Distance measuring apparatus

Abstract: A distance measuring apparatus comprises light projecting means for projecting a light beam toward an object, first light receiving means for receiving the reflected light of the projected light beam from the object, second light receiving means for receiving the reflected light of the projected light beam projected from the light projecting means by glass between the distance measuring apparatus and the object, distance calculator means for evaluating the output from the first light receiving means and calculating the distance of the object, and distance information evaluator means for detecting the presence of glass from the output of the second light receiving means, and setting predetermined distance information irrespective of the result of the calculation by the distance calculator means when glass is detected.

Description: This invention relates to a distance measuring apparatus of the active type for use in an auto focus camera or the like. A distance measuring apparatus of the active type, as shown in Figure 7 of the accompanying drawings, usually has a light projection lens 102 and a light receiving lens 103 fixed to a camera body 101, and light projected from a light projection element 104 through the light projection lens 102 is reflected by through the light projection lens 102 is reflected by an object and is imaged on a light receiving element 105 through the light receiving lens 103. The imaged position on the light receiving element 105 changes in conformity with the distance of the object and therefore, the apparatus is designed such that the light receiving position is detected by a semiconductor position detector (hereinafter referred to as the PSD) and the distance is calculated. In the above-described example of the prior art, however, where glass 106 is in front of the camera body 101, as shown in Figure 8 of the accompagnying drawings, most of the light projected from the light projection element 104 through the light projection lens 102 is transmitted through the glass 106, but light slightly diffused and reflected between the front surface (or the back surface) of the glass 106 and the camera body 101 generally irradiates the light receiving element (PSD) 105 through the light receiving lens 103. Accordingly, when an attempt is made to photograph a distant view from an observation room in a multistory building or a tower through window glass, since the object is a distant view, principal rays transmitted through the glass 106 are not reflected back, while diffused and reflected light generally irradiates the light receiving element 105 and therefore, for example, a medium distance of 1 m to 2 m is measured, and this has led to the disadvantage that an out-of-focus photograph results. This problem becomes particularly remarkable due to the shortened distance between the light projection lens and the light receiving lens resulting from the downsizing of the camera and has therefore formed a bottleneck in the downsizing of the camera. Also, some of distance measuring apparatuses of the active type are provided with a plurality of distance measuring fields of view. In a distance measuring apparatus having a plurality of distance measuring fields of view, as shown in Figure 17 of the accompanying drawings, light projected from a plurality of light projection elements 1, 2 and 3 is projected onto objects 5, 6 and 7 through a light projection lens 4. The light reflected by the objects 5, 6 and 7 is imaged on a plurality of two-division silicon photocells (SPCs) 9, 10 and 11 through a light receiving lens 8. The reference numeral 12 designates a camera body including the distance measuring apparatus. The two-division SPCs 9, 10 and 11, as shown in Figure 18A of the accompanying drawings, are comprised of SPCs 9F, 10F, 11F close to the light projection elements and SPCs 9N, 10N, 11F on the opposite side. The projected lights on the two-division SPCs when the object distances are 6 m, 1.2 m and 0.6 m are imaged as shown by 9B, 10B, 11B in Figure 18B, 9C, 10C, 11C in Figure 18C and 9D, 10D, 11D in Figure 18D, respectively. The distances of the objects 5, 6 and 7 are found by calculating the ratio of quantity of light on 9F and 9N, the ratio of quantity of light on 10F and 10N and the ratio of quantity of light on 11F and 11N. In the above-described example of the prior art, however, when an attempt is made to photograph a distant view through the window glass of an observation room in a multistory building or a tower or through a train window, as shown in Figure 19 of the accompanying drawings, most of light projected from the light projection element 2 through the light projection lens 4 is transmitted through glass 100, but light slightly diffused and reflected between the front surface (or the back surface) of the glass 100 and the camera body 12 generally irradiates the light receiving elements 9, 10 and 11 through the light receiving lens 8 and, therefore, the result of the distance measurement from the output of the light receiving element 10 corresponding to the light projection element 2 is a medium distance of e.g. 1 to 2 m, and this has led to the disadvantage that an out-of-focus photograph results. Also, if a medium distance is measured in any of the plurality of fields of view, an out-of-focus photograph will result, and this has also posed a problem in effecting the enhanced specification of a camera, i.e., a plurality of distance measuring fields of view. In particular, document US-A-4 767 934, discloses an active ranging system, in particular, a distance measuring apparatus comprising a radiation transmitter such as a light emitting diode projecting energy such as infrared energy along an axis to a surface whose position is to be measured. The light reflected from the surface, being illuminated with a spot of light, is incident on energy responsive detectors mounted nearby or around the axis or to an elongated sensor