DE2415394C3 - Arrangement for measuring at least one extreme value of the brightness distribution of a photographic object - Google Patents

Description

Line 5 is connected. The switch 7 is part of the display stage Z. The circuit sections B and C have the same structure as the circuit section A and therefore do not need to be described in more detail here.

The switching voltages of the provided in the circuit sections B and C transistors have the same value as the switching voltage of the transistor 3 has the display level Z except the aforementioned switches 7, which is designed as a break contact and through each existing in the circuit sections A to C Excitation coils, for example the excitation coil 4 in circuit section A, can be actuated, a variable resistor 8 and a time-determining capacitor 9, which form a series circuit with one another and with said switch 7 and are arranged between the positive and negative busbars. The connection point between the variable resistor 8 and the capacitor 9 leads to the base of a transistor 10, the emitter of which is connected to the negative bus line 6 and the collector of which is connected to the positive bus line 5 via a display instrument 11. A supply voltage source 13 is also provided, the negative pole of which is connected to the bus line 6 and the positive pole of which is connected to the positive bus line 5 via a switch 12.

The operation of this circuit is described in more detail below. When the CdS photo resistors are exposed to the object rays, the internal resistance of each of them takes on a value. which corresponds to the partial objectives prevailing on its active surface. They represent aKo as a whole an image of the brightness distribution of the subject. If the holder 12 is now closed, the time-determining capacitor is in each of the circuit sections A to C. eg 2, charged via the assigned CdS photoresistor, eg 1. At the same time the charging of the time-determining capacitor 9 begins in the display stage Z. It is assumed that the greatest partial brightness prevails on the effective surface of the CdS photoresistor 1 in the circuit section A. Its internal resistance is therefore lower than that of the corresponding CdS photoresistors in the other circuit sections: accordingly, the charging voltage of the capacitor 2 connected in series with it increases the fastest, so that the collector current of the transistor 3 controlled by this charging voltage has the highest value and the in the collector circuit inserted coil 4 is excited first and the switch 7 opens.

This interrupts the charging circuit of the capacitor 9, and the display instrument 11 is fixed to a display value which corresponds to the charging voltage of the capacitor 9 present at this point in time. The deflection of the display instrument 11 is therefore a measure of the brightness value to which the CdS photoresistor 1 in the circuit section A is exposed.

The display value of the instrument 11 is through the remaining circuit sections ß and C. their CdS photoresistors are exposed to lower lighting levels, no longer influenced, since the Switch 7 is already open and through the appropriate Excitation coils in the remaining circuit sections is no longer influenced. So that shows Measuring instrument 11 shows a value which characterizes the highest partial object brightness.

The embodiment shown in Fig. 3 is based on the same principle as the circuit according to Fig. 2, however, electromechanical components are replaced by electronic components. Those Components in Fig. 3 that have the same function

ίο like the corresponding components in the circuit according to Fig. 2 are provided with the same reference numerals like these. A.; a more detailed description of their mode of action is unnecessary.

The collector dt s transistor 3 in circuit section A is connected on the one hand via a resistor 14 to the positive bus 5 and on the other hand to the base of a transistor 15, the emitter of which is connected to the negative bus 6 and its collector via a resistor 16 to the positive bus 5 communicates. The circuit sections ß and (are constructed analogously and will not be described in more detail. The transistor 15 and the corresponding transistors from the other circuit sections are connected with their collectors over capacitors 17, 18 and 19 serving as differential elements and resistors 17 ', 18' or 19 ', which serve as attenuation or decoupling elements, are connected to the control electrode of a thyristor 21. This control electrode is also connected to the negative bus line 6 via a resistor 20. The anode of the thyristor 21 is connected to a resistor 22 and the base of a Transistor 23. The other end of resistor 22 and the emitter of transistor 23 are connected to the positive SamineHestup.g, while its collector is connected to a resistor 24 and the base of a switching transistor 25. The other end of resistor 24 leads to the negative bus 6. The emitter and the KoI-lektor of the transistor 2 5 are connected to the positive collecting line or mi 'one end of a variable resistor 8.

In the following, the operation of the Scha device shown in Fig. 1 is explained in more detail: When the switch 12 is closed, a charging process begins for the time-determining capacitors provided in the individual circuit sections Λ to C , for example the capacitor 2 in the circuit section A. In the point in time at which the switch Ii is closed, the transistor 3 and the corresponding transistors in the other circuit sections are in their non-conductive state, since the charging voltage of the capacitors concerned, for example 2, is initially zero. The respective:

downstream transistors, e.g. B. the transistor Ii in the circuit section A , however, are controlled in ih Ren conductive state, so that the capacitors 17, 18 and 19 respectively connected to their collector are practically at the potential of the negativei

Manifold 6 lie. As a result, no signal is generated in the resistor 20 and the thyristo 21 is blocked. The transistor 23, which is driven by the Ano denpotential of the thyristor 21, is also found in its non-conductive state. The switching transistor 25, the switch 7 of Fig. '. corresponds to, is therefore conductive, so that the charging of the capacitor 9 begins via its KoI lektor-emitter path.

controls the transistor 10 so that the pointer of the measuring instrument arranged in its collector circuit deflects according to the collector current that increases over time.

If it is assumed again that the CdS photoresistor 1 is exposed to the highest partial illuminance, the transistor 3 first becomes conductive and controls the transistor 15 downstream of it into its non-conductive state. The signal appearing at the collector 15 passes via the capacitor 17, which serves as a differential element, to the resistor 20 and thus to the control electrode of the thyristor 21. The thyristor 21 is triggered by this control signal, and the transistor 23, which is controlled by its anode voltage, enters its conductive state and switches the downstream transistor 25 off. As a result, the charging process of the customer station 9 is interrupted. The charging voltage of the capacitor 9 reached up to this point in time characterizes the highest partial luminance of the object. This and only this is indicated by the measuring instrument 11, as in the exemplary embodiment according to FIG. The exemplary embodiment shown in FIG. 3 has the advantage over the arrangement according to FIG. 2 of greater response speed and sensitivity and greater accuracy, since the delay time inherent in electromechanical components is avoided due to the use of exclusively electronic components

4 shows an exemplary embodiment. which is used to measure the lowest partial illuminance or object luminance. The circuit elements with an analog function are again provided with the same reference numerals as in the figures described above and should not be explained in more detail. In the circuit section A , a variable resistor 26 is arranged in series with a CdS photoresistor 27 between the positive bus line 5 and the negative bus line 6. The center point α of this series circuit is connected to the base of a transistor 28, in the collector circuit of which a resistor 29 is inserted. The collector of transistor 28 is connected to the base of a transistor 30 for current control. The emitter of this transistor 30 is directly connected to the positive bus, while its collector is connected to the time-determining capacitor 2 and the base of the transistor 3. The circuit sections B and C again have an analog structure and will therefore not be described in more detail.

When the switch 12 is closed, the charging of the capacitor 2 and the corresponding capacitors in the other circuit sections B and C begins. The charging circuit runs via the collector-emitter path of the transistor 30 or the corresponding transistors in the other circuit sections. It is assumed that the CdS photoresistor 27 of the circuit section A is exposed to the object rays corresponding to the lowest partial object luminance. The voltage Va at the circuit point α is therefore higher than at the corresponding circuit points of the various circuit sections. The current of the transistor 28 therefore has the highest value. The transistor 30 controlled by the transistor 28 thus also carries the highest collector current. mi that the charging voltage at the time-determining capacitor 2 grows the fastest and the coil 4 in the collector circuit of the transistor 3 is the first to be effectively energized and the switch 7 opens. The instantaneous value of the display of the measuring instrument 11 is fixed and shows the value corresponding to the lowest partial illuminance.

F i g. 5 shows an exemplary embodiment for determining the highest partial illuminance. In this embodiment, differential amplifiers serve as comparator circuits. Switching means with the same effect are again provided with the same reference numerals as in the preceding figures and are not described again. A resistor 31 is connected in series with a variable resistor 32 between the positive bus 5 and the negative bus 6. The center point α of this series circuit leads to the base of a transistor 33, the collector of which is connected to the positive bus line 5 and the emitter of which is connected to the negative bus line 6 via a resistor 34. The emitter of the transistor 33 is also directly connected to the emitter of a further transistor 35. The two transistors 33 and 35 form a differential amplifier. The circuit sections B and C are constructed analogously and therefore do not need to be described in more detail. The use of differential amplifiers represents an important difference compared to the circuit according to FIG. 2. It reduces the disruptive effects of voltage fluctuations and temperature changes to a minimum. In order to measure a desired output information from one of a plurality of light measuring stages with the required accuracy, the operation of the circuits should be stable and independent of external conditions. It should only be able to be influenced by the test object. The well-known stability of differential amplifiers meets these requirements very well.

When the switch 12 is closed in the exemplary embodiment shown in FIG. 5, the partial voltage of the voltage divider consisting of the resistor 31 and the variable resistor 32 appears at the circuit point a. Corresponding partial voltages are present at the voltage dividers in the remaining circuit stages. The resistances corresponding to the variable resistor 32 in the other circuit sections are set so that the aforementioned partial voltages ir all have the same value Va . In the circuit section A , the charging of the time-determining capacitor 2 begins via the CdS photoresistor 1. The transistor 35 is controlled by the charging voltage of the capacitor 2 in its conductive state as soon as it reaches the value of the partial voltage Va . Then the arranged in the collector circuit of the transistor 35 coil 'is effectively excited. It is assumed that the most partial illuminance has an effect on the effective

So the surface of the CdS photoresistor 1 prevails. The charging voltage of the capacitor 2 rises faster at al? the corresponding charging voltage in dei other circuit sections. so that the coil 4 al first is energized and the switch 7 opens. The mess Instrument 11 then shows again, as in the arrangement according to FIG. 1, that of the highest partial loading bright corresponding value

Dk previously described embodiment I

make use of a measuring method in which the charging process of capacitors is exploited will. The arrangement can, however, also be implemented with circuit arrangements that control the discharge process make use of a capacitor.

