DE2155629B2 - Automatic camera - selects correct flash exposure at low light levels - Google Patents

Abstract

The exposure control circuit has the photocell in one arm of a bridge network in which all the other exposure factors are represented as impedances. These include film speed, object range, aperture and film speed. The system is programmed to select the integral flash gun in the event of low light values, while the automatic/preselected aperture value is fed back into the system. The imbalance of the bridge steers an electric servo motor for correction signals.

Description

The invention relates to an exposure control device according to the preamble of the claim 1.

In one described in FR-PS 1486 011 The camera user must decide for himself whether the natural light is suitable for the installation of this type Recording is sufficient or the artificial light source must be used. When working with artificial light must be operated, a manual switch must be operated with which an adjustable resistor is switched on according to the distance setting of the lens and the guide number of the one to be used Flash unit is set. The exposure control itself is carried out by means of a capacitor that is connected to the photosensitive element or the resistor and the photosensitive element as i? C-member cooperates. The charge on the capacitor starts synchronously with the start of exposure. When the terminal voltage of the capacitor reaches a predetermined value, a switching device from two Ti aufstören is triggered, so that a magnet is de-energized and the light passage opening is closed again. Simultaneously When the magnet is de-energized, a switch is closed so that the flash unit is triggered. A disadvantage of this structure is that the diaphragm is controlled by an ÄC element and the actual movement of the diaphragm setting device is not fed back to the exposure control circuit will. There is therefore no control of the actual aperture, which leads to incorrect settings can lead.

Known automatic flash photography devices (DT-OSen 1 901 850 and 1 903 779) switch on depending on the brightness of the photographing object automatically switches from daylight exposure to flash exposure, the exposure control but itself is carried out by an ÄC member as in FR-PS 1486 011, without any feedback of the actual position of the exposure setting device. In addition, these known devices show no way in the flash exposure Guide number of the flash to be used and the distance setting of the lens automatically consider.

The invention is based on the object of an exposure control device that works very precisely and reliably of the type specified in the preamble of claim 1, in which, moreover, the decision whether the object brightness is sufficient for the picture or artificial light is used must be hit automatically.

This object is achieved according to the invention with the means mentioned in claim 1. The light discriminator circuit relieves the user of the camera of the decision about the type of recording to be made, so that any misjudgment of the lighting conditions is excluded. In addition, the automatically controlled switching device is integrated into a bridge circuit, one branch of which has an adjustable element determined by the actual aperture, so that the exposure setting device is determined not only by the object brightness or the distance setting of the lens and the guide number of a flash light, but also through the feedback aperture itself. This always ensures an exact exposure,

The invention is explained below with reference to the description of an embodiment with reference

3 4

would take on the drawing showing an automatic light discriminator circuit 15 according to the invention

Device shows in a schematic representation, comprises a photosensitive element P ₂ and a

explained in more detail. with transistors Tr _n and 7V ₄ equip Schaiitt-

By means of a shutter factor setting wheel 1, triggers are on, to which the divided voltage supplied by a changeable shutter speed and a film resistor VR _{5 is} fed as a signal corresponding to the sensitivity in an output voltage. The output of the partial rotary movement Schmitt trigger, which can be used for setting or adjusting, is connected to a relay LS , and the setting wheel 1 is convertible. With the on-switch S ₁ and S, in the relay working position setting wheel 1, a wheel 2 is engaged, on the surrounding of which is open in the rest position. The beginning of a variable resistor VR _{1 is} attached. In this way, the order of the circuit 15 is selected on an output shaft of one of the following, that if the amount of light emanating from an object to be photographed is less than a previously driven Sej-vomotors 3 is an under-certain value and that attached by the photosensitive setting wheel GR , which drives intermediate wheels 4 and 5 which are output in accordance with element P _{2 and which are arranged by means of the changer.} A voltage divided by 15 bar resistance VR _{5 is} lower with the wheel 2 coaxially and in a non-rigid connection than a predetermined threshold value, the adjustment wheel 7 arranged on the edge has a resistor TV., And Tr _{4 of} the Schmitt trigger in the state VR _{1 of} the wheel 2 dragging grinder 6. An OFF or ON position is switched, whereby another intermediate wheel 8 engages on the one hand in the intermediate closing of the switches S ₁ and S, the relay LS interchangeable wheel 4 and on the other hand in a rack 9 20 is effected.

