Liquid-crystal luminous quantity adjuster, method for driving liquid crystal luminous quantity adjuster, and camera comprising liquid crystal luminous quantity adjuster

Abstract

A liquid-crystal light-amount adjusting device in which the effective power of driving pulses for acceleration is optimized to improve response characteristics of optical transmittance, a method of driving the apparatus, and a camera including the apparatus. The liquid-crystal light-amount adjusting device according to the present invention includes a driving-pulse generating circuit ( 16 ) for generating driving pulses having pulsed voltages, a liquid-crystal light-amount adjusting unit ( 12 ) for changing the optical transmittance of a liquid crystal according to pulse shapes of the driving pulses, and a microcomputer ( 19 ) for controlling frequencies and duty ratios of the driving pulses. The microcomputer ( 19 ) exercises control so that the driving-pulse generating circuit ( 16 ) generates driving pulses including driving pulses for acceleration, having a pulse shape with a first frequency and a first duty ratio, and driving pulses for dimming, having a pulse shape with a second frequency that is different from the first frequency and a second duty ratio that is different from the first duty ratio.

1 . A liquid-crystal light-amount adjusting device comprising: 
 a driving-pulse generating circuit for generating driving pulses having pulsed voltages;    a liquid-crystal light-amount adjusting unit, to which the driving pulses are supplied, for changing an optical transmittance of a liquid crystal according to pulse shapes of the driving pulses; and    a control circuit for controlling frequencies and duty ratios of the driving pulses;    wherein the control circuit exercises control so that the driving-pulse generating circuit generates driving pulses for acceleration, having a pulse shape with a first frequency and a first duty ratio, and driving pulses for dimming, having a pulse shape with a second frequency that is different from the first frequency and a second duty ratio that is different from the first duty ratio.    
     
     
         2 . A liquid-crystal light-amount adjusting device according to  claim 1 , 
 further comprising a temperature detecting circuit for detecting an ambient temperature of the liquid-crystal light-amount adjusting unit and outputting a result of detection to the controller,    wherein the control circuit changes the frequencies of the driving pulses in accordance with the ambient temperature.    
     
     
         3 . A liquid-crystal light-amount adjusting device according to  claim 1 , 
 further comprising a storage circuit for storing an association table defining association of an optical transmittance with driving pulses for acceleration and driving pulses for dimming for achieving the optical transmittance,    wherein the control circuit exercises control so that the driving-pulse generating circuit, by referring to the association table, generates driving pulses with which a desired optical transmittance is achieved.    
     
     
         4 . A method of driving a liquid-crystal light-amount adjusting device that changes an optical transmittance thereof in accordance with pulse shapes of driving pulses supplied to a liquid crystal, 
 wherein, before driving pulses having a pulse shape in accordance with a desired optical transmittance is supplied to the liquid crystal, driving pulses having a frequency that is different from a frequency of the driving pulses having the pulse shape in accordance with the desired optical transmittance is supplied to the liquid crystal.    
     
     
         5 . A camera comprising: 
 an optical system for focusing light coming from a target on an imaging surface;    a liquid-crystal light-amount adjusting unit for adjusting the amount of the light that reaches the imaging surface, by changing an optical transmittance of a liquid crystal;    a driving-pulse generating circuit for generating driving pulses having pulsed voltages, the driving pulses being supplied to the liquid crystal to change the optical transmittance; and    a control circuit for controlling frequencies and duty ratios of the driving pulses;    wherein the control circuit exercises control so that the driving-pulse generating circuit generates driving pulses for acceleration, having a first frequency and a first duty ratio, and driving pulses for dimming, having a second frequency that is different from the first frequency and a second duty ratio that is different from the first duty ratio.    
     
     
         6 . A camera comprising: 
 an optical system for focusing light coming from a target on an imaging surface;    a liquid-crystal light-amount adjusting unit for adjusting the amount of the light that reaches the imaging surface, by changing an optical transmittance of a liquid crystal;    a driving-pulse generating circuit for generating driving pulses having pulsed voltages, the driving pulses being supplied to the liquid crystal to change the optical transmittance; and    a control circuit for controlling a frequency and a duty ratio of the driving pulses;    wherein the control circuit changes the frequency of the driving pulses during-imaging for one screen.    
     
     
         7 . A camera according to  claim 5 , 
 wherein an imaging time for one screen is a sum of a time during which the driving pulses for acceleration are supplied and a time during which the driving pulses for dimming are supplied.