JPS58163927A - Automatic exposure controlling circuit for ttl auto stroboscope - Google Patents

Abstract

PURPOSE:To obtain a correct exposure value of the background for a main object to be photographed, by hlating an integrating operation for a prescribed time after running of a shutter front curtain ends, then, executing photocurrent integration again, and starting the running of a rear curtain when said result reaches a prescribed level. CONSTITUTION:Even after a correct exposure quantity is provided to a main object to be photographed by light emission of a stroboscope after a shutter front curtain is fully opened, photocurrent integration by stationary light is executed, and exposure is executed to a background. That is to say, integration for controlling the stroboscope light emission for deciding an exposure quantity of the main object to be photographed is executed by the first integration circuit 13, and integration for controlling an exposure time for deciding an exposure quantity of the background is executed by the second integration circuit 17. As a result, output voltage VC2 of an operational amplifier 18 of the integration circuit 17 rises, and when an exposure quantity by stationary light attains to correct level against the background, a running start signal of a shutter rear curtain is sent out, the rear curtain runs, and exposure ends. In this way, an exposure value of the background against the main object to be photographed can be made correct.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an automatic exposure control circuit for TTL auto strobe;
For details, please refer to the film/L-mum surface reflective type T T Li1ll.
In single-lens reflex cameras that use light, T' is used to control exposure during TTL auto strobe photography.
This invention relates to an automatic exposure control circuit for l' L auto strobe.

'T' T L Auto strobe with film surface reflection type T
The technology of TTL auto strobe photography, which is attached to a single-lens reflex camera that performs TL photometry and controls the amount of light emitted by the auto strobe using an exposure control circuit on the camera side, is already well known. In this TTL auto strobe photography, when the shutter is fully open, the strobe fires to compensate for the underexposure of ambient light such as natural light, so the metering integration circuit uses ambient light until the shutter is fully open. The photocurrent is integrated, and as the shutter is fully opened, the photocurrent caused by the strobe light is integrated. Then, when the integral value reaches a predetermined exposure level, T T L
A flash stop signal is sent to the auto strobe.

By the way, in normal TTL auto strobe photography, when charging of the strobe is completed, a charging completion signal is transmitted to the camera side, thereby fixing the shutter time to the strobe synchronization time.

For this reason, for example, because the background is far away from the main subject being photographed with a strobe, and the strobe light does not reach the background sufficiently, the strobe light has no effect on the exposure of the background; When there is a certain amount of constant light, there will be a large difference in the number of exposure steps between the part of the main subject that is exposed to the strobe light and the background part that is exposed only to the constant light. In such a case, the background part becomes too dark compared to the main subject part, and the conventional TTL auto strobe photography described above does not provide enough strobe photography to adjust the tone of the photographic screen.

Therefore, conventionally, as a countermeasure for the above case, the shutter time was manually set to be longer than the strobe synchronization time to appropriately extend the exposure time using the steady light. However, in this case, since the shutter speed is set solely based on the photographer's sense of perspective, it is difficult to appropriately control the number of exposure steps of the background relative to the main subject.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to control the amount of light emitted by a strobe light by integrating the photocurrent generated by the strobe light. Also, the exposure value of the background relative to the main subject is automatically controlled appropriately by making sure that the integration of ambient light and light current is continued, and closing the shutter when the integral value reaches a predetermined value. T T
To provide an automatic exposure control circuit for L auto strobe.

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is an electrical circuit diagram of an automatic exposure control circuit for an 'I' T L autostrobe, showing one embodiment of the present invention. This automatic exposure control circuit is a film surface reflection type 'r'''I
' It is built into single-lens reflex cameras that perform L metering. A photoelectric conversion element 2 for photometry that passes through the lens aperture 1 of this camera and is reflected on the front curtain surface of the focal plane shutter and the film surface exposed by the movement of this front curtain is connected to an inverting input terminal of an operational amplifier 3. The anode is connected between the non-inverting input terminal and the non-inverting input terminal. The non-inverting input terminal of the operational amplifier 3 is connected to the collector of an N P NI type 1 transistor 4 for logarithmic compression, and the output terminal of the operational amplifier 3 is connected to the inverting input terminal of the operational amplifier 30 and the base of the transistor 4. The connection point between the output terminal of the operational amplifier 3 and the base of the transistor 4 is connected to the bases of NPN transistors 5 and 60 having the same characteristics as the transistor 4, and the emitters of the transistors 5 and 6 are grounded.

