The EF 70-300mm f/4-5.6 IS USM provides 2-mode IS for shooting immobile subjects. Mode 1 stabilizes the image along both the horizontal and vertical axes. For shooting while panning to follow a moving subject, Mode 2 turns off correction in the panned direction and prevents the effect of dragging the subject back through the frame.
Тут всё чёрным по белому!
1. для неподвижных объектов;
2. для съёмки с проводкой(стабилизация в одной плоскости)