High speed sync is flash photography technique that you might not need to use very often, but when you do, it will make a huge difference to your photos. The simple definition of high speed sync flash is that you use it in conjunction with fast shutter speeds. But we’ll go into more depth about why you might need to use, when, and how.
Table of contents
How do flashes work?
In order to understand high speed sync, you need to understand how flashes work. So let’s start there.
When you depress the shutter release button on your camera, a curtain (called the front or first curtain) slides away to reveal the sensor and expose it to light. Your shutter speed determines your exposure time and when it’s up, a second curtain (called the rear curtain) slides up to cover the sensor and end the exposure. For very fast shutter speeds, the rear curtain can start to move before the front curtain has exposed all of the sensor. This isn’t a problem in ambient light, but it is with flash.
If you use a flash, it needs to fire after the front curtain has completely exposed the sensor and before the rear curtain has covered it again. A mistimed flash that fires too early or too late will leave you with black bands running across your image.
To avoid these black bands, you need to set your camera’s shutter speed to your flash’s sync speed, or slower. This is usually around 1/250 or 1/200 second.
If your shutter speed is too fast for the flash, the sensor will never be completely exposed to the light from the flash. The shutter curtains will be moving too fast for that.
Most of the time, you won’t need to be using a shutter speed faster than the flash duration. But on the occasions that it is–and we’ll look at those soon–you will need to use high speed sync.
What do we mean by high speed sync?
Instead of the flash firing between the front and rear curtains perfectly exposing the sensor, high speed sync directs your speedlight or strobe to emit a series of smaller flashes. Each of these shorter bursts of flash are less powerful than a single flash, so don’t over-expose your shot. By coming in a sequence of flashes, it makes sure that the sensor receives all the light it needs as the first and second curtains open and close.
You can think of HSS as simulating continuous lighting.
When should I use high speed sync?
Most of the time you won’t need a shutter speed faster than your native sync speed when you use a flash. However, sometimes you will need to use high speed sync.
HSS and action shots
When you’re shooting sports or action shots, for example cyclists, runners, or cars, you might need some fill flash to balance out shadows in the scene. However, in order to freeze the action you will need to use a fast shutter speed. To prevent black bands appearing across your frame when you fire your flash while using a high shutter speed, deploy high speed sync.
Do be aware, though, that high speed sync is very battery hungry. This means that your flash can take longer to cycle than you’re used to and your battery life will be shorter than normal.
HSS and portraits
When you’re shooting an outdoor portrait, you will almost certainly want to use a wide aperture to create a shallow depth of field with plenty of background blur. You will probably need some fill flash to lift shadows, too. If you’re using a wider aperture, it’s likely that you’ll need a shutter speed faster than your native sync speed. In which case, you’ll need to use high speed sync to prevent banding.
HSS and shooting in very bright sunlight
Maybe you don’t need to use a wide aperture or don’t want a blurred background, but because it’s a bright, sunny day, you do need to use a fast shutter speed. You will also need to use flash, otherwise your background will be blown out trying to expose for your subject, or you’ll need to have the sun coming from straight behind you and that can be unflattering. To fire the flash effectively while using a fast shutter speed, you’ll need to use high speed sync mode.
How do I use HSS?
First, you need an off-camera flash, for example a speedlight or strobe, that is HSS-capable. You will also need a transmitter that you fit to the hotshoe of your camera to control the flash. Set both to HSS.
Some light modifiers to help shape the light are a good idea, too.
Set up your shot. HSS works best with your lights relatively close to your subject.
Meter for the ambient light in your scene. You will probably use a wide aperture and keep the ISO low. And of course, the shutter speed will be fast – that’s why you’re using HSS. If you find that your background is too dark, you can decrease the shutter speed. Shutter speed controls ambient light.
If you’re shooting portraits, you might find that a slightly underexposed background will help your subject to stand out.
Set your flash power. It will probably need to be quite high to achieve the brightness you want, and remember that this will drain the battery. Now, balance your background and foreground exposures by increasing or reducing your flash output.
Pros and Cons of HSS
The most significant positive of high speed sync flash is that you can use a large aperture and control your ambient exposure when using flash. You can freeze motion and enjoy a lot of creative control over your photos.
When it comes to negatives, HSS works best with higher power, and therefore higher-end flashes. It uses a lot of flash power that drains batteries very quickly. Your flash can be slower to cycle when shooting HSS. And it can get hot quickly, too. HSS works best when your light is close to your subject, too.
Alternatives to high speed sync
If, for whatever reason, you can’t use high speed sync, you do have some options.
Neutral density filter
Instead of increasing your shutter speed to help control the ambient conditions, you can use a neutral density filter (ND filter). These filters block light from reaching your lens but do not alter the colours in your scene. With an ND filter you can use a wider aperture for a shallow depth of field and still use a slower shutter speed.
Rear curtain sync
Rear curtain sync uses slow shutter speeds in combination with flash, rather than fast shutter speeds. This technique can freeze your subject in your frame, but also creates motion blur trails, too.
Time of day
By shooting early in the morning or towards sunset, when the ambient light is lower, you can use slower shutter speeds together with your flash. It isn’t always convenient, but with amazing skies it can produce terrific results.
High speed sync, or HSS, is a flash technique that you can use with high shutter speeds. HSS sends out pulses of light instead of a single burst.
You sometimes hear it called focal plane sync. The setting for HSS on Nikon cameras is called Auto FP.
If you use a normal flash with a fast shutter speed, you will get black bands across your image because the shutter curtains do not move fast enough.
A shutter speed over 1/200 second or 1/250 second is regarded as fast when it comes to flash.
If you want to use a wide aperture for a shallow depth of field or if you want to freeze motion, HSS will help you do this.