Optical microscopes and filters

Abstract

The present invention provides an optical microscope and filter that can accurately detect the focus position from an acquired image, even when areas with high reflectivity are present within the field of view. [Solution] The imaging optical system 14 guides the reflected light from the object Ob to be measured via an objective lens 24 to the camera 15 when the object Ob to be measured is illuminated by incident illumination. The imaging optical system 14 has a filter 22 at a position conjugate to the pupil position of the objective lens 24, the filter having a transmittance that decreases as it moves away from the optical axis of the imaging optical system 14.

Description

Technical Field

[0001] The present invention relates to a three-dimensional shape measuring apparatus, and particularly to a three-dimensional shape measuring apparatus that measures the three-dimensional shape of a measurement object by the focus variation method.

Background Art

[0002] As a method for measuring a three-dimensional shape using an optical microscope, the focus variation method (focus movement method) is known (for example, Patent Documents 1, 2, etc.). In the focus variation method, the surface of the measurement object is continuously imaged while changing the focus position, the obtained image group is analyzed, the coordinates in focus are extracted, and the three-dimensional shape of the measurement object is measured.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, the focus variation method has an advantage that a low-cost measuring machine can be realized because it does not require special devices in the optical system compared to other measuring methods such as the white light interference method.

[0005] On the other hand, the focus variation method has a problem in that it cannot accurately measure areas with low reflectivity when areas with high reflectivity and areas with low reflectivity coexist within the field of view. This occurs because the contrast of the blur boundary of the high-reflectivity area becomes stronger than the contrast of the surface of the low-reflectivity area. Figure 14 shows an example of an image taken when areas with high reflectivity and areas with low reflectivity coexist within the field of view. The figure shows an example of imaging a cone-shaped object under incident illumination while changing the focal position. The figure also shows an example of an image sliced ​​in the xz plane to make it easier to understand the effect of blur due to the focal position. In the figure, the triangular line L represents the original shape of the object being measured. When imaging a cone-shaped object under incident illumination, the vertex shows strong reflection against the inclined surface with low reflectivity. As a result, as shown in the elliptical region C in Figure 14, the blur of the vertex with strong reflection overwhelms the surface contrast of the original shape, making accurate measurement impossible.

[0006] One way to address this problem is to use a polarizing filter (a method that reduces direct reflection and acquires scattered light). However, using a polarizing filter has the disadvantage of significantly reducing the amount of light and increasing the exposure time. Longer exposure times lead to longer measurement times.

[0007] This invention has been made in view of these circumstances, and aims to provide a three-dimensional shape measuring device that can measure the three-dimensional shape of an object using the focus variation method. [Means for solving the problem]

[0008] To solve the above problems, the three-dimensional shape measuring device according to the present invention comprises an imaging optical system, an imaging unit that images an object to be measured via the imaging optical system, and an image processing unit that processes multiple images of the object to be measured taken at different focal positions to extract the coordinate position in focus and measure the three-dimensional shape of the object to be measured, wherein the imaging optical system has a filter at the aperture position whose transmittance decreases as it moves away from the optical axis.

[0009] In one embodiment of the present invention, it is preferable that the transmittance of the filter decreases curvilinearly as it moves away from the optical axis.

[0010] In one embodiment of the present invention, it is preferable that the filter has a Gaussian distribution of transmittance centered on the optical axis.

[0011] In one embodiment of the present invention, it is preferable that the transmittance of the filter decreases linearly as it moves away from the optical axis.

[0012] In one embodiment of the present invention, it is preferable that the transmittance of the filter decreases in steps as it moves away from the optical axis.

[0013] One embodiment of the present invention further comprises an illumination light source and an illumination optical system that irradiates an object to be measured with illumination light from the illumination light source, and it is preferable to adjust the amount of light incident on the imaging unit by adjusting the amount of illumination light irradiated on the object to be measured. [Effects of the Invention]

