The usual goal in photography is to create an exceptionally sharp image. If you're photographing a bird, for example, most photographers want an image that's so sharp you can see every feather on the bird and every barb on the feather.
To capture that, you typically need a sturdy tripod, a cable release, lots of light — and a stationary subject.
But what if the light is dim and your subject is moving? That's when you need to pan — moving the camera with your subject. It involves moving the camera so that your subject is always at the same spot in the image. If during the exposure your subject is always at the same place on the sensor (or frame of film) it's like your subject isn't moving at all. Meanwhile, everything else blurs into a swath of solid color.
The image of a flock of starlings in flight at the top of this post illustrates the concept. The birds were flying fast and not in the same direction. Some were flying to the right. Some were making a U-turn. Some had already started flying left.
My exposure time of 1/50th of a second was far too slow to capture every bird in sharp detail, so I panned the camera with the birds that were flying to the right. By moving the camera in the same direction at the same speed as they were flying, they are sharp in the final image. All of the other birds appear as streaks of light.
Panning is one of the more difficult photographic techniques to perfect. With most DSLRs, the viewfinder goes black during the exposure so you have to follow your often unpredictable subject without being able to see it.
Despite the challenges, you can raise your chances of success with a lot of practice and these tips:
Get a good tripod. It may seem odd that a tripod, which is designed the hold the camera steady, does anything but hinder panning. I actually think a tripod with a smooth action head is a critical piece of equipment. While you can do without a tripod, I find the support of the tripod results in smoother motion.
A tripod with a ball head, though, probably won't help much. I use a Wimberley II, a gimbal head that places the weight of the lens and head below their pivot point. Set up correctly, even a heavy 600mm lens moves as if it was weightless. A cheaper option is the Wimberley Sidekick, which allows you to temporarily convert any ball head into a gimbal head.
With either, it's important to perfectly balance your camera and lens on the head. Even with the two panning knobs loosened, the camera shouldn't move at all. Gravity should hold everything in place.
While panning, I have the two panning knobs as loose as they will go and I rest one of my arms on the lens to provide varying amounts of tension.
Use "fast" shutter speeds and short lenses. The longer your exposure time, the harder it is to perfectly pan with your subject. Longer exposure times allow you to turn more of the background into a blur, but any mistake you make in tracking your subject will cause it to blur, too. Shorter exposures cut the chances for making mistakes.
Also, shorter lenses are more forgiving than longer ones. Very powerful lenses magnify everything, including any panning mistakes.
The image of the starlings was captured with what's effectively a 1,200mm lens (a 600mm lens with a 2x tele-converter). With that much magnification, an exposure time of 1/50th of a second is plenty slow. With a 50mm lens, however, that same exposure would have captured all the birds sharply. Start off with just a little blur and gradually switch to stronger lenses and longer exposures as your technique improves.
Shoot in a burst and track your progress. Most of my successful images have been in the middle in a series of a half dozen or so shots. The first shot or two are usually off, but by about the third, I'm usually in tune with the animal.
In a flock, I try to pick out one particular bird. When tracking a single bird or other animal, I try to pick out a particular feature, such as its eye. In every shot, I try to make sure that the bird or the feature of the animal is on the same autofocus sensor. I hold down the shutter button and in the split second between shots when the scene is visible in the viewfinder, I adjust for any tracking errors. It's all about getting the rhythm of the animals.
Practice in movie mode. Most digital cameras offer a movie mode nowadays. You can see what you're recording on the LCD screen at all times. Unlike panning with the viewfinder, you don't have to cope with the screen constantly going black.
Practice making movies where you pan with wildlife. Keep practicing until your movies are no longer jerky. You may also find it easier to start your practice on your own pets before graduating to wildlife.
These digital cameras typically let you take still images while the screen is on. If the viewfinder blackouts really bother you, try taking your panning pictures in this mode.
Even with the blackouts, I like using the viewfinder because it allows me to support the camera better, which results in smoother motion. (I also learned how to pan before I had a camera with a live view LCD, so I may be biased for that reason.) But there is no one correct answer. Do what works for you.
Don't give up. Panning is a difficult technique to master. You probably won't master it on your first try. Or your second. Or your third. I didn't. Thanks to digital cameras, however, it's free to practice. Keep trying until you get it. The results are worth it.