US 4,162,839 AGrant
Dual Preference Camera for Digitally Displaying Preset and Computered Valves
Issue Date:1979-07-31
•5 Claims
•5 Drawing Sheets
Abstract
In the camera disclosed, depending upon whether the shutter preference or aperture preference mode is selected, a computer establishes a computed value on the basis of a preset value and other ambient conditions. A number of separate comparators compare the respective values to a single reference wave form and turn off respective gates when the analog voltages achieve predetermined relationships to the reference wave form. The gates passed pulses from a common source from the beginning of the reference wave form until the respective gates are shut off. The values are thus digitized and displayed within the camera.
Metadata
Assignee
- Canon Kabushiki Kaisha
Inventors
- Yukio Mashimo
- Nobuaki Sakurada
- Tadashi Ito
- Fumio Ito
- Nobuhiko Shinoda
- Hiroyashu Murakami
Application Information
Application Number:US 7967160
Filing Date:1977-05-13
Priority Date:1974-08-30
Art Unit:236
Classifications
IPC:
G03B 708
Field of Search:
340354347 AD;347 NT;347 M23 D;24;38;60;60 A;37
Patent Drawings (5 sheets)
Description
Background of the Invention
1. Field of the Invention
The present invention relates to an analog-digital converting device for converting analog quantities into digital quantities, especially to an analog digital converting device for converting many analog inputs into digital quantities at one time.
2. Description of the Prior Art
In known A-D converters which convert analog quantities into digital quantities, a comparator receives each analog voltage along with reference signals from separate reference generating means and compares the analog quantities to the reference values while separate pulse generators pass pulse signals through separate gates. When the reference values equal the analog values the comparators turn off the gates. The analog quantities are then represented by the number of pulses passing through the gates.
In order to convert a number of analog quantities into digital quantities by means of such devices, the number of reference signal sources as well as pulse sources must correspond with the number of analog quantities to be converted. It is also essential that the characteristics of the reference signal sources be identical, and that the pulse sources be identical. This results in space consuming and expensive converters.
This creates a particular problem in cameras attempting to utilize such systems, because the amount of space in a camera is usually limited to keep its size and weight at a minimum.
Summary of the Present Invention
The purpose of the present invention is to offer an A-D converting device for multi-input.
Another purpose of the present invention is to offer an A-D converting device which converts the analog quantities of multi-input into digital quantities by means of a single reference signal generating means.
Further, another purpose of the present invention is to offer an A-D converting device for multi-input so designed that the analog quantities to be converted are respectively put in the one input terminal of the correspnding one of a plural number of the comparison circuits while the reference signal generating means are respectively connected with other corresponding input terminal.
Further, another purose of the present invention is to offer an A-D converting device for a camera composed of either one of the above mentioned A-D converting device, for converting a plural number of the analog quantities representing exposure factors such as the measured light amount, the film sensitivity information and so on into digital quantities at one time.
Further other purposes of the present invention will be disclosed from the following explanation to be made in accordance with the accompanying drawings.
Brief Description of the Drawings
FIG. 1 shows a circuit diagram of an embodiment of an analog-digital converting system which converts a plural number of the analog quantities into digital quantities at one time, making use of conventional A-D converters.
FIG. 2 shows a circuit system diagram for showing the basic composition of the A--A converter in accordance with the present invention.
FIG. 3 shows a diagram for explaining the operation of the device shown in FIG. 2.
FIG. 4(a) shows a circuit diagram of an embodiment of the reference signal generating means in the A-D converter in accordance with the present invention.
FIG. 4(b) shows a diagram of the output characteristics of the reference signal generating means shown in FIG. 4(a).
FIG. 5 shows a circuit diagram of an embodiment of the control signal generating circuit shown in FIG. 2.
FIG. 6 shows a circuit diagram of an embodiment of the multi-input A-D converter in accordance with the present invention applied in the indication circuit of the camera.
FIG. 7 shows a circuit diagram of another embodiment of the control signal generating circuit shown in FIG. 2.
FIG. 8 shows a block diagram of an embodiment of the A-D converter in accordance with the present invention applied for a camera.
FIG. 9 shows a circuit diagram for showing a concrete composition of the block diagram shown in FIG. 8.
