GB2286498A - Automatic focusing apparatus - Google Patents

Description

2286498 1,' AUTOMATIC FOCUSING APPARATUS 0 The present invention relates

to an automatic focus detecting and adjusting apparatus of optical instruments. More precisely, 11 relates to an automatic focusing apparatus which detects a moving object, which is to be photographed, follows the movement of the object and automatically and precisely focuses on the object.

Also, the -present invention relates to an automatic focusing apparatus in which the backlash of a lens driving system can be controlled.

In a known focus detecting focusing apparatus) of a camera predicting AF mode, a projected object (i.e., a future position of the object after a predetermined period of time) is determined in accordance with the movement of the object, so that the focus is adjus"ted for the projected position. In such a known focus detecting apparatus having a moving object predicting AF mode, the mode is switched between the moving object predicting AF mode and a normal AF mode in which the focus is adjusted for a moving or stationary object at the moment apparatus (automatic having a moving object position of the moving of measurement of the Consequently, an object to constant1v at object distance, respectively.

for example, in sports photographing' since be photographed, i.e., a player, is neither rest or in movement, it is necessary to frequently switch the AF mode in accordance with the state of the player. 1 However, freuent switching of the AF mode is troublesome. Furthermore, if sudden movement of the object occurs when a picture is taken in the normal AF mode, a photographer is unable to quickly switch the AF mode to the moving object predicting AF mode, or vice versa, thus resulting in a missed photograph.

Furthermore, in a conventional moving object predicting AF mode, when the object is moving, the projected position thereof at which the object would be in a predetermined period of time is predicted, so that the focus is adjusted for the projected position, as mentioned above. The focusing lens is moved by a predetermined displacement in accordance with the predicted position preceding or---subsequent to the completion of movement of the object.

The prediction requires a complex calculation which takes a relatively long time, resulting in decreased follow-up efficiency. To increase the calculation speed, it is necessary to use an expensive CPU (central processing unit).

There is a known optical instrument, such' as a camera, having an automatic focusing function in which an object distance or amount of defocus by a taking lens is photoelectrically detected to automatically indicate "out of focus" or 'Un focus" (focus indication) or automatically move the taking lens to a focal position (automatic focusing). In a focus detecting apparatus incorporated in such an optical instrument, continuous measurements of the object distance are sometimes carried out to increase focusing accuracyz However, particularly in a phase difference detecting a measurement error the same measuring conditions when the contrast of the object is low. Consequently, due to the measurement error, the focusing lens unit which is located at -a correct focusing position is moved to an incorrect position (i.e., out of focus position) by mistake, or a symbol representing "in focus" flickers to irdicate "out of focus".

Furthermore, an automatc focusing apparatus, in which the object distance or the defocus amount of the object image is photoelectrically detected so that the focusing lens unit is moved in accordance with the detected result to effect automatic focusing, is also known.

type of focus detecting apparatus exists for the same object under In the above described automatic focusing apparatus, backlash between an AF motor (drive source) and ocusing lens unit driving mechanism occurs. Therefore, direction of movement of the focusing lens unit it is necessary to eliminate the backlash effect.

end, in if the changes, To this the prior art, a value (displacement value) corresponding to backlash is added to a value (displacement value) calculated in accordance with the defocus amount, so that the focusing lens unit is moved by the resultant displacement.

An object of the present invention is to provide a focus detecting apparatus which can check whether or not an object to be photographed is a moving object.

Another object of the present invention is to provide an automatic focus adjusting apparatus in which when the object is a moving object, a focusing lens is moved in accordance with the speed of the moving object.

Still another object of the present invention is to provide a focus detecting caused by measurement error, Still another object apparatus free from maloperation particularly at low contrast. of the present invention is to provide an automatic focusing apparatus in which the displacement of a focusing lens unit necessary to absorb a backlash can be easiiy calculated to effect precise control.

According to the present invention, there is provided a focus detecting apparatus including an optical sstem having a group of focusing lenses, an object distance measuring means for measuring the amount of defocus for a specific object imaged by the focusing optical system, a focus judging means for judging the focusing state in accordance with the measurement of the object distance measuring means, and a lens driving means for driving the focusing lens group to a focal position in which the specific object is in focus, in accordance with the amount of defocus, wherein the focus detecting apparatus is characterized by a control means for repeatedly operating the object distance measuring means and the lens driving means, and a moving object judging means for judging that the specific object is a moving object when the focus judging means judges the outof-focus state more than one time during the repeated operations.

Examples of the present invention will be described below in detail with reference to the accompanying drawings, in which; Figure 1 is a block diagram of a single lens reflex camera having therein an automatic focusing apparatus embodying the present invention; Figure 2 is a graph showing an AF mode prior to a moving object predicting AF mode automatic Afocusing apparatus shown in Fig.

oeration in the 1 Figure 3 is a graph showing another AF mode operation prior to a moving object predicting AF mode in the automatic focusing ipparatus shown in Fig. 1; Figure 4 is a graph showing an AF mode operation in a moving object predicting AF mode in the automatic focusing apparatus shown in Fig. 1; Figure 5 is a graph showing an AF mode operation for an excess defocus state in a moving object predicting AF mode in the automatic focusing apparatus shown in Fig. 1; Figure 6 is a graph showing an AF 'mode operation in a moving object predicting AF mode in the automatic focusing apparatus shown in Fig. 1, when a release switch is turned ON while an object to be photographed approaches; Figure 7 is a graph showing an AF mode operation in a moving object predicting AF mode in the automatic focusing apparatus shown in Fig. 1, when a release switch is turned ON while an object to be photogrLphed moves away therefrom; Figure 8 is a flow chart of a main operation of an automatic focusing apparatus embodying the present invention; Figure 9 is a reference timer interruption operation of an automatic focusing apparatus embodying invention; Figures 10A and 10B are flow charts operation of an automatic focusing apparatus the present invention; Fiaures 11A the present of an AF embodying 81 11B and 11C are f low charts of reintegration operation in an AF mode operation and a moving object predicting AF mode operation; Figures 11D is a flow chart of an AFNG operation and terminal point point operation; Figures 12A-,and 12B are flow charts of calculations of defocus amount and drive pulses in an AF mode operation; Figures 13A, 13B and 13C are flow charts of a constant speed control operation in an AF mode operation; Figures 14A, 14B and 14C are flow charts of a defocus calculation operation, 10 bit selection operation, and flicker preventing operation at low contrast, respectively; Figures 15A, 15B and 15C are flow charts of calculation of a moving object following speed and a correction thereof; Figure 16 is a flow chart of a focus state checking operation and flicker preventing operation at low contrast; Figure 17 is a flow chart of an extremity detecting operation; Figure 18 is a graph showing a second moving object - 8 predicting AF mode operation in an automatic focusing apparatus embodying the present invention; Figure 19 is a graph showing the second moving object predicting AF mode operation shown in Fig. 18, when a release switch is turned ON; Figures 20A,, 20B and 20C are flow charts of calculations of a moving object following speed, etc,., in the second moving object predicting AF mode operation shown in Fig. 18; Figures 21A and 21B are flow charts of a constant speed control operation. in the second moving object predicting AF mode operation shown in Fig. 18; and, Figure 22 is a flow chart of an integration operation in the second moving object predicting AF mode operation shown in Fig. 18.

Figure 1 shows a block diagram focusing (AF) single lens reflex camera to present invention is applied. The AF single lens reflex camera includes a camera body 1 and a taking lens 51 which is detachably attached to the camera body 11. A large part of a bundle of rays transmitted through the taking lens 51 of the camera body 11 is reflected by a main mirror 13 toward a pentagonal prism 15 which constitutes a finder of an automatic which the - 9 optical system. A part of the reflected light is made incident upon a light receiving element (not showr-) of a photometering IC 17. The incident light transmitted through the lens 51 is partly transmitted through a half mirror portion 14 of the main mirror 13 and is reflected downwardly by an auxiliary mirror 19 to be made incident on an object distance measuring CCD'sensor unit 21.

The light receiving element provided i th photometering IC 17 outputs electrical corresponding to the quantity of light received thereby.

The output analogue signals are logarithmically compressed in the photometering IC 17 and are then sent to a main CPU through a peripheral control circuit 23 to be converted to digital signals in the CPU 35. The main CPU 35 calculates optimum exposure factors (i.e., shutter speed and/or diaphragm value) in accordance with object brightness and film sensitivity, and so on.. As a result, the releasing operation is carried out (i.e., shutter mechanism 25 and diaphragm mechanism 27 are driven) in accordance with the optimum shutter speed and diaphragm value to expose the film. When the releasing operation is effected, the peripheral control circuit 23 drives a mirror motor 31 through a motor driving circuit 29 to effect the up-down movement of the main mirror 13. Upon completion of exposure, a winding motor 33 is driven to wind the film.

n e sianals The object distance measuring CCD sensor unit 21 is a phase difference detecting type having a beam Plitter for splitting a bundle of rays (object light) and CCD line sensors which receives the respective split beams and integrates them (i.e., photoelectric conversion and accumulation of electric charges). The object distance measuring CC.D sensir unit 21 outputs the integration data by the CCD line sensors to the main CPU 35 as a control means. The object distance measuring CCD sensor unit 21 is driven and controlled by the main CPU 35 and the peripheral control circuit Z3. The CQD sensor unit 21 has a monitoring element through which the peripheral control circuit 23 detects the brightness of an object to be photographed, so that the integration time is varied in accordance with the object brightness.

