GB2287599A - Camera rangefinder - Google Patents

Description

DISTANCE MEASURING DEVICE FOR CAMERAS The present invention relates to a

distance measuring device for cameras.

There have previously been proposed various kinds of light projection and reception type distance measuring devices using an integrated circuit wherein the distance from the camera to the subject is calculated by measuring the number of light projections occurring or the time taken for the integrated voltage, obtained by integrating the output signal of a light receiving circuit for receiving light reflected from the subject, to exceed a predetermined value.

However, the above-described distance measuring devices have the disadvantages that when the subject is at a long distance or has a low level of luminance, the quantity of light reflecting from the subject and reaching the camera decreases so that, with the prior known arrangements, the time required for the integrated voltage to reach a predetermined level becomes long and the number of projections increases. This results in an increase in time for distance measuring and may be an extreme disadvantage in missing an appropriate time for releasing the camera shutter.

Accordingly, the present invention seeks to provide a distance measuring device for cameras which may permit a reduction of the time for distance measuring in such circumstances.

According to one aspect of the present invention there is provided a distance measuring device for cameras, which comprises:

projection means for emitting radiation; means for receiving radiation reflected from an object and which converts it into an electrical signal corresponding to the reflected radiation; an integration circuit incorporating integration capacitance means for integrating the electrical 2287599 signal; means for changing the capacitance value of the integration capacitance; a level discrimination circuit for judging the level of the output of the integration circuit; and a control circuit which receives the output from the level discrimination circuit and which controls the integration capacitance changing means in response to such output.

According to a second aspect of the present invention there is provided a distance measuring circuit device for cameras, which comprises: projection means for applying pulsating light to a subject; is light receiving means which receives light applied from the projection means and reflected from the subject and which outputs an electrical current corresponding to the luminance of the reflected light; a current/voltage conversion circuit for converting an output current of the light receiving means into a voltage; an amplification circuit for amplifying an output signal of the current voltage conversion circuit; an integration circuit having at least two capacitors and switching means for connecting the capacitors in series or parallel with each other and which integrates an output signal of the amplification circuit; a level discrimination circuit which generates an output when the level of an output signal of the integration circuit has reached a predetermined level; and a control circuit which receives the output from the level discrimination circuit and controls the switching means in response to such output of the level discrimination circuit.

In this case, it is preferable for the abovementioned control circuit to operate such that in the initial state of application of pulsating light by the projection means, the capacitors are connected parallel to each other by controlling the switching means and upon reception of the output from the level discrimination circuit, the connection of the capacitors is switched from parallel into series. For a better understanding of the present invention reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. 1 is a block diagram of a distance measuring device according to one embodiment of the present invention; Fig. 2 is a table of data related to the distance measuring device of Fig. 1; Fig. 3 is a timing chart for illustrating the operation of the distance measuring device of Fig. 1; Fig. 4 is another timing chart for illustrating the operation of the distance measuring device of Fig.

1; Fig. 5 is still another timing chart for illustrating the operation of the distance measuring device of Fig. 1; 25 Fig. 6 is a flow chart illustrating the operation of the distance measuring device of Fig. 1; Fig. 7 is another flow charge for illustrating the operation of the distance measuring device of Fig. 1; Fig. 8 is still another flow chart for illustrating the operation of the distance measuring device of Fig. 1; Fig. 9 is a further flow chart for illustrating the operation of the distance measuring device of Fig. 1; and Fig. 10 is a further timing chart for illustrating the operation of the distance measuring device of Fig.

The structure of one embodiment of the present invention will be described with reference to the accompanying drawings, especially Fig. 1, wherein a 5 projection circuit 10 T c " rises a transistor 11, and resistors 12 and 13 driving an iRED (near infra-red emitting diode) 14 as a projection neans. When a projection signal is generated from a control circuit (operation circuit), the IRED 14 emits light. The light thus emitted passes through a projection lens 1, a part of the light reflects on a subject and a part of the reflected light becomes incident upon a PSD (semiconductor position sensitive device) 3 as light receiving means through a light receiving lens 2.

The IRED 14 is actually driven pulsatingly so as to irradiate pulsating light upon the subject.

