DD207269A1 - EXPOSURE MEASUREMENT AND CONTROLLER - Google Patents

Abstract

The invention relates to an exposure measuring and control circuit for photographic camera. The invention is based on the object and the object of reducing the circuit complexity for said device and to ensure that despite the absence of Messverstaerker with high-impedance inputs and without logarithmation of the input signal, a further Objektleuchtdichte range can be processed stoerunanfaellig. According to the invention, an input stage formed by an elementary mode photomultiplier and an A / D converter is used whose output is coupled back on the one hand to the input of the A / D converter connected to the photomultiplier and, on the other hand, through a film exposure and an exposure indicator Counting and computing circuit is connected.

Description

238497 2

Dresden, March 4, 1932 21 / 4-03

Title of the invention

Exposure measuring and control circuit

A field of application of the invention

The invention relates to a Belichtungsmeß- and control circuit for fotografiache cameras.

Characteristic of the known technical solutions

For the measurement of object luminance densities, the processing of the short-circuit current of photodiodes operating in film mode and its conversion into a logarithmic voltage characteristic with logarithm amplifiers has hitherto been known (see, for example, DS-AS 23 56 964). Furthermore, a photoelectric conversion circuit is known, with which a series of oppositely poled photodiodes connected in series and a pair of cascade-connected CJIOS inverters are used to transform a photodiode to an incident light quantity into a corresponding signal (DS-OS 30 48 647). ,

Advanced measuring circuits required a high level of electronic effort for the production of very small photo currents by means of high-impedance amplifiers as well as additional circuit-based measures to compensate for the partial temperature response of the logarithmic stage. The cited omn conversion circuit requires two

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on each other, tuned photodiodes, has in direct light quantity measurements an operating voltage dependence, which can be counteracted only with increased effort and can only be used up to relatively large lower illuminance.

Object of the invention

The invention serves to improve exposure metering and control circuits.

Essence of the invention

The object of the invention is to provide an exposure control and control circuit which, with relatively low outlay, ensures trouble-free processing of a wide range of object luminance ranges.

In the light of the invention, this object is achieved by using a step-input stage formed by a photoreceiver operating in the bluing mode and a resonator, the output of which is fed back, on the one hand, to the input of the A / D converter connected to the photoreceiver and, on the other hand, communicates with an inking device controlling the oil seal and a light-emitting indicator.

embodiment

The invention will be explained in more detail with reference to illustrated embodiments. Ss show:

Pig. 1 block switching scheme aer exposure control and control circuit

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Pig. 2 voltage curve and pulse diagram

According to Fig. 1 is formed as an input stage of the Belichtungsmeß- and control circuit of a photodiode 1 and an A / S Vianaler, the latter acting as a comparator amplifier 2, a frequency generator 3, a gate circuit 4 and a in the feedback path on Combining a capacitor 5 with a feedback diode 6 and a Sntla; dediode include the input of the comparator. The gate circuit 4 is connected to a counter 8, on the one hand, a computing and control circuit 9 for a shutter magnet 10 and a display 11 for previewing exposure data and on the other hand, a switching device 12 is arranged downstream, with letatereein computer flash 13 can be switched «with the. Zählsr 3 is also an encoder 14- to input the Fiimmempfinalichkeit »a Blitasynchronschalter 15 and a memory switch 16 and the computing and control circuit 9, a switch 17 for Sinleitung the exposure time formation and a coding device 13 for aperture values associated * 19 are a Schaltungskapaaität and with 20, 21 capacitors to change the P.ückkoppelimnulae and ir.it 22 denotes a reset line *

The mode of action is the following:

After operating voltage maintenance and digital input of the values for film sensitivity and preselected aperture, the illuminance 3 acting on the photodiode is converted into a short-circuit in known yfeiae

I = a · B (Oa = sensitivity of the photodiode

In conjunction with the fixed reference point ^ at the noninverting input of the amplifier л ' ¹

At the output, a high potential is first created which opens the gate 4 and a sequence то. f *

ν, generated in the generator 3 voltage pulses U ^ via the capacitor 5 and the diode 6 to the inverting SU

of the amplifier 2 Under the assumption that ideal switch diodes find application is in ^. Riidckoppelimpüls the charge

α = ^C - σ (2)

contain. The mean feedback current is soro * = + - = - = о.u.r (, j; r

With. Cl) is obtained.