The main CPU 35 performs a predetermined calculatiop (prediction calculation) to calculate the amount of defocus in accordance with the integration data output from the photometering CCD sensor unit 21 to thereby obtain the direction of -rotation and the number of revolutions (i.e., number of pulses of an encoderp 41) of an AF motor 39 in accordance with the defocus amount. As a result, the main CPU 35 drives the AF motor 39 through an AF motor drive circuit 37 in accordance with the direction of rotation and the number of pulses of the AF motor 39 thus obtained. The main CPU 35 detects and counts the number of pulses output by the encoder 41 in accordance with the rotation of' the AF motor 39 and stops the AF motor 39 when the counted value reaches the number of pulses. The main CPU 35 norially drives the AF motor 39 by DC control, and maintains the AF motor 39 at low constant speed (constant speed control) in accordance with thd- interval of the pulses output from the encoder 41. The rotation of the AF motor 39 is transmitted to the taking lens 51 through a joint 47 provided on a mount of the camera body 11 and a joint 57 provided on a mount of the taking lens 51 to be connected to the joint 47.

"DC control", referred to above, is indicative of the AF motor 39 being driven by a substantially direct current. "Constant speed control", referred to above, is indicative of the AF motor 39 being driven at a constant speed. I'DC control" and "constant speed control" are realized by a PWM control in the illustrated embodiment.

The main CPU 35 is connected to a photometering switch SWS which is turned ON when a release button (not shown) is depressed by a half step, a release switch SWR which- is turned ON when the reAease button is depressed by a full switch step, an automatic focusing switch SWAF, and a main SWM which is actuated to turn ON and OFF the power source connected t the 'main CPU 35 and the peripheral elements, etc. The main CPU 35 indicates the set AF, 1 exposure value, photographic modes, shutter speed, 1 ( B L A N K) diaphragm value, etc., in indicator units 45 which are usually provided on the outer surface of the camera body 11 and within the field of view of a finder.

The main CPU 35 serves not only as a control means for generally controlling the whole camera system, but also as a focus detectIng means and a moving object judging (checking) means. The main CPU 35 constitutes an object distance measuring means together with the CCD sensor unit 21 and the peripheral control circuit 23, etc., and a lens driving means together with the AF motor 39 etc., respectively.

13 The taking lens 51 includes a focus adjusting mechanism 55 for moving a focusing lens unit (grp'up) 53 in the optical axis direction, the lens joint 57 provided on the lens mount of the takIng lens and connected to the body joint 47 of the camera body 11 to transmit the rotation of the AF motor 39 to, the focus adjusting mechanism 55, and a lens CPU 61 for alculating the necessary data of the taking lens 51. The lens CPU 61 is connected to the peripheral control circuit 23 of the camera body 11 through groups of electrical contacts 59 and 49, so that the data communication between the main CPU 35 and the lens CPU 61 is effected through the peripheral control circuit 23. The data sent from the lens CPU 61 to the peripheral control circuit 23 includes an open diaphragm value, maximum diaphragm value, focal length, and K value, etc. The K value represents the number of pulses of the encoder 41 (i.e., number of revolutions of. the AF motor 39) necessary for moving the image plane formed by the taking lens by a predetermined unit displacement (e.g., 1 mm).

The following discussion will be directed to the AF operation with reference to Figs, 2 through 9.

The AF operation of the single lens reflex camera starts when the photometering switch SWS is turned ON. In the AF operation, the photometering CCD sensor unit 21 commences the integration first. Thereafter, the main CPU calculates the amount of defocus and the number of drive pulses in accordance with the integration data.

Consequently, the AF motor 39 is driven in accordance with the number of drive pulses thus obtained. In the illustrated embodiment, the AF mode functions in the same way that the normal AF mode functions when the object is still, and functioHs as the abovementioned moving object predicting AF mode when the object moves. Furthermore, the AF mode also includes an AF single mode in which the focused state is locked when no object moves, and a focus priority AF mode., in which release can be effected only in the focused state.

The operation prior to the moving object tracing AF operation (i.e., moving object predicting AF mode) is as follows (Figs. 2 and 3).

The graphs of Figs. 2 and 3 show the relationshkp between the position of an object image plane and the position of a plane equivalent to a film plane (focal position), with respect to the position (reference position) of -the focusing lens 53 when the moving object approaches the camera. In Figs. 2 and 3, "1" designates the integration operation, "C" the calculation, and "M" the movement of the lens (lens driving operation), respectively.

When control enters the AF operation after the photometering switch SWS Is AF motor 39) is driven in (i.e., number of drive integration operation I turned ON, the lens (i.e., the accordance with the dispXacement pulses) obtained by the first and calculation C. In the illustrated embodiment, as a result of the first integration and calculation after the photometering switch SWS is turned ON, if the defocus amount (i.e., number of drive pulses) is above a predetermined value, the integration operation and calculation are repeated during the movement (drive) of the lens. If the defocus amount becomes smaller than the predetermined value during the repeated integration and calculation, the subsequent integration operation and calculation are stopped, and the lens is moved In accordance with the number of drive pulses obtained by the latest integration operation and calculation. The integration operation and calculation wil,l also be referred to as an object distance measuring operation hereinafter.

Upon completion of the first lens driving operation, the integration operation and calculation are again effected to check whether the? object is in focus. If the object is in focus, the object may be considered still, with a slight possibility that the object is moving. To compensate for the slight possibility that the object is moving, the object distance measuring operation is effected after the lapse of the lens is driven.

the operation of predetermined time interruption, the the - 16 a predetermined time, and if necessary, If the main routine is interrupleo ky release switch SWR during the release is effected. If there is no object distance measuring operation and the lens driving, operation are repeated while the photometering switci SWS is ON.

If a focused state is not attained during a predetermined number of repeated object distance measuring operations and lens driving operations (e.g., three times), the object is deemed a moving object, and the control enters the moving object predicting AF mode routine (Fig.

3).

In an alternative embodiment, the object distance measuring operation and the lens driving operation are repeated, while the photometering switch SWS is ON, and i.f a focused state is not attained during the three consecutive object distance measuring operations and lens driving operations after the object is once focused, control entert the moving object predicting AF mode routine (Fig: 3).

Moving Object Predicting AF Mode:

The moving object- predicting AF mode routine will be discussed below.

1 1 Figures 4 and 5 are graphs showing the operation in the moving object predicting AF mode, by way of dxample. When the defocus amount DP (i.e., number of pulses) is obtained by the calculation C in accordance with the integration operation I, which is performed when the object is a moving object., the lens is driven (lens drive M) in accordance with the'aefocus amount DP.

Upon completion of the lens drive M, the integration operation 1, (11) is carried out again to calculate the defocus pulse number DP, (DPl). Thereafter, the moving speed (moving objject follQwing speed) S of the object image plane is calculated by the calculation C, (Cl) in accordance with the time T, between the intermediate point of the preceding integration operation I and the intermediate point of the present integration operation I, Thereafter, to make the object image plane coincident with the film plane within a short space of time, the constant speed control M, (multiplied speed lens driving operation) is effected in the time TI (T1) at a speed several times (e.g.

two times) the moving object following speed S. While the integration operation I,. is performed after the doubled lens driving operation M, (M1) is completed, the constant speed control (lens driving operation) M, is effected at the moving object following speed S,. The moving speed of the object image plane corresponds to the speed of the - is - movement of the object image plane, formed by the taking lens 51, in the optical axis direction.

Upon completion of the integration operation 12, the lens drive M2 is finished, and the calculation C2 is performed. In the calculation C21 the moving object following speed S, of the object image plane is calculated in accordance witfl the defocus pulse number DP2 the calculated moving pulse number MP, of the moving object, and the time T2 between the integration operations I, and 12. Consequently, the multiplied speed lens drive M3 is performed at a speed two times the moving object following speed S, for the time t2 in which the calculation C, has been effected. When the multiplied lens drive M3 is completed, the integration operation 13 commences. During the integration operation 13. the multiplied lens drive M4 is performed at the moving object following speed S3.

The focusing lens 53 may move beyond the focal' position due to the double speed lens drive. For example, in Fig. 4, the excess displacement is represented by the defocus pulse number DP3 In the double speed lens drive %. If the excess displacemenp (defocus pulse number DP,) is below a predetermined value, it can be considered that the object is continuing to move, and accordingly, the multiplied speed les drive M, is performed at the double speed of moving object following speed S3 after the - 19 calculation C3 is finished.

Conversely, the excess displacement (defocud pulse number DP. may be larger than the predetermined value. There are several cases that may have caused this, for example, the moving speed of the object may have been decreased, the object may have stopped moving, or the direction of the m6vement of the object may have changed, etc. In these cases, the checking operation is performed without effecting the lens driving operation, for example, as shown in Fig. 5.

In Fig. 5j. if the excess defocus pulse number DR, above the predetermined value is obtained by the integration operation 14 no operation (lens driving operation) is effected for the time t4 which has been required for the calculation C,. Thereafter, upon commencement of the subsequent integration operation I&, the tracing (following) lens drive M7 is effected at the object following speed S, obtained in the preceding calculation C4. If the defocus pulse number DPr, within the predeterminedvalue is obtained by the integration operation is, the tracing F operation (i.e., normal multiplied speed lens driving operation)is performed.

If an object image cannot be brought within the focus range, even by the two checking operations in which a multiplied lens driving operation is not effected, and - 20 since it is considered that either the speed of the object has decelerated, the object has stopped moving, 'or the direction of the movement of the object has changed, the control is returned from the moving object predicting AF mode to the normal AF mode, as shown in Fig. 2.

As can be seen from the foregoing, the change in state (i.e., direc.Eion, speed, etc.) of the moving object can be certainly detected by the two checking operations of the focus state. Although the two checking operations are repeated in the illustrated embodiment, the number is not limited to two and can be more than two. Furthermore, it is possible to realize a modified construction in which a tracing lens driving operation is not effected in the checking operations Calculation 1 of Moving Object Tracing Speed (Objec.t Image Moving Speed):

The moving object following speed S can be calculated as follows (Figs. 4 and 5).

The first moving object following speed S, is obtained by the equation belgw, in accordance with the defocus pulse number DPI obtained by the first integration operation I, and the time T1 between the intermediate point of the preceding integration operation I and the intermediate point of the present integration operation I,.

