JPH0132965B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an automatic exposure control device for a focal plane shutter, and more specifically, an automatic exposure control device for a focal plane shutter. The present invention relates to an automatic exposure control device for a focal plane shutter that automatically determines an appropriate exposure time.

The photometering device in a camera measures the light from the subject in order to give the film proper exposure, so ideally it should be placed on the film surface or somewhere equivalent, such as the focal plane shutter in the case of a focal plane shutter. It is desirable to arrange a photoelectric conversion element for photometry on the curtain surface and perform photometry.
However, since this is actually impossible, a method called the so-called direct metering method has been used in the past, in which the subject light reflected from the film surface or an equivalent shutter curtain surface is photometered. As is well known, in the case of a focal plane curtain shutter, the film surface is initially covered with a black cloth shutter front curtain, which is started by the shutter release and moves across the screen frame. When the film is moved, the film surface that was covered by the front curtain is exposed, and after the appropriate exposure time has elapsed, the rear shutter curtain made of black cloth is started and the exposed film surface is covered with the rear curtain again. It is like being covered.

In addition, in the case of a high-speed shutter speed, the rear curtain is started while the front curtain is running to obtain a high-speed speed. The slit spacing becomes narrower. In order to determine the appropriate exposure by measuring the subject light reflected from the shutter front curtain surface and film surface of a curtain shutter operating in this manner, first, the light reflected from the moving front curtain surface is metered. Subsequently, the reflected light from the exposed film surface is photometered, but in this case, since the light reflectances of both are different, it is necessary to make the light reflectances of both substantially the same. In other words, to obtain proper exposure,
If the light reflectances of the light reflected from the front curtain surface and the light reflected from the film surface are not the same, the photometric values of the reflected light will be different, making it impossible to obtain proper exposure.

Therefore, conventionally, in this type of photometry device, in order to make the reflectance of the front curtain surface the same as that of the film surface, a pattern of material having the same reflectance as that of the film surface is placed on the front curtain surface. is printed on.

However, the reality is that the reflectance of a film usually changes depending on the type of film, so even if the above pattern is printed on the shutter curtain surface, in this case, the reflectance of the shutter curtain surface will change. The ratio is merely an approximation to the reflectance of standard film, and depending on the type of film, there may be a difference in reflectance between the shutter curtain surface and the film surface, making it impossible to control exposure properly. There is.

In view of this, various automatic exposure control devices have been conventionally provided that correct the error in the photometric output value due to the difference in reflectance between the shutter curtain surface and the film surface to obtain an appropriate exposure time. ing.

However, the film reflectance correction means in the conventional automatic exposure control device includes, in addition to the first photometry circuit for exposure control, a second photometry circuit that measures the light reflected from the film. Since the exposure control output value is corrected based on the output of the photometering circuit, two photometering circuits are required.
The disadvantage was that the configuration was complicated.

By the way, as shown in FIG. 1, the film surface covered by the front shutter curtain gradually becomes exposed as the front shutter curtain moves. That is,
In FIG. 1, a rectangular image frame F indicates the frame of the photographing screen on the film, and when the front curtain B moves in the direction of travel of the front curtain indicated by the arrow _a0 , it is covered by the front curtain B. The exposed film surface E is successively exposed. Further, the time axis drawn at the bottom of the figure indicates the time t during which the leading curtain B moves. That is, the time t= _T1 when the leading curtain B passes the left end of the image frame F and the film surface E starts to be exposed is the film surface exposure start time, and the time t= _T2 is the time when the film surface E starts to be exposed. is picture frame F
At this time, the front curtain B passes the right end of the picture frame F, and the front curtain B is fully opened. That is, time t= _T2 is the time when the front curtain finishes running and the photographing screen is fully opened. Figure 1 shows
The first curtain B is partially opened and the film surface E is slightly exposed. Let the exposed area of the film surface E be _A2 , and let the area covered by the first curtain B at that time be _A1. , let A ₀ be the total area surrounded by the image frame F, then A ₀ =A ₁ +A ₂ .

