JPS592006B2 - Automatic brightness adjustment type viewfinder display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an in-finder display device that incorporates a circuit system including a TTL photometry circuit and operates under the control of the circuit system using an LED as a light emitting element to display the shutter speed or aperture value. When displaying the shutter speed or aperture value based on photometry results in the viewfinder using a light-emitting element, the light emission intensity of the display section using the light-emitting element is usually maintained at about 300 cd/d.

By the way, the brightness of the viewfinder field of view is within the exposure meter interlocking range (
AS^100 and EV17 to EV3), approximately 100
Since the brightness varies from 0.00 Cd/771" to 0.5 cd/m", the brightness ratio between the display section and the finder image varies extremely widely, from several tenths to several hundred times. Therefore, within the viewfinder field of view, if the display part is relatively dark compared to the viewfinder image, the display part becomes difficult to see, and conversely, if the viewfinder image is relatively dark compared to the display part, the brightness ratio When this occurs, the finder image becomes difficult to see, and in either case, it becomes impossible to provide both the finder image and the display in an easy-to-see state within the viewfinder field of view. Furthermore, in cameras with a built-in TTL exposure meter, the photometric element is placed inside the camera, but when the subject is dark and there is little light entering the camera, the display inside the viewfinder inside the camera still shines too brightly. It also had drawbacks such as ghosting and harmful light entering the exposure meter. An object of the present invention is to provide a camera having an in-finder display device that solves these drawbacks.

In other words, the present invention uses the output of the photometric circuit to control the brightness of the display section according to the brightness of the surrounding light.
The brightness ratio between the display inside the viewfinder and the viewfinder image is automatically maintained at a value that is easy to see, so that both are always easily visible within the field of view of the viewfinder. This prevents the light from shining relatively brightly and causing harmful light to the exposure meter. Note that when controlling the brightness of the light emitting element, a method of changing the voltage applied to the light emitting element may be considered.

However, light emitting elements generally exhibit rapid changes in brightness in response to changes in applied voltage, and LEDs are no exception. On the other hand, the subject light and the brightness of the viewfinder image are proportional to each other. Therefore, if you try to change the voltage applied to the LED according to changes in the subject light, even if the brightness of the viewfinder image changes slightly, the brightness of the LED display will change greatly, and the brightness of the viewfinder display will change. The brightness ratio with the viewfinder image cannot be automatically maintained at a value that is easy to see. Also,
Appropriate control of brightness by voltage is difficult due to the characteristic that brightness changes rapidly due to a slight change in voltage. The present invention has been constructed with practical considerations in mind as well. That is, in controlling the brightness of the LED display section, the present invention provides a method for intermittently connecting a power supply transistor that controls the power supply to the LED and this power supply transistor in a frequency range such that no flicker is felt in the light emission of the LED. and a control circuit connected to its base.

The control circuit includes an oscillator and a rectangular wave output circuit connected to the oscillator to supply the base with an output that always makes the power supply transistor conductive for a certain period of time regardless of the frequency, and adjusts the oscillation frequency of the oscillator to the As a result, the duty cycle of the conduction of the feeding transistor is changed by controlling the output of the photometric circuit,
The present invention is characterized in that the brightness of the LED is thereby controlled in accordance with the brightness of ambient light. Hereinafter, the present invention will be explained with reference to illustrated embodiments.

What is shown in FIG. 1 is one embodiment of the present invention. The present invention requires an oscillator whose oscillation frequency changes depending on the output of the photometric circuit as described above, and in this embodiment, a relaxation oscillator using a PUT is exemplified as such an oscillator. However, it goes without saying that the present invention is not only possible with such a relaxation oscillator, but also with the use of other generally known variable output frequency oscillators under the control of the output of the photometric circuit. It is clear from the above-mentioned gist of the present invention that exactly the same effect can be obtained if In this embodiment, the photometric element of the built-in exposure meter of the camera is shared for adjusting the display brightness in the viewfinder. Reference numeral 11 denotes a logarithmic compression diode, which is connected in series with the photoelectric element 1 to form a photometric circuit.

