What is a TTL Cord?
A TTL cord is a form of a flash sync cord that has the benefit of retaining the advanced TTL metering capabilities of the camera-flash system. This accessory is also known as an off-camera flash cord, as allows an on-board flash to be moved off the camera’s hotshoe while preserving all the electronic communication between them. Essentially, a TTL cord is an extension cable for your hotshoe.
Compared to a traditional single-pin PC sync cord, the TTL cord is a complex accessory. One end features a female hotshoe, identical with the one found on top of your camera. It usually also has a tripod screw socket and a cold-shoe on the bottom to allow for the flash to be mounted on a bracket or a stand. The other end of the cable has a male hotshoe with a locking mechanism, much like the one at the bottom of the strobe unit. High-quality TTL cables, like the Canon OC-E3 above, even feature weather sealing to match their professional camera and flashes.
Depending on the camera system, a TTL cord may feature 5 or more contacts. These cables are usually short, with lenghts between 0.5 to 1 meter, although models up to 5 meters or longer are available. Most off-camera flash cables are coiled to keep them out of the way.
What is a TTL cord used for?
A TTL cord is the easiest, quickest and most reliable way of moving your on-board flash away from the camera’s hotshoe. This allows for much greater freedom when directing light to achieve the desired lighting effect. Some photographers will hold the camera with one hand and the flash with the other, allowing them to rapidly change lighting direction and style.
An off-camera flash cord also allows for the use of advanced flash light modifiers, stands and brackets that cannot be used with a shoe-mounted strobe. The most popular application of the TTL cord is to move the flash onto a flash bracket. This moves the strobe further off the optical axis of the lens, which helps eliminate red eyes or shadows from a larger lens. Most flash brackets pivot, allowing you to keep the strobe above the lens in portrait shooting, eliminating side shadows.
Because of the quick lighting changes they enable, off-camera strobe cords are a popular among wedding, journalism and event photographers. Another popular application for these cords is macro and product photography, especially when using macro bellows or other larger rigs. In addition, a TTL cord the simplest way to use high-speed sync (HSS) with an off-camera flash.