On the other hand, in a photometric device having a center-weighted light distribution characteristic, as the shutter front curtain moves, the photoelectric conversion element for photometry generates a photocurrent as shown in FIG.
Ip changes. In this case, a pattern is printed on the reflective surface of the front curtain surface of the shutter so that it has a reflectance equal to that of a standard film. In Fig. 2, when the front curtain starts traveling and the rear end of the front curtain reaches the approximate center of the image frame F, the photoelectric conversion for photometry continues until the time t=Tc when the front curtain reaches the center. The photocurrent Ip of the element is equal to the photocurrent Is due to the front curtain surface of the shutter, and when the rear edge of the front curtain reaches approximately the center of the frame F and approximately the center of the film is exposed, the photocurrent Ip at this point Tc is reached. Before and after that, the photocurrent Ip changes sharply. If the film loaded in the camera has a film surface with a higher reflectance than the standard film reflectance above, the photocurrent will change as shown by the curve Ia before and after the above time Tc.
Ip rises steeply. Furthermore, if the film in the camera has a film surface with a reflectance lower than the standard film reflectance, the photocurrent Ip decreases steeply as shown by the curve Ib before and after time Tc. point in time
After the photocurrent Ip of the photometric photoelectric conversion element changes sharply before and after Tc, the photocurrents I _F1 and I _F2 correspond to the reflectance of each film surface.

Now, if we consider the case of using a film with a higher reflectance than the standard film reflectance, when we perform photometry using such a film, the integrated voltage of the photometry circuit will be as shown in Figure 3. Change. That is, in FIG. 3, the integrated voltage Vc rises almost linearly with a constant slope from the start of photometry until the time Tc reaches the center of the image frame, but t = Tc
From the point in time, the slope becomes even larger and the integrated voltage
Vc starts to rise, and eventually this integrated voltage characteristic is approximated by two straight lines with the bending point at time Tc. Expressing this mathematically, let C be the integrating capacitor of the photometry circuit, Is be the photocurrent based on the light reflected from the front curtain, I _F1 be the photocurrent based on the light reflected from the film, and Tx be the integration end time.
The integrated voltage Vc is as follows: Vc = 1/C∫ ^Tc ₀ Isdt + 1/C∫ ^Tx _Tc I _F1 dt = Is/CTc + I _F1 /C (Tx - Tc) (1).

In this way, in a photometer with a center-weighted light distribution characteristic, the photocurrent Ip increases until t=Tc, the time from when the front curtain of the shutter starts running until the approximately central part of the film is exposed. There is no change in the photocurrent Ip, and the photocurrent Ip changes sharply at the time Tc, so when considering correction of exposure control based on the difference in reflectance between the shutter curtain surface and the film surface,
The correction circuit may be activated from the above-mentioned time point Tc.

The present applicant previously proposed a device for correcting the difference in reflectance between the shutter curtain surface and the film surface in a photometry device having the center-weighted light distribution characteristic (Japanese Patent Application No. 133992/1983). ). This uses a sampling hold circuit to hold the integrated voltage value of the photometric output at the time when the shutter front curtain passes the center of the film surface, and this held value is captured and added to the above integrated voltage value. This is how it was done. However, in addition to such devices,
without using a sampling hold circuit etc.
Furthermore, it has been desired to provide an apparatus that can easily correct exposure control output values due to differences in film reflectance.

In view of the above-mentioned points, an object of the present invention is to provide a charging circuit consisting of a capacitor and a resistor in a photometric device having a center-weighted light distribution characteristic, and to adjust the characteristic curve in which the charging voltage of this charging circuit changes to the surface of the shutter screen. An object of the present invention is to provide an automatic exposure control device for a focal plane shutter, which corresponds to a characteristic curve of a correction amount based on a difference in reflectance between a film surface and a film surface.

Prior to describing specific embodiments of the present invention, the amount of correction based on the difference in reflectance between the shutter curtain surface and the film surface will be described.

Now, let Vc ₁ be the integrated voltage due to a film with the same reflectance as the standard film reflectance, that is, the integrated voltage due to the shutter front curtain, and Vc be the integrated voltage due to a film with a reflectance different from the standard film reflectance. ₂ . Also, the time t is t≧Tc
(In other words, the time is measured from the time Tc when the rear edge of the front shutter curtain passes the center of the image frame.) Then, the above respective integrated voltages Vc ₁ and Vc ₂ are calculated from the above equation (1) as Vc ₁ = Is /CTc+Is/Ct=Is/C(Tc+t) Vc ₂ =Is/CTc+I _F1 /Ct=1/C(IsTc+I _F1 t) Therefore, when calculating the EV value difference ΔEV between these two integrated voltages Vc ₁ and Vc ₂ , , ΔEV=ln(Vc ₂ /Vc ₁ )/ln2 =ln(IsTc+I _F1 t/Is(t+Tc)/ln2 =ln[Tc/t+Tc+I _F1 /Is(t/t+Tc)]/l
n2 …(2).

