FR2637990A1 - - Google Patents

Abstract

An automatic focusing device by which a focusing lens is controlled in accordance with an object distance measured by a distance measuring unit 10. The distance of an object in a distance measuring area provided in a viewfinder is determined. to detect a sudden change in it. If the object distance is suddenly changed, the focusing lens is not controlled to focus on a new object appearing in the measurement area. Conversely, if the object distance is not suddenly changed, the focusing lens is controlled to again focus on the object in the measurement area.

Description

The present invention relates to an automatic focusing device

  more particularly an automatic focusing device in which a focusing distance limit can be adjusted by

y a photographer.

  In a conventional automatic focusing (AF) device provided in a self-focusing single-lens reflex camera, a distance measuring area is formed in a field of view J of a viewfinder of the camera, so that the photographer can determine which part of an object the camera lens is focused on. The object light entering the distance measurement area is divided into two parts, which are sent to the measurement sensor having a CCD, and a focus calculation is performed by a focus control unit in order to obtain a magnitude and a defocus direction. An AF motor is driven according to this vector value, and the photographic lens is) moved to a position in which the object is focused. The drive of the above automatic focusing device is triggered by a half press of a trigger button. In slave AF, when the shutter button is partially depressed, a distance measurement operation and a focus operation for the photographic lens are performed at predetermined intervals. When a photograph is to be taken using the conventional autofocus camera, if the object to be photographed moves outside the distance measurement area, the camera is controlled to focus on a

  new object entering the distance measurement area.

  ú In particular, when a mobile object must be photographed. the object to be photographed often cannot be tracked correctly and moves

  temporarily outside the distance measurement area.

  In such a case, if another object entering the zone is located at infinity or within, the objective

  photographic is moved to infinity or to -

  short distance focus position. As a result, even if the first moving object moves again in the distance measuring area, it takes a long time to move the photographic lens to a position in which the moving object is focused. When photographing a moving object, generally the camera must be ordered very quickly, and if it takes a long time to focus the lens on the object to be photographed, then the chance to take a photograph

is often lost.

  In particular, when a moving object has to be photographed using a super telephoto lens in which the focusing time is normally long, the

  previous problem occurs easily.

  As a result, the object of the present invention is to create an automatic focusing device in which, even if a mobile object moves out of the distance measurement zone and returns there again, the objective is focused on the mobile object in a while

short by simple operation.

  In accordance with the present invention, there is created an automatic focusing device comprising means for measuring an object distance, means for driving a focusing lens of a photographic objective provided in a photographic camera, means for controlling the lens drive means, and means for determining whether an object distance has or

not suddenly changed.

  The control means controls the lens drive means, based on the object distance measured by the measuring means, so that the focusing lens is driven to focus on an object. That is, the control means controls the lens driving means so that the focusing lens is driven to focus on an object when the determining means determines that the] 0J measured object distance by the measuring means has not changed suddenly, and limits an action of the driving means when the determining means determines that the object distance has changed suddenly. In addition, according to the present invention, an automatic focusing device is created comprising means for measuring an object distance, means for driving a focusing lens of a photographic objective provided in a photographic camera, a mean Zt for controlling the drive means, means for storing a long limit distance and a short limit distance defining object distance limits in which the focusing lens is controlled to focus, and means for determining 2d5 if the distance of object measured using the measuring means is or is not within the long and short distance limits memorized by the means of

memorization of limit distances.

  The control means controls the drive means, based on the object distance measured using the measuring means so that the focusing lens is driven to focus on an object. That is, the control means controls the lens drive means so that the focusing lens is driven to focus on an object when the determining means determines that the object distance measured at l using the measuring means is included in the long and short distance limits, and limits the action of the driving means when the determining means determines that the object distance is not included

  within long and short distance limits.

  Still further, according to the present invention, there is provided an automatic focusing device comprising means for measuring an object distance, means for driving a focusing lens of a photographic objective provided in a photographic camera up to a focusing position, means for memorizing the object distance when it is focused, means for memorizing an allowable difference between a current object distance measured using the measuring means and an object distance when the focus memorized by the object distance memorizing means, and means for controlling a focusing operation on the basis of an object distance measured using the measuring means in order to bring an object into focus . When the object is focused, the control means controls the object distance memorizing means to memorize the object distance when it is focused, and determines whether a difference between a current object distance measured at the using the measuring means and an object distance memorized by the object distance memorizing means is or is not included in the admissible different memorized by the memorizing means of different admissible. If the difference is less than the permissible difference, the drive means is controlled to focus the lens on the object distance measured using the measuring means, and if the difference is greater than the permissible different, the means drive is controlled to focus the lens on the object distance measured by the object distance memory means, or is not controlled and the focal position

current is maintained.

  The present invention will be better understood from

  description of preferred embodiments of

  the invention set out below, at the same time as the drawings anne: xés, in which: iO- Fig. 1 is a block diagram of a construction

of the present invention.

  Fig. 2 is a block diagram of a construction

  of an embodiment of the present invention.

  Fig. Z is a schematic view showing a relationship between the field of vision of a viewfinder and an area

distance measurement.

  Fig. 4 is a flow diagram of a process for verifying the state of the switches of the camera. Fig. 5 is a flow diagram of a process for

establish the distance limits.

  Fig. 6 is a flow diagram of a process for taking a photograph using an operation of

automatic focusing.

  2 'Fig. 7 is a block diagram of a construction

  of another embodiment of the present invention.

  Fig. 8A is a schematic view showing a state in which an object is in a distance measuring area. Fig. 8B is a schematic view of a state in which the object has moved out of the distance measurement area. Fig. 9 is a flow diagram of a process for establishing a mode of a focusing operation

E 'automatic.

