Mouse Wheel Zoom

Rolling the mouse wheel forwards zooms in on the currently active 3D View. Rolling the mouse wheel backwards zooms out on the currently active 3D View.

In both cases, holding down the or Ctrl key at the same time as rolling the mouse wheel controls the speed of the operation. Holding the Ctrl key down makes the mouse wheel zoom in and out faster. Holding the key down makes the mouse wheel zoom in and out slower.