Intermediate Don't use your camera's onboard flash... most of the time.
You already know the reasons why you want to avoid using that onboard flash. It washes out your subjects' faces. It creates harsh and ugly shadows behind everything in the scene. It causes red eye. It is, well, ugly. In most cases, it's better to turn up your ISO than to rely on your flash. ISO technology is leaps and bounds ahead of where it used to be, and today even point-and-shoot cameras can provide good, low-grain images at high ISOs.
So now that I've said that, I'll go on to say this: when used correctly and at the right time, flash can provide your photos with interesting and cool effects. So don't exclude it from your bag of tricks altogether.
Rear curtain flash
You've probably found yourself in a situation where there is plenty of ambient light to take a shot, but not enough ambient light to get a sharp, well exposed image of a moving subject. With the right camera settings, this situation is actually a golden opportunity. You can combine your onboard flash with a slow shutter speed to capture an image with a correctly exposed background, a very cool motion trail and a sharp subject. You can't just make this happen right out of the box, though; you'll need to take advantage of your camera's rear curtain flash setting.
Flow-Like-the-Wind by Flickr user TOKYO COUNTRY BOY
Most advanced DSLRs have different flash modes. The most basic of these modes is Front Curtain Sync, sometimes just called "fill flash". This is the default mode for most cameras, and the one you don't want to use in this situation. Here's why: In this mode, the camera fires the flash at the beginning of the exposure. So if you set your camera up with a slow shutter speed using front curtain flash, what you'll end up with is an image where the motion blur appears in front of the subject instead of behind her. This doesn't look natural - in most cases you'll want the blur to appear behind the subject so that she appears to leave motion trails as she moves forward.
Rear curtain sync, as you might have already guessed, is the opposite of front curtain sync. The shutter opens up first, and the flash fires at the end of the exposure, when the shutter is about to close. Now you get an image where the motion blur appears behind the subject instead of in front of her. Like a front curtain flash image, the subject herself will be sharp, while her movement will be captured in a blur behind her.
When should you use rear curtain flash?
This trick works best in low light situations, not in no-light situations. You need ambient light to illuminate the background and/or to capture that motion blur. The more ambient light you have, the more intense that motion trail is going to seem. Without any ambient light you'll get a sharp subject on a black background regardless of how slow your shutter speed is.
How to do it
A tripod is important when using rear curtain sync. Without one, you'll end up with camera shake as well as motion blur. For the best results, you will also need a camera that can be set to a fully automatic mode.
This type of photography - as with many other types of nighttime photography - does require some experimentation, so start with an aperture somewhere in the f/5.6 to f/8 range and a shutter speed of about one second. Take a few shots and see what you come up with. If you think your motion trails are too short, increase your shutter speed - this will produce a longer trail.
Flea: Over Exposure + Prolonged Shutter Try #1 by Flickr user sandragxh
Chances are some of your images are just going to look weird - photos taken with this technique don't always produce a perfectly lit/frozen subject. You may end up with a double image of your subject depending on how much ambient light there is and what settings you used. Shoot multiple shots at different settings until you find one that works, then shoot some more until you end up with a great image.
If you find that you like this type of photography, you may want to switch to an external flash. Using an external flash instead of your built-in one will help you adjust the amount of light that reaches your subject. With this technique, washed out faces and black "halo" effect shadows can still be a problem, just as they can be a problem for standard photos shot with a direct flash, so it's often helpful to have a flash unit that gives you a little more control.
Helen's Mental State by Flickr user _driftwood
This trick can make for interesting studio images as well as shots out in the field. Using this technique on a black background can produce some very compelling shots - just make sure that you put your background far enough away from your subject that the flash doesn't reach it. If you're using an external flash you can also experiment with side lighting, which will keep the light from falling on the background. This will produce an image with a strong motion trail and no background to distract the viewer from the effect.
In the absence of an external flash you can use all those same tricks for softening flash that you probably already know - for example, use a reflective surface such as a piece of white foam core to bounce the flash in whatever direction you want it to go.
At fast shutter speeds, it really doesn't matter if your flash is set up for rear curtain or front curtain sync. Your shutter speed will be fast enough that the difference won't affect your final image. And let's face it, you want to avoid using that onboard flash for all those usual reasons, anyway. So why not just set your camera up for rear curtain and leave it there? That way, you'll be ready for those one-of-a-kind rear curtain flash shots whenever the opportunity arises.
See the 21 Outstanding Examples of Rear Curtain Flash article for more examples of rear curtain flash.
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