DE2053001A1 - Camera with electronic shutter and automatically controlled exposure time - Google Patents

Description

Case 126

ilippon Kogaku KK
Tokyo / Japan

Camera with electronic shutter and automatically controlled exposure time

For automatic control of an exposure time depending on an output variable behind a Pentaprism of a single-lens reflex camera with electronic The photosensitive element arranged with the shutter becomes the one falling on the photosensitive element Light beam interrupted by the retraction of a mirror, so that the immediately before retraction of the Mirror occurring light intensity must be stored, whereby an exposure time of the shutter after Can be controlled according to the stored information.

A method is proposed to solve this problem in which a circuit for generating an output

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voltage is provided which is proportional to a logarithm of the change in width of the through a taking lens falling light beam intercepting photosensitive Element (this circuit is hereinafter referred to as

■■ · "logarithmic! Compression circuit"); the output variable of this circuit is stored and fed to a further circuit as an input variable (this circuit is hereinafter referred to as "logarithmic expansion circuit"); the latter circuit is of the type. of circuits in which the logarithmic change in the output resistance is made proportional to the change in the input variable. The logarithmic ex-

W expansion circuit is based on its principle on the fact that in the area in which the space between the sink and the source of a field effect transistor can be regarded as resistance, ie in the area in which the current flowing from the source to the sink is proportional to the is the voltage between the two, the logarithm of the resistance between the sink and the source is inversely proportional to the voltage difference between them. The field effect transistor only offers these conditions if the voltage difference between the sink and the source is very small and in the order of magnitude of 0.1 V. There is also the resistance between the sink and the source

φ extraordinarily large, so that numerous problems arise if a circuit is to be developed that works sufficiently stable in practical operation.

An object of the invention is therefore to provide a control system which will be described in detail below and which those in the known logarithmic expansion circuits Overcomes any disadvantages. The invention is, briefly summarized, a circuit with which the geometric Progression of the change in brightness of a

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BATH ORIGINAL

⁷ ψτ ~ '■ ■ ■ ■■ "■ · ■' ■■

- 3 -

object to be included in the arithmetic progression the change in the output voltage is implemented, a circuit with a capacitor for storing the output voltage, a circuit whose change in output voltage proportional to a logarithm from the moment the shutter starts to open elapsed time, and a circuit that operates in accordance with a difference between the two output voltages is switchable, whereby the beginning of the closure of the shutter can be initiated when the difference between the two output voltages a predetermined Jert reached.

The advantages offered by the invention are, in summary, the following:

(1) a controller for an electronic shutter with Storage, simply constructed and reliable in operation, is specified;

(2) a very precisely controlled exposure time can be achieved because of the characteristics of a light-sensitive Elements are easily detectable by calibration;

(3) an exposure time can be set in a wide range of aperture settings of the taking lens and control of film speeds; and

(H) a previous display of the exposure time is possible.

The invention is described in detail below Drawings Fig. 1 and Fig. 2 explain the circuit diagrams of two embodiments of the invention.

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BATH ORIGINAL

i \ lach the circuit in Fig. 1 are ain pliotoltitendes Element 1 and a diode 2 in series with a voltage source 3 switched. It is known that the current flowing in the diode 2 with the voltage V ^ through the relationship

V _d = h log (i + 1) (I)

is connected in what

i = saturation current in reverse direction

kT
h = - with: k = Boltzmann constant

T = absolute temperature q = charge of the electron

Since the amount of i_ is extremely small and 1

Can be neglected if i is more than a few nanoamps

- 9
(10 A) applies approximately

V _d = h log i + V _o (II)

If the voltage of the voltage source is V and the resistance of the photoconductive element 1 is denoted by R, is applicable

V = h log i + V ₀ + iR (III).

The relationship between the resistance R of the photoconductive element and the brightness B of the object to be photographed is given by

R = k B ^- ^, (IV)

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where 'V = constant as a property of a 3S photoconductive Elements. From the relationships (III) and (IV) it follows

V = h log i + V _o + ik ti " ⁰ (V)

Since the arst member is small compared to the second and third senr, it can be neglected, so that follows

ι = —i B * (VI)

respectively

VV
log i = log - ^ - + ^ log B (VII) ■

Inserting equation (VII) into equation (II) results

V-V

V, = h Ylog B + h log - τ- -2. + ν (VIII)

This means that the logarithm of the brightness B of the Object is proportional to the voltage across the diode. In general, the voltage is V, across a series circuit given by m diodes

V - V V ₁ = m (htlor B + h log k + V) (IX)

ClJiI 'O

Furthermore, a capacitor 4 is generally operated by a switch Jj bridged, which is parallel to the capacitor 4, and wira charged via diodes 6 from the voltage source 3, if the switch 5 in connection with the üffηungsbewegung the shutter is opened. The charging current is given by

i = C - (X)

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where C = capacitance of the capacitor Voltu
Load.