Reference numerals 20 and 30 designate respectively, a first current/voltage conversion circuit and a second current/voltage conversion circuit, and reference numeral 3 designates the M. The first and second current/voltage conversion circuits 20 and 30 together with the PSD 3 constitute a light receiving circuit-23. When a light signal (light coming from the projection circuit 10 and reflected from the subject) becomes incident upon the PSD 3, the PDS 3 generates a signal current corresponding to the intensity and the incident position of the light. The first current/voltage conversion circuit 20 comprises an amplifier 21 and a feedback resistor 22 and similarly, the second current/voltage conversion circuit 30 comprises an amplifier 31 and a feedback resistor 32. The first and second current/voltage conversion circuits 20 and 30 receive the signal current from the PSD 3 and generate a voltage proportional to the signal current. Reference numeral 4 designates a switch for selecting one of the outputs of the light receiving circuit 23. This switch 4 is controlled by the a control circuit 80, as described later, and selectively connects to either the output of the circuit 20 or-tlihf- of circuit 30. As will be described later, when a long distance is measured, the output of the first current/voltage conversion circuit 20 is applied to an amplification circuit to be described later and when a short distance is measured, the output of the second current/voltage circuit 30 is applied to the amplification circuit.

Reference numerals 40 and 50 designate amplification circuits, respectively, of which the circuit 40 receives as an input the output signal of the light receiving circuit 23 the DC component of which output signal is eliminated by. a series capacitor 5. The output of the amplification 40 and the input to the circuit 50 are connected in series with each other through a capacitor 6. Both of the circuits 40 and 50 amplify the output signal from the light receiving circuit 23. Further, the amplification circuits 40 and 50 are circuits capable of gain switching. Further, these circuits.

of which the former circuit 40 will for example be described in detail are of the same structure. The amplification circuit comprises an amplifier 41 and three feedback resistors 43 through 45 and amplifies a signal inputted thereto with a predetermined gain. The circuit is provided with switches 46 and 47 which are ON/OFF controlled by a control circuit to be described later. As the feedback resistor 45 is shortcircuited when the switch 46 is turned ON and the feedback resistors 44 and 45 are shortcircuited when the switch 47 is turned ON, the gain of the amplifier 41 changes gradually according to the conditions of these switches. Consequently, the conversion of the signal current into a 6 1 voltage is made according to the gain so changed and is outputted to the circuit of the later stage. Likewise, the amplification circuit 50 also comprises feedback resistors 53 through 55 and switches 56 and 57 and operates such that the switches 56 and 57 are contolled by the control circuit to set up a proper gain and in accordance therewith, the signal outputted from the amplification circuit 40 is amplified.

Further, reference numeral 7 designates a switch controlling the output of the amplification circuit 50 which is tuned ON and OFF by the operation of the control circuit thereby controlling transmission of the output signal of the amplification circuit 50.

Reference numeral 60 designates an integration circuit which comprises an amplifier 61, an input resistor 62, capacitors 63 and 64, switches 65 through 67 and a voltage follower 68 and which integrates the output signal from the amplification circuit 50. The switches 65 through 67 are ON/OFF controlled by the control circuit8Osuch that when the switches 65 and 66 are turned ON simultaneously, the capacitors 63 and 64 are connected parallel to each other and when only the switch 67 is turned ON, the capacitors 63 and 64 are connected in series with each other. Further, when all of the switches 65 through 67 are turned ON, the electrical charges of the capacitors 63 and 64 are released. The voltage output of the integrator is outputted to a level discrimination circuit 70 to be described 1 ater, via a voltage follower 68. In the present embodiment, the capacitors 63 and 64 have the same capacitance value.

The level discrimination 7 ci rcui t 70 comprises a comparator 71, a switch 72, a f irst- reference power source 73, a second reference power source 74 and a third reference power source 75 and discriminates the level of the output voltage from the integration circuit 60. The comparator 71 compares its input voltage with the voltage of the reference power source selected by the switch 72 and converts the result of such comparison into a digital signal to be supplied to the control circuit.

