US4060328A
Expired / Lapsed
US
⏱️ 0.0 years remaining
System for measuring the modulation transfer function of an optical device
Assignee: Varo Inc
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Filing: 1976-02-06
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Granted: 1977-11-29
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Expires: 1996-02-06
Abstract
Abstract A slit image is projected through the optical device being measured and onto the optical input screen of a variable-gain photomultiplier tube. Before it is incident upon the input screen of the tube, the projected image is modulated to develop simultaneously a low-frequency image component and one or more higher-frequency image components. Electronic filters are employed to separate the electrical output signal of the photomultiplier tube into discrete electrical signals each representative of a different one of the image components, and one or more meters are used to indicate the relative amplitudes thereof. A phase-locked-loop detector and an amplifier are employed between each filter and meter to improve the signal-to-noise ratio of the system and increase the signal amplitude to a level suitable for driving the meter. In one embodiment, the overall gain of the system is manually adjusted until the meter reads 100 percent MTF for the low-frequency component. A normalized MTF measurement at each of the higher frequencies is indicated either on the same meter, by using a switch, or on a separate meter for each frequency. In another embodiment, a closed-loop feedback circuit comprising a comparator circuit which compares the amplitude of the low-frequency electrical signal with that of a reference signal and generates an error signal which is coupled to the photomultiplier tube to automatically adjust the system such that a 100 percent MTF reading is obtained for the low-frequency component throughout the entire time that the optical device is being measured.
Inventors
- 👤 William E. Flynt
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 22:29
CPC Classifications
G; G01; G01M; G01M11/00; G01M11/02; G01M11/0292
Claims Analysis
Total Claims: 25
Claim 1
Independent Claim
334 words
A system for determining the image-forming quality of an optical device by projecting an image through said device and measuring the relative amount of light transmitted therethrough at a plurality of spatial frequencies, with said system determinations being normalized automatically and continuously throughout the duration of the evaluation of the optical devices under test, said system comprising: photoelectric transducer means, including an optical input section and an electrical output section, for converting a light signal incident upon said input section into a corresponding electrical signal at said output section; means for projecting said image along a projection path through said optical device and onto said optical input section; means disposed in said projection path for modulating said projected image to produce simultaneously a low-frequency image component incident upon said optical input section and at least one higher-frequency image component incident upon said optical input section; a plurality of filter means respectively tuned to the frequency of each of said image component and coupled to the electrical output section of said photoelectric transducer means for developing a corresponding plurality of discrete electrical signals each representative of a different one of said image components; indicating means coupled to said filter means for indicating the amplitude of said discrete electrical signals; and means for adjusting said system to cause said indicating means to indicate a predetermined amplitude for said low-frequency image component, said adjusting means comprising means for comparing the amplitude of said discrete low-frequency signal with the amplitude of a preselected reference signal and generating an error signal which automatically adjusts said system to substantially equalize the amplitude of said reference signal and said low-frequency signal, whereby the system is automatically and continuously set to a normalized level for the optical device being measured during the evaluation of the optical device under test and with the higher-frequency image components then capable of being measured under a standardized system for determining the image-forming quality of a series of optical devices at one or more higher spatial frequencies.
Claim 2
Independent Claim
334 words
A system for determining the image-forming quality of an optical device by projecting an image through said device and measuring the relative amount of light transmitted therethrough at a plurality of spatial frequencies, with said system determinations being normalized automatically and continuously throughout the duration of the evaluation of the optical devices under test, said system comprising: photoelectric transducer means, including an optical input section and an electrical output section, for converting a light signal incident upon said input section into a corresponding electrical signal at said output section; means for projecting said image along a projection path through said optical device and onto said optical input section; means disposed in said projection path for modulating said projected image to produce simultaneously a low-frequency image component incident upon said optical input section and at least one higher-frequency image component incident upon said optical input section; a plurality of filter means respectively tuned to the frequency of each of said image component and coupled to the electrical output section of said photoelectric transducer means for developing a corresponding plurality of discrete electrical signals each representative of a different one of said image components; indicating means coupled to said filter means for indicating the amplitude of said discrete electrical signals; and means for adjusting said system to cause said indicating means to indicate a predetermined amplitude for said low-frequency image component, said adjusting means comprising means for comparing the amplitude of said discrete low-frequency signal with the amplitude of a preselected reference signal and generating an error signal which automatically adjusts said system to substantially equalize the amplitude of said reference signal and said low-frequency signal, whereby the system is automatically and continuously set to a normalized level for the optical device being measured during the evaluation of the optical device under test and with the higher-frequency image components then capable of being measured under a standardized system for determining the image-forming quality of a series of optical devices at one or more higher spatial frequencies.
