JPS602926A - Auto stroboscope device - Google Patents

Abstract

PURPOSE:To prevent over-exposure at a short-distance side by varying the dimming level of an auto stroboscope according to the photographic distance. CONSTITUTION:A potentiometer 2 is coupled with a photographic lens which is operated manually, and a voltage is inputted as the dimming level to a comparator 4. Reflected light from a subject is inputted to the photodiode 6 of an operational amplifier 5. The output of a capacitor 8 is compared with the dimming level by the comparator 4, which outputs a light emission stop signal to a stroboscope circuit 10 when they coincide with each other to stop a discharge tube 12. The meter 2 generates a voltage corresponding to the photographic distance, and this is sent as the dimming level to the comparator, which compares the input with the terminal voltage of a capacitor 7 integrating the quantity of the reflected light. Therefore, the voltage of the potentiometer 2 is set so that the voltage is low at the short-distance side, thus the quantity of light emission is reduced at the short-distance side to prevent over-exposure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an autostroboscopic device that changes the light control level depending on the photographing distance.

An auto strobe device illuminates a subject with light emitted from a flash discharge tube, measures the reflected light from the illuminated subject with a light receiving element, and detects when the integrated value of the reflected light reaches a predetermined dimming level. At times, the flash discharge tube stops emitting light. When photographing with a flash, the aperture must be adjusted according to the shooting distance to keep the amount of light on the film's image plane constant. However, the auto strobe device automatically adjusts the amount of light emitted from the flash discharge tube according to the shooting distance. It is easy to operate and is currently widely used.

One of the characteristics of silver salt photosensitive materials is reciprocity failure.

This means that even if the exposure amount (j! o g E) is kept constant, if the combination of irradiation light intensity (1) and exposure time (1) changes, the density (D) value will be different. This is a characteristic. Generally, in the case of an auto flash device, the intensity of the irradiated light is stronger and the exposure time is shorter on the short distance side, so if you set the exposure amount to be the same regardless of the shooting distance, the reciprocity law failure mentioned above will result in a predetermined density. This results in overexposure as shown in FIG.

SUMMARY OF THE INVENTION An object of the present invention is to provide an autostroboscopic device that can correct the effects of reciprocity law failure and provide appropriate exposure even for objects at close distances.

In order to achieve the above object, the present invention changes the brightness level depending on the photographing distance.

Embodiments of the present invention will be described in detail below with reference to the drawings.

Figure 2 shows the relationship between shooting distance and light control level.The present invention lowers the light control level on the short distance side and reduces the amount of light irradiated by the flash discharge tube than on the long distance side. This prevents overexposure due to reciprocity law failure.

FIG. 3 shows an embodiment of the invention. Resistance 1. Potentiometer 2. and resistor 3 are connected in series. This potentiometer 2 is linked to a manually operated photographic lens and generates a voltage having a characteristic curve shown in FIGS. 1 and 2, which is input to a comparator 4 as a dimming level.

The reflected light from the object enters a photodite connected to the input terminal of the operational amplifier 5 and is converted into a photocurrent. When the switch 7 is turned off at the same time as the flash discharge tube emits light, the capacitor 8 is charged with a photocurrent. The terminal voltage of this capacitor 8 is input to the comparator 4, where it is compared with the dimming level. When the amount of reflected light integrated by the capacitor 8 and the dimming level match, the comparator 4
A high-level (hereinafter referred to as rHJ) light emission stop signal is output from.

As is well known, the strobe circuit 10 is connected to a synchro switch 1.
1 is turned on, the gate electrode 128 of the flash discharge tube 12
A high voltage is applied to cause the flash discharge tube 12 to emit light. When the light emission stop signal output from the comparator 4 is input, the power supply to the flash discharge tube 12 is stopped.