  Fig. 10 is a flow diagram of a process for verifying a state of a trigger button. and fig. 11 is a flow chart of a process of a

  automatic focusing operation.

  The present invention will now be described with reference to the embodiments shown in the drawings. In fig. 1, a means for memorizing limit distances 11, a determination means 12 and a focusing control means 13 are connected to a distance measuring means 10 measuring a distance from a camera to an object. The limit distance measuring means 11 stores a long limit distance and a short limit distance, and the determining means 12 determines whether the current object distance output from the distance measuring means 10 is within limits of the limit distances. stored in the limit distance storage means 11. The limit distance storage means 11 is connected to the determination means 12 which, in turn, is connected to the control means

focus 13.

  The focus control means 13 is connected to a lens drive means 14 driving a focus lens 15 of a photographic lens so that the focus lens 15 is focused

on an object.

  An object distance signal measured by the distance measuring means 10 is output to the limit distance storage means 11 when storing a limit distance, and is output to the determination means and the control means of

  focus 13 when taking a photograph.

  The limit distance storage means 11 -'F stores two limit distances, that is to say a long limit distance and a short limit distance, and outputs the long limit distance and the short limit distance to the determination means 12 when taking a photograph. The long and short distance limits are limits to the object distance at which the

  focusing lens can be focused on the object.

  The determination means 12 compares the long and short limit distances exited from the limit distance storage means 11 with a measured distance exited from the distance measuring means 10 and determines whether or not the measured distance is included in the within the limits defined by the long and short distance limits, and outputs a signal to the focusing control means 13 indicating whether or not the measured distance lies within the defined limits. The focus control means 13 receives a measured distance signal from the measurement means 10 and the determination signal from the determination means 12. If the determination signal indicates "within limits", the focus control means 13 starts the actuation of the lens drive means 14 (if the lens drive means 14 is in action, the focusing control means 13 continues the actuation of the lens drive means 14), so that the focusing lens is moved to a position in which the focusing lens is focused on the object. Conversely, if the determination signal indicates "outside the limits", the focusing control means 13 does not control the lens drive means 14, or controls the lens drive means 14 so that the focusing lens is moved to the position of long or short limiting distance FIG. 2 shows a simplified diagram of a camera comprising a construction for

limit a focus range.

  A main control unit 20 articulates a distance measured by the distance measuring means 10, i functions as the determining means 12 and the focusing control means 13, and performs system control and calculations for the camera whole. Sensors are connected to the main control unit 20, and include a distance measuring unit 21 comprising a CCD type cantor forming part of the distance measuring means, and a light measuring sensor 22 for measuring

object brightness.

  A limit distance storage unit 25 and a lens drive circuit 24 are also connected to the main control unit 20. The limit distance storage unit 23 functions as the limit distance storage means 11, and the lens drive circuit 24 is connected to the focusing lens 15 of the photographic objective via a lens drive unit 26, and functions as the lens drive means 14 to drive the focusing lens 15. As is well known, an object image in a distance measuring area 30 (see fig. 3) provided in a viewfinder 31 is focused by the photographic lens 25 and is divided into two parts to Be conducted to a light receiving surface of the CCD of the distance measuring unit 21. The CCD outputs image signals corresponding to the divided object images and the image signals are input és in unity

main control unit 20.

  In the main control unit 20, a defocus magnitude and direction are obtained by a well known correlation method, and an object distance is obtained in accordance with the lens position. This object distance is stored in the limit distance storage unit 23 during the establishment of the limit distances. Conversely, in a common photography operation, the lens drive circuit 24 is driven in accordance with the object distance so that the focusing lens 15 is moved to a position at which the object is focused. When a photographing operation is performed with limited focus distances, the object distance is compared to the long and short limit distances stored in the limit distance storage unit 23, and it is determined whether the object distance is within or outside the limits defined by the long and short distance limits. If it is determined that the object distance is within these limits, a focusing operation is performed in the form of a usual photographic operation, and if it is determined that the object distance is not within these limits, the focusing operation is not performed. s such that a trip button 27 and a limit distance setting switch 28 are connected to the control unit

main 20.

  The trigger button 27 is a switch of the well known two-position type, whereby when the trigger button 27 is partially depressed, a distance measurement switch is set to ON, and when the trigger button 27 is fully depressed, the distance measurement switch is kept ON and a trip switch

is set to ON.

  The limit distance setting switch 28 is provided for establishing focus limit distances. When the limit distance setting switch 28 is set to ON, the main control unit 20 begins to establish the limit distances. That is, a first limit distance (which is an object distance) is stored in the limit distance storage unit 23 when the trigger button 27 is partially depressed. Then, the trigger button 27 is triggered and is partially depressed again and a second limiting distance is memorized in the memory storage unit.

limiting distances 23.

  A viewfinder indicator 29 is provided in a field of view of the viewfinder 31 and is connected to the main control unit 20. The viewfinder indicator 29 indicates information relating to exposure, such as shutter speed, information focusing, that is to say whether or not a focusing operation is completed, and information on whether a measured distance is within the limits of the

long and short distance limits.

  The main control unit 20 is a micro-

  computer, which performs the above functions in accordance with the programs stored in a ROM and an AE calculation based on an object brightness signal output from the measurement sensor 22, and further performs calculation and control functions for the entire camera, such as establishing a shutter speed and an aperture value, and controlling a shutter and an aperture.