Claim 3
Dependent Claim
32 words
A system in accordance with claim 1, in which said indicating means comprises a plurality of meters respectively coupled to said filter means for indicating the amplitudes of said discrete electrical signals.
Claim 4
Dependent Claim
97 words
A system in accordance with claim 1 in which said indicating means comprises a meter and switch means having an output terminal, with said meter coupled to said output terminal and said switch means coupled to said filter means, for selectively coupling one of said discrete electrical signals to said meter, whereby the system may be operated with a single meter by first making the low-frequency reading and adjusting the system to the predetermined amplitude for the low-frequency reading to thus normalize the apparatus, and then switching the meter to indicate the amplitude of a higher-frequency signal.
Claim 5
Dependent Claim
60 words
A system in accordance with claim 1, in which said photoelectric transducer means comprises a photomultiplier tube having a light input screen and an electrical output terminal for converting a given amount of light incident upon said input screen into a corresponding electrical signal at said output terminal at an amplitude which varies in accordance with an externally-applied control signal.
Claim 6
Dependent Claim
124 words
A system in accordance with claim 1, in which said image modulating means comprises a motor and a pattern wheel rotationally driven by said motor at a predetermined speed and including a continuous series of alternately transparent and opaque areas, with a predetermined number of said transparent areas having an area which bears a first ratio relative to the area of a corresponding number of said opaque areas and the remaining number of said transparent areas having an area which bears a second ratio relative to the remaining number of said opaque areas, said second ratio being the inverse of said first ratio, whereby the rotating pattern wheel modulates the projected image to produce simultaneously a low-frequency image component and a higher-frequency image component.
Claim 7
Dependent Claim
16 words
A system in accordance with claim 5, in which said predetermined ratio is 1.5 to 1.
Claim 8
Dependent Claim
104 words
A system in accordance with claim 1, in which said modulating means comprises a motor and a pattern wheel rotationally driven by said motor at a predetermined speed, said pattern wheel comprising a plurality of arcuate pattern bands disposed in a concentric relationship, with each said band having a continuous series of alternately transparent and opaque areas of substantially the same size and shape and the total number of said areas representing a predetermined spatial frequency at said rotational speed, whereby one of said bands modulates the image at a low-frequency rate and the other bands simultaneously modulate the image at preselected higher-frequency rates.
Claim 9
Dependent Claim
19 words
A system in accordance with claim 7, in which the shape of said transparent and opaque areas is trapezoidal.
Claim 10
Dependent Claim
18 words
A system in accordance with claim 1, in which said image component frequencies are related by even harmonics.
Claim 11
Dependent Claim
46 words
A system in accordance with claim 1, in which each said filter means includes a phase-locked-loop detector tuned to one of said image component frequencies and responsive to the electrical signal applied to said filter means for increasing the signal-to-noise ratio of said discrete electrical signal.
Claim 12
Dependent Claim
161 words
A system in accordance with claim 1, in which said photoelectric transducer means comprises a photomultiplier tube having a light input screen, an electrical output terminal, and a gain control terminal for converting a selected amount of light incident upon said input screen into a corresponding electrical signal at said output terminal at an amplitude which varies systematically in accordance with an externally-applied gain control signal applied to said gain control terminal; and in which said comparing means comprises a comparator circuit coupled between said filter means and said photomultiplier tube and responsive to said discrete low-frequency signal for comparing the amplitude of said discrete low-frequency signal with a predetermined reference signal amplitude and developing a corresponding error signal which is applied to said gain control terminal of said photomultiplier tube to adjust the amplitude of said electrical signal until the amplitude of said discrete low-frequency signal corresponds to the amplitude of said reference signal, whereby said system is automatically normalized.