In this embodiment, a voltage corresponding to the shooting distance is generated from the potentiometer 2, which is sent to the comparator 4 as a dimming level, and is compared with the terminal voltage of a capacitor 7 that integrates the amount of reflected light. When the two match, a flash is discharged. The tube 12 stops emitting light. Therefore, by setting the voltage of the potentiometer 2 to be lower at the short distance side, it is possible to reduce the amount of light emitted at the short distance side and prevent overexposure.

FIG. 4 shows an interlocking mechanism between the potentiometer and the photographic lens. A brush 17 of the potentiometer 2 is attached to a distance ring 16 of a photographic lens 15. A conductor 19 and a resistance layer 20 are provided on an arc-shaped nonconductor 18, on which a brush 17 slides. Since the brush 17 slides on the resistor 1W17 on the short distance side, the voltage changes depending on the position of the brush 17. Since the brush 17 slides on the conductor 19 on the far side, a constant voltage is generated.

FIG. 5 shows an embodiment in which the aperture level is automatically set by a distance measuring device, and the same components as those shown in FIG. 3 are designated by the same reference numerals. Drive circuit 2
2 is activated by pressing the release button and drives a diode 23 that emits near-infrared light. This near-infrared light passes through the lens 24 and heads toward the subject 25. The near-infrared light reflected by the object 25 passes through the lens 26 and
The signal enters a sense-stable device (hereinafter referred to as PSD) 27. As is well known, in this PSD, a high-resistance semiconductor (silicon) is formed into a uniform resistance layer, and when light hits one point on its surface, the photocurrent generated here is divided in inverse proportion to the position. is pressed and taken out from the electrodes at both ends. Since the position of the light incident on the PSD 27 changes depending on the object distance, the photographing distance can be determined from the two current values taken out from the electrodes at both ends.

The current taken out from the electrodes of the PSD 27 is converted into a voltage by a current-voltage conversion circuit 28.29, further converted into a digital signal by an A/D converter 30.31, and then input to a signal processing calculation circuit 32. The shooting distance is calculated.

The obtained distance information is sent to the correction circuit 33 and corrected so that the value on the short distance side becomes smaller. This corrected digital signal is converted into an analog signal by the A/D converter 34 and sent to the comparator 4. Incidentally, the signal processing calculation circuit 32 and the correction circuit 33 are constituted by a microcomputer. Further, the distance measuring device is not limited to the above-described embodiment, and devices that have been widely used in the past can also be used.

The present invention having the above configuration changes the aperture level according to the photographing distance, thereby preventing overexposure on the short distance side due to reciprocity failure as in conventional autostroboscopic devices. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between density and photographing distance when photographing with a conventional autostroboscopic device. FIG. 2 is a graph showing the brightness level of the autostroboscopic device of the present invention. FIG. 3 is a circuit diagram showing an embodiment of the present invention in which the light adjustment L novel is changed in conjunction with the photographing lens. FIG. 4 is a perspective view showing the interlocking relationship between the photographing lens and the potentiometer. FIG. 5 is a circuit diagram showing another embodiment of the present invention in which the dimming level is automatically changed by a distance measuring device. 2... Potentiometer 5... Operational amplifier 4... Comparator 12... Flash discharge tube 15... Photographing lens 16... Distance ring 17... Brush 19... Conductor 17... - Resistance layer 23...Near infrared light emitting diode 27...PSD.

Claims (1)

[Scope of Claims] (1) The reflected light from the subject illuminated by the light emitted from the flash discharge tube is measured, and when the integral value of this reflected light reaches a predetermined dimming level, the flash discharge tube emits light. What is claimed is: 1. An auto-stroboscopic device for stopping a flash, comprising: means for detecting a photographing distance; and means for correcting the light control level according to the photographing distance detected by the distance detecting means. (Powder) The autostroboscopic device according to claim 1, wherein the correction means is a potentiometer and is operated in conjunction with a manually operated photographic lens. (3) The distance detection means is The autostroboscopic device according to claim 1, which is a distance measuring device.