Such an exemplary embodiment is shown in FIG. 6. In circuit section A , the CdS photoresistor is connected in series with a variable resistor 36 between the positive bus line 5 and the negative bus line 6. The center point of this series connection leads to the rest side 1 of a changeover switch 37, which is mechanically connected to corresponding changeover switches in the other circuit sections, for example in circuit section B. The center spring of the changeover contact 37 is connected to the negative bus line 6 via a time-determining capacitor 38. The working side m of the changeover contact 37 is connected to a variable resistor 39 for setting the time constant and to the base of a transistor 40. Its emitter is connected to the negative bus line together with the emitter of a transistor 41 via a resistor 42. The collector of the transistor 40 is connected to the positive bus 5 via the excitation coil 4. The excitation coil 4 is used to operate a switch 46 in the circuit section Z. The collector of the transistor 40 is also connected to the base of the transistor 41 via a resistor 43. A resistor 45 is inserted into the collector circuit of the transistor 41. The base of the transistor 41 is connected to the negative bus 6 via a resistor 44. The two transistors 40 and 41 form a Schmitt trigger circuit. The section B is constructed in the same way as the section A. The circuit section Z corresponds in its construction to the circuit stages of the same name in the exemplary embodiments described above. The only difference to these is that the switch 46 is a normally open contact, that is to say is open in the idle state, and is closed when the coil 4 (or the corresponding coils in the other circuit sections) is excited. A detailed description of the circuit sections B and Z is unnecessary.

When the switch 12 is closed, a partial voltage arises at the midpoint α of the series circuit consisting of the components 1 and 36, which depends on the illuminance prevailing on the effective surface of the CdS photoresistor 1 and thus on the corresponding partial object brightness. This partial voltage causes the time-determining capacitor 38 to be charged and is stored in it. The excitation coil 4 is de-energized at this point in time, since the transistor 40 in the first stage of the Schmitt trigger circuit is initially non-conductive. The same applies to the excitation coils in the or the other circuit portions, for example, B. If now for the determination of the highest partial object brightness, the changeover switch 37 from its position 1 folded m in its position, reaches the charge stored in the capacitor 38 charging voltage as the control voltage to the base of the first transistor 40 of the Schmitt trigger circuit. The Schmitt trigger circuit is flipped by this control voltage. As a result, the coils 4 are effectively excited, so that the switch 46 is closed immediately. As a result, the charging of the time-determining capacitor 9 begins in the connection section Z. At the same time, the discharge of the capacitor 38 begins via the variable resistor 39.

It is assumed that the CdS photoresistor 1 arranged in the section A is exposed to the highest illuminance. Then the partial voltage at the circuit point α is higher than the relevant partial voltage in the other circuit sections, consequently the charging voltage of the capacitor 38 is also the highest, and the discharge time is the longest for this capacitor. As a result, the Schmitt trigger circuits in the other circuit sections will tilt back into their idle state at an earlier point in time, as a result of which the respective excitation coils are de-energized.

The excitation coil 4 in the maintenance section A , however, is still effectively excited when the other excitation coils are already de-energized. The switch 46 is therefore still closed and the capacitor 9 continues to be charged until the Schmitt trigger circuit in circuit section A also tilts back to its initial state so that the

Current flow through the excitation coil 4 is interrupted and the switch 46 opens again. The pointer deflection of the measuring instrument 11 is fixed in a position corresponding to the instantaneous value of the charging voltage of the Capacitor 9 corresponds and which is characteristic of the highest partial object brightness.

Fig. 7 shows an embodiment that is used to determine is used for the lowest partial object brightness. In this exemplary embodiment, too, the Discharge process of capacitors exploited. in the

the rest is the same as in Fig. 7 with the only exception that the CdS photoresistors and the variable resistors connected in series with them are interchanged. The mode of operation of the circuit according to FIG. 7 is briefly indicated: if, for example, the CdS photocrossland arranged in the section A is weakest illuminated, the highest partial voltage is generated at the circuit point a and in the corresponding one

time-determining capacitor stored. This means that the later capacitor discharge takes the longest and is decisive for the pointer deflection of the measuring instrument, which is the lowest partial object helicity indicates.

FIG. 8 shows a variant of the measuring stages A, B etc. shown in FIG. 7. In this variant, the discharge resistor and the CdS photoresistor are interchanged, so that the internal resistance of the CdS photoresistor serves as a discharge resistor for the time-determining capacitor. This embodiment again serves to determine the lowest partial object brightness, since the excitation coil of that measuring stage is the last to be de-energized whose CdS photoresistor has the highest internal resistance.

The previous description had exemplary embodiments as the subject, which are used to determine either the lowest or de- · highest partial object brightness serve. Suitable combinations of these exemplary embodiments lead to different arrangements, mi; which simultaneously determines both the highest and the lowest partial object brightness can be.

c r e ζ

F Y cst

; r st Is

G t, s e

A corresponding exemplary embodiment is shown in FIG. 9. The circuit sections A and β, which of course can be increased by any number of similar circuit sections, are each divided into subsections A ^ A ₂ , etc. The structure of subsection A ₁ is identical to circuit section A in FIG. 4, it is only "reversed" with respect to the positive and negative bus lines, which of course necessitates the replacement of the npn transistors used there by pnp transistors and vice versa. The structure of the subsection A ₁ is identical to that of the circuit section A in FIG. The subsections B ₁ and ß _; have the same structure as circuit parts A ₁ and A _2. Each of the circuit sections A and B etc. thus contains a pair of detector circuits, one of which is used to determine the highest and the lowest partial object brightness. The photoelectronic components 1 and 51 or 1 and 5Γ are each arranged very close to one another.

The display level Z is also divided into two subsections. The subsection Z ₁ represents a level for displaying the highest, the section Z ₁ a level for displaying the lowest partial object brightness. The switch 7 in the section Z ₁ is controllable by the excitation coils in the subsections A ₁ and S ₁ , the switch 7 'in section Z ₁ , on the other hand, is under the control of the excitation coils in subsections A ₁ and B ₁ .

It is assumed that the CdS photoresistors 1 and S1 arranged in the circuit section A are exposed to the highest illuminance and the CdS photoresistors 1 'and 51' of the circuit section B are exposed to the lowest illuminance. The internal resistance of elements 1 and 51 then has the lowest and the internal resistance of elements 1 'and 51' has the highest value. When the switch 12 is closed, has the the CdS photo-resistor 51-containing circuit A ₁ in the circuit portion A. works in the other in the manner described with reference to FIG. 4 example, the longest switching time, the circuit / I ₁ of the Contains CdS photoresistor 1, has the lowest switching time and otherwise works in the manner described with reference to FIG. The switch 7 is opened and interrupts the charging of the time-determining capacitor connected in series with it, so that the measuring instrument 11 displays a value indicative of the highest partial illuminance.

In circuit section B , the circuit containing the CdS photoresistor 51 'has the shortest and the circuit with the CdS photoresistor 1' has the longest switching time, so that the measuring instrument 11 'displays a value indicative of the lowest partial illuminance.

In the circuits of FIGS. 4 to 9, the changeable Resistors adjustable so that the partial voltage in each circuit section is on a common Voltage level is or such that the trigger voltage, i.e. the response threshold of the Circuit assumes an appropriate value.

In the exemplary embodiments described above the respective measurement result is displayed by a measuring instrument, from the scale of which the value the highest and / or lowest partial illuminance can be read. The pointer deflection of the measuring instrument ends at a point in time that depends on the time constant with the the capacitors in the individual time-determining current branches for measuring the highest or The lowest object brightness can be charged or discharged. The pointer deflection is therefore a function of these time constants. The pointer deflection is therefore greater, the lower the highest partial object brightness is and vice versa. The real one

ίο value of the highest partial object brightness can thus indicated by the height of the pointer deflection.

An RC element is used as the timing element in display stage Z. As is well known, the time course of the charging corresponds to that of an exponential curve with negative Exponents, so that the terminal voltage of the time-determining capacitor increases in the course of Time approaches a limit. This has the consequence that the linearity of the measured value display with increasing Time is getting smaller. It is therefore difficult to determine the value of the highest and lowest partial illuminance quantitatively precisely determined over a large area.

In order to eliminate this disadvantage, the display stage can be equipped with a circuit which generates a linearly increasing voltage. Such circuits are known per se. For example, FIG. 10 shows a so-called bootstrap circuit which satisfies these conditions. In such a bootstrap circuit, the displayed measured value increases linearly with time, as indicated in FIG. 11, in which the time t is plotted on the abscissa axis and the display G of the measuring instrument is plotted on the ordinate axis. The slope of the otherwise linear

running curves can be varied by changing the resistance value of the variable resistor 8 in FIG. The resistance value R should be set so that the entire display range of the instrument can be used in a suitable manner.

