DE2810907A1 - PHOTOGRAPHIC CAMERA WITH AUTO EXPOSURE - Google Patents

Description

Throat D-7390 Es3lingen Dipl.-Ing. Hartmut Kehl Scratch Mülbergerstrasse 63 Oipl.-Ing. Volkhard Kratzsoh Telephone Stuttgart 0711 - 359992 Deutsche Bank Essfingen 210 906 cable «kehlpatent» esslingenneckar Post office Stuttgart 10004-701 Chase Manhattan Bank New York

Rollei - works lawyer file 2423 Franke & Heidecke January 4th 1978

33 Braunschweig

Photographic camera with a shutter speed automatic

The invention relates to a photographic camera with an automatic exposure tent which automatically controls the exposure tent as a function of the object brightness, the entered film sensitivity and the set aperture, with a light measuring circuit that carries a signal proportional to the logarithm of the object brightness, a circuit for determining the exposure value from the signal of the Lichtmeßkreises and the input flare sensitivity and aperture, a storage circuit for storing the output signals of the circuit, which has a capacitor and an operational amplifier, whose inventitrender input is directly connected to its output and whose non-investing input is connected to the storage capacitor , and / a Control circuit for exposure time control according to the output signal stored by the storage circuit, which has a diode with a logarithmic characteristic for delogarithmizing the stored output signal and with Ö Opening a start switch activated during the triggering process is activated.

In a known photographic camera of this type (DE-OS 26 29 025) there is a control circuit for controlling the exposure time from an integrating operational amplifier, the capacitor of which is connected in parallel to the start switch. The start-

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switch is normally closed and coupled to the leading curtain of the shutter. As soon as this curtain is released to the drain, the start switch opens. The Delogarithmier diode. is connected with its cathode to the output of the storage circuit and with its anode to the inverting input of the integrating operational amplifier. The output of the integrating operational amplifier controls a threshold value, which in turn turns off a holding magnet for the trailing shutter curtain mono- or _o. Between the circuit for determining the exposure time and the storage circuit there is a switch which is normally closed _o In this state, the output signal of the circuit for determining the exposure time can be entered into the storage circuit Exposure time separated from the storage circuit and the output signal of the circuit entered in the storage circuit can be stored for any length of time, regardless of whether the brightness of the measured object changes or not coupled with the mirror mechanism and is opened as soon as the mirror leaves its normally assumed viewfinder position due to the release process u starts running * so the start switch and the second switch between the circuit and the storage circuit are opened the stored logarithmic output signal of the circuit is delogarithmized _o As soon as the switching threshold of the threshold switch is reached at the output of the integrating operational amplifier, the holding magnet of the lagging curtain is switched off and the lagging curtain is released to run freely.

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given.

This exposure time automatjjk the well-known photographic The circuitry of the camera is quite complex, as it is used both in the storage circuit and in the control circuit for controlling the exposure time a capacitor and an operational amplifier are necessary. This not only increases the manufacturing cost for the camera, but above all requires a larger one Installation space to accommodate the electronic circuit, which is the general endeavor to create a compact camera with the smallest possible dimensions.

The invention is therefore based on the object of improving the photographic camera of the type mentioned at the beginning to the effect that that for the storage circuit for storing the logarithmic exposure time signal and for the control circuit only a single capacitor and a single operational amplifier are required for exposure time control, so-

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A substantial reduction in the space required to accommodate the automatic exposure time control as well as cheaper production of the automatic exposure time control can be achieved.

In the case of a photographic camera of the type mentioned at the outset according to the invention, the object is thereby solved that the start switch in the connecting line of the output and inverting input of the operational amplifier is arranged that the diode with its anode with the output and its cathode with the non-inverting input of the operational amplifier is connected and that a voltage divider is connected to the output of the operational amplifier, its Divider tap is connected to the inverting input of the operational amplifier »

By means of these measures according to the invention, the storage circuit and the same components are used for the control circuit of the exposure time control. As long as the start switch is closed, the capacitor and the operational amplifier have the function of a storage circuit. As soon

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is opened, the start switch "assume the operational amplifier and the capacitor _t which now acts as Integra" tion capacitor, the function of the control circuit for Belichtungssteuerung.Der capacitor from the output dee operational amplifier via the Delogarithmier- diode in a period of time charged ^ corresponding to the stored output signal. In the camera according to the invention, the exposure time is thus "determined, stored and controlled" in the same way as in the known photographic camera described above, but this is achieved with significantly fewer electronic components.

