Focus controlling method and camera which sets different focus sampling frequencies when recording still images and when recording a series of consecutive images

摘要

A focusing method and apparatus which changes the shutter speed and/or the focusing sampling frequency in order to increase the speed at which an image is brought into focus while at the same time, preventing the influence of flicker from artificial light powered by an AC power source. As the focus evaluation value is based on the brightness of a signal, shutter speeds and frequencies are set in order to avoid the influence of flicker on the focusing process. A shutter speed of {fraction (1/100)}th of a second with a sampling frequency of 60 Hz can be used in environments which are sufficiently bright in order to increase the focusing speed. Also, the focusing sampling frequency may be set to be large when the focus is far from the focusing point in order to quickly bring the image into focus and the sampling frequency subsequently decreases as the focusing position is approached in order to reduce the chances that the focusing position will be passed. Another feature is to record images as the focus position is being approached so that when the in-focus position is passed, there is no need to back up the focusing lens to the in-focus position to obtain the still image as the still image will have been previously recorded. The other frames which have been recorded may then be discarded.