On-camera flash
The simplest way to start with flash photography is by keeping the light source on the camera
almost every Nikon DSLR has a built-in pop-up flash, and for many of us it’s our first foray into flash photography. It’s the most convenient way of providing extra light to our scene. To start with we should think of flash in two distinct modes: manual and automatic (known as ‘TTL’).
Manual flash mode requires the photographer to determine the flash power output. These power levels are measured in fractions, so full power is 1/1, which is then halved to 1/2 power, 1/4 power and so on – usually down to 1/128. The downside is that you have to adjust the power yourself, and without prior calculation, it’ll take a few test shots before finding the correct flash power. But it provides consistent power once set, unlike TTL mode.
Standing for ‘through-the-lens’, in TTL mode the camera automatically assigns the power of the flash. It works by firing a brief ‘pre-flash’ and measuring the light reflected off the subject and into the lens to determine the power of the flash required for a balanced exposure. These settings are communicated to the flashgun electronically and then the main flash is fired virtually instantaneously, so in practice the pre-flash isn’t noticeable.
TTL frees the photographer to concern themselves with things like composition, but the power can fluctuate based on the way the camera meters the scene.