According to a development of the invention is the output of the operational amplifier is connected to a threshold switch which controls a shutter holding magnet. As soon as the start switch is opened, the capacitor acting as an integration capacitor changes to the one at the threshold value switch If the set voltage is charged, the spine is released for the closing movement. The time of opening Until the shutter closes, this is the time it takes to charge the integrating capacitor Capacitor, i.e. the exposure time.

In a further embodiment of the invention is the Threshold switch designed as a transistor whose emitter-collector circuit the closure holding magnet is arranged and its base via a further resistor to the output of the operational amplifier is connected. An adjustable resistor can be used to set the response threshold of the transistor be provided in a PNP transistor between Emitter and base of the transistor is arranged. This results in a particularly simple and inexpensive threshold switch, although one must accept that the set threshold also depends on the internal resistance of the base-emitter path of the transistor is dependent. The spread of this resistance value in the various transistors must be taken into account when setting the threshold value.

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! Lack of a wider Ausfitir-uagafora the Irfladyrag is between a capacitor and not. izivei? t; lö3? ei2lesi Siagaag deia operational amplifier eia, adjustable resistance. ₉ is arranged which is sized to j that his opponent Stan & swert to near the Änspreefaschv / elle of the threshold smaller than Abt differential internal resistance of the diode "In this case, the Sehwellwerteinsteller can be omitted at the transistor, and eggs Swell is the only from the emitter-base Streoke Transistor formed. As long as the differential internal resistance of the diode with the logarithmic characteristic curve due to the current flow from the output of the operational amplifier to the capacitor is smaller than the resistance of the adjustable resistor during the exposure time control, the behavior of the operational amplifier is maintained by the negative feedback of the voltage tapped at the voltage part determines the input of the operational amplifier. At the moment v / o the current flow through the diode has grown so that the diff erential internal resistance of the diode is greater than the resistance value of the adjustable resistor, the positive feedback caused by the diode exceeds the output of the operational amplifier on its non-inverting input ^ where & urc ^ & e ^ iiusgang of the operational amplifier suddenly becomes as positive as possible. As a result, the transistor is suddenly driven very far, so that the influence of the emitter-base path is eliminated when the transistor is driven. A temperature compensation of the transistor, as it would have to be provided if the response threshold of the transistor were set by means of the resistor described above , its unneccessary. The adjustable resistor is therefore also used to determine the shortest controllable exposure time of the camera. It must be set in such a way that when the start switch is opened, after this desired shortest time, such a current flows through the diode that its internal resistance becomes smaller than the resistance value of the adjustable resistor.

According to a further embodiment of the invention is in An adjustable voltage source is arranged in series with the voltage divider. This measure enables the control circuit to control the exposure time to the upstream circuit

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can be adjusted to determine the exposure time. This is necessary when the circuit is used to determine the Exposure time for the longest exposure time to be controlled by the camera emits an output signal in the form of a 0 V voltage.

According to a further embodiment of the invention, the voltage source is temperature-dependent, so that they are simultaneously can be used to compensate for the temperature response of the diode.

In a preferred embodiment of the invention it is provided that the temperature-dependent voltage source of a second diode is formed with a logarithmic characteristic, which with its cathode on the voltage divider and with its Anode is connected to zero potential 'that the cathode of the second diode via an adjustable resistor with the Negative pole of the voltage source feeding the operational amplifier is connected, that the center potential of this voltage source is connected to zero potential and that the , Resistances of the voltage divider are of the same size. This results in a particularly simple design of the temperature-dependent Voltage source. Because the two diodes each have a logarithmic characteristic, a possible decrease or increase of the current in the first diode as a result of a temperature change caused by the same A decrease or increase in the voltage drop across the second diode is compensated. The adjustable resistance allows the longest exposure time can be set for which the circuit for determining the exposure time 'supplies an output signal of the order of 0 volts.

