Slave Flash Trigger

Description: Using any camera in a dull or dark environment generally requires supplementary light. This is a standard technique, and even where adequate natural lighting exists, conventional film pictures can benefit from enhanced contrast by using a fill-in flash for foreground subjects in shade. A flash is often built into the camera body, but the internal flash is typically not powerful enough to illuminate subjects much beyond 3 meters from the camera. On SLR cameras, a hot shoe is provided for triggering an auxiliary, more powerful flash, but small pocket cameras are usually not equipped for this. However, it is possible to trigger a slave flash from the camera flash using optical means. Some cameras, such as Olympus, Nikon, and Canon, may fire twice, appearing as one flash to the naked eye; the first flash sets the exposure, and the second captures the image. Synchronization requirements are available on various websites maintained by professional photographers, along with articles featuring kits by a caving enthusiast. The presented trigger circuit optically receives the camera flashes and can either fire simultaneously with the first flash or have a one flash delay before triggering the slave flash. Additional counting circuitry is necessary for more than one delay, which is covered by a modified circuit not presented here. The circuit operates as follows: the response of phototransistor D5 to the external camera flash is pulsed by a transistorized amplifier T1 into the dual flip-flop clock IC1. One output of a flip-flop illuminates an LED as a "ready" signal. A double pole 3-position slide switch, S1, selects none (e.g., for Kodak cameras) or one (e.g., for Olympus cameras) flash delay before triggering. Both flip-flops are utilized in the 4013, with the clock signal derived from the flash being used (triggered on the rising clock signal) to divide by two and trigger the TIC206 triac on the first or second flash. A simple RC timed reset mechanism consisting of R6-C4 is employed with a relatively long delay (approximately half a second) before resetting the entire circuit. The advantage of the triac is its ability to handle a trigger voltage of either polarity. The 2N3906 transistor may be replaced by its near equivalent, the BC212L. The SFH300-2 photodiode is supplied by Maplin as part number MES NP64U. The triac may also be a TIC126D.

The circuit described is an optical flash trigger designed for use with various camera models, particularly in low-light conditions. The primary function of this circuit is to synchronize an external slave flash with the camera's built-in flash. This synchronization is crucial for achieving the desired exposure and lighting effects, especially when dealing with subjects that are in shadow or at a distance where the internal flash is insufficient.

The circuit utilizes a phototransistor (D5) to detect the flash emitted from the camera. When the camera flash is activated, the phototransistor conducts, sending a pulse to a transistor amplifier (T1). This amplification is necessary to ensure that the pulse is strong enough to trigger the subsequent digital logic components. The dual flip-flop clock IC (4013) is used to manage the timing of the trigger signal. It divides the incoming pulse signal to control whether the slave flash fires immediately with the first flash or with a delay, depending on the configuration of the switch (S1).

The switch allows for flexibility in operation, accommodating different camera flash firing sequences. For example, Kodak cameras may require no delay, while Olympus cameras may need a slight delay to ensure proper exposure. The output from the flip-flop that indicates readiness is connected to an LED, providing a visual confirmation that the circuit is operational and ready to trigger the slave flash.

The use of a triac (TIC206 or TIC126D) as the triggering element allows for handling of both polarities of the trigger voltage, enhancing the robustness of the circuit. The RC timing circuit (R6-C4) introduces a reset delay, ensuring that the system is prepared for the next triggering event. This design consideration is essential for preventing false triggers and ensuring reliability during use.

Overall, this circuit offers an effective solution for enhancing photographic results in low-light conditions by enabling the use of external flash units, thereby providing greater flexibility and control over lighting in various shooting scenarios.Using any camera in a dull or dark environment generally requires the use of supplementary light. This is a standard technique, and even where adequate natural lighting exists, to take conventional film pictures with enhanced contrast using a fill-in` flash for foreground subjects in shade. A flash is often built into the camera body, but the inte rnal flash is not usually powerful enough to illuminate subjects much more that 3 m or so from the camera. On SLR cameras a hot-shoe is provided for triggering an auxiliary, more powerful flash, but the small pocket cameras are not so equipped.

However, it is possible to trigger a slave flash from the camera flash by optical means. Even so, things are not so simple, for some cameras, e. g. Olympus, Nikon, Canon actually fire twice, although it appears to be once to the naked eye. The first flash sets the exposure and the second takes the picture. Help on synchronisation requirements may be found at various websites maintained by professional photographers. See also for a series of articles with kits by a caving enthusiast. The presented trigger circuit optically receive the camera flashes and either fires at the same time as the first flash or has one flash delay before triggering the slave flash.

Additional counting circuitry is required for more than one delay (covered by modified circuit not presented here). Here`s how it works. The response of phototransistor D5 to the external camera flash is pulsed by a transistorised amplifier T1 into the dual flip-flop clock IC1.

One output of a flip-flop illuminates an LED as a ready` signal. A double pole 3-position slide switch, S1, selects none (e. g. for Kodak camera) or one (e. g. for Olympus camera) flash delay before triggering. Both flip-flops are used in the 4013, the clock signal derived from the flash is used (triggered on the rising clock signal) to divide by two` and trigger the TIC206 triac on the first or second flash. A simple RC timed reset mechanism around R6-C4 is used with a relatively long delay (about half a second) before resetting the entire circuit.

The advantage of the triac is that a trigger voltage of either polarity can be handled. The 2N3906 may be replaced by its near equivalent the BC212L. The SFH300-2 photodiode is supplied by Maplin as part number MES NP64U. The triac may also be a TIC126D.