with such a measuring device to obtain MTF measurement values in the central image field region of the optical system to be tested with a high density of measurement points.

[0039] In the camera sizes common in the industry, the first lateral angle is in particular in the range between 2.7° and 3.1°, further in particular in the range between 2.8° and 3.0°, and further in particular at least about 2.9°. The second lateral angle is for example in the range between 3.0° and 9°, in particular in the range between 3.1° and 7°, and further in particular at least about 3.3°. The third lateral angle is for example in particular in the range between 9° and 13°, further in particular in the range between 10° and 12°, and further in particular at least about 11°.

[0040] According to a further advantageous embodiment, the device is improved in that the holders of the holding device extend at least partially along the respective spherical shell surface.

[0041] In the context of the present specification, the term "extend along" is to be understood in that the respective holders of the holding device extend with a constant spacing relative to the respective spherical shell surface. In other words, i.e. the holders do not necessarily have the same radius as the assigned spherical shell surface.

[0042] According to a further advantageous embodiment, the device is improved in that the first holder is embodied as a spherical cap and the second holder and / or the third holder is / are embodied as a spherical cap with a central opening, wherein in particular the second holder and / or the third holder is / are ring-shaped, and wherein in particular the second holder and / or the third holder is / are further embodied in the form of a spherical segment.

[0043] A spherical segment is a portion of a spherical surface which is intercepted by two parallel planes. The curved surface share which is intercepted is generally referred to as the spherical segment or spherical washer of the respective spherical segment. The second holder or the third holder is / are designed in particular such that its / their surface extends along such a spherical segment. This makes it possible for a next higher plane camera to be able to observe through the central opening of the ring-shaped holder located therebelow. Thus, it is possible to provide mechanically stable holders for the MTF measuring devices without the MTF measuring devices interfering with one another or restricting the viewing angle.

[0044] According to a further advantageous embodiment, the device is improved in that the first holder is embodied as a spherical cap and the second holder and / or the third holder is / are respectively embodied as at least one arcuate piece, wherein the arcuate piece respectively extends at a first end near the first holder to a free distal end in the direction of a great circle of the first spherical shell surface or the second spherical shell surface, wherein the great circle runs within a plane which intersects the optical axis of the optical system to be tested.

[0045] The arcuate piece construction of the holders makes it possible to realize a particularly light and also material-saving construction of the relevant holder. Furthermore, when the first holder and the second holder are directly fastened to one another, it is possible to omit a fastening element between the first holder and the second holder or to use a component which is small in construction and thus designed efficiently. The arcuate piece, for example, which configures the second holder, can advantageously be fastened with its first end directly at the first holder which is a spherical cap, for example. According to a preferred embodiment, the spherical cap only receives the axial MTF measuring device which is arranged at the center of the spherical cap. The remaining MTF measuring devices are received at the arcuate piece.

[0046] According to a further embodiment, the device is improved in that the holders of the holding device are provided for realizing a displacement of the MTF measuring devices on the assigned spherical shell surface. Thus, a first group of MTF measuring devices is arranged in a displaceable manner on the first spherical shell surface, a second group of MTF measuring devices is arranged in a displaceable manner on the second spherical shell surface and a third group of MTF measuring devices is arranged in a displaceable manner on the third spherical shell surface. This is realized, for example, by fastening the MTF measuring devices at the holders using long holes. The long holes preferably extend along a great circle on the spherical shell surface.

[0047] According to a further advantageous embodiment, the connection between the spherical cap top and the bow is realized in the case of a long hole, so that the bow can be displaced along the long hole, which preferably extends along a great circle. This makes it possible for the field angle of the device to be flexibly adapted to a given measurement task.

[0048] The great circle preferably also extends in a plane intersecting the common axis. The axis preferably coincides with the optical axis of the optical system to be tested.

[0049] The object is also achieved by a method for measuring the imaging properties of an optical system using a device according to one or more of the preceding embodiments. The method according to the application comprises the steps of arranging the optical system to be tested in the test specimen holder and performing the MTF measurements synchronously with all MTF measurement devices.

[0050] Advantageously, such a method enables the optical system to be tested to be characterized very quickly, since the MTF measurements can all be performed synchronously. The method is also very flexible, since both optical systems having a large field angle and optical systems having a small field angle can be characterized on the same device.