a. This engages drivingly at an intermediate lever 10 when photographing the object

on, who in turn with an actuator 12 closing the main switch SM from the object

a diaphragm setting device 11 is engaged. outgoing and from the light-sensitive elements

The right half of the drawing shows various th P ₁ and P ₂ absorbed light quantities greater than switching arrangements and their electrical connection 25 a predetermined value, so the vorbeschriedung, namely a servo circuit arrangement 13, the arrangement a reduction in resistance, an artificial light circuit arrangement 14 and a value of the photosensitive element P ₂ with automatic light discriminator circuit 15. In the simultaneous increase of the resistor VR ₅ servo circuit arrangement 13, fixed resistors are provided divided voltage above a threshold value predetermined _{for the R 1} and R ₂ as well as a photosensitive element P ₁ 30 transistor Tr ₃ , soft in the shown open position, whereby the transistor 7V _{1 is} switched on and the development of a transistor 7V ₁ to be described in more detail below is switched off and the relay LS switch 5, with the variable resistor VR ₁ when the switches _{S x} and S are open, is ineffective. As a result, the resistors R ₁ and R ₂ are switched together with the wiper 6 to form a bridge circuit. The servo circuit arrangement 35, the photosensitive element P ₁ and the changer-13 also contains a variable resistor VR ₂ coupled together with a removable resistor VR ₁ with current collector 6 on the camera lens (not shown) half of the servo circuit 13 to a bridge circuit-coupled variable resistor VR 2. Since the light sensitivity corresponding to the element P _{1 of the} artificial light circuit arrangement has a resistance VR ₃ , a differential amplifier resistance, which can be changed according to the routing number information supplied by the receiving counterpart 14, this bridge circuit / l, a main switch .SM and an interconnection is not always in a symmetrical state. The control current source E. Differential amplifier circuit A provides the unbalance

The artificial light circuit arrangement 14 has a metric state of the bridge circuit fixed and energized

a conventional rectifier or the like 45 the servo motor 3, whose drive movement via

using high-voltage generator circuit SH, the intermediate gears 4 and 5 transferred to the wheel 7

and a strobe circuit of conventional art which is rotated, wherein

Order with a switching transistor Tr ₁ , a chip- the grinder 6 on the wheel on the changeable resistor

voltage divider fixed resistor R ₉ , a variable stand VR ₁ slides along and thereby the resistance

Voltage divider resistance V ' _K3 , a lightning con-stance value of the on one of the cables of the bridge circuit

densator CM, a xenon stroboscopic tube or connected variable resistor VR ₁ with

Flash tube FT and a trigger circuit CT. Grinder 6 changed. The servo motor 3 rotates under

To regulate the guide number by changing the changeable resistance VR,

changeable voltage divider resistance V \ , continues with slider 6 until the symmetry

the base of the switching transistor Tr _{1 is} reached via a resistor of the bridge circuit. Upon arrival

stood R _t with the collector of a control transistor th this state switches the servomotor 3 off.

Tr ₂ connected, which in turn has a

Via a xenon tube N from the variable clamping wheel 8 and the rack 9, the actuating element 12

voltage divider resistor V ' _Ri supplied divided Sipander diaphragm setting device 11 adjusted so that

nUng picks up. The trigger circuit CT is thus set to a suitable aperture. Then

formed that they the xenon flash tube FT over a is to trigger or open the not shown

Camera shutter contact SX and one by means of the camera shutter in the exposure position

with the light display connected in series with the contact SX , the release button (not shown) is depressed. Since every-

criminator circuit 15 switchable switch 5 ₂ but the switch S _{2 of} the relay LS with the syn-

seized. The Widerstand'werte of the mutually comparable 65 chronkontakt SX is connected in series, remains the

bound variable resistors VR _n and V ' _Ri trigger circuit CT with open switch S ₉ also

are set according to the desired guide number - according to the opening and closing movements

bar. the lock is opened or closed

nem contact SX ineffective and the xenon flash tube FT in the artificial light circuit arrangement 14 is not switched on.

