Automatic focusing device and automatic focusing method
AssigneeNikon Corporation
InventorToru Iwane
Life of this patent
Estimating the term…
Abstract
To improve focusing precision and responsiveness in an automatic focusing device, an accurate lens driving amount is found in a short time from a detected defocus amount. A conversion coefficient .gamma.s is calculated by successively correcting a correction coefficient Lm using the next correction coefficient L(m+1) and the defocus amount .DELTA.Bf and by correcting the specific conversion coefficient .gamma. using these correction coefficients and the defocus amount .DELTA.Bf. Driving of the focusing lens is controlled by calculating a driving amount .DELTA.x for the focusing lens from the defocus amount .DELTA.Bf using the conversion coefficient .gamma.s.
Claims18
An automatic focusing device for a focusing lens in a lens system having a predetermined focal plane and an image forming plane, comprising:
- a focus detection means for detecting a defocus amount .DELTA.Bf of the image forming plane from the predetermined focal plane of the lens system;
- a memory means for storing a specific conversion coefficient .gamma. for converting the defocus amount .DELTA.Bf into a driving amount .DELTA.x for the focusing lens, and for storing a plurality of correction coefficients Lm (m=1, 2, . . . ) for correcting the specific conversion coefficient .gamma. according to the defocus amount .DELTA.Bf;
- a conversion coefficient calculation means for calculating a conversion coefficient .gamma.s based on the specific conversion coefficient .gamma. stored in the memory means and the plurality of correction coefficients Lm (m=1,2, . . . ) stored in the memory means, wherein the conversion coefficient calculation means calculates the conversion coefficient .gamma.s by successively correcting the correction coefficients Lm using a next correction coefficient L(m+1) and the defocus amount .DELTA.Bf and corrects the specific correction coefficient .gamma. using the correction coefficients and the defocus amount .DELTA.Bf;
- lens driving amount calculation means for calculating the driving amount .DELTA.x of the focusing lens from the defocus amount .DELTA.Bf calculated by the focus detection means using the conversion coefficient .gamma.s calculated by the conversion coefficient calculation means;
- and,
- a lens driving means for controlling driving of the focusing lens based on the driving amount .DELTA.x calculated by the lens driving amount calculation means.
An automatic focusing device for a lens system having a focusing lens comprising:
- a focus detection device that detects a defocus amount .DELTA.Bf by determining a deviation amount of the focusing lens from light from a subject passing through the focusing lens;
- a memory that stores a specific conversion coefficient .gamma. and a plurality of correction coefficients Lm (m=1, 2, . . . );
- a conversion coefficient corrector that determines a conversion coefficient .gamma.s by successively correcting a stored correction coefficient Lm using a successive correction coefficient L(m+1) and the defocus amount .DELTA.Bf and correcting the stored specific conversion coefficient .gamma. using the corrected correction coefficient Lm and the defocus amount .DELTA.Bf;
- a driving amount determiner that determines a driving amount .DELTA.x for the focusing lens based on the defocus amount .DELTA.Bf and the conversion coefficient .gamma.s;
- and
- a driving controller that drives the focusing lens by the driving amount .DELTA.x to automatically focus the focusing lens.
A method for automatically focusing a lens system having a predetermined focal plane and an image forming plane, comprising the steps of:
- detecting a defocus amount .DELTA.Bf of the image forming plane from the predetermined focal plane of the photographic lens system;
- storing a specific conversion coefficient .gamma. for converting the defocus amount .DELTA.Bf into a driving amount .DELTA.x for the focusing lens;
- storing a plurality of correction coefficients Lm (m=1, 2, . . . ) for correcting the specific conversion coefficient .gamma. according to the defocus amount .DELTA.Bf;
- calculating a conversion coefficient .gamma.s based on the stored specific conversion coefficient .gamma. and the stored correction coefficients Lm (m=1,2, . . . ), including the steps of
- successively correcting the correction coefficients Lm using a next correction coefficient L(m+1) and the defocus amount .DELTA.Bf, and
- correcting the specific correction coefficient .gamma. using the correction coefficients Lm and the defocus amount .DELTA.Bf;
- calculating the driving amount .DELTA.x of the focusing lens from the calculated defocus amount .DELTA.Bf using the calculated conversion coefficient .gamma.s;
- and,
- controlling driving of the focusing lens based on the calculated driving amount .DELTA.x.
Dependencies are inferred from the claim text.