The collector of the transistor 5 is connected to the second integrating circuit 1.
The base of the transistor 7.8 and the collector of the transistor 7 are connected to the base of the transistor 7.8 and the collector of the transistor 7 of the integral control circuit 12, which is provided in the previous stage of the It is connected to the inverting input terminal of the operational foot 1140 of the first integrating circuit 13. An integrating capacitor 15 is connected between the inverting input terminal and the output terminal of the operational amplifier 14, and an analog switch 16 is connected in parallel with the capacitor 15. The non-inverting input terminal of the operational amplifier 14 is connected to the terminal 21 to which the reference voltage VREF is applied, and the control terminal of the analog switch 160 is a trigger that changes from the "H" level to the "L" level when the shutter front curtain starts running. It is connected to a terminal 22 to which a signal SA is applied.

The emitter of the transistor 7.8 of the integral control circuit 12 is connected to the terminal 23 to which the power supply voltage Vcc is applied, and the collector of the transistor 8 is connected to the collector of the transistor 9.11 and the bases of the transistors 9 and 1o. The emitters of transistors 9, 10, 11 are grounded. The base of the transistor H is connected to a terminal 24 to which an integral pause signal S1 at a level of .degree. transistor 10
The collector of is connected to the inverting input terminal of the operational amplifier 18 of the second integrating circuit 17. An integrating capacitor 19 is connected between the inverting input terminal and the output terminal of the operational amplifier 18, and the analog switch 2 is connected in parallel with the capacitor 19.
0 is connected. The non-inverting input terminal of the operational amplifier 18 is connected to the reference voltage application terminal 21, and the control terminal of the analog/log switch 20 is connected to the trigger signal application terminal 2.
Connected to 2.

The output terminal of the operational amplifier 14 of the first integrating circuit 13 is connected to the inverting input terminal of an operational amplifier 26 forming a comparator of the first determining circuit 25.
The output terminal of the operational amplifier 18 of No. 7 is connected to the inverting input terminal of an operational amplifier 29 forming a comparator of the twentieth determination circuit 28. The non-inverting input terminal of the operational amplifier 26 is
It is connected to the reference voltage application terminal 21 via a resistor 27 for setting the first judgment voltage, and is composed of a variable foot type current flow device 31 for setting film sensitivity and a PNP type transistor 32°33.34. It is connected to the collector of the transistor 33 of the film sensitivity setting circuit 35,
The non-inverting input terminal of the operational amplifier 29 is connected to the reference voltage application terminal 21 via a semi-fixed resistor 30 for setting a second determination voltage, and the transistor 34 of the film sensitivity setting circuit 35 connected to the collector. The emitters of the transistors 32 to 34 of the film sensitivity setting circuit 35 are connected to the power supply voltage application terminal 23, and the bases of the transistors 32 to 34 are commonly connected to each other.
connected to the collector. The constant current regulator 31 is connected between the collector of this transistor 32 and ground.

The output terminal of the operational amplifier 26 of the first judgment circuit 25 is connected via inverters 36 and 37 to a signal transmission terminal 38 for sending a light emission stop signal 8T to the auto strobe, and is connected to the second judgment circuit 25. 28 operational amplifiers 2
The output terminal of 9 is connected to one input terminal of the NOR gate 40. The other input terminal of the NOR gate 40 is connected to the output terminal pressure application terminal 23 of the synchronized time setting circuit 39. An input terminal of the synchronized time setting circuit 39 is connected to the trigger signal application terminal 22. Even if the trigger signal SA changes from the "Hn level" to the "°L" level due to the start of running of the shutter front curtain, the synchronization time setting circuit 39 controls the point at which the trigger signal SA changes from the "Hn level" to the "°L" level for a time corresponding to the strobe synchronization time. It is a delay.