Description of the Embodiments of the Invention
FIG. 1 shows a circuit diagram of an analog-digital converting system which converts a plural number of the analog quantities into digital quantities by making use of conventional A-D converters. Comparators com.sub.1, com.sub.2 and com.sub.3 each has one input terminal a.sub.1, a.sub.2 and a.sub.3 receiving respective analog voltages of each comparator, the voltage V.sub.1, V.sub.2 and V.sub.3, Each of pulse generating circuits PG.sub.1, PG.sub.2 and PG.sub.3 produces pulses at a predetermined period. The output terminal of each pulse generating circuit is connected with one of the reference signal generating means RS.sub.1, RS.sub.2 and RS.sub.3. Each of the latter produces an analog voltage in accordance with the number of pulses generated by the respective pulse generating circuit. The circuits PG.sub.1, PG.sub.2, and PG.sub.3 are also connected with one input terminal of the AND-gate AG.sub.1, AG.sub.2 and AG.sub.3 whose other input terminal is connected with the respective output terminals of the comparators com.sub.1, com.sub.2 and com.sub.3. The output terminals of the reference signal generating means RS.sub.1, RS.sub.2 and RS.sub.3 are respectively connected with the input terminals of the corresponding comparators com.sub.1, com.sub.2 and com.sub.3. converters CAT.sub.1, CAT.sub.2 and CAT.sub.3 are respectively connected with the corresponding output terminals of the AND-gates AG.sub.1, AG.sub.2 and AG.sub.3.
In operation a starting switch not shown in the drawing, is closed. The pulse generating circuits PG.sub.1, PG.sub.2 and PG.sub.3 are brought into operation at the same time so as to produce respectively the pulse signals at a certain same period. These pulse signals are conveyed to respective reference signal generating means RS.sub.1, RS.sub.2 and RS.sub.3 to be converted into the voltages corresponding to the numbers of the corresponding pulse signals. These voltages are respectively compared with voltages V.sub.1, V.sub.2 and V.sub.3 by means of the comparators com.sub.1, com.sub.2 and com.sub.3. When the both voltages are identical with each other com.sub.1, com.sub.2 and com.sub.3 produce logical zeroes so as to close the AND-gate AG.sub.1, AG.sub.2 and AG.sub.3. On the other hand, the pulse signals generated by means of the pulse generating circuits PG.sub.1, PG.sub.2 and PG.sub.3 are counted by means of the counters CAT.sub.1, CAT.sub.2 and CAT.sub.3 through the AND-gates AG.sub.1 , AG.sub.2 and AG.sub.3 until the comparators produce logical zeroes. Thus V.sub.1, V.sub.2 and V.sub.3 are converted from the analog quantities into digital quantities.
In the case mentioned above, a plural number of the analog quantities are converted into digital quantities by means of conventional A-D converters. Thus it is essential provide the same number of the reference signal generating means as that of the analog quantities to be converted. This causes difficulties in the construction of the circuit and its precision.
FIG. 2 shows a circuit diagram of an embodiment of an A-D converter which converts a plurality of analog inputs in accordance with the present invention, and which eliminates the shortcomings of the above mentioned conventional A-D converter.
The respective input terminals I.sub.1, I.sub.2 and I.sub.n receive analog signals V.sub.1, V.sub.2 and V.sub.n. Amplifiers A.sub.1, A.sub.2 and A.sub.n function as respective comparators. Members G.sub.1, G.sub.2, G.sub.n and G.sub.s are AND-gates and CC.sub.1, CC.sub.2 and CC.sub.n pulse counters or registers. Reference signal generating means so produce step-shaped or saw-tooth shaped voltages corresponding to the number of the pulses produced by the clock pulse generating means CP. The control signal generating circuit C produces the starting signal, the reset signal, etc. Reference character S represents the starting pulse while R represents the reset pulse.
FIG. 3 shows the diagram for explaining the operation of the device shown in FIG. 2.
Below the operation of the embodiment shown in FIG. 2 will be explained.