From the foregoing description it can be seen that the arrangement is the highest and the lowest partial brightness of a subject is determined automatically. This measurement is carried out statically by only a corresponding group of photosensitive elements on the subject is directed or by on the effective surface of the light-sensitive arranged in a suitable distribution Elements an image of the subject is mapped. Any movements the measuring device are not required. If the device is built into a camera, can the light measurement can be made without any panning of the camera, and even with objects with difficult exposure conditions can be a suitable and the course of the blackening curve of the film material optimal exposure can be achieved without great demands to the dexterity or the effort of the camera user. One receives on this Wise, high quality photographs. When the light measurement and the determination of the respective partial Extreme values of the lighting with a comparison circuit, for example a differential

amplifier is carried out, the influences of disruptive factors, such as fluctuations the supply voltages or fluctuations in the operating point. based on the temperature

14th

decrease in the dependency of the components, greatly reduced. The device works stably and it works does not have any other external influences on the measurement result than the brightness of the object itself. The difference the switching times, i.e. the time spans in which the time-determining current branches are used to determine the highest and lowest partial illuminance coupled circuits respond, is used to control a timer circuit to display the respective measured brightness value. The indicating member, e.g. Capacity of the last-mentioned timer stage is derived from stored voltage, therefore shows a Value that characterizes the respective brightness information. As mentioned, the pointer deflects of the measuring instrument, the lower the partial object brightness and vice versa, and the The actual value of the highest (or lowest) brightness is determined by the position of the pointer marked.

In the following, with reference to FIGS. 12 to 20, a second group of exemplary embodiments described:

In the circuit shown in FIG. 12, the circuit sections A, β, C and Z correspond to the measuring stages for determining the partial brightness A, B and C or the display stage Z in FIG. 1. The circuit section A in FIG. 12 has a CdS Photoresistor 101 connected in series with a variable resistor 192 between positive bus 109 and negative bus 110. The center point α of this series circuit leads to the base of a transistor 103, the emitter of which is connected to the negative bus line 110 via a resistor 104 and the collector of which is connected directly to the positive bus line 109. Another transistor 105, the emitter of which is interconnected with the emitter of the transistor 103, and its collector via the excitation coil 106 for controlling the switch 111 in the circuit section Z with the positive bus 109 and its base with the connection point α between a variable resistor 109 and a? one determining capacitor 108 is in connection, forms together with the first-mentioned transistor 103 a differential amplifier. The RC timing element, which consists of the variable resistor 107 and the capacitor 108, is connected between the positive and negative bus lines. The circuit sections B and C are constructed in the same way and therefore do not need to be described in detail. The charging curve of the capacitor 108 corresponds in its time characteristic to that in the other circuit sections B and C. The circuit portion Z, which is the display step comprises a normally closed switch 111 through the excitation coil 106 of the Schaltungsabschnitlies A and the corresponding exciting coils in the remaining circuit sections can be actuated. It also includes a variable charging resistor 112 and a timing capacitor 113, which are arranged with each other and with the switch 111 in series between the positive and the negative bus. The connection point between the resistor 112 and the capacitor 113 leads to the hit base of a transistor 114, the emitter of which is directly connected to the negative bus line 110 and the collector of which is connected to the positive bus line 109 via a measuring instrument 115. A supply voltage source 117 is also provided.

hen, which is firmly connected with its negative pole to the negative manifold 110 and its positive Pol can be connected to the positive bus 109 via a switch 116.

The following is the mode of operation as shown in FIG

ίο circuit illustrated explained: When the switch is closed, the charging of the capacitor 113. starts same time, a movement start of the pointer of the measuring instrument 111. On the other hand, appears at the connection point α, a voltage Va, which is indicative of the partial illuminance of the effective surface of the CdS photoresistor 101 is exposed. Furthermore, the charging of the capacitor 108 begins. The transistor 103 is initially in its conductive state, while the transistor 105 is initially non-conductive due to the bias voltage occurring at the common emitter resistor 104. The excitation coil 106 is de-energized in this state. The circuit sections B and C operate in the same way.

It is assumed that the CdS photoresistor is exposed to object beams which correspond to the lowest partial object brightness. The voltage Va is then smaller than the corresponding span

voltages in the remaining circuit sections. Therefore, the charging voltage Va of the capacitor reaches the value Va earlier than the corresponding charging voltages in the other circuit sections. Accordingly, transistor 10J5 will be the first

controlled in its conductive state. As a result, the exciting coil 106 is effectively energized first and opens the switch 111, which controls the charging circuit of the capacitor 113 interrupts and thus another pointing movement of the measuring instrument

115 prevented. This remains in a position that has the value of the lowest partial object brightness indicates.

13 shows a further embodiment, which is also used to measure the lowest partial object brightness. In this, the electromechanical switches of FIG. 12, ie the switching device consisting of the excitation coils 106 and the mechanical contact 111, are completely replaced by electronic components. In the circuit section A , a variable resistor 118 and a CdS photoresistor 119 are arranged in series between the positive bus line 109 and the negative bus line 110. The center point α of this series circuit is connected to the base of a transistor 120, the collector of which is connected on the one hand via a resistor 121 mn to the negative bus 110 and on the other hand directly to the base of a transistor 1L26. The emitter of transistor 120 is connected to positive bus 109 via a resistor 122. This resistor 122 simultaneously forms the emitter resistance of a further transistor 123. The collector of the further transistor 123 is directly connected to the negative bus 110, while its base leads to the connection point α between a capacitor 124 and a variable resistor 125. The capacitor 124 and the resistor 125 form an RC timing element that is between

ir S d V si d rr 1 d π d 1 si

d B π K

d el e si A U si K ti 1 u

ind
the
ien.
; seven
yer
iel-

12th
older
of
veer-
ine
-ke
3es
"mt

I ^he
in-

■ jri n-

i ^s "
i.rs
> en.
he

10

the positive and negative bus lines 109 and 110, respectively, are connected. The emitter of the transistor 126 is directly connected to the negative bus line 110, while its collector is connected to the circuit section Z via a resistor 127 on the one hand with the positive bus line 109 and on the other hand via a capacitor 128 acting as a differentiating element. The circuit sections B and C are constructed in the same way and therefore do not need a detailed description. The circuit of the capacitor 128 is dimensioned so that its charging voltage has the same time curve as the corresponding capacitors of the circuit sections B and C.

The switching step Z is structured as follows: Decoupling resistors 128 ', 129' and 130 'are connected in series with the aforementioned capacitor 128 and corresponding capacitors 129 and 130, which are assigned to the remaining circuit sections B and C that act as detectors. These decoupling resistors are connected to one another with their respective other earth and to the control electrode of a thyristor 132 and to a resistor 131 connected in parallel to the control path of the thyristor. The cathode of the thyristor 132 is also directly connected to the negative bus line at the other end of the resistor 131. The anode of the thyristor 132 is connected on the one hand with a resistor 133 to the positive bus line 109 and on the other hand directly to the B; iiis of a transistor 134, whose E titter is connected to the positive bus line 109 and its collector via a collector resistor 135 to the negative bus line 110 connected. In addition, a direct connection leads from the collector of the transistor 134 to the base of a switching transistor 136, the emitter of which is connected directly to the positive bus line 109 and its collector to the variable resistor 112. The rest of the structure of the circuit section Z is identical to the circuit part of the same name from FIG. 12.

The following is the effectiveness of this arrangement described:

When the switch 116 is closed, a partial voltage Va is generated across the variable resistor 118 and the corresponding resistors of the other circuit stages, by means of which the transistor 120 is controlled into its conductive state. The transistor 126, which is driven by the collector potential of the transistor 120, is also in its conductive state. Thus, the capacitor 1.28 of the circuit section Z is practically at the potential of the negative bus line 110. The same applies to the capacitors 129 and 130, which are also practically short-circuited via the Ete ktorstufe B and C. In this state, no signal is generated at the resistor 131. The thyristor 132 is consequently in its non-ignited state. The transistor 134 is also non-conductive, while the collector-emitter path of the switching transistor 136 is conductive with low resistance, so that the capacitor 1.13 is dissolved and the display instrument 115 is gradually driven by the collector current of the transistor 114. This collector current increases with the increasing charging voltage of its base emitter! connect parallel-sounding capacitor 113. On the other hand, after the switch 116 is closed, the time-determining capacitor 124 in detector stage A and the corresponding capacitors in the other detector stages B and C are charged so that their charging voltages Vd gradually increase. It is assumed that the CdS photoresistor 1X9 assigned to the circuit section A is exposed to an illumination intensity which corresponds to the lowest partial object brightness. The partial voltage Va is then lower than the corresponding partial voltage in the other circuit sections B and C, and the L-i voltage Va reaches the value of this partial voltage Va earliest and has the effect that the transistor 123 is controlled into its conductive state. The bias voltage generated in the common emitter resistor 122 increases until the transistor 120 reaches its non-conductive state and thus also switches the transistor 126, the control voltage of which is formed by the KoJiektorsvoltage of the transistor 120, from its conductive to its non-conductive state. The short circuit of the capacitor 128 is thus canceled, so that it can be charged from the positive bus line 109 via the resistor 127. The corresponding charging pulse reaches the control electrode of the thyristor 132, which is triggered by this control pulse. The transistor 134 is also switched on and in turn controls the switching transistor 136, which corresponds to the switch 111 in FIG. 12, to its non-conductive state. This interrupts the charging of the capacitor 113, so that the measuring instrument 115 displays a measured value which corresponds to the lowest partial object brightness.

In the exemplary embodiments described so far, each of the circuit sections A to C serving as detector stages for determining partial brightness values has an individual timing element, the time-dependent voltage of which is compared with a reference voltage. In the following, some further exemplary embodiments are described which dispense with such individual timing elements and have a common timing element which simultaneously serves as a timer for the display stage.

In Fig. 14 an embodiment modified in this way is shown. It is an arrangement for measuring the highest partial object brightness. The circuit elements which are provided with the same reference numerals as the corresponding circuit elements in the exemplary embodiments described above no longer require a detailed description. In circuit section A , the connection point α between a variable resistor 118 and a CdS photoresistor 119 leads to the base of transistor 103. The same applies to circuit sections B and C. The base of transistor 105 and the corresponding transistors in the other circuit sections are with one another and connected to the connection point between the variable resistor 112 and the capacitor 113 in the circuit section Z.

