Understanding High Speed Sync Flash and Shutter Curtains

Before we talk about sync (high-speed synchronization), let’s first discuss flash sync.

Flash sync can be described as a computer-controlled feature that allows flash and shutter release to be synchronized so that flash illuminates subject at the exact moment that shutter exposes image sensor.

Flash instantly lights up the subject. However, flash travels at the speed light, so it doesn’t last as long as shutter stays open, even though it is extremely fast (1/60s to 1/125s to 1/250s, etc. .

The shutter speed is limited by the camera’s native sync.

What is High Speed Sync Flash and how does it work?

High-speed sync flash allows your DSLR to use flash at shutter speeds that are faster than the camera’s native sync.

Cameras have a native sync speed of 1/250th of one second. Anything faster is beyond the camera’s capability to sync with the flash. If you are in an environment that requires faster shutter speeds, or for aesthetic reasons (such as a large aperture), you will overexpose your image.

High-speed flash/camera combinations permit you to use flash at faster shutter speeds.

How do you use High Speed Sync Flash

High Speed Sync Flash Sample

High-speed flash is used when your shutter speed is slower than the camera’s flash sync speed or when you need a larger aperture setting, such as outdoor daylight photography.

You may decide to take an outdoor portrait. Your TTL meter will tell you that the shutter speed should be 1/125s and the aperture should be set at F/16. These settings will result in too wide a field of view, which is actually a problem. Nearly everything will be in focus. You want a sharp subject but blurred background. This is possible with an aperture of approximately f/2. This is six stops of light differential, so the shutter speed must be increased to 1/5000s. You can achieve this by setting the flash speed to High Sync Speed.

You’ll get that soft, beautiful background when you take your picture.

High Shutter Sync is a great option when shooting with a telephoto lens. It allows you to capture fast action using a high shutter speed and a high fstop. High Shutter Sync works well in sports photography, but it can also be used in wildlife situations.

How High Speed Sync Works

High Speed Sync Flash vs Normal Flash

You only need to set the flash unit and high-speed sync flash camera to your desired setting.

But how does it actually work?

The rear curtain will close at higher shutter speeds before it fully opens. Only a small amount of exposure is moved across the image sensor. The flash is activated within this small area of exposure. The flash is synced to a high-speed shutter speed. The flash fires longer than standard flash mode.

Standard flash mode has a flash duration that is shorter than the shutter’s movement across the sensor. The shutter will partially cover a portion of the frame. This could result in large areas of black being left in your image. This image has a lot of black that is underexposed.

What is Rear Curtain Sync and Front Curtain Sync?

Rear vs Front Curtain Sync Flash

Your DSLR’s shutter is composed of two curtains. The front and rear shutters open and close according to the shutter speed. The front shutter opens at 1/500s and the rear closes at 1/500th of an second.

“Front curtain sync” is the default setting that comes with a flash. This means that the flash will fire as soon as the front curtains begins to move. Thus, the flash illuminates the subject for the duration the shutter speed.

Many 35mm and DSLR cameras allow you to set the flash fire right before the rear curtain (or second curtain) starts to move.

With longer shutter speeds (up to 1 second), you can create stunning, creative motion blur and streaming light effects.


High-speed sync allows you to have more artistic control of your photos, especially in aperture-priority mode.

This is how you can capture photos that grab attention and leave people wondering what you did.

High-speed sync eliminates limitations of the camera’s native flash sync. This is a great advantage for photographers who have always desired a faster shutter speed.