JP3592113B2 - Method and apparatus for measuring light transmittance of thin metal plate having through holes - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is to inspect whether a large number of fine through holes are formed well in a thin metal plate such as a shadow mask for a color picture tube and an aperture grill for a trinitron tube (registered trademark of Sony Corporation). More particularly, the present invention relates to a method for measuring the light transmittance of a thin metal plate and an apparatus for measuring the light transmittance of a thin metal plate used for performing the method.
[0002]
[Prior art]
A metal thin plate with a large number of fine holes formed therein, for example, a shadow mask, is formed by performing a series of photo-etching processes on a metal thin plate material to form a large number of slot-shaped or circular fine fine holes in the metal thin plate material. Manufactured. If a number of fine holes are not formed in the shadow mask in a desired shape and size, the electron beam emitted from the electron gun in the color picture tube when the shadow mask is mounted on the color picture tube. The transmittance at the time of transmission through the shadow mask does not become a desired value, and as a result, image unevenness occurs on the screen of the color picture tube. Therefore, it is necessary to inspect whether a large number of fine through holes are formed as desired in the shadow mask and a desired transmittance can be obtained.
[0003]
As a through-hole inspection apparatus used for this kind of purpose, for example, a shadow mask transmittance measurement apparatus disclosed in Japanese Patent Application Laid-Open No. 7-192618 is known. As shown in the schematic sectional view of FIG. 4, this measuring machine mounts a shadow mask 1 having a measurement opening 3 and a large number of fine holes, and measures a plurality of fine holes of the shadow mask 1. A measuring stage 2 for inspecting the fine through-holes located at the opening 3, and a light source 4 irradiating light through the measuring opening 3 of the measuring stage 2 and capable of changing the inclination angle with respect to the measuring opening 3. The light source 4 is linearly opposed to the light source 4 via the measurement opening 3 of the measurement stage 2, and its position changes synchronously with the change in the inclination angle of the light source 4. And a photodetector 5 for detecting the light that has passed through. The amount of light incident on the photodetector 5 with the shadow mask 1 interposed between the light source 4 and the photodetector 5 does not cause the shadow mask 1 to intervene between the light source 4 and the photodetector 5. The value obtained by dividing by the amount of light incident on the photodetector 5 in the state is calculated as the light transmittance by the arithmetic circuit of the recorder 6 connected to the photodetector 5.
[0004]
[Problems to be solved by the invention]
In a method of using a shadow mask transmittance measuring device having a configuration as shown in FIG. 4 to inspect whether or not fine holes of the shadow mask are well formed and a desired transmittance can be obtained, the light source 4 is used. Is passed through the circular measurement opening 3 of the measurement stage 2 on which the shadow mask 1 is mounted, so that the light is limited to a predetermined spot diameter, and the spot light is applied to the shadow mask 1. Like that. Therefore, there are the following problems.
[0005]
In a color picture tube with a built-in shadow mask, the angle at which the electron beam emitted from the electron gun is incident on the shadow mask changes depending on the position of the shadow mask. The light enters the surface obliquely. Therefore, in order to obtain a value close to the actual transmittance when the electron beam passes through the shadow mask by the transmittance measuring device shown in FIG. Must be applied to the surface of the shadow mask 1 in an oblique direction. For this reason, in the peripheral portion of the shadow mask 1, light from the light source 4 is obliquely incident on the measurement opening 3 of the measurement stage 2 on which the shadow mask 1 is mounted. When light from the light source 4 enters the measurement opening 3 of the measurement stage 2 in an oblique direction, the light passes through the measurement opening 3 because the measurement stage 2 has the circular measurement opening 3. When the vignetting occurs, the spot shape of the light that passes through the circular measurement opening 3 and enters the shadow mask 1 is such that the light from the light source 4 is incident on the measurement opening 3 in the vertical direction. It becomes an ellipse smaller in area than the spot light. Therefore, every time the angle of the light emitted from the light source 4 incident on the shadow mask 1 changes, the amount of light incident on the shadow mask 1 itself changes, and for each incident angle of light on the shadow mask 1 There is a problem that it is necessary to calibrate the amount of light received by the photodetector 5, and extra work is required for the calibration work.