[0051] Further features of the application can be gathered from the description of embodiments according to the application, the technical solutions and the figures. Embodiments according to the application can realize individual features or combinations of features.

[0052] Within the scope of the application, features identified with “in particular” or “preferably” are to be understood as optional features. BRIEF DESCRIPTION OF DRAWINGS

[0053] The application is described below by means of embodiments with reference to the attached drawings, which are conceived without limiting the general aspects of the application, wherein explicit reference is made to the drawings with regard to all details according to the application which are not explained further in the text. In the drawings:

[0054] Figure 1 and Figure 2 show a schematic and simplified perspective view of a device for measuring the imaging properties of an optical system according to a first embodiment,

[0055] Figure 3 shows a view of the device from the bottom side,

[0056] Figure 4 shows a side view of the device,

[0057] Figure 5 shows a top view of the device,

[0058] Figure 6 and Figure 7a schematic and simplified perspective view of a device for measuring imaging properties of an optical system according to a second embodiment, respectively,

[0059] Figure 8 a view from the bottom side of the device is shown,

[0060] Figure 9 a first side view of the device is shown, and

[0061] Figure 10 a further side view of the device is shown, wherein only some of the MTF measurement devices are shown,

[0062] Figure 11 a top view of the device according to the second embodiment is shown,

[0063] Figure 12 and Figure 13 a schematic and simplified perspective view of a device for measuring imaging properties of an optical system according to a third embodiment, respectively,

[0064] Figure 14 a top view of the device is shown,

[0065] Figure 15 a view from the bottom side of the system is shown,

[0066] Figure 16 a schematic and simplified perspective view of the system is shown, wherein only some of the MTF measurement devices are shown,

[0067] Figure 17 a schematic and simplified sectional view of a device for measuring imaging properties of an optical system according to a fourth embodiment is shown.

[0068] In the drawings, identical or similar elements and / or components are provided with identical reference signs, so that a repeated introduction is omitted accordingly. DETAILED DESCRIPTION

[0069] Figure 1A schematic and simplified perspective view of a device 2 for measuring imaging properties of an optical system 4 is shown. The optical system 4 is in particular a refractive optical system 4. In the following description only such a refractive optical system 4 is exemplarily referred to. The refractive optical system 4 is highly schematically shown, which is for example an imaging optical, like an objective, etc. The device 2 comprises a test piece holder 6, which is provided for positioning 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 shown embodiment comprises a first holder 10, a second holder 12 and a diagonal brace 14 connecting the two holders 10, 12, only one of the diagonal braces is provided with a reference sign for the sake of clarity. Exemplarily, the first holder 10 is embodied as a spherical crown top (also called dome). The second holder is ring-shaped, wherein it is likewise embodied as a spherical crown top, but has a central opening 16. The second holder 12 is embodied as a spherical table, i.e. its surface extends along two concentric spherical tables. The first holder 10 also extends along a first spherical shell surface, whereas the second spherical shell surface along which the second holder 12 extends has a larger radius compared to the first spherical shell surface. The first and the second spherical shell surface are arranged concentrically with respect to each other. The centers of the two spherical shell surfaces are located at the spherical center 18 marked with a cross in the middle. Figure 1 The spherical center 18 is preferably located in the plane of the stop of the optical system 4 to be tested.

[0070] A plurality of MTF measuring devices 20 is fastened at the holding device 8. The MTF measuring devices 20 are for example cameras equipped with suitable optics, only one of the MTF measuring devices is provided with a reference sign for the sake of clarity. The MTF measuring devices 20 are fastened at the holding device 8 in a fixably predetermined position. With each of the MTF measuring devices 20 a modulation transfer function (MTF) can be measured in the image field of the optical system 4 at a fixably predetermined angular position.

[0071] The holding device 8 is rigid, i.e. it has no movable parts. The MTF measuring devices 20 are located at fixed positions. However, they can for example be flexibly positioned within the scope of an initial adjustment of the device 2. For this purpose, the first holder has a long hole 22 along which the MTF measuring devices 20 can be displaced. The MTF measuring devices 20 are secured via knurled screws visible on the top side of the first holder 10. The long hole 22 preferably extends along a great circle of the first spherical shell surface along which the first holder 10 extends.