mounted along the axis. The return energy forms a spot or band of light on the detectors which is a first position when the surface is at its far extreme position, at a second position when the surface is at its near extreme position, and at a third intermediate position when the surface is at positions between the far and near extremes. By determining the position of the return spot of band of light, an indication of the range to the remote surface is obtained. Furthermore, from document EP-A-0 291 312, a distance measurement apparatus is known, comprising a plurality of light-emitting elements arranged at different positions in a direction perpendicular to a base line and an optical axis of projected light, and a light-receiving element (i.e. a position sensitive detector) for receiving light emitted from said light-emitting elements and reflected by an object so as to output an electric signal corresponding to a distance of the object. Additionally, this apparatus includes a drive means for causing the light-emitting elements to selectively emit near-distance measurement light and far-distance measurement light having a higher intensity than that of the near-distance measurement light, and arithmetic means for calculating the distance of the object based on the electric signal from the light-receiving element. Moreover, control means are provided for, when an amount of light reflected by an object cannot reach a predetermined value necessary for distance measurement upon emission of a light-emitting element selected by the drive means, controlling an operation of the drive means so as to cause another light-emitting element to emit light. It is the object of the present invention to solve the aforementioned problems peculiar to the prior art apparatuses and to provide an improved distance measuring apparatus which, without making a camera bulky, can appropriately automatically distance measure objects in short distance photographing and long distance photographing through glass or other light transmitting substances. According to the present invention, this object is accomplished by a distance measuring apparatus as defined in claims 1 and 8. Advantageous further developments of the present invention are characterized in the accompanying dependent claims. Other objects, features and advantages of the present invention will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings, of which: Figure 1 is a block diagram of a camera comprising a distance measuring apparatus according to a first embodiment of the present invention. Figure 2 is a circuit diagram of an embodiment of the output discriminator means of Figure 1. Figure 3 is a flow chart showing the operation of the camera of Figure 1. Figure 4 is a block diagram of output level discriminator means in a second embodiment of the present invention. Figures 5A to 5E show the imaging reflected light onto a light receiving element by the object distance. Figure 6 is a flow chart showing the operation of the second embodiment. Figure 7 shows the prior art construction of the light projection and receiving optical system of a distance measuring apparatus in a camera. Figure 8 shows the optical path of reflected light when photographing through glass is effected. Figure 9 is a block diagram of a distance measuring apparatus according to a third embodiment of the present invention. Figure 10 is a circuit diagram of the driver means of Figure 9. Figure 11 is a circuit diagram of the switch means of Figure 9. Figure 12 is a block diagram of the distance calculator means of Figure 9. Figure 13 is a circuit diagram of the output level discriminator means of Figure 12. Figure 14 is a circuit diagram of the integration level discriminator means of Figure 12. Figure 15 is a circuit diagram of the projector/receiver combination selector of Figure 9. Figure 16 is a flow chart showing the operation of a fourth embodiment of the present invention. Figure 17 shows the optical path of a prior art distance measuring apparatus having a plurality of distance measuring fields of view. Figures 18A to 18D show projected images on light receiving elements in a plurality of distance measuring fields of view according to the prior art. Figure 19 shows reflected light through glass during central light projection of the prior art. Figure 20 shows reflected light through glass during right-hand side light projection. First Embodiment Figure 1 shows a first embodiment of the distance measuring apparatus of the present invention. In Figure 1, members designated by the reference numerals 1 to 6 are the same as those in the example of the prior art shown in Figures 7 and 8 and therefore need not be described. The reference numeral 107 denotes a light receiving element for glass detection for receiving light from outside the normal distance measuring range diffused and reflected by glass and a camera body, the reference numeral 108 designates output discriminator means for discriminating the presence or absence of the output of the light receiving element for glass detection, the reference numeral 109 denotes distance calculator means of the conventional double integration type proposed by the applicant, and the reference numeral 110 designates distance determination means which receives the outputs of the output discriminator means 108 and the distance calculator means 109 as inputs. Referring now to Figure 2 which shows an embodiment of the output discriminator means 108, the reference numeral 111 denotes an operational amplifier, and the reference numeral 112 designates a resistor which converts the photocurrent by the reflected light received by the light receiving element 107 for glass detection into a voltage. The reference numeral 113 denotes a comparator, and the reference numerals 114 and 115 designate resistors. The output of the comparator 113 assumes H level when the output of the operational amplifier 111 drops below a voltage obtained by a reference