12 is a transistor for logarithmic expansion. The photoelectric element 1 converts the subject brightness into an electric signal, the diode 11 logarithmically compresses it (current → voltage), and the transistor 12 logarithmically expands it (voltage → voltage).
current) and a current proportional to the subject brightness flows through transistor 1.
2 collector.

Note that the current-voltage temperature characteristics of the diode 11 are as follows:
This cancels out the voltage-current-temperature characteristics of the transistor 12, and as a result, the collector current of the transistor 12 is stable with respect to temperature. Reference numeral 13 denotes a circuit for transmitting the signal at point A to a memory circuit, a shutter speed control circuit, an exposure meter circuit, etc.

In this embodiment, there is no need to provide a special photoelectric element for controlling the brightness of the display section. For example, in a single-lens reflex camera, the photoelectric element 1 is disposed inside the camera to measure light (usually proportional to the brightness of the viewfinder) passing through the lens (TTL photometry). The above transistor 12
A capacitor 2 is connected to the collector of the capacitor 2, and is configured to be charged by the collector current. 3 is a programmable unijunction transistor PUT, and this PUT3 constitutes a relaxation oscillator together with other elements.

That is, when the potential at the connection point a between the collector of the transistor 12 and the capacitor 2 exceeds the voltage at the connection point b between the fixed resistors 6 and 5, the PUT 3 becomes conductive, discharging the charge in the capacitor 2, and discharging the electric charge at one end of the resistor 4. An output pulse is generated at c. 7 is a monostable multivibrator-like circuit that is triggered by this pulse and conducts for a certain period of time.

Reference numeral 8 constitutes a switching circuit using an ordinary power supply transistor, the base of which is connected to the output of a monostable multivibrator, and the collector of which is connected to a display section 9 having an LED as a light emitting element.

In the above device, when a photometric switch (not shown) is turned on, the capacitor 2 starts charging by the collector current of the transistor 12 which is proportional to the intensity of light incident on the photoelectric element 1.
When the terminal voltage (point a) becomes equal to or higher than the potential at the connection point b between fixed resistors 6 and 5, PUT3 becomes conductive and capacitor 2
The stored charge is discharged through the resistor 4.

At this time, an output is generated at the upper end c of the resistor 4. When the discharge of capacitor 2 is completed, point a becomes almost ground potential, and PUT
3 becomes non-conductive, and charging of the capacitor 2 starts again. The above operation is thus repeated and an oscillation pulse is generated as an output at point c. This oscillation pulse is converted into a rectangular wave pulse by the monostable multivibrator 7 and is input to the base of the power supply transistor 8. The power supply transistor 8 becomes conductive or non-conductive depending on the input rectangular wave pulse. The lower limit of the frequency of the rectangular wave pulse is set so as to exceed the limit at which flickering is felt in the light emission of the LED display section 9 due to conduction/non-conduction of the power supply transistor 8. looks like continuous light emission. FIG. 2 shows the output of a rectangular wave pulse point e that is input to the base of the power supply transistor 8, where A, C, and C have different frequencies (1/T).

As shown in the figure, the time t during which these rectangular wave pulses make the feeding transistor conductive is always constant regardless of their frequency. Therefore, as the frequency changes, the duty cycle t/T changes, and the amount of power supplied to the LED display section 9 per unit time changes in proportion to this.
The brightness of the ED can be changed. Since the frequency is changed by also using the output of the photometric circuit, the brightness of the LED is eventually controlled in accordance with the brightness of the subject light. Note that the oscillation frequency f of PUT3 is the same as that of photoelectric element 1.
The resistance value is R, the capacitance of capacitor 2 is C, and the power supply voltage is V
, where the voltage across the diode 11 is VD, and the conduction start level of PUT 3 set by the resistors 5 and 6 is Vt, it is approximately expressed as follows.

Here C. v. vt is constant and VD is also V. This is because it can be considered to be approximately constant with respect to Vt. Now, if the area illuminance of the photoelectric element is L, then γ-
1 is adopted, and if B is the brightness generated on the surface of the focus plate of the viewfinder due to the subject.