Claim 13
Independent Claim
416 words
A system for determining the image-forming quality of an optical device by projecting an image through said device and measuring the relative amount of light transmitted therethrough at a plurality of spatial frequencies, with said system determinations being normalized automatically and continuously throughout the duration of the evaluation of the optical device under test, said system comprising: photoelectric transducer means, including an optical input screen, an electrical output terminal, and a gain control terminal, for converting a light signal incident upon said input screen into a corresponding electrical signal at said output terminal at an amplitude which varies systematically in accordance with an externally-applied gain control signal applied to said gain control terminal; means for projecting said image along a path through said optical device and onto said optical input screen; means, including a motor and a pattern wheel rotationally driven by said motor at a predetermined speed, disposed in said projection path for modulating said projected image to produce simultaneously a low-frequency image component incident upon said optical input screen and at least one higher-frequency image component incident upon said optical input screen; a plurality of filter means respectively tuned to the frequency of each said image component and coupled to the electrical output section of said photoelectric transducer means for developing a corresponding plurality of discrete electrical signals each representative of a different one of said image components; indicating means coupled to said filter means for indicating the amplitude of said discrete electrical signals; means for generating said gain control signal; and means for adjusting said gain control signal generating means to cause said photoelectric transducer means to develop at said output terminal an electrical signal corresponding to said low-frequency image component at an amplitude which causes said indicating means to give a predetermined reading, said adjusting means comprising means for comparing the amplitude of said discrete low-frequency signal with the amplitude of a preselected reference signal and generating an error signal which is applied to said gain control terminal of said photoelectric transducer means to automatically adjust said system to substantially equalize the amplitude of said reference signal and said low-frequency signal, whereby the system is automatically and continuously set to a normalized level for the optical device being measured during the evaluation of the optical device under test and so that the higher-frequency image components are then capable of being measured under a standardized system for determining the image-forming quality of a series of optical devices at one or more spatial frequencies.
Claim 14
Independent Claim
416 words
A system for determining the image-forming quality of an optical device by projecting an image through said device and measuring the relative amount of light transmitted therethrough at a plurality of spatial frequencies, with said system determinations being normalized automatically and continuously throughout the duration of the evaluation of the optical device under test, said system comprising: photoelectric transducer means, including an optical input screen, an electrical output terminal, and a gain control terminal, for converting a light signal incident upon said input screen into a corresponding electrical signal at said output terminal at an amplitude which varies systematically in accordance with an externally-applied gain control signal applied to said gain control terminal; means for projecting said image along a path through said optical device and onto said optical input screen; means, including a motor and a pattern wheel rotationally driven by said motor at a predetermined speed, disposed in said projection path for modulating said projected image to produce simultaneously a low-frequency image component incident upon said optical input screen and at least one higher-frequency image component incident upon said optical input screen; a plurality of filter means respectively tuned to the frequency of each said image component and coupled to the electrical output section of said photoelectric transducer means for developing a corresponding plurality of discrete electrical signals each representative of a different one of said image components; indicating means coupled to said filter means for indicating the amplitude of said discrete electrical signals; means for generating said gain control signal; and means for adjusting said gain control signal generating means to cause said photoelectric transducer means to develop at said output terminal an electrical signal corresponding to said low-frequency image component at an amplitude which causes said indicating means to give a predetermined reading, said adjusting means comprising means for comparing the amplitude of said discrete low-frequency signal with the amplitude of a preselected reference signal and generating an error signal which is applied to said gain control terminal of said photoelectric transducer means to automatically adjust said system to substantially equalize the amplitude of said reference signal and said low-frequency signal, whereby the system is automatically and continuously set to a normalized level for the optical device being measured during the evaluation of the optical device under test and so that the higher-frequency image components are then capable of being measured under a standardized system for determining the image-forming quality of a series of optical devices at one or more spatial frequencies.
