TTL vs manual flash

Manual flash

A flashgun’s maximum power starts at 1/1 (full power), and can be dialled back to lower output settings, halving the power at each full stop (1/2, 1/4, 1/8, 1/16 and all the way down to 1/128 power). Manual flash is ideal when you want a consistent amount of power every time and is best used when working in predictable environments, such as a studio.

Think of TTL as ‘Auto’ for flash. It works by firing a brief pre-flash as you press the shutter. The reflected light from the pre-flash travels back through the lens (hence TTL) and the camera calculates the exact amount of flash required to expose the scene correctly. The ‘full’ flash is then fired. This all takes a split second, so you only see one burst of flash.

Flash exposure compensation

TTL is great for most subjects, but you need to be aware that, as it’s based on reflected light, certain subjects might prove problematic, as the flash power can vary depending on the reflected light received by the camera. So if your subject is under- or overexposed, you can dial in Flash Exposure Compensation to fine-tune your exposure.