According to a further embodiment of the invention, there is between the output of the circuit for determining the exposure time and a memory switch which is coupled to a manually operable button is arranged in the memory circuit.

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As a result, the camera is "known", so-called Memo. Opening this switch can e ^ ii "at When the switch is closed, the output signal is transferred to the storage circuit of the circuit for determining the exposure time are stored unchanged over a longer period of time, regardless of whether, for example, the object brightness changes and the circuit for determining the exposure time changes its output signal.

The invention is described in more detail with reference to two exemplary embodiments shown in the drawing. Show:

Fig. 1 shows the circuit diagram of a simplified embodiment of an automatic exposure time and

2 shows a circuit diagram of an automatic exposure time system with temperature compensation.

The automatic exposure time control of the photographic camera automatically controls the exposure time in a known manner the brightness of the object, the entered film sensitivity and the set aperture. First of all, a Light measuring circuit 1 is provided, which also generates a signal proportional to the logarithm of the brightness of the object 2 to determine the exposure time from this signal of the light measuring circuit and the input film speed DIN and diaphragm f. In Fig. 1, the light measuring circuit 1 and the switching circuit 2 are formed by an operational amplifier 3 the two inputs of which a photodiode 4 is connected, the inverting input of which via a semiconductor diode 5, which has a logarithmic voltage-current characteristic, is connected to its output and to its non-interverting Input a reference voltage source DIN, f is connected, which the manually set aperture value and the Film sensitivity represented.

The output of the operational amplifier 3, which is the output 6 of circuit 2 for determining the exposure time

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stellp is connected to a plate giü® & capacitor 8 via a normally closed memory switch 7, the other plate of which is connected to WüHpoteatlal or ground o This plate of the capacitor connected to output 6 of the circuit for determining the exposure time is connected to the non-inverting input of another operational amplifier 9 connected ^ whose output is directly connected to the inverting input via a start switch 10 _o When the start switch 10 is closed, the capacitor 8 and the operational amplifier 9 form a memory circuit 11 for storing the output signal of the circuit 2 _e The start switch 10 is coupled to the leading shutter curtain of the camera shutter, not shown, in such a way that it opened when this curtain expired

The output of the operational amplifier 9 is furthermore connected via a diode 12, which has a logarithmic voltage-current characteristic curve, to the non-inverting input of the operational amplifier 9, the cathode of the diode at the non-inverting input and the anode of the diode 12 at the output of the operational amplifier 9 is connected. At the output of the operational amplifier 9, a voltage divider consisting of the resistors 13 and 14 is also connected, the divider tap 15 of which is connected to the inverting input of the operational amplifier 9. When the start switch 10 is open, the operational amplifier 9 together with its peripheral circuitry, such as diode 12 and voltage divider 13 and 14, together with the capacitor 8, form a control circuit 16 for exposure time control according to the output signal of the circuit 2 stored by the storage circuit 11 for determining the Exposure time. The output of the operational amplifier ¹ 9, at the same time the output 17 of the control circuit 16 is the exposure time control is connected to a Schwellwertschalter18, which in turn controls a holding magnet 19 for the trailing shutter curtain of the camera. In Fig. 1, the threshold switch 18 is used as a comparator. 20 is formed, the non-inverting input of which is connected to the output 17 of the control circuit 16 for exposure time control and at the inverting input of which a reference voltage Ref for setting the response

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- 12-threshold of the threshold switch is connected.

If the circuit for determining the exposure time is designed so that for the longest exposure time, that of the automatic exposure is to be controlled, the output signal of the circuit for determining the exposure time causes a voltage of 0 volts across the capacitor 8, the control circuit 16 must be connected to this in order to control the exposure time Design of the circuit 2 to be adapted to determine the exposure time. This is done by adding a controllable voltage source 21 in series with the voltage divider 13, 14 of the operational amplifier 9. If this voltage source is designed to be temperature-dependent, it can can be used to compensate for the temperature response of the diode 12.

