Method and control device for adjusting and / or calibrating and / or monitoring the focus value of an optical instrument with zoom function

Abstract

The present invention relates to a method for adjusting and / or calibrating and / or monitoring the focus value of a surgical microscope (1, 40) comprising at least one objective lens (2, 3), an image capture device (5) and a zoom system (8), the surgical microscope (1, 40) being designed to be operated in at least two different zoom positions. The method comprises the steps of: capturing (21) at least one respective image of a fixed object (41) by means of the image capture device (5) at at least two different zoom settings; determining (22) a plurality of contrast values ​​based on the focus value using the at least one detected image; and determining (23) at least one target value of at least one parameter for adjusting and / or calibrating the focus value of the surgical microscope (1, 40) using the determined contrast values ​​for the at least two zoom settings.

Description

[Technical Field]

[0001] The present invention relates to a method for adjusting and / or calibrating the focus value of a surgical microscope, a control device for adjusting and / or calibrating the focus value of a surgical microscope, a surgical microscope, a computer-implemented method, a computer program product, a computer-readable data carrier and a data carrier signal. [Background technology]

[0002] For optical instruments, the adjustment and calibration of the focus usually play an important role. Adjustment is understood to mean the one-time setting of the instrument, for example during servicing or assembly, and calibration is understood to mean the adaptation of one or more parameters during servicing or assembly or operation of the instrument. For calibration, a control curve can for example be stored and applied later.

[0003] To adjust and calibrate the video module, so-called optical reference instruments are usually used, which can be in analog or digital form. These optical reference instruments aim to represent both the optical center of the main observation area and the focal position of the main observation area by means of a strict mechanical tolerance chain, for example a specified positioning of the optical unit relative to the dovetail interface to which the optical reference instrument is attached. The main observation area is already pre-adjusted. The main observation area is therefore used together with the optical reference instrument as a reference, in particular with regard to its position in the image plane (xy plane), the focal position, and rotation. When adjusting the focus, it is intended that the focus value at which the contrast value is greatest differs only slightly or not at all at different zoom positions. Summary of the Invention [Problem to be solved by the invention]

[0004] In view of this background, it is an object of the present invention to provide an advantageous method for adjusting and / or calibrating the focus value of a surgical microscope, an advantageous control device for calibrating the focus value of a surgical microscope, an advantageous surgical microscope, a computer-implemented method, a computer program product, a computer-readable data carrier, and a data carrier signal. [Means for solving the problem]

[0005] The above-mentioned object is characterized by a method for adjusting and / or calibrating the focus value of a surgical microscope according to patent claim 1, a control device for adjusting and / or calibrating the focus value of a surgical microscope according to claim 15, a surgical microscope according to claim 16, a computer-implemented method according to claim 18, a computer program product according to the invention, a computer-readable data carrier according to the invention and a data carrier signal according to the invention. Further advantageous configurations of the invention are contained in the dependent claims.

[0006] A method according to the invention for adjusting and / or calibrating and / or monitoring the focus value of a surgical microscope comprising at least one objective lens, an image capture device, for example in the form of a camera chip, and a zoom system, the optical device being designed to be operated in at least two different zoom positions, i.e., zoom positions offset from one another, comprises the following steps: at least one image, i.e., one image representation, of a specified object is captured by the image capture device in at least two different zoom positions. Then, in the at least one captured image, multiple contrast values ​​are determined as a function of the focus value. At least one respective contrast value can be determined in multiple images captured with respectively different focus values. However, multiple contrast values ​​can also be determined in one captured image. This is possible for images of oblique objects.

[0007] The focus value can be a relative focus value or a focus value difference. Typically, a surgical microscope outputs a focus value that depends only on the position of the optical element of the main objective. In this case, a flat or planar calibration object positioned perpendicular to the optical axis can be used. For surgical microscopes with a constant focal length, it is advantageous to use a flat calibration object tilted relative to the optical axis. For example, a relative focus value in the form of a change in focus or a shift in focus depending on the zoom setting can be determined, e.g., calculated. The terms zoom position and zoom setting are used interchangeably in this specification.

[0008] The contrast value can preferably be determined by image evaluation. Image evaluation can be performed digitally and / or automatically and / or visually. Here, specified image points or image segments or image sections can be evaluated. In a further step, at least one desired value for at least one parameter for adjusting and / or calibrating the focus value of the surgical microscope is determined by predetermined contrast values ​​for at least two zoom positions. For this purpose, a focus value at which the contrast value is maximum for each zoom position can be determined. A parameter for adjusting and / or calibrating the focus value of the surgical microscope is understood to mean a variable that can be changed in the adjustment and / or calibration of the focus value, such as the distance between at least one objective lens and the image acquisition device or the distance between individual lenses or lens groups of the objective lens.

[0009] Depending on the requirements to be met, the method can be performed for all zoom positions or only for a number of selected zoom positions.

[0010] The determination of the desired value can include determining a change value of the focus position of the surgical microscope, in particular a change value that is independent of the zoom. The determination of the desired value, in particular the change value, can be based on evaluation of the slope of at least one curve, for example a line, which maps the dependence of the detected focus change on the focus value or reference variable on the zoom position. The focus change can be specified, for example, with respect to the position of the zoom center or another specified object-side reference point, for example an object mark on the object (calibration object). The focus change can be specified in any unit, which can be defined, for example, by an element imaged on the object.

