E-TTL II flash metering
Use this automatic option to create balanced flash
There are two flash basic flash metering modes: E-TTL (Evaluative Through-thelens) and Manual. But E-TTL can hardly be described as basic… In this mode, the camera will automatically work out the flash exposure for you. To do this, the camera fires a low-powered preflash before the shot is taken, and the light reflected from the subject through the lens is evaluated. The camera then sets the appropriate flash output for the main flash exposure.
All modern EOS cameras use E-TTL II, which can also take into account the subject distance and its positions in the frame for more accurate flash exposures.
Manual flash exposures require you to adjust the power of the flash yourself, which you can do on the camera or on a compatible Speedlite using a scale that runs from 1/1 full power down to 1/128 power. Canon’s pro EL-1 Speedlite can even go as low as 1/8192 power. The camera doesn’t have to be in Manual in order to use Manual flash, and likewise you can use an intelligent E-TTL II automatic flash exposure when you’ve set a Manual exposure on the camera.
Whichever flash metering mode you use, you’ll need to bear in mind that the shutter speed on the camera has to be set to the ‘flash sync speed’ or slower. For most cameras this is 1/200 sec. If you’re using flash in bright daylight which requires a much faster shutter speed (eg 1/2000 sec), then slowing it to 1/200 sec can lead to overexposed shots. To avoid this, activate the ‘high-speed synchronisation’ setting available on certain Speedlites, or reduce the shutter speed by selecting a smaller aperture or lower ISO. More on using HSS mode and the EL-1 Speedlite on page 54.