JPWO2018207400A1 - MTF measuring apparatus and MTF measuring method - Google Patents

Abstract

An object of the present invention is to provide an MTF measuring apparatus and an MTF measuring method capable of measuring the MTF of an optical device for light of any wavelength. The MTF measurement apparatus (100) for measuring the MTF of an optical device comprises a test chart (105) on which a test pattern having a light non-transmissive area and a light transmission area is formed, and light for irradiating the test chart. Using an output signal of a light source (101), a wavelength selection unit (102) for selecting a wavelength of light emitted from the light source, and a converter (solid-state imaging device 10) for photoelectrically converting the light emitted from the test chart And an arithmetic unit (107) for calculating the MTF. The wavelength selection unit (102) splits the light emitted from the light source (101) into a light separating element (diffraction grating 108) for extracting light of a specific wavelength, and the light incident on the light separating element (diffraction grating 108) And an adjusting mechanism (rotation mechanism 109) for changing the angle.

Description

  The present invention relates to an MTF measurement apparatus and an MTF measurement method for measuring the MTF of an optical device.

  Conventionally, OTF (Optical Transfer Function: optical transfer function) is known as a parameter | index which evaluates the performance of optical devices, such as a solid-state image sensor and a lens. MTF (Modulation Transfer Function: MTF), which is the real part of OTF, quantifies the sharpness of the image as a spatial frequency characteristic, and the larger the value of MTF, the higher the performance of the optical device.

  As an apparatus for measuring this MTF, Patent Document 1 discloses an MTF measuring apparatus provided with a light source and a test chart on which a test pattern is formed. The light source, the test chart, and the imaging device are arranged in this order on the optical path. A chart image generated by light emitted from the light source and having passed through the test pattern is photographed by the imaging device, and the MTF of the imaging device is calculated based on the output.

  Further, Patent Document 2 discloses an MTF measuring device provided with a light source, a test chart on which a test pattern is formed, and a light receiving device. Two optical filters having different wavelength selectivity are disposed between the light source and the test chart, and a rod lens is disposed between the test chart and the light receiving device on the optical path. The two optical filters are switched according to a predetermined control program. The MTF is calculated based on the intensity of light emitted from the light source, passing through the optical filter, the test chart, and the rod lens and entering the light receiving element.

JP, 2009-216450, A JP, 2011-164383, A

  Here, in general, optical devices have different MTFs depending on the wavelength of light. Therefore, there is a need for MTF measurement for light of any wavelength for MTF measurement devices. However, Patent Document 1 does not disclose a configuration for measuring MTF for light of a plurality of wavelengths. Moreover, in the MTF measurement device disclosed in Patent Document 2, in order to measure the MTF for light of a plurality of wavelengths (or wavelength ranges), it is necessary to use a plurality of optical filters. Therefore, it is substantially impossible to measure MTF for light of any wavelength using the same apparatus, or at least many optical filters need to be used.

  The present invention has been made to solve the problems as described above, and it is an object of the present invention to provide an MTF measuring apparatus and an MTF measuring method capable of measuring the MTF of an optical device for light of any wavelength. .

In one aspect of the invention:
An MTF measurement apparatus for measuring MTF of an optical device, comprising:
A test chart on which a test pattern having a light non-transmissive area and a light transmissive area is formed;
A light source for irradiating the test chart with light;
A wavelength selection unit for selecting a wavelength of light emitted from the light source;
An arithmetic unit for calculating an MTF using an output signal of a converter that photoelectrically converts light emitted from the test chart;
The wavelength selection unit has a light separating element for separating light emitted from the light source and extracting light of a specific wavelength, and an adjusting mechanism for adjusting an incident angle of light incident on the light separating element.
An MTF measuring device is provided.

  According to one aspect of the present invention, the MTF measurement apparatus includes a wavelength selection unit having a light separating element and an adjusting mechanism for adjusting the incident angle of light incident on the light separating element. The MTF of the optical device can be measured for light.