[0072] The device 2 is provided for receiving a plurality of MTF measuring devices 20. The plurality of MTF measuring devices 20 is divided into a first group of MTF measuring devices 20 and a second group of MTF measuring devices 20. The first group of MTF measuring devices 20 is fastened at the first holder 10. In the shown embodiment, the second group of MTF measuring devices 20 is fastened at the second holder 12.Figure 1 The first set of MTF measurement devices is shown in Fig. 1. A second set of MTF measurement devices 20 (not shown in Fig. 1) is fastened at the second holder 12. The same applies to the first set of MTF measurement devices 20 as described before. They are located at fixably predetermined positions. However, their positions can also be adjusted. For this purpose, the second holder 12 also has long holes 22, of which only one is provided with a reference sign for the sake of clarity. The long holes 22 of the second holder 12 preferably extend along the great circle of the second spherical surface along which the second holder 12 extends. The long holes 22 of the second holder 12 are preferably arranged in a circle. The same applies to the long holes 22 of the first holder 10. Figure 2 The MTF measurement devices 20 held by the first holder 10 shown in Fig. 1 are arranged in a circle. The same applies to the second set of MTF measurement devices 20 (not shown in Fig. 1) held by the second holder 12. The same applies to the first set of MTF measurement devices 20 as described before. They are located at fixably predetermined positions. However, their positions can also be adjusted. For this purpose, the second holder 12 also has long holes 22, of which only one is provided with a reference sign for the sake of clarity. The long holes 22 of the second holder 12 preferably extend along the great circle of the second spherical surface along which the second holder 12 extends. The long holes 22 of the second holder 12 are preferably arranged in a circle. The same applies to the long holes 22 of the first holder 10. Figure 1 The MTF measurement devices 20 held by the first holder 10 shown in Fig. 1 are arranged in a circle. The same applies to the second set of MTF measurement devices 20 (not shown in Fig. 1) held by the second holder 12. The same applies to the first set of MTF measurement devices 20 as described before. They are located at fixably predetermined positions. However, their positions can also be adjusted. For this purpose, the second holder 12 also has long holes 22, of which only one is provided with a reference sign for the sake of clarity. The long holes 22 of the second holder 12 preferably extend along the great circle of the second spherical surface along which the second holder 12 extends. The long holes 22 of the second holder 12 are preferably arranged in a circle. The same applies to the long holes 22 of the first holder 10. Figure 1 The MTF measurement devices 20 held by the first holder 10 shown in Fig. 1 are arranged in a circle. The same applies to the second set of MTF measurement devices 20 (not shown in Fig. 1) held by the second holder 12. The same applies to the first set of MTF measurement devices 20 as described before. They are located at fixably predetermined positions. However, their positions can also be adjusted. For this purpose, the second holder 12 also has long holes 22, of which only one is provided with a reference sign for the sake of clarity. The long holes 22 of the second holder 12 preferably extend along the great circle of the second spherical surface along which the second holder 12 extends. The long holes 22 of the second holder 12 are preferably arranged in a circle. The same applies to the long holes 22 of the first holder 10.

[0073] The MTF measurement devices 20 held by the first holder 10 shown in Fig. 1 are arranged in a circle. The same applies to the second set of MTF measurement devices 20 (not shown in Fig. 1) held by the second holder 12. The same applies to the first set of MTF measurement devices 20 as described before. They are located at fixably predetermined positions. However, their positions can also be adjusted. For this purpose, the second holder 12 also has long holes 22, of which only one is provided with a reference sign for the sake of clarity. The long holes 22 of the second holder 12 preferably extend along the great circle of the second spherical surface along which the second holder 12 extends. The long holes 22 of the second holder 12 are preferably arranged in a circle. The same applies to the long holes 22 of the first holder 10. Figure 1 The MTF measurement devices 20 held by the first holder 10 shown in Fig. 1 are arranged in a circle. The same applies to the second set of MTF measurement devices 20 (not shown in Fig. 1) held by the second holder 12. The same applies to the first set of MTF measurement devices 20 as described before. They are located at fixably predetermined positions. However, their positions can also be adjusted. For this purpose, the second holder 12 also has long holes 22, of which only one is provided with a reference sign for the sake of clarity. The long holes 22 of the second holder 12 preferably extend along the great circle of the second spherical surface along which the second holder 12 extends. The long holes 22 of the second holder 12 are preferably arranged in a circle. The same applies to the long holes 22 of the first holder 10.

