US3810202A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Light-measuring method and structure for cameras
Assignee: Pentax Corp
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Filing: 1972-11-27
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Granted: 1974-05-07
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Expires: 1992-11-27
Abstract
Abstract A method and structure for measuring the light travelling through the objective of a single lens reflex camera. A photosensitive unit is situated adjacent a viewfinder of the camera for receiving not only light which travels along a first path through the objective of the camera but also light which travels along a second path through the eyepiece of the viewfinder. The light which travels along one of these paths is treated by being subjected to the action of a light-chopper, so that the photosensitive unit provides an AC signal from the chopped light and a DC signal from the light which is not chopped. These two signals are superimposed and the superimposed signals are subjected to the action of a suitable filter which extracts from the superimposed signals only the light travelling through the objective. Also, it is possible for the AC signal to be rectified and then to achieve the signal corresponding to the light travelling through the objective by subjecting the rectified AC signal and the remaining DC signal to the action of a differential amplifier.
Inventors
- 👤 N Uno
- 👤 T Sakazaki
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 02:03
CPC Classifications
G; G03; G03B; G03B7/00; G03B7/08; G03B7/099; G03B7/0993; G03B7/0997; G03B7/09971; G03B7/09978; G03B7/09976
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
127 words
In a method for measuring light entering through the objective of a single lens reflex camera having a photosensitive means receiving the light entering through the objective and travelling along a first path as well as light entering through an eyepiece of a viewfinder and travelling along a second path, the steps of treating the light travelling along one of said paths to provide at said photosensitive means from the thustreated light a signal different from that derived from the light travelling along the other of said paths, superimposing the latter two signals upon each other, and extracting from the superimposed signals a signal corresponding to the light travelling through the objective, so that the influence of light entering through the eyepiece of the viewfinder is eliminated.
Claim 2
Dependent Claim
127 words
In a method for measuring light entering through the objective of a single lens reflex camera having a photosensitive means receiving the light entering through the objective and travelling along a first path as well as light entering through an eyepiece of a viewfinder and travelling along a second path, the steps of treating the light travelling along one of said paths to provide at said photosensitive means from the thustreated light a signal different from that derived from the light travelling along the other of said paths, superimposing the latter two signals upon each other, and extracting from the superimposed signals a signal corresponding to the light travelling through the objective, so that the influence of light entering through the eyepiece of the viewfinder is eliminated.
Claim 3
Dependent Claim
32 words
In a method as recited in claim 1 and including the step of indicating the value of the light entering through the objective by utilizing the signal extracted from the superimposed signals.
Claim 4
Dependent Claim
65 words
In a method as recited in claim 1 and wherein the treating of the light which travels along said one path involves chopping the light travelling along said one path to treat the light travelling along said one path to provide therefrom at said photosensitive means an AC signal, while the light travelling along said other path provides at said photosensitive means a DC signal.
Claim 5
Dependent Claim
57 words
In a method as recited in claim 3 and wherein the light chopping takes place at said first path to provide the AC signal from the light which travels through the objective, and the extracting of the signal corresponding to the light travelling through the objective being obtained by a filtering which transmits only the AC signal.
Claim 6
Dependent Claim
65 words
In a method as recited in claim 3 and wherein the light chopping takes place at said second path to provide the AC signal from the light entering through the eyepiece of the viewfinder, and the extracting of the signal corresponding to the light travelling through the objective being achieved by a band-pass filtering action which transmits only the DC component of the superimposed signals.
Claim 7
Dependent Claim
40 words
In a method as recited in claim 3 and wherein the AC component is rectified and the difference between the two signals then being determined to achieve elimination of the influence of light entering through the eyepiece of the viewfinder.
Claim 8
Dependent Claim
188 words
In a single lens reflex camera, viewfinder means having an eyepiece, objective means and reflector means for directing light along a first path through said objective means to be reflected by said reflector means to said viewfinder means, so that the operator may see an image of the object to be photographed when looking into the viewfinder through said eyepiece thereof, photosensitive means situated adjacent said viewfinder means for receiving the light which travels along said first path as well as for receiving light travelling along a second path through said eyepiece of said viewfinder means, light-chopper means extending across one of said paths for chopping the light travelling therealong to provide at said photosensitive means from the light travelling along said one path an AC signal while the light travelling along the other of said paths provides at said photosensitive means a DC signal, said photosensitive means superimposing both of said signals upon each other to combine said signals, and electrical means electrically connected with said photosensitive means for extracting from the superimposed signals that signal which corresponds only to the light travelling through said objective means.
Claim 9
Dependent Claim
188 words
In a single lens reflex camera, viewfinder means having an eyepiece, objective means and reflector means for directing light along a first path through said objective means to be reflected by said reflector means to said viewfinder means, so that the operator may see an image of the object to be photographed when looking into the viewfinder through said eyepiece thereof, photosensitive means situated adjacent said viewfinder means for receiving the light which travels along said first path as well as for receiving light travelling along a second path through said eyepiece of said viewfinder means, light-chopper means extending across one of said paths for chopping the light travelling therealong to provide at said photosensitive means from the light travelling along said one path an AC signal while the light travelling along the other of said paths provides at said photosensitive means a DC signal, said photosensitive means superimposing both of said signals upon each other to combine said signals, and electrical means electrically connected with said photosensitive means for extracting from the superimposed signals that signal which corresponds only to the light travelling through said objective means.
Claim 10
Dependent Claim
27 words
The combination of claim 7 and wherein an electrical indicating means is electrically connected with said electrical means for indicating the light travelling through said objective means.
Claim 11
Dependent Claim
47 words
The combination of claim 7 and wherein the light-chopper means is situated across said first path, so that the AC signal is produced by light travelling through said objective means, and said electrical means being a filter which transmits only the AC component of the superimposed signals.
Claim 12
Dependent Claim
40 words
The combination of claim 7 and wherein the light chopper means is situated across said second path, and said electrical means being a band-pass filter which transmits only the DC signal corresponding to the light travelling through the objective means.
Claim 13
Dependent Claim
49 words
The combination of claim 7 and wherein said electrical means includes a rectifier which rectifies the AC signal and a differential amplifier which transmits the difference between the rectified AC component and the DC component, so that the latter difference corresponds to the light travelling through the objective means.
References Cited (Backward Citations)
US3486814A
Cited
US3633473A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-05-06 | 1977-11-05 | 1978-05-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-05-06 | 1981-11-05 | 1982-05-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-05-06 | 1985-11-05 | 1986-05-07 | $7700.00 | Window Closed / Lapsed |