A possible formation of the temperature-dependent, adjustable Voltage source 21 is included in FIG. 2. The temperature-dependent voltage source 21 is here from a second diode 23 formed the same logarithmic characteristic as diode 12, with their cathode on the voltage divider 13, 14 and their Anode is connected to zero potential. The cathode of the second diode 23 is connected to the via an adjustable resistor 22 The negative pole of a voltage source 24 feeding the operational amplifier 9 is connected, the center potential of which is connected to zero potential or In the emitter-collector circuit of a tran-

• j. oc the, threshold switch 18 forms _and ", _. . Sistor 25, where the pure mix of the voltage source 24 is located, the holding magnet 19 is arranged for the lagging shutter curtain of the camera shutter. The base of the transistor 25 is connected via a resistor 26 to the output 17 of the control circuit 16 for controlling the exposure time. In order to become independent of the emitter-base junction of the transistor 25, an adjustable resistor 27 is switched on between the capacitor 8 and the non-invert animal input of the operational amplifier 9. This resistor 27 is dimensioned so that its resistance value close to the response threshold of the threshold switch 18, ie up to _: ' that voltage at the output 17 of the control circuit, 16 at which the

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Begins to turn off transistor 25 is smaller than the differential .Innenwiderstand of the diode 12 is "Otherwise, the embodiment of FIG ₀ 2 identical with the embodiment in Fig. 1, wherein omitted for simplified illustration of Lichtmeßkreis 1 and the circuit 2 for determining the exposure time and only output 6 is shown.

The memory switch 7 has a so-called memo button 28 coupled in such a way that the memory switch 7 normally is closed and open as long as the memo button 28 is held down. Should the camera be a single lens reflex camera at which the light measurement is interrupted at the moment of the release process by folding up the reflective mirror is, the memory switch 7 is also connected to the mirror mechanism, not shown, in such a way that that when the mirror is in the viewfinder position, the memory switch 7 is closed and the mirror is folded up from the search creation the memory switch 7 opened will. .

The mode of operation of the exemplary embodiments described above is described below with reference to the circuit diagram in Figo 2:

First of all, the film sensitivity and the aperture must be set on the camera, whereby a certain reference potential is applied to the operational amplifier 3 (FIG. 1). The light measuring device 1 measures with the photodiode 4 the light reflected from the object and generates a signal proportional to the logarithm of the object brightness the entered light sensitivity and aperture the exposure time, and at the output of the circuit 2 there is a logarithmized exposure time _{signal o} When the memory switch is closed, this output signal of the circuit 2 is stored in the memory

Circle 11 entered (start switch 10 is closed because the shutter is closed) and stored here. As long as the Start switch 10 is closed, the operational amplifier 9 works as a voltage follower, i.e. the voltage on the capacitor 8 is transmitted to the output of the operational amplifier. As long as the start switch 10 is closed and the output voltage of the operational amplifier 9 is less than the positive voltage of the voltage source 24, the transistor is 25 is conductively controlled via the resistor 26 and the holding magnet holding the trailing shutter curtain of the camera shutter 19 excited. The trailing shutter curtain is in its shutter opening-releasing position by the magnet held.

If the memory switch 7 is opened, for example by pressing the memo key 28, then the description changes State nothing, since the same voltage is present at the output and at the input of the operational amplifier 9, and thus no current can flow through the diode 12. When the memory switch 7 is open, this state can remain unchanged over a longer period of time be maintained even if the output signal of the circuit 2 to determine the exposure time should change in the meantime.

