GB1591340A - Automatic focusing of a photographic camera - Google Patents

Description

PATENT SPECIFICATION

( 11) 1 591 340 ( 21) Application No 6041/80 ( 22) Filed 26 Sep 1977 ( 62) Divided Out of No 1591338 ( 31) Convention Application No 729289 ( 32) Filed 4 Oct 1976 in ( 33) United States of America (US) ( 44) Complete Specification Published 17 Jun 1981 ( 51) INT CL 3 G 03 B 13/20 Index at Acceptance G 3 N 275 381 CA 4 ( 54) AUTOMATIC FOCUSING OF A PHOTOGRAPHIC CAMERA ( 71) We, POLAROID CORPORATION, a corporation organised under the laws of the State of Delaware, United States of America, of 549, Technology Square, Cambridge, Massachusetts 02139, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:This invention relates to camera focusing.

Before photographing a subject, the lens of a variable lens camera must be axially displaced to a position at which the subject is brought into focus; this axial position being a function of the distance of the subject to the camera lens While such function, hereinafter termed the lens/subject function, depends on many parameters associated with the optical system, one of its more important characteristics for purposes of the present discussion is its highly nonlinear nature In general, the slope of this function is greatest for close subjects and decreases asymptotically to zero for objects remote from the camera.

In order to properly set the axial position of the lens, it is conventional to mechanically couple the output arm of an optical range finder to the lens mount through a cam system into which the lens/subject function has been incorporated whereby operation of the range finder imparts proper displacement to the lens In a different approach to powered displacement of the lens mount, the lens/subject function may be generated electrically An example of the latter arrangement is illustrated in U S patent No 3522764 which discloses an arrangement in which the setting of the lens is related to an acoustic range finder that produces a range pulse whose duration is directly related to the distance of the subject to the lens The range pulse is used to control a power-operated focus mechanism that moves the lens to an axial position in which the subject will be in focus.

When the operator does not supply the power for moving the lens to its focused position, he may be unaware of a condition occurring between the driving means and the lens which prevents the lens from reaching the position of focus.

According to the present invention, an automatically automatic focusing camera has a lens movable for focusing an image of a subject on a focal plane, a range finder system for generating a range parameter related to subject distance, and lenspositioning means including driving means operable when energised to move the lens towards a focus position selected in accordance with the range parameter, and further comprises sensing means for producing a stop signal if the lens does not move to the selected focus position in response to operation of the driving means, and means responsive to the stop signal for disabling the driving means.

Thus, if the driving means is supplied with power under the control of a range signal for driving the lens to its focused position and the lens stops before it has reached its focused position, the stop signal disables the driving means.

It may be arranged that the lens is returned to a reference position after each camera operation by a reverse driving means; the sensing means may then produce a stop signal for disabling the reverse driving means if the lens does not return to the reference position.

In one arrangement embodying the invention, the automatic focusing means includes a pulse generator responsive to lens movement for supplying a train of pulses to a counter When the number of counted pulses indicates that the lens is at a focused position, the driving means is disabled The un ( 19) ( 52) 70.

2 1 591 340 2 camera may include a second pulse generator responsive to the stop signals for incrementing this counter independently of lens movement to disable the driving means following the generation of the stop signal.

The sensing means may include a further counter that counts at a predetermined rate during operation of the driving means and is cleared at a rate directly related to the rate of the train of lens-position pulses, a stop signal being produced if the further counting means reaches a predetermined count.

The sensing means is also operative if the range signal is such as to indicate that the subject distance is outside the normal focusing range of the camera and the lens reaches a limiting position without achieving the focused position.

In order that the invention may be better understood some examples of cameras embodying the invention will now be described with reference to the accompanying drawings, in which:Figure 1 is a diagrammatic illustration partly in block diagram form of an automatic focusing snapshot camera embodying the present invention; Figure 2 A is a block diagram of the power-operated focusing mechanism including a lens mount employed in the camera of Figure 1; Figure 2 B is a displacement diagram showing the limits of movement of the lens mount of Figure 2 A; Figure 3 is a composite graph illustrating the operation of a pulse-generating means responsive to the range signal; Figure 4 A is a detailed block diagram of the preferred embodiment of the automatic focusing snapshot camera shown in Figure 1; Figure 4 B is a waveform chart illustrating pulse arrangements formed in the circuit shown in Figure 4 A; Figure SA is a simplified block diagram of another embodiment of a power-operated focusing mechanism suitable for use in the camera of Figure 1; Figure SB is a displacement diagram showing the limits of movement of the lens mount of Figure 5 A; Figure 6 A is a further form of poweroperated focusing mechanism embodying the present invention; Figure 6 B is a displacement diagram showing the limits of movement of the lens mount of Figure 6 A; Figure 7 is a further form of poweroperated focusing mechanism embodying the present invention utilising a voltage controlled oscillator as a pulse source; Figure 8 is a simplified block diagram showing how a manually operated range finding means can be incorporated into an automatic focusing camera embodying the present invention; Figure 9 is a perspective view of one embodiment of a driving means for a lens mount; Figure JOA is a detailed block diagram of an automatic focusing movie camera embodying the present invention; Figure l OB is a waveform diagram associated with the block diagram of Figure 10 A; Figure 11 is a perspective view of an alternative form of lens drive for use in the camera of Figure 1; Figure 12 is another form of a lens drive embodying the invention; Figure 13 is a block diagram of an automatic focusing system employed in conjunction with the lens drive of Figure 12; and Figure 14 is a block diagram of an alternative embodiment wherein a pulse system is employed to directly drive a stepper-motor lens drive.