Reference numeral 80 designates the control circuit 80 which is provided with a CPU (not shown), a RAM 81 as a read/ write volatile memory and a ROM 82 as a readable nonvolatile memory and which controls the entire device of this embodiment. In this embodiment, the RAM 81 is used for temporarily storing operations by the control circuit 80, counts and flags (to be described later) and the ROM 82 is used to store the program and data for the control circuit 80 and particularly, it has a data table (see Fig. 2) for coordinating a value X corresponding to the distance up to the subject to be obtained by a distance measuring operation (to be described later) with the distance D to the subject.

Reference numeral 83 designates a motor which is controlled by the control circuit 80 so as to drive a lens tube 84 to a focusing position.

The detailed operation of the circuit according -to the embodiment of the present invention is described below but first an outline of the operation is given.

When the operation is initiated, the power sources for all the circuits shown in Fig. 1 are turned ON. Next, the content of the RAM 1 is cleared and the optimum gains for the amplification circuits 40 and 50 are determined by a gain 8 1 determining operation to be described later. In performing the gain determining operation, when it is found that the subject lies very close or its luminance is extremely high, the closest distance flag Fn in the RAM 81 is set up. In that case, it is determined without doing any distance measurement that the subject lies at the closest distance and the value X corresponding to the distance up to the subject is set to 1.0.

After determining the optimum gains for the amplification circuits, a long distance measuring operation is performed by using the first current/voltage conversion circuit 20, the number of light projections is counted and the final value of the number of projections Nf is stored in the RAM 81. In this case, if the number of projections Nf during the long distance measuring operation is more than a predetermined value, it is determined that the subject is at a position farther than a predetermined distance, an infinite distance flag Ff is set up to set the value X toO.5 corresponding to infinite.

Next, a short distance measuring operation is performed by using the second current/voltage conversion circuit 30. In this case, the number of projections is counted and the final value of such counting is stored in the RAM 81 as the number of projections Nn. Upon completion of the measuring operation, the distance up to the subject is calculated. In this case, if the infinite distance flag Ff is set, it is determined to be the infinite distance, if the closest distance flag Fn is set, it is determined that the subject at the closest distance and if neither of them are set, the following value X corresponding to the distance up to the 9 i S subject is calculated by using the number of projections Nf and the number of projections Nn stored in the RAM 81 by the following equation.

X = Nf / Of + Nn) When the value X is fixed, the addresses in the ROM 82 which are unconditionally determined by the value X (see Fig. 2) is referred to, thereby obtaining the distance up to the subject. lastly, the lens tube 84 is driven to a focusing point by controlling the motor 83 and then the power source of the distance measuring circuit is turned OFF to clear this routine.

Next, the gain determining operation for the amplification circuits 40 and 50 will be described in detail by using the timing chart of Fig. 3. First, the control circuit 80 turns the switch 4 ON toward the current/voltage conversion circuit 20. Then the switch 72 is connected to the reference power source 73 and the switches 65, 66 and 67 are all turned ON so that the electrical charges stored in the capacitors 63 and 64 are released (Fig. 3, a).After the electrical charges are released sufficiently, the switch 67 is turned OFF (see Fig. 3, b) and the capacitors 63 and 64 are connected parallel to each other. Then a clear signal CR is generated to clear a count value Ne which is incremented every projection (seeFig. 3, c). Then the control circuit 80 operates the projection circuit 10 to generate a projection signal Ve so that the IRED 14 is driven to start projection (see Fig. 3, d). In order to secure the rising time of each of the amplifiers following the initiation of projection and to reduceay influence from fluctuation of the power source, the integration circuit is operated for only a period of time T2 after a lapse of a time TI after projection (see Fig. 3, e).. Upon completion of the above operation, the projection and integration are stopped (see Fig. 3, f) to wait for a period of a time T3 and a count-up signal CU is generated to add 1 to the count value Ne (see Fig. 3, g).