  An operation of the embodiment described below

  above is described below with reference to FIG. 3, which shows a case in which a person 32 must be Isa sa4! WtI saDuelsp sal jFlqe? Jnod uorejdol -a TW TT amue4stp apuomas aunp awJo + el snos úZ sallwiT samuelsXp ap uoiqestJowgw ap 9; unl suep assJowiw; s lesx ao lsa Iztnbsjo [t JayzoJ ne, nbsnF anbtqdeJ oqoqdj tTo anbtqdei o4oqd + Tarqo ;, anb a; dos ap amue; sTp ap uot4estIezo ap la ainsaw ap suoz4eigdo sal Jamuawwo0 Jnod sgpuewwoa uos Z all; zuaI ap 4uawau3ej4uap zTnDJIz al isZuzu apnzu aznu pzuzpn -rD; Ta zp awwon ganb a8InseJ ua II "ZZ 4uawaqDualmgp ap uo4noq al uawallazIJed azuo + ua IT sJole; 3" r J4aqoJ nenbsnr amueqsTp el jaJnsaw Jnod agsnre 4sa O; aDuelsip ap ajnsaw ap auoz el anb aelos ap t Jaqaoj al ins anbrqdeB6oqoqd ITaJedde, 1 ab JTp 1a Z. 4uawaqmualp ap uo; noq al aiqTI aqde Joqoqd al aquiwia.; sa uoaTesilemo ap uoiaibs7. SNOS UZ sa4wx sazuesTp pp uoXesJowgw ap 94Tunl suep agsTJowqw its gsTlemo + U2 aJqJe l.nbsnr anbtqde5o; loqd TIaxedde I Sindap Station IT aDue4sTp el anbsiol uU ajqjel ins gsIle3o + 4SA Sz anbxqdei6Booqd j.Jmarqo anb I a; Jos eaDue4sip ap ap ap + uotpestIeo; has aJnsaw ap suoteJgdo sap JaDuawwon inod sgpuewwoD quos tZ alIT; ual ap quawaurejuap 4TnDJiz al a TZ aDuelsTp ap ainsaw ap gTunl sz aledTDuTLd apuewwon ap g4Tunl anb aUuuuuuu uuuu uuuu uuuu 4u suep aAnoil as ú aiqJei anb alios ap uU aqJel AJS anbtqdeJboo4qd IajeddeI abiJtp aBtnsua Ba saBwil sa3ue4sip 1uawassBiqes ap p APOW a JTlqeql Jnod B3H3fW Mns 8Z saBTWI saMuesP ap ap uaWassIqe; ep inaqeqnWWOD el AMELD aqdeJbooqd aT epioqep 4noi -a nbqde-oooqd jTaJedde, [ap 9u6bowg tú u4aDo un: e anbiqde & oqoqd iTa.eddeI ap sQJd úú ajqje un ai4ua ^ anoJ; as aqtqde-o0oqd

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  thus completed, as described above, and subsequently, the camera will operate to focus only on an object located between the tree 33 and the rock 34; that is, the camera will not work to focus on an object closer than the tree 33 and further away than the rock 34. As a result, when the photographer takes an image while following the movements of person 32, even if person -2 moves out of the 1k area, distance measurement 30, a focusing operation is not performed for an object closer than the SS tree and for an object placed more far away from the rock 34. As a result, when the person 32 moves again into the distance measuring area 30, the camera 1.5 operates to focus on the person 32 in the distance measuring area 30, in a

very short time.

  Operation of the main control unit

  is described below with reference to figs. 4 to 6.

  In fig. 4, after a power supply has been set to ON, the main control unit 20 repeatedly performs, at very short intervals, a check of an ON-OFF condition of the trigger button 27 (i.e. i.e. the SWS measurement switch) and the limit distance setting switch 28 and waits until the distance measurement switch SWS or the limit distance setting switch 28 is set to ON. When the distance measuring switch SWS is set to ON at STEP 101, the process advances to a shooting program, the mode of which has been established in a mode setting program. If the distance measuring switch SWS is set to OFF and the limit distance setting switch 28 is set to ON, the process advances from STEP 1) 2 to a limit distance setting program. IN STEP 102, if the limit distance setting switch 28 is set to OFF, the process

advance to a FIN program.

  As a result, if the photographer places the power supply ON and turns the limit distance setting switch 28 ON, the main control unit 20 starts the program for

establish the distance limits.

  ,; In the mode of establishing limit distances shown in FIG. 5, in a STEP 1115 the main control unit 20 determines whether the button for

  trigger 27 is partially pressed or not,

  i.e. if the SWS distance measurement switch is 1 set to ON. If the SWS distance measurement switch is not set to ON this process of STEP 111 is repeated until the SWS distance measurement switch is set to ON. Note that, even if the photographer fully presses the 2, trigger 27 button incorrectly, that is, even if the SWR trigger switch is set to ON, the process does not advance to an exhibition program. The photographer directs the camera on an object at a distant distance or at a close limit, and then adjusts the distance measuring zone 30 towards the object by partially depressing the trigger button 27. As a result, since the distance measurement switch SWS is set to O ON, at STEP 112, the main control unit begins to drive the CCD of the distance measurement unit 21 to measure the object distance L1 and at STEP 113 controls the lens drive circuit 24 based on the distance L1 so that the focusing lens 3.5 is moved to the 14-focusing position. During a STEP 114, if the focusing lens 15 is not focused on the object, the process returns to STEP 111, and STEPS 111 to 114 are repeated until the object is finds focused, In a condition where the measurement switch

SWS distance is set to ON.

  When the object is focused, at a STEP 115, the main control unit 20 stores the distance L1 in the form of a first limit distance in the unit O for storing limit distances 23 and waits until the SWS distance measurement switch either

placed on STOP at a STEP 116.

  When the control of the lens drive circuit 24 is stopped, or when a focusing indicator light appears in the viewfinder indicator 29, the photographer recognizes that a first distance measurement operation has been completed, and then releases the trigger button 27, and directs the camera on an object in a close limit or at a distance - distant, and when the object appears in the distance measurement zone 30 partially presses the

trigger 27.