After actuating the control generating means C, the starting signal S is applied to the reference signal generating means SO and to the AND-gate G.sub.s while the clock pulse generating means CP is actuated. When the starting signal S is applied to the reference signal generating means SO, the reference signal generating means SO produces a saw-tooth shaped voltage as is shown in FIG. 3, which voltage is put in the input terminals of A.sub.1, A.sub.2 and A.sub.3. On the other hand, the pulse generated by the clock pulse generating means CP is put in the input terminals of G.sub.1, G.sub.2 and G.sub.3 through the AND-gate G.sub.s. The outputs of the comparators A.sub.1, A.sub.2 and A.sub.3 assume a logical "1" until a coincidence signal is produced. Hence the clock pulse generated by means of CP passes through gates G.sub.1, G.sub.2 and G.sub.3 the input of the registers CC.sub.1, CC.sub.2 and CC.sub.n, which count the number of the respective pulses. Then after elapse of the time t.sub.a, the analog voltage at the input terminal equals to the output voltage coming from SO, and the comparator A.sub.1 produces a logical "0". By means of this, the AND-gate G.sub.1 is closed and the counting operation of the register CC.sub.1 is stopped. Therefore the number of the pulses produced by means CP from the time t.sub.s up to t.sub.a is stored in the register CC.sub.1. Thus the analog voltage V.sub.1 is coded into a pulse number and stored in CC.sub.1.
At the time t.sub.b, A.sub.n produces an output "0" so as to open the AND-gate G.sub.n so that the counting operation of the register stops. Now the input V.sub.a is stored by means of CC.sub.1 as digital signal. In a similar way, the analog signal V.sub.c is coded into a digital value and stored in register CC.sub.2. During one cycle of the saw-tooth shaped wave produced by the reference signal generating means the analog input signals V.sub.1 -V.sub.n are connected into digital data as explained above.
The reference signal generating means SO produces a step-shaped voltage corresponding to the number of the clock pulses applied to SO, after having passed through the AND-gate G.sub.s along the dotted line. A-D conversion is performed in the same way as in the above mentioned saw-tooth shaped wave. The reference signal generating means SO utilizes the Flip-Flap counters FF and the rudder circuit as is shown in FIG. 4(a). The output voltage alters the shape of the step according to the elapse of the time as is shown in FIG. 4(b). As shown in the drawing, the output of SO is delivered to the comparators A.sub.1, A.sub.2 and A.sub.n so as to be compared with the corresponding analog inputs. The clock pulses coming from CP trigger the counter of SO through the NOR-gate and inverter Inv.sub.3 and are further counted through the NAND-gate G.sub.1 until the coincidence signal is produced. Further the reset pulse is applied to the reset terminal of the counter through the inverter Inv.sub.1.
Further, the control signal generating circuit C is composed of a current source E, a differentiating circuit and the switching-over switch as is shown in FIG. 5. In order to obtain a starting signal the switch SW is connected to a contact "a", while in order to obtain a reset signal the switch SW is connected to a contact "b". FIG. 6 shows an embodiment of the A-D converter for multi-inputs in accordance with the present invention applied in the indication circuit of a camera, wherein CO is shown as the one which produces saw-tooth shaped wave.
Analog input signals corresponding the shutter time information Tv and the aperture information are applied to the comparator CMP.sub.1 and CMP.sub.2. They are converted into digital values during one cycle of the output of the saw-tooth shaped wave generating means CO and stored in the counter in such a manner that the digital informations are decoded by the decoder and indicated by means of the digital indication means in the view finder or the like.
FIG. 7 shows a circuit diagram of an embodiment of the saw-tooth shaped wave generating means shown in FIG. 6. Here FF.sub.s is a Flip-Flap whose set terminal S receives the starting signal from the above mentioned control signal generating circuit C, so as to produce an output at the output terminal. Member Trs is a transistor provided at the output terminal of FF.sub.s, OP.sub.s an operational amplifier and Cs a capacitor which forms a Miller integrating circuit together with the above mentioned OPs so as to produce a saw tooth shaped voltage at its output terminal. The Miller integrator is actuated when the above mentioned transistor Trs is switched on.