[0011] A functional relationship, e.g., a linear dependency, between the gradient and the focal position or focus setting of the surgical microscope can be inferred or determined by appropriate measurements. From this functional relationship, e.g., the gradient of the corresponding line, the desired value and / or change value can be calculated directly from the identified contrast values ​​for the identified contrast values ​​for at least two different zoom positions or the resulting absolute or relative focus value at which the contrast is maximized. The desired value can be calculated and / or provided and / or displayed and / or monitored, e.g., in the form of a target focus line or target focus area in the captured image of a specified object for a particular zoom setting, allowing the technician to adjust and / or calibrate accordingly. The adjustment and / or calibration can be performed at a preset zoom setting or at any zoom setting.

[0012] The image capture device may be a camera, such as a video camera, which may include a camera chip. The surgical microscope may have a stereoscopic optical system.

[0013] The present invention has the advantage that a surgical microscope with a mechanical zoom system can be focused independently of a main viewing area and an optical reference device. Therefore, no optical reference device is required for focus adjustment and / or calibration. Deviations from an ideal device adjusted to infinity, i.e., pre-adjusted so that the light beams in the magnification system are parallel when the object is in focus, can be quantified, for example, by the deviation of the focus value at which the contrast value is maximized. Focus setting is also independent of a main viewing area and, therefore, does not rely on the absence of an observer or subjective evaluation. Another advantage is that the use of a measured calibration object can be eliminated, since only relative focus values ​​are required for adjustment and / or calibration.

[0014] In a preferred variant, the surgical microscope comprises at least one first objective, for example in the form of a main objective, and a second objective, for example in the form of a video objective, which is arranged in the beam path between the first objective and the image acquisition device.

[0015] In an advantageous variant, at least one correction value for the relative position of at least one objective, e.g., the second objective and / or the first objective, and / or the image capturing device, with respect to the beam path within the surgical microscope can be determined based on at least one desired value.

[0016] The at least one desired value can be specified and / or specified separately for each of the at least two zoom positions. The at least one desired value can be specified and / or specified such that, for the at least two beam positions, the difference between the focus values ​​at which the contrast value is greatest is less than a specified threshold value for the at least two zoom positions. This has the advantage that, if the difference is zero, there is little or no change in the focus value when the zoom position is changed.

[0017] For example, based on the determined focus value at which the contrast value is greatest for each zoom setting, at least one desired value for at least one parameter for adjusting and / or calibrating the focus value of the surgical microscope can be determined and / or specified. As part of the adjustment, the second objective, i.e., for example, a video objective, is preferably displaced so that a corresponding desired value for positioning and / or displacement can be determined and / or specified. The at least one desired value for each of the at least two zoom positions can be determined and / or specified at one of the two zoom positions or at another zoom position. If the check shows that the surgical microscope is correctly adjusted, the desired value is equal to the actual value or is within a tolerance. This also makes it possible to monitor or remotely monitor the surgical microscope.

[0018] In an advantageous variant, at least one image of a planar surface of a designated object can be captured, the surface normal of which forms an angle of 0 to 90 degrees, in particular 85 to 5 degrees, for example 20 degrees, with the optical axis of the objective. In other words, in the above example, the planar surface forms an angle of 90 to 0 degrees, in particular 85 to 5 degrees, for example 70 degrees, with the optical axis of the objective. The use of a planar surface has the advantage that the distance of the object point from the objective is easily determined, thus simplifying image evaluation.

[0019] Preferably, the object used is a known calibration object, which may have a specified pattern, for example, a chessboard pattern. Advantageously, at least one image of a specified calibration object is taken at each of at least two different zoom positions, which has known characteristics, allowing high-contrast regions to be recognized in the image representation. Knowing the geometry of the calibration object allows prediction of high-contrast regions in the image. These can be identified and evaluated in terms of contrast, thereby reducing computation time. For example, the calibration object may be a ChArUco board. The above-described variants facilitate the identification of contrast values ​​and provide a robust solution to possible noise-induced errors. For example, contrast values ​​may be identified and / or evaluated only within a central, specified region of the image, thereby facilitating and speeding up adjustment and / or calibration.

[0020] Advantageously, the dimensions of the pattern, in particular the dimensions of the pattern elements, are known or predetermined, or these dimensions are measured. The dimensions can be known or predetermined or measurable in length units, e.g., millimeters. Preferably, an imaging scale, e.g., in the form of a relationship between the respective dimensions of at least one element of the calibration object, e.g., in millimeters, and the length units of the camera chip, e.g., pixels, is known or predetermined or measured. If the tilt of the calibration object is known or predetermined or set or determined in a defined manner, the focus value can be determined, in particular calculated, using the dimensions and / or the imaging scale relative to a point in the image representation, e.g., relative to the zoom center where the contrast value is maximum. For example, the tilt of the calibration object can be determined using pose estimation. Additionally, the tilt can be determined by evaluating the geometric deformation, e.g., the resulting trapezoid, that occurs in the presence of tilt in the captured image representation of the calibration object. This arrangement has the advantage that the focus value where the contrast value is maximum and the dependency between the contrast value and the focus value can be easily, quickly, and reliably determined.