X, =TI /DPI (ms) S, =1/X, =DPJT, (pulse/ms)... Q wherein X, (Xl) is the output cycle (ms) of the pulses generated by the encoder 41.

The moving object following speed Sg is substantially or approximately eual to the moving speed of the object image plane.

The multiplied lens drive M, is carried out at a speed (2. DP,/T1), two times the moving object following speed S, thus obtained, during the time TI corresponding to the integration operation time (interval) T, so that the focusing lens 53 is moved to the vicinity of the focal position at high speed. Thereafter, the tracing lens drive M, is effected at the moving object following speed S, during the integration operation I, to follow the movement of the moving object.

Calculation 2 of Moving Object Tracing Speed Sn:

During---thetrace of the movement of the moving object, the moving object tracng speed Sn is obtained as follows.

First, the lens drive pulse number MP, corresponding to the displacement whic is obtained on the assumption that the object continues moving at the moving object tracing speed S, in the time T2 between the intermediate point of the preceding integration operation I, 4nd the intermediate point of the present integral I, is obtained by equation below.

MP, =T, x S,...

Thereafter, the output cycle X. of the AF pulse corresponding to Ehe object tracing speed S2 is first obtained in accordance with the time T. between the intermediate point of the preceding integration operation I, and the intermediate point of the present integration operation I,, the pulse number MP, which is assumed to correspond to the displacement within the time T., and the present defocus pulse number DP2. The object tracing speed S2 is then obtained as follows.

X2=T2 / (MP 1 + DP2 S2=1/X2 (ms)... @) =(MP, + DPz)/Ta (pulse/ms)... (5) The lens drive M2 is effected at a speed twice the object following speed S2 for the time t, required for the calculation C-2. Af ter the lens drive M. at double speed is finished, the lens drive % is effected at the moving object following speed S2 for the time period of integration operation 13 to follow the movement of the moving object.

Note that the defocus pulse number DP is represented by a scalar value in the calculations mentioned above, the sign (+ or depends on a front focus or rear' focus.

Accordingly, in case of excess displacement, the pulse number MP, corresponding to the displacement within the time T2 is subtracted by the present defocus pulse number DP,.

For example,

MP, =T, x S. G X,,=Tn/(MP,-, DP,) (ms) a) S,,=1/X,, (pulse/ms) (& The repeated calculations of the equations (D, (D and mentioned above and the lens driving operation and the integration operations in accordance with the calculation results make it possible to follow the movement of the object as shown in the drawings. In the illustrated embodiments, since the calculated moving pulse number MP,,, (MPn-1) of the object image and the calculated defocus pulse number DP, (DPn) are absolute numbers, (MP, - l DP, in equation (D is replaced by (MP, + DP, (MPn-1 + DPn) or (MPn - 1 DPn) (MPn-1 - DPn) in the case of rear f ocus and front focus, respectively.

As can be understood from the above discussion, after the calculation isfinished, the lens is driven at the speed two times the m6Ving object following speed S, for the time required for the calculation. This is because the image plane must be moved by the displacement corresponding to the movement of the moving object after the lens ',driving operation has stopped and before the subsequent lens driving operation is completed. Namely, the relationship defined by S. X (lens stop period+ lens driving period)=(lens driving speed x lens driving period can be obtained by. an esier calculation. Therefore, it is possible to drive the lens at a different object following speed, provided that the above relationship is satisfied.

Operation when the Release Switch is turned ON:

Y The operation when the release switch SWR is turned ON during the moving object predicting AF mode operation is as follows (Fig. 6).

Generally speaking, since the mirror is --moved up after the release switch is turned ON in a single lens reflex camera, a certain amoun t of time Is required before the film is actually exposed after the release switch is turned ON. This is referred to as release time lag RTL. In the case of '& moving object, since the object continues to move during the release timey lag RTL (i.e., after the release switch SWR is turned ON and before the exposure commences), it is preferable to continuously drive the lens to follow the movement of the object.

To this end, in the illustrated embodiment, whether 1 - 25 or not the release switch SWR is turned ON is checked at the completion of the necessary calculations. 'If the release switch SWR is turned ON, the lens drive M, is performed at a speed twice the moving object following speed S. for the calculation time t, plus the release time lag RTL, so that the focusing lens 53 is initially moved in the optical axis direction by an additional (excess) displacement corresponding to the release time lag RTL.

Operation when Object moves away from Camera:

Upon completion of the double speed lens drive the photometering calculation and the upward movement of the mirror are effected, so that the diaphragm is adjusted to a calculated value, and the shutter mechanism 25 is driven at the calculated shutter speed.

The above-mentioned operations are operations n which the object approaches the camera. If the focusing lens is initially moved through the excess displacement, for an object moving away from the camera, as mentioned above, a "rear focus" occurs. Since the depth of field decreases as the object distange decreases, a "front focus" is preferable to rear focus. Furthermore, in the case of the object moving away, the moving speed of the image plane gradually decreases, provided that the moving velocity of the object is constant.

In view of these phenomena, In the present invention, in the case of the object moving away from the camera, the lens is driven at the multiplied speed for a time equal to half the time as in case of the object approaching the camera. Namely, in Fig. 7, the lens driving operation is effected at a speed twice the object following speed S3 for a tide equal to half the calculation time t, plus the release time lag RTL, i.e., the time defined by (t,,+ RTL)/2.

Main Operat-ion:

The main operation of the present embodiment will be discussed below in more detail, with reference to Figs. 8 through 15.

The operation is performed by the main CPU 35 in accordance with the program stored in an internal ROM 3_5a thereof. The data, such "as constants or parameters necessary to conduct the calculations are stored in an E 2 PROM 43.

Figure shows a main routine of the main operation of the main CPU 35. When the xpain switch SWM is turned ON, the control enters the main routine in Fig. 8. First, at step S101, the system of the main CPU 35 including various ports and the memory, etc., is initialized. Thereafter, the power down operation is performed to decrease the 1 1 - 27 unnecessary electrical power consumption (step S103). At step SIOS, whether or not the photometering switch SWS is turned ON is checked (step S105). The power down operation is retained and the checking operations are repeated until the photometering switch SWS is turned ON.

If the photometering switch SWS is turned ON, a reference timer 35c starts, and the states of the switches, such as the AF switch SWAF are checked (steps S107, S109). Thereafter, the data communication with the lens CPU 61 is carried out to receive the lens data, such as the open diaphragm value, the maximum diaphragm value, the focal length, and the K value data, etc., at step S111.

The photometric data is input to the main CPU 35 f rom the photometering IC 17, so that the shutter speed and the diaphragm value are calculated, based on the photometric data and the film sensitivity, etc., in accordance with a predetermined algorithm (step. S113). The calculated shutter speed and the diaphragm value thus obtained are indicated in the indicator unit 45 at step S115. Thereafter, the AF operation is performed.

Every time the set time, of the reference timer 35c has expired during the repeat of the operations of steps S109 through S119, the main routine is interrupted by a reference timer roitine shown in Fig. 9. In the reference timer routine shown in Fig. 9, the loop time is counted and - 28 the states of the photometering switch SWS and the release switch SWR are input (steps S121 and S123).

After the photometering switch has been checked, the release switch SWR is checked after the operation' for detecting terminal, which will be discussed with reference to Fig. 17.

hereinafter If the release switch SWR is turned OFF or if tHe release switch SWR is turned ON but a permission signal of the release is not issued, for example, if the object is not focused in the focus priority mode, control is returned to the step prior to the interruption by the reference timer routine (steps S125 and S127).

If the release switch SWR is turned ON and release is permitted, the release is performed. During the release operation, the mirror motor 31 is driven to move the mirror up and the diaphragm mechanism 27 is driven to adjust the diaphragm value to the calculated value obtained at step S113 (steps S131 and S133).

Upon completion of the upward movement of the mirror, the exposure mechanism 25 is driven to effect the exposure at the shutter speed calculatep at step S113 (steps S135, S137). When the exposure is finished, the mirror motor 31 is driven to move the mirror down and the film winding motor 33 is driven to wind the film by one frame (step S139). Thereafter, control is returned to step S107.

AF Operation:

The following discussion will be directed to' the AF operation of an embodiment of the present invention, with reference to Pigs. 10 through 13.

First, whether the focus mode is the AF mode or the MF mode (manual focus mode) is checked. If the mode is the MF mode, control Simps to step S211 (step S201). The AF mode and the MF mode referred to above are the automatic focus adjusting mode and the manual focus adjusting mode in which the focus is adjusted by a photographer, respectively.

When control enters. the AF operation routine in the Y AF mode for the first time, since an integration operation is not performed, it is not in the AF lock state (i,e., AF lock flag is "0"), the object is not in focus (i.e. the flag IN FOCUS is "0") and the reintegration flag is 11011, control jumps to step S211 (steps S203, S205, S209). In tjie second operation or operation subsequent thereto, if the AF lock flag is I'll', control jumps to the step for performing the AF lock operation. If the AF lock flag is "0", and if the object is focused, i.

elapsed after the object is onpe focused, the AF lock flag is set at "V', and the reintegration operation is performed (steps S203, S205 and S207). If the object is not in focus, but the operation is -the second AF operation or the operation subsequent thereto, since the reintegration flag e., if a predetermined time has 0 30 a is "1", the reintegration operation is carried out (steps S203, S205 and S209).

If the operation is the first AF operation, or ' the focus mode is the manual focus mode, control proceed s to step S211 (steps S201, S203, S205, S209). Whether or not the AF operation is being performed is checked at step S211, and whether or not the MF operation is being performed is checked at step S213, respectively.

If the operation is performed in the AF mode (first AF operation), control proceeds to step S231. If the operation is pefformed, vot in the AF mode but in the MF mode, the object distance measuring operation and focus state indication operation are effected (steps S215 through S227).

At step S215, the integration and calculation operations are carried out. Thereafter, whether or not the calculation results are effective is checked at step S217. If the calculation results are effective, and if the object is in focus, the in-focus state is indicated by lighting a focus indicating LED (not shown) of the indicator unit 45. In addition thereto, an electronic buzzer (PVC) 46 is sounded to alert the photographer of the in-focus state (step S219). If the object is out of focus, an indication operation is not effected.

