Focus detecting method and apparatus

Abstract

An automatic focusing device and method for a camera in which the distance and direction to the focused position of a focusing lens of the camera are quickly determined after which the lens is moved directly to the focused position without the necessity of carrying out calculations as the lens is moved. Images of an object being viewed through the lens are projected onto first and second sensor groups. The outputs of the sensor groups are digitized then calculations are performed to determine the distance and direction to the position of correct focus. The lens is then moved to the focused position directly in accordance wtih the computed values.

What is claimed is: 
     
       1. An automatic focusing device for a camera comprising: first and second sensor groups;   means for projecting images of an object transmitted through a focusing lens onto said first and second sensor groups;   means for shifting at least one of said images on said sensor groups;   means for converting outputs of said first and second sensor groups to digital numbers;   means for storing said digital numbers;   calculating means for determining in succession: (1) a first set of successive values of: ##EQU10## for successive values of p for positive values of F, and a second set of successive values of: ##EQU11## for successive values of p for negative values of F where i k  are ones of said digital numbers corresponding to sensors of said first sensor group, j k  are ones of said digital numbers corresponding to sensors of said second sensor group with k indicating sensor positions within said sensor groups, n is the number of sensors in each said sensor group, p=-1, 0, 1, 2, . . . P with P being an integer less than n, β 0  =A 0  /(n-1), β p+2  =A 0  /(n-p-1) and A 0  is a predetermined constant;   (2) values of F=F S  and F=F S+1  where F S  represents the value of F before a change in the sign of F and F S+1  represents the value of F after a change in the sign of F for successive values of p, and S corresponds to an image movement amount from a prior position to a position corresponding to the value of p before said change in sign of F; and   (3) a value of M=S+F S  /(F S  -F S+1 ) if said change in the sign of said value F occurs during said first set of values and M=S-F S  /(F S  -F S+1 ) if said change in the sign of said value F occurs during said second set of values; and means for moving said lens directly from said prior position to a focused position determined in accordance with said value of M.       
     
     
       2. The automatic focus detecting device of claim 1 wherein said moving means moves said lens linearly in response to said value of M. 
     
     
       3. The automatic focus detecting device of claim 1 wherein P is significantly less than n. 
     
     
       4. A method for automatically focusing a camera having a focusing lens, first and second sensor groups, and means for projecting images of an object transmitted through said focusing lens onto said first and second sensor groups, said method comprising; shifting at least one of said images on said sensor groups;   converting outputs of said first and second sensor groups to digital numbers;   storing said digital numbers; determining first set of successive values of: ##EQU12## for successive values of p for positive values of F, and a second set of successive values of: ##EQU13## for successive values of p for negative values of F where i k  are ones of said digital numbers corresponding to sensors of said first sensor group, j k  are ones of said digital numbers corresponding to sensors of said second sensor group with k indicating sensor positions within said sensor groups, n is the number of sensors in each said sensor group, p=-1, 0, 1, 2, . . . P with P being an integer less than n, β 0  =A 0  /(n-1), β p+2  =A 0  /(n-p-1) and A 0  is a predetermined constant;   determining values of F=F S  and F=F S+1  where F S  represents the value of F before a change in the sign of F and F S+1  represents the value of F after a change in the sign of F for successive values of p, and S corresponds to an image movement amount from a prior position to a position corresponding to the value of p before said change in sign of F;   determining a value of M=S+F S  /(F S  -F S+1 ) if said change in the sign of said value F occurs during said first set of values and M=S-F S  /(F S  -F S+1 ) if said change in the sign of said value F occurs during said second set of values; and     moving said lens directly from said prior position to a focused position determined in accordance with said value of M.   
     
     
       5. The focusing method of claim 4 wherein said positioning is accomplished linearly with respect to M. 
     
     
       6. The focusing method of claim 4 wherein P is significantly less than n.