It is a figure which shows the MTF measuring apparatus based on Embodiment 1 of this invention. It is a top view which shows the test chart in which the pinhole was formed as a test pattern. It is a top view which shows the test chart in which the slit was formed as a test pattern. It is a top view which shows the test chart in which the edge was formed as a test pattern. It is a top view which shows the test chart in which the square wave pattern was formed as a test pattern. It is a flowchart which shows the MTF measurement method of a solid-state image sensor using the MTF measurement apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows the MTF measuring apparatus based on Embodiment 2 of this invention. It is a figure which shows the MTF measuring apparatus based on Embodiment 3 of this invention. It is a flowchart which shows the MTF measurement method of a 2nd optical system using the MTF measurement apparatus which concerns on Embodiment 3 of this invention. It is a figure which shows the MTF measuring apparatus based on Embodiment 4 of this invention.

  An MTF measurement apparatus according to an embodiment of the present invention will be described below with reference to the drawings. In each of the drawings, the same or similar components are denoted by the same reference numerals. In addition, detailed descriptions of already known matters and redundant descriptions of substantially the same configuration may be omitted to avoid unnecessary redundancy and facilitate the understanding of those skilled in the art. . Moreover, the contents of the following description and the attached drawings are not intended to limit the subject matter described in the claims.

Embodiment 1
(MTF measuring device 100)
FIG. 1 shows an MTF measurement apparatus 100 according to Embodiment 1 of the present invention. The MTF measurement apparatus 100 includes a light source 101, a wavelength selection unit 102, a light guide 103, a first optical system 104, a test chart 105, and a second optical system 106. In the first embodiment, the MTF of the solid-state imaging device 10 on which the light emitted from the second optical system 106 is incident is measured using the MTF measurement apparatus 100. The MTF value of the second optical system 106 is previously measured using another device, and is assumed to be a known value. The components (light source, light receiving element, etc.) 101 to 106 may be fixed on the same base member (not shown), or may be separately arranged.

  The solid-state imaging device 10 may be a charge coupled device (CCD) provided with a photodiode, a complementary metal oxide semiconductor (CMOS), or the like. The solid-state imaging device 10 is disposed such that the image forming plane of the solid-state imaging device 10 is a normal plane with respect to a projection center line connecting center points of the first optical system 104, the test chart 105, and the second ing. The solid-state imaging device 10 captures an image of the test chart 105. In the first embodiment, the solid-state imaging device 10 functions as a converter that photoelectrically converts light emitted from the test chart 105. The solid-state imaging device 10 is connected to a drive device 10 a that drives the solid-state imaging device 10 and an arithmetic device 107 capable of transmitting and receiving signals.

  The light source 101 emits light 11. The light source 101 may be any light source, for example, a white light source.

  The wavelength selection unit 102 has a diffraction grating 108 and a rotation mechanism 109. The diffraction grating 108 is an example of a light separating element, and has a function of dispersing the light 11 emitted from the light source 101 and extracting and emitting the light 12 of a specific wavelength. Although a reflective diffraction grating is illustrated as the diffraction grating 108 in the drawing, it may be a transmission diffraction grating. The rotation mechanism 109 is fixed to the diffraction grating 108, and is configured to rotate integrally with the diffraction grating 108 with respect to the light source 101. The rotation mechanism 109 may be a motor having a table on which the diffraction grating 108 is mounted and an output shaft to which the table is attached. The motor may be a motor (for example, a stepping motor, a servomotor) capable of controlling the rotation angle of the table (and hence of the diffraction grating 108). Thus, rotation of the diffraction grating 108 changes and adjusts the incident angle of light incident on the diffraction grating 108 and changes the wavelength of the light 12 emitted.

  The light guide 103 has a function of guiding the light 12 of the specific wavelength emitted from the diffraction grating 108 of the wavelength selection unit 102 to the test chart 105. The light guide 103 has an incident end 103 a and an output end 103 b. In the embodiment, the light guide 103 is an optical fiber having a core and a cladding. By using the light guide 103, the traveling direction of the light 12 emitted from the diffraction grating 108 can be controlled. In addition, the light incident on the light guide 103 travels in the core and is totally totally reflected at the interface with the cladding. Thus, the light 13 can be emitted from the emission end 103 b in a state in which the uniformity of the light 12 incident on the incident end 103 a of the light guide 103 is improved. This improves the accuracy of the measured MTF.