In Figure 1, reference numeral 10 designates, in schematic form, an automatic focusing snapshot camera embodying the present invention Camera 10 includes housing 11 within which film is supported at a focal plane 12 opposite hub 13 within which a lens assembly or lens mount 14 is axially displaceable through a distance M between terminal position I and terminal position II.

Interposed between lens mount 14 and film 12 is shutter 15 for controlling the exposure of film 12 Preferably, shutter mechanism 15 determines exposure time and aperture size in accordance with the light from the scene being photographed The distance N of the lens mount from terminal position I to a location, at which subject 16 at a range R from the camera is in focus, is a predetermined function of the range, such function being highly non-linear and being termed the lens/subject function.

Associated with the camera is a range finding means 17 which, when keyed into operation, produces a range signal or range parameter having a characteristic directly proportional to the distance R The range signal is applied to a pulse generator means 18 which converts the range signal to a lens parameter by generating a train of pulses whose number is representative of the axial position of the lens mount at which a subject at a distance R will be in focus Drive means 19, operatively associated with the lens mount, axially displaces the same in accordance with the total number of pulses applied thereto by the pulse generator means If 1/k is the specific displacement of the lens mount, i e, the displacement per pulse applied to drive means 19, the application to the drive means of k N pulses will displace the lens mount from position I to a position located at a distance N from position I If the lens mount is located at position II, 1 591 340 3 1 591 340 3 k(M-N) pulses applied to the drive means will displace the lens mount to its proper axial position.

When the lens mount 14 reaches its final position or that is, a proper axial position to focus subject 16 on film 12, a correct focus sensor 20 produces a signal which is applied to shutter operator 21 and the latter responds by actuating shutter mechanism 15.

The result is the proper exposure of film 12 to a properly focused subject 16, with the only manual input being the keying of the range finding means.

A mechanical connection employed between hub 13 and lens mount 14 is entirely conventional and may take the form shown in Figure 9 to which reference is now made.

Lens mount 14 may include an internally threaded sleeve 22 carrying the objective lens 23 of the camera Sleeve 22 is mounted on an externally threaded sleeve 24 that is fixed to camera housing 11 so that axial displacement of sleeve 22 occurs in response to rotation of the sleeve The outer cylindrical surface of sleeve 22 is provided with teeth 25 mating with a spur gear 26 rotatably mounted on the housing 11 of the camera.

Gear 26 mates with a corresponding gear 27 rotatably mounted on the housing 11 Rigidly connected to gear 27 for rotation therewith, are a drive gear 28 and a peripherally slotted disc 29 Gear 28 meshes with a pinion 30 connected to the output shaft 31 of a stepping motor 32 When the motor 32 is enabled, the rotation of pinion 30 is transmitted through gears 28, 27 and 26 to the sleeve 22 which upon rotation thereby is displaced axially in one direction or the other depending on the direction of rotation of the motor The teeth 25 on sleeve 22 extend from one axial end of the sleeve to the other in order to permit the axial displacement of the sleeve despite the confinement of spur gear 26 against axial movement.

In order to limit the axial displacement of lens mount 14 in either direction, stops are provided and a slip clutch arrangement is utilized (not shown) between motor 32 and gear 26 Usually, the lens mount rotates through less than 360 in axially moving from a first position (i e, position I) at which a subject in focus may be as close as cm, to a second position (i e, position II) at which a subject in focus may be 9 m or more from the camera By a proper selection of gear ratios, the drive gear 28 may rotate through the same angular displacement as the sleeve 22; and in such case, the stops can be associated with this gear For example, an interrupted slot 33 may be provided in an axial face of gear 28, for cooperation with a stop pin 34 rigidly mounted on the camera housing The engagement of this pin with the closed ends of slot 33 will limit displacement of the lens mount to locations between positions I and II shown in Figure 1.

As will be described in detail below, the slotted disc 29 is part of an auxiliary pulse generator 35 (shown in Figure 2 A) and is associated with the lens drive or lens mount 14 for the purpose of providing feedback information necessary to properly position the lens mount Hence, the generator 35 provides means for sensing the position of the lens 14, or more specifically, for indicating the displacement of the lens from its start position which in the preferred embodiment is set at or just beyond the infinity position Preferably, auxiliary pulse generator 35 (see Figure 2 A), includes a fixed light source 36 (Figure 9), which may be a light emitting diode, and a fixed photocell 37 Source 36 and cell 37 are positioned in alignment on opposite sides of the slotted disc 29 so that light from the source incident on the photocell is periodically interrupted by the rotation of disc 29 The threaded connected between sleeves 22 and 24, between the teeth on sleeve 22 and teeth on gears 26 and 27, and between the number of slots and the parameters just described, define the specific displacement of the lens mount in terms of its axial displacement per pulse produced by the auxiliary pulse generator As indicated above, the specific displacement is termed 1/k Other lens sensing arrangements will also be suitable, for example, the light pulsing system noted above may be replaced by a magnetic system or a mechanical switch, etc.