voltage V REF being divided by the resistors 114 and 115. The reference numeral 116 denotes an SR type flip-flop adapted to be reset by a power up clear signal PUC from a power source ON detecting circuit, not shown, and to be set by the output of the comparator 113 and put out a discrimination output Q OUT . The operation of the above-described construction will now be described with reference to the flow chart of Figure 3. At #1, the power up clear signal PUC during the closing of a power source switch is output, and the discrimination output Q OUT of the flip-flop 116 assumes L level (#2). At #3, light projection by the light projection element 104 is started. (i) The Case of an Ordinary Object Reflected light from an object is imaged on the light receiving element 105, but is not received by the light receiving element 107 and therefore, the output voltage of the operational amplifier 111 is at the same potential as the reference voltage V REF' and the output of the comparator 113 remains at L level and the discrimination output Q OUT of the flip-flop 116 also remains at L level (#4). Accordingly, the distance determination means 110 determines the distance from the output of the distance calculator means 109 (#5). (ii) The Case of a Distant View through Window Glass Since light diffused and reflected by the glass 106 and the camera body 101 enters the light receiving element 107, the output voltage of the operational amplifier 111 drops from the reference voltage V REF by the voltage drop in the resistor 112 and becomes equal to or less than the divided voltage value by the resistors 114 and 115, and the output of the comparator 113 assumes H level and therefore, the discrimination output Q OUT of the flip-flop 116 assumes H level (#4). Accordingly, the distance determination means 110, irrespective of the output of the distance calculator means 109, determines a distance suitable for long distance photographing, such as infinity distance or the over focus distance of a photo-taking lens. While the output discriminator means 108 of the above-described embodiment directly discriminates the sensor output by the comparator 113, most of the projected light beam from the light projection element 104 is transmitted through the glass 106 and the quantity of light diffused and reflected by the surface of the glass 106 and received by the light receiving element 107 for glass detection is small and therefore, when the erroneous discrimination by noise or the like is taken into account, it is preferable to discriminate the sensor output after being integrated. Also, the input to the distance calculator means 109 may be changed over, whereby the outputs of the light receiving element 105 for ordinary distance measurement and the light receiving element 107 for glass detection may be time-divisionally input to the distance calculator means 109, and the distance calculator means 109 may be used also as the output discriminator means. While in the above-described embodiment, the light receiving element 107 for glass detection is disposed usually on the far distance side of the light receiving element 105 for distance measurement, the light receiving element 107 for glass detection may be disposed on the for distance side of the light receiving element 105 for distance measurement because the diffused and reflected light enters the latter. The light receiving element 107 for glass detection need not be arranged in the direction of the base line length. As described above, according to the present embodiment, the presence or absence of the output of the light receiving element 107 for glass detection which receives the light from outside the distance measuring range diffused and reflected by the glass 106 and the camera body 101 is discriminated and when the output is present, a predetermined distance is set, whereby it becomes possible to photograph a distant view from an observation room in a multistory building or a tower or from a train window through glass without affecting the ordinary distance measuring range. Second Embodiment In the first embodiment, provision is made of a light receiving element 107 exclusively for receiving diffused and reflected light from glass and right distance measurement is made possible even through glass. In a second embodiment which will hereinafter be described, the light receiving element 107 for glass detection is used also as a light receiving element for distance detection, whereby the photographing of any object at an extremely close distance which has heretofore been difficult is made possible. The basic construction of the distance measuring apparatus according to the second embodiment is similar to that of the first embodiment (Figure 1), but in the second embodiment, the light receiving element 107 for glass detection is used also as an element for extremely close distance measurement and the output level discriminator means 108 evaluates the output level of the light receiving element in three stages. Figure 4 is a circuit diagram of the output level discriminator means 108 in the second embodiment. The reference numeral 111 designates an operational amplifier, and the reference numeral 112 denotes a resistor which converts the photocurrent received by the light receiving element 107 into a voltage. The reference numeral 117 and 118 designate comparators, and the reference numerals 119, 120 and 121 denote resistors. A value obtained by dividing the reference voltage V REF by the resistors 119, 120 and 121 and the output voltage of the operational amplifier 111 are compared with each other. The reference numerals 122 and 123 designate SR type flip-flops adapted to be reset by the power up clear signal PUC from a power source ON detecting circuit, not shown, and to be set by the H level outputs of the comparators 117 and 118, respectively, and put out a glass detection output G OUT and an extremely close distance detection output N OUT . Figure 5 shows the