[0074] The first group of MTF measuring devices 20 is arranged for performing MTF measurements in the central region of the image field of the optical system 4. Since these MTF measuring devices 20 are arranged at a larger distance from the optical system 4 to be tested, more MTF measuring devices 20 per field angle of the optical system 4 can be arranged than with the second group of MTF measuring devices. This means that four MTF measurement values can be detected in the central region of the image field of the optical system 4 with a higher density of measurement points. At the same time, with the device 2 it is possible to cover large field angles with the MTF measurements, it is possible to perform MTF measurements at large field angles with the second group of MTF measuring devices 20. This makes it possible to test optical systems 4 with large image angles or field angles, wherein the entire image field of the optical system 4 can be tested. At the same time, it is also possible to test optical systems 4 with small field angles, for example telephoto objectives, with the device 2. Advantageously, it is not necessary to retrofit the device 2, for example, between testing wide-angle objectives with large field angles and testing telephoto objectives with small field angles. It is also possible, for example, to use only the first group of MTF measuring devices 20 for testing telephoto objectives. For this purpose, the MTF measuring devices 20 are advantageously arranged such that their imaging regions do not overlap. The first group of MTF measuring devices 20 observes through the central opening 16 present in the second holder 12 during the measurement. At the same time, Figure 1 The second group of MTF measuring devices 20, not shown in

[0075] Figure 2 The device 2 known from Figure 1 is shown in another schematic and simplified perspective view. For the sake of clarity, the refractive optical system 4 to be measured and the specimen holder 6 are not shown in Figure 2 Figure 2 The device 2 is shown from the bottom side. It can be well seen how the MTF measuring devices 20 are received at the first holder 10 at the respective camera holder 24. The first group of MTF measuring devices 20 shown observes the optical system 4 to be tested through the opening 16 of the second holder 12. The optical axes of the MTF measuring devices 20 intersect in the ball center 18.

[0076] Figure 3 A view of the device 2 from its bottom side is shown. The first group of MTF measuring devices 20 observing the ball center 18 is visible. The central MTF measuring device 20 is used for performing on-axis measurements, the four MTF measuring devices 20 grouped around it perform off-axis MTF measurements. For the sake of clarity, the optical system 4 to be tested is still not shown.

[0077] Figure 4 ​Device 2 is shown schematically and in a simplified side view. For clarity, optical system 4 is also not shown in this figure. The optical axis of the central MTF measuring device 20 used for performing in-axis measurements is shown as a dashed line, just like the optical axis of the MTF measuring device 20 used for performing off-axis measurements. The optical axis of the in-axis MTF measuring device 20 coincides with the optical axis of the optical system 4 (not shown) under test.

[0078] As can be clearly seen in the side view, the first radius of the first spherical shell surface in which the first set of MTF measuring devices 20 are arranged is greater than that in which (… Figure 4 The second radius of the second set of MTF measuring devices 20 (not shown). This is directly derived from a comparison of the different radii of curvature of the first holder 10 and the second holder 12.

[0079] Figure 5 The device 2 is shown in a schematic simplified top view. The compact dimensions of the measuring device 2 in the lateral direction can be seen in the top view. The first retainer 10 and the second retainer 12 have only slightly different diameters (see also...). Figure 4 The maximum size is determined by holding device 8.

[0080] In addition Figure 5 As can be seen, the elongated holes 22 of the first retainer 10 and the second retainer 12, oriented along the main axis, are aligned with each other. These are Figure 5 A horizontally or vertically extending elongated aperture 22. To increase the density of measurement points, an additional MTF measuring device 20 can be used to occupy the unused elongated aperture 22 in the illustrated embodiment (which extends along a 45° scale between the horizontal and vertical lines). In this respect, the device 2 is flexible and adaptable to the desired measurement task.