  The main control unit 20 detects that the distance measurement switch SWS is set to OFF (STEP 116) and then set to ON (STEP 121), and during a STEP 122 triggers the CCD of the tracking unit. distance measurement 21 for measuring an object distance L2. The main control unit 20 controls the lens drive circuit 24 based on the distance L2 to move the focusing lens 15 to a focusing position, and then the distance measuring operation and the lens drive operation are repeated during STEPS 121 to 124 until the object is focused, in a condition io the distance measurement switch SWS is placed on

MARKET.

  During a focusing operation, & a STEP, the main control unit 20 stores the distance L2 in the form of a second limit distance in the limit distance storage unit 23, and if the measurement switch SWS is set to OFF during STEP 126, the process for this limit distance setting program is completed and the process returns to the switch verification program (fig. 4) performed at

predetermined intervals.

  The photographer recognizes that the operation of establishing the distance limits is completed when the control of the lens drive circuit 24 is stopped or that a light of indication of focus appears in the viewfinder indicator 29, and he releases then the trigger button 27, on which the operation

  establishment of limit distances is completed.

  A photography operation using the distances _ limits explained above is described below by

reference to fig. 6.

  The photographer points the camera at an object to form a desired image composition, adjusts the distance measurement area 30 to cover the desired object, and then partially presses the button

trigger 27.

  When the trigger button 27 is partially depressed, the distance measurement switch SWS is set to ON and the process advances from STEP 131 to STEP 132, so that the main control unit 20 triggers the CCD of a distance measuring unit 21 for starting a distance measuring operation. A measured distance L obtained by this distance measurement operation in STEP 132 is compared with the first and second limit distances L1 and L2 stored in the limit distance storage unit 23 and, during STEPS 133 and 134, it is determined whether or not the measured distance L is within the limits defined by the first and

second limit distances L1 and L2.

  If the distance L is within the defined limits, during a STEP 135, the lens drive circuit 24 is controlled so that the focusing lens 15 is moved to a focusing position corresponding to a measured distance L. During a STEP 136, if the trigger switch SWR is set to OFF, the process returns to STEP 131. That is to say that these operations of measuring distance and lens drive are repeated until the focusing lens 15 is focused on the object, provided that the trigger switch SWR is set to OFF and the distance measuring switch SWS is set

ON.

  f_ Although the photographer moves the camera following a movement of the object, while partially pressing the release button 27, if the object moves quickly or if an obstacle appears between the object and the photographer, object can move outside the distance measuring zone 30 and consequently the distance measuring zone 30 can cover an object to infinity or an object within a very close limit.-In this case, if the measured distance L is not included in a limit of the first and second limit distances -30 L1 and L2, the main control unit 20 does not carry out a lens drive process but only repeats the distance measurement operation of the STEPS

131 to 134.

  When the photographer has the desired object in the distance measuring area 30, the fact that the main remote control unit 20 performs the lens drive process. is the focusing lens focused on the object? and thus if the measured distance L of the object in the distance measuring zone is not included within the limits of the limit distances L1 and L2, the focusing lens 15 is not driven, and consequently the limits in which the focusing lens 15 is moved are narrow. As a result, even if the object repeatedly enters and leaves the distance measuring area 30, it takes a period of time to focus the lens on the object.

is short.

  When the photographer fully presses the trigger button 27, the trigger switch SWR is set to ON and the process advances from STEP 136 to STEP 137. and so the main control unit 20 controls a shutter and an aperture and so on, allowing exposure of a

wrap is done.

  After this exposure, if the trigger button 27 is still fully depressed, the process returns from STEP 138 to STEP 131 and the distance measurement and focusing operations are repeated. Conversely, if the trigger button 27 is not fully depressed or is released, the process advances to STEP 1359 to determine whether or not the distance measurement switch SWS is OFF. STEP 139 is performed repeatedly until the distance measurement switch SWS is set to OFF, and when the distance measurement switch SWS is set to OFF, the process advances to the END program. Note that when the trigger button 27 is held fully depressed, a trigger mode is commanded in which the exposure process is repeated until the exposure switch

  3- SWR trigger is placed on OFF.

-18

  As is obvious from the description

  above, in accordance with the embodiment, when an object moves within the limits of a constant distance is photographed, if the a distance limits are established, the focusing lens 15 does not move over the range of limit distances. As a result, the amount of movement of the focusing lens 15 to focus is

  negligible and thus the focusing time is short.

  Furthermore, since the limiting distances can be established by software, countermeasures against a shock caused by contact with a stop element and against an overload of a drive source of the focusing lens 15 is not not necessary for the s5 difference from a mechanical limiter which limits a rotation of a distance ring by the stop element. Still in addition to the fact that a mechanical structure is not necessary for the limiting distances, a conventional interchangeable lens for a camera with automatic focusing can be used such

which is.

  Although the lens drive operation is not performed when the measured distance L is not within the limits of the limit distances established by the limit distance establishment program in the previous embodiment, the present invention may be performed in such a way that the lens drive operation is performed within the limit of distance limits, even if) the measured distance L is not within this range. In the above embodiment although the distance measuring operation and the focusing operation are used to establish the distance -5 limits, the limit distances can be established by some other means. For example, the present invention can be designed in such a way that the focusing mode is changed to a manual mode, that a distance ring of the photographic lens is rotated manually, and that an adjustment button is pressed into a position at which the photographer would like to establish the limit distances, in order to memorize this distance in the limit distance memorization unit 23. In this case, the memorized distance is obtained by a distance signal output from the photographic lens by moving the distance ring. The present invention can be designed in such a way that a data return is provided to the camera allowing that desired limit distances are entered by means of a key command, and that the distances entered by the command of keys are stored in the memory storage unit

limiting distances 23.

  Furthermore, the present invention can be implemented in such a way that in the routine routine limit distance establishment program, only a limit distance is entered into the limit distance storage unit 23, and that the other limit distance is selected as infinity, or the shortest

  photographable distance from the photographic lens.