images 20A, 20B, 20C, 20D and 20E of the light projection element 104 formed on the light receiving element 105 and the light receiving element 107 when the object distance is 6.0 m (Figure 5A), 1.2 m (Figure 5B), 0.6 m (Figure 5C), 0.4 m (Figure 5D) and 0.2 m (Figure 5E). As the distance becomes shorter from Figure 5A to Figure 5E, the center of the image of the light projection element 104 moves and the image which is in focus at 1.2 m becomes blurred and larger. Here, the ordinary distance measuring range is 6.0 m - 0.6 m, the image is almost in the light receiving element 105, and the variation in the output for the variation in the distance has linearity. In the case of 0.4 m shown in Figure 5D, the image 20D is astride the light receiving element 105 and the light receiving element 107 and the center thereof deviates from the light receiving element 105 and therefore, the variation in the output for the variation in the distance has no linearity. Also, the rate of the image on the light receiving element 107 is small, but the light receiving power of this element is great because the distance thereof is short. In the case of 0.2 m shown in Figure 5E, the image 20E is not on the light receiving element 105 and the blur of the image is great and therefore, about 1/4 to 1/5 of the image 20E is formed on the light receiving element 107 and the light receiving power of this element is great. The operation of the above-described construction will now be described with reference to the flow chart of Figure 6. When at #1, the power up clear signal PUC during the closing of the power source switch is output, the flip-flops 122 and 123 reset, and the outputs G OUT and N OUT assume L level (#2). At #3, the light projection by the light projection element 104 is started. (i) When the object is in the ordinary distance measuring range (6 m - 0.6 m) The light reception outputs by the projected light images 20A, 20B and 20C formed on the light receiving element 105 as shown in Figures 5A, 5B and 5C are calculated by the distance calculator means 109 and are input as distance information to the distance determination means 110. Since the projected light images 20A, 20B and 20C are not formed on the light receiving element 107, the output of the operational amplifier 111 of the output level discriminator means 108 assumes the same voltage as the reference voltage V REF and the outputs of the comparators 117 and 118 remain at L level. Since the outputs G OUT and N OUT are also at L level, the distance determination means 110 determines the distance by the output of the distance calculator means 109 as shown at #6 via #4 and #5. (ii) When the object is at an extremely close distance (0.4 m - 0.2 m) When as shown in Figure 5D, a part of the projected light image 20D is on the light receiving element 105, the distance information calculated by the distance calculator means 109 is a distance shorter than 0.6 m but longer than 0.4 m. The movement of the center of gravity on the light receiving element 105 is small relative to the movement of the center of gravity of the image. Also, when as shown in Figure 5E, the projected light image 20E is not on the light receiving element 105, there is no signal entering the distance calculator means 109 and therefore, if only the output of the light receiving element 105 is evaluated, the distance information of infinity is put out. On the other hand, in both of the case of Figure 5D and the case of Figure 5E, a part of the projected light image 20D or 20E is on the light receiving element 107 and the distance is short and therefore, the electric current output from the light receiving element 107 is great and the output voltage of the operational amplifier 111 becomes a voltage low enough to render the output of the comparator 118 into H level, and the flip-flop 123 is set and the extremely close distance detection output N OUT also assumes H level and therefore, as shown at #7, irrespective of the output of the distance calculator means 109, it is determined that the object is at an extremely close distance. (iii) When the object is a distant view through glass In this case, the light diffused and reflected by the glass 106 and the camera body 101 generally irradiates the light receiving elements 105 and 107. Accordingly, the center of the light entering the light receiving element 105 is substantially the center of the light receiving element 105 and thus, the distance information calculated by the distance calculator means 109 is a distance of about 1.2 m. Also, most of the light projected from the light projection element 104 is transmitted through the glass 106 and part of the light reflected irradiates the light receiving element 107, and since the light receiving power of the light receiving element 107 is small, the output voltage of the operational amplifier 111 becomes a voltage which renders the output of the comparator 117 into H level but keeps the output of the comparator 118 at L level, and only the flip-flop 122 is set and only the glass detection output G OUT assumes H level and therefore, through #4 and #5, as shown at #8, the distance determination means 110 determines a distance for long distance photographing such as infinity distance or the over focus distance of the photo-taking lens, irrespective of the output of the distance calculator means 109. In the above-described embodiment, glass detection and extremely close distance detection are effected by two comparators 117 and 118, but as compared with the light reception output at the extremely close distance, in glass detection, most of the light is transmitted through the glass 106 and only a slight quantity of reflected light can be received and therefore, it is more preferable that only the extremely close distance be directly detected by the comparator and glass detection be effected by being integrated. The input to the distance calculator means 109 may be changed over, whereby the