JPH035568B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an electric shutter device for a camera.
The present invention relates to an electric shutter device for a camera that controls exposure time based on the stored value.

The camera measures the subject light and digitally stores the shutter time obtained based on the subject brightness.
Several electric shutter devices are already known that use this stored value to control the shutter speed.

However, as is well known, the camera's shutter speed, or exposure time, depends on the shooting conditions.
Shutter speeds range from a few thousandths of a second at high speeds to several minutes at low speeds, and in order to store such a wide range of shutter speeds digitally, the number of elements in the counter and memory circuit must be increased. It had the disadvantage of being very large. For example, 1/20
Shutter seconds from 00 seconds to 3 minutes, frequency
Count using 100KHz clock pulse,
If you memorize this, the period of the clock pulse will be
Since it is 10μsec, 1/2000 second is 5×10 ^-4 ÷10 ^-5 =
50 counts, 3 minutes is 3 x 60 ÷ 10 ^-5 = 18 x 10 ⁶ counts, and to count up to 18 x 6 ⁶ , 2 ²⁵ = 33554432, so a binary counter and 1 bit memory are required. 25 elements are required for each.

Furthermore, since a large number of counters and memory elements are required, there is a problem that power consumption increases.

However, it is clear that when the shutter time is a slow time, it is not necessarily necessary to measure the time with the same precision as when the shutter time is a high speed time. In other words, when counting shutter seconds uniformly using clock pulses of a constant frequency,
In order to improve the timekeeping accuracy in high-speed seconds, it is necessary to increase the frequency of the clock pulse, but since low-speed seconds are measured at the same time intervals as high-speed seconds, the accuracy becomes excessive for low-speed seconds, making it of little use. In addition to this, this also resulted in the need for additional counters and memory elements.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide an electric shutter device for a camera in which the frequency of the clock pulse is gradually decreased to gradually increase the time interval between shutter seconds.

Another object of the present invention is to digitally store the shutter time obtained from a direct photometry circuit that measures the light reflected from the film surface, and to repeatedly take pictures at the same shutter speed based on this stored value. To provide an electric shutter device for a camera in which the frequency of a clock pulse is gradually decreased to gradually increase the time interval for counting the shutter seconds.

According to the present invention, the time measurement interval gradually becomes longer as the shutter time becomes longer and the time becomes slower. Therefore, when the same shutter time is measured, the number of counts is smaller than when the time is measured at equal intervals. . Therefore, the number of counters and memory elements is
It requires less than the conventional one.

Furthermore, since the number of counters and memory elements is small, power consumption can be reduced accordingly.

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

The figure shows an electric circuit of an electric shutter device for a camera according to the present invention. The above-mentioned camera is a direct photometry type single-lens reflex camera having a focal plane electric shutter, and its electric circuit is equipped with a storage means for shutter seconds obtained by direct photometry,
A direct photometry circuit 1 that receives reflected light from the film surface and determines the shutter speed; a shutter control circuit 2 that maintains the trailing curtain of a focal plane shutter (not shown) in a non-travel position; and an output. A clock pulse generation circuit 3 whose pulse frequency gradually decreases over time, a time counter 4 that counts clock pulses output from this clock pulse generation circuit 3, and a latch circuit 5 that stores the contents of this counter 4. , a coincidence detection circuit 6 that compares the output of the latch circuit 5 and the output of the time counter 4;
a flip-flop circuit 7 that inverts the output based on a coincidence output from the camera; and a photographing mode selection switch SW ₁ that selectively connects the direct photometry circuit 1 and the flip-flop circuit 7 to the shutter control circuit 2. It is configured.

The direct photometry circuit 1 includes a photoelectric conversion element (not shown) arranged to face the film surface, and when the amount of light received by this photoelectric conversion element reaches an appropriate level, the rear curtain of the shutter is activated. A shutter close signal for releasing the holding is applied to one fixed terminal a of the changeover switch _SW1 .

The shutter control circuit 2 is connected to the movable contact terminal c of the changeover switch SW ₁ , and in response to switching of the switch SW ₁ , the direct photometry circuit is connected to one fixed terminal a of the switch SW ₁ . A shutter close signal outputted from a flip-flop circuit 7 connected to one or the other fixed terminal b is detected, the holding of the trailing curtain is released, and the exposure is ended.