  Fig. 7 shows a block diagram of another automatic focusing device according to the present invention. Note that in this drawing, the similar or corresponding parts: .0 are represented by the

  same reference numerals as in fig. 2.

  A main control unit 20 generally controls the operation of the

  automatic focusing of the present invention. This is-

  that is to say that the distance measurement unit 21 connected to OZ aledTuTJd apuewwoz ap FTunl apuewwoa ajip-V-sae, ú z 'b el V euasgJdaJ awwom auuotzauo + LZ 4uawaqzualzp ep uo; noq al oz alTedTDuJd apuewwom ap 94 auuoz 4UOs 61 alqTssiwpe a4uajp ++ p ap ainsaw ap Tun aun.a úZ sa4wI sazue4sTp ap uoWesiJow9w ap Tun aun 'LZ; uawaequalp ap uo4noq un 0 -gxsgp 4arqol.ns asieDo + aBi3 uyuu anuuu anuu uuu ,, a bZ ajjTnual ap 4uawaueJ4uap 4TlnzJz el apuewwo3 & uot4esTlemo3p a uoi jp uoea: pea JnapueJ el ins agseq 4a 'aDue4sip Z a asw p a4nsaw ajun unjn ujj uab apun ap s4jos aBewp xneubis apB app s4jos aBewp xneubis apB ap apuewwoD ap qzunl ialjanz.qeB aBlTuew aa UOTaiesTIezo + el Jnod uoDzeeiaBquoD ap aWjS / S a an4T4suom snssap-_t uoatesieS i el -4uawaulejqua p aminos awwom d ina4ow a asTlTqn 9Z allTqual ap 4uawau3evBuaOp WunO -TZ alBITual ap B uawauSei4uap 34TTnmi a SJaAej V 0oz aledTDuxJd apuewwom ap FTun, 1 e aalauuon qsa Ba gZ anbfqdeJbo4oqd; T2arqo 1 un; p qT U011esIIeDo + ap aBjFquaB aun au3eJ-4ua 9z alB [4Ual a uwu3jup uaaueuap Tun; -qz alBITual ap quawau3ei4uap 94Tun aun; p qa tZ aBTIF.ual ap 4uawauSeViuap 4IFnJDji un; p qnfTSUom Bsa allT4ual a uwu3jup uaaueuap uaAeu a -CZ aledTDutJd apuewwn ap QTun apuewwn ap qTun 4aBue; sip ap ainsaw ap amueqsTp ap JnafdeD al aJTp-V - saB, ea33 al '33 al rns gAoAua aiq inod sai; evd xnap ua gStArp Isa Ba 4anbtdo ax ,! ap dno4ne qaFqo un TuawaleJqu5 qsa aiT-ed aa3 -agAoAua Bsa anbfTqdeJ6ooqd TI; arqol r Jed aeWJO + 4aBqo.p aUUaTJe a5ewi aunp aiTJed aun lanbne aJjuqu aJjwu 03A unBjodu an iTiqOs inod arqop a3uetsTp aun aJnsaw-aledTJuTJd apjewwo ap 4TuneI

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  to perform the focusing operation when the trigger button 27 is partially depressed, and to trigger a shutter when the trigger button 27 is fully depressed. The object distance measuring unit 23 stores information regarding an object distance output from the distance measuring unit 21 when the main control unit 20 determines that a focusing operation is completed. The permissible different storage unit 1L) 19 stores a permissible difference between a current object distance measured by the distance measuring unit 21 and a focused object distance stored in the distance storage unit

object 23.

  =, The main control unit 20 is controlled by partially depressing the trigger button 27, and in a focusing operation, when it is determined that the focusing lens 15 is focused on the object, the main control unit 2 ') causes the object distance storage unit 23 to store information relating to a distance output from the distance measurement unit 21 during a focusing operation. Then, the main control unit determines whether or not a difference between the distance stored in the object distance storage unit 23 and the current object distance output from the distance measurement unit 21 is greater than an allowable difference stored in the allowable difference storage unit 19. If the difference is greater than the allowable difference, the main control unit 20 stops the focusing operation in order to maintain the current focal state, and at the opposite if the difference is less than the allowable different, the main control unit 20 continues

  À ', a usual focusing operation.

  The actual use of this automatic focusing device is described below with reference to FIGS. 8A

and SG.

  As shown in the drawings, it will be assumed that a photographer selects an airplane flying in the sky as an object to be photographed. In such a case, in which an aircraft traveling at high speed must be photographed as shown in FIG. 8A, the photographer looks in the viewfinder and directs the camera w (, photographic on the aircraft 35 to place it in the distance measurement zone 30. In this condition, if the trigger button 27 is partially pressed, the focusing lens 15 is driven so that it is always focused on the aircraft 35. If the photographer cannot follow the aircraft 35, and the aircraft moves out of the distance measurement zone 30 as shown in FIG. Fig. 8B, the focusing lens 15 is held in the lens position to which the lens 15 has been focused on the airplane 35 2 () just before it moves out of the measurement area of

distance 30.

  Then, when the photographer moves the camera to again place the aircraft 35 in the distance measurement area 30 as shown in FIG. SA, as described above, the focusing lens 15 is driven to always be

focused on aircraft 35.

  As a result, even if the photographer allows the object to leave the distance measuring zone 30, when the object is again placed in the distance measuring zone 30, the focusing lens 15 can be

  focused on the object in a short time.

  It will be noted that the operation described above can be carried out automatically under the control of a .5 camera, or can be carried out in a mode such that the above operation is carried out.

  only when this mode is selected.