Next, the operation of the automatic exposure control circuit configured as described above will be explained with reference to the time chart shown in FIG. Film surface reflection TTL photometry type with the above automatic exposure control circuit -
When a TTL auto strobe is attached to an eye reflex camera and the power switches of both are turned on, the above terminal 23
The power supply voltage Vcc is applied to the terminal 21, and the reference voltage VR is applied to the terminal 21.
EF is applied. When the power supply voltage Vcc is applied to the terminal 23, a current corresponding to the film sensitivity set by the variable current regulator 31 flows through the collector of the transistor 32, and the current mirror effect of the transistors 32 to 34 causes the transistor to 33 and 34's "Electric Worker" is played on both the 33 and 34 lines. Therefore, if the resistance value of the resistor 27 of the first judgment circuit 25 is R, the non-inverting input terminal of the operational amplifier 26 has the first judgment voltage V, =
VREr +Ij R is applied. Further, in the second judgment circuit 28, the resistance value of the semi-fixed resistor 3o is set to 1, so that the second judgment voltage V2=VREF1J- is applied to the non-inverting input terminal of the operational amplifier 29. applied. Here, when n=2, k is the number of steps of the exposure difference between the exposure value determined by the first determination voltage vI and the exposure value determined by the second determination voltage V2. That is, in order to perform exposure control that lowers the exposure of the background exposed to constant light by kEV relative to the exposure of the main subject exposed to strobe light, as will be described later, the second determination voltage (2) is set. It is set to be the first judgment voltage v1.

When shutter charging is performed in this state, the "use" level signal of the trigger signal SA is applied to the terminal 22, so that the analog switch 16 of the first integrating circuit 13 and the analog switch of the second integrating circuit 17 are switched. 20 is turned on.Then, the operational amplifiers 14 and 18 have their inverting input terminals and output terminals short-circuited, and the integrating capacitor 15.
19 is reset, these operational amplifiers 14,1
The output voltages VCI and VC2 of 8 are equal to the reference voltage VREF applied to each non-inverting input terminal.

Here, when the chanter release button is pressed, the movable reflection mirror rises, and accordingly, the lens aperture 1 is narrowed down, and when the movable reflection mirror completes its rise,
The shutter front curtain starts running. When the photographing optical path is opened by raising the movable reflection mirror, the subject light, which is the steady light reflected by the shutter front curtain surface that passes through the narrowed-down lens diaphragm 1, is received by the photoelectric conversion element 2 for photometry.
When the cathode of the photoelectric conversion element 2 is determined, a photocurrent 1p corresponding to the brightness of the subject begins to flow through the anode. Since this photocurrent ■p flows as the collector current of the transistor 4, a current Jp equal to the photocurrent Ip also flows through the collectors of the transistors 5 and 6 due to the current mirror effect.

When the current Ip flows through the collector of the transistor 5, the same current Ip also flows through the collector of the transistor 7, so that a current ]'l) also flows through the collector of the transistor 8 due to the current mirror effect.

By the way, in this state, since the integration stop signal S1 of '°11' level has not yet been applied to the terminal 24, the terminal 24 is at the L''' level and the transistor 1 is off. Therefore, the transistor 9, 10 habe->ga°'
Since the current ■p flowing through the collector of the transistor 8 also flows through the collector of the transistor 9, also in this case, due to the current mirror effect, the current ■p flowing through the collector of the transistor 8 also flows through the collector of the transistor 10. A current Ip also flows through the collector.

That is, when the photometric moon photoelectric conversion element 2 starts receiving subject light and a photocurrent Jp flows, a current equal to this photocurrent Ip flows through the transistors 6 and 10.
The operational amplifier 1 of the first integrating circuit 13 is
4 and the respective output terminals of the operational amplifiers 18 of the second integrating circuit 17 begin flowing to ground through the respective analog switches 16, 20. Then, when the shutter front curtain starts running, at this point t.

Then, the trigger signal SA at the terminal 22 changes to the Ll+ level, which turns off the analog switch 16.20, and at this time, the current Ip starts to flow through the integrating capacitors 15 and 19, respectively. In the first integrating circuit 13 and the second integrating circuit 17, photometry by integrating the photocurrent Ip is started.

That is, as a result, from the above time point t1, the operational amplifier 1
4's output voltage Vc+ and the operational amplifier 18's output voltage V
C2 gradually increases as an integral voltage of the photocurrent Ip corresponding to the amount of reflected light from the front curtain surface of the shunter and the constant light from the film surface exposed as the front curtain runs. The output voltage MCI, VC2 of the operational amplifier 14.18 is Vc+, where C is the capacitance of the integrating capacitor 15.19.
= VC2= VREF 10-! It is expressed as j2-t.

