High-Speed Sync Flash: What Is It and When Should You Use It?

Editor’s Key Takeaways: Mastering High Speed Sync Flash for Stunning Photos

Woman running on beach with sun in background.

This article provides a thorough explanation of high speed sync (HSS) flash, starting with how a flash normally operates. The process involves the camera’s shutter curtain exposing the sensor, firing the flash, and then closing the curtain to finish the exposure. To avoid black bands in photos, the flash must go off when the sensor is fully exposed, typically at a shutter speed of around 1/200s to 1/250s, referred to as the flash sync speed.

High speed sync (HSS) allows photographers to use flash at higher shutter speeds, exceeding the camera’s sync speed, which is useful in various scenarios:

  • Shooting wide-open in bright conditions
  • Freezing fast action
  • Creative outdoor portraits
  • Balancing flash with natural light

HSS works by rapidly pulsing the flash throughout the exposure, ensuring the entire sensor is illuminated. This article guides photographers on when and how to effectively use HSS to capture stunning photos.

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Are you struggling to understand high speed sync flash? Do you want to know when it makes sense to turn on high speed sync?

You’ve come to the right place.

Because this article will tell you everything you need to know about flash speeds.

Nikon 4814 SB-500 AF Speedlight (Black)
Nikon 4814 SB-500 AF Speedlight (Black) (Image from Amazon)

First, I’ll tell you exactly what high speed sync flash is and how it works.

Then I’ll give several examples of when you might need it—and how you can use it for beautiful photos.

Let’s get started.

How Does a Flash Normally Work?

If you want to understand high speed sync, you have to understand how a camera flash normally works.

When you press the shutter button, a shutter curtain slides up from in front of the camera sensor.

The flash goes off.

Then, as soon as the exposure is complete, a second curtain slides up from below, cutting off the light hitting the sensor.

To repeat:

The first curtain slides up, the sensor is exposed to the light, the flash goes off, and the second curtain slides up to finish the exposure.

But note that the flash should only go off once the first curtain has exposed the sensor completely, and the second curtain hasn’t yet covered the sensor back up.

Because if the flash goes off too early or too late, the sensor will be partially covered by the shutter curtains, and this will cause black bands in your photos.

Normally, when you use flash, you have to set your shutter speed to your camera’s flash sync speed or slower.

(This is usually around 1/200s or 1/250s.)

Otherwise you’ll end up with the black bands I discussed above.

Because once the shutter speed gets to be too high, the camera sensor is literally never fully exposed to the light. Instead, the second curtain starts closing before the first finishes opening.

And since a flash is practically instantaneous…

…the flash never has a moment at which it can fire and illuminate the whole scene.

Hence, it’s impossible to capture a photo over a shutter speed of around 1/200s using flash.

Or it would be, if not for high speed sync:

What Is High Speed Sync?

High speed sync is the perfect way to address the problems I’ve indicated above.

Instead of the flash firing at that perfect moment between when the first curtain is gone and the second curtain starts closing, high speed sync causes the speedlight to fire off a series of flashes.

(These aren’t as bright as a normal flash.)

Therefore, the flash can illuminate the scene at different moments, as the front curtain and rear curtain move.

And because flashes are powerful machines, it’s possible to maintain the flash bursts as the shutter opens and the second shutter closes, which prevents black bands and allows you to capture a uniformly-lit scene.

That way, you can get a well-exposed image, even with a fast shutter speed, like this one:

When to Use High Speed Sync

Most of the time, you should be just fine using your normal flash sync speed.

But you’ll sometimes run into situations where high speed sync is required for a good shot.

The first of these scenarios is when you want to photograph action, but you don’t have enough flash to overpower all the ambient light in the scene.

For instance, if you photograph a biker on a bright day, you might want some fill flash to eliminate high-contrast shadows.

But think about it:

Given the level of action, the biker will become a blur if you photograph the shot at your normal flash sync speed (probably around 1/200s), like this:

You want to take a shot at 1/1000s, but you know that if you try then you’ll end up with only part of your image affected by the flash, because of the problems with flash syncing.

So what do you do?

You use high speed sync!

By selecting the this option, you’ll be able to set your camera to 1/1000s and trigger your flash as the biker goes by.

