Using flash in daylight is great for adding punch to your portraits – it fills in the shadows around the features and adds catchlights to the eyes. But fill flash can force you to compromise on your exposure settings.
Normally, you can’t use shutter speeds that are faster than the flash sync speed – typically 1/200 or 1/250 sec. That means you can’t use the widest aperture on your lens, so the background ends up being more in focus than you’d like.
But some Nikons have a feature called Auto FP that enables you to use any shutter speed.
Also known as high-speed sync flash, Auto FP makes your flashgun work differently. Instead of a single flash, it pulses at a very fast rate, switching on and off at up to 40,000 times a second.
How to set up your camera for high-speed sync
01 Defy the limitations
By default, your Nikon DSLR only lets you use shutter speeds up to the flash sync speed (1/200 sec or 1/250 sec). On advanced Nikon DSLRs, a menu option enables you to use Auto FP (Auto Focal Plane ), which means you can use flash at shutter speeds up to 1/4000 sec or 1/8000 sec.
02 Choose from the menu
On models such as the Nikon D90, you go to the ‘Bracketing/flash’ options in the Custom Settings menu and turn Auto FP on. On high-end models, such as the D800, you go to the ‘Flash sync speed’ option and pick ‘1/250 s (Auto FP)’. It’s not available on the D3100, D3200 or D5100.
03 Pick a suitable flashgun
Auto FP doesn’t work with pop-up flash or with basic add-on hotshoe guns, such as the Speedlight SB-400. But with the right camera and flash, the Auto FP option enables you to use flash with the widest apertures, even in bright daylight. Our shot was taken at f/1.8 at 1/500 sec.
Your flashgun’s power drops in Auto FP mode as the shutter speed gets faster, so you need to be close to the subject