outputs of the light receiving element 105 for distance measurement and the light receiving element 107 for glass detection may usually be time-divisionally input to the distance calculator means, and the distance calculator means 109 may be used also as the output level discriminator means. As described above, according to the distance measuring apparatus of the present embodiment, the light receiving element 107 for glass detection is used also as the light receiving element for extremely close distance detection, and the extremely close distance and glass 106 are distinguished from each other by the magnitude of the light reception output level, whereby long distance photographing through glass becomes possible almost without an increase in cost. Third Embodiment A third embodiment is an application of the present invention to a distance measuring apparatus provided with a plurality of distance measuring fields of view. Figure 9 is a diagram which shows the features of the third embodiment of the present invention best. In Figure 9, the reference numerals 1, 2 and 3 designates light emitting elements such as infrared light emitting diodes, the reference numerals 9, 10 and 11 denote light receiving elements such as two-division SPCs, the reference numerals 13, 14 and 15 designate driver means controlled by control signals T1 and T2 from distance measuring operation controller means 22 which will be described later to cause the light emitting elements 1, 2 and 3 to emit light, the reference numerals 16, 17 and 18 denote switch means controlled by control signals R1, R2 and R3 from the distance measuring operation controller means 22 to change over the light reception outputs of the light receiving elements 9, 10 and 11, the reference numeral 19 designates distance calculator means which outputs distance information such as light reception output magnitude distance signals, the reference numeral 20 denotes a projector/receiver combination selector which determines the combination of the light projection elements and light receiving elements in accordance with a distance measuring operation sequence and outputs the control signals T1, T2, T3 and R1, R2, R3, the reference numeral 21 designates distance information evaluator means which evaluates the distance information from the distance calculator means 19 in accordance with the distance measuring operation sequence and outputs the result of distance measurement, and the reference numeral 22 denotes distance measuring operation controller means which includes the projector/receiver combination selector means 20 and the distance information evaluator means 21 and controls the distance measuring operation sequence. Figure 10 is a circuit diagram of the driver means 13 of Figure 9. In Figure 10, the reference numeral 23 designates a resistor for limiting the electric current, the reference numeral 24 denotes a transistor for driving the light emitting element 1, the reference numeral 25 designates a resistor for limiting the electric current, and the reference numeral 26 denotes an AND gate which receives as inputs the control signal T1 and a light emission timing signal IRON from a timing circuit, not shown, in the distance measuring operation controller means 22. When the control signal T1 is at H level, the light emitting element 1 is caused to emit light by the transistor 24 in accordance with the light emission timing signal IRON. Figure 11 is a circuit diagram of the switch means 16 of Figure 9. In Figure 11, the reference numeral 27 designates an inverter which receives the control signal R1 as an input, and the reference characters ASW1, ASW2, ASW3 and ASW4 denote analog switches. When the control signal R1 is at H level, the output of the inverter 27 assumes L level and the analog switches ASW1 and ASW2 are ON and the analog switches ASW3 and ASW4 are OFF and therefore, the outputs 9F and 9N of the light receiving element 9 are connected to the distance calculator means 19, and when the control signal R1 is at L level, the output of the inverter 27 assumes H level and the analog switches ASW1 and ASW2 are OFF and the analog switches ASW3 and ASW4 are ON and therefore, the outputs 9F and 9N of the light receiving element 9 are connected to the reference voltage V REF . Figure 12 is a block diagram of the distance calculator means 19 of Figure 9. In Figure 12, the reference numeral 28 designates single/sum changeover means for changing over one or the sum of sensor outputs from the switch means 16, 17 and 18, the reference numeral 29 denotes current/voltage converter means for converting the output current of the single/ sum changeover means 28 into a voltage, the reference numeral 30 designates an alternating current amplifier for DC-cutting the output of the current/voltage converter means 29 and amplifying the alternating current signal component by the turn-on-and-off of the light emitting elements 1, 2 and 3, the reference numeral 31 denotes a reverse amplifier for reversing the output of the alternating current amplifier 30, the reference numeral 32 designates synchronized integrator means for selectively integrating the output of the alternating current amplifier 30 or the reverse amplifier 31 in synchronism with the turn-on-and-off of the light emitting elements 1, 2 and 3, the reference numeral 33 denotes output level discriminator means for comparing the amplitude of the alternating current amplifier 30 with a predetermined level and outputting it to the distance information evaluator means 21, and the reference numeral 34 designates integration level discriminator means for comparing the amount of integration by the synchronized integrator means 32 with a predetermined level and outputting it to the distance information evaluator means 21. The distance measuring operation by the single/sum changeover means 28, the current/voltage converter means 29, the alternating current amplifier 30, the reverse amplifier 31 and the synchronized