The mode of operation of this arrangement is described below: When the switch 116 is closed, partial voltages are generated at the connection points a, b and c between the variable resistors and the associated CdS photoresistors in the detector stages A, B and C, respectively

609 683/312

// f

18th

Values of the illuminance prevailing on the effective surfaces of the respective CdS photoresistors is inversely proportional. It is assumed that the .CdS photoresistor 119 assigned to the detector stage A is exposed to the greatest illuminance. The voltage appearing at node a is therefore the lowest. On the other hand, when the switch 116 closes, the charging of the capacitor 1.13 begins in the timer of the display stage Z, so that the charging voltage of this capacitor 113 increases over time. This increasing charge voltage is fed to the respective second transistors, such as transistor 105, of the individual differential amplifiers in circuit sections A to B as input voltage. Since the voltage at the node α is the lowest partial voltage, the bias voltage generated at the common emitter resistor 104 for the transistor 105 is lower than the bias voltages of the corresponding transistors in the other detector stages. Therefore, the transistor 105 is first controlled into its conductive state by the charging voltage of the capacitor 113, so that the excitation coil 106 of the electromagnetic switching device arranged in its collector circuit for actuating the switch 111 is the first to be effectively excited. As a result of this excitation, the switch 111 in the display stage Z is opened and the display of the measuring instrument 115 is accordingly fixed in the position characterizing the highest partial object brightness, so that this value can be read off.

FIG. 15 shows a device for determining the highest partial object holiness, in which the mechanical switching means, as in the arrangement according to FIG. 13, are completely replaced by electronic components. Those components which are provided with the same reference numerals as in FIG. 13 also exercise the same function and are therefore not explained in more detail. In the circuit section A , the connection point between the CdS photoresistor 101 and the variable resistor 102 is connected to the base of the transistor 120. The design of the circuit sections B and C is identical to that of the circuit section A. In the circuit section Z, which represents the display stage, the connection point between the thyristor 132 and the resistor 133 leads to the base of a transistor 137, its collector with the positive bus 109 and its emitter with a resistor 138 and the base of a transistor 139 for current control connected is. The other terminal end of resistor 138 is connected to the negative bus as well as the emitter of transistor 139. The collector of the transistor 139 is connected to a zei'-determining capacitor 140 and the base of a transistor 141, the other terminal end of the capacitor 140 and the emitter of the transistor 141 are connected to the positive bus line. A measuring instrument 142, which is connected to the negative bus line 110, is inserted into the collector circuit of the transistor 141. The base of the transistor 123 is interconnected with the base electrodes of the corresponding transistors in the other circuit sections B and C and with the connection point between the capacitor 140 and the transistor 139. The operation of the circuit shown in FIG. 15 is described below. It is assumed again that the CdS photoresistor arranged in the circuit section A is exposed to the highest illuminance. When the switch 116 is closed, the terminal voltage occurring at the connection terminals of the CdS photoresistor 101 is therefore lower than the corresponding voltages in the other switching circuits.

management sections. The thyristor 132 in the circuit section Z is initially, as in the arrangement according to FIG. 13, in its non-conductive state, so that the transistor 137 is conductive and the transistor is also conductive. The timing capacitor 140 is therefore charged. Its charging voltage, which increases as a result, is applied to the base electrodes of the respective second transistors, for example the transistor 123 of the individual differential amplifiers. The transistor 123 in the circuit

Section A is the first to be switched to its conductive state and in turn switches transistor 120 to its non-conductive state. Otherwise, the further functional sequence up to the point in time at which the thyristor 132 is triggered is the same as that.

which has already been described with reference to FIG. When the thyristor 132 is fired, it controls the Transistors 137 and 139 in their non-conductive state, so that the charging of the capacitor 140 is terminated. The meter 142 shows a value that is the highest partial object brightness is equivalent to.

16 shows an exemplary embodiment for the determination the lowest partial object brightness, at which the timer part of the display level Z the time

replaced members which are provided individually in the individual detector stages A, B and C in the arrangement according to FIG. Otherwise the arrangement shown in FIG. 16 corresponds to the arrangement according to FIG. 14, with the difference that the CdS photovoltaic

resistors and the variable resistors connected in series with one another are interchanged are. The mode of operation of the arrangement shown in FIG. 16 therefore does not require any further explanation more.

Fig. 17 shows a further embodiment Arrangement for determining the lowest partial object brightness, both a single timer circuit, the transistor 139 for current control and the time-determining capacitor 140 in the display stage Z, which replaces the plurality of timing elements required in the arrangement according to FIG. On the other hand, this embodiment largely corresponds to the embodiment according to FIG. 15, with the difference that the CdS photoresistors and those connected in series with them can be changed Resistors are interchanged. The components with the same reference numerals as in Fig. 15 also perform the same function. The mode of operation according to the arrangement After all this, FIG. 17 no longer needs a precise explanation.

In the exemplary embodiments explained above with reference to FIGS. 12 to 17, the electrical Sampling and measurement made by voltage changes resulting from the charging voltage of Timers are derived. The arrangement can, however, also be implemented in such a way that these voltage changes are derived from discharge curves of timing elements.

ti si w F st

te KB do nt w sc

dt D in tu dt

m
-egg
ber
he
n if iie
ilildd,
or
no-
away.
rs-
%

e.
ie
i- Ö η

be directed.

FIG. 1B shows a corresponding exemplary embodiment which is used to determine the highest partial otajectivity. The circuit sections A, B and C each have the same structure as the circuit sections of the same name in FIG negative manifold 110 is arranged. The connection point of this series connection leads to the rest side 1 of a changeover switch 145, the movable center contact of which is connected to the negative bus line 110 via a time-determining capacitor 146. The working side m of the changeover switch 145 leads to the base of a transistor 114. A contact 147, which is open in the idle state and is part of an electromagnetic switching device with excitation coils, for example 106, similar to the individual circuit sections A and B is. and which is closed when one of these coils is effectively energized is connected in series with a variable resistor 148 between the base of transistor 114 and negative bus 110. The base electrodes of the respective second transistors in the differential amplifiers of the individual circuit sections A and B are connected to one another and to the working side m and thus the base of the transistor 114.

When the switch 116 for the supply voltage source 117 is closed, a partial voltage occurs at the dividing point of the voltage divider formed from the variable resistor 143 and the resistor 144 in the circuit section Z. at which the capacitor 146 is charged to a predetermined voltage. As soon as the movable contact piece of the switch 145 is switched from the contact side / to the contact parts m , the voltage stored in the capacitor 146 is applied to the base of the transistor 114 and to the base of each of the second transistors, e.g. B. 105 of the individual differential amplifiers.

The display instrument 115 immediately deflects up to a maximum value which corresponds to the charging voltage present at that moment. The transistor 105 and the corresponding transistors in the other circuit sections are simultaneously controlled into their conductive state and the excitation coils arranged in their collector circuit, e.g. 106, are effectively excited if the stored voltage mentioned is such that it is sufficiently higher than that Partial voltages generated by the CdS photoresistors at the voltage distribution points α etc. Through the effective excitation of the electromagnetic switching device via the excitation coils. eg 106, the contact 147 is actuated and closes a discharge circuit for the capacitor 146. As a result, the pointer of the measuring instrument 115 gradually returns towards its rest position in accordance with the decreasing charge voltage of the capacitor 146. In the course of the discharge of the capacitor 146, the transistor in the second stage of the differential amplifier whose associated CdS photoresistor generates the highest partial voltage is the first to be switched to its non-conductive state. B. 106. However, switch 147 remains closed as long as any of the other coils are still energized.

The capacitor 146 continues to discharge until the last excitation coil is de-energized and the Switch 147 opens. This also stops the backward movement of the pointer of the measuring instrument 115, so that this indicates the brightness value which corresponds to the opening time of the switch 147.

ίο This brightness value corresponds to the highest partial Object brightness, as the mentioned point in time is controlled by that CdS photoresistor, which is most heavily lit.

When in the arrangement shown in FIG

each CdS photoresistor swapped with the variable resistor connected in series with it an arrangement for determining the lowest partial object brightness is obtained. This relationship corresponds to that between the arrangement

ίο according to Fig. 14 and the arrangement according to Fig. 16. so that a detailed description of these variants is not necessary.

As a further exemplary embodiment, FIG. 19 shows an arrangement for determining the highest partial object brightness, in which the mechanical switching devices of the exemplary embodiment shown in FIG. 19 are completely replaced by electronic switching means. Circuit elements with the same effect are again provided with the same reference numerals as in FIG. 18; their more detailed description is unnecessary. In circuit section A , the collector of transistor 105 is connected to a resistor 149 and to the base of a transistor 150, the emitter of which is connected to the other terminal end of the resistor 149 to the positive bus line 109 and its collector to the negative bus line 110 via a resistor 151 communicates. The circuit section ß corresponds in its structure to the circuit section A.

In the circuit section Z, one terminal end of a variable resistor 155 for discharging the capacitor 146 is connected to the connection point between the working side m of the switch 145 and the base of the transistor 114, the other terminal end of the variable resistor 155 is connected to the interconnected collectors of two switching transistors 152 and 153, the emitters of which are connected to the negative bus 110 and the base electrodes of which are connected to the collector of the transistor 150 in the circuit section A and the collector of the corresponding transistor in the circuit section B , respectively.