The above operation is repeated by a predetermined number of times Ng (for example, 10 times), and then the switch 7 is turned OFF to cause the voltage between the terminals of the capacitors 63 and 64, that is, the integrated voltage Vi, to be outputted to the comparator 71 which latter compares the voltage with the voltage V1 of the reference power source 73 and outputs the result of comparison to the control circuit 80 after converting the result into a digital signal. The control circuit 80 turns the switch 46 ON (ng.3, i) if the output of the comparator 71 is at H' level (Fig. 3, N and if the output remains at 'L level, it judges that the optimum gain is reached. Thus, the above operations of integration, comparison and calculation are repeated and if the output of the comparator 71 is at H level, the switches 56, 47 and 57 are turned ON in sequence. On the other hand, if the output of the comparator 71 should remai n at H' 1 eve] whi 1 e al 1 the swi tches are tznr=d ON, the closest distance flag Fn is set up. Thus the gain for the amplification circuit as a whole is determined. Fig. 4 shows a case where the optimum gain has been obtained by the fourth gain determining operation in a state in which the switches 46, 56 and 47 are turned ON.

Next, the distance measuring operation by the first current/voltage conversion circuit 20 will be described in 11 detail with reference to Fig. 5. First, the switch 4 is turned ON toward the current/voltage convers ion circuit 20 while the switch 72 is turned ON toward the reference power source 74 (Fig. 5, a). Next, the switches 65, 66 and 67 are all turned ON and after releasing the electrical charges accumulated in the capacitors 63 and 64 are released and the switch 67 is then turned OFF (Fig. 5, b) so that the capacitors 63 and 65 are connected parallel to each other. After that, the count value Nf is cleared to zero (Fig. 5, c).

The control circuit 80 then operates the projection circuit 10 to drive the IRED 14 and a projection signal Ve is generated to start projection (Fig. 5, d). In order to.secure the rising time of each of the amplifiers and to reduce the effect of fluctuations of the power source, the integration circuit is operated for a period of time T2 after a lapse of a period of time T1 after projection (Fig. 5, e).

Upon completion of the above operation, the projection and integration are stopped (Fig. 5, f) to wait for a period of time T3 and a count-up signal M is generated to add 1 to the count value Nf (Fig. 5, g). The control circuit 80 then repeats the operations of Fig. 5, d to g to increment the count value Nf and when the output of the comparator 71 goes to "H" level (Fig. 5, h), the switch 72 is turned ON toward the reference power source 75 to switch the reference voltage from V2 to V3 and at the same time, the switches 65 and 66 are turned OFF while the switch 67 is turned ON (Fig. 5, i). As a result, the capacitors 63 and 64 are connected in series with each other and the integrated voltage Vi becomes twice that of the case where the capacitors are connected in parallel with one another. Then the projection is repeated again to increment the 1 count value Nf and when the integrated voltage Vi reaches the reference voltage V3 and the output of the comparator 71 goes to "H' level (Fig. 5, j), projection is finished and the final count value Nf is retained as the number of projections Nf. In this case, where the distance to the subject is so long that the integrated voltage Vi does not reach the reference voltage V2 or V3 even if the projection is performed by a predetermined number of times Nf, the distance is judged to be infinite and the infinite distance flag Ff is set up to thereby complete the operation.

likewise, a distance measuring operation is performed by the second current/voltage conversion circuit 30. First, the switch 4 is turned ON toward the current/voltage conversion circuit 30. Then the switches 65 and 66 are turned ON and, after releasing the electrical charges accumulated in the capacitors 63 and 64, the switch 67 is turned OFF (Fig. 5, k). Next, the count value Nn is cleared to zero and subsequently, the projection of light is repeated to increment the count value Nn and when the integrated voltage Vi has reached the reference voltage V3, the final count value Nn is retained as the number of projections Nn to thereby complete the operation.

It is preferable for the reference voltage V2 to be set at a value slightly smaller than one half of the reference voltage V3, e.g., about 0. 3 - 0.45 times the reference voltage V3. For example, where the reference voltage V2 is set to be 0.4 times the reference voltage V3, the distance measuring time as a whole required in a single current/voltage conversion circuit can be reduced by one half than otherwise because the time in which the reference 13 voltage V2 changes to the reference voltage V3 is shortened to one-sixth.

What has been described above is the operatiOn of the circuit according to the present embodiment and this operation may be represented by the flow charts shown in Fig.s 6 to 9. To begin with, the main routine of the operation will be described referring to Fig. 6.