[0006]
The present invention has been made in view of the above circumstances, and when measuring the light transmittance of a metal sheet having a large number of through holes, an angle at which light is incident on the surface of the metal sheet. Provided is a method capable of accurately measuring the light transmittance at a plurality of positions of a metal sheet without being affected by the above, and an apparatus for measuring the light transmittance of a metal sheet capable of suitably implementing the method. The purpose is to provide.
[0007]
[Means for Solving the Problems]
The invention according to claim 1, the light emitted from the light source, shines irradiation to one side of the plurality of metal through holes are formed thin, by the light detecting means light passing through the plurality of through holes of the sheet metal Detected and calculated from the amount of light incident on the light detecting means when the metal thin plate is not interposed between the light source and the light detecting means and when the metal thin plate is interposed between the light source and the light detecting means. In the method of measuring the ratio, the holding means holds each of two opposing sides of the metal sheet and holds the metal sheet in a flat state, and converts the light emitted from the light source into parallel light having a predetermined diameter. After that, the parallel light is directly radiated to one surface side of the metal thin plate.
[0008]
The invention according to claim 2 is a metal sheet having a pair of clamps respectively gripping two opposing sides of the metal sheet and holding the metal sheet in a flattened state, and a metal sheet formed with a large number of through holes. Having parallel light forming means for converting the light emitted from the light source into parallel light having a predetermined diameter, and irradiating the parallel light having a predetermined diameter directly to one surface of the metal thin plate. Light irradiating means, light detecting means disposed on the other surface side of the metal thin plate, detecting light emitted from the parallel light irradiating means and passing through a plurality of through holes of the metal thin plate, and the parallel light irradiating means Calculating means for calculating the light transmittance of the metal sheet from the respective incident light amounts to the light detecting means when the metal sheet is not interposed and when the metal sheet is interposed between the light detecting means, and Light transmittance measurement of a metal sheet with a through hole Characterized by being configured to location.
[0009]
According to a third aspect of the present invention, in the measuring apparatus according to the second aspect, a condenser lens for condensing light emitted from the light source and a collimator for collimating the light condensed by the condenser lens. The parallel light forming means is constituted by a lens and a diaphragm mechanism which is interposed on an optical path between the condenser lens and the collimator lens and has an opening through which light collected by the condenser lens passes. It is characterized by the following.
[0010]
According to a fourth aspect of the present invention, in the measuring apparatus according to the third aspect, the size of the aperture of the diaphragm mechanism is adjustable.
[0011]
According to a fifth aspect of the present invention, in the measuring device according to any one of the second to fourth aspects, an LED (light emitting diode) is used as the light source.
[0012]
The invention according to claim 6 is the measuring device according to any one of claims 2 to 5, further comprising a lens position adjusting mechanism for adjusting a relative position between the condenser lens and the collimating lens. It is characterized by the following.
[0013]
According to the light transmittance measuring method of the invention according to the first aspect, the light emitted from the light source is converted into parallel light having a predetermined diameter, and then held in a state where two sides are gripped and flattened by the holding means. since direct irradiated to the one surface side of the metal sheet, regardless of the incident angle of light with respect to the surface of the sheet metal, therefore regardless measurement position of the light transmittance in the sheet metal, the amount of light incident on the sheet metal is constant Become. For this reason, it is not necessary to calibrate the amount of light received by the photodetector for each incident angle of light on the metal thin plate.
[0014]
When the light transmittance measuring device of the invention according to claim 2 is used, in the parallel light irradiating means, the light radiated from the light source is converted into parallel light having a predetermined diameter by the parallel light forming means , and is held by the parallel light irradiating means . By means , parallel light having a predetermined diameter is directly radiated to one surface side of the thin metal plate which is held in a flat state by holding two sides by a pair of clamps . For this reason, regardless of the angle of incidence of light on the surface of the metal sheet, and therefore, regardless of the position where the light transmittance is measured on the metal sheet, the amount of light incident on the metal sheet becomes constant. This eliminates the need to calibrate the amount of light received by the light detecting means. The light emitted from the parallel light irradiating means and passing through the plurality of through holes of the metal sheet is detected by the light detecting means, and the calculating means interposes the metal sheet between the parallel light irradiating means and the light detecting means. The light transmittance of the thin metal plate is calculated from the amount of light incident on the light detecting means when it is not interposed and when it is interposed.