Your flash will fire in a series of short bursts.

And your final shot will turn out sharp.

The same is true when you’re photographing a runner with flash, or a fast-moving car, or even a bird in flight.

Assuming the ambient light is adding some noticeable illumination to your subject, you’re going to struggle to get a sharp-looking photo unless you turn on high speed sync.

Another situation where you might want to use high speed sync is when you’re shooting a portrait subject in bright sunlight.

You want to fill in the shadows, hence the need for some fill flash.

But you also want to create a nice background blur. And to do this, you need an aperture of around f/2.8.

Given the bright light and the wide aperture, to pull off the exposure you need a shutter speed of at least 1/1250s.

But your flash sync speed only lets you go to 1/200s.

That’s when you activate high speed sync, which allows you to boost your shutter speed without sacrificing the overall exposure.

In fact, this last scenario is something you’ll often encounter when using flash in bright light. You need a high shutter speed to prevent overexposure, but if you use a high shutter speed you’ll end up with parts of the image underexposed (due to the banding issues I mentioned above).

So just keep high speed sync in mind as an option, and you’ll be capturing stunning shots with flash in no time.

However, if you don’t want to use high speed sync, you have an additional option:

Rear curtain sync.

What Is Rear Curtain Sync?

While high speed sync allows you to fire a flash at high shutter speeds, rear curtain sync offers an entirely different approach.

You use a slow shutter speed—one below your sync speed.

And when you take a shot, the flash will fire at the end of the exposure, just before the shutter mechanism covers the sensor.

If you do this with decent ambient lighting, you’ll end up with a frozen subject—but the subject will have “trails” of motion coming out of it.

Like this:

What causes these trails?

Well, before the flash goes off, the photo will begin to expose. And your moving subject will be shown as a blur.

Then, when the flash actually goes off, your subject will be frozen.

And while it’s not a look that every photographer favors, it can give you some truly unique shots!

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High Speed Sync: Conclusion

Now that you’ve finished this article, you have everything you need to start using high speed sync with your flash.

That way, you’ll be able to capture photos with flash—even when it’s too bright for a slow shutter speed, and even when you’re photographing action.

So get outside, and get shooting!

What is high speed sync?

High speed sync is a flash setting that allows you to shoot with a fast shutter speed (one that’s above your flash sync speed, which is often 1/200s or 1/250s). Without high speed sync, you’ll be forced to use a slower shutter speed, which can cause problems such as blurring (with moving subjects).

Do I need high speed sync flash?

That depends on the type of photography you do! You need high speed sync if you shoot portraits with flash plus ambient light (because high speed sync will allow you to widen your aperture and compensate by boosting your shutter speed). You’ll also need high speed sync if you use flash with moving subjects and ambient light is affecting your scene; in cases like these, you’ll end up with a blurry subject unless you employ high speed sync, which will allow you to boost your shutter speed, thus preventing blur.

What will occur if you use a shutter speed faster than the recommend sync speed with flash?

You’ll end up with black bars along the bottom or top of your photo. This is because the shutter curtains will never leave the sensor fully exposed to the light of the flash. Of course, if you use high speed sync, you can prevent this problem; with high speed sync, your flash will fire several times in quick succession, allowing your camera to capture the entire scene with well-exposed subjects.

When should I use high speed sync?

I recommend using high speed sync in two main scenarios. First, you should use high speed sync if you’re shooting action and ambient light is affecting your subject. In a case like this, a normal flash sync speed will leave your photos full of blurry subjects, assuming the ambient light isn’t completely overpowered by the flash. But a high speed sync setting will let you capture the entire scene and keep everything looking nice, bright, and sharp. Second, you should use high speed sync if you’re shooting portrait or street subjects with flash in daylight and you want a shallow depth of field. A shutter speed of 1/250s or so just won’t limit light enough for an f/2.8 aperture – but if you use high speed sync, you can boost your shutter speed higher, use that f/2.8 aperture, and capture a powerful image with stunning bokeh.

About the Author
jaymes dempsey author

Jaymes Dempsey is a professional macro and nature photographer from Ann Arbor, Michigan; his work is published across the web, from Digital Photography School to PetaPixel. You can connect with Jaymes on Instagram, Facebook, and LinkedIn.

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