When in the circuit arrangement shown in FIG the switch 116 is closed, there are the transistors, e.g. 105, each of the form the second stage of the differential amplifier in each circuit section, in its non-conductive State as was explained in the description of the circuit according to FIG. The transistor 150 and the corresponding transistors in the remaining circuit sections with their bases connected to the collector the second stage, e.g. 105, of the differential amplifier are also non-conductive, so that the transistors 152 and 153 in the circuit section Z, which are from the transistors 105 and 150 are driven, are also non-conductive. This switching state corresponds to the open one State of switch 147 in Fig. 18. If the switch

switch 145 for measuring the object brightness is thrown from its normally closed contact side / to its normally open contact side m , the capacitor 146 is charged to a relatively high voltage. This voltage is applied as a control voltage to transistor 105 in circuit section A and to the corresponding transistors in the other circuit sections and controls them into their conductive state. In this way, the transistors 150, etc. and the transistors 152 and 153 in the circuit section Z are controlled in their conductive state. In this way, the discharge of the capacitor 146 begins via the variable resistor 155. This discharge continues until. As in the exemplary embodiment according to FIG. 18, the transistor 105 in the circuit section A, whose CdS photoresistor may be exposed to the highest partial object brightness, and which therefore causes the lowest bias voltage via dt η transistor 103 at the common emitterw'di -Mild 104 ι. was the last to succeed in its non-conductive state! uii thus also causes the transistor 150 downstream of it to be blocked. The switching transistor 152, which was conductive up to this point in time, is also blocked and interrupts the discharge circuit for the capacitor 146. The measuring instrument 115 indicates the highest partial object brightness prevailing at this point in time.

The last-described exemplary embodiments represent arrangements with which either the highest or the lowest partial object brightness is measured. These arrangements can also be combined with one another in such a way that both the highest and the lowest object brightness can be measured with one and the same device. Such a combination is shown in FIG. 20: The circuit sections A. and Z correspond to the circuit sections A and Z in FIG. 15. The circuit sections A ₂ and Z ₂ correspond to the circuit sections A and Z in FIG In practice, a large number of such pairs of stages are provided, each of which has a detector for the highest and a detector for the lowest partial brightness, the structure of which corresponds to the circuit stages A ₁ and A ₂ , respectively, and which each have a pair of CdS photoresistors which are arranged in close proximity to one another in the relevant areas of the measuring field, so that the information about the highest and lowest partial brightness of a photographed object are displayed _{simultaneously by the corresponding measuring instruments in display levels Z 1} and Z _1. The mode of operation of this arrangement does not require any further description, since it results from the combination of the arrangements already described.

In the following, a third group of exemplary embodiments will be described with reference to FIGS will. These are arrangements that simultaneously measure both the highest and the highest enable even the lowest partial illuminance. The above-described exemplary embodiment c were used to measure either the highest or the lowest partial illuminance determined or they set, such as the exemplary embodiment according to FIG. 20, a Combination of both arrangements represent that at the same time <. itu measurement μn \ (»hl the highest as well as the lowest illuminance allowed. The group of exemplary embodiments described below also allow both the highest and the lowest to be measured at the same time Illuminance. In these arrangements for the simultaneous determination of both the highest and The two corresponding circuit parts work even with the lowest partial illuminance completely independent of each other. The light-sensitive elements of the individual circuit parts must be arranged in a suitable relationship to the measurement field. To determine the highest and or lowest Brightness of an object must be a multitude of point measurement t η can be carried out in which the individual measuring points have the smallest possible extent, so that the extreme values actually occur the illuminance can be determined. As with the last-mentioned combinations, however, for everyone Measuring point two light-sensitive elements have to be used, the measuring surface of each one becomes d: e Measurement point enlarged in a way that can have a detrimental effect on accuracy. About it In addition, the arrangement of two light-sensitive elements per measuring point means a large one Effort and requires a complicated mechanical and circuit structure.

The following exemplary embodiments avoid these disadvantages. They have light-sensitive elements for measuring the partial object brightness appropriately distributed over the measuring field. Electric each of these light-sensitive elements is connected in series with a resistor. Each of the in Series-connected elements, provides information that is necessary for those at the location of the light-sensitive element prevailing partial brightness is characteristic. This information is separated corresponding detector circuits to determine the respective higher or lower illuminance fed. The highest or lowest value of the output signal · - 'of the individual detector circuits denotes the sought extreme values of the illuminance and is displayed in a corresponding display level.

In contrast to the above-mentioned combinations, there are two photosensitive elements needed - only as many photosensitive elements used as There are measuring points, and each photosensitive element delivers together with the one with it in so series connected resistor information to detector circuits of different kinds.

Such an arrangement is shown schematically in FIG. There are photosensitive elements, e.g. B. CdS photoresistors 201,201 ', ... are provided. those with resistance elements 202, 202,. . are connected in series. The light-sensitive elements 201, 201 '.... are connected to detector circuits A _x , B _x ,. The resistance elements 202, 202 ', ... are connected to the detector circuits A ₂ , B ₂ for measuring the lower illuminance, which in turn control a corresponding display stage W. The detector circuit A _x for measuring the higher illuminance and the detector circuit A ₂ for measuring the lower illuminance

i r r 1 c c ι ι c c \ r

s'n
ur
us
Ice
tie
Ii in
et

ghl
in

f "
• te

έ- nch
ir it-

jn
e-
;in
ch

ia-Ie-
: hint

in ieen

domestic / egg
so
rie
iliin
ie-

ia te,
: n,
hey

lene

together a circuit section A. Correspondingly, the detector _{circuits B 1} and B _{2 form} a circuit section B. Of course, such circuit sections are provided in such a large number that overall a sufficiently large group of measuring points is detected in the measuring field. The other circuit sections, which consist of a detector circuit for the higher and a detector circuit for the lower illuminance. are indicated by the circuit block shown in dashed lines. The individual light-sensitive elements and resistance elements connected in series with them can - as indicated in FIG. 22 - be interchanged. The decisive factor for this is the characteristic mode of operation of the detector circuits used in each case, with which the individual elements are coupled.

FIG. 23 shows an embodiment which corresponds to the block diagram of FIG. The components with the same effect are again provided with the same reference numerals. The detector circuit A ₁ contains the variable resistor 202 and the CdS photoresistor 201 for point-by-point measurement of the object brightness. Both elements are connected in series with one another between a positive bus line 215 and a negative bus line 216. The center point α of this series connection leads to the base of a transistor 203, the collector of which is directly connected to the positive bus line 215 and the emitter of which is connected to a resistor 204 and the emitter of a transistor 205. The other end of resistor 204 is connected to negative bus 216. An excitation winding 206 of an electromagnetic switching device is inserted into the crater circuit of the transistor 205 and is used to actuate the switch 217 in the display stage Z , which is designed as a break contact. The base of the transistor 205 is connected to the connection point between a variable resistor 207 and a time-determining capacitor 208, which bumps are arranged in series between the positive bus line 215 and the negative bus line 216. The two transistors 203 and 205 form a differential amplifier. In the detector circuit A ₁ , the center point α of the series circuit consisting of the variable resistor 202 and the CdS photoresistor 201 is connected to the base of a transistor 209, the collector of which is connected to the negative bus line 216 and its emitter to a resistor 210 and the Emitter of a transistor 211 is connected. The other connection of the resistor

210 is connected to the positive manifold 215. An excitation coil 212 of an electromagnetic switching device for actuating the switch 224, which is designed as a break contact and which is arranged in the display stage W , is inserted into the collector circuit of the transistor. The base of the transistor

211 leads to the connection point between a variable resistor 214 and a time-determining one Capacitor 213, which acts as a timer in series between the positive bus 215 and the negative manifold 216 are connected. The two transistors 209 and 211 form one further differential amplifier.

The circuit section B has the same structure as the circuit section.-4 In the display stage Z 'is the break contact 217, which is in the aforementioned manner under the control of the excitation coil 206 and a corresponding excitation coil in the circuit section B , with a variable resistor 218 and a timing capacitor 219 connected in series between positive bus 215 and negative bus 216. The connection point between the variable resistor 218 and the capacitor 219 leads to the base of a transistor 220, the emitter of which is directly connected to the negative bus line 216 and the collector of which is connected to the positive bus line 215 via a measuring instrument 221. A supply voltage source 223 has its negative pole connected to the negative bus line 216, while its positive pole can be connected to the positive bus line 215 by a switch 222. The display stage W has a similar structure: The normally closed contact 224, which is under the control influence of the excitation coil 212 of the circuit section A and a corresponding excitation coil of the circuit section B , has a variable resistor 225 and a time-determining capacitor 226 in series between the positive bus line 215 and the negative bus line 216 switched. The connection point between the variable resistor 225 and the capacitor 226 leads to the base of a transistor 227, the emitter of which is directly connected to the positive bus line 215 and the collector of which is connected to the negative bus line 216 via a measuring instrument 228. Each timer stage in each of the detector circuits for determining the respective higher illuminance and each timer stage in the detector circuits for determining the respective lower illuminance have the same charging characteristic. The mode of operation of the embodiment shown in FIG. 23 is described below: When the switch 222 is closed, the charging of the time-determining capacitors 219 and 226 begins in the display stages Z 'and W. As the charging voltage of the capacitors increases, so does the collector current with them connected transistors 220 and 227. The deflection of the measuring instruments 221 and 228 inserted into the collector circuits increases accordingly. It is assumed that the CdS photoresistor 201 'assigned to the circuit section B measures the lowest brightness.

Power is also effective in the RC time Glienicke which the detector circuits so that aud the capacitors 208 are charged 213 ... at the voltage dividing point of the of the CdS photo resistor 201 and the variable resistance α was 202 serial connection formed will see a <partial voltage , by means of which the transistors 203 and 20i are controlled into their conductive state. Accordingly, transistors connected to the voltage divider point b are conductive in the circuit section B du. The transistors 205, 211, .... the di <each second stage of the differential amplifier images, however, are initially non-conductive because the terminals

voltage of the capacitors 208, 213 according to the

Switching on the voltage source 223 is initially practically zero.