When this main routine starts, the control circuit 80 turns ON the power source of the entire device of the instant embodiment-(#001) so as to set up each of the switches (#002). Specifically, switch 4 is turned ON towards the first current/voltage conversion circuit 20 with the remaining switches being kept OFF. Next, the content of the RAM 81 is cleared (#003), the gains is for the amplification circuits 40 and 50 then determined (#004) and the condition of the closest distance flag Fn is confirmed (#005). In this case, if the closest distance flag Fn is being set, the value X is set to 1.0 (corresponding to the closes distance) (#006) to jump to step #013. On the other hand, if the closest distance flag Fn is not set, the distance is measured by the second current/voltage conversion circuit 20 (#007), the condition of the infinite distance flag Ff is confirmed (#008) and in this case, if the infinite distance flag Ff is being set, the value X is set to 0.5 (corresponding to infinite distance) (#009) to jump to step #013.

Subsequently, the distance is measured by the second current/voltage conversion circuit 30 (#010), then the condition of the infinite distance flag Ff is confirmed (#011) and in this case, if the flag Ff is being set, the value X is set to 0.5 (corresponding to infinite distance) (#009) to jump to step #013.

A From the number of projections Nf and the number of projections Nn obtained by the operations of the sub-routines #007 and #010, the value X is calculated (#012). As a result, the distance to the subject is obtained by referring to the addresses in the ROM 82 which are readily determined from the value X (#013). Then the lens tube 84 is driven by the motor 83 to a focusing position 0014) and the power source of the device is turned OFF (1015) thereby to clear this routine.

Next, the operation in each of the sub-routines will be described. First, the subroutine for determining the gains for the later stage amplification circuits (40 and 50) will be described by referring to Fig. 7. When this sub-routine =..ces,the control circuit 80 turns ON the switch 4 toward the current/voltage conversion circuit 20 (C01), the count value Ns is cleared to zero 0#102), the switches 65 through 67 are turned ON, then after releasing the electrical charges accumulated in the capacitors 63 and 64, - the switch 67 is turned OFF (4103) and a clear signal CR is generated to clear the count value Ne to zero (#104). In this case, the count value Ne corresponds to the number of projections and a count value Ns is incremented one by one every time when either one of the switches 65 through 67 is turned ON.

Subsequently, the control circuit 80 generates a projection signal Ve to operate the projection circuit 10 to start the projection of light (#105) and after waiting for a period of time T1 (#106), the switch 7 is turned ON to wait for a period of time T2 while an integrating operation is performed (#107). During this waiting time, electrical is charges are accumulated in the capacitors 63 and 64 (;;'1108). Then the operation of the light projection circuit 10 is stopped to complete its light projecting operation, the switch 7 is turned OFF to complete the integrating operation (4109) and a count-up signal CU is generated to add 1 to the count value Ne U110). If the count value Ne is less than the predetermined value Ng, the step is jumped to #104 (f111). If the count value Nf has reached the value Ng, the switch 7 is turned OFF (#112). In this case, the integrated voltage Vi has already been outputted to the comparator 71 while the latter compares the integrated voltage Vi with the voltage V1 and outputs to the control circuit 80 the comparison result as an output voltage Vo. On the basis of this voltage Vo, the control circuit 80 compares the integrated voltage Vi with the voltage V1 0113) and if the voltage Vi is less than the voltage V1, the gain determinating operation is terminated to thereby return to the main routine.

Where the integrated voltage Vi is larger than the voltage V1, if the count value Ns is zero (t'114), the switch 46 is turned ON (14M5), if the count value Ns is 1 (f116), the switch 56 is turned ON (4117), if the count value Ns is 2 (#118), the switch 47 is turned ON 0119) and if the count value Ns is 3 (#'120), the switch 57 is turned ON (#121). In this casei every time any of the switches is turned ONj the count value Ns isincreased byl (#122) and a jump is made to #102. If the count value Ns is not any one of 0 through 3, that is, even when all the switches 46, 56, 47 and 57 are turned ON, if the output of the comparator 71 still remains at "H' level, the subject is considered to lie very close or 16 1 1 a the luminance of the subject is considered high so that the closest distance flag Fn is set 0123) to clear this subroutine to return to the main routine.

