Automatic focusing system employing two variable frequency oscillators
AssigneeAsahi Kogaku Kogyo Kabushiki Kaisha
InventorTsukumo Nobusawa
Life of this patent
Estimating the term…
Abstract
In an automatic focusing system having an objective spaced an adjustable distance from an image plane, two variable frequency oscillators, each controlled by a separate photoconductor element, produce two variable-frequency signals that have substantially the same frequency when light passing through the objective is brought into focus at the image plane. The two variable-frequency signals are compared, and, upon detecting a difference in frequency between them, the spacing between the objective and the image plane is adjusted to a relative position at which the frequencies thereof are substantially the same.
Claims5
In an automatic focusing system having an objective spaced an adjustable distance from an image plane, apparatus which comprises:
- first means for producing first and second variable-frequency signals that have substantially the same frequency when light passing through the objective is brought into focus at the image plane, the first means including
- a first photoconductor element having impinging on it light which has traversed a first distance from the objective to reach the first photoelectric element, the first distance being less than the adjustable distance by a predetermined amount
- a second photoconductor element having impinging on it light which has traversed a second distance from the objective to reach the second photoelectric element, the second distance being greater than the adjustable distance by a predetermined amount
- each of the photoelectric elements serving as a variable resistor having a peak resistance value when the light impinging on it is in focus;
- a first variable frequency oscillator controlled by the resistance value of the first photoelectric element for producing the first variable frequency signal, and
- a second variable frequency oscillator controlled by the resistance value of the second photoelectric element for producing the second variable frequency signal;
- and
- second means responsive to a difference in frequency between the first and second variable-frequency signals for adjusting the spacing between the objective and the image plane to a relative position at which the frequencies thereof are substantially the same.
In an automatic focusing system having an objective spaced an adjustable distance from an image plane, apparatus which comprises:
- first means for producing first and second variable frequency signals that have substantially the same frequency when light passing through the objective is brought into focus at the image plane, the first means including
- a first photoconductor element having impinging on it light which has traversed a first distance from the objective to reach the first photoelectric element, the first distance being less than the adjustable distance by a predetermined amount;
- a second photoconductor element having impinging on it light which has traversed a second distance from the objective to reach the second photoelectric element, the second distance being greater than the adjustable distance by a predetermined amount;
- each of the photoelectric elements serving as a variable resistor having a peak resistance value when the light impinging on it is in focus;
- a first variable frequency oscillator controlled by the resistance value of the first photoelectric element for producing the first variable frequency signal;
- and
- a second variable frequency oscillator controlled by the resistance value of the second photoelectric element for producing the second variable frequency signal;
- and
- second mens responsive to a difference in frequency between the first and second variable-frequency signals for adjusting the spacing between the objective and the image plane to a relative position at which the frequencies thereof are substantially the same, wherein the second means includes a first digital circuit arrangement responsive to the first and second variable-frequency signals for producing a drive-direction control signal to specify the direction in which the adjustable distance should be adjusted to bring the image into focus, and includes a second digital circuit arrangement responsive to the first and second variable frequency signals for producing a coincidental signal when the frequencies thereof are substantially the same.
Dependencies are inferred from the claim text.