V = voltage across the capacitor, t seconds after

From equations (II) and (X) it follows

dV V = V _c + h log (C - ^ S) + v _o (XI)

^V - ^V c " ^V o dt = Ce h dV

t = Ce h h dV

e c

V-V-V

O C

= Ch.e "" h + A

For t = 0, V _c = 0 and therefore

VV ο

A = - Ch.e h

thus V - V

t = Ch.e H '\ ~ T " ^λ \ (XII)

VV V _c = h log 4 ~. e "Ti t + 1)

Since 1 in brackets can be neglected, the result is

V _c = V - V _o + h log ^ (XIII)

That means: the voltage on the capacitor is proportional to that

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BAD OWGLAL

Logarithm of the charge time. The relationship between V / and t connected in series via η when charging the capacitor Diodes is generally to be represented by

V _c = V - nV _o + nh log ^ Jj

(XIV)

If the difference between V- and V reaches a predetermined one Value, w-nn for example V-V, = V, becomes the Closure closed. Then can t, i.e. the exposure time of the closure, with the brightness B of the object can be linked as follows:

V - mV nV _Q - nn log γ ^ = mh * V log B + rnh log -ρ + η; V ₀

thats why

.t = CnA (

= constant

If ^ f = 1 and m = n, then Bt =

= constant

(XI)

if X ^ 1, then m and π can be chosen such that - =

Hence Bt =

V - mV

. e

= ^{Constant (XVI)}

In this way the condition for the automatic Control of the shutter exposure time as a function from the brightness B.

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"* O -

Based on the principle given above, differential _{amplifiers T 1} and T _{2 are} provided in the first embodiment of the circuit, so that (V - V,) and V _Q zvrci inputs and circuits T ₃ and T _{1+ are} supplied, 'which are dependent on the output variables of these differential amplifiers designed as field effect transistors can be switched. The voltage (V − V _dn ) is fed to the gate of the field effect transistor T 1, ie one of the inputs of the differential amplifier circuit, via a switch 8 when a voltage source switch 7 is closed. This voltage is stored in a capacitor 9, which is located between the gate of the field effect transistor T ^ and the negative pole of the voltage source 3. For example, in order to automatically control the exposure time as a function of the output of the light-sensitive element, which is arranged behind a pentaprism of a single-lens reflex camera, the light intensity measured immediately before the mirror is withdrawn must be stored, because when the mirror is withdrawn, no light falls more on the photosensitive element. The switch 8 is opened immediately before the mirror is withdrawn. If the switch 10 is now closed to operate the shutter, the capacitor 4 is still short-circuited by the switch 5, so that the potential at the gate of the field effect transistor T _{2 is} extremely much lower than that of the field effect transistor T ₁ . This means that the field effect transistor T ₂ blocks almost completely. Therefore, a transistor T _{3 is} non-conductive while a transistor T _{1+ is} conductive. The current flows through a winding 11 of a magnet in the collector circuit of the transistor T ₁₊ , so that the As a result of the opening of the shutter, the switch 5 is opened, so that the capacitor 4 is charged via the diodes 6. When the voltage V on the capacitor 4 _{becomes almost the same (V-V 0n} ), current suddenly begins through the Field effect transistor T ₂ to flow, so that a voltage drop across a

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. ■ / icerstand 12 arises, as a result of which the asispotentisl aes transistor T _{0 is} lowered. Hence ^T .; Irc the transistor T ₀

ο ύ

leitenü, w-.ihrond the base.lotvjitial ά <^ 3 transistor T ₁ .

Zunin: ri: t, so dab the emitter; ctential off. De-nsuf ol ^ e blocks transistor T ₁ , so that j cer </ la ⁷ n -1 11 enti'ept vird and di; r closure is borne. Di --- on dir st- wise :: controlled exposure time 1 hä.- _t <rt, ν / ic durci: die el: .ichunr ^ r. (XV) Uno (XVI) after ;;; _ v; i..sen, from the ij-3llirkfc.it . * O, e. Subject.

