From Lightstalking
A good photo isn’t automatic. It doesn’t matter how new or expensive your camera is; good shots don’t just happen because you press the shutter. There are all sorts of things that can ruin a shot: overexposure, underexposure, poor composition, missed focus. Regardless of what camera you’re using, things like this are remedied almost entirely by way of good technique. It’s a must that your camera have a reliable metering system and an accurate focusing system, but you, the photographer, have to make sure you’re making proper use of it all in order to minimize the number of useless photographs you make.
Go Away, Camera Shake!
Perhaps chief among factors that can ruin a shot is (unintentional) camera shake; you’ve got a proper exposure, you’ve locked focus, you’ve got a good composition…and you’re rewarded with a blurry shot. Exasperated and disappointed, you’re thinking to yourself — probably aloud — “What gives?!”
The most common culprit is shutter speed. Trying to handhold a camera at too slow a shutter speed is going to be a problem. The rule of thumb concerning how to achieve sharp images when handholding your camera is to use a shutter speed faster than or equal to the focal length of your lens. This means that if you’re using a 50mm lens, then you’ll want to set your shutter speed to no slower than 1/50. It’s an easy rule to remember and it’s generally effective, but there are time when you simply need a more powerful solution.
Image Stabilization
Enter image stabilization technology. It goes by many different proprietary labels: Nikon’s Vibration Reduction (VR), Canon’s Image Stabilization (IS), Sigma’s Optical Stabilizer (OS), Tamron’s Vibration Compensation (VC), Sony’s Super SteadyShot, Pentax’s Shake Reduction (SR). Nicknames and particular implementation methods notwithstanding, the goal of all this is to allow photographers to capture sharp images using shutter speeds significantly slower (usually up to four times slower) than would otherwise be possible.
Oxford School of Photography 