If the object contrast is low and the operation is J -1 the first operation of the routine, control jumps to step S229, and if the operation is not the first AF operation at low object contrast, whether or not the object is in-focus is checked (steps S221 and S223). If the object is in-focus, the release permission flag is set at 'Ul' and control proceeds to step S229 (steps S223 and S225).

Conversely, if the--- object is not in-focus, the secondary focus width (focal range) flag is cleared and the focus, release permission flag and the AF lock flag are cleared.

Thereafter, the indication of the indicator unit 45 and the operation of the. buzzer...46 are ceased (steps S223 and S227). Thereafter, control proceeds to step S229.

If the calculation results are not effective, the secondary focal width is cleared, and the focus, release permission flag, and the AF lock flag are cleared. Thereafter, the indication of the indicator unit 45 and the operation of the buzzer 46 are ceased (steps S217 and S227). Thereafter, control proceeds to step S229 in which the loop time is checked. If a predetermined loop time has not elapsed, lbontrol is returned to step S211 to repeat the operations mentioned above. It a predetermined loop time has elapsed, control is returned to step S109 of the main routine.

If the operation 'Is the AF operation at step S211, control proceeds to step S231 to enter the AF operation 1 1 routine. At step S231, the integration and calculation operations are effected. Thereafter, whethek the calculation results are effective is checked at step S233.

If the calculation results are effective, control jumps to step S261 in which the focus state is checked. Conversely, if the calculation, results are not effective, whether or not the mode. is an-auxiliary light emission mode is checked (step S233). In the auxiliary light emission mode, infrared auxiliary light (contrast pattern) is emitted toward the object from an auxiliary light emitter (not shown) when the brightness of the object, is smaller than a predetermined value. In the auxiliary light emission mode, since it is difficult to follow the movement of the moving object, the moving object predicting mode forbidding flag is set (step S237). Thereafter, the auxiliary light is emitted and the integration and calculation are effected. Thereafter, the calculation results are checked(steps S239 and S241). if the calculation results are effective, control proceeds to state is checked. Conversely, are not effective, control thop mode is not the auxiliary light emission mode, control jumps steps S237 through S241 and goes to step S243. The steps following S243 involve a search integration operation.

At step S243, the AF motor 39 is driven by the DC step S261 in which the focus if the calcUlation results proceeds to step S243. if control, since effective calculation results were not obtained. Thereafter, the search integratioh and calculation are effected to detect the focal point at step S245. The calculation results are checked at step S247. if the calculation results are not effective, the search integration and calculation are effected again, and if the calculation results--- are effective, control proceeds to step S373 where the driving direction is checked (step S245 and S247).

Reintegration and Focus Check Operation:

Figures 11A and 11B show the sub-routine of the reintegration and focus check operation.

Reintegration is a second integration operation or an integration operation subsequent thereto. In the reintegration operation, the reintegration flag is set gt 11111, and then, the integration and the calculation for obtaining the defocus amount are effected (steps S251, S253). Ther-eafter, if the calculation results of the defocus amount are not effective, control proceeds to the AFNG operation, and if thq calculation results are effective, control proceeds to the step that checks the focus state (step S255).

In the focus state checking operation, whether the object is in focus is checked. If the object is in focus, - 34 the focus indicating LED of the indicator unit 45 is lightened and the electronic buzzer (PCV) 46 is dctuated (step S261). Conversely, if the object is out of focus, no operation is effected.

Thereafter, at step S263, if the object is out of focus for the first time at a low object contrast, control -is returned to ste;b S251, and the integration operations, etc., are carried out. If the object is not out of f ocus at a low object contrast at step S263, if it is in focus at S265, and if the mode is not the moving object predicting mode, the AF rebease permission flag is set at I'll' (steps S263, S265, S267 and S269).

If the mode is not the AF lock mode (i.e., if the AF lock flag is not set), control proceeds to step S273.

Namely, the AF lock flag is set in the first operation after the object is in focus, and if the AF lock flag has already been set, the operation is the second operation or the operation subsequent thereto (steps S271, S273). So that control proceeds to AF lock operation S283.

If the.-AF lock flag is set at 11111 at step S273, control does not proceed for a,predetermined period of time in which the operation may be interrupted by the release operation, provided that the object contrast is high and the moving object predidtion forbidding flag is "0". If no interruption occurs within the predetermined time, the AF - 35 release permission flag is cleared to forbid the releasing, and the AF lock flag is cleared to permit the AF operation (steps S275, S277, S279 and S281). Thereafter, the AF lock operation starts. When the loop time has elapsed, control is returned to step S109 in the main routine (step S283). If the object contxast is not high, or the moving object prediction forbiddi6g flag is set at 1, control immediately proceeds to the AF lock operation without waiting for a predetermined time (i.e. operation interruption by the release operation). The preceding is shown at steps S275, S277, S283. In --,the AF 1.ock operation, once the object is focused, an AF operation is not performed while the photometering switch SWS is turned ON.

In the focus checking operation at step S265, if the object is out of focus, the control skips to step S285 to check whether or not the mode is the moving object predicting mode. If the mode is not the moving object predicting mode, the control proceeds to step S301 moving object^ checking operation), and if the mode moving object- predicting mode, the control proceeds (i.e., is the to step S321 (step S285).

In the moving object checking operation where it is checked whether or not the object is the moving object (Figs. 2 and 3), te se';do'ndary focal width flag, the focus flag, the release permission flag and the AF lock flag are - 36 cleared and the focus indicating LED of the indicator unit 45 and the electronic buzzer (PCV) 46 are turned OFF (step S301).

Thereafter, if the reintegration flag is clear at step S303, control jumps to the pulse number calculation operation and if the reintegration flag is set, control proceeds to step S3D5 in which the direction of the present movement of the lens is compared with the direction of the previous movement thereof (step S305). If the directions J, themoving object judging counter s decremented by one, provided that the object contrast is high and the moving object prediction forbidding flag is clear (steps S307, S309, S311 and S313). Note that the initial value of -the moving object judging counter is "3" in the illustrated embodiment.

Conversely, if the direction of the present movement of the lens is not identical to the direction of the previous movement thereof at step S305, the object contrast is not high,' or the moving object prediction forbidding flag is set-at "111, control jumps to the pulse number the counting of the movements are identical to each other calculation operation without, performing operation (steps S307, S309 and S311) After the moving object judging counter is decremented by one, it 'Is checked if the counted value is 0. If so, the moving mode predicting mode flag is set and 1 1 - 37 the moving object judging counter is reset (steps S315, S317 and S319). Thereafter, the pulse number calculation operation is performed. If the counted value is not 0, control proceeds directly to the pulse number calculation operation (step S315).

If the mode is the moving object predicting mode at.step S285, the focus flag, the release permission flag and the AF lock flag are cleared, and the focus indicating LED of the indicator unit 45 and the electronic buzzer 46 are turned OFF (step S321).

Thereafter,- the defocus pulse number is calculated in accordance with the result of the latest integration operation at step S323. The defocus pulse number thus obtained is a value for the object at an intermediate point of the integration operation time.

Thereafter, the speed (following speed) of the movement of the object is calculated in accordance with the calculated pulse number for the movement of the object, the present defociis pulse number, and the integration operation time between,' the intermediate points of the integration operations. Upon completion of, the calculation, the object following flag, which is indicative of the object being traced, is set at 1 (steps S325 and S327). Thereafter, the defocus pulse number is get in the counter 35d, so that the operation for controlling the AF motor speed constant is 1 - 29 commenced (steps S329 and S331).

If the mode is the moving object predicti" mode within the focusing range at step S267, control proceeds to step S323.

The following discussion will be directed to the operation which is, effected when the result of the AF calculation -operation is void (AFNG operation), with reference to the flow chart shown in Fig. 11D. The AFNG operation is also performed as a part of the "terminal operation", which is performed when the focusing lens reaches the telephoto or wide extremity.

When the result of the AF calculation operation is void, in-focus indication LED 46 is effected to emit light in a blinking manner to inform the photographer that it is impossible to focus (S341). Then, the reintegration flag is set. The AE calculation operation is performed if the loop time has elapsed after thb loop time is checked. The control returns to the reintegration operation if the loop time has not dlapsed (S342, S343).

Pulse Calculation and Backash Drive:

The following discussion will be directed to the calculation of pulse number and backlash drive, with reference to Figures'12A-ard 12B.

The pulse calculation calculates the number of pulses 1 1 - 39 corresponding to the defocus amount and the number of pulses necessary for eliminating backlash.

The backlash drive referred to is indicative of, the driving of internal gears of the AF motor 39, the jints 47 and 57, and the lens driving mechanism 55 to eliminate backlash, for example, when the direction of the driving operation of the Alr motor 39 changes. In the illustrated embodiment, the backlash driving operation is separately carried out prior to the driving operation based on the defocus amount.

In the pulse calculation, first, the defocus pulse number is calculated. If the direction of the driving operation is different from that of the previous driving operation, the backlash pulse quantity is calculated, and the backlash drive flag is set at 1 (steps S351 and S353). The backlash pulse quantity referred to is indicative Qf the pulse number and direction necessary to remove the backlash. The backlash value of the camera body 11 stored in the E2PROM 43, and the backlash value of taking lens 51 is stored in the ROM of the lens CPU 61 1 is the and can be stored in the RAM 35b of, the main CPU 35 through the peripheral control circuit 23 by the data communication.

If the backlash drive flag is not set, the defocus pulse number is set as' the AF pulse number in the counter and if the backlash drive flag is set, the backlash pulse a 40 a number is set as the AF pulse number in the counter, respectively. Thereafter, the DC drive of the AF mbtor 39 is commenced (steps S355 and S357).