Turning now to Figure 2 A, the preferred form of the power-operated focusing mechanism is shown in simplified form and is designated by reference numeral 38 In this embodiment, the range signal is pulse whose duration or length X is proportional to the distance to the subject being photographed as determined by range finding means 17 The range finding means can be optical, in which case the output of its movable arm could drive a linear potentiometer whose resistance could determine a range pulse proportional to subject distance Preferably, the range finding means is an acoustic transponder of the type shown in Patent No 3,522,764 In either event, X is a function of the range R of the subject.

Pulse generator means 18 of the focusing mechanism 38 includes a pulse generator 39 having a programmed time-variable pulse repetition frequency, and a gate 40, responsive to the duration of the range pulse for gating the output of pulse generator 39 into a counter 41 via an OR-gate 42 The counter 41, together with a decoder 43, are a part of the drive means 19 of the mechanism which also includes, in addition to motor 32 a lens pulse generator or auxiliary pulse generator 1 591 340 1 591 340 which operates as a lens position indicator and a power input 44 which can be applied to motor 32 by a gate 45 when the latter is enabled by a latch 46.

The state of the power focusing mechanism 38 before a range pulse is applied to the input terminal is as follows: pulse generator 39 is dormant, counter 41 is cleared, gate 45 is disabled (in a non-conductive state) and the lens mount is in its initial position (i e, position I) which would correspond to its position for focusing on a subject at infinity.

Since the lens mount is stationary, there is no output from auxiliary pulse generator 35.

In operation, the leading edge of the range pulse is detected at 47 triggering pulse generator 39 into operation and enabling gate 40 The repetition rate of this pulse generator is programmed such that it produces k N pulses during the time interval T, which pulses are accumulated in counter 41.

That is to say, counter 41, at the end of the range pulse, contains a number representative of the axial position of the lens mount at which the subject will be in focus.

Latch 46 is set by the trailing end of the range pulse thereby opening or enabling gate 45 that is, rendering gate 45 conductive or transmissive and causing motor 32 to rotate thereby axially displacing lens mount 14 Auxiliary pulse generator 35 is activated simultaneously with displacement of the lens mount, and begins to supply pulses to counter 41 through OR-gate 42.

As motor 32 moves lens mount 14 from its position II towards position I, counter 41 accumulates pulses produced by the auxiliary pulse generator 35 When k(M-N) pulses have been produced, the contents of counter 41 will be the number k M, and output pulse 48 is produced by the decoder.

Pulse 48 resets latch 46 disabling (closing) gate 45 and turning off motor 32 No further pulses are produced by the auxiliary pulse generator, and lens mount 14 will now be located a distance N from position I since the auxiliary pulse generator will have produced k(M-N) pulses in the time interval T during which latch 46 was set The object at range R, producing the range pulse, will be in proper focus upon occurrence of the reset pulse 48 This reset pulse is also applied to shutter mechanism 15 initiating exposure.

Coupled to the shutter (not shown) of the shutter mechanism is an end-of-exposure detector 49 whose output is used for the purpose of returning mechanism 38 to its original state described above In order for the puse generator 39 to produce the proper number of pulses during the range pulse, the pulse repetition rate of the pulse generator must vary in accordance with the timederivative of at least an approximation of the lens/subject function This can be seen by considering the curve shown in Figure 3 to which reference is now made.

A given objective contained in a lens mount establishes the lens/subject function relating the axial position of the lens mount at which a subject is in focus to the distance of the subject to the lens mount A typical lens/subject function is illustrated in Figure 3 by curve 50 where the ordinate and abscissa units are normalized for convenience It should be understood that curve 50 is intended to represent the general shape of a typical lens/subject function, and is not drawn to scale When the maximum permissible circle of confusion of the camera lens is specified, it is possible to compute the two curves identified by numerals 51 and 52 containing the curve 50 which take into account the depth of field for the lens system For example, a subject located within the distance A defined by the intersection of the curves 51 and 52 with the ordinate line 0 4 M will be in focus when the lens mount is at the axial position 0 4 M As indicated above, curves 51 and 52 are merely representative of the curves associated with an actual lens/subject function, and the distance A is only representative of a typical distance taking into account the size of the circle of confusion which is permitted by the designer As a consequence of the existence of curves 51 and 52 in a given optical system, the actual lens/subject function can be approximated by a piecewise linear curve designated by reference numeral 53 As long as this piece-wise linear curve or stepped approximation curve fits within the envelope of curves 51 and 52 a subject is said to be "in focus" since the lens position and subject distance intersect within the envelope defined by curves 51 and 52.

For a subject located a distance R from the lens mount, inspection of Figure 3 reveals that the axial position of the lens mount should be a distance N from the terminal position of the lens mount corresponding to position I at which a subject closest to the lens mount will be in focus.

Assuming that the range finding means of the camera produces a range pulse of duration T, it can be seen that the piece-wise linear function designated by the curve 53 is parametrically related to time by reason of the functional relationship between the distance to the subject and time indicated by the curve 54 in the fourth quadrant of Figure 3 Where the range finding means is an acoustic transponder, the slope of curve 54 will be proportional to the speed of sound in the medium within which the range finding means is operated.

