PURPOSE: To prevent the oscillation at the time of a small aperture and to obtain a stable operation by compressing the signal component of a high level at the time of high luminance and thereby lowering the loop gain of a driving system.
CONSTITUTION: A high level signal detector 12 and a signal compressor 13 are added to the conventional system so that the loop gain of a driving system is lowered by detecting and compressing the signal component of the specified threshold or above and sending this to an integrator 6 when the light of high luminance enters the device and the signal level rises. The signal component of the high level is thereby compressed when the light of the high luminance is made incident and, therefore, the loop gain of the driving system in the direction where the diaphragm closes is lowered and the oscillation is prevented so that the stable operation is assured. The responsiveness in the open direction is assured in this way even if the oscillation in the direction where the diaphragm closes is not taken into consideration.
OHIRA YUSUKE
SHIMIZU TOMIO
| JPH01106023A | 1989-04-24 |