Posted by Chris Hulme
- Digital SLR
- Standard Zoom Lens
- Flash Gun
- Remote cable/wireless release
- Hot flask/hobnobs
Rear curtain sync is a low-light technique associated with blending a long exposure usually of a moving subject with a burst of flash, so that the long exposure element captures movement (usually a blur trail) and the flash then captures a defined sharp rendition of your subject, all on the same frame.
Rear curtain sync is so called because the flash fires at the end of the exposure just before the shutter closes, so that the blurred element of the image is streaked behind your flash-lit subject and therefore looks natural, giving the impression that your flash-lit subject is followed by speed blur. If you were using front curtain sync mode (which is the standard default mode on most cameras/flashguns) the flash would fire at the beginning of the exposure with the blurred element recorded after; this doesn’t look natural. The trick therefore to rear-curtain sync is timing your exposure so that your subject is positioned where you want them, to coincide with the flash firing at the end of the sequence. Definitely the tricky bit!
To capture the canoeists, we switched our cameras to both manual mode and manual focus to then find a correct exposure for the ambient lighting without flash. It was dark but the area was reasonably well lit with artificial lighting.
Things to consider:
- You want a reasonably long shutter speed so as to record plenty of movement blur. We used 8 secs.
- You need to have your camera locked off on a tripod with your lens set to manual focus and focused on the position where you hope your subject will be positioned when the flash fires and the shutter then closes.
- You need a mid-range aperture to provide extra depth of field so as to ensure your subject will be in focus, you can’t predict exactly where that is.
- You should first watch the action and guesstimate the time it takes for the canoeist to start off and finish the pass. You will want to trip your shutter so that the exposure ends just as the canoeist arrives at the position where you have framed/focused, and is then frozen by the flash.
This is the tricky bit but once you have observed and had a few attempts, you start to get the feel for it.
- Manual mode and manual focus
- Aperture – f/8
- Shutter speed – 8 secs
- ISO – 200
- The above settings gave a reasonably balanced and well exposed ambient lighting exposure.
- Camera set to rear curtain sync. (on Nikon cameras, press the flash button and rotate the rear dial until ‘rear’ appears on the top plate panel.)
- Flash set to TTL exposure setting (note that your flash will fire a ‘preflash’ burst at the beginning of the exposure. This does not affect anything, its your camera and flash working out how much power to give out to achieve a correct flash exposure at the end of the sequence.)
The above gives you a starting point on settings. There are no rules and plenty of opportunity to experiment on exposure lengths, apertures etc. It can be hit and miss, it takes a bit of practice at first to get the timing right from tripping your shutter to the subject being in the right place when the flash fires – but the more we practiced we did start to get better and more consistent results.
Here are 2 example photos that show the difference between front curtain and rear curtain sync flash. The first example shows front curtain sync. With camera locked off on a tripod, I used an 8 sec exposure. The flash fires at the beginning of the sequence and then the 8 sec exposure continues with me walking from right to left across the frame holding the candle. The candle trail appears unnaturally in front of the subject. With the second example set to rear curtain sync, The exposure begins with me walking across the frame with just the candle light recording, the flash then fires at the end of the exposure when I reach the left hand side of the frame leaving a candle trail behind me.