[0081] Figure 6 A schematic and simplified perspective view of a device 2 for measuring the imaging characteristics of a refractive optical system 4, according to another embodiment, is shown. The optical system 4 is again shown highly schematically. It is arranged on a specimen holder 6, which positions the optical system 4 at a predetermined test position. Similarly, in... Figure 6 The image shows the center 18 of the sphere, which is preferably located in the plane of the aperture of the optical system 4 to be tested.

[0082] The device 2 shown in turn comprises a first holder 10 in the shape of a spherical cap or dome, which, together with a second holder 12 which is annular (but could in other cases also be designed in the shape of a spherical cap or dome) and a diagonal brace 14 connecting them, forms a holding device 8 for the MTF measuring devices 20 of the device 2. The second holder 12 in turn comprises a central opening 16 through which the first group of MTF measuring devices 20 looks. In the embodiment shown, a second group of MTF measuring devices 20 is also shown, which is received at the second holder 12.

[0083] Figure 7 The device 2 known from Figure 6 is shown in another perspective view, in this case more from its underside. The second group of MTF measuring devices 20 can be seen very well, the optical axes of which, like those of the first group of MTF measuring devices 20, intersect in the sphere centre 18. The second group of MTF measuring devices 20 enables MTF measurements at large field angles at the optical system 4 to be tested. The high density of measuring points provided by the large number of first group of MTF measuring devices 20 in the central imaging region of the optical system 4 can likewise be seen very well. In Figure 7 the device 2 known from can likewise be seen very well. The camera holder displaces the MTF measuring devices 20 radially inwards, so that the first group of MTF measuring devices 20 is arranged on a first spherical shell surface and the second group of MTF measuring devices 20 is arranged on a second spherical shell surface having a second radius. It can be seen that the first radius is greater than the second radius of the second spherical shell surface.

[0084] The MTF measuring devices 20 are mounted at fixedly predetermined positions at the holding device 8. However, for the purpose of adjustment, they can be displaced along the long holes 22. The radial spacing of the MTF measuring devices 20 along the camera holder 24 can likewise be changed in a similar manner. For this purpose, it likewise has long holes 22.

[0085] Figure 8 The device is shown in the manner of a view from the underside of the device 2 known from Figure 6 and Figure 7 For the sake of clarity, the optical system 4 to be tested is not shown again, only the sphere centre 18. The first group of MTF measuring devices 20 looks through the opening 16 of the second holder 12. Their visible more dense arrangement ensures a high density of measuring points in the central imaging region of the optical system 4 to be tested.

[0086] Figure 9A schematic simplified side view of the apparatus 2 according to the second embodiment is shown. It can be well seen that the first set of MTF measurement devices 20 is arranged on a first spherical shell surface having a larger radius than the second set of MTF measurement devices 20 (held by the second holder 12), the second set of MTF measurement devices 20 is arranged on a second spherical shell surface having a smaller radius. The optical axes 26 are exemplarily drawn for the first set of MTF measurement devices 20 in dotted lines. The optical axes 26 are likewise exemplarily shown in dotted lines for the second set of MTF measurement devices 20. The optical axes 26 of all MTF measurement devices converge in the sphere center 18, which is exemplarily located in the stop of the optical system 4 to be tested.

[0087] Figure 10 A schematic simplified side view of the apparatus 2 according to the second embodiment is shown, wherein only one of the on-axis MTF measurement device 203, one of the first set of MTF measurement devices 201 and one of the second set of MTF measurement devices 202 are shown. The respective optical axes 263, 261 and 262 converge in the sphere center 18. The optical axis 263 of the on-axis MTF measurement device 203 corresponds to the optical axis of the optical system 4 to be tested, which is not shown.

[0088] A first lateral angle a1 between the optical axis 263 of the optical system 4 to be tested and the optical axis 261 of the first set of MTF measurement devices 201 is smaller than a second lateral angle a2 measured between the optical axis 263 of the optical system 4 to be tested and the optical axis 262 of the second set of MTF measurement devices 202. This applies to all of the first set of MTF measurement devices 201, which enclose with the optical axis 263 of the optical system 4 to be tested a smaller lateral angle, respectively, than any of the second set of MTF measurement devices 202. In other words, this means that the first set of MTF measurement devices 201 is arranged for detecting measurement values in a central imaging region of the optical system 4 to be tested.