  The focusing operation described above is explained below with reference to the flowcharts represented in FIGS. 9 to 11. This operation is carried out in accordance with the programs stored in a RAM provided in the main control unit 20. It will be noted that, in a usual camera operation, although a calculation of AE to obtain a exposure value such as a shutter speed and an aperture value, an exposure process in which a shutter and an aperture are controlled in accordance with the exposure value for exposing film, a process for film wrapping and other processes are carried out, these processes are not necessary for an understanding of the present invention and, therefore, the explanations of

these are omitted.

  Fig. 9 is a flowchart of a mode setting program 29 for performing an operation of

  focusing of the embodiment described above.

  When the mode is set, first of all a mode switch provided on a camera is controlled to select a slave AF mode during a STEP 201. If this mode is selected, the camera is positioned in slave AF mode during a STEP 202. Note that, as described above, this mode can be performed automatically as a series of commands by the device

- photographic.

  Fig. 10 is a flow diagram of a program for determining a state of the trigger button 27 during the execution of the focusing operation. This program is executed at predetermined intervals by a

S timer interrupt.

  2A4 When an interrupt signal is output, during a STEP 211, a commanded state of the trigger button 27 is entered. The commanded state means a state in which the release button 27 is not pressed, a state in which the trigger button 27 is not fully pressed, and a state in which

  the trigger button 27 is fully depressed.

  During a STEP 212, if the trigger button 27 is not pressed, that is to say if the distance measurement switch SWS is not set to ON, the process advances from STEP 212 to an END process, and then this program waits until a timer interrupt is made. If it is determined in STEP 212 that the trigger button 27 i5 is not fully depressed, i.e. if the distance measurement switch SWS is set to ON, the process advances to STEP 215 in which it is determined whether or not the trigger button 27 is fully depressed, that is to say whether or not the trigger switch SWR is set to ON. In STEP 213, if the trigger button 27 is not fully depressed, it is considered that the trigger button 27 is partially depressed, and thus the process advances to a focusing program. Conversely, if the trigger button 27 is fully depressed, the process advances to STEP 214 to perform exposure, and then to a FIN process. It will be noted that, in the exposure process, a light measurement and an AE calculation are performed before an exposure operation of a film, and after an exposure, the film is wound in front of an image. This interrupt program shown in fig. 10 is provided for periodically determining whether or not the trip switch 27 is partially pressed. The focusing program is a subroutine for the AF mode positioned in the mode setting program shown in FIG. 9. In this embodiment, since the slave AF modc has been

  selected, the process advances to the slave AF program.

  Fig. 11l is a flowchart of an AF operation controlled by this embodiment. The process is described below with reference to FIG. 11 at the same time

y that with fig. 8A and SB.

  During a STEP 221, it is determined whether the trigger button 27 is partially pressed or not. If the trigger button 27 is partially depressed, the process advances to a STEP 222 and conversely if the trigger button 27 is not controlled, the process advances to an END process. During a STEP 222, it is determined whether or not the trigger button 27 is fully pressed. If the shutter button 27 is fully depressed, the -0 process advances to an exposure program to perform an exposure operation in which light metering and AE calculation are performed before exposure of a film. If the trigger button 27 is not fully depressed, it is considered that the trigger button 27 is partially depressed, and thus the process advances to STEP 223 to perform

a focusing operation.

  IN STEP 223, the distance measurement unit 21 is controlled to measure an object distance, and the main control unit 3.0 performs a measurement calculation based on a distance signal obtained from the distance measurement unit 21 in order to obtain a magnitude and a defocusing direction (i.e. a number

  of turns and a direction of rotation of an AF motor).

  Then, the process advances to a STEP 224 in the Fqop aDue4sTp e TS auiepnos aQTuew ap 596ueq uou no 9 e 4aCqop azue4sip el TS uTwia4gp; sa ITTnb aJip-V-jsa3 61 alqTSsTwpe a4uad utpw uupp 94 aDuaBd.Tp aun e aJnaTJgdns uou no 4sa 01 aginsaw amuelsTp el Ba gsTIeDo + qsa ITnbs.ol 4arqo unp 1 aDue4sTp el a4ua auuaioJ. p aunp anIosqe JnaLe ^ el Ts suT1wJap Isa 13 ltZ 3dJ13 aun V TZ 3dV13 aun V sJoIe aue ^ Ae snssaDoJd ae - (ó <aginsaw aDue4sTp) O0 4aFqo.p amue4sTp aun JTuaQaaab aan Sú 3dd13 aun V aDueAe snssaBoJd QZ al puo0ua quawaJTqua sed qsau LE 4uaBwaqualDp ap uolnoq al Fs anb la uo1TTsodxa aun janza ++ a inod uorTsodxap awwei6oJd ne azue ^ e snssoQuu 4u V aBue ^ e snssaeodd al eepuewwoD sed.sau oz LZ quawaqmualTp ap uo; noq al Fs anb ejaqou uo guTwia. sp 4SA Lz.uawaqmualmgp uoInoq ap np ele ZZZ has IZZ S3dV13 sal suep ANB awgw ap been Buz S3dV3 XNV r2Z 3DU 3 aun e aDueAe snssaBoJd lT eaITnsu3 'ú qaqo; p! aDue4sTp ap ap uolTestJQow9 qTunfl suep apsTJowgw 4SA psTIeDo + Aqsa ITenbsJoil arqozl ap q aDueqsTp el Bllanbel suep 9Z 3dY13 aun B gZ 3d13e! ap amue ^ e snssaDoJd aB baquTwJBa.sa uoTieslTeDo + ap UOT) 1.Jedp.ITS BaT ^ TnsJnod 1sa uotesTIeDo + ap UoT4eiJdoT Ba TZZ 3dVi3zl? auJnoqaJ snssaBoad d al BagAaqJe sed sa; u uoTiestIeBo. ap uo; eidoI TS -agAaqDe lsa uoT0esileDo1 ap uoTieJqdOI Ts aJTp ---- saD iagsTIezo + uo4T.sod ua UoU no aAnoJ4 as gl uorTesiTLeo + ap aTITqual el Ts5 eu] wJa9p qsa TT IT ZA TT IT snssaoJd d aq uoT1esije3oa ap UOTiTsod aun ienbsn? aBeldT p sa 1 uoTîestIeDo + ap anlT4uat el anb alos ap eC allT3UTl ap quawau3eJquaPp lTnDJTa al sJaA ^ eW Y aBpUeWWoD lsa 9Z alITuaI ap 4uaBwau3eJ4uap 4Tunl all