FIG. 8 shows a circuit system diagram of an embodiment of the A-D converting device in accordance with the present invention applied in a camera. In the diagram 1 is a light measuring circuit, S.sub.1 a storage switch, S.sub.2 a temporary storage switch (EE lock) and C the storage condenser. 2 is an amplifier with high input impedance, for example FET. An analog processing circuit 3 produces, analog information (shutter time information or aperture information) at its output out of various kinds of photographic input data members 4 to 8 supply various forms of photographic data, for example, 4 furnishes the film sensitivity Sv, 5 the lens aperture adjusting information Ave, 6 the shutter time information -Tv, 7 the aperture information -(Av-Avo) and 8 the aperture value of the totally opened lens -Avo. Members S.sub.3, S.sub.4, S.sub.5 and S.sub.6 are mechanically linked selector switches for selecting operation with priority on shutter selections or that with priority on aperture selection. Members 9 and 11 are buffer amplifier, 10 a shutter time control circuit, 12 an aperture control circuit, 13, 14 the comparators, 15 the D-A converter, 16 the control pulse generating circuit, 17, 18 the gate circuits, 19, 20, 21 and 22, 23 and 24 respective LED indication devices a decorder and a counter, and 25 the current source.
Then the light measuring circuit operates as part of a totally opened TTL light measurement system as shown in the drawing, the light sensing element 1 receives the light beam Bv-Avo-Avc. Here Bv is the Apex-value of the object to be photographed, Avo the Apex-value of the totally opened F value and Avc the Apex-value for the aperture adjustment. Release of the shutter button opens the storage switch S.sub.1 before the mirror is lifted. This stores the signal of the output BV-Avo-Avc of the light sensing element in the condenser C. In the operating mode with priority on the shutter the switches S.sub.3, S.sub.4 and S.sub.5 are moved to the position shown in the drawing (connected to the side T). The processing circuit 3 receives the value Bv-Avo-Avc stored in C through the amplifier 2, and Sv, Avc and -Tv from the information sources 4 to 6. Hereby Sv is the Apex-value of the film sensitivity and Tv the Apex-value of the shutter time. Thus these analog Apex-values are processed in the processing circuit in such a manner that the inversed output -(Av- Avo) of (Bv-Avo-Avc)+ Sv-Tv+Avc=Av-Avo (inverted by 3) is put in the buffer-amplifier 11 through S.sub.5, in which the inverted process (Av) of the output of the Avc information source 8 and - (Av-Avc)- Avc= -Av is carried out in such a manner that at the output of 11 Av namely the Apex-value of the aperture is produced. This Av analog information is applied to the comparator 13. Further, from the Tv information source 6 its output -Tv is applied to the buffer amplifier 9 through switches S.sub.3 and S.sub.4, inversed by the buffer amplifier 9 so that the value applied to Tv is the comparator 14. The pulses from the clcok pulse generating means are applied to the D-A converter 15, whose output signal is put in 13 and 14, so as to be compared with the analog signals of Av and Tv. The counters 21 and 22 continue to count the clock pulses through the AND-gates 17 and 18 until the comparators 13 and 14 produce a coincidence signal in such a manner that the digital informations corresponding to the analog signals of Av and Tv are set respectively in 21 and 22. The prolongation of the Apex-value into the actual value is carried out by means of the decoders 20 and 23 in such a manner that the shutter time is indicated in the LED indication means 19 and 24. The shutter time control circuit 10 and the aperture control circuit 12 respectively control the shutter curtain and the diaphragm blade in the conventional way respectively by means of the input signals Tv and Av so as to obtain a proper exposure.
In aperture priority mode the switches S.sub.3, S.sub.4 and S.sub.5 shown in the drawing are connected to the contacts A. Hence the shutter time and the aperture are indicated in the same way as in the above mentioned case, while the shutter time and the aperture are controlled in the same way as above. Specifically, in the processing circuit 3, the information Bv-Avo-Avc from the light sensing element 1, the film information Sv from 4, the Apex-value Avc for aperture adjustment from 5 and the aperture information -(Av-Avc) from 7 are put, the inversed output -Tv of (Bv-Avo- Avc)+Sv+Avc-(Av-Avo)=Tv is applied to the buffer circuit 9 through the switch S.sub.5 so as to be inversed in the circuit 9 in such a manner that Tv (analog value) is applied to the comparator. On the other hand, the output - (Avo-Avc) from 7 and that -Avo from 8 are put in the buffer-circuit 11, so as to produce Av as the output of the circuit 11. The value Av is transferred to the comparator 13 and then converted into digital value in the same way as in case of the mode with shutter priority in such a manner that the shutter time and the aperture value are indicated digitally. The switch S.sub.6 is mechanically linked with the switches S.sub.3 -S.sub.5 so as to indicate in the view finder whether the priority is on the shutter time or on the aperture, whereby the indication means 19 and 24 are supplied with current from the current source through the switch S.sub.6 and the resistances R.sub.1 and R.sub.2. With shutter priority the S.sub.6 is located as is shown in the drawing, the brightness of LED.sub.24 for indicating the shutter time is higher than the LED.sub.19 for indicating the aperture. This, which indicates that the mode is with priority on shutter time. In case of the mode with priority on aperture the switch S.sub.6 is connected to the side "A", whereby the brightness of LED.sub.19 is higher than that of LED.sub.24. This indicates that the aperture priority mode.