  The first optical system 104 is disposed between the emission end 103 b of the light guide 103 and the test chart 105 on the light path. The first optical system 104 has a function of condensing the light 13 emitted from the light guide 103 and causing the light 13 to be incident on the test chart 105. Although one lens is shown as the first optical system 104 in the drawings, the present invention is not limited to this, and the first optical system 104 may be configured by a plurality of lenses, for example. By configuring the first optical system 104 with a plurality of lenses, there is an advantage that aberration correction and focal length adjustment become possible.

  The test chart 105 is formed with a test pattern having a light non-transmissive area and a light transmissive area. The test pattern may have any shape but is for example selected from the group consisting of pinholes (FIG. 2), slits (FIG. 3), edges (FIG. 4), and square wave patterns (FIG. 5) Ru. The test pattern of the test chart 105 is formed by providing a light impermeable material on the light transmitting member. The light transmitting member may be, for example, a transparent film or a transparent glass, and may be rectangular or flat. The light impermeable material may be made of any material, such as, for example, chromium oxide, and may be provided using any method, such as, for example, painting, printing, vapor deposition.

  The second optical system 106 is disposed between the test chart 105 and the solid-state imaging device 10 on the light path. The second optical system 106 has a function of focusing the light 14 having passed through the light transmission area of the test pattern formed on the test chart 105 on the pixel area of the solid-state imaging device 10. The second optical system 106 is preferably a telecentric optical system in which the chief ray is arranged to pass through the focal point. By using a telecentric optical system as the second optical system 106, the chief ray emitted from the test chart 105 passes through the focal point, so that the size of the image center changes even if the focal point deviates, and uniform illuminance is obtained over the entire field of view. Has the advantage of Although one lens is shown as the second optical system 106 in the drawings, the present invention is not limited to this, and the second optical system 106 may be composed of, for example, a plurality of lenses. By configuring the second optical system 106 with a plurality of lenses, there is an advantage that aberration correction and focal length adjustment become possible.

  The arithmetic unit 107 may be a microcomputer having a CPU (central processing unit) and a memory storing a predetermined program, and performs a predetermined operation on pixel signals output from the solid-state imaging device 10. , MTF can be calculated. The specific calculation method of MTF is mentioned later.

(Measurement method of MTF)
Next, a method of measuring the MTF of the solid-state imaging device 10 using the MTF measuring device 100 according to the first embodiment will be described with reference to FIG.

  In step 111, the test chart 105 is irradiated with the light 11 emitted from the light source 101 via the diffraction grating 108 of the wavelength selection unit 102, the light guide 103, and the first optical system 104. At this time, the incident angle of the light 11 emitted from the light source 101 is set to a predetermined angle by the rotation angle of the rotation mechanism 109. Thereby, the wavelength of the light taken out by the diffraction grating 108 is determined. A part of the light 13 irradiated to the test chart 105 is blocked by the light non-transmissive area in the test pattern of the test chart 105, and another part is transmitted through the light transmissive area. Thereby, the test pattern of the test chart 105 is projected onto the pixel area of the solid-state imaging device 10 via the second optical system 106 (that is, the chart image of the test chart 105 is photographed by the solid-state imaging device 10).

  In step 112, the light of the projected test pattern (that is, the light transmitted through the light transmission region) is photoelectrically converted by the solid-state imaging device 10, the test pattern is photographed, and is output as a pixel signal and input to the arithmetic device 107. Be done.

  In step 113, the pixel signal output from the solid-state imaging device 10 is processed by the arithmetic device 107 to calculate MTF. Here, the MTF may be calculated by any method, for example, may be calculated using a known Fourier transform method, or may be calculated using a known contrast method.

  In the Fourier transform method, first, an output distribution for a local light input is measured to obtain a spread function (SF) of the output. A spread function obtained when light enters the solid-state imaging device 10 through the light transmission regions of the test charts 105A, 105B, and 105C in which pinholes, slits, and edges are formed as test patterns shown in FIGS. 2 to 4. Are respectively called PSF (Point Spread Function), LSF (Line Spread Function), and ESF (Edge Spread Function). By Fourier transforming the spread function SF, an OTF is obtained. The resulting OTF is a complex function whose real part is the MTF. LSF can also be determined by differentiating ESF.