Therefore, ΔEV expressed by the above equation (2) corresponds to the amount to be corrected based on the difference in reflectance between the shutter front curtain surface and the film surface. Here, when t→∞, lim t→∞=ln(I _F1 /Is)/ln2...(3) Therefore, if this t→∞ correction amount is 100%, then at t=nTc When calculating each correction amount from the above formula (2), t = 1/4Tc is 60%, t = 1/2Tc is 66%, t = Tc is 75%, t = 2Tc is 83%, t = 4Tc is 90% %, t
= 94% at 8Tc. Therefore, when the above equation (2) is expressed graphically, a characteristic curve of the correction amount as shown in FIG. 4 is obtained.

In the present invention, the characteristic curve of the correction amount as shown in FIG. 4 is approximated by the characteristic curve of the changing charging voltage of the charging circuit having an appropriately determined time constant. This is to control the reference potential of the image to perform appropriate exposure control.

Hereinafter, the present invention will be explained with reference to Examples.

FIG. 5 is an electrical circuit diagram of an automatic exposure control device showing one embodiment of the present invention. A photoelectric conversion element 1 for photometry, which is provided to receive reflected light from the shutter curtain surface and film surface at an actual aperture with center-weighted light distribution characteristics, is connected between an inverting input terminal and a non-inverting input terminal of an operational amplifier 2. It is connected. operational amplifier 2
An integrating capacitor 3 is connected between the inverting input terminal and the non-inverting input terminal of the operational amplifier 2, and the non-inverting input terminal of the operational amplifier 2 to which the anode of the photoelectric conversion element 1 is connected is connected to the terminal 4 to which the reference voltage V _R1 is applied. It is connected. An analog switch 5 is connected in parallel with the integrating capacitor 3, and the control terminal of the switch 5 is a terminal to which a trigger signal _S1 whose level changes from "H" to "L" when the front curtain starts running is applied. 6. An exposure control comparator 8 is connected to the non-inverting input terminal of the output terminal of the integrating circuit 7 configured as described above, that is, the output terminal of the operational amplifier 2. This comparator 8 has an inverting input terminal applied with a voltage V _J for judgment, and has an integrated voltage Vc from the operational amplifier 2.
When the voltage exceeds the judgment voltage V _J , the comparator 8
The output level of the switch changes from "L" to "H". The output terminal of the comparator 8 is connected to one end of a magnetic coil 9 for keeping the shutter rear curtain in a restrained state. The other end of the magnet coil 9 is connected to a terminal 10 to which an "H" level potential is applied simultaneously when the power switch is turned on.

The judgment voltage V _J of the comparator 8 is provided by a correction circuit 11 and a film sensitivity information setting circuit 12. Correction circuit 11
is a charging circuit 15 consisting of a series circuit of a capacitor 13 and a resistor 14, and analog switches 16, 17,
The film sensitivity information setting circuit 12 includes an operational amplifier 21, a resistor 22, and a variable resistor 23. That is, in the correction circuit 11, one end of the capacitor 13 of the charging circuit 15 is connected via the analog switch 16 to a terminal 24 to which the reference voltage V _R1 is applied, and the other end of the capacitor 13 is connected via the resistor 14 to the terminal 24 to which the reference voltage V R1 is applied. It is connected to terminal 25 to which _R2 is applied. The reference voltages V _R1 and V _R2 are
The relationship is V _R1 > V _R2 . The control terminal of the analog switch 16 is set to "L" when the front shutter curtain runs and the rear end of the front curtain passes approximately the center of the film surface, that is, the approximately center of the film surface is exposed. It is connected to a terminal 26 to which a signal _S2 whose level changes from "H" to "H" is applied. An analog switch 1 is connected in parallel with the resistor 14 of the charging circuit 15.
7 is connected. This analog switch 17
The control terminal of is connected to a terminal 27 to which a signal _S3 whose level changes from "L" to "H" from the TTL autostrobe is applied during charging or when charging is completed.