[0014] According to the present invention, the three-dimensional shape of an object to be measured can be accurately measured using the focus variation method. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 shows a schematic configuration of a three-dimensional shape measuring device. [Figure 2] Figure 2 shows an example of the hardware configuration of an image processing device. [Figure 3] Figure 3 is a block diagram of the main functions of the image processing device. [Figure 4] Figure 4 is a front view showing an example of a filter configuration. [Figure 5] Figure 5 is a graph showing the transmission distribution characteristics of the filter. [Figure 6] Figure 6 is a conceptual diagram of imaging using a typical optical microscope. [Figure 7] Figure 7 is a conceptual diagram of the blurred image produced in an imaging optical system without a filter. [Figure 8] FIG. 8 is a conceptual diagram of a blurred of a blurred image generated by an imaging optical system equipped with a filter. [Figure 9] FIG. 9 is a diagram showing an imaging object and its imaging method. [Figure 10] FIG. 10 is an enlarged view of a part of an image captured by an imaging optical system without a filter. [Figure 11] FIG. 11 is an enlarged view of a part of an image captured by an imaging optical system equipped with a filter. [Figure 12] FIG. 12 is a graph showing another example of the transmission distribution characteristics of a filter. [Figure 13] FIG. 13 is a graph showing another example of the transmission distribution characteristics of a filter. [Figure 14] FIG. 14 is a diagram showing an example of an imaging image when a high reflectivity portion and a low reflectivity portion coexist within the field of view.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0017] [Three - dimensional Shape Measuring Device] FIG. 1 is a diagram showing the schematic configuration of a three - dimensional shape measuring device.

[0018] As shown in the figure, the three - dimensional shape measuring device 1 of the present embodiment includes an imaging device 10 and an image processing device 100.

[0019] [Imaging Device] The imaging device 10 is configured by a so - called optical microscope and captures an image of the measurement object Ob while changing the focal position. The imaging device 10 is an example of an imaging unit. As shown in FIG. 1, the imaging device 10 of the present embodiment includes a stage 11, an illumination light source 12, an illumination optical system 13, an imaging optical system 14, a camera 15, a focus drive unit 16, an operation unit 17, a control unit 18, and the like.

[0020] Stage 11 has a mounting surface 11a on which the object to be measured Ob is placed. The mounting surface 11a is a flat surface and constitutes the reference surface for measurement. Specifically, the X and Y axes are set on the mounting surface 11a. The X and Y axes are set as two mutually orthogonal axes.

[0021] The illumination light source 12 can be a halogen lamp, metal halide lamp, mercury lamp, xenon lamp, light-emitting diode (LED), or the like.

[0022] The illumination optical system 13 includes an illumination lens 20, a beam splitter 21, a filter 22, an aperture diaphragm 23, and an objective lens 24. Light emitted from the illumination light source 12 (illumination light) is irradiated onto the object to be measured Ob placed on the stage 11 via the illumination lens 20, beam splitter 21, aperture diaphragm 23, and objective lens 24 (so-called reflected illumination). By adjusting the amount of this illumination light, the amount of light incident on the camera 15 is adjusted. The amount of illumination light is adjusted, for example, by the amount of light emitted from the illumination light source 12. Alternatively, the illumination light can be guided from the illumination light source 12 to the illumination optical system 13 using a ride guide.

[0023] The imaging optical system 14 includes an objective lens 24, a filter 22, an aperture diaphragm 23, a beam splitter 21, and an imaging lens 25. The beam splitter 21, filter 22, aperture diaphragm 23, and objective lens 24 are shared with the illumination optical system 13. Light reflected from the object Ob is incident on the camera 15 via the objective lens 24, filter 22, aperture diaphragm 23, beam splitter 21, and imaging lens 25.

[0024] The filter 22 is positioned at the aperture diaphragm 23 (diaphragm position) and has the following configuration: namely, it has a configuration in which the transmittance decreases as it moves away from the optical axis. By positioning such a filter 22 at the diaphragm position, high-precision measurements can be made using the focus variation method even if the field of view includes areas with high reflectivity. This point will be described in detail later.

[0025] The camera 15 has an image sensor 15A and electronically captures an image of the object Ob to be measured. The image sensor 15A can be, for example, a CMOS image sensor (complementary metal oxide semiconductor image sensor), a CCD image sensor (charge-coupled device image sensor), etc. The image captured by the camera 15 is output to the image processing device 100.