[0089] It further applies that a further lateral angle between two adjacently arranged MTF measurement devices 201 of the first set of MTF measurement devices 201 is always smaller than a lateral angle between two adjacently arranged MTF measurement devices 202 of the second set of MTF measurement devices 202. In other words, this means that the first set of MTF measurement devices is arranged more closely together than the second set of MTF measurement devices.

[0090] Figure 11The device 2 according to the second embodiment is shown schematically and in a simplified top view. Also in this figure, the higher density of the first group of MTF measuring devices 20 can be seen at the fastening elements (e.g., knurled screws) located on the back side of the first group of MTF measuring devices 20, which are respectively located on the top side of the first retainer 10 and the second retainer 12. The arrangement of the MTF measuring devices 20 is merely exemplary, and the density of the arrangement can be increased or decreased by adding and / or removing corresponding first or second group MTF measuring devices 20 at the first retainer 10 and / or the second retainer 12. The device 2 can be flexibly adapted according to the measurement task, wherein the MTF measuring devices 20 are retained in fixed, predetermined positions for the corresponding measurement task. For flexible assembly of the MTF measuring devices 20, elongated holes 22 are provided in the first retainer 10 and the second retainer 12. The elongated holes 22 of the first retainer 10 and the second retainer 12 can be aligned along... Figure 10 The horizontal and vertical extensions are again arranged in a way that aligns with each other.

[0091] Figure 12 A schematic and simplified perspective view shows a device 2 for measuring the imaging characteristics of a refractive optical system 4 according to a third embodiment. Device 2 includes a first holder 10, which is implemented as a dome-shaped dome. A single MTF measuring device 20 is directly fastened to the center of this dome-shaped first holder 10, and this single MTF measuring device performs on-axis measurements. Figure 12 At the center of the first retainer 10, a knurled threaded connector 28 is visible, which secures the MTF measuring device 20 to the dome-shaped first retainer 10. The remaining MTF measuring devices 20 are secured to a second retainer 12, which is implemented in the form of multiple bow-shaped members 30. These bow-shaped members 30 are secured to the dome-shaped first retainer 10 via columnar connectors 32.

[0092] The arcuate pieces 30, which construct the second holder 12, extend along the great circle of the second spherical surface in the direction from the first end 34 towards the free distal end 36. The arcuate pieces 30 are connected at their first end 34 via the connecting pieces 32 with the first holder 10, respectively. Due to the connection with the first holder 10, which can be changed along the long hole 22 located in the first holder 10 along the great circle, the second holder 12 constructed from the arcuate pieces 30 is flexible. For example, the arcuate piece 30a can be fastened in a manner closer to the centre of the first holder 10, the other arcuate piece 30b can be fastened more distally at the edge of the first holder 10. The MTF measuring devices 20 are likewise fastened in an adjustable manner at the arcuate pieces 30. For this purpose, the arcuate pieces 30 are also equipped with long holes 22, which extend in the longitudinal extension direction of the respective arcuate piece 30.

[0093] Figure 13 A device 2 according to a third embodiment is shown in another schematic and simplified perspective view, more from the bottom side. The MTF measuring devices 20 are all oriented such that their optical axes intersect in the sphere centre 18, which can in turn be located in the opening stop of the optical system 4 to be tested. For the sake of clarity, the optical system 4 is not shown. The shown embodiment is primarily suitable for testing optical systems 4 having a very large image angle. The MTF measurements can be recorded over a very large image angle range.

[0094] Figure 14 A top view is shown, looking down on the top side of the device 2. The compact dimensions of the device 2 can be seen. The second holder 12 constructed from the arcuate pieces 30 only slightly projects beyond the outer edge of the first holder 10, only the free ends 36 of the arcuate pieces 30 can be seen. The long holes 22 located in the first holder 10 can be well seen, which extend star-shaped from the middle of the holder 10 in the direction of its edge and along which the arcuate pieces 30 of the second holder 12 can be displaced.

[0095] Figure 15 The device 2 is shown from the bottom side. Three or two MTF measuring devices 20 are alternately mounted at the arcuate pieces 30 of the second holder 12, respectively. All MTF measuring devices 20 are directed towards the sphere centre 18. The MTF measuring devices 20 are located centrally to perform on-axis measurements.

