As Matt said, the mystery cord would connect to the side of the radio transmitter, and the end that doesn't fit anything would attach to your camera, if you had one that used a connector instead of a hot shoe.
The long black tether can be used instead of the wireless adapter. Assuming your camera doesn't have the pc connector (the tiny end that doesn't fit anything), you can get a hotshoe adapter like this:
Link to BHPhotovideo product
With the wireless trigger, its not really necessary, but the wired option is great to have for a backup. |