IBIS stands for In-Body Image Stabilization – an image stabilization scheme which does not rely on lenses. IBIS thus differs from lens based image stabilization systems in that IBIS systems can (theoretically) offer stabilization to any lens (assuming the system can be informed of the lens’ focal length).
IBIS systems work by moving the imaging sensor in order to compensate for camera shake. The effectiveness of such schemes is usually graded on the number of stops of stabilization it offers (i.e. how much longer shutter speeds you can use) in normal circumstances. Various manufacturers use different trade names for their IBIS systems (e.g. Sony calls it SteadyShot, Pentax calls it Shake Reduction, etc.).
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