When you set the synchronization mode to high-speed sync (FP flash), the camera can synchronize with the 550EX all all shutter speeds. When high speed sync has been set is displayed in the viewfinder

• High-speed sync can be used in the E-TTL and M flash modes
• High-speed sync is especially effective for fill-flash portraits in daylight since you can:

1. Obtain better background blur with a larger aperture

2. Create a catchlight in the subject's eyes

3. Soften shadows on the subject's face

Select the camera's picture-taking mode and the Speedlite's flash mode. If you want to use a large aperture (smaller f-number) set the Av or M mode Press the <+> and <-> buttons simultaneously to select on the LCD panel. Each time you press the +/_ buttons simultaneously, the setting changes in the following loop 3. Focus the subject 4. Check that the subject is within the flash range displayed on the 550EX'x LCD panel 5. Check that the icon is displayed in the viewfinder, then take the picture

• If you set a shutter speed that is the same or slower than the camera's maximum flash sync speed, will not be displayed in the viewfinder
• With high-speed sync, the faster the shutter speed, the shorter the effective flash range will become. Check the LCD panel for the effective flash range
• To return to normal flash, press the button again. The icon will disappear
• Stroboscopic flash cannot be set