Capacitor 13 and resistor 14 of the charging circuit 15
The connection point with is connected to the non-inverting input terminal of the operational amplifier 19. The operational amplifier 19 has an inverting input terminal and an output terminal connected to form an impedance converter. The output terminal of the operational amplifier 19 is connected to the operational amplifier 2 of the film sensitivity information setting circuit 12 via an analog switch 18 and a variable resistor 20 for film reflectance correction connected in series with the analog switch 18.
It is connected to the inverting input terminal of 1. Simultaneously with the analog switch 16, the analog switch 18 is connected to a terminal 26 to which a signal _S2 whose level changes from "L" to "H" is applied when the shutter front curtain runs and the center of the film surface is exposed. It is connected. In the film sensitivity information setting circuit 12, the inverting input terminal of the operational amplifier 21 is connected via a resistor 22 to the terminal 25 to which the reference voltage V _R2 is applied, and the non-inverting input terminal of the operational amplifier 21 is connected to the terminal 25 to which the reference voltage V _R1 is applied. It is connected to the above-mentioned terminal 24. Further, a variable resistor 23 for setting film sensitivity information is connected between the inverting input terminal and the output terminal of the operational amplifier 21. The output terminal of the operational amplifier 21 is connected to the inverting input terminal of the comparator 8.

Next, the operation of the automatic exposure control device configured as described above will be explained.

When the front shutter curtain starts running due to the shutter release, the level of the trigger signal _S1 at the terminal 6 of the integrating circuit 7 changes from "H" to "L" as shown in FIG. Photometry starts when =0. That is, when the level of the control terminal of the analog switch 5 becomes "L", the switch 5
is opened, integration by the integrating capacitor 3 is started, and the integrated voltage Vc from the operational amplifier 2 increases. At this point, the analog switch 16,1
7 and 18 are open, the detection circuit 11 does not operate, and the determination voltage from only the film sensitivity information setting circuit 12 is applied to the comparator 8.
That is, the resistor 22 of the film sensitivity information setting circuit 12
is in a biased state by the reference voltage (V _R1 − V _R2 ), and therefore, the current I ₂₃ flowing through the variable resistor 23 is I ₂₃ = (V _R1 − V _R2 )/R ₂₂ …(4) where R ₂₂ is the resistance value of the resistor 22.
Therefore, the output voltage V _J of the operational amplifier 21 is (4)
From the formula, V _J = I ₂₃ R ₂₃ = R ₂₃ / R ₂₂ (V _R1 − V _R2 )...(5). This voltage V _J is the film sensitivity information voltage, and serves as the judgment voltage V _J of the comparator 8.

Time point t= when the shutter front curtain runs and photometry starts
When the central part of the film surface is exposed after time Tc has elapsed from 0, the signal _S2 at the terminal 26 becomes "L".
level changes to "H" level, and analog switches 16 and 18 are closed. By closing the analog switch 16, the capacitor 13 of the charging circuit 15
A current flows between the terminals 24 and 25 through the resistor 14, and charges are accumulated in the capacitor 13. Therefore, at this time, capacitor 13 and resistor 1
The potential V ₀ at the connection point with 4 is V ₀ = (V _R1 − V _R2 )e ^-t/C13R14 (6), and as shown in Figure 7, the potential V 0 at the connection point with V _R1 is
V changes towards _R2 . However, C ₁₃ is the capacitance of the capacitor 13, and R ₁₄ is the resistance value of the resistor 14. This voltage V ₀ is taken out as the output of an operational amplifier 19 forming an impedance converter. By the way, since the potential of the inverting input terminal of the operational amplifier 21 is V _R1 - V _R2 , if we ignore the resistance of the analog switch 18 which is closed at this time, the current I flowing through the correction variable resistor 20 will be ₂₀ is I ₂₀ = {(V _R1 −V _R2 )−(V _R1 −V _R2 )e ^-t/C13R14 }/R
₂₀ V _R1 −V _R2 /R ₂₀ (1-e ^-t/C13R14 )…(7).

