Automatic focusing system employing two variable frequency oscillators

Claim 2

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.

Claim 3

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.

Claim 4

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.

Claim 5

The apparatus of claim 2 wherein the first digital circuit arrangement includes first and second counters, first and second parallel-input shift registers, and a logic circuit arrangement; the first and second counters respectively responding to the first and second variable-frequency signals to accumulate first and second multi-bit counted values, the first and second shift registers receiving the first and second multi-bit counted values in parallel and shifting them out in serial format to the logic circuit arrangement; the logic circuit arrangement including circuit means responsive to the serial-format counted values to produce the drive-direction control signal.

Claim 6

The apparatus of claim 2 wherein the first digital circuit arrangement includes first and second frequency divider circuits, first and second serial-input shift registers, and a logic circuit arrangement; the first frequency dividers being connected between the first varible-frequency oscillator and the first shift register; the second frequency divider being connected betwen the second variable-frequency oscillator and the second shift register; the logic circuit arrangement being connected to both the shift registers and having an output for providing the drive-direction control signal.

Claim 7

The apparatus of claim 2 wherein the first digital circuit arrangement includes first and second counters, each including a counter output for specifying an overflow condition; the first counter being responsive to the first variable-frequency signal; the second counter being responsive to the second variable-frequency signal; the first digital circuit arrangement further including circuit means, connected to the counter outputs, for producing the drive-direction control signal.