B = ^ ™ - · f = const · f (4)

It can be seen from (4) _t that the Impulsfolgefreauenz a

Measure for the illuminance S is »

From Pig · 2-. Is evident that the backgekopp

These are the 3-input inputs of Amplifier 2

same voltage Ui at the time ti to the value 0 grain uen ™ siert. This is the short-term mitigation '

the input sounding finished. As soon as the voltage tT-j becomes slightly negative due to a pulse, the stronger output assumes LOW potential and the gate circuit is blocked, so that no further pulses are fed back to the amplifier input. Each additional charge of the capacitor 19 to a positive voltage d

urcii

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the illuminated photodiode 1 leads to the renewed. Opening the gate 4 and again for Hullkompensation of bathing and voltage at the comparator input. Thus, in the measurement phase, a pulse sequence sets in, which causes a constant! Julie compensation at the comparator input. The film exposure is defined as the product of illuminance and time. With (4) one therefore obtains at constant illuminance

B. t = SjS. f. t (5)

The product

f. t = η (S)

represents the number of feedback pulses. With (6) you get

E β t = const.n,

that is, the number of feedback pulses is a measure of the prevailing illuminance on the photodiode 1 at time t.

The relationship between the illumination of the photodiode and the film exposure is now established such that the same number of pulses, as a measured quantity already digitized in the input stage, are also written in the counter 3, the latter being fed to the meter before each measurement via the stficksetleitung 22 -iusgangsstand brought and after pulse injection then periodically queried. The 'processing of 2 counter information takes place in the arithmetic and control circuit 9, by which first the display 11 for previewing the expected

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Exposure time or aperture size is to be controlled via the memory switch 16, the counter reading is speichej-bar. When the shutter is triggered, the switch i7 closes after an exposure time determined in the arithmetic circuit, the shutter magnet 10 is activated or deactivated. When using the flash unit 13 Computer 15 _<ц е Blitszündung, also is closed in the closure actuated switch flash synchronously initiated and after a Blitsdauer, which is dependent on the light that is reflected from the photographic subject or the Piim.

Instead of the described input of the Pilmempf i by specifying a Pulsesteilerverhältnisses іц, аеш counter is for the same purpose, however, also EiOgIT _- Ci ₁ J to change the size of the feedback charge pulses, Z. Be characterized in that dan capacitor 5 one of the capacitors 20, 21 is assigned or switched on instead ·

The feedback of the charge impulses need not be addressed in <3, he-the ^ -table-aiT-wsis.e ^ see "about the 'Dorschaltu ^ кяял also an electro-optical assembly with a light emitting diode whose light pulses on éідец asr iOtodiode- 1 antiparallel connected Zusatzempfänga.x be conducted. Likewise, an inductive feedback can take place.

If the pulse frequency exceeds certain threshold values, then by switching the capacitors 5, 20, 21 and at the same time the divider ratio _φ counter 3 the product

3.0 kept constant. Thus, зіп very größei _"e r Kelligkeitsbereich störuhanfällig from the camera verarbei.tbar.

Claims (9)

238497 2 3rf indung: запзтз rucii 1. Exposure measuring and control circuit for photographic cameras, characterized in that one of a working in Sleisentenbetrieb photoreceiver and an A / D converter 3input stage is applied, whose output on the one hand connected to the Jotoempfanger input of the A / D converter is feedback and on the other hand with a film exposure and an exposure indicator controlling counting and arithmetic circuit is in communication. 2, circuit according to item 1, characterized in that to the A / D converter operates as a comparator working amplifier (2), is connected between the inputs of the Jotoempfanger and that the comparator as an actuator for a pulse generator with a (3) connected Gate circuit (4) is used and the latter is in communication with both the one input of the! Comparator and with the counting and arithmetic circuit (9). 3 · circuit according to item 1, characterized in that the A / D-ifandler is capacitively fed back. 4. Exposure measuring and control circuit according to item 3, characterized in that the Sueckkoppelungspfad between gate and Somparator input of a diode (6) and a capacitor (5) is formed and the latter in the blocking phases of the X Pulsgenerators lying on a fixed reference potential weiters diode (7) is reloadable. 5. A circuit according to item 1, characterized in that antiparallel to said photoreceiver another 238497 2 Photoenfänger is switched, on which the Α / Ό converter output opt o-electrically fed back. 6. Circuit after. Item 1, characterized in that the output of the A / DW ^r andlers is inductively fed back to its input. 7. The circuit according to item 1, characterized in that the Piljnenipfindlichiceit on the selectable divider ratio of the counter or the size of the feedback pulses is entered. 8. circuit ласд point 1, characterized in that the arithmetic circuit is designed as a counter in which the signal information is periodically transferable, and which is designed as a control element for the shutter time or Blitsaeit of computer flashes. 9. Circuit according to item 2, characterized in that the pulse difference between the measuring phase (photodiode illuminated) and the exposure phase (photodiode unlit) emitted by the A / D converter is a manipulated variable for the regulation of the unwanted current of the comparator and simultaneously for the exposure time or aperture size forms. C For this 1 sheet drawing)