  In the contrast method, the output to the input of sine waves having various frequencies is measured, the response function is obtained from the contrast ratio of the input and output, and the MTF is calculated from this response function. The rectangular wave response function obtained when light enters the solid-state imaging device 10 through the light transmission region of the test chart 105D in which the rectangular wave pattern shown in FIG. 5 is formed is called SWRF (Square Wave Response Function). Ru. The MTF is obtained by correcting the SWRF to a sinusoidal response function.

  The MTF obtained by the measurement is a value obtained by adding the MTF of the second optical system 106 and the MTF of the solid-state imaging device 10. By subtracting the MTF of the known second optical system 106 from the measured MTF, the MTF of only the solid-state imaging device 10 is calculated.

  Next, the rotation mechanism 119 is rotated at a desired angle to change the incident angle of light incident on the diffraction grating 108, whereby the wavelength of the light 12 emitted from the diffraction grating 108 is changed. And MTF of solid-state image sensor 10 can be measured about the wavelength after change by carrying out Steps 111-113 shown in Drawing 6 again. By repeating this operation, the MTF of the solid-state imaging device 10 can be measured for light of any wavelength.

  Here, in the solid-state imaging device 10, it is preferable to measure the MTF for light of any wavelength. In the first embodiment, MTF measurement of the solid-state imaging device 10 can be completed using one MTF measurement device 100. In addition, one type of solid-state imaging device may require MTF measurement of light of a certain wavelength, and another type of solid-state imaging device may require MTF measurement of light of another wavelength. In the first embodiment, even in such a situation, MTFs of plural types of solid-state imaging devices can be measured using one MTF measuring device 100.

Second Embodiment
FIG. 7 is a diagram showing an MTF measurement apparatus 200 according to Embodiment 2 of the present invention. In the description of the MTF measurement apparatus 200, the same or similar components as or to those of the MTF measurement apparatus 100 according to the first embodiment may be assigned the same reference numerals and descriptions thereof may be omitted.

  The MTF measurement apparatus 200 includes a second wavelength selection unit 202 in addition to the MTF measurement apparatus 100 according to the first embodiment. The second wavelength selection unit 202 includes an optical filter 203 and a reflector 204. The optical filter 203 has a function of selectively transmitting light of a specific wavelength or light of a specific wavelength range. For example, the optical filter 203 may be a long pass filter, a short pass filter, or a band pass filter that transmits light in a predetermined wavelength range. The optical filter 203 may be a dielectric multilayer film which selects a wavelength by an interference effect of light, or may be a filter glass which selects a wavelength by absorption of light. The reflecting plate 204 has a function of changing the traveling direction of the light 11 emitted from the light source 101.

  The second wavelength selection unit 202 is provided so as to be switchable between the wavelength selection unit 102 having the diffraction grating 108 and the rotation mechanism 109 (hereinafter, referred to as a first wavelength selection unit). The switching operation between the first wavelength selection unit 102 and the second wavelength selection unit 202 may be performed manually or may be performed automatically by an actuator (not shown). For example, the wavelength selection units 102 and 202 are disposed on a turntable provided with a switch, and the turntable is rotated by pressing of the switch by the user, and the first wavelength selection unit 102 and the second wavelength selection unit 202 May be switched.

  The MTF measurement method of the solid-state imaging device 10 described in the first embodiment can be implemented using the MTF measurement device 200 according to the second embodiment. When the first wavelength selection unit 102 is selected among the first and second wavelength selection units 102 and 202, the first wavelength selection unit 102 is selected according to the rotation angle of the rotation mechanism 109, and is extracted by the diffraction grating 108. Light is incident on the test chart 105. On the other hand, when the second wavelength selection unit 202 is selected out of the first and second wavelength selection units 102 and 202, the optical filter 203 among the light emitted from the light source 101 and reflected by the reflection plate 204. For example, the light of a specific wavelength range extracted by the above is incident on the test chart 105.