Since the CdS photoresistor 2Oi assigned to the circuit section A has the highest lighting intensity. exposed and therefore the lowest

Has internal resistance, the voltage Va occurring at the node α is lower than the voltage at the node b in the circuit section B. Therefore, the charging voltage of the capacitor 208 first reaches the value Va and controls the transistor 205 in its conductive state, so that the Coil 206 arranged in its collector circuit is effectively excited and the normally closed contact 217 opens. This interrupts the charging circuit of the capacitor 219 and the measuring instrument 221 displays a value. which corresponds to the highest partial illuminance at this point in time.

The display of the measuring instrument 221 is made by the excitation of the exciter coils in the other detector circuits for measuring the highest illuminance is not affected, since the switch 217 is already open.

Since the CdS photoresistor 201 'associated with the circuit section B is exposed to the lowest illuminance and therefore has the highest internal resistance, the voltage Vb at the dividing point b is relatively the highest. Therefore, the capacitor 213 'is the first to reach a charging voltage equal to this value Vb. It controls the transistor 21Γ in its conductive state and thus causes the excitation of the coil 212 '. whereby the normally closed contact 224 in the display level W is opened. As a result, the charging of the time-determining capacitor 226 ends and the display of the measuring instrument 228 is fixed at a value which is characteristic of the lowest partial illuminance prevailing at this point in time.

In this way, the excitation coil 206 is activated in the circuit section A for measuring the highest and the excitation coil 212 ' in the circuit section B for measuring the lowest partial illuminance, so that the corresponding measured values can be displayed simultaneously by the measuring instruments 221 and 228.

The circuit shown in FIG. 24 represents a variant of the exemplary embodiment according to FIG. 23, in of the timers in the individual detector circuits are replaced by common timers, which are already present in the display stages Wund Z ' Timers are formed. This results in an extremely advantageous simplification of the overall circuit. Otherwise, the embodiment according to F.g. 24 largely to that shown in FIG Exemplary embodiment. Components with the same effect are provided with the same reference numerals as there. A detailed description is therefore unnecessary.

The mode of operation also essentially corresponds to the function of the exemplary embodiment shown in FIG. 23 with the exception of the fact that the charging voltage of the time-determining capacitor 219 in the display stage Z 'is used in all detector circuits (A _} , B ₁ , ...) for measuring the highest illuminance is supplied as a control voltage and the charging voltage of the capacitor 226 in the display stage W is used jointly by all the other detector circuits as a control voltage or comparison voltage. If it is assumed again that the CdS photoresistor 201 is exposed to the highest and the photoresistor 201 'to the lowest illuminance, the detector circuit A _x in the circuit section A and the detector circuit Β- in the circuit section B are activated first and operate via the corresponding excitation coils, the contacts 217 and 224. The display level Z 'and the display level W again indicate the highest and lowest partial illuminance at the same time. In addition to the great savings in components and a correspondingly simplified circuit, the embodiment according to FIG. 24 according to the circuit according to FIG. 23 has the further advantage that the setting and adjustment effort is greatly reduced.

As has already been mentioned in connection with the block diagram in FIG. 21, in the exemplary embodiments according to FIGS. 23 and 24 the CdS photoresistors and those connected in series with them Resistances are interchanged. Then the detector circuits for the higher illuminance replaced by the detector circuits for the lower illuminance and vice versa. The same applies to the two display levels.

FIG. 25 shows an exemplary embodiment which corresponds to the block diagram of FIG. 22 and in which the change in voltage when discharging a time-

use the determining capacitor as the measuring voltage 1. The detector circuit A _x in the circuit section A has a CdS photoresistor 231 and a variable resistor 232, which are connected in series with one another and the positive bus line 215 and the negative bus line 216 are connected. The center point a of this series connection leads to the normally closed contact side / a changeover switch 233, the movable contact piece of which is connected to the negative bus line 216 via a time-determining capacitor 234. The operational contact side m is connected to a variable resistor 235 for setting the discharge line constant and to the base of a transistor 236. The other connection of the variable resistor 235 leads to the negative bus line 216. The collector of the transistor

236 is via an electromagnetic excitation coil

237 connected to the positive manifold 215. The excitation coil 237 is part of an electromagnetic switching device for actuating a switch 253 in the display stage Z. The emitter dc transistor 236 is connected to a resistor 238 and to the emitter of a transistor 239. The other end of the resistor 238 is connected to the negative bus line 216. The collector of the transistor 239 is connected to the positive bus line 215 via a resistor 240, so that the two transistors 236 and 239 form a Schmitt trigger circuit. In the detector circuit A _{2 of} the circuit section A , the center point α is connected to the normally closed contact side / 'of a changeover switch 243. The movable contact piece of this switch is connected to the positive bus line 215 via a time-determining capacitor 244, while its normally open contact side rri is connected to a variable resistor 245 for setting the discharge time constant and to the base of a transistor 246. The other end of the variable resistor 245 is connected to the positive manifold 215 in connection. The collector of the transistor 246 is connected to the negative bus line 216 via an excitation coil 247. This excitation coil 247 is part of a

electromagnetic switching device for actuating a switch 254 in the display level W. The emitter of transistor 246 is on the one hand directly connected to the emitter of a transistor 249 and also via an opposing land 248 to the positive bus line 215, so that the transistors 246 and 249 a further Schmitt -Trigger circuit form. The circuit section B has the same structure as the circuit section A and is not shown in detail. The normally open contact 253 in the display stage Z \, which can be actuated by the excitation of the coil 237 in the detector circuit A, and by the corresponding exciter coils in the other detector circuits to determine the highest illuminance, has a variable resistor 218 and a time-determining capacitor 219 connected in series between positive manifold 215 and negative manifold 216. Otherwise, the arrangement is the same as that of the circuit shown in FIG. Correspondingly, in the display stage W, the normally closed contact 254 is actuated by the exciter coils 247 or the corresponding exciter coils in the other detector circuits to measure the lowest illuminance, with a variable resistor 218 'and a time-determining capacitor 219' connected in series between the positive bus line 215 and the negative manifold 116 are arranged. Otherwise, the arrangement corresponds to the display ' level Z'.

; The circuit shown in Fig. 25 operates in the following manner: Assume that the CdS photoresistor 231 associated with the circuit section A is the photoresistor "on des-". sen effective surface the highest lighting; strong prevails. When switch 222 is closed, a partial voltage Va appears at point a. Compared to the corresponding partial voltages in the other circuit sections, this voltage has the highest value, since the internal resistance and thus the terminal voltage of photoresistor 231 are lowest. Accordingly, the timing capacitor 244 is charged to the highest voltage and the timing capacitor 244 is charged to the lowest voltage.

If the changeover switches 233 and 243 are turned over at the same time from their normally closed contact side / or Γ to their working side m or m , the two Schmitt trigger circuits toggle. which are provided in each circuit section in their conductive state, so that the excitation coils 237 and 247 arranged in the collector circuits of the transistors 236 and 246 are effectively excited and the switches 253 and 254 in the display stages Z and W close at the same time. The charging of the time-determining capacitors 219 and 219 'and the needles of the measuring instruments 221 thus begin and begin to deflect.

At the same time, the time-determining capacitors 234 and 244 begin to discharge via the variable resistors 235 and 245, respectively. The charging voltage of these capacitors decreases over time in accordance with the effective time constants. The initial charging voltage of the capacitor 234 in the detector circuit A is, as required, higher than the corresponding charging voltage in one of the other detector circuits for determining the highest illuminance. As a result, the Schmitt trigger circuit, consisting of transistors 236 and 239, is the last to switch back to its idle state and thus causes contact 253 to open via excitation coil 237. This contact opening separates the charging circuit of time-determining capacitor 219, so that the opening time existing instantaneous value of the charging voltage is fixed.

The pointer deflection of the measuring instrument 221 o is therefore also fixed and indicates the highest partial object brightness prevailing at this point in time. The initial charging voltage of the capacitor 244 in the detector circuit A ₂ is too low in this case and the capacitor is accordingly discharged too quickly to have any noticeable influence in the determination of the lowest partial object brightness.

It is assumed that the photosensitive element associated with the circuit section B is exposed to the lowest illuminance. The relatively lowest partial voltage then arises at the circuit point b corresponding to point u , since the internal resistance of the CdS photoresistor has the relatively highest value. The terminal voltage on the CdS photoresistor is therefore also relatively the highest. The charging voltage of the time-determining capacitor 244 'in the detector circuit /? ,, which is charged in parallel to the CdS photoresistor 231' is accordingly the highest, so that the associated Schmitt trigger circuit is the last to return to its starting position and the excitation coil in the detector circuit R ₂ is the last to be de-energized and the switch 254 in the display stage W opens. The measuring instrument 221 'is fixed at a display value which characterizes the lowest partial illuminance. The time-determining capacitor 234 'in the detector circuit B ₁ has such a low charging voltage that it is completely discharged in a comparatively short time and cannot influence the measurement of the highest partial illuminance.

