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7 Slow Sync Flash Questions Answered

Learn what slow sync flash is and how you can use it to capture more creative shots of people.

|  General Photography
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Car on race track


What Is Slow Sync Flash?

Slow sync flash combines a burst of flash with a slow shutter speed. On compact cameras, slow sync flash is often known as night mode and you can't control the speed of the shutter or the strength of the flash but you can with a DSLR. If you're working with a DSLR you'll probably find you have rear curtain sync and front curtain sync options among the various flash modes available, although some camera models don't have this option so do check your manual. 


Why Do I Need It?

Slow Sync Flash can be used to capture subjects in low light as well as action shots. 


Do I Need A Tripod?

When working with slow shutter speeds a tripod is recommended, however, rear or front curtain sync can create some interesting backgrounds when you work hand-held, particularly when taking your photos in an area with various light sources as the flash will freeze your subject in place while the long exposure will blur the lights into an interesting mix of colour.


What's The Difference Between Rear And Front?

Rear-curtain sync tells your camera to fire the flash just before the photograph is finished exposing. As you pan, this creates a long trail but a nice, crisp shot of your subject. Front curtain fires the flash at the beginning of the exposure then the shutter remains open, continuing to record the ambient light. As a result, your images will appear differently depending on which method you choose.

How Does It Help With Action Shots?

Car on race track


Your camera's flash can provide a burst of light in a split second that will highlight your subject. However, if you're trying to capture a moving subject, the flash will freeze them in their tracks and all sense of movement will be lost. However, by combining a slow shutter speed with a pop of flash, you can create a sense of action through blur but still have your subject sharp too.

It's ideal for capturing action shots of bikes or cars moving, although it can be used to capture creative shots of any scene which has a moving subject in the foreground. Try using it next time you're photographing your child playing on a swing, for example. If you find there's blur in front of your subject rather than behind, you need to select rear curtain sync so that the ambient blur exposure is captured before the flash fires. This results in a more natural-looking shot where the blurred streak follows your subject who will be sharp thanks to the flash firing just before the exposure ends. 

You need to give your subject time to move through the frame to give the slower shutter speed time to blur their movement before the pop of flash at the end of the exposure will leave them sharp. It's also worth perfecting your panning technique before you start experimenting with this technique so your pan stays smooth and straight. You also need to ensure your panning speed is correct. For example, shoot too slow and you'll see the trail but it'll merge/blur into the background. Too fast and everything freezes.

How Can It Help In Low Light?

Low Light Portrait


When photographing people in low light you can try and use flash or you can turn your flash off and use slower shutter speeds to capture enough light to create a well-exposed image.

If you're using your camera's built-in flash your subject can often take on the 'rabbit in the headlights' look thanks to the bright flash illuminating them but leaving the background dark. If you go for the slow shutter speed option you're fine if you're working with a street performer whose occupation is to be a human statue but for anyone else who tends to move around a lot, you'll just end up with motion blur spoiling your shot.

As a result, you're better off using slow sync flash so you get a relatively sharp shot of your subject but also capture enough light throughout the image to create a shot that's better exposed throughout. In other words, the camera records the background and then illuminates the subject with flash to balance the exposure between the two areas. This makes it a good mode to use when shooting portraits at night although a tripod may be necessary to keep the background sharp.

What Shutter Speeds Are Needed?

This will change depending on the amount of blur you want to capture in your shot. It's also worth noting that the speed your subject is moving at and how intense the light around them is can affect the final look if the image so it's worth experimenting. As you're not controlling when the flash will fire you may need to take a few shots to get to grasps with your timing too. 

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