[0015]
In the measuring device according to the third aspect of the present invention, in the parallel light forming means, the light emitted from the light source is collected by the condenser lens, and the light collected by the condenser lens passes through the aperture of the aperture mechanism. Then, after the light flux is restricted so as to obtain a predetermined spot diameter, the light is converted into parallel light having a predetermined diameter by a collimating lens.
[0016]
In the measuring device according to the fourth aspect of the present invention, the size of the aperture of the aperture mechanism is adjustable, so that parallel light having a desired spot diameter can be easily obtained.
[0017]
In the measuring device according to the fifth aspect of the present invention, when an LED that emits monochromatic light or light close to monochromatic light is used as a light source, an optical filter for calibration is used when calibration is performed by measuring the transmittance of the optical filter. It is easy to obtain, and there is no problem such as generation of a beat due to light interference in a periodic hole pattern as in the case where a laser diode is used as a light source.
[0018]
In the measuring apparatus according to the sixth aspect of the present invention, the relative position between the condenser lens and the collimating lens is adjusted by the lens position adjusting mechanism, so that the in-plane distribution of the parallel light irradiated on the thin metal plate is adjusted. And it can be optimized.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS.
[0020]
FIG. 1 shows an embodiment of the present invention, and shows a basic configuration of a light transmittance measuring apparatus used for measuring the light transmittance of a metal thin plate having a large number of fine holes, for example, a shadow mask. It is the schematic diagram which shows typically. This measuring device has a pair of clamps 12, 12 respectively gripping two sides of the shadow mask 10, and one main surface side of the shadow mask 10 (the shadow mask 10 is gripped by the pair of clamps 12, 12). A parallel light irradiating device 14 is provided on one side of the electron gun side when incorporated in the color picture tube, and the other main surface side of the shadow mask 10 (when the shadow mask 10 is incorporated in the color picture tube). An optical sensor 16 is provided on one surface side that is the optical body side). The parallel light irradiation device 14 and the optical sensor 16 are arranged on a straight line so as to face each other, and the parallel light 20 emitted from the parallel light irradiation device 14 is incident on the optical sensor 16. . The optical sensor 16 is connected to a personal computer 18, and the personal computer 18 has a display and a printer.
[0021]
The clamp 12 is constituted by a pair of upper and lower plate-like grippers 12a and 12b, and the plate-like grippers 12a and 12b have a length equal to the dimension of the long side of the shadow mask 10 and are perpendicular to the paper surface. It has an elongated rectangular shape extending in the direction. The pair of upper and lower plate-like grippers 12a and 12b is an unnecessary part (a part to be cut off before becoming a product) and a part of an effective part, for example, about 5 mm to 10 mm from the periphery of the effective part. Of the width of Although not shown, the pair of clamps 12 and 12 are attached to a clamp table, and the pair of upper and lower plate-like grippers 12a and 12b is one plate-like member so as to approach and separate from each other by a cylinder. The gripper 12a is reciprocated up and down. Further, the pair of clamps 12, 12 are reciprocated by a cylinder in a direction of approaching and separating from each other, and are also moved by a small distance in a direction of separating from each other by the cylinder while holding two sides of the shadow mask 10 respectively. It is supposed to be.
[0022]
As shown in FIG. 2, the parallel light irradiation device 14 is configured by arranging a light source 22, a condenser lens 24, a diaphragm mechanism 26, and a collimator lens 28 in a line in this order. As the light source 22, it is most preferable to use an LED that emits monochromatic light or light close to monochromatic light. An incandescent lamp can be used as the light source 22. However, in measuring the light transmittance of the shadow mask, it is necessary to measure and calibrate the transmittance of a general-purpose optical filter. However, there is a disadvantage in that it is difficult to obtain an optical filter for calibration (since filters are commercially available for each wavelength). A laser light emitting device using a laser diode may be used as the parallel light irradiation device. However, since the laser light has a uniform wavefront, the laser light is irradiated on the shadow mask and passes through a plurality of through holes. In this case, there is a problem that a beat is generated due to light interference in the periodic hole pattern. Each of the condenser lens 24 and the collimator lens 28 may be a single lens or a lens composed of a plurality of lenses, for example, a lens having two lenses.