FIG. 26 shows an embodiment which corresponds to the circuit according to FIG. 24, but in which the electromechanical components have been completely replaced by electronic components. In the detector circuit A ₁ of circuit section A , the center point α of the series circuit consisting of the CdS photoresistor 231 and the variable resistor 232 is connected to the base of a transistor, the collector of which is connected to a resistor 261 and the base of a transistor 264. Its emitter is connected to a resistor 262 and to the emitter of a transistor 263. The collector of transistor 263, the other end of resistor 261, and the emitter of transistor 264 are connected to negative bus 216. The second terminal of the resistor 262 is connected to the positive bus line 215. The two transistors 260 and 263 together form a differential amplifier. The base of the transistor 263 is connected to a connection of a time-determining capacitor 282 in the display stage Z. and the collector of the transistor 264 is connected to one terminal of serving as a differentiator Kone ₅ densators 272 in the display stage Z. The mentioned center point α leads in the detector circuit A ₂ to the base of a transistor 266, its collector with a resistor 267 and with the base

of a transistor 270 is connected. Its emitter is connected to a resistor 263 and the emitter of a transistor 269, the collector of which, like the other terminal of the resistor 267, is connected to the positive bus. The other end of resistor 268 and the collector of transistor 270 are connected to negative bus 216. The emitter of the transistor 270 is also connected to the positive bus line via a resistor 271. The two transistors 266 and 269 form a differential amplifier. The base of the transistor 269 is connected to one terminal of a time-determining capacitor 295 in the display stage W , while the emitter of the transistor 270 is connected to one terminal of a capacitor 285 serving as a differentiating element in the display stage W. The structure of circuit section B is identical to that of circuit section A. In the display stage / ', decoupling resistors 274 and 275 connect the other connections of the two capacitors 272 and 273 serving as differentiators to the control electrode of a thyristor 277. The thyristor 277 can therefore be controlled by the output signal of the detector circuits A _x and B _2. The cathode of the thyristor 277 is directly connected to the negative bus line 216. Its control path is bridged by a resistor 276. Its anode is connected on the one hand to the base of a transistor 279 and on the other hand via a resistor 278 to the positive bus. A connection leads from the collector of the transistor 279 to the positive bus line 215, while its emitter is connected on the one hand to the base of a transistor 281 for current control and on the other hand via a resistor 280 to the negative bus line 216. The emitter of transistor 281 is also directly connected to the negative bus line. Its collector is connected to the Zeitbesrimmendcpi capacitor 282 and the base of a transistor 283 in connection. The other connection of this capacitor 282 and the emitter of the transistor 283 are connected to the positive bus, the collector of the transistor 283 is connected via a measuring instrument 284 to the negative bus. The connection point between the transistor 281 and the capacitor 282 leads to the base of the transistor 263 in the detector circuit A ₁ and to the base of the corresponding transistor in the detector circuit B ₁ . In the display stage W , decoupling resistors 287 and 288 connect the capacitors 285 and 286, which serve as differentiators, to the control electrode of a thyristor 290. The decoupling resistors enable the output signals of the detector circuits A ₂ and B ₂ to be transmitted to this thyristor 290. The cathode of the thyristor 290 is directly connected to negative manifold 216. Its control path is bridged by a resistor 289. Its anode is connected on the one hand to the base of a transistor 292 and on the other hand via a resistor 291 to the positive bus. The emitter of transistor 292 is connected to negative bus 216. Its collector is connected to the base of a transistor 294 for current control and, via a resistor 293, to the positive bus line 215, to which the transistor 294 is also connected. The collector of this transistor 294 is connected to a time-determining capacitor 295 and the base of a transistor 296. The other end of the capacitor 295 and the emitter of the transistor 296 are connected to the negative bus line 216, and a measuring instrument 297 is inserted into the collector circuit of the transistor 296. The connection point between the transistor 294 and the capacitor 295 leads to the base of the transistor 269 in the detector circuit A ₂ and to the base of the corresponding transistor in the detector circuit B ₂ .

The mode of operation of the circuit shown in FIG. 26 will now be described: When the switch 222 is closed, a partial voltage appears at the node α in the circuit section A , by means of which the transistors 2 (SO and 266 are controlled into their conducting state) the transistors 263 and 269 remain in their non-conductive state and the transistors 264 and 270 also become conductive. In the circuit section B, the corresponding transistors are influenced in the same way.

As a result, in the two display stages Z ' and W , the connections of the capacitors 272, 273, 285 and 286 facing the inputs are practically at the potential of the negative bus line 216 so that no signal is fed to the control electrodes of the thyristors 277 and 290 and they are switched off State remain. The transistors 279 and 292, like the transistors 281 and 294, are therefore in their conductive state. The time-determining capacitors 282 and 295 begin to charge, and the needles of measuring instruments 284 and 297 begin to deflect. This pointer deflection increases continuously as the terminal voltages of capacitors 282 and 295 rise. The eye-low voltage of the time-determining capacitor 282 is applied as a control voltage to the base electrode η of the respective second transistors of the associated differential amplifiers in the detector circuits A ₁ and B ₁ , the voltage of the time-determining capacitor 295 forms the control voltage for the corresponding transistors in the detector circuits A ₂ and B ₂ and serve as a comparison voltage for the differential amplifier.

It is assumed again that the CdS photoresistor 231 assigned to circuit section A is exposed to the greatest brightness, so that its terminal voltage has the lowest value relative to the corresponding voltages in the other circuit sections. As a result, the transistor 263 in the detector circuit A _{1 is switched} to its conductive state at an earlier point in time than the comparable transistors in the other detector circuits in order to determine the highest partial illuminance. The transistor 263 controls the transistor 260 in its non-conductive state. As a result, the transistor 264 is also controlled in its non-conductive state and the short circuit of the capacitor 272 serving as a differentiating element, which up to this point was practically at the potential of the negative bus, is canceled. The voltage which then occurs on the capacitor 272 reaches the control electrode of the thyristor 277 and ignites it. Thvristor 277 in turn controls the

s is

279 and this the transistor 281 in his

• Sliding state. This will make the charging

"Vreis for the condenser ml are separated and f ° measuring instrument 284 is fixed to a measured value

• the highest prevailing at this point in time rti'plle indicates object brightness.

^P Now, it is assumed that the scarf section A zugeorcnete CdS photo resistor R "i is the lowest BeleuehtungsstE was exposed jke, hatred between the Schaltun ippunkt α and olive manifold 216 prevailing voltage Ü lowest value relative to the corresponding cn" nnunee ^D n in the other circuit portions St in this case, in the Detektorschal- Ta 'provided differential amplifier as the first * 3tenn zurückfaUen its idle state the Anipestufe W operates in the same way as the α 7eieestufe Z.' is: After the Aafladestromkreis for ^ n capacitor 295 After the ignition of the thyrite 290 and the associated blocking of the transistors 292 and 294 is interrupted, the measuring instrument 297 is fixed at a measured value which corresponds to the lowest partial illuminance prevailing at this point in time.

FIG. 27 shows a further exemplary embodiment which is based on the principle given in the block diagram according to IiE 22. Each Zeitgehprschaltung is directly the brightness information detected by the CdS-Pho-Mwiderständen feeds _T he desired extreme values are determined as the differences of I ind-individual timing circuits that come leitkonstanten jeweus by the different state.

In the detector circuit A of the circuit section. A is the doubt point ύ of the series circuit consisting of the CdS photoresistor 231 and the variable resistor 232 connected to the base of a transistor 301, the emitter of which is connected to Her neeative collecting 2H5 and its collector to a resistor 302 and the base of a transistor 303 Stromsteuerang are connected. The other connection ide of the resistor 302 and the emitter of the transistor 303 are connected to the positive bus line 215. The collector of transistor 303 is connected to a time-determining capacitor 304 and the base of the transistor. The other terminal of capacitor 304 and the emitter of transistor 305 are connected to the reactive bus line 216. The collector of the transistor 305 is connected to the positive bus line via the exciter coil 206 for controlling the switch 217 in the display stage Z '. The voltage divider α leads in the detector circuit A ₁ to the base of a transistor whose emitter is connected to the positive bus and whose collector is connected to a resistor 307 and the base of a transistor 308 for current control. The other terminal end of resistor 307 and the emitter of the transistor are connected to negative bus 216. The collector of transistor 308 is connected to a timing capacitor 309 and the base of a transistor 310 in connection. The other terminal of the capacitor 309 and the emitter of the transistor 310 are connected to the positive bus, while the collector of the transistor 310 is connected to the negative bus 216 via an excitation coil 212 for controlling the switch 217 'in the display stage W. The circuit section B is constructed in the same manner as the circuit section A. The display levels Z 'and W have the same structure as the Aiizeigetufe Z.

To describe the mode of operation of this circuit, let us first assume again that the CdS photoresistor 231 assigned to circuit section A is exposed to the highest brightness, while the photoresistor in circuit section B is least strongly illuminated. When the switch 222 is closed, the charging of the time-determining capacitors 219 and 219 'begins in the display stages Z' and W. Partial voltages Va and Vb occur at the midpoints α and b of the voltage dividers containing the CdS photoresistors. Under the conditions mentioned, the partial voltage Va has the highest and the partial voltage Vb the lowest. As a result, the conductivity of the transistor 301 in the detector circuit A _{x is} the greatest compared to the conductivity of the corresponding transistors in the other detector circuits for determining the highest illuminance, and the transistor 303 for current control, which receives its control signal from this transistor 301, has relative to the corresponding transistors of the remaining detector circuits have the lowest internal resistance. The terminal voltage of the time-determining capacitor 304 accordingly rises the fastest, so that the transistor 305 is the first to be switched to its conductive state and the excitation coil 206 for actuating the normally closed contact 217 provided in the display stage Z is the first to be effectively energized so that this contact is opened and the measuring instrument 221 is fixed at a measured value which characterizes the highest partial illuminance prevailing at this point in time.

45 In the circuit section B , the voltage Vb appearing at the node b has the lowest value, as mentioned. Accordingly, the terminal voltage of the photoresistor 231 'connected to this node b has the highest value. As a result, the excitation coil 211 'is effectively excited earlier than the corresponding excitation coils in the other detector circuits for measuring the lowest object brightness and opens the normally closed contact 217' in the display level W, so that the measuring instrument 221 'displays the lowest partial illuminance prevailing at this point in time.