Referring now to the curves shown in the third quadrant of Figure 3, the staircase or stepped curve 55 represents the timederivative of the piece-wise linear curve 53 shown in the first quadrant of Figure 3 For 1 591 340 example, curve 53 is linear between the origin and the distance O 1 D and has a slope of 4 within that interval Thus, during the interval on the range-time axis of Figure 3 corresponding to the range 0 1 D, curve 55 has a value of 4 and is constant indicating that the slope in that interval is constant.

Curve 56 represents the indefinite integral of curve 55 which of course has the same shape as curve 53 since the integral of the derivative of a function is the function itself.

As indicated in Figure 3, a subject at a distance R from the lens mount will have associated with it a range pulse of duration t By integrating curve 55 between the limits 0 and T, one will obtain a number proportional to the number N The constant of proportionality chosen is k, the reciprocal of the specific displacement associated with the drive means and lens mount of a given camera Integration of the output of a pulse generator whose pulse repetition rate varies in accordance with the time-derivative of curve 53 is accomplished by accumulating the pulses in a counter Integration between definite limits t= 0 to t=r is accomplished by gating the input into the counter As shown in Figure 3, the cross-hatched area above curve 55 is the value of curve 56 at time t = T.

From the above, it can be seen that any lens/subject function can be approximated by a piece-wise linear curve using the constraints imposed upon the system by reason of the maximum circle of confusion permitted for the system Furthermore, once a relationship is established between the distance of a subject from the lens mount and the characteristic of the range signal which directly relates the characteristic to the subject range, the time-derivative of the piece-wise linear approximation of the actual lens/subject function is known.

The pulse repetition rate is scaled in accordance with the time derivative of the lens/ subject function such that the number of pulses produced by the pulse generator at the end of a time interval associated with the distance to the subject will be representative of the axial position of the lens mount at which the subject will be in focus.

The curve 50 may be divided by any piece-wise linearization, and the pulse rate scaled for each Hence, the pulse repetition is scaled in progressive steps, with each step corresponding to one of piece-wise linearizations of the actual lens/subject function.

Reference is now made to Figure 4 A which shows the preferred embodiment of the present invention illustrating in more detail the principles illustrated in Figures 1-3 The automatic focusing camera 10 includes a manually keyable acoustic range finding means 17, and a power-operated focus mechanism 38 A that includes pulse generator 18 A and drive means 19 A In operation, a manual start signal applied to leading edge detector 47, such as the closing of a pushbutton, initiates a keying transmit signal to a clock oscillator 58 which continues to run until a stop signal is applied on line 59 The transmit signal also keys the acoustic range finding device 17 which responds by producing an outgoing wave a that is reflected back to the device 17 from a subject 16 after a period of time T, dependent on the range of the subject The output of oscillator 58 is applied to a counter whose contents are decoded at 62 in accordance with the breakpoints of the lens/subject function in order to change the number by which the output of oscillator 58 is divided by a programmed divider 63.

The pulse repetition frequency of the output of divider 63 decreases with time in accordance with the principals discussed in connection with Figure 3 The output of divider 63 is termed the "scaled clock," and is applied to counter 41 through gate 40 and OR-gate 42 Gate 40 is held open (conductive) during the range pulse by reason of the operation of latch 64, which is set by the transmit signal of detector 47, and which is reset by the receive pulse 48 (Figure 4 B) furnished by range finder 17 a period of time T subsequent to the transmit pulse Consequently, for a subject located such that the lens mount 14 should be located a distance N from position II (see Figure 1), k N pulses are supplied to counter 41 during the range signal defined by the period of time elapsed between the set and reset of the latch 64.

Hence, the range pulse provides a distance parameter, and the oscillator 58, counter 60 and divider 63 as well as their gate controls provide means for converting the subject distance parameter to a lens parameter in accordance with the lens/subject distance function.

The receive pulse 48, in addition to acting on latch 64 and simultaneously shutting down oscillator 58, also sets trailing edge latch 65 to its "on" or operating condition (the latch 65 being held in this state until decoder 43 detects the number k M in counter 41) Latch 65 opens (enables) gates 66 and 68 during the time X that it is set thereby respectively allowing power 44 to be applied to the forward motor control 67 and auxiliary pulses to be received from auxiliary pulse generator 35 The former causes motor 32 to operate in a direction driving the lens mount from its infinity position II toward its close-up position I as indicated in Figures 2 A and 2 B The rotation of motor 32 or of lens mount 14 also causes auxiliary pulse generator 35 to have an output that is applied by gate 68 to counter 41 through OR-gate 42.

Eventually, the auxiliary pulse generator 6 1 591 340 6 applies k(M-N) pulses to counter 41, whose contents will then be the number k M, allowing decoder 43 to reset latch 65 thus disabling gates 66 and 68 The output of decoder 43 also is applied to shutter actuator 69 which operates shutter mechanism 15 allowing exposure to take place A detector 49, e g, a switch arrangement, is employed to detect the end of exposure and its output is applied to a one-shot multivibrator 70 which in turn supplies a returnpulse of predetermined length to gate 71, to enable the latter thereby allowing power 44 to be applied to the backward control 72 of the motor The duration of the pulse produced by multivibrator 70 is sufficiently long for motor 32 to drive the lens mount from position II to position I In the normal course of events, the lens mount will reach the end of its travel before the return-pulse terminates to de-energize motor 32; and for this reason a slip clutch arrangement (not shown) is incorporated between the motor and the lens mount As explained below, a jam sensor 74 is effective to shut down the reverse motor drive once the lens movement stops.