If the backlash drive flag is cleared, and if the mode is not the moving object predicting mode (i.e. the moving object predicting mode flag is cleared), the value of the counter i!j compared with a predetermined pulse number (steps S363 and S365). If the counted value is above the predetermined pulse number, the moving object prediction mode is cleared (S367) and an overlap calculate the defocus overlap integration operation referred to is indicative of an integration operation being executed during the lens driving operation.

After the defocus amount is calculated, whether or not the defocus amount is effective is checked at step S371. If the defocus amount is ineffective, control is returned to step S363 and if the defocus amount is effective, control proceeds to the checking operation of the direction- of movement (steps S373 - S377).

In the direction checkng operation, whether the focal position is before or after the object image position and within a predetermined range (allowance) is checked in accordance with the defocus amount (steps S373, and S375). If the focal position is before the object image position integration operation is commenced to Y amount (steps S367 and S3691. The 1 1 and out of the predetermined range, the defocus pulse number is calculated in accordance with the defocus' amount calculated at step S369, and then, the calculated number is set in the counter (steps S375 and S377). Thereafter, control is returned to step S363. If the focal position is beyond the object image position, or within the predetermined range. the AF motor 39 is braked to stop the driving operation of the taking lens. Thereafter, control is returned to the reintegration operation (steps S375 and S379). The braking of the AF motor 39 is indicative of a short circuit of,the input terminals of the AF motor 39 in the illustrated embodiment.

If the backlash driving operation is necessary, the mode is the object moving predicting mode, or the counted value is smaller than the predetermined pulse number, the counted value of the AF pulse counter is compared with the predetermined pulse number. Control does not proceed until the AF counter value is smaller than the predetermined pulse number (steps S359- S365, S381 and S383).

If the-AF pulse counter value is smaller than the predetermined pulse number, the, AF motor 39 is braked when the mode is not the backlash drive mode. Thereafter, the constant speed control operation commences (steps S385 and S387).

In the case of the backlash drive mode, the AF pulse 1 1 - 42 number Is compared with the predetermined pulse number. if the AF pulse number is smaller than the predetermined pulse number, the AF motor 39 is braked, so that control proceeds to the constant speed control (steps S389, S391, S387).

The backlash driving 6Deration Is performed by the constant speed control.

if the AF pulse number is larger than the predetermined pulse number, control does not proceed until the DC drive, fow eliminciting backlash, is finished. Upon completion of the DC drive, the AF motor 39 is braked, so that the backlash drive flag is cleared to finish the backlash driving operation (steps S391, S393, S395 and S397). Thereafter, control is returned to step S355. In the case that the predetermined pulse numbers in S365, S383 and S391 are p, P2, i and P3 the following relationship is satisfied: P,> Pz = P,.

The defocus pulse number is set in the AF pulse counter, so that the lens driving operation for the normal AF operation is performed.

Thus, the backlash driving operation is carried out prior to the defocus driving operation. Furthermore, if the backlash pulse number is larger than a predetermined value, the backlash driving operation is performed by the 1 43 DC drive within an extremely short space of time, and if the backlash pulse number is smaller than a predetermined value, the backlash driving operation is performed by the constant speed driving operation so as not to exceed the predetermined backlash.

( B L A N K) 1 1 Constant Speed Control:

The following discussion will be directed to Constant speed control, with reference to Figs. 13A and 13B.

Constant speed control involves the control of the AF motor 39 at a constant speed. In the illustrated embodiment, the main CPU 35 controls the AF motor 39 so as to rotate the samg at a predetermined constant speed in accordance with the pulse interval output from the encoder 41. In a preferred embodiment, the AF motor 39 is rotated at a constant speed equal to or twice the moving speed S of the object image...

In the constant speed control operation, X, is set as the constant speed control time (pulse width) and the counter for the constant speed control is set (step S401). Thereafter, if the moving object is being traced, a double speed 2Sn twice the constant speed Sn is set (steps S403 and S405). If the integration operation is effected, the constant speed Sn is set to trace the moving object at thh tracing speed, and then control proceeds to step S411. no integral is effected, control proceeds directly to step S411 (steps S407 and S409).

At step S411, it is checked if the object is being traced and integration is underway. If the object is being traced and the integration is underway, control jumps to step S459 to check for the completion of integration.

Conversely, if neither the object is being traced nor the integration is underway, control proceeds to stdp S413 (step S411).

At step S413, whether or not the constant speed control time has elapsed is checked. When the constant speed control time has elapsed, the counter for the constant speed control is ieset, then the terminal point detecting timer is counted (S415). If the constant speed control time has elapsed, control proceeds to step S415 where it is checked whether or not the focusing lens has - 46 come to a terminal point. Thereafter, if the AF motor is being driven, control returns to step S411. If the AF motor is not being driven, the drive AF motor operation is carried out at step S419 and control is returned to step S401. Conversely, if constant speed control time has not elapsed, control proceeds to step S421. At step S421, whether or not the AF pulses are outputted from the encoder 41 is checked. If the AF pulses are not outputted, control is returned to step S411, and if AF pulses are outputted, control proceeds to step S423, respectively.

At step S423, whether the count of the pulses is completed when not in the moving object tracing mode, or the drive time for following the moving object has elapsed when in the moving object tracing mode is checked. If the count of the pulses is completed, or the drive time has elapsed, thebraking operation is effected. If neither the count of the pulses is completed, nor the drive time has elapsed, control proceeds to step S425.

At step S425, whether or not the focusing ens 53 reaches the terminal point is checked and the terminal point detecting timer Is reset. Thereafter, whether or not the counted value of the AF pulse counter is below a certain speed switching pulse number is checked. If the counted value is Selow the speed switching pulse number, the drive speed is switched to low speed, and then, the AF motor 39 is braked. Thereafter, control proceeds to step S433 (steps S427, S429, S431). At step S433, whether or not the AF motor 39 ts driven. is checked. If the AF motor 39 is driven, the AF motor 39 is braked. Thereafter, control is returned to step S401. Conversely, if the AF motor 39 is not driven, control is directly returned to step S401.

If the count of the pulse number is finished or the AF motor 39 Is or not the AF mode is set i drive time has elapsed at step S423, the braked at step S437. Thereafter, whether lock flag in the moving object predicting S checked. It the AF lock flag is set, the AF release permission fl:ag is set. Thereafter, control proceeds to the release operation (steps S439, P441 and S443). If the mode is not the moving object predicting mode, or the AF lock flag is cleared, whether or not backlash drive is effected, that is, whether or not the drive at present is backlash drive is checked. If backlash drive is effected, control proceeds to the backlash drive completion operation (S397).

If backlash drive is not effected, the reintegration flag is set and the loop time is checked. If the loop time ' has elapsed, control is returned to step S109. If loop time' has not elapsed, control proceeds to the reintegration operation (steps S445, S446 and-S447).

Fig. 13C shows the start integration, input CW data, and integration operation performed by defocus calculation (S215, S231, and S253). In the reintegration operation, the initialization for integration and calculation is effected. Thekreafter, integration commences and the integration flag is set (steps S451, S453 and S455). If the moving object is traced, control jumps to step S401 (i.e., constant speed control operation), and if the moving object is not being traced, whether or not integration is finished is checked (steps S457 and S459).

If integration is not completed, control proceeds to step S461 to check whether integration time is longer than a predetermined time. If integration time is longer than a predetermined- time, the moving object predicting mode forbidding flag is set at step S463, since the object brightness is considered to be small. Conversely, if the integration time is shorter than a predetermined time, control proceeds to'step 9465. If the moving object is not traced at S465, control is returned to step S459 to wait 1 1 for the completion of integration (steps S459 - S465). if the moving object is traced at S465, control is rettirned to step S413.

When integration is completed, and if the object is being traced, the AF motor 39 is braked. Thereafter, the integration data. is input_ from the object distance measuring sensor uilit 21 to determine the defocus amount.

After that, control is returned to the step that is subsequent to the step at which integration starts (steps S467, S469, S471 and S473). If the object is not being traced at S467, S-469 is skipped and control goes to S471.

Y Determination of Defocus Amount The following discussion will be directed to the determination of defocus amount which is performed at S473 with reference to Fig. 14. First, the calculation and check of contrast are effected (step S501). In the calculation of contrast, the sum of the differences of the integration data of the adjoining light receiving portions in - the CCD object measuring sensor unit are calculated. After that, whether,the contrast is high enough to calculate the phase difference is checked. If the contrast is low, control is returned, and if the contrast is sufficiently hight, the calculation of the phase difference is effected (steps S503 and S505).

At step S505, the phase difference is calculated, for example, by a correlation method or the like. If the mode is the 10 bit select mode, control proceeds to step 5551 (10 bit select operation), and if the mode is not te 10 bit select mode, control proceeds to step S509 (step S507). When the control first enter this routine, the mode is not the proceeds to referred to correlation comparative line sensor bif select mode, and accordingly, control step S509 (step S507). The 10 bit select mode is indicative of an operation in which, if the (identity) of the integration data between the portion and the reference portion of the CCD is not satisfactory, a plurality of 10 bit areas are successively selected from among the comparative portion and the reference portion of the CCD line sensor to obtain high correlative areas.

At step S509, whether or not the calculation results of the phase difference are effective is checked calculation results of the phase difference effective, control is returned.

If the are not Conversely, if the calculation -results are effective, the correlation is checked (steps S509 and S511)., If the correlation is good, a calculation of the defocus amount is carried out (steps S511 and S530). If the first out-of-focus flag at low contrast flag is et, and the defocus amount is smaller than a predetermined value, the defocus amount determined 1 by the by the present amount, value, S543).

present calculation is compared with that determined previous calculation (steps S533,S535,S537). If the defocus amount is smaller than the previous defocus the present defocus amount is set as an effective and the defocus OK flag is set (steps S539, S541 and Thereafter,.control is returned.

If the first--- out-of-focus flag at low contrast flag is not set, the present defocus amount is effective, so that the defocus OK flag is set (steps S533, S541 and S543). Thereafter, control is returned.