[0026] The focus drive unit 16 moves the illumination light source 12, illumination optical system 13, imaging optical system 14, and camera 15 integrally along the imaging optical axis Lz to vary the focal position. The imaging optical axis Lz is set perpendicular to the mounting surface 11a of the stage 11. Therefore, the illumination light source 12, illumination optical system 13, imaging optical system 14, and camera 15 move perpendicular to the mounting surface 11a of the stage 11. The axis parallel to the imaging optical axis Lz is defined as the Z-axis. The focus drive unit 16 includes a guide mechanism and a drive mechanism. The guide mechanism guides the unit (optical head) including the illumination light source 12, illumination optical system 13, imaging optical system 14, and camera 15 along the Z-axis. The drive mechanism consists of, for example, a lead screw mechanism and a motor that drives the lead screw mechanism.

[0027] The control unit 17 has various operation buttons for operating the imaging device 10 and accepts operation input from the user. The various operation buttons include a touch panel.

[0028] The control unit 18 provides overall control over the operation of the imaging device 10. Specifically, it performs light emission control (including light intensity control) for the illumination light source 12, image capture control for the camera 15, and drive control (feed control) for the focus drive unit 16. The control unit 18 is composed of a computer. In other words, the computer functions as the control unit 18 by executing a predetermined program.

[0029] The imaging device 10, configured as described above, images the object Ob placed on the stage 11 while changing the focal position at a constant pitch. Specifically, the focus drive unit 16 moves the optical head along the Z-axis at a constant pitch, and images the object Ob at each position. The captured images are output sequentially to the image processing device 100.

[0030] [Image processing device] Figure 2 shows an example of the hardware configuration of an image processing device.

[0031] The image processing device 100 is composed of a so-called computer and includes a processor 101, main memory 102, auxiliary storage 103, input device 104, output device 105, and input / output interface 106, etc.

[0032] The processor 101 is composed of components such as a CPU (central processing unit) and a GPU (graphics processing unit).

[0033] The main memory 102 is composed of, for example, DRAM (dynamic random access memory), SRAM (static random access memory), etc.

[0034] The auxiliary storage device 103 is composed of, for example, an SSD (solid state drive), an HDD (hard disk drive), etc. The auxiliary storage device 103 stores programs executed by the processor 101 and various data.

[0035] The processor 101 reads the program stored in the auxiliary storage device 103, loads it into the main memory device 102, and executes it, thereby realizing various functions as described later.

[0036] The input device 104 is a device for the user to input instructions to the image processing device 100, and consists of, for example, a mouse, keyboard, or touch panel.

[0037] The output device 105 is a device that outputs (including display) measurement results, etc., and is composed of, for example, a liquid crystal display (LCD), an organic electroluminescent display (OELD), etc.

[0038] The input / output interface 106 is an interface for connecting input / output devices, and is configured as, for example, USB (universal serial bus). The camera 15 of the imaging device 10 is connected to the image processing device 100 via the input / output interface 106.

[0039] Figure 3 is a block diagram of the main functions of the image processing device.

[0040] As shown in the figure, the image processing device 100 has the functions of an image acquisition unit 100A and an image processing unit 100B. The functions of each unit are realized by the processor 101 executing a predetermined program.

[0041] The image acquisition unit 100A acquires image data of the object to be measured Ob captured by the imaging device 10. This image data is image data of the object to be measured Ob captured while changing the focal position (so-called multi-focus image data). The acquired series of image data is recorded in the auxiliary storage device 103.

[0042] The image processing unit 100B applies the focus variation algorithm to the image data acquired by the image acquisition unit 100A to measure the three-dimensional shape of the object Ob. Specifically, it extracts the in-focus coordinate position from multiple images of the object Ob, which are captured at different focal points, to measure the three-dimensional shape of the object. The measurement result is acquired as three-dimensional shape data of the object Ob. Three-dimensional shape data is a data set in which information about the height of the object represented by each pixel is assigned to every pixel that makes up the image of the object. By acquiring three-dimensional shape data, it becomes possible to display the object Ob in three dimensions using computer graphics.

[0043] The focus variation method itself is a well-known technique. Therefore, a detailed explanation will be omitted, but roughly speaking, three-dimensional shape data is generated from multifocal images using the following procedure.

[0044] First, the obtained image is subjected to differential calculus for each pixel to calculate an evaluation value for the degree of focus. The degree of focus is a numerical value that indicates the degree to which the image is in focus.

