Patent ID: 7228069
Filing Date: 2007-06-05
Classification: G02B,H04N

Abstract:
1. An automatic focusing method for a digital camera, comprising the following steps: providing a digital camera module, which comprises a lens member, an image sensor member, a distance-measuring member, a signal-processing member, a drive control member, and a drive member; measuring an object distance by the distance-measuring member, and transmitting the object distance to the signal-processing member, for generating a control signal; the drive control member driving the drive member according to the control signal; and the drive member driving the image sensor member or the lens member to a position determined by the control signal, wherein: the step of providing the digital camera module comprises the following steps: providing the lens member, the image sensor member, and the distance-measuring member; measuring a depth of focus of the lens member with a fixed object distance; establishing a range of error of movement of the drive member, based on the depth of focus of the lens member, the range of error of movement of the drive member being not larger than half of the depth of focus of the lens member; and selecting a suitable signal-processing member, drive control member, and drive member; wherein the step of measuring the depth of focus of the lens member with the fixed object distance comprises the following steps: measuring a first MTF (Modulation Transfer Function) on the image sensor member, when a first spatial frequency on an axis of the image sensor member is predetermined; calculating a first shift of focus on the axis of the image sensor member, when the numerical value of the first MTF is required to be in a certain range; measuring a second MTF on the image sensor member, when a second spatial frequency away from the axis of the image sensor member is predetermined; calculating a second shift of focus away from the axis of the image sensor member, when the numerical value of the second MTF is required to be in a certain range; and calculating the depth of focus of the lens member, which is an overlap of the first shift of focus and the second shift of focus.