  According to the second embodiment, the first and second wavelength selection units according to the characteristics of the solid-state imaging device 10, that is, according to the wavelength (or wavelength range) where the measurement of the MTF is required in the solid-state imaging device 10. 102 and 202 can be switched and used as needed. For example, one type of solid-state imaging device may require MTF measurement for light of a particular wavelength, and another type of solid-state imaging device may require MTF measurement for light of a certain wavelength range. In the second embodiment, even in such a situation, MTFs of a plurality of solid-state imaging devices can be measured using one MTF measuring device 100.

Third Embodiment
FIG. 7 is a diagram showing an MTF measurement apparatus 300 according to Embodiment 3 of the present invention. In the description of the MTF measurement apparatus 300, the same or similar components as or to those of the MTF measurement apparatus 100 and 200 according to the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The MTF measurement apparatus 300 includes a light receiving element 310 in addition to the light source 101 described in the first embodiment, the wavelength selection unit 102, the light guide 103, the first optical system 104, and the test chart 105. In the third embodiment, the light receiving element 310 functions as a converter that photoelectrically converts light emitted from the test chart 105. In the third embodiment, the MTF of the second optical system 30 disposed between the test chart 105 and the light receiving element 310 on the optical path is measured using the MTF measuring device 300. The value of the MTF of the light receiving element 310 is previously measured using another device, and is assumed to be a known value. The parts 101 to 105, 310 may be fixed on the same base member (not shown) or may be separately arranged.

  Similar to the solid-state imaging device 10 described in the first embodiment, the light receiving device 310 is connected to a driving device 310 a that drives the light receiving device 310 and an arithmetic device 107 capable of transmitting and receiving signals. The arithmetic device 107 is configured to calculate MTF by performing a predetermined operation on the pixel signal output from the light receiving element 310.

  Next, a method of measuring the MTF of the second optical system 30 using the MTF measuring device 300 according to the third embodiment will be described with reference to FIG.

  In step 311, the test chart 105 is irradiated with the light 11 emitted from the light source 101 via the diffraction grating 108 of the wavelength selection unit 102, the light guide 103, and the first optical system 104. At this time, the incident angle of the light 11 emitted from the light source 101 is set to a predetermined angle by the rotation angle of the rotation mechanism 109. Thereby, the wavelength of the light taken out by the diffraction grating 108 is determined. A part of the light 13 irradiated to the test chart 105 is blocked by the light non-transmissive area in the test pattern of the test chart 105, and another part is transmitted through the light transmissive area. Thereby, the test pattern of the test chart 105 is projected on the light receiving surface of the light receiving element 310 via the second optical system 30.

  In step 312, the light of the projected test pattern (that is, the light transmitted through the light transmission region) is photoelectrically converted by the light receiving element 310, and an output signal is input to the arithmetic device 107.

  In step 113, the output signal of the solid-state imaging device 10 is processed by the arithmetic unit 107 to calculate MTF. Here, the MTF may be calculated by any method, for example, may be calculated using a Fourier transform method, or may be calculated using a contrast method. These methods are as described above.

  The wavelength of the light 12 emitted from the diffraction grating 108 is changed by rotating the rotation mechanism 119 at a desired angle and changing the incident angle of the light incident on the diffraction grating 108. And MTF of the 2nd optical system 30 can be measured about the wavelength after change by performing steps 311-313 shown in FIG. 9 again. By repeating this operation, the MTF of the second optical system 30 can be measured for light of any wavelength.

Fourth Embodiment
FIG. 8 is a diagram showing an MTF measurement apparatus 400 according to Embodiment 4 of the present invention. In the description of the MTF measuring apparatus 400, the same or similar components as or to those of the MTF measuring apparatuses 100, 200, and 300 according to the first to third embodiments are designated by the same reference numerals, and the description thereof is omitted.

  The MTF measurement apparatus 400 includes the second wavelength selection unit 202 described in the second embodiment, in addition to the MTF measurement apparatus 300 according to the third embodiment. The configuration of the second wavelength selection unit 202 is as described above.

  The MTF measurement method of the second optical system 30 described in the third embodiment can be implemented using the MTF measurement device 400 according to the fourth embodiment.