Therefore, the output voltage V _J of the operational amplifier 21 is V _J = (I ₂₀ + I ₂₃ )・R ₂₃ = R ₂₃ (V _R1 − V _R2 ) {1/R ₂₂
+1/R ₂₀ (1-e ^-t/C13R14 )}...(8). As is clear from this equation, the output voltage of the operational amplifier 21 in this case is equal to the constant film sensitivity information voltage when the correction circuit 11 does not operate, and the charging voltage from the correction circuit 11 that increases with the passage of time t. The output voltage is the sum of

Here, since the charging voltage V ₀ is expressed as V ₀ α1−e ^-t/C13R14 , when t=Tc, that is,
When the front curtain finishes traveling and the entire film surface of the photographic frame is exposed, the correction amount is 75%, so if we solve this by setting 1-e ^-Tc/C13R14 = 0.75, we get C ₁₃ R ₁₄ =0.72Tc.

Therefore, the capacitance of the capacitor 13 of the charging circuit 15
The product of C ₁₃ and the resistance value R ₁₄ of resistor 14, that is, the time constant
By choosing 0.72Tc, the charging curve can be made to approximately match the correction curve shown in FIG. Note that the above charging curve and correction curve are the above t.
Even if you match not only at the time of =Tc but any time before or after that, almost the entire result will match.

The corrected judgment voltage V _J and the integrated voltage Vc are compared by the comparator 8, and when the integrated voltage Vc exceeds the judgment voltage V _J , the output of the comparator 8 becomes “H” level, and the output is sent to the magnet coil 9. The current is cut off, the rear curtain runs, and the exposure ends.

In this way, even if there is a difference in reflectance between the shutter front curtain surface and the film surface, the determination voltage V _J is changed by the charging circuit 15 according to the amount of correction of the integral value based on the difference in reflectance. , exposure control correction is performed. Correction circuit 11 having this charging circuit 15
is connected to the film sensitivity information setting circuit 12, and can perform film reflectance correction in the same way as exposure multiple correction of film sensitivity.

Next, we will discuss the case of using TTL auto strobe. TTL auto strobe is fully charged,
When the signal S ₂ becomes "H" level, the signal S ₃ applied from the strobe to the terminal 27 becomes "H" level as shown in FIG. 6 in synchronization with this. Therefore, analog switch 17 is closed in synchronization with analog switches 16 and 18. Then, since the capacitor 13 is charged with an extremely fast time constant, the non-inverting input terminal of the operational amplifier 19 instantly becomes equal to the reference voltage V _R2 . Therefore, when the shutter curtain is fully opened and the strobe fires, the above-mentioned judgment voltage has already been corrected by the amount of correction from t→∞, and even in TTL auto strobe photography, appropriate exposure control can be performed. become. Note that the signal _S3 for controlling the opening and closing of the analog switch 17 is sent to the AND gate 28 shown in FIG.
It may also be used as an output signal. That is, in FIG. 8, one input terminal of the AND gate 28 is connected to the terminal 29 to which the sequence signal _S4 , which becomes "H" level when the strobe completes charging, is applied.
The other input terminal of the AND gate 28 is connected to a terminal 30 to which is applied a strobe set signal _S5 which becomes "H" level when the strobe is attached to the camera. Therefore, in this case, when the above-mentioned signals S ₄ and S ₅ are generated, the analog switch 17 is closed and the exposure control correction in the case of the above-mentioned TTL autostroboscopic photography is performed.