From equation (XVI) it can be seen that .ν im n / r. - It .ejriacnt: -? Ird, the r_, i ..e ns charter des pnotol ^ itenciv-i: ^, le: ^ ents in pabsenoer /.'eise corrected cciir be calibrated k "'nner;. Dos btceutst, uüij photolei L ^. !!: dc Tle; rente i'.it differenti ^. "- licnen hirensch ^ iten used in combination κϋηη <n, j,; but η α cn ü, the number of diodes 2 and ϋ in. hi: on the stability. '- the ochaltun ^ in tensions; rs- una returscüvjankun ^ en. The ^ of the CdS and other photoconductors is kleirr-r than 1, so that bc-i of the first, in Fir. 1 shown ^ chaltun ^ Sv / eise, on the field effect transistor 'f "a source' n resistance 13 before-7es; here is to the correction of 'ft aurcii ^ assende ihinst-; llun: ^T des Qu ^ ll ^ nwid ir-3 Leines 13 watch. ir, \ inz- In ^ n assume α ie ^ in r ^ saes FilauTi ekttrensistors T _? and dar-it cer Ser.k ^ nstrc

to, v .'- jj'.n eier capacitor '^ ', elad-; n u'ird. Joaoci, the rjpannunr.sabf all ή; η .vid. ^ Rs ta id 13 between Tor uno source TL negative i i'.ijcki; oi) plun.; ·· entered "hrt, so you. '^;> the increase de -: .-; 'jenlcenst /' OJiis suppressed w <.; / oen]: ann., tit anaer-ii words, difi sctieiuDare ^ in;.; an; ss ₁ ; -xinun .; oes Ft: lrieff ej; ttraiisistor: j

T, becomes low; vr as ci.e ct.j T ¹ = · Ldef f ext transistors 1 ' _Λ . Da / j.

der '..'iu'irstano 13 seiir; - precisely adjusted v; erden Jcann, let sicii vort (-; ilhai terv / els- pnotol -; itende Ulcii / v-nte r.it arbitri) ;. «ju ^ use .

dJ.e the lielicutunr, ^ e *. in rivers, about di ^

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Adjustment of the taking lens, ie film sensitivity, etc., can be adjusted by ...; in potentiometer 14, the center tap of which is, for example 3, coupled with the setting of the aperture value, the film sensitivity is changed approximately as if a release level is changed. Since in ä ^<: n amplifiers, the large log or log B t as input: ingi-.nen, the Concerned; the change in the output parameters of the amplifier when there is a change by one: step in the exposure factor B or t! constant. Control in a wide range by setting the potentiometer 14 is also possible.

IS when an exposure time becomes very long, air becomes the Capacitor 4 charging current lower, so that3 the problem thaw the sireu loss of the capacitor 4!:! ", Un this To eliminate the difficulty, a relatively high resistor 15 is connected in parallel with the diodes υ.

In the second embodiment according to FIG. 2, ede output variable of a logarithmic compression circuit with a diode sequence 15 unc. a photoconductive lern 17 stored in a capacitor IS via a switch 18. The voltage across the capacitor 19 is applied to dcrr. Gate of a field effect transistor T ₅ , which together with a v: t.iteren field effect transistor T- represents a first differential v-r-φ more strongly. At iin-m further input, namely at the gate of the field effect transistor T,. c: -r ./iderstand 21 is in series with a diode sequence 20, which includes as many diodes as the mode sequence 16. Since the adjustable resistor 21 corresponds to the ik; lichtungi \ ;. ctoren (for example aperture setting of the recording lens, film sensitivity etc.) is adjusted, the voltage dropping across the resistor 21 and fed to the gate of the field leakage transformer Tp is of course in iie / .i '. hung,:; u dt. nt

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exposure factor. A voltage dropping across an output resistance of the field effect transistor T 1 therefore becomes a function of the brightness of the picture, the object and the aperture setting such as the film speed. In the sink circle of the field affect transistor T _fi , a display device 2 3 is arranged, which previously displays a controlled exposure time. The display device 23 can lie in the sink circle of the field effect transistor T ₅ or between the sinks of the field effect transistors T _r and T _g .