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  has changed suddenly, a movement of the focusing lens 15 is not carried out and the process returns to STEP 231. Conversely, if the object distance has not changed suddenly, the process advances to STEP 234. By the process described above, it is determined whether or not the distance from the camera to the object has suddenly changed, that is, it is determined whether the object has or has not left the area of

  If. distance measurement 30, as shown in FIG. 8B.

  IN STEP 234, the focusing lens 15 is driven in accordance with the measured distance Lo and the process then advances to STEP 235 in which it is determined whether or not the focusing operation is completed. If the focusing is not completed, the process returns to STEP 231 to carry out the focusing operation again and conversely if the focusing is completed the process advances to STEP 236. It will be noted that if the value | L - Law obtained by L0 measured in STEP 233 after returning to STEP 231 is greater than the admissible difference A, an action of the lens drive unit 26 is stopped, or the drive unit of lens 26 is controlled so that the focus of the lens is adjusted to the object distance L stored in the storage unit

object distance 29.

  IN STEP 236, the measured distance L0 is stored according to a distance L from a focused object and then the process returns to STEP 231 to repeat the

previously described process.

  As described above, the automatic focusing device of this embodiment is constructed in such a way that once a focusing operation is completed, then it is determined whether the object distance (the measured distance Lo) 4Sa IT.nbsJoî laCqol ap q amuelstp el anb eJa4ou uo V ajqtssTwpe a3uaJ ++ Tp el ainaiJgdns auua ^ Aap amuaJ. ++ Tp el anb queAe a4snr aginsaw azue4sTp aun q4snre a saBAupAbAupAbAupAbAuApAbAuAtAbAuApAyAuAp - z jarqop azuelsTp ap uoTFesTJow9w ap 3TUnl suep gsTJOWgw 9sTIeDo + 02 4sa TinbsJol 4aCqoT ap 1 azue3sTp el V; snce 4sa aIT; Bual el ap jaAo + al anb ajZaUuAupuuuuuu 4u4 4Auuu 4Auuu 4Auuu 4Auuu 4Auuu 4Auuu 4Auuu 4Auuuu 4AuAuuuu 4Auuuuuuuuuu 4u4uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuqu 1 aeqS S Pe aqTsuasJ Tp gel V aJnafTJdns: uaT ^ ap TúZ 3dBl3, le Jno4aa sde úZ 3dfl3, T e aiJnsaw 9z O0 jed anua4qo 01 - 1 JnaleA el Fs 4apAaqme sTo + aun gq eoo uoo uoo uoo ; eJgdoT 4uaB4dJ 9z alBT [ual ap; uawau3eJ; uap qTunT 4a TZ aBue4sTp ap aJnsaw ap qTun ;, anb uatf V aTqTSsTwpe a uaBqg +. p el e aJnafli + u auuaTiap B aBuaJg ++ Tp el anb az VnbsnC _jje sa ST uoT estTIe [o + ap alITfuaI el ap 4uawaBeldpp al qa eV alqTssTwpe auaJ ++ fTp el e ainatiJdns 4sa ansaw afswsqsqsqsqsq qq 7 aBueqsTp el a-Jua aDua9 ++ TP aun Fs ItZ: - Tú2 S3di3B xne aiPid2 BTi aJiTUew ap euTwjaBp 4sa IT 'euo + ua quawaIlaTJLed 4sa LZ quawa4nuaTgp ap uolnoq al anb; uJpuu apuupuu apuupu uap apo uupuu apuupu uap apuuu apu uu apu 0 pus Fsi 1na1TTe jed -emuoua 4uawalilaiJed sa Zz luawaqmuaIpp p uofnoq aI anb sdwaBIuol o'ú Tssne 9úC e TúZ S3dVl3 Sal suep s ldej 4uos snssaDoid sad '92Z 3dfl3, 1? aBlaAnouaJ B sa _ 7aFqop a3uesp el easA ^ aqze qsa uoTiestiemo + ap uoT3ejqdo aunnb sTo + anbebqL 4a 'túZ 3dV13! Ie ljanoe Ieo 4eqI mTuajuvew inod aBu3e> Jua $ a S i uoTlesTIemo + ap aIiTual eT alIqTssTwpe aDuaJ ++ Tp eI e aJnaTiJeUT amuaj + + Tp el TS -g8 '6T' el V euDJA no qsa -ú UOTA ^ el TS euTwiaqp sa IT aldwaxa Jed {(ITZ 3dV13) (auTepnos aiJTuew ap pbueq4 uou no e

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  focus stored in the object distance memory unit 2Z is initialized when an operation

  button 27 is interrupted.

  As described above, in the automatic focusing device of the present invention if the distance from the object is suddenly changed after a focusing operation has been completed, since a lens driving operation does not take place. is not

  done, the time for focusing is shortened.

  If the magnitude of change of the object distance is within the allowable difference A, since the focusing operation is always performed, a moving object can be easily tracked and

kept in focus.