[0021] At each of the at least two zoom positions, images of a specified object can be captured at multiple focus values. The focus values ​​can be adjusted by a configurable focus system. Unlike the aforementioned variant, in which different focus values ​​are obtained by tilting the calibration object in the image representation, the normal to the planar surface of the calibration object can form an angle of 0 degrees with the optical axis. For this, the surgical microscope must be equipped with an objective lens with a variable focal length. With corresponding automatable focusing, a numerical table and / or curve can be specified for each of the at least two zoom positions that maps contrast values ​​to focus values. The focus values ​​of the surgical microscope can be adapted using the contrast value curves. Alternatively, the calibration object can be moved along the optical axis.

[0022] In an advantageous variant, the focus values ​​of the surgical microscope for each of the at least two zoom positions are adjusted and / or calibrated separately, i.e., individually for each zoom position, so that the contrast value for each of the at least two zoom positions is maximized. In other words, therefore, when the zoom position is changed, the focus values ​​are readjusted or reset, for example by means of stored data, which are then permanently used to set or correct the focus values ​​accordingly during operation. Additionally or alternatively, in another advantageous variant, the focus values ​​of the surgical microscope in the at least two beam positions can be adjusted and / or calibrated so that the difference between the focus values ​​at which the contrast values ​​for the at least two zoom positions are maximized is less than a specified threshold value.

[0023] The focus value of a surgical microscope can be adjusted and / or calibrated in several ways. For example, the focus value of a surgical microscope can be adjusted and / or calibrated by adapting the distance between an object plane, for example a designated object, and at least one objective, for example a first objective, for example a main objective, and / or a second objective, for example a video objective. Thus, in this variant, the focal length is adapted by displacing at least one objective and / or the object relative to one another along the optical axis of this at least one objective.

[0024] In addition to or as an alternative to the first variant described above, the focus value of the surgical microscope can be adjusted and / or calibrated by adapting the distance between the objectives, e.g. the first and / or second objectives, and the image plane of the image-capturing device. Thus, in this variant, at least one objective and the image-capturing device are moved relative to each other in the direction of or along the optical axis of this objective, whereby the objective and / or the image-capturing device can be moved.

[0025] At least one objective, for example the first and / or second objective, may include a first optical element and a second optical element. In addition to or as an alternative to the two aforementioned variants, the focus value of the surgical microscope can be adjusted and / or calibrated by displacing the first optical element of the objective relative to the second optical element of the objective. Optical element is understood to mean multiple optical components that are fixedly positioned relative to each other. For example, the optical element may include only one lens or multiple lenses. Thus, in this variant, inner focusing is performed in each objective, for example, in the main objective or the video objective. In particular, the optical instrument may include a first objective, for example, the main objective, and a second objective, for example, a video objective, where the first objective is arranged in the beam path between the object plane and the second objective. For example, the focus value of a surgical microscope can be adjusted and / or calibrated by displacing a first optical element of a first objective lens relative to a second optical element of the first objective lens and / or by displacing a first optical element of a second objective lens relative to a second optical element of the second objective lens.

[0026] Advantageously, the zoom position and / or focus value are set automatically, which makes adjustment and / or calibration easier and reduces the time required for adjustment and / or calibration.

[0027] The surgical microscope may include a stereoscopic optical system, which has or defines a first optical path and at least one other optical path. At least one desired value and / or calibration data for the first optical path can be determined and transmitted to at least one other optical path. An optical path is understood to mean the path of light from the object through the optical system to the image plane. The above-mentioned variant has the advantage that only one of the optical paths needs to be adjusted and / or calibrated, and the results of this process are immediately available for at least one other optical path, without the latter having to be adjusted and / or calibrated separately. This reduces the time required to adjust and / or calibrate the stereoscopic optical system.

[0028] A control device according to the invention for adjusting and / or calibrating and / or monitoring the focus value of a surgical microscope comprising at least one objective, an image acquisition device and a zoom system, the surgical microscope being designed to be operated in at least two different zoom positions, is designed to carry out the aforementioned method according to the invention and has the features and advantages already mentioned.

[0029] The surgical microscope according to the invention comprises at least one objective lens, an image acquisition device, for example a camera, in particular a video camera, and a zoom system. The surgical microscope is designed to be operated in at least two different zoom positions. The surgical microscope is also designed to carry out the method according to the invention already described above. The surgical microscope may also comprise the control device according to the invention described above. The surgical microscope according to the invention has the features and advantages already described. It preferably has a stereoscopic optical system.

[0030] A computer-implemented method according to the invention comprises instructions that, when executed by a computer, cause the computer to carry out the method according to the invention as described above. A computer program product according to the invention comprises instructions that, when executed by a computer, cause the computer to carry out the method according to the invention as described above. A computer program product according to the invention is stored on a computer-readable data carrier according to the invention. A data carrier signal according to the invention carries the computer program product according to the invention. The computer-implemented method according to the invention, the computer program product according to the invention, the computer-readable data carrier according to the invention and the data carrier signal according to the invention have the features and advantages described above.

