Rear-Sync Flash Photography

I have just been investigating my Canon 430EX Speedlite's functionality, as I only ever use the flash for quite basic lighting techniques.  I decided to work on my rear-sync flash technique, so thought I'd share with you what I now know!

What is rear-sync flash?


Your camera shutter is actually made up of two curtains - a front curtain and a rear curtain.  When you take a photograph, the front curtain reveals your sensor and then the rear curtain comes across to cover your sensor again.

Your flash will normally go off when the first curtain goes up.  This lights the scene immediately and will freeze the action at that moment.

With rear-sync flash - you've guessed it - the flash fires at the end of the shot, just before the rear curtain closes.  It is often also known as rear-curtain flash.

What happens in practice is that your camera shutter will open and begin to record the movement of you scene on the sensor, quite  blurry.  Then, when the flash fires, a sharp image is recorded over the blurred information of any subject that is within the flashes firing range.

How do I do it?


Firstly you usually need an on-camera flash, although some camera models may have a rear sync flash option.  In small point and shoot cameras, this is effectively what Night Portrait or Party mode is doing.

• This works best at night.  Try taking a friend/model out into a fairly busy area where there is a lot of motion or if, like me, you head out alone, look for a still subject in front of a moving scene.
• Take a tripod, although this is not essential.
• Set your flash to rear sync mode.  In Canon cameras, this is done by pressing the H button on your flash until three fast forward triangles are revealed. In Nikon, press the flash symbol button on your camera body, and your LCD will cycle between various modes until it reads REAR.  Refer to your manual for rear-sync if in doubt.
• Set your camera to TV or S mode and select a slow shutter speed, I found that anything from 0.5" works. 
• Place camera on tripod.
• Focus on your subject and take the shot when motion is detected behind - e.g. car passes, crowd passes.
• Play with different shutter speeds for different effects.
• Take the camera off the tripod and try shooting whilst you are moving for more creative effects.

Why would I use it?


This technique gets you away from the boring shots where your flash exposes your subject but the  background is in darkness.  It allows ambient light into the background that is filled with motion.

It is often used to great effect at weddings to get the bride and groom sharp but an active background.   I've also seen some great shots where it is used to accentuate the idea of motion, e.g. the blur of an arm frozen at the last minute, e.g. in a chopping or violin action.

Go on, be adventurous and give it a go, it's easier than it seems and the unpredictability of the shots is quite exciting!

Happy snapping,

Nic