Digital imaging devices with an adjustable focus may employ one of many types of lens actuators, including a voice coil motor (VCM) actuator, a microelectromechanical systems (MEMS) actuator, or a Shape Memory Alloy (SMA) actuator etc.,. Image capture devices may also have a lens driver controlling an actuator that moves a lens assembly for adjusting focus in the image capture device. During operation of the actuator to adjust the position of the lens, vibration may be introduced to the lens.
This vibration may come from many sources. For example, in a lens adjustment mechanism employing a voice coil motor design, the stimuli for movement of the lens induces vibration in springs supporting the lens. The vibration of the lens may continue for some time before settling at the desired lens position. For example, this vibration or ringing of the lens may last anywhere from approximately 50 milliseconds to approximately 200 ms, and can adversely affect auto-focus (AF) speed and accuracy. The ringing may also adversely affect desired image capture settings and hence image quality. To mitigate the adverse effects of lens ringing, imaging devices may wait a predetermined threshold period of time after completing a lens movement before capturing an image with the lens. This predetermined threshold period of time may allow the lens to stop ringing before an image is captured, but also reduces the speed of autofocus operation.
The need for an imaging device to wait for a predetermined threshold period of time after completing a lens movement may have adverse effects on the speed at which an imaging device may capture images. For example, in imaging environments with dynamic scenes and focus conditions, a photographer may desire to minimize any delay between when a scene is presented and when the scene may be captured by an imaging device. To the extent the imaging device introduces a delay in image capture to provide for any lens ringing to settle, the captured image may vary from the image selected by the photographer. Similarly, video image capture may also be adversely affected by lens ringing, given the frame rate at which most video is recorded.