[0031] The present invention will be described below on the basis of exemplary embodiments with reference to the accompanying drawings. The present invention will be more particularly illustrated and explained in detail by preferred exemplary embodiments, nevertheless the present invention is not limited to the disclosed examples, and those skilled in the art can devise other variants therefrom without departing from the scope of protection of the present invention.

[0032] The drawings are not necessarily accurate in all details and may be presented to scale for clarity, and may be enlarged or reduced in size for clarity. As such, it should be understood that the functional details disclosed herein are not limiting, but are merely exemplary to provide guidance to those skilled in the art to use the present invention in various ways.

[0033] As used herein, the term "and / or," when used in the context of a list of two or more elements, means that any listed element can be used alone, or any combination of two or more of the listed elements can be used. For example, if a structure is described as including components A, B, and / or C, the structure can include A alone, B alone, C alone, a combination of A and B, A and C, B and C, or a combination of A, B, and C. [Brief explanation of the drawings]

[0034] [Figure 1] 1 shows a schematic representation of the beam path through a surgical microscope for two beam positions. [Figure 2] 1 illustrates a method according to the present invention in the form of a flow chart. [Figure 3] 3 shows a schematic representation of contrast value curves as a function of focus value for two zoom positions; [Figure 4] 3 shows a schematic representation of contrast value curves as a function of focus value for four zoom positions; [Figure 5] 1 shows a schematic representation of a surgical microscope and a calibration object to be calibrated; [Figure 6] 1 shows schematically two images of a calibration object taken at different zoom positions. [Figure 7] 1 shows a schematic diagram of the variation of focus values ​​as a function of zoom position for three different adjustment or calibration states; [Figure 8] 1 shows a schematic representation of the contrast line (actual focus line) and the desired focus line in a captured image of a calibration object. [Figure 9] 1 shows diagrammatically a first variant of a surgical microscope according to the invention with a control device according to the invention; [Figure 10] 2 shows diagrammatically a second variant of a surgical microscope according to the invention with a control device according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0035] The background of the present invention will be explained in more detail below with reference to Figure 1. Figure 1 shows a schematic diagram of a beam path 10 in a surgical microscope at two zoom positions. At the top of Figure 1, a first zoom position with a low zoom value is set, and at the bottom of Figure 1, a second zoom position with a high zoom value is set. Therefore, the zoom value of the beam path shown at the top is smaller than the zoom value of the beam path shown at the bottom.

[0036] The surgical microscope 1 includes a first objective 3 in the form of a main objective and a second objective 2 in the form of a video objective, each of which includes at least one lens or lens group. The second objective 2 is arranged in the beam path between the first objective 3 and an image capture device 5. A beam path 10 is shown upstream of the surgical microscope 1 on the left side of FIG. 1 and downstream of the surgical microscope 1 on the right side. Therefore, the beam direction in FIG. 1 runs from left to right. Starting from the object plane 4, an object point is imaged in the image plane of the image capture device 5, for example, onto a camera chip. In the illustrated example, a first beam 11 and a second beam 12 each image an object point onto the camera chip 5. The beams 11 and 12 first pass through the first objective 3. The beam paths downstream of the first objective 3 and upstream of the second objective 2 are afocal. The regions from which the afocal radiation beams originate are each designated by the reference numeral 6. Therefore, in region 6 there are parallel beam paths.

[0037] When adjusting and / or calibrating the surgical microscope 1, at least one lens, a lens group of the video objective 2, or the camera chip 5 is moved along the optical axis 7, i.e., horizontally in Fig. 1. When the video objective 2 is correctly focused as shown in Fig. 1, the beams forming the axial beam, i.e., in this case the second beam 12, each converge to a point on the camera chip 5, which is therefore neither in front of nor behind the camera chip 5, regardless of the zoom position.

[0038] An example of a method according to the invention for adjusting and / or calibrating the focus value of a surgical microscope is explained in more detail below with the aid of Figures 2 to 6. The surgical microscope comprises at least one objective, for example a first objective 3 in the form of a main objective, a second objective 2 in the form of a video objective, an image acquisition device 5, and a zoom system, and is designed to be operated in at least two different zoom positions. The video objective 2 is arranged in the beam path 10 between the main objective 3 and the image acquisition device 5.

[0039] FIG. 2 illustrates a schematic diagram of a method according to the present invention in the form of a flowchart. In a first step 21, at least one image or image representation of a specified object, preferably a known calibration object, is captured by the image capture device 5, each at at least two different zoom positions. In a second step 22, one or more contrast values ​​are determined from the at least one captured image as a function of the focus value. This is preferably performed by suitable image evaluation software, which is configured, for example, to quantify the black-white transition of the image in terms of contrast. In a third step 23, at least one desired value and, optionally, a correction value for at least one parameter for adjusting and / or calibrating the focus value of the surgical microscope are determined from the determined contrast values ​​for at least two zoom positions. In this regard, the focus value at which the contrast value for each zoom position is maximized can be determined. An example of the implementation of step 23 is described in more detail below with the aid of FIGS. 6-8.

