Focusing system, interchangeable lens, and image-capturing device
View Patent ↗A focusing system includes a first drive unit for driving a first focus lens along the optical axis, a second drive unit for driving a second focus lens along the optical axis, a determining unit for periodically detecting a focus state of a subject image formed via the optical system and determining a focus position of the optical system based on the detected result, and a control unit for controlling the first and second drive units according to a result of determining the focus position of the optical system by the determining unit. The control unit controls the second drive unit to drive the second focus lens independently of the first focus lens, in the focus operation.
1. A focusing system having an optical system including first and second focus lenses for regulating a focus state of a subject image, the focusing system being capable of performing a focus operation for automatically controlling the first and second focus lenses on a focus position, the focusing system comprising:
a first drive unit configured to drive the first focus lens along the optical axis;
a second drive unit configured to drive the second focus lens along the optical axis;
a determining unit configured to periodically detecting detect a focus state of the subject image formed via the optical system and determine a focus position of the optical system based on the detected result in the focus operation; and
a control unit configured to control the first and second drive unit according to a result of determining the focus position of the optical system by the determining unit,
wherein:
the control unit controls the first drive unit to drive the first focus lens slightly forward and backward along the optical axis and controls the second drive unit to drive the second focus lens independently of the first focus lens in order to detect a focus state of the subject image by the determining unit in the focus operation,
the second focus lens has tracking positions corresponding to positions of the first focus lens, which provide suitable optical performance according to positions of the first focus lens,
the control unit controls the second drive unit to drive the second focus lens independently of the first focus lens in the focus operation so as not to trace the tracking position corresponding to the position of the first focus lens, and
when a center position of the first focus lens in driving forward and backward shifts, the control unit controls the second drive unit to drive the second focus lens at a constant speed.
2. The focusing system according to claim 1 , wherein the control unit controls the first drive unit to drive the first focus lens slightly forward and backward along the optical axis and controls the second drive unit to drive the second focus lens at a constant speed, in order to determine the focus position of the optical system by the determining unit.
3. The focusing system according to claim 1 , wherein when the center position of the first focus lens in driving slightly forward and backward shifts and a difference between a tracking position of the second focus lens with respect to a current position of the first focus lens and a current position of the second focus lens is equal to or more than a predetermined value, the control unit controls the second drive unit to drive the second focus lens at a constant speed.
4. The focusing system according to claim 3 , wherein
the focusing system is installed in an image-capturing device for capturing a subject image formed via the optical system,
the predetermined value is set according to a recording condition of the image-capturing device.
5. The focusing system according to claim 4 , wherein
the recording condition is a mode selection between a still image recording mode and a moving image recording mode,
the predetermined value set when the still image recording mode is selected is set to a smaller value than that set when the moving image recording mode is selected.
6. The focusing system according to claim 4 , wherein
the recording condition is a level of an open/close state of a diaphragm included in the optical system,
the predetermined value is set to a larger value as the diaphragm changes from the open state into a closed state.
7. The focusing system according to claim 4 , wherein
the recording condition is an image quality level of image data created based on the imaged subject image,
the predetermined value is set to be larger as the image quality level is changed from high image quality into low image quality.
8. The focusing system according to claim 1 , wherein the control unit controls the second drive unit to drive the second focus lens along the optical axis in order to assist the regulation of the focus state of the subject image by the first focus lens.
9. An image-capturing device comprising the focusing system according to claim 1 .
10. An interchangeable lens mountable to a camera body, comprising the focusing system according to claim 1 .