Most of you probably know that electromagnetic waves travel at the speed of light, which is 299,792,458 meters per second (in vacuum. It is slower in air or other media but that won’t really change the discussion). If you use a set of RF wireless triggers for remotely firing flash across a distance of 100 meters, a simple math tells you that it takes less than a microsecond for the signal to propagate. However, that’s not where the most delay comes from when a typical RF flash trigger is used.

The transmitter, sitting on the hot shoe of your camera or hooked up to the PC sync port, detects the change of voltage as the sync signal from camera, then sends command over the RF to the remote receiver. The receiver determines a correct trigger command has been received then it fires the connected flash. All of the above happens really fast but it still takes time.

The following is the result of delay test on the cheap eBay triggers.

X-sync trace shows the trigger signal on the camera’s hot shoe. Remote trace shows the trigger signal on the remote flash’s x-sync pin. The Flash trace shows the output of the remote flash. The flash should fire when the x-sync terminal is pulled to ground.

The time between T (red) and X1 (blue) is about 745 microseconds. The time between X1 (blue) and X2 (cyan) is about 14 microseconds. These numbers appear to be very consistent from each trigger test. The delays from the transmitter to each of the 4 receivers are also the same.

The delay of 745 microseconds seems to be a little long, it is definitely longer than the delay using a PC sync cable. The delay could reduce the fastest sync speed you can use with your camera. On a Nikon D200, I haven’t seen a problem if I stay below the specified sync speed of 1/250s. Some triggers might have longer delay. For example, people have trouble getting the specified sync speed of Nikon D200 with Cactus V2.


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