[0023]
In the parallel light irradiation device 14 having the above-described configuration, light emitted from the light source 22 is collected by the condenser lens 24, and the collected light passes through the opening 27 of the diaphragm mechanism 26 and then passes through the collimating lens 24. The collimated lens 28 forms a parallel light 20 having a predetermined diameter, for example, a diameter of 12 mm. Then, the parallel light 20 is emitted from the parallel light irradiation device 14 to one main surface of the shadow mask 10. The aperture mechanism 26 can easily obtain the parallel light 20 having a desired spot diameter by making the size of the opening 27 adjustable. Also, by providing a mechanism for adjusting the relative position between the condenser lens 24 and the collimating lens 28, for example, by providing a mechanism for adjusting the optical axis and the eccentricity of the condenser lens 24 By adjusting the in-plane distribution of the parallel light 20 radiated to the shadow mask 10, it is possible to optimize the distribution.
[0024]
In the illustrated example, the condensing lens 24 and the collimating lens 28 are used to convert the light emitted from the light source 22 into parallel light, but the parallel light is generated using a Fresnel lens, a concave mirror, or the like. You may.
[0025]
FIG. 3 is a view of the light transmittance measuring device as viewed from the front. In this measuring device, the parallel light irradiation device 14 and the optical sensor 16 are three pairs in a direction parallel to the short side of the shadow mask 10 held by the pair of clamps 12, 12 (not shown in FIG. 3). It is juxtaposed. The central parallel light irradiation device 14a and the optical sensor 16a are fixed, and are arranged such that a line connecting the parallel light irradiation device 14a and the optical sensor 16a is perpendicular to the shadow mask 10. Further, the left and right parallel light irradiation devices 14b and optical sensors 16b and the parallel light irradiation devices 14c and optical sensors 16c respectively rotate integrally in a vertical plane along the shorter side of the shadow mask 10. So that they are supported by a lower movable plate 30 and an upper movable plate 32 which are interlocked with each other. The lower movable plate 30 and the upper movable plate 32 are movably supported by being guided by guide rails 34 and 36 disposed in parallel with the shorter side of the shadow mask 10, respectively, and the shadow to be inspected is provided. The positions of the parallel light irradiation devices 14b and 14c and the optical sensors 16b and 16c can be changed according to the size of the mask 10. Note that a plurality of parallel light irradiation devices 14 and optical sensors 16 may be arranged in parallel in a direction parallel to the long side of the shadow mask 10 gripped by the pair of clamps 12. Further, the configuration may be such that the parallel light irradiation device 14 and the optical sensor 16 rotate integrally in a vertical plane along the long side of the shadow mask 10.
[0026]
Further, the measuring device includes a pair of left and right ball screws 38, 38 arranged in the horizontal direction so as to be orthogonal to the paper surface of FIG. 3, and a stepping motor for rotating the respective ball screws 38 in the forward and reverse directions. 40, a driving mechanism including a driving pulley 42, a timing belt 44, and a driven pulley (not shown), a pair of left and right guide rails 46, 46 fixed in parallel with the ball screw 38, and screwed with the ball screw 38. A pair of left and right movable blocks 50, 50 having a nut member 48 and being intermittently moved in the front-rear direction by being guided by the guide rail 46 with forward and reverse rotation of the ball screw 38 are provided. The clamp table to which the pair of clamps 12, 12 are attached is connected to the pair of left and right movable blocks 50, 50, and the clamp table intermittently moves in the front-rear direction as the movable block 50 moves. It is configured as follows. The configuration may be such that the clamp table to which the clamps 12 holding the shadow mask 10 are attached is intermittently moved in a direction along the short side of the shadow mask 10. Further, the clamp table can be rotated in a horizontal plane about a vertical line passing through the center of the shadow mask 10 gripped by the pair of clamps 12 attached thereto, as a rotation center. A configuration having a moving mechanism may be adopted.
[0027]
Next, the operation of measuring the light transmittance of the shadow mask will be described. In the following description, the measurement operation will be described by taking as an example a case where the light transmittance at nine positions of the shadow mask is measured.