[0096] Figure 16A device 2 according to a third embodiment is shown in a schematic and simplified perspective view, wherein only two arches 30 of the second holder 12 are shown. The first arch 30a, which is received at the opposite center of the first holder 10 via a connection 32, exemplarily receives two MTF measuring devices 20. The second arch 30b, which is mounted at the first holder 10 via its connections 32 at a relatively outer side, exemplarily receives three MTF measuring devices 20. As already described in the context of the other embodiments, the MTF measuring devices 20 are fastened at the second holder 12 formed by the arches 30 and the connections 32 with the respective camera holder 24.

[0097] Figure 17 A further device 2 for measuring imaging properties of a refractive optical system 4 according to a fourth embodiment is shown in a highly schematic and simplified sectional view. The device 2 comprises a first holder 10, which is also embodied as a spherical cap. It is provided for fastening a first group of MTF measuring devices 20 on a spherical shell surface having 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 surface. The device 2 further comprises a second holder 12, which is designed as a ring and has an opening 16 in the center. It is provided for holding a second group of MTF measuring devices 20 on a spherical shell surface having a second radius R2. The image sensors 38 of these MTF measuring devices 20 are also arranged on this second spherical shell surface. The device 2 further comprises a third holder 40, which holds a third group of MTF measuring devices 20 arranged such that their image sensors 38 are located on a third spherical shell surface having a third radius R3. It applies there that R3≤ R2≤ R1.

[0098] All features mentioned, including the features known from the drawings and the individual features disclosed in combination with other features, are considered important to the invention, both individually and in combination. Embodiments according to the invention can be realized by individual features or combinations of features.

[0099] List of reference signs

[0100] 2 device

[0101] 4 optical system

[0102] 6 test specimen holder

[0103] 8 holding device

[0104] 10 first holder

[0105] 12 second holder

[0106] 14 diagonal brace

[0107] 16 opening

[0108] 18 ball center

[0109] 20 MTF measuring device

[0110] 201 first group MTF measuring device

[0111] 202 second group MTF measuring device

[0112] 203 on-axis MTF measuring device

[0113] 22 long hole

[0114] 24 camera holder

[0115] 26 optical axis

[0116] 261 first optical axis

[0117] 262 second optical axis

[0118] 263 optical axis of the optical system

[0119] 28 knurled screw

[0120] 30 bow

[0121] 30a, 30b bow

[0122] 32 connecting piece

[0123] 34 first end

[0124] 36 free end

[0125] 38 image sensor

[0126] 40 third holder

[0127] α1 first angle

[0128] α2 second angle

[0129] R1 first radius

[0130] R2 second radius

[0131] R3 third radius

Claims

1. An apparatus (2) for measuring imaging properties of an optical system (4), wherein the apparatus (2) comprises: a test specimen holder (6) arranged for positioning the optical system (4) to be tested at a predetermined test position, a rigid holding device (8) and a plurality of MTF measuring devices (20) arranged at fixedly predetermined positions of the holding device (8) such that a modulation transfer function can be measured with each of the MTF measuring devices (20) at a likewise fixedly predetermined angular position in the image field of the optical system (4) which is different from each other, characterized in that the holding device (8) comprises at least one first holder (10) and at least one second holder (12) and the plurality of MTF measuring devices (20) comprises a first group of MTF measuring devices (20) and a second group of MTF measuring devices (20), wherein the first holder (10) is arranged for holding the first group of MTF measuring devices (20) at a first position such that the first group of MTF measuring devices (20) is arranged on a first spherical shell surface, the second holder (12) is arranged for holding the second group of MTF measuring devices (20) at a second position such that the second group of MTF measuring devices (20) is arranged on a second spherical shell surface, wherein the first spherical shell surface and the second spherical shell surface have different radii and are arranged concentrically with respect to each other.

2. The device (2) according to claim 1, characterized in that the MTF measuring devices (20) are arranged at the holding device (8) such that the optical axes of the MTF measuring devices (20) intersect in the plane of the stop of the optical system (4) to be tested.