[0045] Next, for each pixel making up the image of the object to be measured, the focal position (focus position) that maximizes the evaluation value of the degree of focus is identified. From the information of the identified focus position, the height information of the object to be measured Ob at the position corresponding to each pixel is obtained. For example, suppose the focus position of the pixel located at coordinates (xn,yn) is Pn. In this case, the height zn associated with that position Pn is obtained as the height information (information of the focused coordinate position) for the pixel located at coordinates (xn,yn). By obtaining the height information for all pixels, the three-dimensional shape data of the object to be measured Ob can be obtained.

[0046] Typically, imaging is performed by changing the focal point at a constant interval from a reference point (origin). Therefore, the order of imaging can also be assigned to height information.

[0047] The measurement results (three-dimensional shape data) are associated with the image data obtained by imaging and recorded in the auxiliary storage device 103.

[0048] [Imaging optics] As described above, in this embodiment, the imaging optical system 14 has a filter 22 having predetermined transmission distribution characteristics positioned at the position of the aperture diaphragm 23 (aperture position).

[0049] Figure 4 is a front view showing an example of the filter configuration. Figure 5 is a graph showing the transmission distribution characteristics of the filter.

[0050] The filter 22 of this embodiment has the characteristic of being symmetrical with respect to the optical axis and having transmittance that decreases as it moves away from the optical axis. The example shown in Figure 4 is an example in which transmittance decreases curvilinearly as it moves away from the optical axis. In particular, it is an example in which the transmittance distribution centered on the optical axis has a Gaussian distribution. In this case, as shown in Figure 5, the transmittance is high in the center and decreases smoothly towards the periphery.

[0051] By equipping the aperture with a filter 22 of this configuration, the brightness distribution of the bokeh boundary (outline) can be controlled, and the contrast of the bokeh boundary can be reduced. The principle is explained below.

[0052] First, let's explain the mechanism of imaging using an imaging device.

[0053] Figure 6 is a conceptual diagram of imaging using a typical optical microscope. This figure shows an example where the relationship between the object to be measured Ob and the image sensor 15A is in focus. The figure also shows an example where the objective lens 24 is composed of a telecentric lens (object-side telecentric lens). A telecentric lens is suitable for measurement using the focus variation method because even if the position of the object plane is slightly shifted, the image on the fixed image plane will only be blurred, and the position of the center of the blur will not shift. In a telecentric lens, the aperture position (exit pupil position) is set at the rear focal point. Therefore, the aperture position is set at the rear focal point of the objective lens 24.

[0054] As shown in Figure 6, light reflected from each point of the object Ob is focused by the objective lens 24. The light focused by the objective lens 24 has a portion of its beam restricted by the aperture diaphragm 23 and enters the imaging lens 25. The light beam that enters the imaging lens 25 is focused onto the image sensor 15A and forms an image.

[0055] Figure 7 is a conceptual diagram of the blurred image produced in an imaging optical system without a filter. The figure focuses on a single point on the object Ob (a point on the imaging optical axis) and shows the light beam emitted from the object Ob. The aperture diaphragm 23 has a circular shape. For convenience, aberrations are assumed to be absent.

[0056] As shown in the figure, the light beam passes through the entire aperture diaphragm 23 and is projected onto the light-receiving surface IP of the image sensor 15A. When the relationship between the object to be measured Ob and the image sensor 15A is in focus, a sharp resolution is obtained on the light-receiving surface (imaging surface) IP of the image sensor 15A. On the other hand, at the front position P1 and the rear position P2 of the light-receiving surface, blur is projected. The blurred images IB1 and IB2 have a nearly uniform brightness distribution.

[0057] Figure 8 is a conceptual diagram of the blurred image produced in an imaging optical system equipped with a filter.

[0058] As described above, the aperture position allows the constraints reflected from each point of the object Ob to pass through uniformly. Therefore, by placing the filter 22 at this position, it can act uniformly on blurs projected anywhere within the field of view.

[0059] As shown in Figure 8, by placing the filter 22 at the aperture position, it is possible to maintain sharp resolution at the light-receiving surface (image-forming surface) IP while mitigating the contrast of the outlines (boundaries) of the blurred images IB1 and IB2 that occur at positions P1 and P2 before and after it.

