Automatic focusing apparatus

• US 20070279365A1
• Filed: 05/29/2007
• Published: 12/06/2007
• Est. Priority Date: 05/31/2006
• Status: Active Grant

• Current Assignee: Citizen Watch Co Limited (Citizen Electronics Company Limited)
• Original Assignee: Citizen Holdings Co., Ltd. (Citizen Electronics Company Limited)
• Inventors: Kageyama, Yasuhiro
• Granted Patent: US 7,683,975 B2
• Time in Patent Office: Days
• US Class Current: 345/100
• CPC Class Codes: G02B 7/38 measured at different points on the optical axis , e.g. focussing on two or more planes and comparing image data
• CPC Class Codes: G02F 1/13306 Circuit arrangements or driving methods for the control of single liquid crystal cells G02F1/132, G02F1/133382 take precedence
• CPC Class Codes: G02F 1/29 for the control of the position or the direction of light beams, i.e. deflection
• CPC Class Codes: G02F 1/294 Variable focal length devices
• CPC Class Codes: G02F 2203/60 Temperature independent
• CPC Class Codes: G03B 3/00 Focusing arrangements of general interest for cameras, projectors or printers
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method

Abstract

An object of the present invention is to provide an automatic focusing apparatus which can reduce the time required to detect focused position in accordance with the operating environment by adjusting the voltage applied to a liquid crystal lens. The apparatus includes a liquid crystal lens whose focal length varies with an applied voltage, a liquid crystal lens driving unit which applies a prescribed voltage to the lens, an optical-to-electrical converter which produces an image signal from an optical image passed through the lens, a temperature sensor which detects temperature near the lens, and a control unit which extracts a plurality of focus signals by adjusting the prescribed voltage and controlling the driving unit based on the temperature or on the image signal acquisition period of the converter, and which controls the driving unit based on the extracted plurality of focus signals so that a maximum focus signal is achieved.

Claims

1. An automatic focusing apparatus comprising:

a liquid crystal lens whose focal length varies with an applied voltage;

a liquid crystal lens driving unit which applies a prescribed voltage to said liquid crystal lens;

an optical-to-electrical converter which produces an image signal from an optical image passed through said liquid crystal lens;

a temperature sensor which detects temperature near said liquid crystal lens; and

a control unit which extracts a plurality of focus signals by adjusting said prescribed voltage and controlling said liquid crystal lens driving unit based on the temperature near said liquid crystal lens or on an image signal acquisition period of said optical-to-electrical converter, and which controls said liquid crystal lens driving unit based on said extracted plurality of focus signals so that a maximum focus signal is achieved.

2. An automatic focusing apparatus according to claim 1, wherein said control unit adjusts said prescribed voltage in such a manner that said prescribed voltage increases as the temperature near said liquid crystal lens decreases.

3. An automatic focusing apparatus according to claim 1, wherein said control unit adjusts said prescribed voltage in such a manner that said prescribed voltage increases as said image signal acquisition period becomes shorter.

4. An automatic focusing apparatus according to claim 1, wherein said control unit extracts said plurality of focus signals in accordance with focus signal collective extraction control in which the image signal output from said optical-to-electrical converter is sampled with said image signal acquisition period while causing said liquid crystal lens to undergo a transient response by applying said prescribed voltage by controlling said liquid crystal lens driving unit.

5. An automatic focusing apparatus according to claim 1, wherein said control unit extracts said plurality of focus signals in accordance with focus signal successive extraction control in which the image signal output from said optical-to-electrical converter is sampled after liquid crystal in said liquid crystal lens has fully responded to the voltage applied to said liquid crystal lens when said voltage is varied by controlling said liquid crystal lens driving unit.

6. An automatic focusing apparatus according to claim 1, wherein said control unit can extract said plurality of focus signals either in accordance with focus signal collective extraction control in which the image signal output from said optical-to-electrical converter is sampled with said image signal acquisition period while causing said liquid crystal lens to undergo a transient response by applying said prescribed voltage by controlling said liquid crystal lens driving unit, or in accordance with focus signal successive extraction control in which the image signal output from said optical-to-electrical converter is sampled after liquid crystal in said liquid crystal lens has fully responded to the voltage applied to said liquid crystal lens when said voltage is varied by controlling said liquid crystal lens driving unit, and wherein

said control unit selects either said focus signal collective extraction control or said focus signal successive extraction control, based on said temperature or on said image signal acquisition period.

7. An automatic focusing apparatus according to claim 6, wherein said control unit estimates a time required for the transient response of said liquid crystal lens based on said temperature, and computes the number of focus signals obtainable during said transient response by dividing said estimated time by said image signal acquisition period, and wherein when the number of focus signals is not smaller than a prescribed number, said focus signal collective extraction control is selected, while when the number of focus signals is smaller than said prescribed number, said focus signal successive extraction control is selected.

8. An automatic focusing apparatus comprising:

a liquid crystal lens whose focal length varies with an applied voltage;

a liquid crystal lens driving unit which applies a prescribed voltage to said liquid crystal lens;

an optical-to-electrical converter which produces an image signal from an optical image passed through said liquid crystal lens;

a temperature sensor which detects temperature near said liquid crystal lens; and

a control unit which can extract a plurality of focus signals either in accordance with focus signal collective extraction control in which the image signal output from said optical-to-electrical converter is sampled with said image signal acquisition period while causing said liquid crystal lens to undergo a transient response by applying said prescribed voltage by controlling said liquid crystal lens driving unit, or in accordance with focus signal successive extraction control in which the image signal output from said optical-to-electrical converter is sampled after liquid crystal in said liquid crystal lens has fully responded to the voltage applied to said liquid crystal lens when said voltage is varied by controlling said liquid crystal lens driving unit, wherein said control unit selects either said focus signal collective extraction control or said focus signal successive extraction control based on said temperature or on said image signal acquisition period, and controls said liquid crystal lens driving unit based on said extracted plurality of focus signals so that a maximum focus signal is achieved.

9. An automatic focusing apparatus comprising:

a liquid crystal lens whose focal length varies with an applied voltage;

a liquid crystal lens driving unit which applies a prescribed voltage to said liquid crystal lens;

an optical-to-electrical converter which produces an image signal from an optical image passed through said liquid crystal lens;

a temperature sensor which detects temperature near said liquid crystal lens; and

a control unit which adjusts said prescribed voltage based on the temperature near said liquid crystal lens or on an image signal acquisition period of said optical-to-electrical converter, acquires a signal representing focal length of said liquid crystal lens corresponding to a focus signal maximum value from a focus signal extracting unit for extracting a plurality of focus signals by sampling with said image signal acquisition period the image signal being output from said optical-to-electrical converter, and controls said liquid crystal lens driving unit based on said acquired signal.