Rear Curtain Flash

Have you ever wondered what ‘Rear Curtain’ or ‘Rear Sync’ means in your flash menu? All DSLRs and some compacts have this option. To put it simply, rear curtain flash enables your flash to fire at the end of the exposure time, as opposed to firing as soon as the shutter opens. In most cases, this wouldn’t really make a difference, and that is probably why this feature so often goes unnoticed. When you are synchronizing your flash with slow shutter speeds… it makes a world of a difference! Take a look at the image above (photographer Kent Simpson)

This has been photographed on a slow shutter speed (2 sec or more), and the ambient light was enough to capture the motion blur of the basket ball. The flash fired at the END of this exposure time, capturing the ball and freezing it nice and sharp. The end result, as you see is an informative image which tells us the ball has travelled before it came to rest. Now, imagine if Kent Simpson had NOT used a rear curtain option for this photographed, in which case the flash would have fired at the BEGINNING of the exposure time, freezing the basket ball towards the left of the frame, followed by a motion blur. Now this would lead the viewer to believe that the ball was travelling from right to left, painting quite a different picture for us!

One of the most common subjects people shoot to practice rear sync, is moving cars. You could try with a model car to see how effective rear sync can be. The first step would be to get an ambient light exposure reading using a shutter speed of 1 or 2 seconds. Next, turn the rear curtain feature on, and pop your flash open. Then, get a moving subject to practice with and fire the shutter capturing motion blur followed by a nice sharp image of the subject…

Here’s a good example of what a model car can look like when photographed with a motion blur and a rear sync flash.

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