Making deliberately out-of-focus images isn’t an especially common need, but it’s a skill that does come in handy. Let’s say you want to make an abstract art image. Rendering the scene completely out of focus can be a great way of achieving beautiful, soft swaths of color, light, pattern and texture. It works especially well if you’ve got a background of specular light sources—like holiday lights or sunlight reflecting off of water. But here’s the thing: focus blur isn’t just for artsy abstracts. It has another much more practical use: making beautifully abstract backgrounds in portraits. The same blurry background of holiday lights or sunlight reflections becomes a gorgeous canvas against which you can set off a subject. Long lenses and wide apertures create the shallowest depth of field possible, especially if you’re working close to the subject with the background far behind, and that will deliver beautifully focus-blurred abstract backgrounds that are simple and perfect for portraits and many other subjects.
If you’re photographing something that’s moving very fast, whether it’s a cheetah or a racecar or a bicyclist, one great method for depicting speed is with the use of deliberate motion blur. You can pan your camera by moving it laterally to follow the motion of the subject and create a fairly sharp subject on a blur-streaked background. Or, you can lock down the camera (or hold it very steady) to create a sharp background and a highly-blurred subject. Each has its place, and it’s up to you to decide what better tells the story on a shot-by-shot basis. The longer the shutter speed, the more blur you’ll create, but it’s a trade-off with diminishing returns. Too much blur can become a mess and defeat the purpose; successful motion blur photos require at least some elements of the scene to remain sharp. Sure, with the camera locked down you’ll always know you’ve got a sharp background, but instead of a nicely motion-streaked subject you may have a ball of indecipherable blur if your shutter speed is too long. There’s no hard-and-fast rule for what shutter speed is perfect for creating motion blur, but remember this: the faster the subject is moving (across the sensor, mind you, not necessarily in real life) the faster the shutter speed you can use and still create a motion blur effect. For a subject running or cycling through your frame at a decent distance and with a normal lens, maybe a shutter speed of 1/15th is the perfect place to start. A streaking racecar, however, may only require 1/250th of a second to deliver motion blur, and a slowly babbling brook may need several seconds of exposure to register the beautiful blur that represents motion.
Similar to motion blur, the blur caused by camera shake has its place as well—although it’s not necessarily as practical as traditional motion blur. I like to use a bit of camera shake to create an edge of separation when I’m mixing strobes and ambient light in a single exposure. A point-and-shoot camera’s Night Portrait mode, for instance, represents the ideal time to introduce a hint of camera shake. The strobe fires to illuminate the subject in the foreground, but during the longer exposure the camera shake can create a bit of a silhouetted space at the edges of the subject that are no longer illuminated by the flash. Long story short, a bit of camera movement during a mixed strobe and ambient exposure can add some depth and interest to a photograph. (In fact, a world-class photographer once told me that this is his preferred way of exposing fashion and beauty portraits in the studio. The hint of motion blur from “dragging the shutter” and moving the camera is crucial for adding depth and life to his photographs.)
If a little bit of subtle camera blur just isn’t cutting it for you, you could go wild and add a lot of blur by zooming your lens during a long exposure. The technique is especially effective when mixing strobe with ambient, but it’s not necessary. As long as you’ve got enough exposure to make a relatively sharp central subject area (usually a face in a portrait, for instance) then use of zoom blur can literally drive the viewer’s attention directly to that face. Not only does it render the background relatively indecipherable and out of focus, but by creating literal lines and streaks of light that point from the edges of the frame to the center where your subject can be found, the viewers’ eyes are driven directly to the center of interest. Zooming out during a long exposure creates a different effect than zooming in, but I’ve had great success by starting with a relatively wide shot for the flash-lit sharp area of the frame, then zooming in after the flash fires. (The reverse works equally well with a rear-curtain flash sync.) Also, bear in mind that you don’t need to zoom all the way across the range on your extreme zoom lens. Sometimes a subtle change is just the right amount of zoom to create pleasing blur without completely obliterating the readability of the scene.