Off-camera flash refers to the technique of placing an external flash out of the camera. The important question is “Why separated from the camera?”

So that we can put the flash anywhere we want. Be able to control the direction of light is something that is very valuable for photographer.
We can install light-shaper (forming light) such as umbrella, softbox, snoot and others to soften or adjust the spread of lights. If the flash is on camera, it will difficult to attach accessories. Controlling the quality of light is really meaningful for photographer.
Can use more than one flash to illuminate many things, for example it could illuminate the face, hair, and other specific area on portrait photography. Creativity will be infinite!

Well, I would like to explain you a little about how to fire off-camera flash.

Firstly, you have to know that to fire a flash which is separated with your camera, you need a trigger. Here are some kind of flash trigger.

1. Cable (off shoe cord)
   Pros: Usually quite affordable and dependable.
   Weakness: distance between camera and flash is limited about 60cm away.
2. Optic / flash trigger (built-in flash, flash, infrared transmitter)
   Pros: Practical.
   Weakness: If the light is blocked or too far (over 10 meters) flash may fail.
3. Radio trigger
   Pros: can reach tens to 100 meters distance.
   Weakness: usually quite expensive, especially that supports automatic (TTL) and high-speed sync.

Nowadays many types of cameras that have built-in flash which can be used to trigger off-camera flash, for example various Canon’s DSLR cameras such as 600D, 650D, 700D to sophisticated such as 60D, 70D and 7D.

For Nikon DSLR camera, semi-pro like Nikon D90, D7000, D7100, D300s, D600, D610, D700, D750, D800, D810. For Sony SLT cameras, the flash can be used as trigger, but its mirrorless like Sony Nex or Sony A6000 are not be able.

Flash which has function of Master / Commander / Controller can trigger and send instructions to flash that is set as a slave to fire with flash light. The advantages of this setting is not needed additional trigger anymore. Example: Canon 580EX II, 600RT, Nikon SB900, 910, Sony HVL 60, 43, Shanny SN600SC, YN568

Another simple alternative trigger is a pair of wireless radio trigger. The transmitters mounted on the camera and receiver units installed under the flash. This kind of wireless trigger has quite a lot of variations. Essentially there are manual, auto / TTL to HSS. The good thing of this kind of trigger is its distance that can reach 100 meters.

Infrared / Radio triggers are also quite popular as a trigger, especially because there are some flash that already has a built-in receiver such as Canon 600RT. Flash which has a receiver in the flash unit makes everything more symple. We also don’t need to worry to forget some extra batteries for the receiver trigger.

Typically, such a sophisticated transmitter such as E3-RT allows us to harness the power of the flash light and divide some flash into groups. Example: Canon E3-RT, Phottix Odin, Shanny SN E3-RT.