In the preferred embodiment, the initial lens mount position is slightly beyond the infinity position, e g, rotated 10 beyond this point at which subjects at infinity are in focus Since subjects located at 24 feet or further will be in focus when the lens is set at its hyperfocal distance of 30 feet, once the range pulse duration exceeds a predetermined time (representative of a subject at 24 feet) a signal is in effect substituted for the echo signal to thereby move the lens to its hyperfocal position This is accomplished by the use of counter 60, since if the latter, whose contents are linearly related to time, reaches a count representative of 24 feet, there is no need to continue range conversion and decoder 62 produces a reset pulse that resets latch 64 allowing motor 32 to drive the lens mount to its 30 foot focus position.

In order to overcome a system malfunction, occurring subsequent to the manual start, resulting in no output from the end of exposure detector 49, the multivibrator 70 is triggered after a suitable delay within which the system would complete its operation if the malfunction had not occurred Additionally for a malfunction occurring between the motor connection and the lens mount, power would be supplied to the motor without any rotation or displacement being given to the lens mount This situation is protected against by utilizing an OR-gate 73 to which the outputs of forward and backward drive controls 67 and 72 are applied.

The output of this gate 73 and of auxiliary pulse generator 35 are applid to a jam sensor 74 which produces a jam signal when either of the controls 67 and 72 is operating under the condition that no pulses are being generated by the auxiliary pulse generator When jam sensor 74 produces its jam signal output, gate 71 becomes enabled,gate 68 is disabled and pulse generator 75 is energized for the purpose of filling up counter 41 and causing actuator 69 to trip shutter mechanism 15.

The jam sensor 74 may take the form of a timing device, i e, a conventional clock and counter which will be repeatedly reset by pulses from the auxiliary pulse generator 35.

When lens movement stops and no further pulses are received, the jam sensor 74 counts to completion and emits its jam signal which is applied to both the pulse generator 75 to thereby fill up the counter 41 and thereby stop forward lens drive and to the backward drive control 72 to stop the latter.

For purposes of illustration, the outputs of the decoder 43 and the jam sensor 74 are illustrated as "stop" signals applied to motor controls 67 and 72; however, these signals may be conveniently applied as disable signals to gates 66 and 71 respectively The jam sensor 74 may be gated into operation by the motor controls 67 and 72 or by gates 66 and 71 In normal operation, forward drive of the lens mount produces pulses which reset the jam sensor Subsequently, the jam sensor is again reset by the backward drive of the lens mount If, however, lens movement is not achieved, the jam signal shuts down the system.

As indicated, the motor 32 shown in Figure 4 A is preferably a stepper motor.

Consequently, the lens sensing may be eliminated and the motor driven in step with simulated lens pulses For example, as shown in Figure 14, pulses intended to fill the counter 41 may be provided from either the aforementioned auxiliary pulse generator 35 or a separate generator and fed directly to the motor 32 In this arrangment the trailing edge latch 65 enables the gate 66 to set a forward control circuit 202 and activates a pulse generator 204 The latter feeds pulses to both the motor 32 and the counter 41 When the decoder 43 trips, the gate 66 is disabled and the motor drive stops Following exposure, the multivibrator 70 enables the gate 71 and again activates the pulse generator 204 to drive the motor in reverse in accordance with reverse control 205.

Another embodiment of an automatic focusing mechanism is illustrated in Figure A by reference numeral 38 B Gated pulse generator 80, which operates in the manner described above, reponds to a range pulse by producing k N pulses which are accumulated in counter 81 The contents of this counter are thus representative of the axial 1 591 340 1 591 340 position of the lens mount for the subject to be in focus The range pulse is also applied to a trailing edge detector latch 82 which opens (enables) gate 83 at the end of the range pulse allowing power source 84 to be applied to motor 85 This motor drives lens mount 86 from its initial position (i e, position I as shown in Figure 5 B), toward position II In addition, the motor causes auxiliary pulse generator 87 to produce a train of pulses functionally related to the axial displacement of the lens mount in the manner previously described The pulses from pulse generator 87 are accumulated in counter 88 whose contents are continuously compared with the contents of counter 81 by means of comparator 89.

When the contents of counters 81 and 88 reach equivalence, i e, when auxiliary pulse generator 87 has produced k N pulses, the output of comparator 89 resets latch 82 when thereby closing (disabling) gate 83 and de-energizing motor 85 Thus, in the interval T 1, following the range pulse, the motor will have driven lens mount 86 to an axial position at which the subject will be in focus.