Next, the long distance measuring operation, the sub-routine for calculating the number Nf by the first current/voltage conversion circuit 20 will be described by referring to Fig. 8. When the sub-routine for distance measurement by the current/voltage conversion circuit 20 has commence!, switch 4 is turned ON toward the first current/voltage conversion circuit 20, the switch 72 is turned ON toward the reference power source 74 and the switches 65 through 67 are turned ON (#201). After releasing the electrical charges accumulated in the capacitors 63 and 64, switch 67 is turned OFF (#202) so as to clear the count value Nf corresponding to the number of light projections (#203).

Subsequently, the projection circuit 10 is operated to project light 0204) and after waiting for a period of time T1 (#205), switch 7 is turned ON to perform an integrating operation (#206) and to wait for a period of time T2 (t207). During this waiting period, electrical charges are stored in the capacitors 63 and 64. Then the operation of the projection circuit 10 is stopped to terminate its light projecting operation, the switch 7 is turned OFF to terminate the.integrating operation 0208) and the count value Nf is increased ty 101'209). In this case, the count value Nf is compared to a predetermined value Nm (#210) and if the count value Nf is larger than the predetermined value Nm, the infinite long distance flag Ff is set up (#212) to return to the main routine. On the contrary, if the count value Nf is 17 less than the predetermined value Nm, the comparator 71 compares the output integrated voltage Vi of the integration circuit 60 with the reference voltage V2 and the output voltage Vo as a result of such comparison is outputted to the control circuit 80. The control circuit 80 judges the level of the output voltage Vo (#211) and if it is found to be at 'L' level, the step is jumped to #1204. On the contrary, if it is found to be at 'H' level, the switch 72 is turned ON toward the reference power source 75 to switch the reference voltage of the comparator 71 to V3, the switches 65 and 66 are turned OFF while the switch 67 is turned ON to connect the capacitors 63 and 64 in series with each other (#1213). In this case., the integrated voltage Vi becomes twice that obtained for the capacitors 63 and 64 parallel with one another.

connected in Subsequently, the projection circuit 10 is operated to start projection (#214) and after waiting for a period of time T1 (C1215) the switch 7 is turned ON to perform an integrating operation (#216) and to wait for a period of time T2 (#217) during which electrical charges are accumulated in the capacitors 63 and 64. Then the operation of the projection circuit 10 is stopped to terminate its projection, the switch 7 is turned OFF to terminate the integrating operation (,',,218) and the count value Nf is increased by 2 (#219). The reason for the addition of 2is that due to the series-connection of the capacitors 63 and 64, the apparent capacitance of the capacitors as a whole has reduced to half so that the amount of variation of the voltage in the same integration time ' doubles. In this case, the count value Nf is compared to the predetermined value Nm (#220) and 18 k if the count value Nf is larger than the Predetermined value Nm, the infinite long distance flag Ff is set up (#212) to return to the main routine. On the contrary, if the count value Nf is less than the predetermined value Nm, the comparator 71 compares the integrated voltage Vi from the integration circuit 60 with the voltage V3 and outputs to the control circuit 80 the output voltage Vo as a comparison result. The control circuit 80 judges the level of the output vol tage Vo (#221) and i f i t i s f ound to be at L' 1 evel, the step is jumped to #'214. On the contrary, if it is found to be at 'H' level, the final count value Nf is retained as the number of projections Nf and the long distance measuring operation is terminated to return to the main routine.

Next, the short distance measuring operation, that is, the subroutine for calculating the number of projections Nn by the second current/voltage conversion circuit 30 will be described with reference to Fig. 9. -When the distance measurement subroutine by the current/voltage conversion circuit 30 commences, switch 4 is turned ON toward the second current/voltage conversion circuit 30, the switch 72 is turned ON toward the reference power source 74 and the switches 65 through 67 are turned ON (#301) to allow the electrical charges accumulated in the capacitors 63 and 64 to be discharged and thereafter the switch 67 is turned oFF (#302) to clear the count value Nn to zero.