FIG. 9 shows circuit details of the block diagram shown in FIG. 8, wherein the same elements are identified by the same reference characters.
Below the composition of each block in FIG. 9 is explained in accordance with FIG. 9. The light measuring circuit 1 consists of a photovoltaic element SPC for receiving the light beam coming through the photographic lenses (not shown in the drawing), the operation amplifier OP.sub.1 whose input terminals are connected with both terminals of the SPC, and the diode D connected between the input terminal and the output terminal in such a manner that incident light beam is compressed logarithmically. The amplifier 2 is composed of an operational amplifier OP.sub.2, while the processing means 3 is composed of an operational amplifier OP.sub.3 between whose input terminal and output terminal a resistance R.sub.1 is connected. Hence the data are respectively set by the value of the resistances VR.sub.2 -VR.sub.6. The shutter time control circuit 10 composed of a time constant circuit having a condenser C and of a transistor Tr.sub.1 whose base is connected with the output terminal of the amplifier OP.sub.4, of a comparator com.sub.5 connected with the time constant circuit and of a magnet connected with the output of the comparator. The aperture control circuit 12 is composed of a comparator 6 whose one input terminal is connected with the output terminal of the amplifier OP.sub.5. It is also composed of a variable resistance VR.sub.7 which is connected with the other input terminal of the comparator 6 and whose resistance value varies in accordance with the aperture value, and of a magnet Mg.sub.1 connected with the output terminal of the comparator com.sub.6, so as to hold the preset ring (not shown in the drawing). The operation of the embodiment shown in FIG. 9 is same as that in FIG. 8.
As explained above in detail in the A-D converting means for multi-inputs in accordance with the present invention the one input terminals of each of a plural number of the comparator is connected with a common reference signal generating means so that a simple structure permits simultaneous conversion the analog quantities of many inputs into digital quantities. A single reference signal generating means is sufficient. Thus a even a low precision reference signal generating means can produce high precision A-D conversion. This contrast with the conventional A-D converting means in which all the reference signal generating means have to possess the same characteristics, while the tolerances have to be considerably smaller. The A-D converting means in accordance with the present invention can be said to be extremely effective for small appliances such as camera.
Claims
What is claimed is:
1. A camera comprising: (a) a light measuring circuit for producing an analog signal corresponding to the brightness of a photographic object. (b) shutter speed signal forming means for producing an analog signal corresponding to a preset shutter speed value, (c) a computing circuit for producing an analog signal corresponding to an aperture value for correct exposure on the basis of said analog signals from light measuring circuit and shutter speed signal forming means, (d) pulse generating means for producing pulses, (e) reference signal forming means for forming an analog signal corresponding to a number of pulses from pulse generating means, (f) a first comparison circuit for comparing the analog signals from said computing circuit and said reference signal forming means, and producing a signal when both analog signals have a predetermined relationship, (g) a second comparison circuit for comparing the analog signals from said shutter speed signal forming means and said reference signal forming means and producing a signal when both analog signals have a predetermined relationship, (h) first counter circuit for counting said pulses from said pulse generating means and terminating the counting operation in response to the signal from said first comparison circuit, (i) a second counter circuit for counting said pulses from said pulse generating means and terminating the counting operation in response to the signal from said second comparison circuit, (j) a first display circuit for displaying an aperture value for correct exposure on the basis of content of said first counter circuit, (k) a second display circuit for displaying said preset shutter speed value on the basis of content of said second counter circuit.