integrator means 32 is similar to the one by the known double integration method disclosed in applicant's Japanese Laid-Open Patent Application No. 19116/1985. Figure 13 is a circuit diagram of the output level discriminator means 33 of Figure 12. In Figure 13, the reference numerals 35 and 36 denote resistors for dividing the reference voltage V REF , and the reference numeral 37 designates a comparator for comparing the value divided by the resistors 35 and 36 with the output of the alternating current amplifier 30 and outputting it to the distance information evaluator means 21. When the light reception output is great, the output of the comparator assumes H level and decreases the gain of the alternating current amplifier 30 as required. Figure 14 is a circuit diagram of the integration level discriminator means 34 of Figure 12. In Figure 14, the reference numerals 38 and 39 denote resistors for dividing the reference voltage V REF , the reference numeral 40 designates a comparator for comparing the output of the synchronized integrator means 32 with the reference voltage V REF and outputting it to the distance information evaluator means 21, and the reference numeral 41 denotes a comparator for comparing the output of the synchronized integrator means 32 with the value divided by the resistors 38 and 39 and outputting it to the distance information evaluator means 21. When the output of the comparator 41 is at L level after the synchronized integrator means 32 has integrated one light reception output for a predetermined time, the light reception output is small and therefore, the distance information evaluator means 21 judges that the light reception output is null, and when the output of the comparator 41 is at H level, the synchronized integrator means 32 reversely integrates the both light reception outputs and when the result becomes equal to or greater than the reference voltage V REF , the output of the comparator 40 changes from H level to L level, and by the time required therefor, the distance information evaluator means 21 calculates the distance. Figure 15 is a circuit diagram of the projector/receiver combination selector means 20 of Figure 9. In Figure 15, the reference numerals 42 and 43 designate OR gates which output T1 and R1 to select the combination of the light projection element 1 and the light receiving element 9 by STEP1 signal from the timing circuit, not shown, of the distance measuring operation controller means 22, output T2 and R2 to select the combination of the light projection element 2 and the light receiving element 10 by STEP2 signal through the OR gate 42, output T3 and R3 to select the combination of the light projection element 3 and the light receiving element 11 by STEP3 signal through the OR gate 43, and output T2 and R3 to select the combination of the light projection element 2 and the light receiving element 11 by STEP4 signal through the OR gates 42 and 43. In the above-described construction, under the control of the distance measuring operation controller means 22, distance information for an object in the ordinary distance measuring range is obtained at STEP1, STEP2 and STEP3. At STEP4, the combination is the combination of the light projection element 2 and the light receiving element 11 and therefore, for an object in the ordinary distance measuring range, the projected light image is not incident on the light receiving element 11 as shown in Figures 18B, 18C and 18D and thus, the outputs of the comparators 37 and 41 are at L level, but in the case of a distant view through glass, as shown in Figure 19, slightly diffused and reflected light generally irradiates the light receiving element 11 and the light receiving power is small and therefore, the output of the comparator 37 is at L level, but the output provided by the synchronized integrator means 32 having integrated one light reception output for a predetermined time becomes an amount of integration sufficient to render the output of the comparator 41 into H level. Accordingly, the distance information evaluator means 21 can detect the situation for photographing a distant view through glass, by evaluating the output of the comparator 41 when at STEP4, a combination differing from the combination of the light projection and light receiving elements for the ordinary distance measuring field of view is selected, and in this case, a distance suitable for long distance photographing is selected irrespective of the result of distance measurement by a regular combination of the light projection and light receiving elements. In the above-described embodiment, the light reception output by the combination of the light projection element 2 and the light receiving element 11 has been evaluated, but as can be seen from Figure 19, the light reception output by the combination of the light projection element 2 and the light receiving element 9 may be evaluated, or as shown in Figure 20, any combination differing from the regular combination, such as the combination of the light projection element 1 and the light receiving element 10 or 11 will do. In the above-described embodiment, the evaluation of the light reception output is effected by the output of the comparator 41 of the integration level discriminator means 34, but as can be seen from Figure 19, the light receiving element 11 is generally irradiated and therefore, if distance calculation is effected, a distance output similar to that when the projected light image is formed substantially at the center of the light receiving element 11 (Figure 18C) is calculated and therefore, by the measured distance being not a long distance, a distance through glass may be detected. As described above, according to the present embodiment, a combination differing from the combination of the light projection and light receiving elements for the ordinary distance measuring field of view is selected, and the light reception output thereof is evaluated