Digital SLR Photography

How to use Slow-Sync flash

By Caroline Schmidt. Posted

As the name suggests, slow-sync flash is the complete opposite of high-speed sync; rather than using a fast shutter speed, you instead tripod mount the camera and combine a long exposure – such as several seconds – with flash. The idea behind this is that the aperture controls the flash exposure on the model, while the longer shutter speed is used to draw in more ambient light at night, so the background looks well lit rather than underexposing to appear black. With streetlights and other illumination in the background, night portraits can really come to life with this technique when used properly.

Compose your shot with your camera attached to the tripod and ask your model to stay still. The flashgun can be positioned direct, at 45° or to the side – it really depends on the location and the pose of the model. We shot with the light to the side and the model looking towards it and away from the camera. Set your camera to shoot in manual mode with the ISO between 100-400, and an aperture that’s f/5.6 or wider. We shot at ISO 100, with a one-second exposure at f/3.2 for a shallow depth-of-field and the flash at 1/8 power. To avoid camera shake, use the self-timer or better still a wireless remote release.



Shooting in a lit area next to a main road meant that exposures had to be carefully timed to avoid capturing trails from car headlights that would cause overexposing the background with uneven light.


When shooting slow-sync portraits at night you need an incredibly low flash output. Shoot wide open, ideally wider than f/5.6, to allow as much light through the lens as possible.

Slow Sync Camera Settings


By increasing the shutter speed by five stops to 1/30sec and maintaining the same flash power, the result is a massively underexposed background with virtually no visible detail.

Shutter speed too fast


The combination of low-powered flash, which ‘freezes’ any subject movement from the model, and the one-second shutter speed has created a well-balanced exposure where the flash and ambient light have blended together.

Main Slow Sync Image Option 2

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