[0028]
First, the positions and inclinations of the parallel light irradiation devices 14b and 14c and the optical sensors 16b and 16c in the left and right direction are set according to the type and size of the shadow mask to be inspected, and then the shadow mask is moved to the parallel light irradiation devices 14a and 14b. , 14c and the optical sensors 16a, 16b, 16c are not interposed, and the parallel light irradiators 14a, 14b, 14c irradiate parallel light to measure the amount of incident light on the optical sensors 16a, 16b, 16c. Then, the measured value is input to the personal computer 18 and stored. Next, the shadow mask 10 to be inspected is set on a setting stand (not shown) with the surface on the phosphor side facing up when assembled into a color picture tube, and the pair of clamps 12, 12 is used to set the shadow mask 10. The ears on the two sides on the longitudinal side are gripped, and then a pair of clamps 12 and 12 are moved in the opposite directions by a small distance to apply tension to the shadow mask 10 so that the shadow mask 10 is completely flattened. State.
[0029]
When the above operation is completed, the clamp table is moved so that the first three measurement positions of the shadow mask 10 are within the vertical plane including the parallel light irradiation devices 14a, 14b, 14c and the optical sensors 16a, 16b, 16c. When it is positioned, the shadow mask 10 is stopped, and the parallel light irradiation devices 14a, 14b, and 14c irradiate parallel light. The parallel light irradiation devices 14a, 14b, and 14c irradiate the first three masks of the shadow mask 10. The parallel light transmitted through the measurement position is detected by the optical sensors 16a, 16b, and 16c, and the measured value of the amount of light incident on the optical sensors 16a, 16b, and 16c is input to the personal computer 18. Next, the clamp table is moved again so that the second three measurement positions (the center position in the longitudinal direction of the shadow mask 10) of the shadow mask 10 are aligned with the parallel light irradiation devices 14a, 14b, 14c and the optical sensors 16a, 16b, 16c, the shadow mask 10 is stopped again, and the parallel light irradiators 14a, 14b, and 14c irradiate parallel light, and the parallel masks are irradiated from the parallel light irradiators 14a, 14b, and 14c. The parallel light transmitted through the second three measurement positions of the shadow mask 10 is detected by the optical sensors 16a, 16b, and 16c, and the measured value of the amount of light incident on the optical sensors 16a, 16b, and 16c is input to the personal computer 18. Subsequently, the clamp table is moved again, and when the third three measurement positions are located in the vertical plane including the parallel light irradiation devices 14a, 14b, and 14c and the optical sensors 16a, 16b, and 16c, the shadow is returned again. The mask 10 is stopped, and parallel light is irradiated from the parallel light irradiation devices 14a, 14b, and 14c. The parallel light that is irradiated from the parallel light irradiation devices 14a, 14b, and 14c and passes through the third three measurement positions of the shadow mask 10 is transmitted. Light is detected by the optical sensors 16a, 16b, 16c, and the measured value of the amount of light incident on the optical sensors 16a, 16b, 16c is input to the personal computer 18. In this way, the measurement of the transmitted light amount at the nine measurement positions of the shadow mask 10 is performed. The light transmittance at each measurement position of the shadow mask 10 is determined by the light sensor 16a when the shadow mask 10 is not interposed between the parallel light irradiation devices 14a, 14b, 14c and the light sensors 16a, 16b, 16c. The ratio of the amount of incident light to the optical sensors 16a, 16b, and 16c at each measurement position with respect to the amount of incident light to 16b and 16c is determined by the personal computer 18 calculating the ratio.
[0030]
When the measurement of the amount of transmitted light at the third measurement position of the shadow mask 10 is completed, the shadow mask 10 is returned to the original set position. Then, after releasing the tension applied to the shadow mask 10, the clamp 12 is separated from the ear of the shadow mask 10, the shadow mask 10 is discharged out of the apparatus, and a series of measurement operations is completed.
[0031]
【The invention's effect】
According to the light transmittance measuring method of the invention according to claim 1, when measuring the light transmittance of a metal thin plate having a large number of through-holes, the angle of incidence of light on the surface of the metal thin plate is affected. It is possible to accurately measure the light transmittance at a plurality of positions on the thin metal plate without receiving it.
[0032]
The use of the light transmittance measuring device according to the second aspect of the present invention makes it possible to suitably execute the measuring method according to the first aspect of the present invention, and measures the light transmittance of a thin metal plate having a large number of through holes. In this case, the light transmittance at a plurality of positions on the thin metal plate can be accurately measured without being affected by the angle of incidence of light on the surface of the thin metal plate.