by the integrated level or the result of distance calculation, whereby the photographing situation through glass can be detected easily and thus, it becomes possible to automatically select a distance suitable for long distance photographing. Fourth Embodiment The distance measuring apparatus according to the above-described third embodiment which has the through-glass photographing detecting function is designed to select a distance suitable for long distance photographing independently of the light reception output by the original combination when there is the light reception output by a combination of the light projection and light receiving elements for detecting the light outside the distance measuring range which differs from the original combination of the light projection and light receiving elements for distance measurement. In the above-described construction, however, when an attempt is made to photograph exhibits or the like through a show window (glass window), if there is the output of the light receiving element for glass detection, the distance for long distance photographing will be unconditionally selected and therefore, the photograph of an exhibit lying at a distance of 1 to 2 m will be out of focus. A fourth embodiment of the present invention which will hereinafter be described is a distance measuring apparatus in which the output of a combination of light projection and light receiving elements differing from the original combination of light projection and light receiving elements for distance measurement is evaluated and the distance for through-glass photographing is selected and wherein when the light receiving power by the original combination of light projection and light receiving elements for distance measurement is great, provision is made of distance information evaluator means 21 for selecting the original measured distance, whereby the photographing of an exhibit or the like through glass is made possible. The basic construction of the fourth embodiment is similar to that of the third embodiment (Figures 9 to 15) and therefore need not be described in detail. As already described, when at the STEP1, STEP2 and STEP3 of Figure 15, the output of the comparator 37 of the output level discriminator means 33 assumes H level, it shows that the light receiving power is great and the object is within 2 m to 3 m in the regular distance measuring field of view and therefore, the distance information evaluator means 21 memorizes a signal L OUT . Also, when at the STEP4, the output of the comparator 37 of the output level discriminator means 33 assumes H level, it shows that the object distance is an extremely close distance and therefore, the distance information evaluator means 21 memorizes a signal N OUT . When at the STEP 4, the output of the comparator 37 of the output level discriminator means 33 assumes L level and the output of the comparator 41 of the integration level discriminator means 34 assumes H level, it shows that slight reflected light from the glass enters and therefore, the distance information evaluator means 21 memorizes a signal G OUT . On the basis of these signals, the operation will hereinafter be described with reference to a flow chart shown in Figure 16. (i) The Case of an Ordinary Object For an ordinary object, light reception at the STEP 4 does not take place and therefore, neither of the signals N OUT and G OUT is memorized and therefore, advance is made to #4, where the object distance is determined on the basis of the measured distance in the normal distance measuring field of view. (ii) The case of an Extremely Close Object Since at the STEP 4, a projected light image is formed on the light receiving element 11, the light receiving power is great and the output of the comparator 37 assumes H level and the signal N OUT is memorized and therefore, advance is made from #1 to #5, where an extremely close distance is selected irrespective of the measured distance in the normal distance measuring field of view, and close distance alarm, release lock, etc. are effected. (iii) The Case of a Distant View through Glass At STEP 1, STEP 2 and STEP 3, a medium distance is measured by the slight reflected light by glass 100, but the light receiving power is small and therefore, the signal L OUT is not memorized, and also at STEP 4, the output of the comparator 37 is at L level and the signal N OUT is not memorized, but yet the output of the comparator 41 assumes H level and the signal G OUT is memorized and therefore, advance is made from #1, #2 and #3 to #6, where a distance suitable for long distance photographing is selected irrespective of the measured distance in the normal distance measuring field of view. (iv) The case of an Exhibit through Glass (Close Distance) At STEP 1, STEP 2 and STEP 3, most light transmitted through the glass 100 is reflected from the object and is again transmitted through the glass 100 and is imaged on the light receiving element and therefore, the light receiving power is great and the signal L OUT is memorized. At STEP 4, the signal N OUT is not memorized and the signal G OUT is memorized and therefore, advance is made from #1 and #2 to #4, where the object distance is determined on the basis of the measured distance in the normal distance measuring field of view. The calculation of the measured distance at this time is affected by the slight reflected light from the glass, but the light receiving power differs greatly and therefore, the difference can be neglected. As described above, according to the present embodiment, when the light receiving power by the original combination of light projection and light receiving elements for distance measurement is great, the distance for long distance photographing is not selected, but the measured distance is selected and therefore, even in the photographing of exhibits or the like through glass, in-focus photographing is made possible without any increase in cost.

