專利摘要：
Disclosed is focus control method for Delta-Sigma based image formation devices in which a steering term and a focusing term of a delay formula are respectively quantized, and corresponding two channels at both sides of the probe are synchronized by a delay produced during dynamic focusing. During synchronizing the two channels, two numeral values with equal absolute value but with opposite signs are respectively inserted so as to eliminate extra noise the signals are after summing up, and controlling common delay of the two channels is performed by same one controller. After summing up the inserted two values, the dynamic aperture control of the Delta-Sigma based image formation device can be effectively realized and noise during dynamic focusing also is eliminated thereby achieving an ideal single bit output.