  According to the fourth embodiment, the first and second wavelengths are determined according to the characteristics of the second optical system 30, that is, according to the wavelength (or wavelength range) in which the MTF needs to be measured in the second optical system 30. The selection units 102 and 202 can be switched and used as needed. For example, one type of optical system may require MTF measurement of light of a particular wavelength, and another type of optical system may require MTF measurement of light of a certain wavelength range. In the fourth embodiment, even in such a situation, MTFs of a plurality of types of second optical systems can be measured using one MTF measuring device 400.

(Modification)
Although the present invention has been described above using a plurality of embodiments, the features described in each embodiment may be freely combined. In addition, various improvements, design changes, and deletions may be added to the above-described embodiment, and various modifications exist to the present invention.

  For example, although the above-mentioned embodiment explained the example which uses diffraction grating 108 as a spectroscopy element, the present invention is not limited to this, and may use other spectroscopy elements, such as a prism.

  Further, in the above embodiment, the rotation mechanism 109 is used as an adjustment mechanism for changing the incident angle of light incident on the diffraction grating 108, but the present invention is not limited to this, for example, A rotatable mirror provided between the diffraction grating 108 may be used as an adjustment mechanism.

  In the above embodiment, although the example using the light guide 103 and the first optical system 104 has been described, the present invention is not limited to this, and these components are omitted, and the wavelength selection units 102 and 202 are used. The light may be made to enter the test chart 105 directly.

  In the above embodiment, an example using the light guide 103 has been described as a mechanism for improving the uniformity of light, but the present invention is not limited to this, and light such as a diffusion plate or a lens array may be used. Other mechanisms may be utilized to improve the uniformity of the Furthermore, the light guide 103 may be used in combination with a diffusion plate or a lens array.

  In the above-described embodiments, the first and second embodiments are described as an example of measuring the MTF of the solid-state imaging device 10, and the third and fourth embodiments are described as an example of measuring the MTF of the second optical system 30. For example, a second optical system having a known MTF value is arranged to constitute an MTF measuring device for measuring the MTF of the solid-state imaging device, and then the solid-state imaging device is replaced with a light receiving element having a known MTF value, The second optical system may be replaced with one whose MTF is not known to constitute an MTF measuring device for measuring the MTF of the second optical system.

(Aspects of the Invention)
Next, the MTF measuring apparatus according to the first aspect of the present invention and the MTF measuring method according to the second aspect will be described using the reference numerals given in the above-described embodiment. It is to be understood that the reference numerals given to the respective constituent elements do not limit the scope of the present invention.

  In a first aspect of the invention, an MTF measuring device 100, 200, 300, 400 for measuring the MTF of an optical device is provided. The MTF measuring apparatus includes a test chart 105 on which a test pattern having a light non-transmissive area and a light transmission area is formed, a light source 101 for irradiating the test chart 105 with light, and wavelengths of light emitted from the light source 101. The wavelength selection unit 102 for selection and an arithmetic unit 107 for calculating the MTF using an output signal of a converter that photoelectrically converts light emitted from the test chart 105 are provided. The wavelength selection units 102 and 202 have a spectral element for separating light emitted from the light source 101 and extracting light of a specific wavelength, and an adjustment mechanism for changing the incident angle of light incident on the spectral element. ing.

  According to the first aspect of the present invention, the MTF measurement apparatus 100, 200, 300, 400 includes the spectral element and the wavelength selection unit 102 having the adjustment mechanism for changing the incident angle of light incident on the spectral element. By measuring the MTF of the optical device for light of any wavelength.

  In one embodiment of the first aspect of the present invention, a solid-state imaging device 10 is used as a converter. Further, the MTF measuring apparatus 100, 200 is disposed between the test chart 105 and the solid-state imaging device 10 on the optical path, and focuses the light passing through the light transmission region of the test pattern on the pixel region of the solid-state imaging device 10. The second optical system 106 is further provided. Then, the MTF measuring devices 100 and 200 measure the MTF of the solid-state imaging device 10 as the MTF of the optical device.

