Unidirectional focussing system
First Claim
1. In a photographic-camera focussing system having an objective adjustable in a first direction from a first extreme subject-distance setting to a second extreme subject-distance setting, in combination:
- first and second photodetector means located to receive light from a subject to be photographed;
comparing means for comparing the light incident on the first and second photodetector means and generating in dependence upon the present subject-distance setting of the objective a first signal when the camera-objective subject-distance setting should be changed in the first direction, a second signal when the camera-objective subject-distance setting should be changed in an opposite second direction, and generating both the first and second signals concurrently when the camera-objective subject-distance setting is within a predetermined tolerance range of acceptable error;
means constraining the camera objective to be at the first extreme subject-distance setting at the start of a focussing operation, whereby in order to bring the camera objective to the correct subject-distance setting it is necessary that the camera-objective subject-distance setting be changed in the first direction from the first extreme setting towards the second extreme setting thereof; and
stop-signal-generating means operative in response to said second signal for generating a stop signal commanding that adjustment of the camera-objective subject-distance setting be stopped, whereby as the subject-distance setting is changed in said first direction from said first extreme setting towards said second extreme setting the stop signal is generated in response to generation of said second signal as the subject-distance setting error just enters into the range of acceptable error.
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Accused Products
Abstract
At the start of each focussing operation, the camera objective is at a first extreme subject-distance setting and is moved in a first direction therefrom towards the second extreme subject-distance setting. A focus-evaluating circuit comprises first and second photodetectors located to receive light from the subject and a comparing circuit which compares the light incident on the photodetectors and in dependence upon the present subject-distance setting generates first and second signals respectively indicating that the subject-distance setting should be changed in the first direction or in the opposite second direction, such circuit having bidirectional character and furthermore establishing a tolerance range of acceptable distance-setting error within which both the first and second signals are generated. During the unidirectional change of subject-distance setting, the appearance of the first signal leads to generation of a stop signal commanding that the progressive change of distance setting be stopped. Accordingly, the unidirectional change of setting is commanded to stop at the point where the changing distance setting just enters into the tolerance range of the bidirectional evaluating circuitry.
11 Citations
12 Claims
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1. In a photographic-camera focussing system having an objective adjustable in a first direction from a first extreme subject-distance setting to a second extreme subject-distance setting, in combination:
- first and second photodetector means located to receive light from a subject to be photographed;
comparing means for comparing the light incident on the first and second photodetector means and generating in dependence upon the present subject-distance setting of the objective a first signal when the camera-objective subject-distance setting should be changed in the first direction, a second signal when the camera-objective subject-distance setting should be changed in an opposite second direction, and generating both the first and second signals concurrently when the camera-objective subject-distance setting is within a predetermined tolerance range of acceptable error;
means constraining the camera objective to be at the first extreme subject-distance setting at the start of a focussing operation, whereby in order to bring the camera objective to the correct subject-distance setting it is necessary that the camera-objective subject-distance setting be changed in the first direction from the first extreme setting towards the second extreme setting thereof; and
stop-signal-generating means operative in response to said second signal for generating a stop signal commanding that adjustment of the camera-objective subject-distance setting be stopped, whereby as the subject-distance setting is changed in said first direction from said first extreme setting towards said second extreme setting the stop signal is generated in response to generation of said second signal as the subject-distance setting error just enters into the range of acceptable error. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
- first and second photodetector means located to receive light from a subject to be photographed;
Specification