A further embodiment of the focusing mechanism according to the present invention is shown in Figure 6 A, and is designated by reference numeral 38 C Mechanism 38 C includes a gated pulse generator 80 which produces k N pulses in response to the application of a range pulse These pulses are applied to up/down counter 90 through OR-gate 91 The direction of counting of counter 90 is determined by the relative levels at terminals 92, 93 The range pulse is applied simultaneously to leading edge detector 94 and trailing edge detector 95 such that a signal is applied to "up" counting terminal 92 coincident with the leading edge of the range pulse, and a signal is applied to "down" terminal 93 by detector 95 coincident with the trailing edge of the range pulse Thus, the range pulse initially causes the pulses k N derived from generator 80 to be added in counter 90 The range pulse is also applied to the trailing edge latch 96 which is set by the trailing edge of this pulse thus enabling gate 97 and applying power source 98 to motor 99 which moves lens mount 100 from position I as shown in Figure 6 B towards position II As the motor drives the lens mount axially, auxiliary pulse generator 101 produces a train of pulses which are applied to counter 90 through OR-gate 91 However, just before these pulses are applied to the counter, the trailing edge of the range pulse will have caused detector 95 to switch the direction of counting of counter 90, and the pulses produced by generator 101 will be subtracted from the accumulated count in counter 90 Decoder 102 senses when the counter 90 reaches zero and resets latch 96 thereby disenabling gate 97 and removing power from motor 99 Consequently, generator 101 will have produced k N pulses as the lens mount is moved to an axial position at which the subject will be in focus.

Another embodiment of the pulse generator means is shown in Figure 7 and is designated by reference numeral 18 B In this emnbodiment, leading edge detector 103 detects the leading edge of the range pulse and opens (enables) gate 104 applying a step function to differentiator circuit 105.

The parameters of circuit 105 are selected such that the exponentially decaying output of the circuit closely matches the timederivative of the actual lens/subject function The variable voltage input to voltage controlled oscillator 106 causes the output of this device to produce a train of pulses whose repetition rate varies in accordance with the output of differentiating circuit 105.

The train of pulses produced by oscillator 106 is gated into counter 107 through a gate 108 whose conduction of transmission time is controlled by the range pulse As a consequence, the number of pulses accumulated in counter 107 will be a measure of the axial position of a lens mount at which a subject will be in focus Counter 107 could be used with the arrangements shown in Figures 5 A and 6 A, for example, to properly position a lens mount.

Referring now to Figure 8, an arrangement is shown for generating a range signal manually or automatically This arrangement includes an optical range finder 110 providing an analog input to transducer 111 in response to the manual setting of the optical range finder to a condition at which the subject being photographed is in focus.

The output of transducer 111 converts the range of the subject to a range signal having a characteristic directly proportional to the subject range The output of transducer 111 is applied to pulse generator means of the type described above through OR-gate 112.

The other input to this OR-gate is an acoustic transducer 113 of the type described above With this arrangement, the focusing of the lens mount of a camera is mechanized using the circuits described above while providing the flexibility of using either a conventional optical range finder or an acoustic transducer.

In the preferred embodiment of Figure 4 A, the conversion from the linear range signal to the nonlinear lens position is accomplished by the scaled clock arrangement prior to lens operation However, 'this conversion may be provided in the lens feedback loop as illustrated in Figure 11, wherein a lens mount 158 carries a slotted disc 159 which in conjunction with a light source 36 and a photocell 37 form an 8 1 591 340 8 auxiliary pulse generator or lens position sensor similar to that described with respect to Figures 2 A and 9.

Contrary to the previously described S embodiments, the disc 159 is not uniformly slotted but rather includes a plurality of slots which are spaced at progressively decreasing spacing along the disc perimeter to provide a nonlinear lens position sensor corresponding to relationship of lens position versus subject distance Hence, in this embodiment each lens or drive pulse is equal to a lens displacement required per unit change in subject distance.

In operation, as the lens sleeve 158 is driven from its illustrated terminal position (slightly beyond its infinity position) counter-clockwise as viewed in Figure 11, the number of slots passing the light source for each unit angle of revolution continually increases at a rate following the lens/subject curve 50 of Figure 3 A linear range signalto-drive pulse arrangement may then be employed with one-to-one correspondence to the feedback pulses For example, in the embodiment illustrated in Figure 4 A, the scaled clock 63 would be eliminated and uniformly spaced pulses fed directly to the counter 41 during the ranging operation.

A solenoid controlled lens drive arrangement 166 which is recocked in conjunction with operation of a film processing station 168 is illustrated in Figures 12 and 13 As shown therein, a lens drive disc 170 carries a plurality of slots 172 which form part of a lens position sensor or auxiliary pulse generator as in the preferred embodiment.

The disc 170 is biased in a counterclockwise direction as viewed in Figure 12 by means of a spring (not shown) During processing, as explained below, a dc motor 176 also drives the disc (and the lens 14) in a clockwise direction, to recock the disc against the bias of the spring A latch solenoid 180 by means of its latch arm 181 pivotally mounted at 183 captures and holds the disc 170 in its recocked position upon engagement of arm 181 with a stud 182 A rack arrangement 184 carried on the periphery of the disc 170 cooperates with a focus solenoid 186 to stop the lens in the proper focus position as described below in detail with regard to Figure 13 Energization of the focus solenoid 186 rotates its arm 187 around pivot point 189 for disc engagement.

As previously indicated, the lens drive system 166 is operated in conjunction with a processing station 168 such as is often employed in so called "self-developing" cameras In such cameras, following exposure the film unit is advanced between pressure applying members, for example, rollers 190 and 192 which operate to spread developing fluid across portions of the film material Preferably one of the rollers 190 is rotated during this operation by the motor 176 through a gear train 194.