[0033]
In the measuring device according to the third aspect of the present invention, parallel light with high parallel accuracy can be created with a simple configuration.
[0034]
In the measuring device according to the fourth aspect of the present invention, parallel light having a desired spot diameter can be easily obtained.
[0035]
In the measuring device according to the fifth aspect of the present invention, when performing calibration by measuring the transmittance of the optical filter, it is easy to obtain an optical filter for calibration, and it is also possible to use a laser diode as a light source. Furthermore, there is no problem such as generation of a beat due to light interference in the periodic through hole pattern.
[0036]
In the measuring apparatus according to the sixth aspect of the present invention, it is possible to adjust the in-plane distribution of the parallel light applied to the thin metal plate to make it optimal.
[Brief description of the drawings]
FIG. 1 shows an embodiment of the present invention, and shows a basic configuration of a light transmittance measuring device used for measuring the light transmittance of a metal thin plate in which a large number of fine holes are formed, for example, a shadow mask. It is the schematic diagram which shows typically.
FIG. 2 is a schematic diagram showing a configuration of an optical system of a parallel light irradiation device which is one of the components of the light transmittance measurement device shown in FIG.
FIG. 3 is a view showing an example of the entire configuration of a light transmittance measurement device having the basic configuration shown in FIG. 1, and is a view of the measurement device as viewed from the front.
FIG. 4 is a schematic cross-sectional view schematically showing a basic configuration of a conventional shadow mask transmittance measuring device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Shadow mask 12 Clamp 14, 14a, 14b, 14c Parallel light irradiation device 16, 16a, 16b, 16c Optical sensor 18 Personal computer 20 Parallel light 22 Light source (LED)
24 Condensing lens 26 Aperture mechanism 27 Aperture aperture 28 Collimating lens

Claims (6)

The light emitted from the light source, shines irradiation to one side of the plurality of metal through holes are formed thin, and detected by the light detecting means light passing through the plurality of through holes of the metal sheet, said light source and said In the method of calculating the light transmittance of the metal thin plate, calculating from the respective incident light amounts to the light detecting unit when the metal thin plate is not interposed and between the light detecting unit ,
The holding means holds the two opposite sides of the metal thin plate respectively to hold the metal thin plate in a flattened state, and converts the light emitted from the light source into parallel light having a predetermined diameter, and then converts the parallel light into parallel light. A method for measuring the light transmittance of a metal sheet having a through hole, wherein the light is directly applied to one surface side of the metal sheet. Holding means having a pair of clamps respectively gripping two opposite sides of the metal sheet, and holding the metal sheet in a flattened state;
It is provided on one surface side of the metal sheet on which a large number of through holes are formed, and has parallel light forming means for converting light emitted from the light source into parallel light having a predetermined diameter, and directly to the one surface side of the metal sheet. Parallel light irradiation means for irradiating parallel light of a predetermined diameter,
Light detection means disposed on the other surface side of the metal thin plate and detecting light emitted from the parallel light irradiation means and passing through the plurality of through holes of the metal thin plate,
Calculate the light transmittance of the metal sheet from the respective amounts of light incident on the light detection means when the metal sheet is not interposed between the parallel light irradiation means and the light detection means and when the metal sheet is interposed. Computing means for performing
A light transmittance measuring device for a thin metal plate having a through hole, characterized by comprising: The parallel light forming means,
A condenser lens for condensing light emitted from the light source,
A collimating lens that converts the light condensed by the condensing lens into parallel light,
A diaphragm mechanism that is interposed on an optical path between the condenser lens and the collimator lens and has an opening through which light collected by the condenser lens passes;
3. The light transmittance measuring device for a metal thin plate having a through hole according to claim 2, wherein: The light transmittance measurement device for a metal thin plate having a through hole according to claim 3, wherein the aperture mechanism is capable of adjusting the size of the opening. The light transmittance measuring device for a thin metal plate having a through hole according to any one of claims 2 to 4, wherein the light source is an LED. 6. The light transmission of a metal thin plate having a through hole according to claim 2, further comprising a lens position adjusting mechanism for adjusting a relative position between the condenser lens and the collimating lens. Rate measuring device.

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