Setting Up a Flash on a dSLR Camera
Your dSLR camera may have different flash options, including fill flash and high-speed sync. The lighting and photographic effect you want is how you determine which flash setting to use.
Auto TTL is automatic flash mode. The camera and flash determine the flash strength. TTL stands for "through the lens," which is how the flash assesses the scene.
Red-eye reduction fires a series of pre-flashes to constrict pupils, lowering the chances of red-eye.
Fill flash forces the flash to fire when it isn't necessary (from an overall exposure standpoint). Use fill flash outdoors to keep faces from being in shadow. Use fill flash indoors to balance bright light from windows.
Slow sync slows the shutter and flash to increase the amount of ambient light, resulting in brighter backgrounds. You may have to raise ISO to keep shutter speed fast enough for hand-held photography.
High-speed sync is for when you have an external flash mounted on your camera's hot shoe. This mode allows much faster shutter speeds than you can get with pop-up flashes. Use for action shots or in bright light when you need a very fast shutter.
Rear curtain waits to fire the flash until just before the exposure ends.
Repeating flash divides the flash into a number of discrete pulses, triggering them over the length of the exposure.
Wireless enables wireless mode on compatible flashes and camera bodies. When you set it up properly, it syncs the off-camera flash with your camera, so you can trigger the off-camera flash remotely.
Manual is the flash mode that lets you set the flash strength yourself.