The clock pulse generation circuit 3 includes a read-only memory 11 that stores information on a plurality of frequencies of clock pulses, an address counter 12 that specifies a read address of the read-only memory 11, and a read-only memory 11 that specifies a read address of the read-only memory 11.
It is composed of a DA converter 13 that converts the frequency information read out from the DA converter 13 into an analog quantity, and a V-F converter that converts the analog voltage value outputted from the DA converter into a frequency signal, and the above-mentioned Frequency signal is address counter 1
2, and is also input to the time counter 4 as a clock pulse.

This clock pulse generation circuit 3 stops operating with the address counter 12 cleared to zero before the front curtain of the shutter starts running, and operates in synchronization with the start of photometry in the direct photometry circuit 1. is beginning to start. Now, suppose that the address counter 12 increases its output by 1 every 50 counts, for example, and the frequency information of the read-only memory 11 is such that the period increases arithmetic by 10 μsec for each address, for example. The clock pulse output from the clock pulse generation circuit 3 has a period of 50 pulses from immediately after the circuit 3 starts operating.
It is 10 μsec, and thereafter increases arithmetic by 10 μsec every 50 pulses.

The time counter 4 is formed of a series of binary counters. The number of binary counters is selected to be 16 when the clock pulses from the clock pulse generating circuit 3 are used to measure the time from, for example, 1/2000 seconds to 3 minutes.
That is, the total number of pulses P output until 3 minutes elapse from the start of operation of the clock pulse generation circuit 3.
Since the minimum integer n that satisfies 50×10 ^-5 × (1+2+…+n)>3×60 is 849, it must satisfy P<50×849=42450. On the other hand, since 2 ¹⁶ = 65536, 16 binary counters are sufficient.

The latch circuit 5 is connected to the time counter 4.
The same number of D-type flip-flops as the number of binary counters are arranged in parallel, and the T input terminal of each flip-flop serves as the control terminal of the latch circuit 5, and this control terminal is connected to the changeover switch _SW1. is connected to the movable contact terminal c.

This latch circuit 5 receives a shutter close signal applied to the terminal c of the changeover switch _SW1 , and stores the contents of the counter 4 at this time in the circuit 5. Note that the latch circuit 5 is constantly supplied with an operating voltage to prevent the stored contents from volatilizing.

As described above, the electric shutter device of the present invention is constructed.

Next, the operation of this electric shutter device will be explained.

(1) In the case of direct metering shooting mode in which the movable contact of switch SW ₁ is connected to fixed terminal a, first press the shutter release button (not shown).
When the button is pressed, all the electric circuits except the latch circuit 5 are reset and returned to the initial state. As a result, the shutter control circuit 2 starts holding the rear curtain. Next, when the front curtain of the shutter starts moving, the direct metering circuit 1
starts measuring the light reflected from the front curtain of the shutter and the film surface. At the same time, the clock pulse generation circuit 3 starts operating, and the time counter 4 starts counting the clock pulses output from the circuit 3.

When time has elapsed since the direct photometry circuit 1 started photometry and the film surface is exposed to an appropriate amount of light, the state of the photometry circuit 1 is reversed and a shutter close signal is output. As a result, the shutter control circuit 2 releases the holding of the trailing curtain, the trailing curtain runs, and the exposure of the film surface is completed. At the same time, the latch circuit 5 receives the shutter close signal and holds in the circuit 5 the contents of the counter 4 at this time, that is, the count number corresponding to the shutter seconds. Thereafter, even if the contents of the counter 4 change, the contents stored in the latch circuit 5 do not change.

(2) In the direct metering memory shooting mode where the movable contact of switch SW ₁ is connected to fixed terminal b, first, when the shutter release button is pressed, all electric circuits except latch circuit 5 are reset. and returned to the initial state. As a result, the shutter control circuit 2 starts holding the rear curtain. Subsequently, when the front curtain of the shutter starts running, the clock pulse generation circuit 3 starts operating, and the time counter 4 starts counting the clock pulses output from the circuit 3.

The time counter 4 is counted up,
When the contents match the contents stored in the latch circuit 5, that is, when the shutter time of the previous direct photometry photographing is reached, the coincidence detection circuit 6 detects this and outputs a coincidence signal to the flip-flop circuit 7. In response to this coincidence signal, flip-flop circuit 7 inverts its state and outputs a shutter close signal. As a result, the shutter control circuit 2 releases the holding of the trailing curtain, the trailing curtain runs, and the exposure of the film surface is completed. Therefore, the electric shutter device performs the photographing operation again at the shutter time of the previous direct photometry photographing.