Subsequently, the projection circuit 10 is operated to start projection (#304) and after waiting for a period of time T1 (#305), the switch 7 is turned ON to perform integration (#306) and to wait for a period of time T2 at the same time 0307) during which time electrical charges are 19 accumulated in the capacitors 63 and 64. Then the operation of the projection circuit 10 is stopped to terminate its projecting operation, the switch 7 is turned OFF to terminate integration (#308) and the count value Nn is increased by (#309). In this case, the count number Nn is compared to the predetermined number Nm (#310) and if the count number Nn is larger than the predetermined value Nm, the infinite long distance flag Ff is set up (#312) to return to the main routine. On the other hand, if the count value Nn is less than the predetermined value Nm, the comparator 71 compares the integrated voltage V! with the voltage V2 and outputs to the control circuit 80 the output voltage Vo as a comparison result. Further, on the basis of the voltage Vo,if the voltage Vo is found to be at 'L' level, the control circuit 80 judges the integrated voltage Vi is smaller than the voltage V2, the step is jumped to t304, if the voltage Vo is found to be at H' level, the control circuit 80 causes the switch 72 to turn ON toward the reference power source 75, to turn the switches 65 and 66 OFF and to turn the switch 67 ON so that the capacitors 63 and 64 are connected in series with each other again (1313). At this time, the integrated voltage Vi becomes twice that o:Ethe case for the capacitors 63 and 64 being connected parallel with one another.

Subsequently, the projection circuit 10 is operated to start projection (#314) and after waiting for a period of time T1 0315), the switch 7 is turned ON to perform integration and at the same time, to wait for a period of time T2 (#317) during which electrical charges are accumulated in the capacitors 63 and 64. Then the operation A of the projection circuit 20 is stopped to terminate its projecting operation, the switch 7 is turned OFF to terminate integration (#318) and the count value Nn is increased by 2 (#319). At this time, the count value Nn is compared with the predetermined value Nm (#320) and if the count value Nn is larger than the predetermined value Nm, the infinite long distance flag Ff is set up 0312) to thereby return to the main routine. On the other hand, when the count value Nn is less than the predetermined value Nm, the comparator 71 compares the integrated voltage Vi from the integration circuit 60 with the voltage V2 and outputs to the control circuit 80 the voltage Vo as a comparison result. Further, the control circuit 80 judges the level of the output voltage Vo 0 321) and. if it is found to beat'L' level,.the step is jumped to #314. On the other hand, if it is found to be at "H' level, the final count value Nn is retained as the number of projections Nn and the short distance measuring operation is terminated to return to the main routine. Thus, by the above- described operations, the distance to the subject is measured.

The operations of the present embodiment described above may be summarized into a single timing chart as shown in Fig. 10 wherein timings a10, blO, c10 and d10 correspond to timings a, i in Fig. 3 and timings a, b in Fig. 5, respectively. That is, the timings a10 - c10 designate gain determining operations and the timings a10 - b10 indicate a period of time until the switch 46 is turned ON. Further, the timings c10 - d-10 designate a long distance measuring operation and the timings d10 - e10 designate a short distance measuring operation.

21 As described above, in the case of the present embodiment, when the long distance measuring operation (or short distance measuring operation) is started, the capacitors 63 and 64 as integrating elements for integrating the output signal from the light receiving circuit 23 amplified by the amplification circuits 40 and 50 are first connected parallel to each other and integrate the output voltage until the integrated voltage Vi of the capacitors 63 and 64 reaches the reference voltage V2. The integrated voltage Vi at this time rises up with the inclination shown by the timings c10 - d10 (or the timings d10 - e10) in Fig.

10. This inclination (unless the distance to the subject changes) is determined by so determining the gain that when the gain determining operation is performed, the integrated voltage Vi does not exceed the reference voltage V1 during the time in which the projection of light is repeated by a predetermined number of times. Consequently, during the time in which the integrated voltage Vi reaches the reference voltage V2, the amount of variation of the integrated voltage Vi due to a single projection is controlled within a predetermined range in accordance with a predetermined gain so that during such time a predetermined degree of distance measuring accuracy is secured. Further, when the parallel connected capacitors 63 and 64 are reconnected in series with each other the terminal voltage doubles and the capacitance of the capacitors as a whole is reduced to one half so that it becomes possible thereafter to shorten the distance measuring time in which the integrated voltage Vi becomes equal to the reference voltage V3.

