Method of auto-focussing and system therefor

摘要

A novel method and apparatus for auto-focussing which includes determining a focus voltage ES0 in a current position of a focus lens and focus voltages ES+ +and ES- when the focus lens is moved by a distance dx in both a front and rear direction along an optical axis, so that a focussing shift value is calculated more accurately and quick focussing is achieved. A distance X0 from the current position of the focus lens to the focussing position is calculated based on the focus voltages ES0, ES+ and ES- according to: X0=dx (R+-R-) / 2 (R++R-) where R+=LN (ES+/ ES0) R-=LN (ES-/ ES0). With this arrangement, the distance X0 can be determined without factors for determining curves of the focus voltages and the magnitude of the width of the differential.