Lets you zoom in and out of the view, but does not change the direction in which the camera is pointing. This type of movement is also called dollying.
When the Zoom tool is active, the cursor displays a magnifying glass.
In the Perspective view,
the Zoom tool acts differently than in the other views. Hold down the 
to zoom in, and the 
or 
to zoom out. Release the
mouse button to halt the action.
In the top, side or back views, the Zoom tool draws a square before magnifying or minimizing. Click any mouse button and draw a square from the top left corner down to the bottom right corner (top-down) to zoom in. Draw a square in the opposite direction to zoom out.