The latch circuit 5 receives the shutter opening signal output from the flip-flop circuit 7 and transfers the stored contents to the contents of the time counter 4, but the contents of the counter 4 at this time are as follows.
Since it matches the memory contents of latch circuit 5,
Substantially, the count number corresponding to the shutter speed during the previous direct photometry shooting is stored again. Therefore, unless the changeover switch _SW1 is switched to the fixed terminal a and direct photometry photography is performed again, it is possible to take any number of frames at the same shutter speed used in the previous direct photometry photography.

As described above, according to the present invention, the frequency of the clock pulses output from the clock pulse generation circuit is gradually decreased, so the number of counters and memory elements can be reduced without substantially reducing timekeeping accuracy. It is possible to provide an electric shutter device which is extremely advantageous in manufacturing and use.

In the above embodiment, the electric shutter device is of a direct photometry type, but it goes without saying that the electric shutter device may be of a memory type. If the electric shutter device is of a memory type, prior to exposing the film surface, the photometric circuit is activated and the latch circuit stores a count number corresponding to the proper exposure time, and this stored value is used as the actual value. What is necessary is to check the contents of the time counter in parallel with the exposure.

Further, although a read-only memory for storing frequency information is provided in the clock pulse generating circuit, it is of course possible to omit this and input the output of the address counter directly to the DA converter.

Furthermore, it goes without saying that the clock pulse generation circuit and the like can be configured by software as part of the control system of the central processing unit. In this way, the device of the present invention can be easily realized using simple software.

[Brief explanation of the drawing]

The figure is an electric circuit diagram of an electric shutter device showing one embodiment of the present invention. 1... Direct photometry circuit (photometering circuit), 2...
... Shutter control circuit, 3 ... Clock pulse generation circuit, 4 ... Time counter, 5 ... Latch circuit, 6 ... Coincidence detection circuit, 11 ... Read only memory, 12 ... Address counter, 1
3...D-A converter, 14...V-F converter, SW ₁ ...changeover switch.

Claims (1)

[Scope of Claims] 1. A clock pulse generation circuit that starts generating output pulses in synchronization with the start of photometry in the photometry circuit or the start of exposure on the film surface, and a time counter that counts the clock pulses output from this clock pulse generation circuit. a latch circuit that stores the contents of this time counter in synchronization with the completion of photometry in the photometry circuit; and contents already stored in this latch circuit.
An electric shutter for a camera, comprising: a coincidence detection circuit that successively compares the newly counted up contents of the time counter; and a shutter control circuit that closes the shutter based on the output of the coincidence detection circuit. In the device, the clock pulse generation circuit includes a read-only memory that stores frequency information, a DA converter that converts the frequency information read from the read-only memory into an analog voltage value, and an output from the DA converter. A V-F converter converts the analog voltage value generated into a frequency signal and outputs it as a clock pulse, and the output of this V-F converter is counted.
An electric shutter device for a camera, comprising: an address counter that sequentially changes the read address of the read-only memory, and gradually reduces the frequency of the clock pulse. 2. A clock pulse generation circuit that starts generating output pulses in synchronization with the start of photometry of the direct photometry circuit that measures light reflected from the shutter curtain surface and the film surface, or the start of exposure on the film surface, and an output from this clock pulse generation circuit. a time counter for counting clock pulses, a latch circuit for storing the contents of this time counter in synchronization with the completion of photometry in the direct photometry circuit, and contents already stored in this latch circuit;
a coincidence detection circuit that successively compares the newly counted up contents of the time counter; a shutter control circuit that closes the shutter based on the output of the coincidence detection circuit or the direct photometry circuit; A switch for selectively connecting a photometry circuit and the coincidence detection circuit to the shutter control circuit; In an electric shutter device for a camera, the clock pulse generation circuit comprises: a read-only memory for storing frequency information; A DA converter that converts the frequency information read from the read-only memory into an analog voltage value, and a V-F that converts the analog voltage value output from the DA converter into a frequency signal and outputs it as a clock pulse. Count the output of the converter and this V-F converter,
An electric shutter device for a camera, comprising: an address counter that sequentially changes the read address of the read-only memory, and gradually reduces the frequency of the clock pulse.