It is an advantage of the embodiment shown in FIG. 27 that that the circuit structure is particularly simple and the manufacturing costs accordingly are low, since neither differential amplifiers nor Schmitt trigger circuits are used.

In addition 11 sheets of drawings

609 683/312

Claims (11)

Patent claims: 1. Arrangement for measuring at least one extreme value of the brightness distribution of a photographic object, with a plurality of C photoelectric converters which are arranged distributed within a measuring field, in particular the image plane of an optical system, with display devices having memory circuits and with circuits for selective coupling of the display devices with the outputs of those photoelectric converters which are exposed to an extreme value of the brightness distribution of the photographic <* n object, characterized in that the ¹ S memory circuits have partial memories assigned to the extreme values to be measured (e.g. 219 and 226 in FIG. 23), that the Partial memories can be connected to a charging source (e.g. 223 in Fig. 23) via switches (e.g. 217, 222 and 224 in Fig. 23), and the position of the sounder can be influenced in this way by the circuits (e.g. 203 to 214 in Fig. 23) is that the state of charge of the partial memory to each train corresponds to an ordered extreme value. 2. Arrangement according to claim 1, characterized in that the circuits (203 to 213 in FIG. 23) in each case one of the photoelectric converters (201 in FIG. 23) associated with Zek memberscr (203 to 205,207 to 211,21? And 214 in Fig. 23), whose time constant is determined by the photocurrent dt: s photoelectric converter and excitation circuits controlled by these timers (206 and 212 in Fig. 23) for operating the switches (217, 224 in Fig. 23). 3. Arrangement according to claim 1, characterized in that the circuits (2, 4, 31 to 35 in FIG. 5) in each case one of the photoelectric converters (1 in FIG. 5) assigned comparison circuits such as differential amplifiers (33, 34, 35 in Fig. 5), at one input of which a fixed reference voltage is applied and the other input is connected to a capacitor is that of the photoelectric converter (1 in Fig. 5) and thus with one of the relevant partial brightness dependent time constant is chargeable. 4. Arrangement according to claim 1, characterized in that the circuits (102 to 108 in Fig. 12) one of the photoelectric converters (101 in Fig. 12) assigned comparator circuits such as differential amplifiers (103,104,105 in Fig. 12), on one of which Input is a function of the terminal voltage of the photoelectric converter (101 in FIG. 12) Reference voltage is applied, and the other input each with a capacitor (108 in Fig. 12) is connected via a lighting-independent Resistor (107 in Fig. 12) is chargeable. 5. Arrangement according to claim 1, characterized in that the circuits (103 to 106, 118 in FIG. 14) each associated with one of the photoelectric converters (119 in FIG. 14) (103, 104, 105 in Fig. 14), each of which has a on the terminal voltage of the associated photoelectric converter (119 in Fig. 14) dependent Reference voltage is applied, and their other inputs each with each other and with a common Condenser (113 in Fig. 14) are connected via a lighting-independent Resistor (112 in Fig. 14) is chargeable. 6. Arrangement according to claim 5, characterized in that the common capacitor (113 in FIG. 14) is identical to one of the partial memories assigned to the extreme values to be measured is. 7. Arrangement according to claim 1, characterized in that the circuits (4, 36 to 45 in Fig. 6) each have a lighting-independent resistor (36 in Fig. 6) connected in series to one of the photoelectric converters (1 in Fig. 6) and each contain a changeover switch (37 in Fig. 6), the normally closed contact side (1) with the connection point (a) of the series circuit, its control contact with a capacitor (38 in Fig. 6) and its normally open contact side (m) with a discharge resistor (39 6) for the capacitor as well as a threshold value circuit such as a Schmitt trigger (40 to 45 in FIG. 6) and that all changeover switches assigned to the individual photoelectric converters (1 in FIG. 6) can be operated together . 8. Arrangement according to claim 1, characterized in that the circuits (Fig. 8) each contain one of the photoelectric converters associated switch, through which a capacitor between a lighting-independent voltage divider that supplies a reference voltage and the photoelectric converter functioning as a discharge resistor is switchable and that the photoelectric converter is provided with a threshold circuit such as a Schmitt trigger connected is. 9. An arrangement according to claim 2, characterized in that the timing elements (1, 2, in FIG and 3) capacitors (2 in Figs. 2 and 3), the terminal voltage of which is the control signal for an electronic switching stage (3 in Fig. 2 and 3) forms the controlled circuit of which the excitation circuit such as a relay coil (4 in Fig. 2) or a semiconductor switch (15 in Fig. 3) for Contains switching of the charging circuit for the partial memory (9 in FIGS. 2 and 3). 10. The arrangement according to claim 9, characterized in that the excitation circuit is a semiconductor switch (15 in Fig. 3) and that the outputs of all of a partial memory (9 in Fig. 3) associated circuits (A, B, C in Fig. 3 ) are connected via decoupling members (17 ', 18', 19 'in Fig. 3) to the control electrode of a bistable semiconductor switch such as a thyristor (21 in Fig. 3) for switching the charging circuit of the partial memory (9 in Fig. 3). 11. Arrangement according to claim 1, 2, 9 or 10, characterized in that each of the circuits (203 to 214 in Fig. 23) has both a circuit section (A _x in Fig. 23) for measuring the relatively lower and a circuit section (A ₂ in Fig. 23) for measuring the relatively higher object brightness at a pixel and that the control signal for the first-mentioned circuit section (A ₁ ) depends on the terminal voltage of the photoelectric converter (201 in ghd ζ ν I ζ I d η s k U e d b il P d si π b SK gg ii b ti η g te η 23) and the control signal for the second circuit section (A ₂ ) is formed by the terminal voltage of a passive two-terminal network (202 in FIG. 23) connected in series with the photoelectric converter (201 in FIG. 23). The invention relates to an arrangement of the type mentioned in the generic term of claim 1. The exposure of photographic layers should take into account the brightness range of the The subject to be taken so that the individual brightness values in a suitable relationship to The blackening curve of the film material used. In the case of negative films, for example, this should be of interest an optimal copyability and a maximum utilization of sensitivity the exposure take place in such a way that the darkest parts of the image (slightest blackening of the film material) are as close as possible to the The limit of the linear part of the blackening curve. When exposing slide film material on the other hand, the exposure should be such that the brightest parts of the image are in one area of the blackening curve lie, which (after the reversal has taken place) has a sufficiently high level of transparency. In order to be able to carry out the film exposure in this way, it is necessary to determine the extreme values of the To determine the brightness distribution of the object to be photographed. It is known to be the highest and determine the lowest partial object brightness by point measurements. For such measurements Photoelectric exposure meters with a very small measuring angle are available, some of which are special Have search facilities. Such exposure meters can also be placed in the beam path on the image side of the camera lens, in particular a single-lens reflex camera, be inserted, so that the measuring field is observed directly in the viewfinder beam path and the individual parts of the object are observed their brightness can be judged. A photometric device for light contrast measurement has become known through DT-AS 1 908 587, with the help of which the highest and lowest brightness value of the object can be determined separately be able. The user must, as it were, scan the object field with the measuring beam path. This handling is comparatively cumbersome. The DT-AS 2 145491 is an arrangement for Measurement of the illuminance of photographic objects became known, at which a cattle number of photoelectric converters within a measuring field, in particular the image plane of an optical system, are arranged distributed so that a point measurement is possible without the Mess'Ornchtung is moved. There are display devices with memory circuits and circuits for selective Coupling of the display devices with the outputs of the respective photoelectric converters provided, which are exposed to an extreme value of the brightness distribution of the photographic object. The invention is based on the object of developing this known arrangement and the disadvantages to avoid the: result from the fact that the memory circuits directly from the output signals the photoelectric converter circuits are charged by signals that are have a comparatively low amplitude and a low energy content, so that impedance converters and voltage amplifiers are unavoidable. This object is achieved by the features mentioned in the characterizing part of claim 1. Refinements of the invention are the subject of the subclaims. The output signals of the photoelectric conversion circuits control in the arrangement according to FIG Invention the charging process of the memory circuits from a charging source that is independent of the converter. In the following, the invention will be explained in more detail with reference to the exemplary embodiments shown in the drawings explained: Fig. 1 is a block diagram of the arrangement in which FIGS. 2 to 11 show a first group of exemplary embodiments in which each photoelectronic Component is assigned a timing element whose charging or discharging time constant or voltage depends on the respective terminal voltage of the photoelectronic component itself. In the 12 to 20, a second group of embodiments is described in which the terminal voltage of the individual photoelectronic components as reference voltage for comparator circuits in which these reference voltages are compared with time-dependent voltages, by RC elements, in particular by a common RC element can be generated. the Figures 21 and 22 are block diagrams of a third one Group of exemplary embodiments. In the remaining 23 to 27 is this third group of embodiments shown, in which each pholoelectric component part of both the circuit part to determine the highest as well as the circuit part to determine the lowest partial Illuminance is. 1 shows the block diagram of a first group of exemplary embodiments. The switching stages A, B and C are light measuring stages for determining the partial illuminance of the object. They are in an appropriate number and distribution z. B. arranged in the image or adjustment level of an optical system. The switching stage Z is a display stage which is under the control of the switching stages A, B and C and displays the value of the highest and / or lowest partial illuminance. F i g. 2 shows an embodiment for measuring the highest partial illuminance of a recording object. The circuit sections A to C correspond to the circuit stages of the same name in the block diagram according to FIG. 1. Z is the display stage for displaying the measured light value. The circuit section A comprises a CdS photowide wall 1, which serves as a detector for the partial brightness of the object and which is connected in series with a time-determining capacitor 2 between a positive bus line 5 and a negative bus line 6. The connection point of the series connection leads to the base of a transistor 3, the emitter of which is connected to the negative bus and the collector of which is connected to the positive sam-