Autofocus device and digital camera
An autofocus device is provided that includes a lens drive system, an imager, a contrast detector, first and second peak detectors, and a backlash detector. The lens drive system translates a lens. The imager captures an image through the lens. The contrast detector detects the contrast of an image captured by the imager. The first peak detector detects a first contrast peak of images captured at different lens positions when the lens is translated in a forward direction. The second peak detector detects a second contrast peak of images captured at different lens positions when the lens is translated in a backward direction. The detection of the second peak is carried out after detection of the first contrast peak. The backlash detector detects the backlash in the lens drive system according to the positions of the first and second contrast peaks.
1. An autofocus device comprising:
a lens drive system for translating a lens;
an imager for capturing an image through the lens;
a contrast detector for detecting a contrast of an image captured by the imager;
a first peak detector for detecting a first contrast peak of images captured at different lens positions as the lens is translated in a forward direction;
a second peak detector for detecting a second contrast peak of images captured at different lens position as the lens is translated in a backward direction, the second peak detector operating after the first contrast peak is detected; and
a backlash detector for detecting a backlash in the lens drive system according to the positions of the first contrast peak and the second contrast peak;
wherein the lens is moved from an exceeding position to an in-focus position according to the previously detected backlash, the exceeding position is a position at which the first contrast peak is detected when the lens is translated in the forward direction.
2. The autofocus device according to claim 1 , wherein detection of the second contrast peak by the second peak detector is performed as the lens is translated in the backward direction for a predetermined distance that is greater than the backlash.
3. The autofocus device according to claim 2 , wherein at least one of the backlash and a drive amount from the exceeding position to the in-focus position is subjected to a learning process.
4. The autofocus device according to claim 3 , wherein the learning process is carried out in consideration of at least one of a lens type, a drive direction, a drive speed and an attitude of a camera body.
5. A digital camera comprising:
a camera body and a lens;
a lens drive system for translating the lens;
an imager for capturing an image through the lens;
a contrast detector for detecting a contrast of an image captured by the imager;
a first peak detector for detecting a first contrast peak of images captured at different lens positions when the lens is translated in a forward direction;
a second peak detector for detecting a second contrast peak of images captured at different lens positions as the lens is translated in a backward direction, the second peak detector being operated after the first contrast peak is detected; and
a backlash detector for detecting a backlash in the lens drive system according to the positions of the first and second contrast peaks;
wherein the lens is moved from an exceeding position to an in-focus position according the previously detected backlash, the exceeding position is a position at which the first contrast peak is detected when the lens is translated in the forward direction.
6. The digital camera according to claim 5 , wherein detection of the second contrast peak by the second peak detector is carried out as the lens is translated in the backward direction for a predetermined distance that is greater than the backlash.
7. The digital camera according to claim 6 , wherein at least one of the backlash and a drive amount from the exceeding position to the in-focus position is subjected to a learning process.
8. The digital camera according to claim 7 , wherein the learning process is carried out in consideration of at least one of a lens type, a drive direction, a drive speed and an attitude of a camera body.