High-Speed Sync (HSS) lets you use flash at shutter speeds faster than your camera’s native sync speed — typically above 1/200s or 1/250s. This seemingly technical feature solves a very practical problem that every outdoor portrait photographer encounters: balancing flash with bright ambient light while maintaining shallow depth of field.
The Sync Speed Problem
Your camera’s sync speed is the fastest shutter speed at which the entire sensor is exposed simultaneously. Above this speed, the shutter uses a traveling slit — the second curtain starts closing before the first curtain fully opens. The result: at shutter speeds above sync, a normal flash only illuminates a band of the sensor, leaving the rest as a dark bar.
This creates a practical limitation. On a sunny day at ISO 100, a proper exposure at f/2.8 requires approximately 1/2000s shutter speed. But if your sync speed is 1/250s, you can’t use flash at 1/2000s. To stay at 1/250s, you’d need to stop down to f/11 or f/16 — losing the shallow depth of field you wanted.
How HSS Works
High-Speed Sync doesn’t fire a single burst. Instead, it fires the flash as a rapid series of pulses throughout the entire duration of the shutter’s travel across the sensor. Each part of the sensor receives flash illumination as the slit passes over it. The result appears as even flash illumination across the entire frame, regardless of shutter speed.
The trade-off: HSS dramatically reduces the flash’s effective power. A flash that delivers full power at normal sync might deliver only 1/4 to 1/8 power in HSS mode, because the light is being spread across time rather than delivered in a single burst. This means you need your flash closer to the subject, or you need a more powerful flash unit.
When You Need HSS
Outdoor Portraits With Shallow Depth of Field
The primary use case. You want to shoot a portrait outdoors at f/1.8 for a blurred background, but the bright sun requires a fast shutter speed that exceeds your sync speed. HSS lets you use flash as fill or key light while maintaining both the wide aperture and the fast shutter speed.
Overpowering the Sun
Sometimes you want flash as the dominant light, with the sun as fill — creating dramatic, directional lighting outdoors. This requires enough flash power to exceed the bright ambient, which means shooting at a shutter speed and aperture that darken the ambient to the desired level. Often, that shutter speed is above sync speed.
Action and Motion Control
At outdoor sporting events or dance performances, you might need flash at 1/500s or faster to freeze motion. HSS enables flash at these speeds, though the reduced power limits the effective range.
HSS vs. ND Filters
The alternative to HSS is using a neutral density filter to reduce the light entering the lens, allowing you to shoot at sync speed with a wide aperture.
ND filter advantages:
- Full flash power available (no HSS power loss)
- Any flash or strobe works (no HSS capability needed)
- Consistent and reliable
ND filter disadvantages:
- Affects autofocus performance (darker viewfinder)
- Adds another piece of glass in front of the lens
- Fixed reduction (unless using a variable ND, which can affect image quality)
HSS advantages:
- No additional hardware on the lens
- Full autofocus performance
- Quickly adjustable by changing shutter speed
HSS disadvantages:
- Significantly reduced flash power
- Requires HSS-capable flash and trigger
- Battery drain increases due to rapid pulse firing
For most outdoor portrait photographers, both tools are worth having. Use ND filters when you need maximum flash power (overpowering the sun), and HSS when you need convenience and flexibility (run-and-gun environmental portraits).
Practical HSS Settings
Aperture Priority Approach
- Set your aperture to the desired depth of field (f/1.8, f/2.8, etc.)
- Set ISO to 100
- Let the camera determine the shutter speed for correct ambient exposure
- Enable HSS on your flash
- Set flash to TTL mode — let the flash computer determine the power needed to fill the subject
This approach is fast and reliable for fill-flash portraits where the ambient provides the base exposure and the flash lifts the subject.
Manual Control Approach
- Set your desired aperture and shutter speed
- The shutter speed controls ambient brightness (faster = darker ambient)
- Flash power controls subject brightness
- These two controls are essentially independent, giving you precise control over the ambient-to-flash ratio
Darken the ambient to your desired background tone by increasing shutter speed. Then set flash power to properly expose the subject. This separation of ambient and flash control is the foundation of off-camera flash technique.
Flash Power Management
HSS eats power. Strategies to maximize what you have:
Get the flash close. Moving your flash from 10 feet to 5 feet gives you 4x more light on the subject (inverse square law). The closer the better.
Use efficient modifiers. A bare flash or small reflector delivers more light than a large softbox, which absorbs significant power. When HSS power is limited, use the smallest modifier that produces acceptable light quality.
Don’t exceed what you need. If you’re using HSS for fill (just opening shadows, not overpowering sun), you need less power than if you’re trying to use flash as the key light. Adjust your expectations to match available power.
Battery awareness. HSS drains batteries roughly 3-4 times faster than normal sync firing. Carry extra battery packs and monitor power levels throughout the shoot.
Which Flashes Support HSS
Most modern speedlights support HSS when paired with a compatible wireless trigger. Many battery-powered studio strobes now offer HSS as well. Check that your flash, trigger, and camera all support HSS — the chain breaks if any component lacks the feature.
Dedicated HSS triggers from Godox, Profoto, and PocketWizard handle the communication between camera and flash. The camera tells the trigger it’s using a fast shutter speed, and the trigger tells the flash to switch to HSS pulse mode automatically.