A capacitor charging circuit contains a diode sequence 24, a capacitor 25 and a switch 26 connected in parallel to the capacitor, as in the first embodiment of the circuit according to the invention. Ss would be possible to compare the voltage across the capacitor 25 with that across the dsm output resistor 22, but in the second embodiment, in view of the variations in the voltage source and the temperature, the voltage across the capacitor 25 is fed to a second differential amplifier made up of the field effect transistors T ₇ and Tg supplied so that a comparison voltage at the output resistor 2 7 results.

The voltages appearing at the output resistors 22 and 27 are fed to the inputs of a third differential amplifier made up of the transistors T _g and T. _Q. Since the switch 26 short-circuits the capacitor 25 before the shutter is actuated, the input variable at the transistor T _{g is} greater than that at the transistor T ^ ₀ , so that no current flows through the transistor T ^ _n . Infoljredassen is the basic

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potential of a transistor T ^ _{1 of} a circuit formed from the transistor T ^ and a further transistor T ^ approximately zero. The circuit is excited in accordance with a voltage drop across the output resistor 28. Therefore, the transistor T ₁₁ blocks while the transistor T ₁₂ conducts,

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so that the magnet 29 is energized, whereby the closing movement of the shutter is prevented. If the switch is opened because of the opening of the shutter, the capacitor 25 is charged, so that the current suddenly flows through the transistor T ₁₀ . Therefore, the voltage across resistor 28 increases and transistor T ₁₁ becomes conductive while transistor T ₁ 2 becomes non-conductive. Thereupon the magnet 29 is de-energized, so that the closing movement of the shutter begins.

In the second embodiment, the voltage gain can be precisely controlled by the variable resistor 22, so that the second embodiment has the advantages that the voltage stored in the capacitor 19 can be linearly expanded and compressed to correct or deposit the f of the photoconductive element , and that the preceding display of a controlled exposure time can be done in a simple manner, as described above.

Patent claims :

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Claims (1)

η ς) η ('' ■ "■ e η τ. a η s: τ Kdrn ⁿ rd ^T jii.T € · I κ) 't ro ;; L; -; <:: ■ ■ ".-"'': - controlled .ieiichvui; - s.- ,. 1 I , (a) a ·: 'Jc ;;, il ⁺ : i: i ·!' ■ '■;: ■'.'- · ■ "*. (b) a Scn ^ lturv-, 'Jo proportional line ... blicA d ^ 3 ^^. firuiö
elapsed time (c) a ^ caalixrei ^, der Ausi-antsspdnn ^ is cash is , i '7j- _; : cilje Jer Dir / ^ reü ζ x · '.;eid3;. Schaltuneei,: "; oiv: .It · whereby jv; '. "inn die' _-ϊ fi -ri ^ nz eier DeLc ;;, Aus,; j ;..: ■" · · ■■ nungon ^ -inc η νοίί ·. COe ^- Kn. .: r τ τ: τΐοΓ \ ν, ^ r. ^v c :: '■. Ti η Z ei 1 Π; il i 'X , (i'.l i-, (. ":. · ■ /' ■ ·: '-. i'icspr ^; 3'j GuI JC.iiil tli! .- / ....., : tzen dor. ^ - onetrisciier Pro ^ reü ^ ion of .'uiUorun :, air l'ror.rüCüioji der Arüiürunp der Ausrjan ^ -saponnun, ·. in 1098 ^ 0 / UU BAD CWGiNAL this capacitor is stored. 3. Camera according to claim 1, characterized by switching elements, the at least one of the two output voltages expand or compress. <4. Camera according to claim 1, characterized in that the Circuit for implementing the we one tr is eh.-: η Progr · :. scion of Changing the brightness of an object to be recorded into the arithmetic progression of the output voltage has a differential amplifier, at one of which input a voltage is applied, which is a Fi! ^ sensitivity and an aperture value of a recording lens corresponds, so that this output voltage is used as an output variable of the differential amplifier can be aogelcitit. 5. Camera according to claim 1, characterized in that the circuit for implementing the geometric progression of the Changing the brightness of an object to be recorded in the arithmetic progression of the output voltage has a differential amplifier, at one of which A voltage is applied to the input, which corresponds to a film speed and corresponds to a diaphragm value of a taking lens, so that this output voltage is used as an output variable of the differential amplifier can be derived, as well as a display device that is in one of the two output circuits or is switched on in both output circuits. 10 9820 / U U BAD OWGtNAL