Additionally, the lens disc 170 is also driven to its recocked position shown in Figure 12, by means of a second gear train 196; the latter including a clutch 198 which permits continued operation of the motor 176 once the lens mount 14 reaches its terminal position.

Turning now to Figure 13, the operation of the above described solenoid controlled lens drive will be explained with regard to the ranging and scaled counting arrangment of Figure 4 A Assuming that during the range pulse of Figure 4 A the counter 41 is partially filled thereby representing the desired lens position, the trailing edge signal (coincided with the echo signal) stops further range counting pulses from entering counter 41 and energizes the latch solenoid This releases the spring driven lens mount 14 such that the disc 170 and the lens mount 14 rapidly spins in a counterclockwise direction which displaces the lens from its terminal position towards a close up focal position As the lens rotates, the counter 41 is rapidly filled by the auxiliary generator 35 When the counter 41 becomes filled, decoder 43 trips thereby energizing focus solenoid 186; the latter, in turn, engaging and stopping disc rotation so that the system is focused.

As shown, the decoder 43 also initiates shutter operation, however, the latter could be derived from the focus solenoid actuation such as by means of a switch coupled to the arm 187 Once the exposure is completed, an end of exposure detector 49 starts the motor 176 which processes the film and at the same time rewinds the lens assembly to its cocked position.

While the above drive system is illustrated and described as a motor driven device, it lends itself to manually recocking with the latter being provided by manual processing or separately thereof.

Advantageously, the embodiments described above when employed in still (snapshot type) cameras may initiate actuation of the shutter in response to arrival of the lens mount to a position at which the subject is in focus Since a relatively long period of time generally elapses between each manual input to the range finder, this allows sufficient time for the lens mount to be driven back to a known start position which simplifies the logic since there is no need to remember the last position of the lens mount at which a previous subject had been in focus By expanding the amount of logic, however, it is possible to incorporate a memory into the circuitry so that the start position of the lens mount for a given focusing operation will be in the just previous position of the lens The availability of a memory of this type permits 1 591 340 1 591 340 the present invention to be expanded as discussed below into use with a movie camera in which the shutter mechanism is operated continuously over a period of time, and the lens mount must be adjusted during this period in the event the subject distance changes.

An automatic focusing mechanism for a movie camera is illustrated in Figure 10 A and is designated by reference numeral 120.

In response to the manual setting of trigger 121 of the camera, the movie shutter 122 begins to operate in a conventional manner and continues as long as trigger 121 remains set When manually reset, trigger 121 halts operation of the shutter The setting of trigger 121 is applied to keying circuit 123 through OR-gate 124 causing circuit 123 to transmit pulse 126 that is applied to acoustic transponder 125 In response to the application of pulse 126, transponder 125 transmits an interrogation pulse toward a subject being filmed The echo from the subject is received by transponder 125 and converted to an echo pulse 127 (see Figure 10 B) which is applied to trailing edge latch 128, resetting the same a time T following the setting of this latch by the output of leading edge detector 129 which detects the occurrence of pulse 126 produced by keyer 123 As a consequence, latch 128 produces a range pulse, designated by reference numeral 130, which enables gate 131 during the existence of this pulse to gate the output of pulse generator means 18 into "current" counter 132 The contents (A 2) of counter 132, at the termination of the range pulse, is representative of the position to which movie lens mount 133 should occupy in order for the subject being filmed to be in focus At this point, the contents (A 1) of "previous" counter 134 is representative of the actual position of lens mount 133 When subtractor is operated in response to receive pulse 127, subtractor 135 will subtract the contents of counter 132 from the contents of counter 134 and thereafter contain a number whose magnitude is representative of the distance that the lens mount must move to bring the subject being filmed into focus, and whose sign is indicative of the direction in which the lens mount must be moved.

The sign of the contents of subtractor 135 is determined by circuit 136 A negative sign is detected by circuit 137 indicating that the motor should move in one direction; and a positive sign is detected by circuit 138 indicating that the motor should move in the opposite direction The number in subtractor 135 is also tested by circuit 139 to determine whether the number is zero since the subject may already be in focus If the number in subtractor 135 is not zero, its absolute value is transferred into register 140 in preparation for the movement of the lens mount 133 by motor 141 Such movement causes the pulses produced by the auxiliary pulse generator 142 to count down the contents of register 140.

If the sign of the number in subtractor 135 is such that latch 143 is set (thereby enabling gate 145) by circuit 138 causing the motor 141 to run backwards as power 144 is applied through gate 145 to the motor, rotation of the motor drives the lens mount toward a position at which the subject being filmed will be in focus The resetting of latch 143 (thereby disabling gate 145), when circuit 146 detects the presence of zero in register 140, stops the motor with the lens mount at that point being at a position at which the subject is in focus The opposite situation occurs if the sign of the number in subtractor 135 is negative.

When the lens mount has reached its proper position, indicated by an output from decoder 146, a "continuation" pulse is produced which is applied to keying circuit 123 through OR-gate 124 causing circuit 123 to produce another transmit pulse, and the cycle described above is repeated, providing that trigger 121 is still set In addition, the "continuation", pulse also enables transfer gate 147 which is effective to transfer the contents of current counter 132 into previous counter 134.