[0040] The determined focus values ​​at which the contrast values ​​for the respective zoom positions are maximum can be used in optional step 24 to adjust and / or calibrate the surgical microscope, for example by adjusting and / or calibrating the surgical microscope in such a way that the focus position, in particular the focus position of the video objective 2, is adapted so that the maxima of the contrast curves, i.e. at least two maxima of the contrast curves, occur at the same focus value or with a focus difference smaller than a specified threshold. As soon as the desired focus difference is reached, the surgical microscope, in particular the video objective, is adjusted and / or calibrated correctly in focus. When the focus difference is zero, the surgical microscope, in particular the objective, is adjusted to infinity.

[0041] Alternatively, or in addition, in step 24, the determined focus values ​​that maximize the contrast value for each zoom position can be stored for controlling the surgical microscope and used when using individual zoom positions to adjust and / or calibrate the focus value. For example, after installing and adjusting the surgical microscope, contrast value curves for various zoom positions can be recorded and stored in the device. Therefore, if the zoom setting is changed, new operating values ​​for the focus system can be determined and set from the stored curves. This ensures that sharp images are obtained. Therefore, only coarse adjustments need to be made, or in some cases, no adjustments may be necessary. This digital calibration can be performed by displacing the main objective, the video objective, or the camera chip. Therefore, the magnification system does not need to be perfectly aligned to infinity. However, other image errors may occur and can be corrected digitally.

[0042] FIG. 3 schematically illustrates contrast value curves as a function of focus value for two zoom positions. FIG. 4 schematically illustrates contrast value curves as a function of focus value for four zoom positions. On the x-axis, focus values ​​f are plotted in millimeters, and on the y-axis, contrast values ​​normalized to 1 are plotted. In FIG. 3, contrast value curve 31 is identified at a zoom position with a zoom value of 1.0 and has a maximum value at a focus value of 211.6 mm. Contrast value curve 32 is identified at a zoom position with a zoom value of 2.4 and has a maximum value at a focus value of 211.4 mm. The focus values ​​of maximum contrast are relatively close to each other here, thereby making it possible to omit further adjustments and / or calibrations, if appropriate. In FIG. 4, contrast value curve 33 at a zoom position with a zoom value of 1.0, contrast value curve 34 at a zoom position with a zoom value of 1.5, contrast value curve 35 at a zoom position with a zoom value of 2.0, and contrast value curve 36 at a zoom position with a zoom value of 2.4 are identified. Here, the focus values ​​of maximum contrast are relatively far apart, so that adjustment and / or calibration of the surgical microscope can be performed using the contrast value curve.

[0043] There are various options for performing step 22, i.e., for determining a number of contrast values ​​as a function of the focus value by the captured images. If the surgical microscope has a focus system, i.e., if the focus value can be set automatically, the curves shown in Figures 3 and 4 can be obtained automatically. Thus, focusing can be performed automatically, and images of the calibration object can be taken for each individual focus value and evaluated in terms of contrast. If an automatic zoom system is also available, the individual zoom settings can also be set automatically.

[0044] If the focus value cannot be set automatically, the difference in focus obtained from the two zoom positions using an obliquely positioned target as the object can be read visually or, preferably, determined by the image evaluation already mentioned above. The difference in focus value results in the required setting of the focus position of the optical instrument, in particular of the video objective. This variant is explained below with reference to Figures 5 and 6.

[0045] 5 shows diagrammatically a surgical microscope 40 to be adjusted and / or calibrated and a calibration object 41. The calibration object 41 is or can be firmly connected to the surgical microscope 40.

[0046] A calibration object 41, preferably having a planar surface 42 with a known pattern, preferably a ChArUco pattern, is positioned at an angle to the optical axis 7. In this case, a surface normal 43 of the surface 42 of the calibration object 41 may form an angle of 5 to 85 degrees, e.g., 20 degrees, with the optical axis 7. This corresponds to an angle 45 between 85 to 5 degrees, e.g., 70 degrees, between the surface 42 and the optical axis 7. For a tilted calibration object 41, contrast values ​​can be calculated for multiple focus values ​​within an image.

[0047] Advantageously, the dimensions of the pattern, in particular the dimensions of the pattern elements, are known or predetermined, or these dimensions are measured. The dimensions can be known or predetermined or measurable, for example in length units of millimeters. Preferably, the imaging scale, e.g., in the form of a relationship between the respective dimensions of at least one element of the pattern in pixels and length units, is known or predetermined or measured. If the tilt of the calibration object 41 is known or predetermined, or is set or determined in a defined manner, for example, by pose estimation, the focus value at which the contrast value is greatest can be determined, in particular calculated, using the dimensions and / or the imaging scale. This configuration has the advantage that the focus value at which the contrast value is greatest and the dependency between the contrast value and the focus value can be easily, quickly, and reliably determined.

[0048] The variant using a tilted calibration object 41 also offers the advantage that optical systems with a fixed focal length, in particular surgical microscopes, can also be adjusted and / or calibrated. For this purpose, contrast value curves for at least two zoom positions are first determined, after which a desired focus position for at least one zoom position can be calculated and / or provided and / or displayed, whereby a technician can adjust and / or calibrate the optical system using the displayed desired focus position (see, for example, FIG. 8 below).