  According to this embodiment, the light emitted from the light source 101 is irradiated to the light separating element of the wavelength selection unit 102, while a part of the light emitted from the light separating element is blocked by the light non-transmissive area in the test pattern of the test chart 105. And another part is transmitted through the light transmission area. Thereby, the test pattern of the test chart 105 is projected onto the pixel area of the solid-state imaging device 10 via the second optical system 106, and the output of the solid-state imaging device 10 is transmitted to the arithmetic device 107. Thus, the MTF of the solid-state imaging device 10 is calculated. In this manner, the effects obtained by one aspect of the present invention are specifically achieved.

  In an embodiment of the first aspect of the present invention, the MTF measuring device 300, 400 comprises a light receiving element 310 as a transducer. In addition, the MTF measuring devices 300 and 400 are disposed between the test chart 105 and the light receiving element 310 on the optical path as MTFs of an optical device, and form a test pattern on the light receiving surface of the light receiving element 310. The MTF of the optical system 30 is measured.

  According to this embodiment, the light emitted from the light source 101 is irradiated to the light separating element of the wavelength selection unit 102, while a part of the light emitted from the light separating element is blocked by the light non-transmissive area in the test pattern of the test chart 105. And another part is transmitted through the light transmission area. Thereby, the test pattern of the test chart 105 is projected onto the light receiving surface of the light receiving element 310 through the second optical system 30, and the output of the light receiving element 310 is transmitted to the arithmetic device 107. The MTF is calculated. In this way, the effects obtained by the first aspect of the present invention are specifically achieved.

  Here, the second optical system 106 may be a telecentric optical system. By using a telecentric optical system, the chief ray passes through the focal point, so that the size of the image center changes even if the focal point deviates, and uniform illuminance can be obtained over the entire field of view.

  In the first aspect of the invention, the spectroscopic element may be a diffraction grating 108 or a prism.

  In a first aspect of the invention, the adjustment mechanism may comprise a rotation mechanism 109 configured to rotate the spectroscopic element relative to the light source.

  In one embodiment of the first aspect of the present invention, the MTF measurement apparatus 200, 400 includes a second wavelength in addition to the wavelength selection unit (referred to as a first wavelength selection unit) 102 having a dispersive element and an adjustment mechanism. A selection unit 202 is further provided. The second wavelength selection unit 202 is provided switchably with the first wavelength selection unit 102. The second wavelength selection unit 202 has an optical filter 203.

  According to this embodiment, in the optical device to be subjected to MTF measurement, the first and second wavelength selectors 102 and 202 can be arbitrarily switched and used according to the wavelength (or wavelength range) where the MTF needs to be measured. .

  In one embodiment of the first aspect of the present invention, the MTF measuring apparatus 100, 200, 300, 400 includes the light guide 103 for guiding the light of the specific wavelength emitted from the wavelength selecting unit 102, 202 to the test chart 105. The optical system further includes a first optical system 104 disposed between the exit end 103b of the light guide 103 and the test chart 105 on the optical path and for condensing light emitted from the light guide 103.

  According to this embodiment, by using the light guide 103, the traveling direction of the light emitted from the light separating element can be controlled. In addition, the light incident on the light guide 103 travels in the core and is totally totally reflected at the interface with the cladding. Thereby, the light can be emitted from the emission end 104 b in a state where the uniformity of the light incident on the incidence end 104 a of the light guide 103 is improved. This improves the accuracy of the measured MTF.

  In the first aspect of the present invention, the test pattern formed on the test chart 105 may be selected from the group consisting of pinholes, slits, edges, and square wave patterns.

  In a second aspect of the present invention, an MTF measurement method for measuring the MTF of an optical device (solid-state imaging device 10, second optical system 30, etc.) is provided. In the MTF measuring method, a step of selecting a wavelength of light emitted from the light source 101 using the wavelength selection unit 102, and a test pattern having a light non-transmissive region and a light transmission region of the light emitted from the wavelength selection unit 102 And a step of photoelectrically converting light emitted from the test chart 105 by using a converter (the solid-state imaging device 10, the light receiving element 310, etc.), and a step of Calculating the MTF using the output signal. The step of selecting the wavelength of light includes the step of separating the light emitted from the light source 101 using the spectral element (such as the diffraction grating 108) included in the wavelength selection unit 102 and extracting light of a specific wavelength; Adjusting the incident angle of the light incident on the light separating element 108 using the adjusting mechanism (rotation mechanism 109 or the like) included in 102.