Further, in the above-described embodiment, two 22 capacitors 63 and 64 are used to constituting integrating elements for the integration circuit but the present invention is not limited thereto and therefore, three or more capacitors may be connected parallel or in series with each other depending on the integrated voltage of the integration circuit as has been described in the foregoing.

Further, in the above embodiment, the integration time after switching the mode of connection of the two capacitors from parallel to series is the same as that prior to the switching but if the integration time after switching is reduced to one half, a distance measuring operation may be performed in a shorter time wihtout lowering rneasuring accuracy.

Moreover, in the above embodiment, each of the switches in Fig. 1 has been described as being semiconductor switches but they made be fo by switches having mchanical contacts such as lead relays.

In the arrangenent according to the present invention, at least tw: capacitors of the integration circuit for integrating a voltage proportional to the luminance of pulsating light generated from the projection means and reflected from the subject, can be connected in parallel or in series with each other, so that the time involved in the integration by the integration circuit can be controlled. In other words, the distance measuring accuracy can be controlled. For example, if the capacitors are connected parallel with each other in the initial state of irradiation of pulsating light by the projecting means, the desired distance measuring accuracy can be secured by the composite capacitance of the capacitors and if the capacitors are connected in series with each other 23 thereafter, it is possible to reduce the composite capacitance of the capacitors, to increment the integrated voltage thereby to shorten the integrating time which results in a shortening of the distance measuring time. Consequently, the invention is advantageous in providing a quicker opportunity for taking a photograph.

1 1 i

Claims (9)

1. A distance measuring device for cameras, which comprises:

projection means for emitting radiation; means for receiving radiation reflected from an object and which converts it into an electrical signal corresponding to the reflected radiation; an integration circuit incorporating integration capacitance means for integrating the electrical signal; means for changing the capacitance value of the integration capacitance; a level discrimination circuit for judging the level of the output of the integration circuit; and is a control circuit which receives the output from the level discrimination circuit and which controls the integration capacitance charging means in response to such output.

2. A distance measuring device according to claim 1 wherein the integration capacitance comprises at least two capacitors and said means for changing the capacitance value comprises switching means for switching between parallel and series combinations of the capacitors.

3. A distance measuring circuit according to claim 1 or 2 wherein the emitted radiation is pulsating light.

4. A distance measuring circuit according to any preceding claim wherein the receiving means produces an electrical current representative of the received reflected radiation and the circuit further includes a current/voltage circuit for converting the representative current to a voltage output.

5. A distance measuring circuit according to claim 4 wherein the circuit further includes an amplification circuit for amplification of said voltage output.

6. A distance measuring circuit according to claim 5 wherein said amplification circuit is a variable gain amplification circuit the gain of which is variable under the control of said control circuit.

7. A distance measuring circuit device for cameras, which comprises:

projection means for applying pulsating light to a subject; light receiving means which receives light applied from the projection means and reflected from the subject and which outputs an electrical current corresponding to the luminance of the reflected light; a current/voltage conversion circuit for converting an output current of the light receiving means into a voltage; an amplification circuit for amplifying an output signal of the current voltage conversion circuit; an integration circuit having at least two capacitors and switching means for connecting the capacitors in series or parallel with each other and which integrates an output signal of the amplification circuit; a level discrimination circuit which generates an output when the level of an output signal of the integration circuit has reached a predetermined level; and a control circuit which receives the output from the level discrimination circuit and controls the switching means in response to such output of the level discrimination circuit.

8. A distance measuring device for cameras according to claim 7, wherein said control circuit operates such that in an initial state of amplification of the pulsating light by said projection means, it connects said capacitors parallel to each other by 1 controlling said switching means and connects said capacitors in series with each other upon reception of the output of said level discrimination circuit.

9. A distance measuring device substantially as hereinbefore described with reference to the accompanying drawings.