Digital still cameras require both accuracy with the focal function and quick response. We developed a new focus home position detection system that consists of two algorithms. The first, the home position judging algorithm, detects the home position as the level of the photo sensor changes, and it memorizes the excitation position of the stepping motor for the lens drive. When it detects the home position again, it judges the level change of a photo sensor in the excitation position distant from the memorized excitation position by a half of an excitation pattern cycle. It then reproduces the original home position. The second algorithm, the temperature compensation algorithm, makes the memorized excitation position follow the temperature change. The new system cancels out any home position error by the camera posture difference and improves the initialization time (by about 0.3 seconds). We introduced this system into our camera DMC-LC1.
