Take control of flash power
Switch to Manual for the full power of a flashgun, or tone it down for a gentle ‘blip’
Unlike E-ttl ii flash exposures, Manual flash provides a consistent output; once you’ve set the power of the flash, it stays locked in.
The drawback is that the flash output won’t be adjusted automatically to take account of changes to camera settings, or if you move closer to or further from an object, or if you add light-sapping modifiers.
The camera doesn’t have to be in Manual mode to take advantage of Manual flash; you can use it when the camera’s set to any Creative Zone mode, such as Aperture Priority and Program. You select the output in 1/3 fractional steps, from 1/1 (or full) power down to 1/128 power, either on the flashgun or on the camera’s Speedlite control screen; look for ’Flash control’ in the red Shooting menu on an EOS with a pop-up flash module, on those without a pop-up flash it’s under ‘External Speedlite control’.
The lower the power setting, the shorter the duration of the flash burst; the benefits are shorter recycling times and the ability to use the flash up close without overwhelming the subject. Start at around 1/8 power and check the results; for a brighter flash exposure, use a high power (such as 1/4); to reduce it, use a lower power (such as 1/16). In sunlight, you might have to go all the way to 1/1 (full) power – and it really is the full power of the flash unit, as in E-TTL mode some power is used up on the pre-flash.
You can also increase the flash exposure by moving the flashgun closer to subject, choosing a larger aperture or increasing the ISO.