High-Speed Sync (HSS), also known as Auto FP (Focal Plane) sync, is a flash technology that allows photographers to use flash at shutter speeds faster than their camera’s maximum flash sync speed. This capability opens up creative possibilities for using flash with wide apertures in bright conditions, particularly valuable for outdoor portrait photography.
In traditional flash photography, you’re limited to your camera’s sync speed—typically 1/200th to 1/250th of a second. HSS overcomes this limitation by rapidly pulsing the flash throughout the entire duration of the exposure as the shutter curtain travels across the sensor. Instead of a single bright flash burst, HSS creates a continuous stream of light that ensures even illumination across the entire frame at any shutter speed.
The Trade-Off: Power vs. Speed
While HSS provides tremendous flexibility, it comes with a significant drawback: reduced flash power. The pulsing nature of HSS means the effective Guide Number of your flash is dramatically decreased—often by two to three stops or more as shutter speeds increase. At 1/8000th of a second, your flash might only deliver 10-15% of its normal power output.
This power reduction means you’ll need to compensate in other ways: moving your flash closer to the subject, using a more powerful flash unit, opening your aperture, or increasing ISO. For example, if you’re shooting at 1/4000th with HSS, you might need to position your flash 4 feet from your subject instead of the 8 feet that would work at normal sync speed. This is why many professional photographers invest in high-powered flash units or battery-powered strobes for outdoor HSS work.
Practical Applications
HSS truly shines when you want to shoot with wide apertures for dramatic bokeh and shallow depth of field in bright daylight while using fill flash. Imagine shooting a portrait at f/1.4 in midday sun—without HSS, you’d be limited to f/16 or smaller at 1/250th, eliminating any possibility of background blur. HSS lets you maintain that f/1.4 aesthetic by allowing shutter speeds of 1/4000th or faster.
This technique is particularly popular in fashion and wedding photography, where photographers want to create dramatic rim lighting effects while maintaining shallow depth of field. By positioning an off-camera flash behind or to the side of the subject and using HSS with fast shutter speeds and wide apertures, you can create stunning backlit portraits with beautifully blurred backgrounds even in bright sunlight.
HSS also proves valuable when you want to freeze motion while using flash. Sports or action photographers might use HSS at 1/2000th to freeze a subject’s movement while adding fill flash to enhance detail and reduce shadows, all while maintaining control over ambient light exposure.
When using HSS with light modifiers like softboxes or diffusers, remember that these already reduce light output, compounding the power loss inherent in HSS. You may need to work with the modifier closer to your subject or choose more efficient modifiers like beauty dishes that lose less light than large softboxes.