How to use Rear-Curtain Flash on your Nikon D-SLR

Have you ever wanted to shoot an image that is a combination of a long exposure with a perfectly sharp subject? Rear-curtain flash is your answer.

Have you ever wanted to shoot an image that is a combination of a long exposure with a perfectly sharp subject? Have you seen those pictures of people writing their names with a sparkler or torch but with the people sharply rendered? Rear-curtain flash is your answer.

It's easy to find yourself in a situation where you have a lot of natural light but not enough to get a shutter speed fast enough to actually freeze any motion in your subject. When using flash you can combine them to get the best of both worlds – an image with some motion in it and a sharp subject. To do this you need to set your camera to rear-curtain flash, as it will not be configured to do this ordinarily.

Most Nikon D-SLRs have different flash modes which work with both the pop-up flash and Nikon Speedlights. The standard mode for the flash set-up is front curtain, denoted by the flash or lighting symbol on the display. While this is great for using your flash to freeze the subject and add light as fill flash, it won't convey any feeling of motion in your image if you use a normal shutter speed of around 1/60-1/100sec.

In front-curtain mode the camera fires the flash at the beginning of the exposure and, if you are working with a faster shutter speed, the flash light appears instantaneously as you press the shutter on the camera. If you set up your camera with a slow shutter speed and front-curtain flash, as described above, the flash will fire at the start of the exposure and capture the motion of the long exposure with the slow shutter speed. This gives you an interesting image, but potentially an odd and unnatural looking one, where the motion appears in front of the frozen subject.

Rear-curtain flash or rear-curtain sync is the opposite of front-curtain flash, with the flash burst firing at the end of the exposure. If you're using a fast shutter speed on your camera you won't notice any difference between the front and rear-flash setting. It only starts to make a difference when you use a slow shutter speed in conjunction with rear-curtain flash.

One of the best ways to use rear-curtain flash is in when you have a low-light scene. You need some ambient light to help you capture the motion in the image, and the more ambient light you have, the better the motion trail is going to show up. You can shoot rear-curtain flash images handheld, but you do run the risk of camera shake as well as the motion blur you are trying to capture – remember that you are intentionally using slow shutter speeds, so for best results use a tripod.

To set rear-curtain flash with the in-camera flash, pop the flash up and then hold down the flash button on the camera and rotate the rear command dial until it shows REAR on the camera's back LCD or top display. If you are using a Speedlight (which will give superior results to the pop-up flash), mount it on the camera's hotshoe, then press the flash button on the side of the camera and rotate the rear command dial until it shows REAR on the camera's back LCD or top display.

For your camera settings, shoot in aperture/shutter priority or, if you are comfortable using it, manual mode, which will give maximum control over the light in the scene. Using rear-curtain flash is not a precise science; it will require a little bit of experimentation on your part to decide how much motion you want in the scene.

You could start with an aperture of f/5.6, a shutter speed of 1sec and an ISO of 200 and then adjust accordingly, depending on the light you are working in and the motion you want to capture. Put your Speedlight or pop-up flash onto TTL and use flash-exposure compensation to fine-tune the output of the flash accordingly. Now take a few images as a reference point to gauge the motion in the image. If you want longer trails, make your shutter speed slower i.e. from 1-4sec; if you want the movement to be shorter, go for a faster shutter speed i.e. 1sec to 1/10sec.

Your first attempts at rear-curtain flash might look a bit odd, as images taken with this technique will not always produce the results you expect. You don't always get a perfectly frozen subject, and sometimes you may have a double image of your subject depending on the combination of settings you've used and the ambient light you are shooting with. But persevere and, with practice, you'll get some great results.

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