20th September 2002, 08:31 AM
Slave or External flash
Recently I come to realize the existence of slave flash. How does it differ from the normal external flash other than it is being triggered by another flash? What shortcomings does it have? I find it quite flexible(can be placed anywhere) and cheap as compared to external flash. Also it saves the cost of getting a sync cable for those digicam without a hotshoe. So what is the 'catch'?
20th September 2002, 08:48 PM
Is it possible to control the flash intensity of the slave flash?
20th September 2002, 09:00 PM
A slave flash relies on the burst of light from the main flash to trigger itself. Most dumb slave flashes are well, dumb. They simply fire when they see the main flash fire. Exposure can be a problem for such flashes as the camera obviously does not know about its existence. The more advanced flashes by the major camera makers have a slave mode built-in, and they are more intelligent in that they will work together with the main (master) flash to get the light intensity right.
Cheap slave flashes either operate in full manual mode or auto mode (using its own sensor), and depending on the specific model, may or may not have power control for adjusting intensity.
There are also radio controlled slave flashes triggered via a RF transmitter. These are not easily fooled by flashes of light (like switching on flourescent tubes, lightning, other people's flashes etc).
A point of interest is that optical slaves are also triggerable by a burst of IR light, so if you do not want your master flash to affect the final exposure, you can tape a piece of unexposed but developed SLIDE (not negative) film over the main flash reflector. This will block out almost all visible light but allow IR energy to go through and trigger the slaves.