Claim 15
Dependent Claim
32 words
A system in accordance with claim 12, in which said indicating means comprises a plurality of meters respectively coupled to said filter means for indicating the amplitudes of said discrete electrical signals.
Claim 16
Dependent Claim
109 words
A system in accordance with claim 12, in which said indicating means comprises a meter and switch means having an output terminal, with said meter coupled to said switch means output terminal and said switch means coupled to said filter means, for selectively coupling any one of said discrete electrical signals to said meter, whereby the system may be operated with a single meter by first making the low-frequency reading and adjusting the gain of the photoelectric transducer to obtain the predetermined reading for the low-frequency image component, to thus normalize the apparatus, and then switching the meter to another filter to indicate the amplitude of a higher-frequency signal.
Claim 17
Dependent Claim
61 words
A system in accordance with claim 12, in which said photoelectric transducer means comprises a photomultiplier tube having a light input screen and an electrical output terminal for converting a selected amount of light incident upon said input screen into a corresponding electrical signal at said output terminal at an amplitude which varies systematically in accordance with said gain control signal.
Claim 18
Dependent Claim
123 words
A system in accordance with claim 12, in which said image modulating means comprises a motor and a pattern wheel rotationally driven by said motor at a predetermined speed comprising a continuous series of alternately transparent and opaque areas, with a predetermined number of said transparent areas having an area which bears a first ratio relative to the area of a corresponding number of said opaque areas and the remaining number of said transparent areas having an area which bears a second ratio relative to the remaining number of said opaque areas, said second ratio being the inverse of said first ratio, whereby the rotating pattern wheel modulates the projected image to produce simultaneously a low-frequency image component and a higher-frequency image component.
Claim 19
Dependent Claim
16 words
A system in accordance with claim 16, in which said preselected ratio is 1.5 to 1.
Claim 20
Dependent Claim
21 words
A system in accordance with claim 16, in which said predetermined number equals one-half of the total number of said areas.
Claim 21
Dependent Claim
103 words
A system in accordance with claim 12, in which said modulating means comprises a motor and a pattern wheel rotationally driven by said motor at a predetermined speed, said pattern wheel comprising a plurality of arcuate pattern bands disposed in a concentric relationship, with each said band having a continuous series of alternately transparent and opaque areas of the same size and shape and the total number of said areas representing a predetermined spatial frequency at said rotational speed, whereby one of said bands modulates the image at a low-frequency rate and the other bands simultaneously modulate the image at preselected higher-frequency rates.
Claim 22
Dependent Claim
19 words
A system in accordance with claim 19, in which the shape of said transparent and opaque areas is trapezoidal.
Claim 23
Dependent Claim
18 words
A system in accordance with claim 12, in which said image component frequencies are related by even harmonics.
Claim 24
Dependent Claim
48 words
A system in accordance with claim 12, in which each said filter means includes a phase-locked-loop detector tuned to a different one of said image component frequencies and responsive to the electrical signal applied to said filter means for increasing the signal-to-noise ratio of said discrete electrical signals.
Claim 25
Dependent Claim
156 words
A system in accordance with claim 12, in which said photoelectric transducer means comprises a photomultiplier tube having a light input screen, an electrical output terminal, and a gain control terminal for converting a selected amount of light incident upon said input screen into a corresponding electrical signal at said output terminal at an amplitude which varies systematically in accordance with said gain control signal; and said comparing means comprises a comparator circuit coupled between said filter means and said photomultiplier tube and responsive to said discrete low-frequency signal for comparing the amplitude of said discrete low-frequency signal with the amplitude of said preselected reference signal and developing a corresponding control signal which is applied to said gain control terminal of said photomultiplier tube to adjust the amplitude of said electrical signal until the amplitude of said discrete low-frequency signal is substantially equal to the amplitude of said reference signal, whereby said system is automatically normalized.
References Cited (Backward Citations)
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Cited
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1980-11-28 | 1981-05-30 | 1981-11-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1984-11-28 | 1985-05-30 | 1985-11-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1988-11-28 | 1989-05-30 | 1989-11-29 | $7700.00 | Window Closed / Lapsed |