Even if the first out-of-focus at low contrast flag is set, if the defocus amount Is larger than a predetermined value, the previous defocus amount is made effective, and then, the defocus OK flag is set (steps S533, S535 and S543). Thereafter, control is returned. Even if the first out-of-focus flag at low contrast is set apd the defocus amount is less than a predetermined value, if the previous defocus amount is smaller than the present defocus amoufit, the previous defocus amount is retained. Thereafter, the defocus OK flag is set (steps S533, S535, S537r S539 and S543). Thereafter, control is returned.

As can be understood from the above discussion, if the object contrast is low, a smaller defocus amount is selected from thos of he present and previous defocus amounts, a maloperation due to a possible measurement 52 error, for example, an unsteady flicker of the indication of the infocus state or a failure to operate the AIP motor 39 does not occur.

If there is a poor correlation in the integration data at S511, the searching flag is checked at S513.Since the flag is 11011 when control first comes to this operation, continuation of for phase difference is performed at S515. If the result of calculation for phase difference is effective, control goes back to S511, and if not effective, the searching flag is set. Control then goes back to S505 (S517 and S519). After the searching flag has been set, control proceeds from S513 to S521 and, the phase deviation is compared with a reference value (S521). If the phase deviation is smaller than the reference value, the contrast is checked (steps S521 and S523). If the contrast is low, control proceeds to step S530. If the contrast s high, the 10 bit select mode -flag and the moving object predicting mode forbidding flag are set to select the first 10 bits. Thereafter, the number of checking operations is set (the- number is 4 in the illustrated embodiment). Thereafter, control is returne91 to step S505 (steps S523, S525, S527 and S529).

If the 10 bit select mode flag is set, control proceeds to step S551 (16 bit select operation) from step S507. In the 10 bit select operation, whether or not the 53 effective defocus amount based on the selected 10 bits is obtained by one operation is checked. If so, and' if the contrast is more than twice the previous contrast, the 10 bit select defocus OK flag is cleared to make the preious data null. Thereafter, control proceeds to step S559 (steps S551, S553,, S555 and S557). If the 10 bit select defocus amount is dot obtained at S551, control proceeds to step S559 directly. If the contrast is lower than the previous contrast, control proceeds to step S571, since the presently selected 10 bit data is not used (steps S551 and S555). If the present crast is greater than the previous contrast, but less than twice the previous contrast, control proceeds to step S559 without clearing the 10 bit select defocus OK flag (steps S551- S557).

At step S559, if the calculation result of the phase difference is effective, the defocus calculation is performed, provided that there is a good correlation (steps S559, S561 and S563). After the defocus calculation, 'the bit select defocus OK flag is checked (S565). If the 10 bit select defocus OK flag is set, the smaller of the present defocys amount and the previous defocus amount, i.e., a smaller defocus amount is selected (S565, S567). Thereafter, the 10 bit select OK flag is set and control proceeds to'step S571 (S569). If the 10 bit select defocus OK flag has been cleared control proceeds directly to step S569 and the flag is then set (S565,S569). Thereafter, control proceeds to step S57r (steps S565, S567, and S569). If the calculation result of the phase difference is not effective, or the correlation is bad, control proceeds to step S571 without calculating the defocus amount (steps S559 and S561).

At step S571',' the subsequent 10 bits are selected.

Thereafter, the counter that counts the number of 10 bit select checking operations is decremented by one. If the counter value is not 0, control is returned to step S505.

The operations from step. S551 to step S575 are repeated until the counter value is 0 (steps S573 and S575). The initial value of the counter is set at 11411 in the illustrated embodiment. If the counter value is 0, control proceeds to step S533 (i.e., the operation that prevents the unsteady flicker at low contrast), on the conditipn that the 10 bit select defocus OK flag is set. If no 10 bit select defocus OK flag is set, the 10 bit select mode flag is cleared '(steps S575, S577 and S579). Thereafter, control is returned.

Thus, the integration daa can be selected from the bit group of the CCD sensors having good correlation by the operations of steps S505, S507, S551-S575. Although the bit number is 10 ('10 bits) in the illustrated embodiment, the number is not limited to 10.

Calculation of Tracing Speed of Moving Object:

The tracing speed of the moving object is calculated as follows (Fig. 15). First, the time T, between. the intermediate point of the previous integration and the intermediate point of the present integration is calculated (step S601). The reason that the intermediate point of the integration is usgd as a reference point is that the integration time varies depending on the object brightness.

If the object is not traced, that is, it is the first time for control to come to this operation after the moving object tracing mode has been set, the speed S, of the movement of the object image is calculated from time T, and the defocus pulse number DP, in accordance with equations (1) and (2). Thereafter, TI is set at the object tracing time (i, e., constant speed control time, and control is returned (step S605 and S606). If the object i's being traced, that is, it is the first time for control to come to this operation after the moving object tracing mode has been set, the number of pulses MP,, in which the object image-would move within the time T, form the time T, and speed S,-, in accorpance with equation is calculated (step S607). The suffix 'In-11' mentioned above refers to a variable of the previous integration, calculation or driing operation, whereas 'In" stands for current value. Thereafter, the direction of the present movement of the focusing lens is compared with that of the previous movement thereof. If the directions are identical to each other, the over displacement flag (i.e., over displacement of the focusing lens beyond an intended position) is cleared. Thereafter, the pulse number MP,,-, is added to the- present defocus pulse number DPn. Control then proceeds to s'ep S617 (i.e., tracing speed correcting operation) (steps S609, S611, S613 and S615). If the directions of movement of the focusing lens are different from each other, control proceeds to step S637, since it can be considered that the moving speed of the object image is decreased or the object image is stopped at an extreme position beyond the intended position, or that the direction of the movement thereof is changed (steps S609 and S611). If an error occurs, i.e., if it is impossible to detect the difference in the direction of the movement of the focusing lens, the moving -object predicting mode flag is cleared and control proceeds to the reintegration operation (steps S611, S613 and S655).

Tracing Speed Correcting Cplculation 1:

In the tracing speed correcting calculation 1, the object tracing speed S, is obtained by the following formula (step S617)f X,, = T,, / (MP. - l + DP.

1 - 57 S. = 1 /X,, =(MP, + DP.)/T. (pulse/ms) Thereafter, the object tracing time (sum of. the integration data input time and the calculation time) C. is set at step S621. If the object is in focus (step S623) and the release-switch SWR is turned ON (step S625), the AF lock flag is set "(step S627). Thereafter, the time lag correcting time (i.e., the object tracing time C. plus the time corresponding to the release time lag) is calculated at step S629. If the object moves away from the camera, the constant speed control time is set to be half the time lag correcting time (step S633). If the object approaches the camera, the constant speed control time is set to be identical to the time lag correcting time (step S635).

If the object is out of focus, or if the release switch SWR is not turned ON, even if the object is in focus (steps S623 and S625), control proceeds to step S635 to continue the tracing operation, so that the constant speed control time is set to be identical to the object tracing time C, (step-'S635).

If the direction of the present movement of the focusing lens is different from that of the previous movement, whether (MP, DP, is positive or negative is checked at step S637. If (MP,, DP,, 0, the value of (MP, - 1 DP, is calculated at step S639. Thereafter, the - 58 correcting calculation of the tracing speed S,, is effected based on the following equations and the state 'of the release switch SWR is checked (step S641).

X,, =T,, / (MP. DP.

S, = 1 /X,, =(mpn-l DI.)/T. (pulse/ms) If the object is in focus at step S643, the over the out step been set is checked (step S647). If the over displacement flag has not been set, it is set at step S649. Thereaf ter, the calculation time C. is set at step S651. Control then waits for the calculation time C, and proceeds with reintegration---. If the over displacement flag has been set at step S647, the moving object predicting mode flag is cleared at step S655.

displacement flag representing the over displacement of focusing lens is cleared (step S645). If the object is of focus at step S643, or if (MP,, 1 - DP.) < 0 at S637, whether or not the over displacement flag has Focus Check: ? Figure 16 shows the focus checking operation. In this operation, the focus range (width) is expanded to increase the permissibility range of the releasing operation when the object is traced.

First, the predetermined focus range (i.e. predetermined defocus amount) is maintained if the)node is not the moving object predicting mode. If the mode is- the moving object predicting mode, the focus range is expanded (enlarged). Thereafter, whether or not the present defocus amount is smaller, than a predetermined value is checked (steps S701,. S703 aJd S705).

If the present defocus amount is larger than a predetermined value (which is larger than the focus width), the first out-of-focus at low contrast flag is reset at step S719.

If the defocus amount is smaller than a predetermined value, and the object is in focus (within the focus width), the in-focus flag is set. Thereafter, the first out-of-focus at low contrast flag is cleared. Thereafter, the focus indicating LED of the indicator unit 45 is illuminated, and the electronic buzzer (PCV) 46 is sounded (steps S705, S707, S709, S711 and S713).

If the AF operation is effected, a predetermined focus range -'(width) corresponding to the moving speed of the object image is set top check the moving object. Conversely, if the AF operation is not effected, control is directly returned (steps S715 and S717).

If the defocus amount is larger than a predetermined focus width of S707 and smaller than the predetermined - 60 value of S705, the operation to prevent the unsteady flicker at low contrast is carried out. If the first out-6f-focus flag at low contrast has been set, or even if it has. not been set, but the mode is the moving object predicting mode, the first out-of-focus at low contrast flag is cleared and control is returned (steps S721, S723 and S719).

If the first" out-of-focus at low contrast flag has been cleared at S271, the mode is not the moving object predicting mode, emission mode, S723 and S725).

if the and the mode is the auxiliary light control is directly returned (steps S721, If the. mode is not the auxiliary light emission mode, and the 10 bit select mode flag is set, the first out-of-focus at low contrast flag is set (steps S727 and S733). Even if the mode is not the 10 bit select mode ' integration operation time is longer than a predetermined time, control is directly returned(S727 and S729). Even if the integration operation time is shorter' than a predetermined time, if the contrast is not low, the control is directly returned. If the contrast is low, the first out- of-focus at low contrast flag is set. Thereafter, control is returned (steps S79, S731 and S733). If the contrast is high, control is directly returned (step S731).