2. A camera comprising: (a) a light measuring circuit for producing an analog signal corresponding to the brightness of a photographic object, (b) aperture value signal forming means for producing an analog signal corresponding to a preset aperture value, (c) a computing circuit for producing an analog signal corresponding to a shutter speed value for correct exposure on the basis os the analog signals from light measuring circuit and aperture value signal forming means. (d) pulse generating means for producing pulses, (e) reference signal forming means for forming an analog signal corresponding to the number of pulses from said pulse generating means, (f) a first comparison circuit for comparing the analog signals from said computing circuit and said reference signal forming means, and producing a signal when both analog signals have a predetermined relationship, (g) a second comparison circuit for comparing the analog signals from said aperture value signal forming means and said reference signal forming means, and producing a signal when both analog signals have a predetermined relationship. (h) first counter circuit for counting the pulses from said pulse generating means and terminating the counting operation in response to the signal from said first comparison circuit, (i) second counter circuit for counting the pulses from said pulse generating means and terminating the counting operation in response to the signal from said second comparison circuit, (j) a first display circuit for displaying a shutter speed value for correct exposure on the basis of content of said first counter circuit, and (k) a second display circuit for displaying said preset aperture value on the basis of content of said second counter circuit.
3. A double preference type camera according to claim 1, further comprising first switch means operatively coupled to said mode selecting means for connecting an output terminal of computing circuit to said second input terminal of said first comparison circuit in a shutter speed priority automatic exposure mode and for connecting an output terminal of said aperture information setting means to said second input terminal of said first comparison circuit in an aperture priority automatic exposure mode, and second switch means operatively coupled to said mode selecting means for connecting an output terminal of computing circuit to said second input terminal of second comparison circuit in an aperture priority automatic exposure mode and for connecting an output terminal of said shutter speed information setting means to said second input terminal of second comparison circuit in a shutter speed priority automatic exposure mode.
4. A double preference type camera according to claim 1, further including a switching means operatively coupled to said mode selecting means to selectively impress a high electrical power upon said first or second indication circuit to indicate the selected priority mode.
5. A double preference type camera which, according to an operating mode selected, computes either a shutter time for a preset diaphragm aperture value or an aperture value for a preset shutter speed, said camera comprising: (a) a light measuring circuit for producing an analog signal corresponding to the brightness of a photographic object, (b) shutter speed information setting means for presetting a shutter speed value and producing an analog signal corresponding to a preset shutter speed value, (c) aperture information setting means for presetting an aperture value and producing an analog signal corresponding to a preset aperture value, (d) a computing circuit, connected to the light measuring circuit, for producing an analog signal corresponding to a shutter speed value for correct exposure based on the analog signal from light measuring circuit and analog signal from aperture information setting means or producing an analog signal corresponding to an aperture value for correct exposure based on the analog signal from light measuring circuit and analog signal from shutter speed information setting means, (e) mode selecting means for selecting a shutter speed priority automatic exposure mode or an aperture priority automatic exposure mode and for connecting said shutter speed information setting means to said computing circuit when said shutter speed priority automatic exposure mode is selected and connecting said aperture information setting means to said computing circuit when said aperture priority automatic exposure mode is selected, (f) an analog to digital converter including: (1) a pulse generator for producing a series of pulses at a given frequency, (2) reference signal forming means for forming an analog reference signal corresponding to the number of pulses generated by pulse generator, (3) a first comparison circuit having a first input terminal connected to said reference signal forming means, said comparison circuit having a second input terminal connected to said computing circuit when said shutter speed priority automatic exposure mode is selected, said second input terminal being connected to said aperture information setting means when said aperture priority automatic exposure mode is selected, said first comparison circuit comparing the analog signals applied at said first and second input teriminals for producing a signal when the value of analog signals applied at first and second input terminal have a predetermined relationship, (4) a second comparison circuit having a first input terminal connected to said reference signal forming means, said second comparison circuit having a second input terminal connected to said computing circuit when said aperture priority automatic exposure mode is selected, said second input terminal being connected to said shutter information setting means when said shutter speed priority automatic exposure mode is selected, said second comparison circuit comparing the analog signals applied at said first and second input terminals for producing a signal when the value of analog signal applied at first and second input terminal have a predetermined relationship, (5) first counter circuit for counting said pulses from said pulse generator and terminating the counting operation in response to the signal from said first comparison circuit, and (6) A second counter circuit for counting said pulses from said pulse generator and terminating the counting operation in response to the signal from said second comparison circuit, (g) a first indication circuit for displaying the aperture value on the basis of the content of said first counter circuit, and (h) a second indication circuit for displaying the shutter speed value on the basis of the content of said second counter circuit.
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