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.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a focus detection and processing method and apparatus employing a double-image coincidence technique by which an object's image is divided into two parts, the two parts are displaced in opposite directions or one of the two parts is displaced. When the object is in focus, the relative displacement of the two parts becomes a minimum. The outputs of a pair of photoelectric conversion element groups (hereinafter referred to as "sensor groups", when applicable) are processed to electrically detect the focusing position. More particularly, the invention relates to a focus detection and processing method and apparatus for a camera in which the sign of a focus detection output is changed before and after focusing. Not only front and rear foci are detected, but also an amount of movement of the photographing lens to the focusing position is instantly detected wherever the photographing lens is positioned.

A number of focus detecting techniques utilizing variations of spatial frequency, variations in contrast of an object's image or the above-described double-image coincidence technique have been proposed in the art and some of them have been put into practical use.

However, most of the conventional focus detecting techniques are disadvantageous in the following points. In these systems, when an object is in focus, the focus detection output has an extreme value, either a maximum value or a minimum value, and hence front and rear focus information is not available. Accordingly, in order to detect a focusing position, the focus detecting operation must be carried out over an entire photographing range of from infinity to the closest focusing distance. Thus, the operation of the device is intricate and the required detection time is long with the result that focus detection is impossible for a quickly moving object.

A focus detecting technique capable of providing front and rear focus information has been also proposed in the art. However, even with this technique, it is difficult to sufficiently carry out focus detection for a quickly moving object. Accordingly, the use of the camera is greatly limited and it is difficult to make the optimum use of all the functions of the camera.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a focus detecting method and apparatus for a camera in which the principle of double-image coincidence is utilized so that the focus of a quickly moving object, such as a moving automobile or a ball or players in sports which cannot be detected with a conventional focus detecting technique, can be satisfactorily detected, that is, the foci of a variety of objects over a wide speed range can be satisfactorily detected.

Specifically, in accordance with this and other objects of the invention, there is provided an automatic focusing device for a camera including means for determining a distance and direction to a focused position of a focusing lens while the focusing lens remains stationary and means for moving the focusing lens directly to the focused position in response to an output of the distance and direction determining means. The distance and direction determining means preferably includes first and second sensor groups, means for projecting images of an object transmitted through the focusing lens onto the first and second sensor groups, and means for shifting at least one of the images on the two sensor groups.

In preferred embodiments, the focused position of a lens is quickly calculated in accordance with formulas disclosed herein, such as with a micro-processor, so that the lens can be quickly moved to the correct focused position without having to perform successive calculations as the lens is moved as was needed with prior art focusing devices. Furthermore, the invention encompasses a method by which this focusing device operates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a focus detecting device utilizing the conventional principle of double-image coincidence;

FIG. 2 is an explanatory diagram showing the arrangement of light receiving surfaces of two sensor groups and the relationships thereof;

FIG. 3A is a graphical representation indicating an object's image on a second sensor group which is shifted to the left with respect to that on a second sensor group;

FIG. 3B is a graphical representation indicating an object's image on the second sensor group which coincides with that on the first sensor group;

FIG. 3C is also a graphical representation indicating an object's image on the second sensor group which is shifted to the right with respect to that on the first sensor group;

FIG. 4A is a graphical representation indicating variations of a sensor difference output V₀1 in the case where the object's image on the second sensor group is moved to the right from the first left sensor;

FIG. 4B is a graphical representation indicating variations of a zero position detection output F₀1 corresponding to the variations of the sensor difference output V₀1 in FIG. 4A;

FIG. 4C is a graphical representation indicating variations of a sensor difference output V₀2 in the case where the object's image is moved to the left from the first right sensor;

FIG. 4D is a graphical representation indicating variations of a zero position detection output F₀2 corresponding to the variations of the sensor difference output V₀2 in FIG. 4C;

FIG. 4E is a graphical representation indicating variations of a focus detection output V_out obtained according to the invention;

FIG. 5 is a block diagram showing a processing circuit for practicing a focus detecting method according to the invention; and

1i_l i₁ through i_n and j_l j₁ through j_n of sensor groups 8 and 9 are applied to an analog-to-digital converter 11 where they are converted to digital data which is stored in order in a memory circuit 12. The converter 11 and memory circuit 12 are controlled by a control circuit 15. The above-described sensor difference outputs V₀1 and V₀2, zero position detection outputs F₀1 and F₀2, sensor movement amount M and focus detection output V_out are calculated in an arithmetic circuit 13 under the control of the control circuit 15. The focus detection output V_out of the arithmetic circuit 13 is applied to a drive circuit 14, including a lens drive circuit and a display circuit, to carry out the focusing operation. The above-described arrangement can be simplified by the utilization of a microprocessor. For example, the memory, arithmetic circuit and the control circuit can be implemented with an Intel Corporation type 8080 microprocessor integrated circuit.

FIG. 6 is a flow chart FIGS. 6A-6C are flow charts showing operations according to the invention. By way of example, the case of p=53 will be described. (Although any value p<n is acceptable, it is desirable that p be small because the result of addition of the sensor difference outputs V₀1 and V₀2 becomes small as the value p approaches the value n.)

With a focus detection start signal obtained, for instance, by actuation of a focus detection start switch, as a trigger signal, the sensor outputs i_l i₁ through i_n and j_l j₁ through j_n are read into the memory circuit as digital numbers. Then, after the reference sensor difference output V_α0 in the case when the object's image on the sensor group 9 is moved to the right from the first left (-1) sensor) is calculated, the sensor difference outputs V(-1), V(0) . . . and V(3) are computed. Then, the output V_α0 is multiplied by the outputs V(p) successively thereby to obtain a sensor movement amount p which is at first different in sign from V_α0. The actual sensor movement amount M is calculated from the value p from which a focus detection output V_out is obtained. According to the focus detection output V_out, the display device and the photographing lens are operated to set the lens to the focusing position.

When no sign change is included in the product V_α0 ×V(p), the reference sensor difference output V_α00 in the case where the object's image is moved to the left from the first right sensor is calculated. Similar to the above-described case, calculations are carried out to obtain a sensor movement amount p. The focusing position is obtained from the value p.

If the sensor movement amount p cannot be obtained, it is displayed that focus cannot be detected.

As is apparent from the above description, in the focus detecting method and appartus according to the invention, an optical system utilizing the principle of double-image coincidence, which is simple to implement, is used, and immediately upon the focus detection being carried out according to the particular calculation method of the invention with the camera directed towards the object, a direction and a distance to the focusing position can be obtained. Accordingly, the camera can be focused on a quickly moving object which a device using the conventional detecting method cannot follow. That is, a camera using the invention can be focused on a variety of objects, either stationary or moving.

Claims

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, β₀ =A₀ /(n-1), β_p+2 =A₀ /(n-p-1) and A₀ 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, β₀ =A₀ /(n-1), β_p+2 =A₀ /(n-p-1) and A₀ 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.