Image Stabilizer
Image Stabilizer (IS) also known as Vibration Reduction (VR) in some cameras, are systems that minimizes the motion blurr due to uncontrollable jiggle when shooting handheld. Image Stabilizers detect small movements while the shutter is released and moves either the lens or the image sensor accordingly to counteract this movements. The result is a sharper image.
As a rule, most photographers use the reciprocal of the focal length of the lens as the shutter speed in order to obtain an optimum sharpness when shooting without a tripod. For example if you are using a camera set at a focal length of 125mm, a shutter speed of 1/125 sec should be used if you are shooting handheld. This rule applies effectively for cameras without Image Stabilizers. With IS however, you can get the same quality even when you are using 3-4 stops slower shutter speeds. In the case above, instead of using 1/125 sec, you can use 1/15 sec or 1/8 sec shutter speed with about the same results. This helps a great deal when the shutter speed is restricted due to poor lighting or when shooting with long telephoto lenses.
There are three common Image Stabilization modes found in most cameras.
Continuous Image Stabilization - In this mode, the IS system is continually active, making sure that motion blur is eliminated or reduced all the time. This mode is used mostly when capturing videos, although some photographers prefer this mode even for still photography because it gives them a stabilized view of the image through the viewfinder or LCD monitor so composing the image is much easier. It is especially useful when shooting with a long telephoto lens since with a long focal length, a slight movement will produce a very significant blurring. IS helps reduce this blurring and makes framing a lot easier.
Shoot Only Image Stabilization - Shoot Only IS mode activates the Image Stabilizer only at the moment the shutter-release button is pressed. It offers the greatest degree of stabilization. Because it is enabled when the shutter button is pressed, Shoot Only mode generally produces sharper photos than Continuous mode.
Panning Image Stabilization - Moving a camera in the same direction as a moving subject is called panning. This technique is used when capturing a moving subject like a moving car, a man running, or a biker passing by in order to produce images with the subject in sharp focus and the background blurred. Panning IS mode only makes corrections for vertical movement and is activated when the camera shakes up and down.
Some camera manufacturers falsely claim that their products have Image Stabilization when the only thing it does is increase the ISO sensitivity while using a faster shutter speed to reduce motion blurring, almost like setting the shooting mode to Sports. These cameras don't actually employ a real Image Stabilizer system so it would be best to check the specifications thoroughly.