  Note that, although the difference between object distances is used as a parameter to determine whether or not the lens drive should be performed, in the above embodiment, the rate of difference in object distances can be used as this parameter. In addition, although the object distance is used as the judgment standard in the above embodiment, a magnification and defocus direction and magnification of an image obtained by the CCD can be used instead of the distance.

object.

  Still further, the allowable difference is preferably modified in accordance with a focal length of the lens and an object distance when it is focused. For example, the longer the focal length of the lens, the smaller the allowable difference, and the shorter the distance of the object when it is focused, the shorter the

admissible difference.

  Although the embodiments of the present invention have been described herein with reference to the accompanying drawings, it is obvious that any modification and change can be made by those skilled in the art.

  the technique without departing from the scope of the invention.

Claims (16)

CLAIMS:   1. An automatic focusing device for a photographic camera, said automatic focusing device characterized in that it comprises: means for measuring an object distance (10); means for driving a focusing lens (14) of a photographic objective provided in said camera; means for controlling said drive means 10 (13), based on said object distance measured by said measuring means (10), so that said focusing lens is driven to focus on an object, and means to determine (12) whether or not said object distance has changed suddenly; said control means (13) controlling said lens driving means (14) so that said focusing lens is driven to be focused on said object when said determining means (12) determines that said object distance does not has not suddenly changed, and to limit operation of said drive means (14) when said determining means (12) determines that said   object distance changed suddenly.   2. Automatic focusing device according to claim 1, characterized in that said determining means (12) determines whether or not said object distance has changed suddenly, based on a current object distance measured by said measuring means. measure (10) and an earlier object distance when focused   obtained by said control means.   3. An automatic focusing device according to claim 2, characterized in that said determining means (12) determines whether a difference between said current object distance and said previous object distance 3z is or is not included in a admissible difference.   4. Automatic focusing device according to claim 3, characterized in that said admissible difference is modified in accordance with a length   focal length of said photographic objective.   5. Automatic focusing device according to claim 3, characterized in that said different permissible is modified in accordance with a distance object when focused.   6. Automatic focusing device according to claim 4, characterized in that said admissible difference becomes smaller while said length focal length becomes longer.   7. Automatic focusing device according to claim 2, characterized in that said determining means (12) determines whether said object distance   current is or is not included in a long distance -   limit and within a short distance limit to determine whether or not said current object distance has changed from suddenly.   8. Automatic focusing device according to claim s1, characterized in that said determining means (12) uses a value and a direction of   defocus as said object distance.   9. Automatic focusing device according to claim 1, characterized in that said determining means (10) uses an amplification of an image obtained by a CCD image sensor as said distance object.   10. Automatic focusing device according to claim 1, characterized in that said control means (13) stops operation of said lens drive means (14) when said determining means (12) determines that said distance d 'object suddenly changed.   11. Automatic focusing device according to claim 1, characterized in that said control means (13) controls said lens drive means (14) so that said focusing lens is moved over a long limit distance and a short distance limit when said determining means (12) determines that said distance   object suddenly changed.   12. Automatic focusing device for a photographic camera, said automatic focusing device characterized in that it comprises: means for measuring an object distance (10); means for driving a focusing lens (14) of a photographic lens produced in the camera; means for controlling said driving means (13), based on said object distance measured by said measuring means so that said focusing lens is driven to be focused on an object and; means for determining (12) whether said distance loaded suddenly or not; said control means (13) controlling said lens driving means (14) so that said focusing lens is driven to be focused on said object when said determining means (12) determines that said object distance measured by said measuring means <10) is between said long limiting distance and, said short limiting distance, and limiting an operation of said lens drive means (14) when said determining means (12) determines that said distance of object is not included within said long limit distance and said short limit distance. 13. The automatic focusing device according to claim 12, characterized in that said control means (13) stops an operation of said lens drive means (14) when said determining means (12) determines that said distance d object is not included within said long   distance limit and said short distance limit.   14. Automatic focusing device according to claim 12, characterized in that said control means (13) controls said lens drive means (14) so that said focusing lens is moved to one of said long limiting distance and short distance limit when said determining means <12) determines that said object distance is not included within said long   distance limit and said short distance limit.   15. Automatic focusing device according to claim 12, characterized in that said long limit distance and said short limit distance are determined in accordance with a distance signal entered from a distance ring supplied in said photographic lens.   17. Automatic focusing device according to claim 12, characterized in that said long limit distance and said short limit distance are determined in accordance with a distance signal entered from a data panel supplied in said camera, by means a key command. 18. Automatic focusing device according to claim 12, characterized in that one of said long limit distance and said short limit distance is established at infinity or within a photographable limit   closest to said camera.   19. An automatic focusing device for a photographic camera, said automatic focusing device characterized in that it comprises: means for measuring (10) an object distance; means for driving (14) a focusing lens of the photographic objective provided in said camera to a focusing position; means for storing (23) said object distance when it is focused; in0 means for storing (19) an allowable difference between a current object distance measured by said measuring means (10) and an object distance when it is focused stored by said distance storing means (23) object, and means for controlling (13) a focusing operation based on an object distance measured by said measuring means (10), for focusing on an object and when said object is focused said control means (13 ) controlling said object distance storage means (23) to store said object distance when it is focused and to determine whether a difference between a current object distance measured by said measuring means (10) and a object distance measured by said object distance storage means (23) is or is not included within said allowable difference stored by said allowable difference storage means (19), allowing said means to lens drive (14) is controlled to focus said lens on said object distance measured by said measuring means (10) if said difference is less than said allowable difference, and said lens drive means (14) is controlled to focus said lens on said object distance measured by said object distance storage means (23) or is stopped for - alqTssTwpe aquait + lp call. ainaTiJdns 4sa amuaJ + s.p a4TPel Ts' aIlan4e alezo + uo.x; sod aun ja ^ iasuoj TsuTe 9ú -066Zú9Z