  According to the second aspect of the present invention, the light emitted from the light source 101 is dispersed by using the light separating element 108, and light of a specific wavelength is extracted. At this time, the incident angle of light incident on the light separating element 108 is adjusted using the adjusting mechanism 109. In this way, the MTFs of the optical devices 10 and 30 can be measured for light of any wavelength.

DESCRIPTION OF SYMBOLS 10 solid-state image sensor, 10a drive device, 11-14 light, 30 2nd optical system, 100, 200, 300, 400 MTF measuring apparatus, 101 light source, 102, 202
Wavelength selector 103 light guide 104 first optical system 105, 105A, 105B, 105C, 105D test chart 106 second optical system 107 arithmetic unit 108 diffraction grating 109 rotation mechanism 310 light receiving element 310a drive apparatus

Claims (11)

An MTF measurement apparatus for measuring MTF of an optical device, comprising:
A test chart on which a test pattern having a light non-transmissive area and a light transmissive area is formed;
A light source for irradiating the test chart with light;
A wavelength selection unit for selecting a wavelength of light emitted from the light source;
An arithmetic unit for calculating an MTF using an output signal of a converter that photoelectrically converts light emitted from the test chart;
The wavelength selection unit has a light separating element for separating light emitted from the light source and extracting light of a specific wavelength, and an adjusting mechanism for adjusting an incident angle of light incident on the light separating element.
MTF measuring device. A solid-state imaging device is used as the converter,
The optical system further includes a second optical system disposed on the light path between the test chart and the solid-state imaging device, for focusing light passing through the light transmission region of the test pattern on a pixel region of the solid-state imaging device. ,
The MTF measurement apparatus measures the MTF of the solid-state imaging device as the MTF of the optical device.
The MTF measuring device according to claim 1. A light receiving element is provided as the converter,
The MTF measurement apparatus is disposed between the test chart and the light receiving element on an optical path as an MTF of the optical device, and a second optical system for forming an image of the test pattern on the light receiving surface of the light receiving element. To measure the MTF of
The MTF measuring device according to claim 1. The second optical system is a telecentric optical system.
The MTF measuring device according to claim 2 or 3. The spectroscopic element is a diffraction grating or a prism.
The MTF measuring device according to any one of claims 1 to 4. The adjustment mechanism comprises a rotation mechanism configured to rotate the dispersive element relative to the light source,
The MTF measuring device according to any one of claims 1 to 5. It further comprises a second wavelength selector switchably provided between the light separating element and the first wavelength selector having the adjusting mechanism,
The second wavelength selector includes an optical filter.
The MTF measuring device according to any one of claims 1 to 6. A light guide for guiding light of a specific wavelength emitted from the wavelength selection unit to the test chart;
The optical system further comprises: a first optical system disposed on the light path between the exit end of the light guide and the test chart, for condensing light emitted from the light guide.
The MTF measuring device according to any one of claims 1 to 7. A diffuser plate or a lens array for guiding light of a specific wavelength emitted from the wavelength selection unit to the test chart;
The optical system further comprises a first optical system disposed on the light path between the diffusion plate or lens array and the test chart, for condensing light emitted from the diffusion plate or lens array.
The MTF measuring device according to any one of claims 1 to 8. The test pattern formed on the test chart is selected from the group consisting of pinholes, slits, edges, and square wave patterns,
The MTF measuring device according to any one of claims 1 to 9. A method for measuring MTF of an optical device, comprising:
Selecting a wavelength of light emitted from the light source using a wavelength selection unit;
Causing the light emitted from the wavelength selection unit to be incident on a test chart on which a test pattern having a light non-transmissive area and a light transmissive area is formed;
Photoelectrically converting light emitted from the test chart using a converter;
Calculating MTF using the output signal of the converter;
The step of selecting the wavelength of the light comprises
Using the spectral element included in the wavelength selection unit, to split the light emitted from the light source to extract light of a specific wavelength;
Adjusting an incident angle of light incident on the light separating element using an adjusting mechanism included in the wavelength selection unit.
MTF measurement method.

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