WHEN SHOOTING flash-lit portraits in sunlight it can be tricky to blur backgrounds. The problem is our shutter speed which, when coupled with a flash, is often restricted to a max flash sync speed around 1/200 sec. If we use the sunny f/16 rule (page 45), then with a shutter speed of 1/200 sec, even if we drop to ISO100, we could only open the aperture up to f/11, which isn’t wide enough for a shallow DoF (as the inset image below shows). The solution is to use a flash capable of high speed sync. This pulses the flash, enabling higher shutter speeds and wider apertures (1/4000 sec with aperture f/2.5 in the shot on the right). There are catches – camera and flash have to be compatible, and it reduces the max output of the light.