In the circuit state described above, the diaphragm setting device is servo-controlled by means of the light-emitting element P _{1 in} order to take a picture in natural lighting.

If the amount of light emanating from the subject falls below a predetermined value, the relay LS comes into action and closes its switches S ₁ and S ₂ in the manner described above, with the closing of switch S ₁ creating a bridge sound between VR ₁ and slider 6, VR _x , VR ₃ , R ^, R ₁ and P ₁ come about. Since the resistance value of the resistor VR ₁ adapts to the distance of the subject and that of the resistor KA ₃ adapts to the guide number used, the aperture setting device 11 can be used to adjust the aperture in a manner similar to that described above so that the bridge circuit depends on the distance from the subject Amount of light and is balanced according to the selected guide number. The set aperture is determined based on the distance of the subject and the guide number.

When the release button is pressed to open the shutter, the xenon flash tube FT is switched on by closing the contact SX via the trigger circuit CT using the charge occurring in the flash capacitor CM , which is dependent on the selected guide number, since the conduction level of the transistor Tr ₁ is determined by the variable resistor V ' _Rs which regulates the guide number.

The xenon flash tube FT therefore emits an amount of light proportional to the charge of the capacitor CM , so that an automatic flash exposure is carried out with the guide number and the exposure distance corresponding to the aperture and shutter setting.

As the above description shows, in a device and circuit arrangement according to the invention the reference variable fed to the servo device corresponding to that of the artificial light source set amount of light output changed and thus with simple and precisely working means enables the production of an automatic flash exposure and the technical possibilities of the recording the camera expanded. In addition, by using the light discriminating circuit, the camera automatically switched to recording with normal or natural and artificial lighting In the latter case, an exposure-technically precise setting results. the Egg-finding therefore creates a camera that is extremely easy to use.

1 sheet of drawings

Claims (5)

Patent claims: 1. Exposure control device with an exposure control circuit which, depending on a switching device, can be controlled either by a light-sensitive element or by adjustable impedances depending on the distance setting of the lens and the guide number of an artificial light source and which in turn controls an exposure setting device, characterized in that for automatic control the switching device (S ₁ ) is provided with a light discriminator circuit (15) which detects the brightness of the object, since the exposure control circuit has a bridge circuit (VR _x , VR. ₂ , VR ₃ , R ₁ , R ₂ , P ₁ ) , and the switchable '(VR _1), the light-sensitive element (P ₁₎ depending on the switching means (S _1), corresponding to the other recording information set impedances (-; in which branches in addition to a controlled by the Belichtungseinstelleinrichtung (8 to 23) Eleme VR ₂ , VR ₃ ) are effective, and that a motor (3) is provided which controls the setting adjustment device (8 to 12) via the output signal of the bridge circuit. 2. Exposure control device according to claim 1, characterized in that of the impedances set according to the other recording information one (VR _S ) with an impedance (V _Rr ) - »is bound, which is the amount of charge of an artificial light circuit arrangement (14) associated with a flash capacitor ( CM) controls. 3. Exposure control device according to Anspnich 1 or 2, characterized in that In the bridge circuit of the series circuit of the controlled element (VR ₁ ) and the photosensitive element (P ₁ ) a series circuit of the resistor (R ₁ ) and the resistor (A ₂ ) is connected in parallel that the distance setting by the switching device (S ₁ ) corresponding impedance (VR ₂ ) to the light-sensitive element (P ₁ ) and the impedance corresponding to the guide number (VR _{: i} ) to the resistor (A ₃ ) can be connected in parallel and that the bridge circuit has a differential circuit arrangement (A) on the output side. 4. Exposure control device according to one of the preceding claims, characterized in that the light discriminator circuit (15) is assigned a light-sensitive element (P ₂ ) for measuring the object brightness and a Schmitt trigger which is reversible by means of the output variable of the light-sensitive element (P ₂ ) and its output the switching device (S ₁ ) controls. 5. Exposure control device according to one of the preceding claims, characterized «that the light discriminator circuit (15 ) controls a second switching device (S ₂ ) which is connected in series with a camera shutter contact (SX).