[0049] FIG. 6 schematically shows two images 18 of a calibration object 41 taken at different zoom positions. The zoom center is preferably located at the image center. If the zoom center is not located at the image center, it is useful to place the coordinate origin of the object-side coordinate system used at the object point at the zoom center (projection of the zoom center onto the object). In particular, the zoom center is a point in the captured image representation that does not move between different magnification levels. The zoom center can be seen, in particular, as the optical center of the observer's beam path. Camera systems are typically designed and / or adjusted so that the object point imaged at the center of the camera chip does not move in the image representation during zooming. In this case, the optical axis defined by the zoom system intersects with the center of the camera chip. The calibration object 41 is tilted so that the focus values ​​in FIG. 6 change from left to right. The image shown on the left was taken at a first zoom position, and the image shown on the right was taken at a second zoom position. The line of highest contrast in the images, i.e., the vertical line, is designated by reference numeral 46. The contrast line 46 in the second zoom position, i.e., the depiction shown on the right side of FIG. 6 , appears in the image further to the right of the calibration object 41 relative to the object mark 17 on the calibration object 41 than the contrast line 46 in the first zoom position, shown on the left side of the figure. In other words, the contrast line 46 is approximately three squares to the left of the chessboard pattern (white or black squares) of the object mark 17 in the depiction shown on the left side of FIG. 6 , and approximately two squares to the left of the chessboard pattern of the object mark 17 in the depiction shown on the right side of FIG. 6 . Therefore, the contrast line 46 shifts relative to the calibration object 41 or the object mark 17. This means that the focal plane moves, or in other words, translates, along the optical axis 7 when switching between the two zoom positions. If the contrast line 46 were always located at the same position on the object, the difference in focus value would be zero. The object mark 17 could be placed anywhere on the object; the relative change or movement of the contrast line 46 would remain the same. However, it is preferable to choose an object point that coincides with the zoom center and therefore with the optical axis of the zoom system.

[0050] The horizontal displacement of the contrast line 46 of the calibration object 41 from the first zoom position (see the left-hand depiction in FIG. 6 ) to the second zoom position (see the right-hand depiction in the figure) converted into a vertical difference, i.e., a difference in the direction of the optical axis 7, corresponds to a difference in focus value. This difference in focus value can be calculated from the displacement of the contrast line 46 and the geometry and scale of the experimental arrangement, e.g., the size of the ChArUco marks of the pattern on the planar surface 42 of the calibration object 41. Typically, the focal plane is spherical, so the contrast line 46 in the figure represents an approximation of the contrast curve. If the curvature of the contrast curve, i.e., the deviation of the contrast line 46 (straight line) in the figure from the actual contrast curve, is small, then the linear approximation is justified. Otherwise, the actual contrast curve must be taken into account.

[0051] In all variants, it is advantageous to use a known calibration object, for example a chessboard or a ChArUco board, which facilitates the detection and evaluation of contrast.

[0052] The change in the contrast line shown in FIG. 6 indicates the shift or change in focus value depending on the zoom position. This is shown diagrammatically in FIG. 7 . The zoom position Z is plotted on the x-axis, and the focus value F is plotted on the y-axis. The focus value can be specified in millimeters or pixels, or any unit that characterizes the shift in focus relative to the calibration object 41, e.g., relative to the object mark 17 on the calibration object 41. The dimensions of the geometric shapes or structures imaged on the calibration object 41 can be used as a scale. For example, in the example shown in FIG. 6 , the width of one of the imaged rectangles can be used as a scale. The procedure according to the invention, described in detail below, has the advantage that adjustment and / or calibration can be performed on any calibration object 41, since only the relative focus values, i.e., the deviations of the determined focus values ​​from a reference point or from each other, are required. Therefore, a measured calibration object is not required.

[0053] FIG. 7 shows the results of three measurements. For example, a focus value F was determined for zoom position Z1 and zoom position Z2. A focus value F is preferably determined for three or more zoom positions Z. A function of focus value F=f(Z) can be determined from the measurements as a function of zoom position. This is preferably determined by a slope g(F~g * Z). The shift in focus value relative to the calibration object is represented by the gradient g. The absolute value of the gradient g should be small during adjustment and / or calibration, and is preferably set close to or near zero. In other words, a straight line should preferably run parallel to the x-axis in the adjustment and / or calibration results.

[0054] In FIG. 7, during the first measurement, a focus value F1 at zoom value Z1 and a focus value F2 at zoom value Z2 were determined, and a line 25 with a slope g = (F2 - F1) / (Z2 - Z1) was determined from this. The focus value of the surgical microscope was then increased or decreased by ΔF, and a second measurement was performed similarly to the first. This increase or decrease can be performed at any zoom position. Here, a line 26 with a slope smaller than line 25 was determined. The focus value of the surgical microscope was then further increased or decreased, and a third measurement was performed similarly to the first two measurements. In this case, a line 27 with a negative slope was determined.

[0055] Based on the thus determined dependence between the change in focus value ΔF of the surgical microscope and the gradient g (g = f(ΔF)), the focus value of the surgical microscope can be adjusted or calibrated so as to obtain a gradient g that is zero or close to zero, taking into account a predetermined tolerance. It has been found that there is usually a linear dependence (g ~ m * (ΔF), where m indicates the increment) that is independent of the zoom, so that only two measurements, e.g., a first measurement with a tilted gradient object at a first zoom position and a second measurement with a tilted calibration object at a second zoom position, are essentially sufficient to determine the desired or target value for adjustment and / or calibration, in particular the numerical value by which the current focus value of the surgical microscope must be increased or decreased to achieve the desired change in the absolute value of the gradient g. Therefore, on the one hand, the dependence between the change in focus value ΔF of the surgical microscope and the gradient g for the method of the present invention described herein can be determined and assumed to be known. In the latter case, the surgical microscope can be adjusted and / or calibrated based on the determination of only one gradient. The required change in focus value can be specified, for example, in millimeters.