In the event that the lens mount is already positioned for the subject to be in focus, the number in subtractor 135 will be zero and the circuit 139 will produce a "next" pulse which will be applied to keying circuit 123 which will produce another transmit pulse in response.

Shutter 122 remains operating as long as trigger 121 remains set, and transponder 125 is keyed periodically independently of the operation of the shutter The rate at which transponder 125 is keyed depends only on the time required to drive the lens mount from one position to the next in synchronism with changes in range of the subject.

Such time is relatively small, and is measured in terms of milliseconds thus ensuring that the subject being photographed will remain in focus during filming.

The cameras described above are also disclosed in our co-pending application No 39979/77 (Serial No 1591338) (from which the present application is divided), in which the claims are directed to a camera having a lens mount displaceable between a pair of terminal positions, the distance from one terminal position to a lens-mount location at which a subject at range R is in focus being defined as the distance N which is a predetermined function of R, and range-finding means for generating a range signal whose time duration is directly proportional to R, the camera further comprising driving means displacing the lens mount and means 1 591 340 responsive to the duration of the range signal for controlling the amount of the lens-mount displacement; the displacementcontrolling means including: a pulse generator providing a train of pulses which has a repetition frequency varying as the time derivative of at least an approximation of the function relating N to R; and counting means for accumulating pulses received from the pulse generator; the termination of the displacement of the lens mount by the driving means being effected by the displacement-controlling means in accordance with the contents of the counting means.

Claims (11)

WHAT WE CLAIM IS:-

1 An automatically focusing camera, having a lens movable for focusing an image of a subject on a focal plane, a range finder system for generating a range parameter related to subject distance, and lenspositioning means including driving means operable when energised to move the lens towards a focus position selected in accordance with the range parameter, the camera further comprising sensing means for producing a stop signal if the lens does not move to the selected focus position in response to operation of the driving means, and means responsive to the stop signal for disabling the driving means.

2 An automatically focusing camera in accordance with claim 1, in which the lens-positioning means further comprises reverse driving means responsive to the completion of an exposure cycle of the camera to move the lens back to a reference position, the said sensing means producing a stop signal for disabling the reverse driving means if the lens does not return to the reference position in response to the operation of the reverse driving means.

3 An automatically focusing camera in accordance with claim 2, including means responsive to the completion of the movement of the lens to its focus position for continuing a cycle of camera operation to provide a photographic exposure, the reverse driving means being responsive to completion of the exposure to return the lens to the reference position, and in which the means for continuing the camera cycle of operation is also responsive to the stop signal generated when the lens does not move to the selected focus position in response to operation of the driving means.

4 An automatically focusing camera in accordance with claim 1, 2 or 3 in which the means responsive to the stop signal to disable the driving means also disables the driving means in the absence of a stop signal when the lens reaches a selected focus position.

An automatically focusing camera in accordance with any one of claims 1 to 4, in which the lens-positioning means includes a pulse generator responsive to the lens movement for generating a train of pulses related to the lens movement.

6 An automatically focusing camera in accordance with claim 5, in which the lens-positioning means includes a counter for receiving the train of lens-position pulses during lens movement and means for disabling the driving means responsible for the lens movement in response to the detection of a given count, related to the said range parameter, in the said counter.

7 An automatically focusing camera in accordance with claim 5 or 6, further comprising a second pulse generator responsive to the said stop signal for incrementing the counter of the lens-positioning means independently of lens movement, whereby the driving means will be disabled, in response to the said given count in the counter, following the generation of the stop signal.

8 An automatically focusing camera in accordance with claim 5, 6 or 7, in which the said sensing means includes a further counter that counts at a predetermined rate when the driving means, or one of the driving means, is enabled and is cleared at a rate directly related to that of the said train of lens-position pulses, and a decoder responsive to sensing a predetermined count in the counter of the sensing means for producing the stop signal, whereby the sensing means produces the stop signal when the driving means is enabled and the lens fails to move.

9 An automatically focusing camera in accordance with any one of claims 1 to 8, including means for limiting the displacement of the lens so that light rays from subjects located within a limited subject distance range can be focussed, and in which the range finder may provide an electric range signal for a subject located at a distance within a distance range of greater extent than the distance range corresponding to the said limited range of lens displacement, the said sensing means providing the said stop signal when the lens reaches the limit of its displacement without achieving the focus position corresponding to the said range signal.

An automatically focusing camera according to claim 9, in which the means for limiting the displacement of the lens includes a stop engaged by a mount for the said lens to prevent movement of the lens to beyond a close-up position corresponding to a predetermined minimum subject distance.

11 An automatically focusing camera in accordance with any one of the preceding claims, in which the range finding system generates a range signal the duration of which is linearly related to the subject distance, and in which the camera further comprises pulse-generating means responsive to the start of a range signal to generate 11 1 591 340 11 a train of pulses whose repetition rate varies during the said range signal approximately as the time derivative of a non-linear function defining the settings of the lens for subjects at different distances, whereby the number of pulses generated during the range signal is linearly related to the setting of the lens at which the subject will be in focus, and a counter for accumulating the said pulses during the range signal, the driving means displacing the lens until its setting corresponds to the total of pulses accumulated in the counter during the range signal.

GILL JENNINGS & EVERY, Agents for the Applicants, 53/64 Chancery Lane, London, WC 2 A 1 HN.

England.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1981.

Published by The Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.