Output voltage V of the operational amplifier 14 of the first integrating circuit 13
CI is applied to the inverting input terminal of the operational amplifier 26 of the first judgment circuit 25, and the output voltage VC2 of the operational amplifier 18 of the second integrating circuit 17 is applied to the inverting input terminal of the operational amplifier 29 of the second judgment circuit 28. Therefore, while the output voltage VCI of the operational amplifier 14 and the output voltage 'VC2 of the operational amplifier 18, which increase at the same level as the shutter front curtain runs, are lower than the first determination voltage v1, the output of the operational amplifier 26 is "'". Since the output of the operational amplifier 29 is also at the "H" level and the output of the NOR gate 40 is at the "L" level, the magnet coil 41 is excited. The rear curtain of the shutter is held in a charged state.

When the front curtain of the shutter finishes traveling and the shutter base is fully opened at time t2, a synchro contact (not shown) closes and a light emission signal is sent to the strobe, causing the TTL auto strobe to fire. When the main subject is irradiated with this strobe light, the reflected light is transmitted to the photoelectric conversion element 2 for photometry.
Since the photocurrent Ip increases rapidly, the output voltage VCI of the operational amplifier 14 of the first integrating circuit 13 rises with a steep slope from the time t2.

By the way, at the time point t2 when the shutter base is fully open, the "use" Lebel integration stop signal S1 is applied to the terminal 24, so the transistor 11 is turned on at this time.

Then, since the transistors 9 and 10 are turned off, the current Ip that had been flowing to charge the integrating capacitor 19 of the second integrating circuit 17 through the transistor 10 stops flowing at the above-mentioned time t2, and the second The integration operation of the integration circuit 17 is stopped. For this reason,
Output voltage VC2 of the operational amplifier 18 of the second integrating circuit 17
The output voltage from the above-mentioned time point t2 to the same time point t2 is held constant.

That is, in the first product 1-minute circuit 13, integration is performed using steady light from time t1 when the front shutter curtain starts traveling, and then the integration is switched to perform integration using strobe light at time t2 when the shutter base is fully open. On the other hand, in the second integrating circuit 17, from the above-mentioned time point t1, integration using the steady light is performed in the same way as the above-mentioned first integrating circuit 13, and when the above-mentioned time point t2 is reached, the integration is stopped.

Photocurrent integration by the strobe light is performed in the first integrating circuit 13, and when the strobe light reaches an appropriate amount of light for the main subject, the output voltage Vc+ of the operational amplifier 14 of the integrating circuit 13 changes to the first value. The point in time when 1 = 1
At step 3, the output of the operational amplifier 26 changes to the °'L" level, so at this time, a 1-flash stop signal ST of the °'L" level is sent to the strobe from the signal transmission terminal 38, and the strobe stops emitting light. .

While the first integrating circuit 13 is performing photocurrent integration by strobe light, the second integrating circuit 17 is in an integration halt state. Since the integration stop signal S1 of the terminal 24 is applied from the time t2 of the strobe to the time corresponding to the full flash time Tf, the second integration circuit 17 starts to emit full light from the time t2. The above integration pause state continues until time t, when time Tf has elapsed.After the strobe stops emitting light, at time t4, the terminal 24
Since the integration stop signal S1 becomes "°L" level, at this time, the transistor 11 of the integration control circuit 12 is turned off and the transistors 9 and 10 are turned on.
A current Ip to further charge 9 begins to flow,
The integration operation of the second integration circuit 17 is restarted. Time t4
Since the strobe has already stopped emitting light, the second integrating circuit 17 restarts the integrating operation and performs photocurrent integration using the steady light, so that the output voltage VC2 of the operational amplifier 18 increases again from the above-mentioned time point t4. The inclination of the shutter front curtain during travel is a gentle inclination similar to y. In this way, after the shutter base is fully opened, photocurrent integration of the strobe light is performed by the strobe light emitted,
Even after the proper exposure amount has been given to the main subject, photocurrent integration using constant light is performed, so even backgrounds that are far away from the main subject and where the strobe light did not reach sufficiently can still be exposed using constant light. will be carried out. That is, the integration for strobe light emission control that determines the exposure amount of the main subject is performed by the first integration circuit 13, and the integration for exposure time control that determines the exposure amount of the background is performed by the second integration circuit 13. It will be carried out by 17.