[0056] For adjustment and / or calibration, the specified desired or target values ​​can be displayed to the technician, for example, in the form of a tolerance bar, a tolerance strip, in particular a straight line or curve running parallel to the specified contrast curve or contrast line 46. Figure 8 shows this diagrammatically. In the example shown, the calibration object 41 is tilted so that the focus changes from top to bottom. In Figure 8, in the captured image 18 of the calibration object 41, the desired line is indicated with reference number 29 and the line of currently highest contrast, i.e. the current contrast line, is indicated with reference number 28.

[0057] There are various options for adjusting and / or calibrating the focus values ​​of the surgical microscope 1 for each or all zoom positions, which can be applied individually or in combination with one another. A first variant is to change the focal length, i.e. the distance between the object or object plane 4 and at least one of the objectives 2, 3. In a surgical microscope comprising a main objective 3 and a video objective 2, the main objective 3 can then be moved relative to the object or object plane 4. A second variant is to change the distance between the objective 2 and the image plane 5 of the surgical microscope 1. In this case, the image acquisition device 5, i.e. for example a camera or camera chip, or the second objective 2 can be moved, i.e. displaced, relative to one another.

[0058] A third variant is to use objectives 2, 3 that are capable of inner focusing and therefore include at least one first optical element and at least one second optical element, which are displaceable relative to each other. This means that at least one of the optical elements can be displaced, while the other optical element is fixed. In the case of a surgical microscope, the main objective 3 can be designed as an objective with a variable focal length. Additionally or alternatively, the video objective 2 can be capable of suitable inner focusing.

[0059] 9 shows a schematic diagram of a first variant of a surgical microscope 40 according to the invention. The surgical microscope 40 comprises a control device 13 according to the invention, which is designed to carry out a variant of the method according to the invention, for example the method described above with reference to FIGS. 2 to 8. The illustrated surgical microscope 40 comprises a first objective 2, for example in the form of a video objective 2, a second objective 3, for example in the form of a main objective 3, a zoom system 8 for changing the zoom position, and an image acquisition device 5, for example a camera 5. The first objective 2 and / or the second objective 3 can be designed as objectives with a variable focal length and therefore each comprise at least two lenses or lens groups that are displaceable relative to one another.

[0060] The first objective lens 3, the zoom system 8, the second objective lens 2 and the image capture device 5 are optically connected to each other in this order, i.e. arranged consecutively in the beam path 10. A control device 13 is connected to the above-mentioned components 2, 3, 5 and 8 for signal transfer 15 and controls in particular the zoom system 8.

[0061] 10 shows a schematic diagram of a surgical microscope 40 according to the invention, which is a second variant of a stereoscopic configuration. Unlike the variant shown in FIG. 9, two video objectives 2 and two image acquisition devices 5, in particular camera chips, are arranged parallel to one another in the beam path 10. The zoom system 8 can have its own elements for each beam path, i.e., the first and second beam paths (separate beam paths or optical paths). The same, simultaneous displacement of the lenses can be achieved by mechanical, electronic, or electromechanical coupling. With the method according to the invention, at least one desired value and / or calibration data for the first optical path can be determined and transferred to the second optical path.

[0062] If a calibration of the stereoscopic system exists (e.g., in the form of camera matrices and / or distortion coefficients), a topography can be created during operation. The plane or sphere of the topography has the highest contrast and intersects with the topography. This contrast evaluation can be performed in one and / or both camera images. In the image representation, the point with the highest contrast can be represented by a free curve in the camera image. If the focus value of the surgical microscope is set correctly, this free curve will move with the object in the camera image when the zoom setting is changed. This focus shift can then be calculated as a function of the zoom (slope of the line in Figure 7). If this is not the case, or if the relative shift in the topography is too large, a service technician can be notified for readjustment purposes and / or the user can be informed. Alternatively, the user can be asked to perform this monitoring periodically. This method therefore also allows for on-site focus value monitoring. [Explanation of symbols]

[0063] 1 Surgical microscope 2. Second objective lens, video objective lens 3. First objective lens, main objective lens 4 Object plane 5. Imaging equipment, camera chips, and image planes 6 Afocal beam 7 Optical axis 8 Zoom System 10 Beam Path 11 First Beam 12 Second Beam 13 Control equipment 15 Signal Transmission 17 Object Mark 18 Images of the surface of the calibration object 21 Take at least one respective image of a specified object at at least two different zoom positions 22. Identifying one or more contrast values ​​as a function of focus values ​​by at least one captured image. 23. Using the determined contrast values ​​for at least two zoom positions, determine at least one desired value of at least one parameter for adjusting and / or calibrating the focus value. 24 Adjust and / or calibrate the surgical microscope 25 First Measurement 26 Second Measurement 27 Third Measurement 28 Actual Focal Line 29 Target Focus Line 31 Contrast Value Curve 32 Contrast Value Curve 33 Contrast Value Curve 34 Contrast Value Curve 35 Contrast Value Curve 36 Contrast Value Curve 40 Surgical microscope 41 Calibration Objects 42 Planar surface 43 Surface normal 44 angle 45 angle 46 Contrast Line f focus