If the camera release button (not shown) is now activated, the memory switch 7 is opened if it has not already been opened by manually holding down the memo key 28. In the case of a single-lens reflex camera, this is done by the mirror _{mechanism r} which opens the memory switch 7 when it leaves its viewfinder position. Then the leading shutter curtain of the camera shutter, which covers the shutter opening in a light-tight manner, is released to run freely. When this leading shutter curtain starts running, the start switch 10 coupled to this shutter curtain is opened. The operational amplifier 9 and the storage capacitor 8 now act as a control circuit for the exposure time control, and the time formation is started. One denotes with R ^, and R .., the resistance values of the resistors

8 3 ^ 9/00

and 14, with I ₂ ^ and i _i4 the currents flowing through the diode 23 ″ or the resistor 14 and with U ₁ - ,, ^U 14> ^U 23 ^U 8 those at the resistors 13, 14, at the capacitor 8 and at the diode 23 falling or applied voltages, then applies under the assumption

* 13 = R ₁ 4

U ₁₃ = U ₁₄ = U ₂₃ + U ₈ ,

since the same voltage is present at the inverting output of the operational amplifier 9 at the moment of opening the start switch 10 as at the non-inverting input of the operational amplifier 9, that is to say the voltage Ug of the capacitor 8. The _{voltage labeled U 1} ″ at the output 17 of the operational amplifier 9 is then

U ₁₇ = U ₈ + U ₁₃ = 2 U ₈ + U ₂₃ . The voltage drop across the diode ₁₂ is then U 12

U ₁₂ = U ₁₇ - U ₈ = U ₈ + U ₂₃ .

As a result of the logarithmic current-voltage characteristic of the diode 12, a current designated _{by i 12 then flows through the diode 12}

X ₁₂ = exp. U _{12 m}

This current is equal to the charging current i ₈ for the capacitor 8, which flows from the output 17 of the operational amplifier 9 to the capacitor 8. The following then applies to the charging current ig

i ₈ = exp. (U ₂₃ + U ₈ ).

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This current charges the capacitor 8, whereby the The voltage Ug at the capacitor increases and, due to the relationship between the last-mentioned equation, the Charging current increases.

If a silicon diode is used as diode 12, the current doubles when the voltage U ^ p ^on the diode increases by about 20 mV, i.e. when the expression in brackets in the last-mentioned equation increases by about 20 mV. This "doubles the charging current ig for the capacitor 8. This in turn has the effect that in a time interval T in which the capacitor 8 is charged by approx. 20 mV, the charging current for the capacitor 8 has doubled, thus increasing the charge by more 20 mV takes place in a time interval of 1/2 T, the further charging by another approx. 20 mV in 1/4 T, etc.

The relationship described above only applies as long as the voltage drop across resistor 27 is negligibly small. If the voltage U ^ ₂ at the diode rises so far that the differential internal resistance of the diode 12 becomes smaller than the resistance value of the resistor 27, the positive feedback of the output of the operational amplifier 9 via the diode 12 outweighs that via the voltage divider 13, 14 causes the output of the operational amplifier 9 to be counter-coupled to the input of the operational amplifier 9. As a result of this positive feedback, the output 17 of the operational amplifier 9 suddenly rises as positively as possible. As a result, the transistor 25 is suddenly blocked, the magnet 19 is de-energized and releases the lagging shutter curtain of the camera shutter to cover the shutter opening.

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Through the resistors 27 and 22, the shortest and the longest exposure time that can be controlled by the control circuit is set. The resistors 27 and 22 must be adjusted so that that the time for the above-described exponential charging of the capacitor 8 with the start switch open 10 " starting from a stored memory corresponding to the output signal of the circuit 2 for determining the exposure time Capacitor voltage, up to the point in time at which positive feedback of the operational amplifier 9 begins, the correct one in each case Exposure time corresponds.

The mode of operation of the temperature compensation can also easily be read from the relationship dealt with in the above equations. A change in temperature takes effect in the same way on the diode 23 and on the diode 12, so that the charging current ig does not affect the capacitor will.

