TW200606553A - Camera autofocus - Google Patents

Abstract

A camera comprises an image sensor arranged to generate an image signal, and a lens arrangement which focusses an image onto the image sensor, the focus being variable in accordance with a control signal applied thereto. In the case that the a piezoelectric actuator experiencing hysteresis is used to drive movement of the lens arrangement to vary the focus of the image, autofocussing is achieved by applying a control signal to the piezoelectric actuator with a value at an extreme of a predetermined range and subsequently changing the control signal monotonically across the predetermined range to determine a position at which the focus quality is at an acceptable level. Thus, this position may be returned to despite the hysteresis. In the case that an encoder is arranged to encode the image signal from the image sensor into an encoded signal compressed form, the encoder is operated m two modes in which different spatial frequency components are encoded preferentially, the amount of data in one of the modes being used as the basis for autofocussing. To assist in autofocussing the position of the lens arrangement maybe determined using a light source and an optical element which is fixed to and movable with the lens arrangement, the optical element being arranged so that movement of the lens arrangement causes variation in the light incident on the image sensor.