The output voltage VC2 of the operational amplifier 18 of the second integrating circuit 17 increases as the photocurrent integration is performed using the constant light, and when the amount of exposure due to the constant light becomes appropriate for the background, the output voltage of the operational amplifier 18 increases. VC2 reaches the second determination voltage V2. Then, at the time point t when this p y"=■"・1 is reached, the output of the operational amplifier 29 changes to the °+L+" level, and a state is reached in which a signal to start running the shutter trailing curtain is sent. Also, the strobe After the time t2 when starts emitting light, the synchronized time setting circuit 39
Since the output of the operational amplifier 29 is at the Ll+ level, the output of the operational amplifier 29 reaches the Ll level at the time t.

The output of the Noah gate 40 becomes the "■1" level. Therefore, the magnet coil 41 becomes de-energized, the shutter trailing curtain runs, and the exposure by the above-mentioned constant light ends.

The second determination voltage v2 for determining exposure due to steady light is set to 1//n of the first determination voltage v1 for determining exposure due to strobe light. In the exposure control using the above TTL auto strobe, the number of steps of exposure difference between the main subject, which is mainly exposed to strobe light, and the background, which is mainly exposed only to constant light, is from n-2k to kEV. For example, to set the background to an exposure difference of -lEv with respect to the main subject, set n=2 when the resistance value of the semi-fixed resistor 30 is 1A, and to set the background to an exposure difference of -2EV, set n
= 4, exposure using strobe light and constant light will be performed with the set exposure difference.

In addition, in the above-mentioned TTL auto strobe photography, if there is relatively sufficient steady light, the output voltage VC2 of the above operational amplifier [8] reaches the second judgment voltage v2 before reaching the time t2 when the shutter base is fully opened. However, even if the output of the operational amplifier 29 changes to L1 level at this time, the output of the synchronized time setting circuit 39 is at the 1%L+ level before the above-mentioned time t2. The rear curtain of the shutter never moves.

As described above, according to the present invention, even after the strobe light is controlled to provide proper exposure for the main subject, the integration using the steady light before the strobe light is continued,
When the integral value of this steady light reaches an appropriate value, the shutter base is closed and the exposure is completed.
The main subject exposed to strobe light and the background exposed to constant light are automatically controlled to the appropriate exposure ratio, and TTL auto strobe and film surface reflection type TT
(combined with an L metering single-lens camera)
It is possible to take pictures with good exposure control that takes advantage of the characteristics of the lens.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of an automatic exposure control circuit for an 'I' T L auto strobe showing an embodiment of the present invention, and FIG. 2 explains the operation of the automatic exposure control circuit shown in FIG. 1 above. 2 is a time chart of signals in each part for 12... Integral control circuit 13... First integrating circuit 17... Second integrating circuit 25... First determination circuit 28... ...Second judgment circuit

Claims (1)

[Claims] In a film surface reflection TTL 1llll optical camera having a function of controlling the amount of light emitted by a TTL auto strobe, while the front curtain of the shutter is running, the front curtain surface and the running of the same front curtain are At the same time, photocurrent integration is performed based on reflected light of steady light from the exposed film surface, and from the end of the travel of the shutter front curtain, photocurrent integration is performed based on reflected light including strobe light from the film surface. an integrating circuit; a first determining circuit that sends a light emission stop signal to the strobe when the output of the first integrating circuit reaches a predetermined first determining level; Photocurrent integration is performed based on the reflected light of steady light from the front curtain surface and the film surface exposed as the front curtain runs, and from the time the shutter front curtain ends running, at least the first integrating circuit a second integrating circuit that suspends the integration operation while performing photocurrent integration based on the reflected light including the strobe light, and then performs photocurrent integration again based on the steady light reflected from the film surface; A TTL characterized by comprising: a second determination circuit that sends a shutter trailing curtain travel start signal when the output of the second integration circuit reaches a predetermined second determination level. Automatic exposure control circuit for auto strobe.