[0060] The aperture diaphragm 23 mounted in the imaging optical system 14 of this embodiment is a so-called fixed diaphragm (a diaphragm with a constant aperture diameter). In optical microscopes, a movable diaphragm (a diaphragm with an adjustable aperture diameter) is usually used to adjust the amount of light incident on the image sensor or to adjust the depth of field. However, for measurements using the focus variation method, a movable diaphragm is not always necessary. This is because the amount of light incident on the image sensor can be adjusted by the amount of light from the illumination light source. Also, for measurements using the focus variation method, a shallower depth of field is preferable. For this reason, a fixed diaphragm is used for the aperture diaphragm 23 in the imaging optical system 14 of this embodiment. When a fixed diaphragm is used for the aperture diaphragm 23, it is preferable that its aperture diameter (diameter of the opening) is larger than the effective diameter of the filter 22. The effective diameter refers to the diameter in the range from the center until the transmittance becomes 0% (the diameter in the range through which light is transmitted). In this case, if the aperture diameter of the aperture diaphragm 23 is larger than the effective diameter of the filter 22, the aperture diaphragm 23 can be omitted. In other words, the filter 22 can be placed in place of the aperture diaphragm 23. In this case, the area outside the effective diameter of the filter 22 effectively functions as an aperture diaphragm. Alternatively, the filter 22 can be attached to the opening of the aperture diaphragm 23.

[0061] The filter 22 is produced, for example, by depositing a light-absorbing material onto a transparent parallel plate (for example, a parallel plate made of transparent glass) to have predetermined transmission distribution characteristics. Alternatively, it can be produced, for example, by depositing a light-reflecting material onto a transparent parallel plate to have predetermined transmission distribution characteristics.

[0062] As described above, the imaging optical system 14 of this embodiment, by providing a filter 22 having predetermined transmission distribution characteristics at the aperture position, can reduce the contrast at the boundary of the blur that occurs before and after the focus position. As a result, even if there are areas with high reflectivity in the field of view, the contrast at the boundary of that blur can be reduced. Furthermore, as a result, even if there are areas with high reflectivity in the field of view, the focus position can be accurately detected from the captured image and accurately measured by the focus variation method.

[0063] Furthermore, compared to the case where a polarizing filter is used, the reduction in light intensity can be suppressed. In the configuration using a polarizing filter, more than 90% of the light intensity is lost, but in the configuration using filter 22 with transmission distribution characteristics (Gaussian distribution) as shown in Figure 4, the loss of light intensity can be suppressed to about 58%.

[0064] [Examples] An experiment was conducted to confirm the difference in images obtained using an imaging optical system without a filter and an imaging optical system equipped with a filter (the imaging optical system of this embodiment).

[0065] Figure 9 shows the object to be imaged and the method of imaging it.

[0066] As shown in the figure, a frustoconical object O was placed on the imaging optical axis Lz, and imaging was performed from above in a vertical downward direction. The upper surface Ot of the object O is positioned perpendicular to the imaging optical axis Lz. Under incident illumination, the upper surface Ot of the object Ob positioned in this way becomes the high-reflectivity area, and the inclined surface Os becomes the low-reflectivity area.

[0067] Image Im was captured by focusing on the inclined surface Os near the upper surface Ot (focusing on a position zn that is lower in height than the upper surface Ot).

[0068] Figure 10 is a magnified view of a portion of an image captured with an imaging optical system without a filter. Figure 11 is a magnified view of a portion of an image captured with an imaging optical system equipped with a filter. The magnified area is the region S that includes both the upper surface Ot of the object to be imaged O and the focused inclined surface Os, as shown in Figure 9.

[0069] As shown in Figure 10, in images captured with an imaging optical system without a filter, the contrast at the boundary of the high-luminance blur on the highly reflective upper surface Ot is high, exceeding the contrast of the in-focus area on the less reflective inclined surface Os. In other words, the contrast at the boundary of the blur on the upper surface Ot outweighs the surface contrast of the original shape on the inclined surface Os.

[0070] In contrast, as shown in Figure 11, in images captured with an imaging optical system equipped with a filter, the contrast at the boundary of the high-brightness blur on the highly reflective upper surface Ot is reduced, achieving a contrast equal to or lower than that of the in-focus area on the less reflective inclined surface Os. Therefore, the focus position can be appropriately extracted from the image captured with the imaging optical system of this embodiment.