As can be seen from the above discussion, when control enters this routine for the first time, if the object is out of focus, and the contrast is low, the first out-of-focus flag at low contrast is set. As a result, even if the focus state is switched from the in-focds state to the out-of-focus state, the out-of-focus indication operation (step S301) is not effected at the hrst out-of-focus state. Accordingly, unsteady flicker of the indication lamp does not occur. Although the out-of-focus state is indicated" when the two consecutive out-of-focus states occur in the illustrated embodiment, the number of the occurrence of the out-of-focus state is not limited to two, and can be for example three or more than three.

L A IV R 1 Terminal Point Detecting Operation:

The operations when the focusing lens goup 53 reaches a closest extremity (i.e., shortest focal position) and a farthest extremity (i.e., infinite focal position) will be discussed below with reference to Fig. 17.

In this operation, when the arrival of the focusing lens group 53 o the terminal points (i.e., two extremities) or the impossibility of the drive of the focusing lens group 53 by some reason is detected, the AF motor 39 is stopped.

Whether or,,knot the AF motor 39 is driven is checked. If the AF motor is not driven, control proceeds to step S791 to perform the terminal point detecting timer resetting operation. If the pulse interruption flag is set (i.e., the encoder 41 outputs the pulses) during the drive of the AP motor 39, the terminal point checking operatiQn is carried out (step S771)._ Conversely, if the pulse interruption flag is not set (i.e., pulse is not issued), control proceeds to step S755 (i.e., counting operation of the terminal Point detecting timer).

- In the terminal point, detecting timer counting operation, the AF motor 39 is stopped when no pulse is outputted from the encoder 41 for a predetermined time during the drive of the AF motor 39, since it is assumed that the focusing lens group 53 is at one of the extremities or the focusing lens group 53 can notmove.

First, the pulse flag which represents the presence bf the pulse at the terminal point PAWDT is cleared, and the terminal point detecting timer count flag which indicites that the counting operation of the timer is being effected, is set. The counting operation of the timer is decreased (steps S755, S757 afia S759). If the counted number is 0, it is detected that the focusing lens group has come to the terminal point and control goes to the terminal process operation. If the counted number is not 0, control is returned (step S80i).

The following discussion will be directed to the operation which is performed when the time of the terminal point detecting timer is up, with reference to the flow chart regarding terminal operation shown in Fig. 11D.

In the terminal operation, the AF motor is first braked to a stop (S345). Then, when the result of the calculation is effective while the AF motor is being driven, control goes to S342 in the AFNG operation to set the reintegration operation. Then, the AE calculation operation is performed If the, loop time has expired. Control goes back to the reintegration operation if the loop time has not expired (S346, S342, S343). When the result of calculation it not effective and the driving direction is reversed, control proceeds to the AFNG 1 - 64 operation (S341) and the operations S341-S343 are performed (S346, S347, S341). If the driving direction is determined not to be reversed in step S347, control proceeds to step S348 to reverse the driving direction prior to going to a search reintegration operation.

- 65 In the terminal point checking operation, the terminal point of the focusing lens group 53 is detected by the change of the pulses outputted from the encoder 41. In this operation, the pulse interrupting flag is cleared (step S771).

Thereafter, the counting operation of the terminal point detecting timer is checked (step S775). If counting is not effected or if the pulse flag PAWDT is set during the counting operation, control proceeds to the terminal point detecting time resetting operation. If the pulse flag PAWDT is not set during the counting operation, the pulse flag PAWDT Is set. Thereafter, if the constant speed control is effected, control is returned, and if constant speed control is not effected, control proceeds to step S757 (steps S777, S779 and S781).- The timer resetting operation is effected to initialize the data regarding the detection of the terminal point. In this operation, the timer count flag and the pulse flag PAWDT are cleared and the terminal point detecting timer data is set (steps S791, S793 and S795).

Second Operation:

Embodiment of Moving Object Predicting AF 1 1 - 66 A second embodlifient predicting AF operation will reference to Figures 18 and 19.

In the second embodiment, the constant speed control continues even during the calculation. Namely, the lens driving speed corresponding to the moving speed of the object image is dLlculated, and the tracing speed is corrected by the integration while driving the focusing lens group at the constant speed identical to the calculated speed. The basic principle of the second embodiment is same as that of the first embodiment, except that the constant speed control is effected during the necessary calculation in the second embodiment. To this end (i.e., constant speed control in parallel with the necessary calculation), the CPU 36 is provided to control the motor driving IC 37 in the second embodiment.

First, the DC lens drive M is effected in accordance with the defocus pulse DP when the mode is the moving object predicting mode. Upon completion of the DC lens drive M, the -integration operation I, is carried out. In the calculation C,, the speed S, of the movement of the object image in the period of time T, between the intermediate point of the integration operation I and the intermediate point of the integration operation I, is calculated by equations Q) and a mentioned above, so that of the moving object be discussed beloipi with 1 1 - 67 the lens driving time can be obtained by the following equation (T, + 11 /2+ Cl) /2... 0) Consequently, the lens drive M, is performed a a constant speed identical to the triple speed of the tracing speed S, for the drive time calculated by the equationg As a result of the' lens drive M, at the constant speed control, the focusing lens group 53 is moved to the vicinity of the focal position within a short space of time. The effect substantially similar to that obtained by the driving operation at the speed twice the moving speed S, of the object image for the time (T, + 1, 12+ C,) is also obtained by the lens driving operation at triple speed.

Upon the completion of the lens drive M, at triple speed, the integration operation 12 and the calculation C, are effected while performing the constant speed drive M, at the tracing speed S,. In the calculation C,, the pulse number MP, corresponding to the displacement of the object image on the hssumption that the object image moves at the 'tracing speed -.S, for the time T. between the intermediate point of the previous integration operation 1, and the operation I. is calculated based on the equation (MP, =T, x S, mentioned above. Thereafter, the moving speed S2 of the object image for the time T2 is obtained by the following intermediate point of the present integration - 68 equations, similar to the equations g) and above; X2 =T2 / (MP 1 + DP2 S2 =1/X2 =(MP, + DP2)/T, (pulse/ms) The lens drive M, at the constant tracing speed S, continues during tfle integration operation I, and the calculation C,.

Thereafter, similar to the foregoing, the tracing speed S. is obtained in accordance with the pulse number MP. (MP. - 1 =T. S. - 2 rorresponding to the displacement of the object which would move at speed S, within the time T, The lens drive M,. i continues at the constant tracing speed S, during the integration operation I,. and the calculation C,.,.

The tracing control as mentioned above ensures that the moving object is substantially always kept in focus. If the release switch is turned ON during the tracing operation, the constant speed control is effected at the tracing speed -.S, obtained in the previous calculation while the mirror is in an upward popition. The focusing lens group stops before the shutter leading curtain moves (Fig. 19). Thus, the object is substantially in focus when the leading curtain starts -to move (i.e., when the exposure commences).

(5) mentioned 1 Figures 20 (20A-20C) and 21 (21A-21B) show flow charts of the second tracing operation of the moving object.

In this embodiment, the operations shown in Figs. 8-14C and 17 mentioned above and 20B, 20C, 21A, 21B are performed by the main CPU 35, whereas the operation for calculation of the moving object tracing speed 2, shown in Fig. 20A, and the operation of stai:ting integration, shown in Fig 22, are performed by the sub CPU 36 at the same time as the main CPU 35 operation. In the second embodiment, the reintegration operation shown in Fig. 13C has been performed at S253, in the..reintegration operation shown in Fig. 11A before the moving object prediction mode flag is set. When the moving object prediction mode flag has been set, the reintegration operation shown in Fig. 22 is performed. Further, when the moving object prediction mode flag has been set, S326 and S325 are skipped to perform the, defocus pulse calculation at the middle point of integration which is equivalent to S323, before the calculation fok the moving object tracing speed at S921 in the reintegration operation. First, the time T,, betweer) the intermediate point of the previous

integration operation and the intermediate point of the present integration operation is calculated (step S801).

Thereafter, whether or not the object is being traced is checked is, if the first time the control speed S, of T, and at step S803. If the object is not traced, that object has not yet been traced, since it is the for the control to come to this operation, after had entered the moving object tracing mode, the the object image movement is calculated with the DPl values (step S805). Thereafter, {(T,+I,/2+Cl)/2 is set as the objet tracing time (i.e., constant speed control time. If the object is traced and the calculation is the first calculation during tracing operation, that is, if the object has already been traced once, since it is the second time for the control to come to this this operation, the pulse number MP, corresponding to the displacement of the object image within the time T2 is calculated with the T2 and S values. After the second calculation, the pulse number MP,-, corresponding to the displacement of the object image within the time T, is calculated with the T, and S.-, values (steps S803, S807, S809, S811).

Thereafter, the direction of the present movement of the focusing lens group 53 is compared with the direction of the previous movement at step S813. If the directions are identical to each other, thq over displacement flag is cleared and the calculated pulse number MP.. 1 is added to the present defocus pulse number DP, (steps S813, S815, S818 and S819). Theeafter',, control proceeds to step S821 (i.e., tracing speed correcting calculation 2).

Conversely, if the directions of movement of the focusing lens group are different from each other, 'It is assumed that the moving speed of the object has decreased, the object has stopped, or the direction of movement of the object image has changed, resulting in displacement beyond the intended positipn. Accordingly, control proceeds to step S833 (steps S813).

If direction cannot be detected, for example, by an unexpected error, the moving object predicting mode flag is cleared. Thereafter, control proceeds to the reintegration operation (steps S815, S817 and S849).

