The sync socket on the Canon Speedlite 580EX flash is located on the front of the flash to the left the infrared sensor. It is a small socket used to connect the flash with sync cords so that photographers can fire the 580 EX when it is not mounted on a camera. Photographers can link the flash to a remote trigger, such as a pocket wizard (see Resources), or connect the flash to a camera hot shoe with an extra-long sync chord. Using an off-camera flash allows photographers to execute lighting techniques that will improve the quality of their photographs.
Rim Lighting
Rim lighting is a photography technique that adds depth to pictures by making subjects "pop." Place the light behind your subject and to a 45-degree angle from either side. The flash of light from behind will add a glow of light on one side of the subject, creating visual interest around the subject and separating it from the background.
Side Lighting
Light your subject from the front at a 45-degree angle for proper side lighting. Lighting from the side looks better than simply shooting with an on-camera flash because it creates shadow on the subject, making it look more three-dimensional. Photographers can also use a second flash on the opposite side to soften the contrast. When using a fill light, be sure not to let it overpower the main light, or else the illusion of depth in the picture will disappear.
Background Lighting
Point an off-camera 580 EX toward the background of your picture to add another visual element to your pictures. Using a flash for your background adds tonal variation to it. Photographers will often use a back light behind their subject, pointed toward the backdrop to create a halo effect around the subject. Using a back light can also help to direct viewer's attention to elements in the photograph that are import to what story the photographer is attempting to tell.
Hairlight
Point an off-camera 580 EX at a human subject's hair from above and to the side to a add an extra glow. Hair lights are commonly used in fashion photography to make hair look more flattering.
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