[0071] [Differentiation]

[0072] [Filter variations] In the above embodiment, the case in which the transmittance of filter 22 has a so-called Gaussian distribution was described as an example, but the transmittance distribution characteristics of filter 22 are not limited to this. Any configuration in which the transmittance decreases as the distance from the optical axis increases is acceptable.

[0073] Figure 12 is a graph showing another example of the transmission distribution characteristics of a filter.

[0074] The filter shown in the figure is symmetrical with respect to the optical axis, and its transmittance decreases linearly as it moves away from the optical axis. A similar effect can be obtained in this case as well. The loss of light intensity is approximately 50%.

[0075] Figure 13 is a graph showing another example of the transmission distribution characteristics of a filter.

[0076] The filter shown in the figure is symmetrical with respect to the optical axis, and its transmittance decreases in stages as it moves away from the optical axis. Thus, a configuration that gradually reduces transmittance is also possible.

[0077] [Imaging optics] In the imaging optical system 14, the configuration of the objective lens 24 is not particularly limited. It may be a telecentric lens (object-side, image-side telecentric lens, or bilateral telecentric lens) or a non-telecentric lens (a so-called ordinary lens). However, to achieve higher accuracy measurements, it is preferable to use an object-side telecentric lens.

[0078] Furthermore, as described above, the position where the filter 22 is placed is the "aperture position." The aperture position is the place where all light passes uniformly. In an optical microscope, the aperture diaphragm 23 is placed at the pupil position. In other words, the position where the aperture diaphragm 23 is placed (aperture position) is the "pupil position." Therefore, "aperture position" is synonymous with "pupil position." In an optical microscope, the objective lens 24 determines the pupil position. Therefore, the filter 22 can be placed at the pupil position of the objective lens 24, or at a position conjugate to the pupil position of the objective lens 24. In this invention, the term "aperture position" is a concept that includes its vicinity. That is, it includes cases where it is considered to be placed at substantially the same position as the aperture position. The same applies to the pupil position.

[0079] [Imaging conditions] When imaging an object to be measured, the image should be captured in such a way that the brightness does not saturate in any of the images. That is, the maximum and minimum brightness values ​​of the object to be measured should fall within the dynamic range that the imaging device can capture. Therefore, it is preferable to use a camera with a wide dynamic range (a so-called wide dynamic range camera) in the imaging device.

[0080] [Imaging device] In the above embodiment, the optical head is moved relative to the object to be measured to capture multiple images with different focal positions. However, the optical head may be fixed, and the object to be measured may be moved to capture images. Alternatively, both may be moved to capture images. In other words, the movement to change the focal position may be relative.

[0081] [Image processing device] In the above embodiment, a case was described in which the image processing device is configured as a separate computer from the imaging device, but the functions of the image processing device can also be integrated into the imaging device. [Explanation of symbols]

[0082] 1...Three-dimensional shape measuring device, 10...Imaging device, 11...Stage, 11a...Mounting surface, 12...Illumination light source, 13...Illumination optical system, 14...Imaging optical system, 15...Camera, 15A...Image sensor, 16...Focus drive unit, 17...Operation unit, 18...Control unit, 20...Illumination lens, 21...Beam splitter, 22...Filter, 23...Aperture diaphragm, 24...Objective lens, 25...Imaging lens, 100...Image processing device, 1 00A...Image acquisition unit, 100B...Image processing unit, 101...Processor, 102...Main memory, 103...Auxiliary memory, 104...Input device, 105...Output device, 106...Input / output interface, IB1...Blurred image, IB2...Blurred image, IP...Light-receiving surface of image sensor, Im...Image, Lz...Imaging optical axis, Ob...Measurement target, O...Imagine target, Os...Inclined surface of image target, Ot...Top surface of image target

Claims

1. The system includes an imaging optical system that guides reflected light from an object to be measured to a camera via an objective lens when the object to be measured is illuminated by incident light. The imaging optical system has a filter at a position conjugate to the pupil position of the objective lens, the filter whose transmittance decreases as it moves away from the optical axis of the imaging optical system. Optical microscope.

2. A filter mounted on an optical microscope equipped with an imaging optical system that guides reflected light from an object to be measured to a camera via an objective lens when the object to be measured is illuminated by incident illumination, The imaging optical system has the characteristic that its transmittance decreases as it moves away from the optical axis, The objective lens is configured to be positioned at a location conjugate to the pupil position. filter.

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