3. The device (2) according to claim 1, characterized in that the holding device (8) comprises a third holder (40) and the plurality of MTF measuring devices comprises the first group of MTF measuring devices and the second group of MTF measuring devices and an additional third group of MTF measuring devices, wherein the third holder (40) is arranged for holding the third group of MTF measuring devices at a third position such that the third group of MTF measuring devices is arranged on a third spherical shell surface, wherein the third spherical shell surface has a third radius which is different from the first radius and the second radius and is arranged concentrically with the first spherical shell surface and the second spherical shell surface.

4. The device (2) according to claim 1, characterized in that the first radius of the first spherical shell surface is greater than the second radius of the second spherical shell surface, whereby the first group of MTF measuring devices (20) is respectively farther away from the optical system (4) to be tested than the second group of MTF measuring devices (20).

5. The device (2) according to claim 3, characterized in that the second radius of the second spherical shell surface is greater than the third radius of the third spherical shell surface, whereby the second group of MTF measuring devices (20) is respectively farther away from the optical system (4) to be tested than the third group of MTF measuring devices (20).

6. The device (2) according to claim 1, characterized in that The first lateral angle a1 between the optical axis (263) of the optical system (4) to be tested and the optical axis (261) of the MTF measurement device (201) is smaller than the second lateral angle a2 between the optical axis (263) of the optical system (4) to be tested and the optical axis (262) of any of the second group of MTF measurement devices (202) for all of the first group of MTF measurement devices (201).

7. The device (2) according to claim 3, characterized in that The second lateral angle between the optical axis (262) of the optical system (4) to be tested and the optical axis of the MTF measurement device is smaller than the lateral angle between the optical axis (263) of the optical system (4) to be tested and the optical axis of any of the third group of MTF measurement devices for all of the second group of MTF measurement devices (202).

8. The device (2) according to claim 1, characterized in that The lateral angle between two adjacently arranged MTF measurement devices (20) of the first group of MTF measurement devices (20) is smaller than the lateral angle between two adjacently arranged MTF measurement devices (20) of the second group of MTF measurement devices (20).

9. The device (2) according to claim 3, characterized in that The second lateral angle is smaller than a third lateral angle between two adjacently arranged MTF measurement devices of the third group of MTF measurement devices.

10. The device (2) according to claim 1, characterized in that The first holder (10) and the second holder (12) of the holding device (8) extend at least partially along the respective spherical shell surface.

11. The device (2) according to claim 1, characterized in that The first holder (10) is embodied as a spherical crown top and the second holder (12) is embodied as a spherical crown top with a central opening (16).

12. The device (2) according to claim 3, characterized in that The first holder (10) is embodied as a spherical crown top and the second holder (12) and / or the third holder (40) is / are embodied as a spherical crown top with a central opening (16).

13. The device (2) according to claim 12, characterized in that The second holder (12) and / or the third holder (40) is / are ring-shaped.

14. The device (2) according to claim 12, characterized in that The second holder (12) and / or the third holder (40) is / are further embodied in the form of a spherical table.

15. The apparatus (2) according to claim 1, characterized in that The first holder (10) is embodied as a spherical crown top and the second holder (12) is embodied as at least one arch (30), wherein the arch (30) is respectively fastened at the first holder (10) at a first end (34) close to the first holder (10) and extends in the direction of a distally free end (36) of a great circle of the first spherical shell surface or of the second spherical shell surface, wherein the great circle runs within a plane that intersects along an optical axis of the optical system (4) to be tested.

16. The apparatus (2) according to claim 3, characterized in that The first holder (10) is embodied as a spherical crown top and the second holder (12) and / or the third holder (40) is / are respectively embodied as at least one arch (30), wherein the arch (30) is respectively fastened at the first holder (10) at a first end (34) close to the first holder (10) and extends in the direction of a distally free end (36) of a great circle of the first spherical shell surface or of the second spherical shell surface, wherein the great circle runs within a plane that intersects along an optical axis of the optical system (4) to be tested.

17. The apparatus (2) according to claim 1, characterized in that The first holder (10) of the holding device (8) is provided for effecting a displacement of the MTF measuring device (20) on the assigned spherical surface.

18. A method for measuring imaging properties of an optical system (4) using a device (2) according to any one of claims 1 to 17, comprising the following steps: arranging the optical system (4) to be tested in the test specimen holder (6), performing MTF measurements synchronously with all MTF measuring devices (20).

Images