Claims

1. A method for adjusting and / or calibrating and / or monitoring the focus value of a surgical microscope (1, 40) comprising at least one objective lens (2, 3), an image acquisition device (5) and a zoom system (8) and designed to be operated in at least two different zoom positions, comprising: The following steps: - taking (21) at least one image of a designated object (41) by means of said image taking device (5) for at least two different zoom positions; - determining (22) a plurality of contrast values ​​depending on said focus values ​​by means of said at least one captured image; - determining (23) by means of the contrast values ​​determined for the at least two zoom positions at least one desired value of at least one parameter for adjusting and / or calibrating the focus value of the surgical microscope (1, 40); A method comprising:

2. At least one correction value for the relative position of the at least one objective lens (2, 3) and / or the image capture device (5) with respect to the beam path in the surgical microscope (1, 40) is determined based on the at least one desired value. characterized in that The method of claim 1.

3. The at least one desired value for each of the at least two zoom positions is specified and / or specified separately, and / or the at least one desired value for the at least two zoom positions is specified and / or specified such that the difference between the focus values ​​at which the contrast value is greatest is less than a specified threshold for the at least two zoom positions (24). characterized in that 3. The method according to claim 1 or 2.

4. As part of said capturing at least one image of the designated object (21), at least one image (18) of a planar surface (42) of said designated object (41) is captured, said planar surface (42) having a surface normal (43) that forms an angle (44) of between 5 and 85 degrees with said optical axis (7) of said objective lens (2, 3). characterized in that The method according to any one of claims 1 to 3.

5. For each of the at least two zoom positions, images (18) of the specified object (41) are taken at multiple focus values. characterized in that The method according to any one of claims 1 to 4.

6. The focus value is set using a configurable focus system characterized in that The method of claim 5.

7. the focus value of the surgical microscope (1, 40) for each of the at least two zoom positions is adjusted and / or calibrated separately (24) so ​​that the contrast value for each of the at least two zoom positions is maximized, and / or The focus values ​​of the surgical microscope (1, 40) for the at least two zoom positions are adjusted and / or calibrated (24) so ​​that the difference between the focus values ​​at which the contrast value is greatest is less than a specified threshold for the at least two zoom positions. characterized in that The method according to any one of claims 1 to 6.

8. The focus value of the surgical microscope (1, 40) is Adapting the distance between the object plane (4) and the objective lenses (2, 3); and / or By adapting the distance between the objective lenses (2, 3) and the image plane of the image capture device (5), and / or by displacing a first optical element of said at least one objective lens (2, 3) relative to a second optical element of said at least one objective lens (2, 3); Adjusted and / or calibrated characterized in that The method according to any one of claims 1 to 7.

9. The zoom position and / or focus value are set automatically characterized in that The method according to any one of claims 1 to 8.

10. At least one image of a designated calibration object having known characteristics is taken at each of the at least two different zoom positions such that high contrast regions are recognizable in the image representation and / or contrast values ​​are identified and / or evaluated only within a central designated region of the image. characterized in that The method according to any one of claims 1 to 9.

11. The surgical microscope has a stereoscopic optical system, the stereoscopic optical system having a first optical path and at least one other optical path, and at least one desired value and / or calibration data for the first optical path is identified and transferred to the at least one other optical path. characterized in that The method according to any one of claims 1 to 10.

12. The focus value (22) is a relative focus value or a focus value difference. characterized in that The method according to any one of claims 1 to 11.

13. The determination of the desired value includes determining a change value of the focus of the surgical microscope, and the determination of the desired value and / or the change value is based on an evaluation of the slope of at least one curve mapping the dependence of the captured focus change on the focus value or a reference variable from the zoom position, and a functional relationship between the slope and the focus setting of the surgical microscope is used. characterized in that The method according to any one of claims 1 to 12.

14. The desired value is calculated and / or provided in the form of a target focus line or target focus area in a captured image of the specified object. characterized in that The method according to any one of claims 1 to 13.

15. A control device (13) for adjusting and / or calibrating and / or monitoring a surgical microscope (1, 40) comprising at least one objective lens (2, 3), an image acquisition device (5) and a zoom system (8) and designed to be operated in at least two different zoom positions, The control device (13) is designed to carry out the method according to any one of claims 1 to 14. A control device (13) characterized in that

16. A surgical microscope (1, 40) comprising at least one objective lens (2, 3), an image capture device (5) and a zoom system (8) and designed to be operated in at least two different zoom positions, Designed to carry out the method according to any one of claims 1 to 14 and comprising a control device (13) according to claim 15. A surgical microscope (1, 40) characterized in that

17. Has a stereoscopic system characterized in that A surgical microscope (1, 40) according to claim 16.

18. A computer-implemented method comprising instructions which, when executed by a computer, cause the method to be performed as claimed in any one of claims 1 to 14.

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