Claims: A distance measuring apparatus comprising: light projecting means (1 to 3; 104) for projecting at least one light beam onto an object; light receiving means (9 to 11; 105, 107) for receiving reflected light from the object by said light projection, said light receiving means having at least first (105) and second (107) photosensitive distinct ranges; and a processing circuit (22) having first processing mode means in the form of distance calculator means (19; 109) for calculating the distance of the object from a signal based on reflected light received in the first range of said light receiving means; characterized in that the processing circuit further comprises second processing mode means (20, 21; 108, 110) for setting a predetermined distance information when said second processing mode means judges in response to the signal from the light receiving means associated with the second range that the light projection has been effected through a light-transmitting member (100; 106) positioned between the apparatus and the object. A distance measuring apparatus according to claim 1, characterized in that said predetermined distance information is long distance information. A distance measuring apparatus according to claim 1, characterized in that long distance information is set as distance information when said second processing mode means (20, 21; 108, 110) judges hat the light projection has been effected through a light-transmitting member (106; 100). A distance measuring apparatus according to claim 1, 2 or 3, characterized in that said at least first (105) and second (107) photosensitive distinct ranges are disposed at locations spaced apart from each other. A distance measuring apparatus according to claim 4, characterized in that said second photosensitive distinct range (107) serves also for detecting an object at an extremely close distance. A distance measuring apparatus according to claim 5, characterized in that said processing circuit (22) judges the light receiving states of said at least first (105) and second (107) photosensitive distinct ranges, and when said second photosensitive distinct range (107) mainly receives the reflected light, judges that the object is at an extremely close distance. A distance measuring apparatus according to any of the preceding claims 1 to 6, characterized in that even when it has been judged that the light projection has been effected through a light-transmitting member (106; 100) from the output of said second photosensitive distinct range (107), said processing circuit (22) determined distance information on the basis of the result of the calculation by said distance calculator means (19; 109) determined from the output of said first photosensitive distinct range (105) if the quantity of the light received by said first photosensitive distinct range (105) exceeds a predetermined value. A distance measuring apparatus comprising: light projecting means (1 to 3) for projecting a light beam onto different areas of a scene; a plurality of light receiving means (9 to 11) for receiving light reflected from an object illuminated by the light beam projected onto each of said different areas; and a processing circuit (22) for combining the light reflected from the object illuminated by the light beam projected onto each of said areas and said light receiving means (9 to 11) so as to correspond to each other by a predetermined combination, and finding the distance of the object in each of said different areas by means of the output of each of said light receiving means (9 to 11) in said predetermined combination, characterized in that the processing circuit (22) further comprises selector means for combining the light reflected from the object illuminated by the light beam projected onto each of said areas and said light receiving means corresponding to each other by a combination other than said predetermined combination, and judging means for judging whether the light projection has been effected through a light transmitting member (100; 106), by means of the outputs of said light receiving means (9 to 11) in said combination other than said predetermined combination, wherein said judging means judges that said light projection has been effected through the light transmitting member (100; 106) in response to an output of a predetermined light receiving means (9 to 11) in said combination other than said predetermined combination. A distance measuring apparatus according to claim 8, characterized in that said processing circuit selects a predetermined distance when said judging means judges that the light projection has been effected through the light transmitting member (100; 106). A distance measuring apparatus according to claim 9, characterized in that said predetermined distance is a long distance. A distance measuring apparatus according to claim 8, characterized in that said judging means judges that the light projection has been effected through the light transmitting member (100; 106) when the amount of integrated output of said predetermined light receiving means (9 to 11) is larger than a predetermined value and the output of said predetermined light receiving means is smaller than a predetermined value. A distance measuring apparatus according to claim 11, characterized in that the distance of the object is closer than said predetermined distance when the output of said predetermined light receiving means (9 to 11) is larger than the predetermined value.

Inventors: MAEDA KAZUYUKI, TAKA HIDEO, MAEDA, KAZUYUKI, TAKA, HIDEO, Maeda, Kazuyuki, c/o Canon Kabushiki Kaisha, Taka, Hideo, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G03B13
IPC codes: G02B7