On the other hand, if the brightness of the LED display section is Be, as is clear from Figure 2, it goes without saying that it is much more effective than the conventional LED display section where the brightness does not change, and in practical terms the brightness ratio is approximately constant. Since it is considered as such, there is no problem.

The present invention is like a douki, and because the brightness ratio between the LED display section and the viewfinder image is automatically adjusted to be approximately constant, the display is difficult to see due to its relative relationship with the viewfinder image. The image of the viewfinder does not become blurred, or conversely, the image of the viewfinder does not become difficult to see, and both images can always be provided within the view of the viewfinder in an easy-to-see state. In particular, the effect of being able to display the LED in the focuser L adjacent to the focuser image without impairing the visibility of the focuser L' image, which is the original function of the focuser L, is of great significance in the focuser L' image. Furthermore, it is possible to prevent harmful light from appearing on the exposure meter due to ghosting due to the brightness of the display section being too large relative to the human light entering the camera.
A TL photometric camera can be improved in terms of both photometry and display.

In addition, in the present invention, a photometric circuit that has conventionally been used only to obtain information such as shutter speed and aperture value can be replaced with an LED that displays shutter speed and aperture value.
It is also used to control the brightness of the camera, making it possible to more completely and efficiently transmit the shutter speed and aperture value using the output of the photometry circuit in the camera.

In addition, the power supply battery built into the camera has a limited capacity, but the LED display section consumes relatively high power, so when the subject is dark, the amount of power supplied to the LED is reduced. A configuration that makes the image darker also leads to power savings and is practical for cameras. In addition, in terms of power saving, the LED display is not simply dimmed all at once, but when the subject is bright, the LED display becomes brighter, so it goes without saying that the visibility of the viewfinder display is not sacrificed in any way. . By the way, in the present invention, L
In controlling the brightness of the ED display, the power supply transistor that controls the power supply to the LED is made to conduct intermittently in a frequency range that does not cause flickering in the LED light emission, and the conduction time width is determined by the frequency. Regardless, the frequency is always constant and the output of the photometric circuit is also used to change the frequency, so that the duty cycle of conduction changes as a result.

Therefore, the brightness change of the LED can be easily controlled by changing the frequency of the input signal to the power supply transistor, and the range of brightness change ranges from the lower limit frequency that does not cause flickering to the eyes to the saturation of the light emission intensity in relation to the duty cycle. It can be easily realized as needed within a wide range up to the upper limit frequency. Therefore, the ease of controlling the brightness of this display makes it particularly useful as a display device within the viewfinder of a camera.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG.
Figure 3 shows the brightness of the viewfinder image when the γ value of the photoelectric element (CdS) is 0.5. It is a graph which shows the brightness ratio of an LED display part. 1...Photoelectric element, 2...Capacitor,
3... Programmable unijunction transistor, 4, 5, 6... Fixed resistor, 7...
... Monostable multivibrator, 8 ... Power supply transistor, 9 ... Display unit using LED as a light emitting element, 11 ... Logarithmic compression diode, 12.
...Logarithmic expansion transistor, 13...Circuit that transmits the signal at point A to the shutter speed control circuit, exposure meter circuit, etc.

Claims (1)

[Claims] 1 Built-in circuit system including TTL photometry circuit,
In a camera having an in-finder display device that uses an LED as a light emitting element and operates under the control of the circuit system to display the shutter speed or aperture value, a power supply transistor that controls power supply to the LED, and a power supply transistor that controls the power supply to the LED. A control circuit connected to the base thereof is provided so as to conduct intermittently in a frequency range where flickering is not felt in the light emission, and the control circuit includes an oscillator and the power supply transistor connected to the oscillator regardless of the frequency. comprises a rectangular wave output circuit that supplies the base with an output that always makes the transistor conductive for a certain period of time, and by controlling the oscillation frequency of the oscillator by the output of the photometric circuit, the duty cycle of the conduction of the feeding transistor is changed as a result. An automatic brightness adjustment type viewfinder display device, characterized in that the brightness of the LED is controlled according to the brightness of ambient light.