The automatic exposure control device of the embodiment shown in FIG. In order to be able to perform exposure correction even for a film having a reflectance lower than the average film reflectance, a part of the circuit shown in FIG. 5 may be constructed as shown in FIG. 9. In FIG. 9, in addition to the terminal 25 to which the reference voltage V _R2 is applied, a terminal 31 to which the reference voltage V _R3 is applied is provided. And charging circuit 1
A changeover switch 32 is connected to the end of the resistor 14 of 5, and a contact terminal 32a of the switch 32 is connected to the end of the resistor 14.
is connected to the terminal 25, and the contact terminal 32b is connected to the terminal 31. Reference voltage V _R1 ,
The relationship between V _R2 and V _R3 is V _R3 > V _R1 > V _R2 , and V _R1
−V _R2 =V _R3 −V _R1 . Therefore, when the film in the camera has a reflectance higher than the standard film reflectance, the changeover switch 3
2 is switched to the contact terminal 32a, and when the film has a reflectance lower than the standard film reflectance, the changeover switch 32 is switched to the contact terminal 32b. When the changeover switch 32 is connected to the contact terminal 32a, the reference voltage V _R2 is set to the charging circuit 1.
5, so when the analog switches 16 and 18 are closed, a correction voltage that changes in the positive direction with respect to a constant film sensitivity information voltage as a reference is added to the judgment as explained in the above embodiment. A voltage is applied to comparator 8 to perform proper exposure control. In addition, when the changeover switch 32 is connected to the contact terminal 32b, the reference voltage
Since V _R3 is applied to the resistor 14 of the charging circuit 15, when the analog switches 16 and 18 are closed, the judgment voltage to which the correction voltage that changes in the negative direction based on constant film sensitivity information is added is applied to the comparator 8. Proper exposure control is achieved in a film whose reflectance is lower than the standard film reflectance given and which varies as shown in curve Ib shown in FIG.

In each of the above embodiments, the film reflectance correction amount is manually set using the variable resistor 20 prior to shooting, but when the shutter front curtain travels and reaches the center of the shooting image frame. It may be configured so that it is automatically set.

As described above, according to the present invention, since the charging circuit that changes the charging voltage with a predetermined time constant is added to the circuit that provides the judgment voltage for exposure control, the circuit is extremely simple and has high accuracy. The amount of compensation for film reflectance is controlled, and when using a TTL auto flash, the amount of compensation is automatically set to the appropriate amount, and appropriate exposure control is performed depending on the shooting mode. Demonstrates excellent effects.

[Brief explanation of drawings]

Fig. 1 is a front view of the photographic frame to explain the exposure state of the film surface due to the running of the shutter front curtain, and Fig. 2 shows the change in photocurrent of the photoelectric conversion element for photometry with respect to the running time of the shutter front curtain. Characteristic curve diagrams. Figure 3 is a diagram showing the change in integral voltage with respect to the running time of the shutter front curtain. Figure 4 is a characteristic curve showing the amount of correction based on the difference in reflectance between the shutter front curtain surface and the film surface. 5 is an electric circuit diagram of an automatic exposure control device for a focal plane shutter showing an embodiment of the present invention, and FIG. 6 is a time chart of signals of each part of the device shown in FIG. 7 is a characteristic curve diagram of the charging circuit of the device shown in FIG. 5 above, and FIG. 8 is a characteristic curve diagram of the charging circuit of the device shown in FIG. 5 above.
FIG. 9 is an electric circuit diagram showing the operating section of the analog switch during TTL auto strobe photography. FIG. 9 is an electric circuit diagram of a focal plane shutter automatic exposure control device showing another embodiment of the present invention. 7...Integrator circuit, 8...Comparator for exposure control,
11... Correction circuit, 15... Charging circuit.

Claims (1)

[Scope of Claims] 1. A photoelectric conversion element having a center-weighted light distribution characteristic and photoelectrically converting subject light reflected from the shutter front curtain surface, the film surface, or one of them; and the output of this photoelectric conversion element. an integrating circuit that integrates current and generates an integral output; a switching element that performs an opening/closing operation when the leading shutter curtain runs and the trailing edge of the leading curtain passes approximately the center of the photographic image frame; and the switching element and includes a charging circuit consisting of a series circuit of a capacitor and a resistor,
a correction circuit that outputs a charging voltage; and a judgment circuit that generates a judgment output based on the film sensitivity information up to the above-mentioned point, and after the above-mentioned point, generates a judgment output based on the charging voltage of the correction circuit in addition to the film sensitivity information. An output generation circuit, a comparator for inputting and comparing the integral output and the judgment output, and a shutter trailing curtain driving means driven based on the output of the comparator, and charging the charging circuit. An automatic exposure control device for a focal plane shutter, characterized in that the change in voltage corresponds to a characteristic curve of the correction amount of the integrated output based on the difference in reflectance between the shutter front curtain surface and the film surface. 2. A patent claim characterized in that a switching element is connected to both ends of the capacitor of the charging circuit, and the switching element is closed by a signal indicating that a TTL auto strobe attached to the camera is being charged or that charging has been completed. The automatic exposure control device for a focal plane shutter according to item 1.