Tracing Speed Correcting Calculation 2:

In the tracing speed correcting calculation 2, the object tracing speed S, is obtained by the following formula (step S821); X.=T./(MP.-1+ DP.) S.=1M.

=(MP.-i" + DP.)/T2 (pulse/ms) If the object is in focus and the release switch SWR is turned ON, the AF lock f l ag and the AF release permission flag are set. Thereafter, control is returned (steps S825, S827, S829 and S831). If the object is out of focus or the rlease 'switch SWR is not turned ON, control is directly returned (steps S825 and S827).

i If the direction of the present movement of the focusing lens is different from that of the p-evious movement, whether (MP,-I-DP,) is positive or negative,-is checked. If (MP,,-, -DP.)Z-. 0, the tracing speed Sn is obtained by the following equations (steps S815, S833, S835 and S837). 1 X. =T. / (MP., DP.

S,, = 1 /X,, =(MP.-, DP.)/T. (pulse/ms) If the object is in focus at step S839, the over displacement flag ",representing the over displacement of the focusing lens is cleared (steps S839, S841). If the object is out of focus at S839 or if (MP, -DP.) < 0 at S833, whether or not the over displacement f lag is set is checked (step S843). If the over displacement flag has been set, the moving object predicting mode flag is cleared at step.

S849, since over displacement occurs for the second time.

Namely, if over displacement (excess displacement) of the focusing lens group takes place, this may be caused by an error. This i't because the two over displacements occur, the moving object predicting mode flag is cleared.

lternatively, it is possible to clear the moving object predicting mode flag by one over displacement or more than two over displacements.

If an over displacement flag is not set at S843,, it is set at step S845, since over displacement occurs for the first time. Thereafter, integration data is input ahd the calculation time C, is set. Control then waits for the calculation time C, and proceeds to the reintegration operation (steps S843, S845 and S847).

Constant Speed'Control 2:

The following discussion will be directed to another constant speed control, with reference to Figs. 21A and 21B.

The pulse duration X, is set (S851). Thereafter, if the moving objeat is bQing traced, the tracing speed S.(11X,) is set (S853,S855). If the object is traced, and if the operation is the first operation after the tracing operation commences, the triple speed 3S. of the tracing speed S, is reset (S857, S859). But, if the operation is the second or subsequent operation, reset of the tracingspeeQ is not effected (steps S853, S855, S857). If the is completed (i.e., calculation completion flag=l), data,' such as AF pulse, tracing speed S,, etc., is input and set-. Thereafter, the calculation completion flag is cleared (steps S861, S863 anq S865). Thereafter, control is returned to step S851.

If the calculation is not finished (i.e., calculation completion flag=O), whethr or not the constant speed control time has elapsed is checked at step S867. If the calculation constant speed control time has elapsed, the terminal point detecting counter begins counting. If the AF motor '39 is driven, control is returned to step S861 (steps S867, S869 and S871). If AF motor 39 is not driven, the Af motor 39 starts and control is returned to step S851 (steps S871 and S873). 1 If constant peed control time has not elapsed, whether or not the AF pulses are outputted is checked (steps S867 and S875). If there is no output of the AF pulses, control is returned to step S861, and if the pulses are output, control proceeds to step S877.

At step S877, whether or not the upward movement of the mirror is completed is checked. If the upward movement of the mirror is completed, the AF motor 39 is braked and stopped (steps S877 and S879).

Conversely, if upward movement of the mirror is not whether or not the "count of the AF pulses is is checked. If the count is finished, the AF is stopped. Thereafter, the loop time is If the loop time has elapsed, the AE operation is if loop time has not elapsed, control proceeds to the reintegration operation (steps S879, S881 and S883).

If the counting operation of the AF pulses is not finished, the checking operation of the terminal point and the setting of the terminal point detecting timer are completed, completed motor 39 checked. effected, effected. Thereafter, whether or not the value of the AF pulse counter is below the speed switching pulse number is checked (steps S879, S885, S887). If the value of the. AF pulse counter Is below the speed switching pulse number, the speed control is switched to a low speed control and the AF motor 39 is, braked. Thereafter, control proceeds to step S893. Convdrsely, if the value of the AF pulse counter is not smaller than the speed switching pulse number, the control directly proceeds to step S893 (steps S887, S889 and S891).

At step S89.3, whether or not the AF motor 39 is driven is checked. If AF motor 39 is not driven, control is directly returned to step S851. Conversely, if the AF motor 39 is driven, the AF motor 39 is braked. Thereafter, control is returned to step S851 (step S895).

Integration Operation..

In the subroutine of the reintegration operation (Fig. 22) the reintegration operation commences after initialization, and the reintegration operation flag is set (steps S901, S903 and S905). The integration operation time is checked until the integration operation is completed (steps S907 and S909). If the integration operation time is longer than a predetermined time, the object is too dark to be photographed. Accordingly, the moving object predicting mode forbidding flag is set (steps S909 and S911).

if the integration operation is finished,' the integral data is input to calculate the defocus amount (steps S907, S913 and S915).

* t If the calculation result is effective and the mode is the moving object predicting mode, the object tracing speed is calculated. Thereafter, the calculation completion flag is set. Thereafter, control proceeds to step S925. If the calculation result is not effective, control is returned to step S901 (steps S913.

S915 and S917). At step S925, whether or not the AF release permission flag is set is checked. If the AF release permission flag is not set, control is returned to step S901, and if the AF release permission flag is set, control proceeds to the release operation.

As can be understood from the above discussion, since the focusing lens group 53 is driven by constant speed control during the integration and calculation, as shown in Figs. 18 and 19, the moving object can be precisely kept in focus.

With the present invention, even if the object is once in focus, if the. object is out of focus in the AF operation at a predetermined time later, it is assumed that the object is moving. Accordingly, the movement of the otject -an be detected even when the object is accidentally in focus, for example, in the case - 77 that the object approaching the camera is focused with the focusing lens group moving from a near focal position to a far focal position.

Although the object is judged to be a moving object when three consecutive out-of-focus states are detected in the AF operation after the object is once in focus, as in the illustrated emBodiment, the number of out-of-focus states to be detected is not limited to three. Furthermore, it is possible to judge the moving object when more than one discontinuous or consecutive out-of-focus state detected in the -AF operation after the detection of one in-focus state.

As can be seen from the above discussion, with the present invention, when the focus judging means judges that the object is in focus, the object distance measuring means and the lens driving means are actuateo after the lapse of a predetermined time. Thereafter, if the focus judging means judges that the object is out of focus more than one time, the object is considered to be a moving object. Consequently, the moving object can be detected even if the object continues moving after it is once focused or the focusing lens is moved in the direction opposite to the direction of movement of the object, thereby bringing the bjeet'into focus.

Furthermore, with the present invention, is - 78 when the object moves, the focusing lens group is moved at a speed corresponding to the speed of movement df the object image, Accordingly, the moving object can be precisely brought into in focus.

Furthermore, if the object is a moving object, the measurement of the defocus amount and the calculation of the speed of movemdht of the object image are repeatedly effected, and the lens driving means drives the focusing lens group at the latest tracing speed during the measurement or the calculation. Consequently, the in-focus state can be substantially. always maintained. With the present invention, since the focusing lens group is driven at the same speed as the speed of movement of the object image until the exposure commences, the exposure can be effected in the in-focus state.

In addition to the foregoing, with the, present invention, if the object contrast is low defocus object amount stored amount occurs. moving f ocus, 11 the. amount for the object is temporarily stored and the distande is again measured, so that the defocus obtained by the re-measurement is compared with the defocus amount. As a result, a smaller defocus is selected and little or no measurement error Namely, there is little or no possibility that the object, which is- in focus, is judged to be out of thus resulting in the elimination of unsteady - 79 flicker of the focus state indication light.

Furthermore if there is a backlash, driven amount sinch the focusing lens groups is to compensate for the displacement corresponding to the backlash, independetly of the driving operation based on the defocus amount, calculation for obtaining the sum of the displacement based on the backlash and the displacement based on the defocus is not necessary, thereby simplifying the calculation.

With speed for displacement is a large shorten the the driving group from displacement the present invention, the lens driving the defocus amount varies depending on the of the focusing lens group. Namely, if there displacement, the driving speed is increased to drive time. If there is a small displacement, speed is decreased to prevent the focusing lens moving beyond the intended position (over, p 1 1 - so -

Claims (6)

CLAIMS:

1. An automatic focusing apparatus comprising an optical system having a group of f ocusing lenses, a def ocus amount measuring means for measuring the amount of defocus, lens driving means for driving the focusing lens group, lens displacement calculating means for calculating the displacement of the focusing lens group, including the direction and amount of the movement thereof, in accordance with the defocus amount measured by the defocus amount measuring means; and a control means for driving the lens driving means in accordance with the displacement calculated by the lens displacement calculating means and for controlling a displacement necessary to compensate the backlash independently of the drive based on the defocus amount when the direction of the movement of the focusing lens group changes.

2. An automatic focusing apparatus according to claim 1 comprising a control means for driving the lens driving means by the displacement corresponding to the backlash at high speed and low speed when the displacement based on the defocus amount is above and below a predetermined value, respectively.

3. An automatic focusing apparatus according to claim 1 1 - 81 or 2 wherein it is applied to a camera which has therein a memory means for storing data on the displacement corresponding to the backlash.

4. An automatic focusing apparatus according to claim 3 wherein he camera includes a camera body, and a taking lens detachably attached to the camera body, so that the defocus amount measuring means, the lens driving means, the lens displacement calculating means, and the control means are provided in the camera body.

5. An automatic focusing apparatus according to claim 4 wherein the camera body has a memory means for storing the data of the displacement corresponding to the backlash on the camera body side, and the taking lens has a memory means for storing the data of the displacement corresponding to the backlash on the taking lens side, respectively.

6. An automatic focusing apparatus according to claim 5 wherein said control means drives the lens driving means by a displacement necessary to absorb the backlash in accordance with the backlash data read from the memory means of the camera body and taking lens.