The mode of operation of the exemplary embodiment in FIG. 2 described above in terms of equations can be carried out in the same way can also be applied to the embodiment in FIG. All that is needed for this is the voltage drop across the diode UV ^ to be replaced by the voltage Up-i of the voltage source 21. For the rest, a positive feedback described above does not take place here. As soon as the voltage at the output 17 of the Operational amplifier 9 exceeds the reference voltage of the comparator 20, the output of the comparator 20 is abrupt positive, and the holding magnet 19 for the trailing shutter curtain is de-energized in the same way »

Is the circuit 2 for determining the exposure time designed so that the longest exposure time to be controlled is determined by an output signal _? which supplies a voltage deviating from 0 volts for the capacitor 8, the voltage source 21 can - as already mentioned - be omitted. In this case it is in those listed above

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Equations to set the voltage Up ^ zero. The resistance values of the resistors 13 and 14 of the voltage divider at the output of the operational amplifier can be chosen arbitrarily. They only have to be identical if, as in Fig. 2, the The temperature response of the diode 12 is compensated with an identical diode 23 shall be.

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Claims (8)

Patent attorneys 9-73C0 Esclingen 2810907 ■ Throat ! Vliilbnrgerstr 55 Dipl.-Ing. Hartmut Kehl Scratchy eyes Dipl.-Ing. Volkhard Kratzsch Telephone Stuttgart 0711 - 3599 92 cable «kehlpatent» esslingenneckar Deutsche Bank Esslingen 210906 Post office Stuttgart 10004-701 Chase Manhattan Bank New York Rollei works
Franke & Heidecke Attorney File 2423
4th January 1978 Braunschweig Claims \ 1 J Photographer isehe camera, with an automatic exposure control ₉ which automatically controls the exposure time depending on the object brightness, the entered film sensitivity and the set aperture _s with a light measuring circuit that generates a signal proportional to the logarithm of the object brightness, a circuit for determining the exposure time from the signal of the light measuring circuit and the input film sensitivity and aperture, a memory circuit for storing the output signal of the circuit, which has a capacitor and an operational amplifier, whose inverting input is directly connected to its output and whose non-inverting input is connected to the storage capacitor> and / a Control circuit for exposure time control according to the output signal stored by the storage circuit, which has a diode with a logarithmic characteristic curve for delogarithmizing the stored output signal and with opening one when off release process actuated start switch is activated, characterized in that the start switch (10) is arranged in the connection line from output (17) and inverting input of the operational amplifier (9), that the diode (12) with its anode to the output (17) and its cathode with the non-inverting input of the operational amplifier (9) 909839/0063 bionden and that at the output of the operational amplifier (9) a voltage divider (13, 14) is connected, the divider tap (15) with the inverting input of the Operational amplifier (9) is connected. ' 2. Camera according to claim 1, characterized in that that the output (17) of the operational amplifier (9) is connected to a threshold switch (18), the one Lock holding magnet (19) controls. 3. A camera according to claim 2, characterized geke η n is characterized in that the threshold value switch is designed as a transistor (25) (18) in whose emitter-collector circuit of the shutter holding magnet (19) is arranged and its base connected through a further resistor (26 ) is connected to the output of the operational amplifier (9). 4. Camera according to claim 3, characterized in that between the capacitor (8) and not an adjustable resistor (27) is arranged on the inverting input of the operational amplifier (9) and is dimensioned in this way is that its resistance value up to near the response threshold of the threshold switch (18) is less than is the differential internal resistance of the diode (12). 5. Camera according to one of claims 1-4, characterized in that in series with the voltage divider (13, 14) an adjustable voltage source (21) is arranged. 6. Camera according to claim 5, characterized in that the voltage source (21) is temperature-dependent. 909839/0063 • - 3 - 7. Camera according to claim 6, characterized in that the temperature-dependent voltage source (21) of a second diode (23) with a logarithmic mixer Characteristic curve is formed with its cathode on the voltage divider (13, 14) and with its anode at zero potential: that the cathode is connected. the second diode (23) via an adjustable resistor (22) is connected to the negative pole of the operational amplifier (9) feeding voltage source (24) that the Center potential of the voltage source is connected to zero potential and that the resistors (13 »14) of the Voltage divider are dimensioned the same size. 8. A camera according to any one of claims 1-7, characterized ge tj that between the output (6) of the Circuit (2) for determining the exposure time and the memory circuit (1.1), a memory switch (7) is arranged is coupled to a manually operable button (28). 909839/0063